全文获取类型
收费全文 | 1077篇 |
免费 | 77篇 |
国内免费 | 1篇 |
专业分类
林业 | 36篇 |
农学 | 17篇 |
基础科学 | 15篇 |
146篇 | |
综合类 | 163篇 |
农作物 | 20篇 |
水产渔业 | 33篇 |
畜牧兽医 | 651篇 |
园艺 | 7篇 |
植物保护 | 67篇 |
出版年
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 26篇 |
2014年 | 19篇 |
2013年 | 39篇 |
2012年 | 30篇 |
2011年 | 46篇 |
2010年 | 31篇 |
2009年 | 18篇 |
2008年 | 35篇 |
2007年 | 38篇 |
2006年 | 43篇 |
2005年 | 31篇 |
2004年 | 29篇 |
2003年 | 32篇 |
2002年 | 21篇 |
2001年 | 33篇 |
2000年 | 24篇 |
1999年 | 26篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1992年 | 17篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1974年 | 10篇 |
1973年 | 25篇 |
1972年 | 19篇 |
1971年 | 12篇 |
1970年 | 9篇 |
1969年 | 10篇 |
1967年 | 11篇 |
1966年 | 15篇 |
排序方式: 共有1155条查询结果,搜索用时 15 毫秒
61.
Water uptake and water use of field beans and oats grown on a loess-derived grey-brown podzolic soil (Eutroboralf) The terms of the water-balance equation were determined, when field beans (Vicia faba L.) and oats (Avena sativa L.) were grown on a loess-derived soil during two seasons (1982 and 1983). A specific objective of this investigation was to quantify the water uptake from different layers and the total transpiration of both crops, as field beans are known to be susceptible to water shortage. Beside soil physical measurements climatological data for calculation of potential evapotranspiration were recorded. Plants were analyzed due to leaf area and root length density once a week. Actual evapotranspiration including interception, as determined by the soil physical approach, was split up by calculation procedures into actual evaporation, interception and actual transpiration. Total root length and root length density of field beans were much smaller and the rooting system was shallower as compared with oats. Development of leaf area and of roots was slower with beans than oats and was retarted by 2 to 3 weeks. Accordingly the time of maximum transpiration was found begin of June with oats and at begin of July with field beans. Despite reduced root growth Vicia faba transpired 250 mm in total, that is 86 % of what was found for the cereal crop (290 mm). Water uptake field beans however, was restricted to the upper 80-cm profile with 90 % of total uptake. The water uptake per unit length of root was substantial higher with beans than with oats. Due to the delayed development of the bean crop the losses by evaporation and seepage exceeded those from the soil grown to oats by 40mm (64 %). These investigations support the conclusion that yield stability of field beans may be substantially improved by selection of new varieties with increased rooting depth. 相似文献
62.
Schneweis I Meyer K Engelhardt G Bauer J 《Journal of agricultural and food chemistry》2002,50(6):1736-1738
An LC-MS method was developed for the analysis of zearalenone-4-beta-D-glucopyranoside and zearalenone in wheat (Triticum aestivum). The limit of determination for zearalenone-4-beta-D-glucopyranoside and zearalenone was 10 microg/kg. The recovery rates were calculated to be 69% and 89% at a concentration of 100 microg/kg for zearalenone-4-beta-D-glucopyranoside and zearalenone, respectively. Twenty-four Bavarian wheat samples from a 1999 harvest were analyzed. Zearalenone was present in 22 of 24 field samples, the levels ranged from 11 to 860 microg/kg. Zearalenone-4-beta-D-glucopyranoside was found in 10 of the zearalenone positive samples (42%) at levels ranging from 17 to 104 microg/kg. The amounts of zearalenone-4-beta-D-glucopyranoside were correlated to those of zearalenone (r2 = 0.86, b = 0.10). After gastrointestinal hydrolyzation, zearalenone-4-beta-glucopyranoside might be implicated in the development of a zearalenone-syndrome. Therefore, more attention should be focused on conjugated mycotoxins in food and feed. 相似文献
63.
64.
Positive feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none outputs. Here we investigate why the positive feedback switches that regulate polarization of budding yeast, calcium signaling, Xenopus oocyte maturation, and various other processes use multiple interlinked loops rather than single positive feedback loops. Mathematical simulations revealed that linking fast and slow positive feedback loops creates a "dual-time" switch that is both rapidly inducible and resistant to noise in the upstream signaling system. 相似文献
65.
66.
The feasibility of studying avian primordial germ cells in blood smears has been demonstrated. Blood smears prepared from chick embryos of stages 13 to 15 (48 to 55 hours) contained primordial germ cells, which were revealed by the periodic acidSchiff reaction. The presence of glycogen in the cytoplasm of the primordial germ cells facilitated their selective identification. 相似文献
67.
Meyer AH 《Science (New York, N.Y.)》1930,71(1844):461-462
68.
Castro-Rodriguez I Nakai H Zakharov LN Rheingold AL Meyer K 《Science (New York, N.Y.)》2004,305(5691):1757-1759
The electron-rich, six-coordinate tris-aryloxide uranium(III) complex [((AdArO)3tacn)U(III)] [where (AdArOH)3tacn = 1,4,7-tris(3-adamantyl-5-tert-butyl-2-hydroxybenzyl)1,4,7-triazacyclononane] reacts rapidly with CO2 to yield [((AdArO)3tacn)U(IV)(CO2)], a complex in which the CO(2) ligand is linearly coordinated to the metal through its oxygen atom (eta1-OCO). The latter complex has been crystallographically and spectroscopically characterized. The inequivalent O-C-O bond lengths [1.122 angstroms (A) for the O-C bond adjacent to uranium and 1.277 A for the other], considered together with magnetization data and electronic and vibrational spectra, support the following bonding model: U(IV)=O=C*-O- <--> U(IV)-OC-O-. In these charge-separated resonance structures, the uranium center is oxidized to uranium(IV) and the CO2 ligand reduced by one electron. 相似文献
69.
Fritz J Baller MK Lang HP Rothuizen H Vettiger P Meyer E Güntherodt H Gerber C Gimzewski JK 《Science (New York, N.Y.)》2000,288(5464):316-318
We report the specific transduction, via surface stress changes, of DNA hybridization and receptor-ligand binding into a direct nanomechanical response of microfabricated cantilevers. Cantilevers in an array were functionalized with a selection of biomolecules. The differential deflection of the cantilevers was found to provide a true molecular recognition signal despite large nonspecific responses of individual cantilevers. Hybridization of complementary oligonucleotides shows that a single base mismatch between two 12-mer oligonucleotides is clearly detectable. Similar experiments on protein A-immunoglobulin interactions demonstrate the wide-ranging applicability of nanomechanical transduction to detect biomolecular recognition. 相似文献
70.
Rendulic S Jagtap P Rosinus A Eppinger M Baar C Lanz C Keller H Lambert C Evans KJ Goesmann A Meyer F Sockett RE Schuster SC 《Science (New York, N.Y.)》2004,303(5658):689-692
Predatory bacteria remain molecularly enigmatic, despite their presence in many microbial communities. Here we report the complete genome of Bdellovibrio bacteriovorus HD100, a predatory Gram-negative bacterium that invades and consumes other Gram-negative bacteria. Its surprisingly large genome shows no evidence of recent gene transfer from its prey. A plethora of paralogous gene families coding for enzymes, such as hydrolases and transporters, are used throughout the life cycle of B. bacteriovorus for prey entry, prey killing, and the uptake of complex molecules. 相似文献