全文获取类型
收费全文 | 1436篇 |
免费 | 64篇 |
国内免费 | 1篇 |
专业分类
林业 | 77篇 |
农学 | 44篇 |
基础科学 | 17篇 |
246篇 | |
综合类 | 215篇 |
农作物 | 40篇 |
水产渔业 | 109篇 |
畜牧兽医 | 611篇 |
园艺 | 36篇 |
植物保护 | 106篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 23篇 |
2020年 | 38篇 |
2019年 | 40篇 |
2018年 | 35篇 |
2017年 | 32篇 |
2016年 | 37篇 |
2015年 | 25篇 |
2014年 | 31篇 |
2013年 | 56篇 |
2012年 | 93篇 |
2011年 | 89篇 |
2010年 | 51篇 |
2009年 | 56篇 |
2008年 | 112篇 |
2007年 | 97篇 |
2006年 | 90篇 |
2005年 | 73篇 |
2004年 | 89篇 |
2003年 | 82篇 |
2002年 | 76篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 19篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1968年 | 4篇 |
1926年 | 5篇 |
排序方式: 共有1501条查询结果,搜索用时 390 毫秒
91.
On the cause of the 1930s Dust Bowl 总被引:3,自引:0,他引:3
Schubert SD Suarez MJ Pegion PJ Koster RD Bacmeister JT 《Science (New York, N.Y.)》2004,303(5665):1855-1859
During the 1930s, the United States experienced one of the most devastating droughts of the past century. The drought affected almost two-thirds of the country and parts of Mexico and Canada and was infamous for the numerous dust storms that occurred in the southern Great Plains. In this study, we present model results that indicate that the drought was caused by anomalous tropical sea surface temperatures during that decade and that interactions between the atmosphere and the land surface increased its severity. We also contrast the 1930s drought with other North American droughts of the 20th century. 相似文献
92.
93.
94.
95.
96.
Seeman P 《Science (New York, N.Y.)》2004,305(5681):180; author reply 180
97.
Rolef Ben-Shahar T Heeger S Lehane C East P Flynn H Skehel M Uhlmann F 《Science (New York, N.Y.)》2008,321(5888):563-566
Replicated chromosomes are held together by the chromosomal cohesin complex from the time of their synthesis in S phase onward. This requires the replication fork-associated acetyl transferase Eco1, but Eco1's mechanism of action is not known. We identified spontaneous suppressors of the thermosensitive eco1-1 allele in budding yeast. An acetylation-mimicking mutation of a conserved lysine in cohesin's Smc3 subunit makes Eco1 dispensable for cell growth, and we show that Smc3 is acetylated in an Eco1-dependent manner during DNA replication to promote sister chromatid cohesion. A second set of eco1-1 suppressors inactivate the budding yeast ortholog of the cohesin destabilizer Wapl. Our results indicate that Eco1 modifies cohesin to stabilize sister chromatid cohesion in parallel with a cohesion establishment reaction that is in principle Eco1-independent. 相似文献
98.
Yang H Jeffrey PD Miller J Kinnucan E Sun Y Thoma NH Zheng N Chen PL Lee WH Pavletich NP 《Science (New York, N.Y.)》2002,297(5588):1837-1848
Mutations in the BRCA2 (breast cancer susceptibility gene 2) tumor suppressor lead to chromosomal instability due to defects in the repair of double-strand DNA breaks (DSBs) by homologous recombination, but BRCA2's role in this process has been unclear. Here, we present the 3.1 angstrom crystal structure of a approximately 90-kilodalton BRCA2 domain bound to DSS1, which reveals three oligonucleotide-binding (OB) folds and a helix-turn-helix (HTH) motif. We also (i) demonstrate that this BRCA2 domain binds single-stranded DNA, (ii) present its 3.5 angstrom structure bound to oligo(dT)9, (iii) provide data that implicate the HTH motif in dsDNA binding, and (iv) show that BRCA2 stimulates RAD51-mediated recombination in vitro. These findings establish that BRCA2 functions directly in homologous recombination and provide a structural and biochemical basis for understanding the loss of recombination-mediated DSB repair in BRCA2-associated cancers. 相似文献
99.
Hong D Gupta R Ancliff P Atzberger A Brown J Soneji S Green J Colman S Piacibello W Buckle V Tsuzuki S Greaves M Enver T 《Science (New York, N.Y.)》2008,319(5861):336-339
Understanding cancer pathogenesis requires knowledge of not only the specific contributory genetic mutations but also the cellular framework in which they arise and function. Here we explore the clonal evolution of a form of childhood precursor-B cell acute lymphoblastic leukemia that is characterized by a chromosomal translocation generating a TEL-AML1 fusion gene. We identify a cell compartment in leukemic children that can propagate leukemia when transplanted in mice. By studying a monochorionic twin pair, one preleukemic and one with frank leukemia, we establish the lineal relationship between these "cancer-propagating" cells and the preleukemic cell in which the TEL-AML1 fusion first arises or has functional impact. Analysis of TEL-AML1-transduced cord blood cells suggests that TEL-AML1 functions as a first-hit mutation by endowing this preleukemic cell with altered self-renewal and survival properties. 相似文献
100.
Boyd P 《Science (New York, N.Y.)》2004,304(5669):396-397