全文获取类型
收费全文 | 789004篇 |
免费 | 88960篇 |
国内免费 | 443篇 |
出版年
2018年 | 6680篇 |
2016年 | 9122篇 |
2015年 | 12889篇 |
2014年 | 14834篇 |
2013年 | 21478篇 |
2012年 | 24010篇 |
2011年 | 24552篇 |
2010年 | 16478篇 |
2009年 | 15177篇 |
2008年 | 21702篇 |
2007年 | 22722篇 |
2006年 | 20975篇 |
2005年 | 20324篇 |
2004年 | 20137篇 |
2003年 | 19417篇 |
2002年 | 18853篇 |
2001年 | 34076篇 |
2000年 | 34282篇 |
1999年 | 27585篇 |
1998年 | 10074篇 |
1997年 | 10475篇 |
1996年 | 10071篇 |
1995年 | 9239篇 |
1994年 | 9258篇 |
1993年 | 9093篇 |
1992年 | 22938篇 |
1991年 | 22357篇 |
1990年 | 22069篇 |
1989年 | 21776篇 |
1988年 | 20046篇 |
1987年 | 19147篇 |
1986年 | 17633篇 |
1985年 | 17900篇 |
1984年 | 15000篇 |
1983年 | 13005篇 |
1982年 | 10177篇 |
1981年 | 9175篇 |
1980年 | 8550篇 |
1979年 | 14321篇 |
1978年 | 11197篇 |
1977年 | 10445篇 |
1976年 | 9860篇 |
1975年 | 10557篇 |
1974年 | 11466篇 |
1973年 | 11262篇 |
1972年 | 10415篇 |
1971年 | 9505篇 |
1970年 | 8054篇 |
1969年 | 8011篇 |
1968年 | 7256篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
851.
Inflammatory reaction to ocular trauma is known to be related to prostaglandins. To further evaluate this phenomenon in human, PGE1 and E2 were measured by R.I.A. after silicic acid chromatography in aqueous humour of 26 patients before and 3 days after surgery for unilateral senile cataract (posterior chamber implant after extracapsular surgery). 13 out of these patients were treated with indomethacin by enteral route and 13 were not treated.PGE2 levels increased in all non-treated patients from : m < 214 pg/ml before surgery, to 2666 ± 869 pg/ml (range : 257 - 8728) p < 0.001 after surgery. PGE2 levels did not increase in indomethacin-treated patients. PGE1 levels did not increase significantly in non-treated as in treated patients.1) Intra-ocular surgery is followed in human by a constant increase of the only PGE2 in the aqueous humour. 2) Indomethacin inhibits this increase. 3) The post-surgical increase in the permeability of blood-aqueous barrier appears to be related to a release of PGE2. 相似文献
852.
A.S. Tsaftaris J.C. Sorenson J.G. Scandalios 《Biochemical and biophysical research communications》1980,92(3):889-895
A protein isolated from maize scutella which inhibits catalase in vitro has been shown to contain 12% carbohydrate in the form of galactose. This corresponds to four galactose molecules per inhibitor subunit. Removal of the carbohydrate with β-galactosidase or blockage with a galactose-specific lectin abolished activity of the inhibitor. 相似文献
853.
W.M.F. Jongen P.H.M. Lohman M.J. Kottenhagen G.M. Alink F. Berends J.H. Koeman 《Mutation research》1981,81(2):203-213
Several short-term mammalian test systems were used for mutagenicity testing of the organic solvent dichloromethane. The compound was negative in the forward mutation test on the HGPRT locus in Chinese hamster cells and the unscheduled DNA synthesis test in both human and hamster cells. In the test on DNA synthesis inhibition, dichloromethane caused an aspecific inhibition in both human and hamster cells, but in this test the effect did not indicate a DNA-damaging action. A weak positive effect was found in the test on sister-chromatid exchanges in hamster cells. 相似文献
854.
C. Sanderson 《BMJ (Clinical research ed.)》1974,1(5901):245-246
855.
856.
857.
Elena C. Guzman Alfonso Jimenez-Sanchez Elisha Orr Robert H. Pritchard 《Molecular & general genetics : MGG》1988,212(2):203-206
Summary A temperature shift-up accompanied by a reduction in RNA polymerase activity in Escherichia coli causes an increased rate of initiation leading to a 1.7- to 2.2-fold increase in chromosome copy number. A temperature shift-up without a reduction in polymerase activity induces only a transient non-scheduled initiation of chromosome replication caused by heat shock with no detectable effect on chromosome copy number. 相似文献
858.
STEVEN C. BEADLE 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1988,21(1):1-12
The cyclocrinitids are an extinct tribe of dasycladacean green algae. They were anatomically very similar to certain Recent dasyclads, even at early growth stages. The morphology and preservation of cyclocrinitids strongly suggest that they had a siphonous cellular organization with extracellular, aragonitic calcification; these features are characteristic of living dasyclads. The light surficial calcification of cyclocrinitids and other dasyclads had important paleoecological effects. It restricted them to low-energy waters, as it provided relatively little structural support. It also confined them to warm, tropical waters; they are good paleoequatorial indicators. The decline of these algae during the late Ordovician and early Silurian may therefore reflect the simultaneous cooling and glaciation. Receptaculitids are entirely unrelated organisms. Their meroms have several distinctive features; they are not homologous to the lateral branches of cyclocrinitids or dasyclads. Receptaculitid calcification was extensive and their thalli were apparently quite sturdy; they often occurred in reefs. Receptaculitids also lived in high-latitude, cold-water environments. Thus, they were ecologically unlike any calcareous green algae, and cannot be used as paleoequatorial indicators. Receptaculitids remain problematical, although the arrangement of meroms suggests plant affinities. □ Calcareous algae, Problematica, Dasycladales, Cyclocriniteae, Receptaculitales, morphology, classification, paleoecology, paleogeography . 相似文献
859.
860.