全文获取类型
收费全文 | 201篇 |
免费 | 26篇 |
专业分类
林业 | 4篇 |
农学 | 12篇 |
36篇 | |
综合类 | 18篇 |
农作物 | 8篇 |
水产渔业 | 11篇 |
畜牧兽医 | 125篇 |
园艺 | 4篇 |
植物保护 | 9篇 |
出版年
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 7篇 |
2011年 | 16篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1995年 | 2篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 5篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1964年 | 1篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1954年 | 2篇 |
1953年 | 2篇 |
1948年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有227条查询结果,搜索用时 15 毫秒
221.
Abramson J Smirnova I Kasho V Verner G Kaback HR Iwata S 《Science (New York, N.Y.)》2003,301(5633):610-615
Membrane transport proteins that transduce free energy stored in electrochemical ion gradients into a concentration gradient are a major class of membrane proteins. We report the crystal structure at 3.5 angstroms of the Escherichia coli lactose permease, an intensively studied member of the major facilitator superfamily of transporters. The molecule is composed of N- and C-terminal domains, each with six transmembrane helices, symmetrically positioned within the permease. A large internal hydrophilic cavity open to the cytoplasmic side represents the inward-facing conformation of the transporter. The structure with a bound lactose homolog, beta-D-galactopyranosyl-1-thio-beta-D-galactopyranoside, reveals the sugar-binding site in the cavity, and residues that play major roles in substrate recognition and proton translocation are identified. We propose a possible mechanism for lactose/proton symport (co-transport) consistent with both the structure and a large body of experimental data. 相似文献
222.
D. McGregor 《Land Degradation \u0026amp; Development》2001,12(1):90-91
223.
Eugene MARAIS Gillian MAGGS-KÖLLING Chen SHERMAN Tirza DONIGER LIURentao Binu M TRIPATHI Yosef STEINBERGER 《干旱区科学》2020,12(1):130-143
Functional structure and diversity of soil free-living nematodes in a desert environment depend on plant gender and sampling site.The objective of this study was to compare the composition,abundance and tropic group of soil free-living nematodes in the upper 0–10 cm soil layer under the male and female Acanthosicyos horridus Welw.ex Hook.f.plants and in the inter-shrub open areas(control)in the Namib Desert,Namibia in April 2015.Soil moisture,organic matter(OM)and pH was also analyzed.Free-living nematodes were extracted from 100 g soil using the Baermann funnel procedure,and total number of nematodes was counted under a microscope.Community composition and diversity of soil free-living nematodes were analyzed using 18S rDNA sequences.Results indicated that a total of 67 groups,including 64 species,2 genera and 1 family were identified.Feeding behavior of 58 species were identified as follows:15 bacteria-feeding species,12 fungi-feeding species,10 plant-parasite species,5 omnivorous-predator species,8 animal-parasite species,5 invertebrate-parasite species and 3 non-free-living nematodes,known as marine species.Moreover,soil free-living nematodes were found to be affected by sampling locations and plant gender,and community composition and density of these nematodes were strongly influenced by soil OM content.Result confirmed that spatial location and plant cover were main factors influencing the diversity of soil free-living nematodes.Moreover,molecular tools were found to be very useful in defining the richness of soil non-free-living nematodes.In conclusion,the results elucidated the importance of biotic variables in determining the composition and abundance of soil free-living nematodes in the Namib Desert,Namibia. 相似文献
224.
Duncan McGregor 《Land Degradation \u0026amp; Development》1990,2(4):325-327
225.
Ambrose-Oji Bianca Atkinson Mark Petrokofsky Gillian Hemery Gabriel 《Small-Scale Forestry》2020,19(2):159-185
Small-scale Forestry - Forest and woodland owners and managers are generally perceived to be acting slowly in addressing environmental change by adapting their forestry practice. Diversification of... 相似文献
226.
227.