首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   422篇
  免费   22篇
林业   30篇
农学   9篇
  87篇
综合类   32篇
农作物   11篇
水产渔业   46篇
畜牧兽医   224篇
植物保护   5篇
  2020年   5篇
  2019年   12篇
  2018年   5篇
  2017年   13篇
  2016年   7篇
  2015年   6篇
  2014年   7篇
  2013年   16篇
  2012年   13篇
  2011年   14篇
  2010年   9篇
  2008年   16篇
  2007年   14篇
  2006年   14篇
  2005年   21篇
  2004年   12篇
  2003年   12篇
  2002年   10篇
  2001年   11篇
  2000年   11篇
  1999年   7篇
  1998年   5篇
  1997年   6篇
  1996年   5篇
  1995年   7篇
  1993年   6篇
  1992年   5篇
  1991年   9篇
  1990年   10篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1985年   5篇
  1984年   7篇
  1983年   6篇
  1981年   3篇
  1979年   3篇
  1978年   5篇
  1977年   4篇
  1976年   6篇
  1975年   10篇
  1974年   9篇
  1973年   4篇
  1972年   8篇
  1971年   7篇
  1970年   9篇
  1969年   10篇
  1968年   13篇
  1967年   6篇
  1966年   5篇
排序方式: 共有444条查询结果,搜索用时 359 毫秒
81.
The assessment of genetic diversity and structuration of germplasm is essential for the efficient organization of breeding material. The objectives of the study were to (i) examine the population structure of elite sugar beet germplasm, (ii) investigate genetic diversity within and among subgroups of elite sugar beet germplasm, and (iii) assess the extent of linkage disequilibrium (LD) within elite sugar beet germplasm. A total of 111 and 178 inbred lines from the seed and pollen parent (SP and PP) heterotic gene pools, respectively, which had been genotyped with 23 SSR markers, were used in this study. Two distinct subgroups were detected within the entire germplasm set by STRUCTURE and principal coordinate analysis (PCoA). This observation was not expected because the SP heterotic pool of sugar beet was developed out of the PP heterotic pool in the late 1970s. Our observation of high LD in elite sugar beet germplasm suggests that association mapping will be possible in the examined germplasm set using a relatively low numbers of markers. However, to reduce the problem of false-positive marker-phenotype association, it might be necessary to examine the subgroups separately or apply association mapping methods which take into account this structure.  相似文献   
82.
Apparent nutrient, energy and amino acid (AA) digestibilities of wheat starch (WS), corn starch (CS), pea protein concentrate (PPC), soy protein concentrate (SPC), corn gluten meal (CGM) and soybean meal (SM) were assessed indirectly in common carp by applying the marker‐based indicator method. Each test diet consisted of 70% reference diet and 30% test ingredient. Stripping as faeces collection technique was applied to obtain faecal material two times a day for 9 weeks. Apparent digestibilities of ingredients (ADIs) for crude protein (CP) were higher in SM (79.5 ± 5.1%) and SPC (75.2 ± 4.8%) than in CGM (59.2 ± 6.6%). Regarding ADIs of individual AAs, SM and SPC always showed higher values than CGM and PPC. ADIs for crude carbohydrates in CS (90.4 ± 2.2%), WS (88.8 ± 2.0%) and CGM (82.3 ± 3.9%) exhibited higher amounts than in SM (26.3 ± 1.0%). Evaluated apparent digestibilities indicate that in particular SM and SPC are good protein and CGM, WS and CS are promising carbohydrate sources to be included in diets for common carp. A strong correlation between ADICP and ADIAA was determined. Stripping used for digestibility measurement in carp was found to be a viable method as conventional passive faeces collecting techniques such as sedimentation or sieving.  相似文献   
83.
This study assessed specific peaks obtained by diffuse reflectance Fourier transform mid‐infrared spectroscopy (DRIFTS) for characterizing the soil organic matter (SOM) composition of a Haplic Chernozem. Soils were collected from the Static Fertilization Experiment, Bad Lauchstädt, Germany, during 5 years from the farmyard manure (FYM), mineral fertilizer (NPK), combination (FYM + NPK) and no fertilizer (Control) treatments. Soils were extracted with hot water (HWE), and fractionated by size and density. Bulk soil and fractions were analysed by DRIFTS. Peak areas at 2930, 1620, 1530 and 1159 cm?1 were selected as a range of organic functional groups (with limited mineral interference), integrated with a local baseline (corrected peak area) and each was divided by the summed area of the four peaks (relative peak area). Positive correlations between carbon (C) in fractions representing labile OM (<1.8 g cm?3, 1.8–2.0 g cm?3, CHWE) and the corrected peak area at 2930 cm?1 (3010–2800 cm?1) in the bulk soil indicated that this aliphatic peak corresponded to the more labile C compounds. Negative correlations between the same fractions and the corrected area of the predominantly aromatic peak at 1620 cm?1 (1660–1580 cm?1) in the bulk soil suggested a relationship with more stable SOM compounds. All relative peak areas were significantly affected by fertilizer treatment, with an increasing relative peak area at 2930 cm?1 in FYM compared with non‐FYM treatments. The ratio of the peaks at 1620 and 2930 cm?1 was positively correlated with the ratio of stable C (sum of C in >1.8 g cm?3 and clay fractions) to labile C (C content of <1.8 g cm?3 fraction) and thus taken as an indicator of SOM stability. The DRIFTS peak area method reflected changes in SOM quality and composition under long‐term management as measured by size and density fractionation, indicating heterogeneous chemical composition of the latter. Further, the DRIFTS analysis of undiluted soil samples can be used to assess SOM composition in small sample sets if specular reflection and mineral interferences are considered.  相似文献   
84.
85.
In 1998, the Organic Arable Farming Experiment Gladbacherhof (OAFEG) was started in order to explore the impact of different organic arable production systems (mixed farming, stockless farming with rotational ley, stockless cash crop farming) and of different tillage intensities (conventional plough as a full inversion tillage, two-layer plough, inversion tillage at reduced depth, non-inversion tillage) on sustainability parameters. In this article, we present results on the development of soil organic matter (SOM) levels. Starting with organic mixed farming with approximately 0.7 livestock units (LU) per ha cattle before set-up of the experiment, only the mixed farming system in the experiment was able to maintain SOM levels. The stockless system with ley maintained soil organic carbon (SOC), but lost soil total nitrogen (STN), and the stockless cash crop system had a significant SOM loss in the magnitude of 7.7 t SOM ha?1, or roughly 8.4% of the initial SOM mass. Reducing tillage intensity had no impact on SOM masses, but only on organic matter stratification in soils. We conclude that specialization of organic farms towards stockless arable crop production requires special attention on SOM reproduction to avoid detrimental effects. Further, reduced tillage intensity does not necessarily have a positive effect on SOM.  相似文献   
86.
Norchief is a medium late maturing, red variety with high total solids. In yield, the new variety is quite comparable to Red Pontiac and La Rouge but higher than Norland. Norchief has shown a certain degree of field tolerance to potato flea beetle,Epitrix cucumeris.  相似文献   
87.
88.
Summary In the normal process of digestion, not only substances in solution are absorbed. Solid, undissolved food particles, in macrocorpuscular form, are regularly kneaded into the mucosa during their passage through the digestive tract. They pass between the epithelial cells into the subepithelial layer. From here, they are transmitted both by the lymph vessels and by the mesenteric veins into the circulation, where they remain for a considerable time.This process was discovered in 1844 by the Göttingen physiologistHerbst, and later confirmed by others, but was generally considered an impossible and therefore untenable theory, since the passage of such large particles through the mucous membrane does not fit our conception of the physiological mechanism of absorption. We have investigated this phenomenon in detail in recent years with the help of a large team of colleagues under the general heading of persorption. For these investigations, we used among other things starch granules as models, as the starch granule possesses outstanding qualities on the one hand for administration and on the other for demonstration in body fluids and tissues.The mechanism of passage through the epithelial cell layer has been reconstructed, and transportation through the intestinal membrane investigated. Quantitative observations of the number of persorbed starch granules in the blood were made. It was found that within a few minutes of the consumption of rolled oats, wheat flakes, whole-meal, or of the same amount of starch in the form of potato- or corn-starch, numerous unchanged starch granules can be demonstrated in the blood. A prerequisite for this mechanism is the persorbability of the starch granules, which is limited by the size and consistency of the uncooked starch granules. Persorption was observed up to a diameter of 110 microns. The persorbability of starch granules may be recognized by their polarizing capacity.Numerous foods when ready to eat contain masses of such persorbable starch granules. In particular, they are present in cereals in flake form (rolled oats, wheat flakes) in whole-meal, in crisp-bread, also in short-bread pastries, biscuits and cakes in which no milk or water is used in the preparation. Dry heat does not affect the persorbability of starch granules. Boiled starch granules lose their persorbability.The mechanism of transportation of persorbed starch granules in the body, deposition as micro-emboli in the lumen of the minute vessels, and elimination from the vascular system were also studied. Phagocytosis of small starch granules (e.g. rice) by leukocytes was observed. Alterations in the vascular system of animals, due to such granules which had been persorbed or had entered the circulation, were also seen.Other particles of vegetable origin can also be persorbed. The phenomenon of persorption was also demonstrated in man and animals with cellulose particles, pollen, spores, fragments of plant hairs. Yeast cells are found in the chyle, blood, urine, cerebrospinal fluid after oral administration.
Zusammenfassung Beim normalen Verdauungsvorgang werden auch feste, ungelöste Nahrungspartikel in großkorpuskulärer Form mit konstanter Regelmäßigkeit während ihrer Passage durch den Verdauungstrakt in die Schleimhaut eingeknetet. Sie gelangen zwischen den Epithelzellen hindurch in die Region unterhalb der Epithelzellschicht. Von dort werden sie in den Blutkreislauf eingeschleust, in welchem sie über längere Zeit zirkulieren.Mit einem großen Team von Mitarbeitern haben wir in den letzten Jahren dieses Phänomen unter dem Arbeitstitel Persorption eingehender untersucht. Bei diesen Untersuchungen bedienten wir uns unter anderem der Stärkekörner als Modellkörper, weil das Stärkekorn ausgezeichnete Qualitäten für die Applikation einerseits, sowie für den Nachweis in Körperflüssigkeiten und im Gewebe andererseits besitzt.Auch andere Partikel pflanzlicher Herkunft können persorbiert werden. Mit Zellulose-Partikeln, Pollen, Sporen, Bruckstücken von Pflanzenhaaren wurde das Phänomen der Persorption sowohl tierexperimentell als auch am Menschen nachgewiesen. Hefezellen werden nach oraler Applikation ebenfalls im Chylus, im Blut, im Harn, im Liquor cerebrospinalis gefunden.Die Mechanismen für den Durchtritt solcher Partikel durch die Epithelzellschicht konnten rekonstruiert werden. Der Transport durch die Darmschleimhaut wurde untersucht. Quantitative Beobachtungen über die Anzahl der persorbierten Partikel im Blut wurden angestellt. Hierbei zeigte sich, daß bereits wenige Minuten nach Einnahme von Haferflocken, Weizenflocken, Weizenschrot, oder auch der gleichen Gewichtsmenge Stärke (Mais, Kartoffel), zahlreiche Stärkekörner in unveränderter Form im Blut nachweisbar sind. Vorbedingung für diesen Mechanismus ist die Persorptionsfähigkeit dieser Partikel, welche durch die Größe und den Härtegrad der Partikel begrenzt ist. Die Persorptionsfähigkeit von Stärkekörnern ist an der erhaltenen Polarisationsfähigkeit erkennbar.Zahlreiche speisefertige Nahrungsmittel enthalten massenhaft solche persorptionsfähigen Stärkekörner. Insbesondere sind sie in Cerealien in Flockenform (Haferflocken, Weizenflocken), in Weizenschrot, in Knäckebrot, sowie in Gebäcken mit Mürbteigcharakter, Keksen, Biskuits, und in Kuchensorten, welche ohne Verwendung von Wasser, bzw. Milch hergestellt werden, vorhanden. Die Trockenerhitzung verändert die Persorptionsfähigkeit von Stärkekörnern nicht. Gekochte Stärkekörner verlieren ihre Persorptionsfähigkeit.Es wurden ferner die Transportmechanismen von persorbierten Stärkekörnern im Organismus, ihre Deponierung als Mikro-Emboli im Lumen kleinster Gefäße, sowie die Eliminationsmechanismen aus dem Gefäßsystem untersucht. Eine Phagocytose kleinster Stärkekörner (z.B. Reis) konnte durch Leukozyten beobachtet werden. Außerdem wurden tierexperimentell Veränderungen am Gefäßsystem durch solche persorbierte, bzw. in den Blutkreislauf eingebrachte Stärkekörner beobachtet.

Résumé Les aliments résorbés dans le cadre du processus physiologique de digestion ne sont pas tous solubilisés. Des particules de nourriture solides, se présentant sous la forme de gros corpuscules, vont également se nicher avec régularité dans la muqueuse du tractus digestif. Se frayant un chemin entre les cellules épithéliales, ils pénètrent souls la couche épithéliale. Repris par le système lymphatique et les veines mésentériques, ils sont finalement déversés dans la circulation sanguine où ils se maintiennent relativement longtemps.Découvert en 1844 par le physiologisteHerbst et confirmé plus tard par d'autres auteurs, ce processus fut généralement mis en doute parce que le passage de la muqueuse intestinale par des particules solides aussi volumineuses est contraire à l'idée que l'on se fait communément des mécanismes physiologiques de la résorption. Avec une equipe nombreuse de collaborateurs, nous avons, ces dernières années, étudié de plus près ce phénomène que nous nommons la persorption. Nous prîmes pour modèle les granules d'amidon qui se laissent particulièrement bien mettre en évidence dans les humeurs et les tissus.Le mécanisme du passage de la couche des cellules épithéliales a ainsi pu être reconstitué. Nous avons en outre étudié le transport à travers la muqueuse intestinale et établi la quantité des granules d'amidon passant dans le sang. On observe notamment des granules d'amidon intacts dans le sang quelques minutes déjà après l'absorption de flocons d'avoine ou de froment ou d'une quantité équivalente d'amidon (maïs, pommes de terre). La persorbabilité des granules d'amidon est évidemment limitée par leur taille et leur dureté à l'état cru. Au-delà de 110 microns de diamètre, ils ne sont plus persorbés. La persorbabilité des granules d'amidon se reconnaît au maintien de leur faculté de polarisation.Beaucoup d'aliments prêts à la consommation contiennent une foison de granules d'amidon persorbables, à savoir les céréales sous forme de flocons d'avoine ou de froment, le Knäckebrot, les gâteaux secs, cakes, biscuits et gateaux préparés sans eau ni lait. L'échauffement à sec ne modifie pas la persorbabilité des granules d'amidon tandis que la cuisson la détruit.Nous avons étudié également les mécanismes de transport des granules d'amidon persorbés dans l'organisme, leur dépôt sous forme de micro-embolus dans la lumière des plus fins vaisseaux ainsi que leur élimination du système vasculaire. Les granules particulièrement petits (par exemple dans le riz) sont phagocytés par les leucocytes. Chez l'animal de laboratoire, on a pu observer des modifications vasculaires provoquées par des granules d'amidon ayant pénétré dans la voie sanguine.Le phénomène de la persorption a également été constaté chez l'homme et chez l'animal avec des particules de cellulose, du pollen, des spores et des fragments de poils végétaux. On retrouve également des cellules de levure après application orale dans le chyle, le sang, l'urine et le liquide cérébrospinal.


With the technical assistance ofHannelore Wendlandt, Ursula Kiessling, Christa Krone.  相似文献   
89.
90.
Our contemporary society is struggling with soil degradation due to overuse and climate change. Pre‐Columbian people left behind sustainably fertile soils rich in organic matter and nutrients well known as terra preta (de Indio) by adding charred residues (biochar) together with organic and inorganic wastes such as excrements and household garbage being a model for sustainable agriculture today. This is the reason why new studies on biochar effects on ecosystem services rapidly emerge. Beneficial effects of biochar amendment on plant growth, soil nutrient content, and C storage were repeatedly observed although a number of negative effects were reported, too. In addition, there is no consensus on benefits of biochar when combined with fertilizers. Therefore, the objective of this study was to test whether biochar effects on soil quality and plant growth could be improved by addition of mineral and organic fertilizers. For this purpose, two growth periods of oat (Avena sativa L.) were studied under tropical conditions (26°C and 2600 mm annual rainfall) on an infertile sandy soil in the greenhouse in fivefold replication. Treatments comprised control (only water), mineral fertilizer (111.5 kg N ha–1, 111.5 kg P ha–1, and 82.9 kg K ha–1), compost (5% by weight), biochar (5% by weight), and combinations of biochar (5% by weight) plus mineral fertilizer (111.5 kg N ha–1, 111.5 kg P ha–1, and 82.9 kg K ha–1), and biochar (2.5% by weight) plus compost (2.5% by weight). Pure compost application showed highest yield during the two growth periods, followed by the biochar + compost mixture. biochar addition to mineral fertilizer significantly increased plant growth compared to mineral fertilizer alone. During the second growth period, plant yields were significantly smaller compared to the first growth period. biochar and compost additions significantly increased total organic C content during the two growth periods. Cation‐exchange capacity (CEC) could not be increased upon biochar addition while base saturation (BS) was significantly increased due to ash addition with biochar. On the other hand, compost addition significantly increased CEC. Biochar addition significantly increased soil pH but pH value was generally lower during the second growth period probably due to leaching of base cations. Biochar addition did not reduce ammonium, nitrate, and phosphate leaching during the experiment but it reduced nitrification. The overall plant growth and soil fertility decreased in the order compost > biochar + compost > mineral fertilizer + biochar > mineral fertilizer > control. Further experiments should optimize biochar–organic fertilizer systems.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号