全文获取类型
收费全文 | 890篇 |
免费 | 6篇 |
专业分类
林业 | 30篇 |
62篇 | |
综合类 | 407篇 |
农作物 | 14篇 |
水产渔业 | 6篇 |
畜牧兽医 | 362篇 |
园艺 | 2篇 |
植物保护 | 13篇 |
出版年
2012年 | 43篇 |
2011年 | 54篇 |
2010年 | 6篇 |
2008年 | 40篇 |
2007年 | 47篇 |
2006年 | 52篇 |
2005年 | 50篇 |
2004年 | 53篇 |
2003年 | 52篇 |
2002年 | 48篇 |
2001年 | 31篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1976年 | 12篇 |
1974年 | 5篇 |
1970年 | 10篇 |
1969年 | 6篇 |
1968年 | 8篇 |
1966年 | 5篇 |
1963年 | 10篇 |
1960年 | 5篇 |
1958年 | 5篇 |
1957年 | 10篇 |
1955年 | 7篇 |
1954年 | 8篇 |
1953年 | 7篇 |
1948年 | 5篇 |
1947年 | 6篇 |
1946年 | 4篇 |
1945年 | 6篇 |
1928年 | 4篇 |
1924年 | 5篇 |
1922年 | 4篇 |
排序方式: 共有896条查询结果,搜索用时 640 毫秒
91.
Baldwin RB 《Science (New York, N.Y.)》1970,170(3964):1297-1300
Analysis of physical and chemical observations shows that the interior of the moon is now and always has been hot. It is close to the melting point at each level beneath a cool outer zone. 相似文献
92.
93.
Increasing river discharge to the Arctic Ocean 总被引:10,自引:0,他引:10
Peterson BJ Holmes RM McClelland JW Vörösmarty CJ Lammers RB Shiklomanov AI Shiklomanov IA Rahmstorf S 《Science (New York, N.Y.)》2002,298(5601):2171-2173
Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 +/- 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate. 相似文献
94.
95.
96.
97.
98.
99.
The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of approximately 1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out. 相似文献
100.
Although it is well established that mammalian class switch recombination is responsible for altering the class of immunoglobulins, the mechanistic details of the process have remained unclear. Here, we show that stable RNA/DNA hybrids form at class switch sequences in the mouse genome upon cytokine-specific stimulation of class switch in primary splenic B cells. The RNA hybridized to the switch DNA is transcribed in the physiological orientation. Mice that constitutively express an Escherichia coli ribonuclease H transgene show a marked reduction in RNA/DNA hybrid formation, an impaired ability to generate serum immunoglobulin G antibodies, and significant inhibition of class switch recombination in their splenic B cells. These data provide evidence that stable RNA/DNA hybrids exist in the mammalian nuclear genome, can serve as intermediates for physiologic processes, and are mechanistically important for efficient class switching in vivo. 相似文献