全文获取类型
收费全文 | 1022篇 |
免费 | 43篇 |
国内免费 | 2篇 |
专业分类
林业 | 50篇 |
农学 | 16篇 |
基础科学 | 7篇 |
155篇 | |
综合类 | 154篇 |
农作物 | 58篇 |
水产渔业 | 51篇 |
畜牧兽医 | 515篇 |
园艺 | 27篇 |
植物保护 | 34篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 25篇 |
2012年 | 32篇 |
2011年 | 51篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 42篇 |
2007年 | 47篇 |
2006年 | 41篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 21篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1979年 | 10篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1973年 | 12篇 |
1972年 | 17篇 |
1971年 | 9篇 |
1970年 | 27篇 |
1969年 | 15篇 |
1968年 | 9篇 |
1967年 | 11篇 |
1966年 | 9篇 |
排序方式: 共有1067条查询结果,搜索用时 15 毫秒
71.
Internal heat flow from radioactive decay in Triton's interior along with absorbed thermal energy from Neptune total 5 to 20 percent of the insolation absorbed by Triton, thus comprising a significant fraction of Triton's surface energy balance. These additional energy inputs can raise Triton's surface temperature between approximately 0.5 and 1.5 K above that possible with absorbed sunlight alone, resulting in an increase of about a factor of approximately 1.5 to 2.5 in Triton's basal atmospheric pressure. If Triton's internal heat flow is concentrated in some areas, as is likely, local effects such as enhanced sublimation with subsequent modification of albedo could be quite large. Furthermore, indications of recent global albedo change on Triton suggest that Triton's surface temperature and pressure may not now be in steady state, further suggesting that atmospheric pressure on Triton was as much as ten times higher in the recent past. 相似文献
72.
Concentration oscillations and efficiency: glycolysis 总被引:3,自引:0,他引:3
The oscillations observed in glycolysis are analyzed from the point of view of efficiency of free energy conversion. It is suggested that the mechanisms generating these oscillations may have evolved in order to reduce the dissipation of free energy. 相似文献
73.
Ten amphibole specimens from a variety of metamorphic rocks such as talc schists, eclogites, and metamorphosed iron formations contain lamellae of a second amphibole oriented parallel to ([unknown]101) or (100), or both, of the host. Tremolites, actinolites, and hornblendes commonly have lamellae of a calcium-poor clinoamphibole with P2(1)/m space-group symmetry, or lamellae of cummingtonite with C2/m space-group symmetry. Likewise cummingtonites and P2(1)/m clinoamphiboles commonly contain lamellae of calcium-rich C2/m amphiboles such as tremolite. Results of x-ray diffraction, electron-probe, and microscope studies indicate that most lamellae result from unmixing of a homogeneous amphibole. The P2(1)/m clinoamphibole is analogous to the clinopyroxene pigeonite in agreement with the results of M. G. Bown. 相似文献
74.
Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142Nd/144Nd ratios than the terrestrial standard (epsilon142Nd = -0.07 to -0.15). Within a mafic amphibolite unit, 142Nd/144Nd ratios correlate positively with Sm/Nd ratios and produce a 146Sm-142Nd isochron with an age of 4280(-81)(+53) million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth. 相似文献
75.
76.
77.
Ross IM 《Science (New York, N.Y.)》1982,217(4555):130-131
The promise of technology for improving the quality of life has never been greater, and American science and technology has led the way toward fulfillment of that promise. Now this preeminence is threatened by forces that may affect technological progress throughout the world. It is up to those of us in science, industry, and government to strengthen the institutions that have made us the leaders and to restore our initiative. 相似文献
78.
Reoviruslike agent in stools: association with infantile diarrhea and development of serologic tests 总被引:39,自引:0,他引:39
A Z Kapikian H W Kim R G Wyatt W J Rodriguez S Ross W L Cline R H Parrott R M Chanock 《Science (New York, N.Y.)》1974,185(156):1049-1053
Reoviruslike particles were visualized by electron microscopy in stool filtrates prepared from stools of infants and young children with severe acute gastroenteritis. Patients who had such particles in their stools and whose paired acute and convalescent serums were tested developed an antibody response to the reoviruslike agent, which was measured by immune electron microscopy and by complement fixation. The reoviruslike agent was antigenically related to the epizootic diarrhea of infant mice virus and the Nebraska calf diarrhea virus. 相似文献
79.
The Law of the Sea treaty will clearly affect the way U.S. marine scientists operate in about 40 percent of the ocean. The matter will be made even more complex by the apparent intention of the Reagan Administration to remain outside the treaty. 相似文献
80.