全文获取类型
收费全文 | 83278篇 |
免费 | 5105篇 |
国内免费 | 894篇 |
专业分类
林业 | 3281篇 |
农学 | 2588篇 |
基础科学 | 738篇 |
10031篇 | |
综合类 | 16912篇 |
农作物 | 3068篇 |
水产渔业 | 3796篇 |
畜牧兽医 | 42663篇 |
园艺 | 1200篇 |
植物保护 | 5000篇 |
出版年
2021年 | 794篇 |
2020年 | 870篇 |
2019年 | 1031篇 |
2018年 | 1396篇 |
2017年 | 1639篇 |
2016年 | 1433篇 |
2015年 | 1377篇 |
2014年 | 1562篇 |
2013年 | 2986篇 |
2012年 | 2970篇 |
2011年 | 3536篇 |
2010年 | 2341篇 |
2009年 | 2224篇 |
2008年 | 3136篇 |
2007年 | 3025篇 |
2006年 | 2728篇 |
2005年 | 2618篇 |
2004年 | 2330篇 |
2003年 | 2377篇 |
2002年 | 2227篇 |
2001年 | 2506篇 |
2000年 | 2545篇 |
1999年 | 1954篇 |
1998年 | 801篇 |
1997年 | 717篇 |
1995年 | 749篇 |
1993年 | 667篇 |
1992年 | 1532篇 |
1991年 | 1721篇 |
1990年 | 1645篇 |
1989年 | 1593篇 |
1988年 | 1477篇 |
1987年 | 1532篇 |
1986年 | 1573篇 |
1985年 | 1398篇 |
1984年 | 1191篇 |
1983年 | 1015篇 |
1982年 | 681篇 |
1979年 | 1058篇 |
1978年 | 830篇 |
1977年 | 672篇 |
1976年 | 712篇 |
1975年 | 748篇 |
1974年 | 1007篇 |
1973年 | 987篇 |
1972年 | 951篇 |
1971年 | 878篇 |
1970年 | 852篇 |
1969年 | 805篇 |
1967年 | 701篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The earliest fossil record of African anthropoid primates (monkeys and apes) comes from the Jebel Qatrani Formation in the Fayum depression of Egypt. Reevaluation of both geologic and faunal evidence indicates that this formation was deposited in the early part of the Oligocene Epoch, more than 31 million years ago, earlier than previous estimates. The great antiquity of the fossil higher primates from Egypt accords well with their primitive morphology compared with later Old World higher primates. Thus, the anthropoid primates and hystricomorph rodents from Fayum are also considerably older than the earliest higher primates and rodents from South America. 相似文献
122.
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
123.
L K 《Science (New York, N.Y.)》1986,232(4751):780
124.
125.
126.
Curtis RA Viel L McGuirk SM Radostits OM Harris FW 《The Canadian veterinary journal. La revue veterinaire canadienne》1986,27(4):170-172
The purpose of this paper is to emphasize the importance of pulmonary auscultation for the clinician. It suggests a clarification and simplification of the terminology to be used which would be helpful to veterinary students and allow better communications between veterinarians. The interpretation of these sounds and the relationships to conditions and diseases of the lungs in cattle, horses, sheep and goats are discussed. 相似文献
127.
128.
129.
Klopfer LE 《Science (New York, N.Y.)》1986,232(4753):1010-1011
130.
H L 《Science (New York, N.Y.)》1986,232(4758):1653