全文获取类型
收费全文 | 907篇 |
免费 | 116篇 |
国内免费 | 2篇 |
专业分类
林业 | 32篇 |
农学 | 39篇 |
基础科学 | 5篇 |
147篇 | |
综合类 | 131篇 |
农作物 | 49篇 |
水产渔业 | 33篇 |
畜牧兽医 | 517篇 |
园艺 | 15篇 |
植物保护 | 57篇 |
出版年
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 38篇 |
2012年 | 37篇 |
2011年 | 43篇 |
2010年 | 37篇 |
2009年 | 17篇 |
2008年 | 38篇 |
2007年 | 42篇 |
2006年 | 40篇 |
2005年 | 44篇 |
2004年 | 38篇 |
2003年 | 41篇 |
2002年 | 55篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 22篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1969年 | 5篇 |
1943年 | 5篇 |
排序方式: 共有1025条查询结果,搜索用时 0 毫秒
81.
82.
A record of foraminiferal shell weight across glacial-interglacial Termination I shows a response related to seawater carbonate ion concentration and allows reconstruction of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestions that higher atmospheric carbon dioxide directly affects marine calcification, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcification on atmospheric carbon dioxide and is of practical importance to the application of paleoceanographic proxies. 相似文献
83.
84.
Atlas R Campbell P Cozzarelli NR Curfman G Enquist L Fink G Flanagin A Fletcher J George E Hammes G Heyman D Inglesby T Kaplan S Kennedy D Krug J Levinson R Marcus E Metzger H Morse SS O'Brien A Onderdonk A Poste G Renault B Rich R Rosengard A Salzburg S Scanlan M Shenk T Tabor H Varmus H Wimmer E Yamamoto K;Journal Editors Authors Group 《Science (New York, N.Y.)》2003,299(5610):1149
85.
86.
87.
88.
Pang PT Teng HK Zaitsev E Woo NT Sakata K Zhen S Teng KK Yung WH Hempstead BL Lu B 《Science (New York, N.Y.)》2004,306(5695):487-491
Long-term memory is thought to be mediated by protein synthesis-dependent, late-phase long-term potentiation (L-LTP). Two secretory proteins, tissue plasminogen activator (tPA) and brain-derived neurotrophic factor (BDNF), have been implicated in this process, but their relationship is unclear. Here we report that tPA, by activating the extracellular protease plasmin, converts the precursor proBDNF to the mature BDNF (mBDNF), and that such conversion is critical for L-LTP expression in mouse hippocampus. Moreover, application of mBDNF is sufficient to rescue L-LTP when protein synthesis is inhibited, which suggests that mBDNF is a key protein synthesis product for L-LTP expression. 相似文献
89.
Kilimanjaro ice core records: evidence of holocene climate change in tropical Africa 总被引:1,自引:0,他引:1
Thompson LG Mosley-Thompson E Davis ME Henderson KA Brecher HH Zagorodnov VS Mashiotta TA Lin PN Mikhalenko VN Hardy DR Beer J 《Science (New York, N.Y.)》2002,298(5593):589-593
Six ice cores from Kilimanjaro provide an approximately 11.7-thousand-year record of Holocene climate and environmental variability for eastern equatorial Africa, including three periods of abrupt climate change: approximately 8.3, approximately 5.2, and approximately 4 thousand years ago (ka). The latter is coincident with the "First Dark Age," the period of the greatest historically recorded drought in tropical Africa. Variable deposition of F- and Na+ during the African Humid Period suggests rapidly fluctuating lake levels between approximately 11.7 and 4 ka. Over the 20th century, the areal extent of Kilimanjaro's ice fields has decreased approximately 80%, and if current climatological conditions persist, the remaining ice fields are likely to disappear between 2015 and 2020. 相似文献
90.
Thornalley DJ Barker S Broecker WS Elderfield H McCave IN 《Science (New York, N.Y.)》2011,331(6014):202-205
Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon ((14)C)-depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation. 相似文献