全文获取类型
收费全文 | 696篇 |
免费 | 64篇 |
专业分类
林业 | 20篇 |
农学 | 12篇 |
基础科学 | 7篇 |
90篇 | |
综合类 | 173篇 |
农作物 | 21篇 |
水产渔业 | 40篇 |
畜牧兽医 | 344篇 |
园艺 | 18篇 |
植物保护 | 35篇 |
出版年
2023年 | 10篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 9篇 |
2014年 | 24篇 |
2013年 | 17篇 |
2012年 | 37篇 |
2011年 | 44篇 |
2010年 | 29篇 |
2009年 | 23篇 |
2008年 | 34篇 |
2007年 | 44篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 28篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1997年 | 5篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1974年 | 14篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 11篇 |
1968年 | 5篇 |
1967年 | 4篇 |
1930年 | 5篇 |
1920年 | 4篇 |
1904年 | 4篇 |
排序方式: 共有760条查询结果,搜索用时 46 毫秒
31.
32.
Stevens FL 《Science (New York, N.Y.)》1915,41(1068):912-913
33.
34.
35.
36.
Potassium-argon dates obtained from extrusives collected on a traverse across the Mid-Atlantic Ridge at 45 degrees N are consistent with the hypothesis of ocean-floor spreading. The dates suggest a spreading rate in the range of 2.6 to 3.2 centimeters per year near the axis of the ridge; the rate agrees with that computed from fission-track dating of basalt glasses. Additional data for a basalt collected 62 kilometers west of the axis gives a spreading rate of 0.8 centimeter per year, which is similar to the rate inferred from magnetic anomaly patterns in the area. Reasons for the difference in calculated spreading rates are discussed. 相似文献
37.
38.
Temporal variability of the Atlantic meridional overturning circulation at 26.5 degrees N 总被引:4,自引:0,他引:4
Cunningham SA Kanzow T Rayner D Baringer MO Johns WE Marotzke J Longworth HR Grant EM Hirschi JJ Beal LM Meinen CS Bryden HL 《Science (New York, N.Y.)》2007,317(5840):935-938
The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5 degrees N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 +/- 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 10(6) cubic meters per second). Interannual changes in the overturning can be monitored with a resolution of 1.5 Sv. 相似文献
39.
Observed flow compensation associated with the MOC at 26.5 degrees N in the Atlantic 总被引:3,自引:0,他引:3
Kanzow T Cunningham SA Rayner D Hirschi JJ Johns WE Baringer MO Bryden HL Beal LM Meinen CS Marotzke J 《Science (New York, N.Y.)》2007,317(5840):938-941
The Atlantic meridional overturning circulation (MOC), which provides one-quarter of the global meridional heat transport, is composed of a number of separate flow components. How changes in the strength of each of those components may affect that of the others has been unclear because of a lack of adequate data. We continuously observed the MOC at 26.5 degrees N for 1 year using end-point measurements of density, bottom pressure, and ocean currents; cable measurements across the Straits of Florida; and wind stress. The different transport components largely compensate for each other, thus confirming the validity of our monitoring approach. The MOC varied over the period of observation by +/-5.7 x 10(6) cubic meters per second, with density-inferred and wind-driven transports contributing equally to it. We find evidence for depth-independent compensation for the wind-driven surface flow. 相似文献
40.
Structure and receptor specificity of the hemagglutinin from an H5N1 influenza virus 总被引:3,自引:0,他引:3
Stevens J Blixt O Tumpey TM Taubenberger JK Paulson JC Wilson IA 《Science (New York, N.Y.)》2006,312(5772):404-410
The hemagglutinin (HA) structure at 2.9 angstrom resolution, from a highly pathogenic Vietnamese H5N1 influenza virus, is more related to the 1918 and other human H1 HAs than to a 1997 duck H5 HA. Glycan microarray analysis of this Viet04 HA reveals an avian alpha2-3 sialic acid receptor binding preference. Introduction of mutations that can convert H1 serotype HAs to human alpha2-6 receptor specificity only enhanced or reduced affinity for avian-type receptors. However, mutations that can convert avian H2 and H3 HAs to human receptor specificity, when inserted onto the Viet04 H5 HA framework, permitted binding to a natural human alpha2-6 glycan, which suggests a path for this H5N1 virus to gain a foothold in the human population. 相似文献