全文获取类型
收费全文 | 943篇 |
免费 | 38篇 |
专业分类
林业 | 31篇 |
农学 | 19篇 |
基础科学 | 5篇 |
118篇 | |
综合类 | 176篇 |
农作物 | 26篇 |
水产渔业 | 46篇 |
畜牧兽医 | 501篇 |
园艺 | 12篇 |
植物保护 | 47篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 20篇 |
2013年 | 29篇 |
2012年 | 30篇 |
2011年 | 51篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 33篇 |
2005年 | 35篇 |
2004年 | 29篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 24篇 |
2000年 | 25篇 |
1999年 | 26篇 |
1998年 | 11篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1979年 | 8篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1969年 | 14篇 |
1967年 | 8篇 |
排序方式: 共有981条查询结果,搜索用时 715 毫秒
51.
52.
Morgan WW 《Science (New York, N.Y.)》1934,79(2055):454-455
53.
The adenovirus major late transcription factor activates the rat gamma-fibrinogen promoter 总被引:45,自引:0,他引:45
L A Chodosh R W Carthew J G Morgan G R Crabtree P A Sharp 《Science (New York, N.Y.)》1987,238(4827):684-688
54.
The carbon in ancient carbonaceous chondritic meteorites is mainly in a hydrocarbon composite similar to terrestrial kerogen, a cross-linked structure of aliphatic and aromatic hydrocarbons. Until recently, the composite has been commonly thought to have been produced in the early solar nebula by a Fischer-Tropsch-type process, involving the catalytic synthesis of hydrocarbons from carbon monoxide and hydrogen on grain surfaces. Instead, the aromatic hydrocarbons may form in gas-phase pyrolysis of simple aliphatics like acetylene and methane by a mechanism developed recently to explain formation of soot in combustion and of aromatic molecules in circumstellar envelopes. Nonequilibrium chemical kinetic calculations indicate that this mechanism can produce meteoritic aromatics if the initial concentration of simple hydrocarbons in the solar nebula was sufficiently but not unreasonably high. 相似文献
55.
V Ciaravino A Brulfert M W Miller D Jacobson-Kram W F Morgan 《Science (New York, N.Y.)》1985,227(4692):1349-1351
Human lymphocytes were exposed in vitro to ultrasound from two clinical devices, one of which was previously reported to have increased the frequency of sister chromatid exchanges. The ultrasonic exposures had no significant effect on the frequency of sister chromatid exchanges from three blood donors. Exposure to ultrasound also had no effect on cell cycle progression. A concomitant positive control (mitomycin C) resulted in a significant increase in sister chromatid exchanges. 相似文献
56.
Core soil sampling followed by laboratory analysis is the traditional method used to map soil pH prior to variable rate application (VRA) of lime on cropland. A recently developed automated soil sampling system capable of measuring soil pH on-the-go has significantly increased sampling resolution. However, adoption of such systems must be justified economically. This paper presents a method for assessing the economic benefit from automated mapping of soil pH prior to variable rate lime application. In this work, geostatistical, agronomic, and economic methods were used to generate a comprehensive numerical model for quantitative assessment of the net return over cost of liming for different lime management strategies. The strategies included: automated pH mapping, manual grid soil sampling, and whole field sampling used in combination with either variable or fixed rate liming. The model was demonstrated using a simulated field with known average pH and semivariogram model. The analysis showed the largest benefit ($6.13ha–1year–1) from using VRA with automated soil pH mapping versus VRA based on 1ha (2.5acres) manual grid point sampling for the selected simulated field conditions. A sensitivity analysis demonstrated that for a wide range of field conditions and crop prices, VRA plus automated mapping promises higher relative benefits than VRA based on either manual grid point or grid cell sampling. 相似文献
57.
Individual tumors of multifocal EB virus-induced malignant lymphomas in tamarins arise from different B-cell clones 总被引:10,自引:0,他引:10
M L Cleary M A Epstein S Finerty R F Dorfman G W Bornkamm J K Kirkwood A J Morgan J Sklar 《Science (New York, N.Y.)》1985,228(4700):722-724
Cotton-top tamarins were inoculated with sufficient Epstein-Barr virus to induce multiple tumors in each animal within 14 to 21 days. The tumors consisted of large-cell lymphomas that contained multiple copies of the Epstein-Barr virus genome and generated Epstein-Barr virus-carrying cell lines showing no detectable consistent chromosomal abnormality. Hybridization of tumor DNA with immunoglobulin gene probes revealed that each lymphoma was oligo- or monoclonal in origin and that individual tumors from the same animal arose from different B-cell clones. Thus the virus induced multiple transformation events in tamarins in vivo to cause malignant tumors resembling the Epstein-Barr virus-associated lymphomas of patients with organ transplants. 相似文献
58.
Monochromatic images of Mercury at the sodium D(2) emission line showed excess sodium emission in localized regions at high northern and southern latitudes and day-to-day global variations in the distribution of sodium emission. These phenomena support the suggestion that magnetospheric effects could be the cause. Sputtering of surface minerals could produce sodium vapor in polar regions during magnetic substorms, when magnetospheric ions directly impact the surface. Another important process may be the transport of sodium ions along magnetic field lines toward polar regions, where they impact directly on the surface of Mercury and are neutralized to regenerate neutral sodium atoms. Day-to-day variations in planetary sodium distributions could result from changing solar activity, which can change the magnetosphere in time scales of a few hours. Observations of the sodium exosphere may provide a tool for remote monitoring of the magnetosphere of Mercury. 相似文献
59.
Cloned viral protein vaccine for foot-and-mouth disease: responses in cattle and swine 总被引:88,自引:0,他引:88
D G Kleid D Yansura B Small D Dowbenko D M Moore M J Grubman P D McKercher D O Morgan B H Robertson H L Bachrach 《Science (New York, N.Y.)》1981,214(4525):1125-1129
A DNA sequence coding for the immunogenic capsid protein VP3 of foot-and-mouth disease virus A12, prepared from the virion RNA, was ligated to a plasmid designed to express a chimeric protein from the Escherichia coli tryptophan promoter-operator system. When Escherichia coli transformed with this plasmid was grown in tryptophan-depleted media, approximately 17 percent of the total cellular protein was found to be an insoluble and stable chimeric protein. The purified chimeric protein competed equally on a molar basis with VP3 for specific antibodies to foot-and-mouth disease virus. When inoculated into six cattle and two swine, this protein elicited high levels of neutralizing antibody and protection against challenge with foot-and-mouth disease virus. 相似文献
60.