全文获取类型
收费全文 | 721篇 |
免费 | 19篇 |
专业分类
林业 | 51篇 |
农学 | 10篇 |
基础科学 | 2篇 |
86篇 | |
综合类 | 278篇 |
农作物 | 18篇 |
水产渔业 | 35篇 |
畜牧兽医 | 195篇 |
园艺 | 18篇 |
植物保护 | 47篇 |
出版年
2023年 | 9篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 23篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 16篇 |
2012年 | 46篇 |
2011年 | 49篇 |
2010年 | 29篇 |
2009年 | 19篇 |
2008年 | 57篇 |
2007年 | 55篇 |
2006年 | 68篇 |
2005年 | 56篇 |
2004年 | 39篇 |
2003年 | 38篇 |
2002年 | 37篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1995年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1966年 | 2篇 |
1954年 | 1篇 |
1946年 | 1篇 |
1944年 | 1篇 |
1936年 | 1篇 |
1931年 | 2篇 |
排序方式: 共有740条查询结果,搜索用时 473 毫秒
161.
Macrae IJ Zhou K Li F Repic A Brooks AN Cande WZ Adams PD Doudna JA 《Science (New York, N.Y.)》2006,311(5758):195-198
The specialized ribonuclease Dicer initiates RNA interference by cleaving double-stranded RNA (dsRNA) substrates into small fragments about 25 nucleotides in length. In the crystal structure of an intact Dicer enzyme, the PAZ domain, a module that binds the end of dsRNA, is separated from the two catalytic ribonuclease III (RNase III) domains by a flat, positively charged surface. The 65 angstrom distance between the PAZ and RNase III domains matches the length spanned by 25 base pairs of RNA. Thus, Dicer itself is a molecular ruler that recognizes dsRNA and cleaves a specified distance from the helical end. 相似文献
162.
163.
164.
Cho A 《Science (New York, N.Y.)》2006,314(5798):403
165.
Sonkusare SK Bonev AD Ledoux J Liedtke W Kotlikoff MI Heppner TJ Hill-Eubanks DC Nelson MT 《Science (New York, N.Y.)》2012,336(6081):597-601
Major features of the transcellular signaling mechanism responsible for endothelium-dependent regulation of vascular smooth muscle tone are unresolved. We identified local calcium (Ca(2+)) signals ("sparklets") in the vascular endothelium of resistance arteries that represent Ca(2+) influx through single TRPV4 cation channels. Gating of individual TRPV4 channels within a four-channel cluster was cooperative, with activation of as few as three channels per cell causing maximal dilation through activation of endothelial cell intermediate (IK)- and small (SK)-conductance, Ca(2+)-sensitive potassium (K(+)) channels. Endothelial-dependent muscarinic receptor signaling also acted largely through TRPV4 sparklet-mediated stimulation of IK and SK channels to promote vasodilation. These results support the concept that Ca(2+) influx through single TRPV4 channels is leveraged by the amplifier effect of cooperative channel gating and the high Ca(2+) sensitivity of IK and SK channels to cause vasodilation. 相似文献
166.
167.
168.
Nancy P Tagliani E Tay CS Asp P Levy DE Erlebacher A 《Science (New York, N.Y.)》2012,336(6086):1317-1321
The chemokine-mediated recruitment of effector T cells to sites of inflammation is a central feature of the immune response. The extent to which chemokine expression levels are limited by the intrinsic developmental characteristics of a tissue has remained unexplored. We show in mice that effector T cells cannot accumulate within the decidua, the specialized stromal tissue encapsulating the fetus and placenta. Impaired accumulation was in part attributable to the epigenetic silencing of key T cell-attracting inflammatory chemokine genes in decidual stromal cells, as evidenced by promoter accrual of repressive histone marks. These findings give insight into mechanisms of fetomaternal immune tolerance, as well as reveal the epigenetic modification of tissue stromal cells as a modality for limiting effector T cell trafficking. 相似文献
169.
170.
Bertagnoli A Räber M Morandi N Mortellaro CM Steiner A 《Veterinary journal (London, England : 1997)》2012,191(1):121-127
The aim of this study was to describe the tenovaginoscopic approach to the bovine common digital flexor tendon sheath (CDFTS). A comparative anatomical, ultrasonographic and endoscopic study was undertaken using 26 healthy cadaver feet from adult dairy cows. Tenovaginoscopy was performed using a rigid, 30° arthroscope (length 18 cm; outer diameter 4mm) enabling a direct view of the synovial cavity and the following structures: digital flexor tendons, digital annular ligaments, lateral and medial pouches, three mesotendons, the vinculum of the superficial digital flexor tendon, and a slot-shaped opening in the manicaflexoria of the hind feet. Additionally, four clinical cases of septic tenosynovitis treated with lavage under tenovaginoscopic control were examined. Tenovaginoscopy represents a feasible, minimally invasive method for the diagnosis and treatment of septic tenosynovitis of the CDFTS, which allows the degree of alterations of the normal structures to be evaluated. 相似文献