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   202篇
  免费   7篇
  国内免费   2篇
林业   26篇
农学   14篇
基础科学   3篇
  68篇
综合类   6篇
农作物   19篇
水产渔业   9篇
畜牧兽医   33篇
园艺   4篇
植物保护   29篇
  2023年   1篇
  2022年   5篇
  2021年   9篇
  2020年   8篇
  2019年   6篇
  2018年   9篇
  2017年   9篇
  2016年   5篇
  2015年   4篇
  2014年   9篇
  2013年   10篇
  2012年   6篇
  2011年   17篇
  2010年   5篇
  2009年   5篇
  2008年   9篇
  2007年   7篇
  2006年   9篇
  2005年   9篇
  2004年   10篇
  2003年   11篇
  2002年   7篇
  2001年   5篇
  2000年   2篇
  1999年   4篇
  1998年   3篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1981年   3篇
  1980年   1篇
  1977年   1篇
  1959年   1篇
排序方式: 共有211条查询结果,搜索用时 15 毫秒
1.
Gastrointestinal microbiota play a key role in the nutrients digestion and hence maintaining animal health and welfare. The diet offered to the animals in captivity may differ considerably from that on natural pastures. In a stabled maintenance system, horses have a limited choice of habitat and feed. Time spend for feeding is relevant for equine welfare because the reduction of the time devoted for foraging may be responsible for inducing gastric inflammation and ulceration. Therefore, in the present study, it was hypothesized that fecal bacterial fermentative processes differ between free-roaming and stabled Konik Polski Horses (KPHs) with respect to microbial enzymatic activity, and thus the fecal concentration of short-chain fatty acids (SCFA), which can be further utilized for assessing the feeding behavior and welfare in free-roaming versus stabled horses. The SCFA concentration and profile, as well as the extracellular and intracellular activities of selected bacterial enzymes, were characterized in horse feces collected during the winter and summer feeding seasons. The results showed higher enzymatic activity and SCFA production in the feces excreted by free-roaming versus stabled horses, especially during summer. An increase in pasture plant diversity may be beneficial for the gastrointestinal microbiota and hence for maintaining health and welfare.  相似文献   
2.
3.
4.

Forest transformation from coniferous monocultures to mixed stands is being promoted worldwide, including the introduction of fast-growing broadleaved tree species within native stands. Here, we studied how enrichment of temperate European Scots pine (Pinus sylvestris) forest by North-American northern red oak Quercus rubra impacted macronutrient concentrations in two long-lived and dominant components of the forest understory: bilberry Vaccinium myrtillus and lingonberry V. vitis-idaea. Study sites were located in forest complexes (central Poland) which occupy continuously reforested lands (hereafter ancient forests) as well as post-agricultural lands (recent forests), all suitable for mesic pine forests. Samples of bilberry and lingonberry leaves, stems, and fruits were collected in pine stands and in adjacent Scots pine-red oak stands, in both ancient and recent forests. Concentrations of macronutrients (C, N, P, K, Ca, S, and Mg) in aboveground biomass components were analysed using standardized chemical procedures. The study revealed intra- and interspecific (bilberry vs. lingonberry) differences in concentrations of all nutrients in leaves, stems, and fruits, except for invariable C concentrations. Macronutrient accumulations in plants were decreased by land-use discontinuity and favoured by enrichment of tree stands by Q. rubra. The estimated macronutrient pools were much higher for V. myrtillus than V. vitis-idaea in all forest types studied. They were lower in forests enriched with Q. rubra, both ancient (up to 25.5% for bilberry and 99.9% for lingonberry) and recent (46.9% and 99.9%, respectively), as well as in recent pine forest (46.6% and 81.1%, respectively) than in ancient pine forest. Higher K and S pools (39.3% and 6.5%, respectively) noted for bilberry in an ancient forest with Q. rubra were exceptions. Despite more effective accumulations of elements at the species level, macronutrient pools of Vaccinium myrtillus and V. vitis-idaea decreased significantly in the presence of introduced Q. rubra due to negative impacts of this broadleaved tree on bilberry and lingonberry cover and biomass. Therefore, the limitation of alien Q. rubra planting in sites of mesic pine forest with the abundant occurrence of V. myrtillus and/or V. vitis-idaea is recommended.

Graphic abstract
  相似文献   
5.
The objective of this study has been to determine the influence of food and ions on the pharmacokinetics of enrofloxacin (ENRO) in turkeys, administered per os at a dose of 10 mg/kg of body weight (b.w.). Co-administration of ENRO with ions or with food significantly retarded its absorption, and the interaction was more pronounced when the drug was given together with food. The bioavailability of ENRO was 65.78 ± 7.81% and 47.99 ± 9.48% with ions and food, respectively. The maximum concentration (Cmax) in plasma of animals exposed to ions reached 0.87 ± 0.26 μg/ml in a tmax of 2.07 ± 0.76 h; in animals which were fed while medicated, the analogous parameters were 0.36 ± 0.13 μg/ml and 8.06 ± 3.08 h. The PK/PD analysis demonstrated that a decrease in the concentration of ENRO in turkeys’ blood due to the interaction with ions or food might impair the drug's clinical efficacy toward some pathogenic microorganisms in turkeys if a routine dose of 10 mg ENRO/kg b.w. is administered.  相似文献   
6.
Proteolytic activity of sea trout hatching liquid was examined towards casein and azocazein as a function of pH and temperature. The optimum pH for caseinolytic and azocaseinolytic activities were 9.4, and 9.0, respectively. At alkaline pH the enzyme was activated by low concentrations of Zn2+ ions (10−5 M). Maximum proteolytic activity of the hatching liquid was observed at 25°C. Temperatures exceeding 30°C caused a rapid reduction in enzyme activity. Proteolytic activity observed at 10°C was approximately 50% of that observed at 25°C. In general, a pseudo-Arrhenius plot indicated a Q10 of 1.6 between 6 and 25°C.  相似文献   
7.
Jerzy Drzewiecki 《Euphytica》2001,119(3):279-287
Wheat-rye translocation line (2BS/2RL) has been developed for resistance to biotype L of Hessian fly and agronomically useful traits. AFLP analysis using 64 primer pairs was conducted in order to identify 2RL-specific polymorphisms between “Coker 797” (non-2RL), near-isogenic line (NIL) carrying 2RL, and “Hamlet”. Nine primer combinations identified twelve reproducible polymorphic fragments in the NIL carrying 2RL. These twelve fragments were cloned and sequenced with an aim towards converting AFLP markers into sequence tagged sites (STS). A comparison of the 12 sequences with non-redundant accessions in the NCBI database using the BLAST search option indicated that one fragment of approximately 200 bp in length (amplified using primer combination E+AAC / M+CTA) was highly homologous with the rye-specific repetitive sequence R173-1 and Wis-2-lA, a retrotransposon-like element in wheat. Two STS primers (SJ07 and SJ09) out of twelve STS primer sets enabled the detection of polymorphisms between Coker 797 and NIL carrying 2RL. In order to verify whether the polymorphism detected by primers SJ07 and SJ09 was in fact the result of the presence of 2RL, additional plant material was examined. Amplified products of about 260 bp fragment with the SJ07 primer set were generated in rye cvs.“Chilbohomil” and “Jochunhomil”, triticale experimental line Suwon 15, and wheat experimental line K-14 (1AL/1RS & 2BS/2RL), as well as NIL carrying 2RL and Hamlet, but not in Coker 797 (non-2RL), “Keumgangmil” (non-translocation wheat), KS92WGRC17 (PI592729 /;/ 6BS/6BL-6RL), KS92WGRC19 (P1592731 /;/ 4BS/4BL-6RL), “TAM200” (1AL/1RS), and “Siouxland” (1BL/1RS). Our data suggest that primer set SJ07 amplifies a “2RL-specific” fragment of diagnostic value. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
8.
Among the wheatgrasses that are possible sources of genetic resistance for wheat to barley yellow-dwarf-virus disease (BYD) are those that have been commonly subsumed under the name Agropyron elongatum (Host) P. Beauv. Two of these wheatgrass species are the diploid Lophopymm elongatum (Host) Á. Löve (2n = 2x = 14) and the decaploid L. ponticum (Podp.) Á. Löve (2n = 10x = 70). These two species, the addition and substitution lines of L. elongatum chromosomes in hexaploid wheat (Triticum aestivum L.), and derivatives of hybrids between hexaploid wheat and L. ponticum, were screened for resistance to BYD, as defined by visual symptoms in field-grown plants. The two species, an amphiploid derived from L. elongatumבChinese Spring’ wheat, and the derivatives involving L. ponticum chromosomes were all highly resistant. The substitution and addition lines of L. elongatum chromosomes in ‘Chinese Spring’ revealed that the genetic control of resistance in L. elongatum must be complex, with more than one critical locus involved. Chromosomes 2E and 5E are involved and there are lesser contributions to resistance from the remaining wheatgrass chromosomes. One highly resistant derivative was determined to have only three pairs of L. ponticum chromosomes. It has a wheat-like morphology and shows promise for further characterization.  相似文献   
9.
Total concentrations of mercury were determined using cold-vapor atomic absorption spectroscopy (CV-AAS) in the fruiting bodies of 16 species of wild mushrooms and underlying soil (0-10 cm) substrates collected in the areas of the Communes of Morag and ?ukta in the county of Ostróda in northeastern Poland in 1997-1998. A total of 174 composite samples of caps, 174 stalks, 80 whole fruiting bodies (collectively 1254 specimens), and 252 soils were examined. Among several species of mushrooms analyzed, the greatest concentrations were between 1300 and 71000 ng.g(-1) of dry matter. These levels were found in the caps of Sweating mushroom (Clitocybe rivulosa), King Bolete (Boletus edulis), and Common Puffball (Lycoperdon perlatum) and also were characterized by the highest bioconcentration factors (BCF) for Hg, which ranged between 160 +/- 82 and 110 +/- 34. The cap to stalk quotient for mercury concentrations was approximately 2 for most of the species except Poison Pax (Paxilus involutus), which had a greater concentration in caps than in stalks and a quotient of 4.4 +/- 7.2. Hg concentrations in the underlying soil substrates (0-10 cm layer) ranged between 21 +/- 21 and 390 +/- 130 ng.g(-1) of dry matter. The results showed that the consumption of mushrooms, considered to be the sole dietary source of mercury at the highest or mean element concentrations found, is not hazardous at daily ingestion rates of less than 70 and 210 g of fresh product, which would result in a hazard index value of less than unity.  相似文献   
10.
The volatile composition (volatile phenols, phenolic aldehydes, furanic compounds, lactones, phenyl ketones, and other related compounds) of Spanish oak heartwood of Quercus robur, Quercus petraea,Quercus pyrenaica, and Quercus faginea was studied by gas chromatography/mass spectrometry, in relation to the processing in barrels cooperage and in relation to the French oak of Quercus robur (Limousin) and Quercus petraea (Allier) and American oak of Quercus alba (Missouri), which are habitually used in cooperage. The volatile composition of seasoned oak woods varied according to individual trees, species, and origins, and the differences were more significant in Spanish species with respect to American species than with respect to French species. The toasting process influenced the volatile composition of wood. It led to high increases in the concentration of volatile phenols, furanic aldehydes, phenyl ketones, and other related structures, but the effect on w-lactones levels depended on species and origin. The volatile composition in Spanish oak species evolved during toasting like in French and American oak, but quantitative differences were found, especially important in American species with respect to European species.  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