全文获取类型
收费全文 | 187264篇 |
免费 | 9909篇 |
国内免费 | 142篇 |
专业分类
林业 | 8254篇 |
农学 | 5891篇 |
基础科学 | 1116篇 |
22880篇 | |
综合类 | 33432篇 |
农作物 | 7473篇 |
水产渔业 | 9117篇 |
畜牧兽医 | 94497篇 |
园艺 | 2510篇 |
植物保护 | 12145篇 |
出版年
2018年 | 2570篇 |
2017年 | 2870篇 |
2016年 | 2648篇 |
2015年 | 2245篇 |
2014年 | 2827篇 |
2013年 | 7075篇 |
2012年 | 5180篇 |
2011年 | 6412篇 |
2010年 | 4155篇 |
2009年 | 4234篇 |
2008年 | 6292篇 |
2007年 | 6038篇 |
2006年 | 5607篇 |
2005年 | 5277篇 |
2004年 | 5003篇 |
2003年 | 5147篇 |
2002年 | 4664篇 |
2001年 | 5573篇 |
2000年 | 5689篇 |
1999年 | 4554篇 |
1998年 | 1956篇 |
1997年 | 1874篇 |
1996年 | 1704篇 |
1995年 | 2109篇 |
1994年 | 1807篇 |
1993年 | 1734篇 |
1992年 | 3587篇 |
1991年 | 3783篇 |
1990年 | 3778篇 |
1989年 | 3782篇 |
1988年 | 3461篇 |
1987年 | 3419篇 |
1986年 | 3502篇 |
1985年 | 3437篇 |
1984年 | 2796篇 |
1983年 | 2536篇 |
1982年 | 1724篇 |
1979年 | 2693篇 |
1978年 | 2168篇 |
1977年 | 1819篇 |
1976年 | 1837篇 |
1975年 | 1985篇 |
1974年 | 2416篇 |
1973年 | 2467篇 |
1972年 | 2384篇 |
1971年 | 2217篇 |
1970年 | 2139篇 |
1969年 | 2090篇 |
1968年 | 1765篇 |
1967年 | 1858篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
B C Flann B A Lodge 《Journal of the Association of Official Analytical Chemists》1986,69(6):1026-1030
The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%. 相似文献
942.
943.
Alexandrov YN Crymov AA Kotelnikov VA Petrov GM Rzhiga ON Sidorenko AI Sinilo VP Zakharov AI Akim EL Basilevski AT Kadnichanski SA Tjuflin YS 《Science (New York, N.Y.)》1986,231(4743):1271-1273
From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled. 相似文献
944.
945.
Lipps JH 《Science (New York, N.Y.)》1986,233(4764):672-673
946.
Birds Their Structure and Function, By A. S. King and J. McLelland, 1984. 2nd ed. 334 pp. illustrated. London, Baillière Tindall. £9.50. ISBN 0 7020 0872 9.
Proceedings of the 2nd European Symposium on Poultry Welfare, 1985. 360 pp. illustrated. German Branch of the World's Poultry Science Association, Celle, Institut für Kleintierzucht. 相似文献
947.
948.
Recent optical experiments have demonstrated cases in which mirror symmetry in stable atoms is broken during absorption of light. These results, which are in contradiction with quantum electrodynamics, support the theory of unification of the electromagnetic and weak forces. The interpretation of these experimental results is based on exchanges of weak neutral Z(0) bosons between the electrons and the nucleus of the atom. The information obtained from low-energy experiments is different from, but complementary to, the results of high-energy experiments. Sensitive measurements in a simple, reliably computable atom are in quantitative agreement with the standard electroweak theory and put stringent constraints on alternative models. Attaining sufficient accuracy in the experiments and the computations for the electroweak radiative corrections to manifest themselves is now the challenge for experimenters and theorists. 相似文献
949.
950.
Temperature profiles measured in permafrost in northernmost Alaska usually have anomalous curvature in the upper 100 meters or so. When analyzed by heat-conduction theory, the profiles indicate a variable but widespread secular warming of the permafrost surface, generally in the range of 2 to 4 Celsius degrees during the last few decades to a century. Although details of the climatic change cannot be resolved with existing data, there is little doubt of its general magnitude and timing; alternative explanations are limited by the fact that heat transfer in cold permafrost is exclusively by conduction. Since models of greenhouse warming predict climatic change will be greatest in the Arctic and might already be in progress, it is prudent to attempt to understand the rapidly changing thermal regime in this region. 相似文献