全文获取类型
收费全文 | 306076篇 |
免费 | 35983篇 |
国内免费 | 198篇 |
专业分类
342257篇 |
出版年
2016年 | 2833篇 |
2015年 | 4260篇 |
2014年 | 4953篇 |
2013年 | 7550篇 |
2012年 | 7949篇 |
2011年 | 7917篇 |
2010年 | 5486篇 |
2009年 | 5319篇 |
2008年 | 7242篇 |
2007年 | 7453篇 |
2006年 | 7023篇 |
2005年 | 6995篇 |
2004年 | 6754篇 |
2003年 | 6868篇 |
2002年 | 6566篇 |
2001年 | 11126篇 |
2000年 | 11263篇 |
1999年 | 9303篇 |
1998年 | 3669篇 |
1997年 | 3839篇 |
1996年 | 3870篇 |
1995年 | 3604篇 |
1994年 | 3580篇 |
1993年 | 3660篇 |
1992年 | 8387篇 |
1991年 | 8172篇 |
1990年 | 7986篇 |
1989年 | 8067篇 |
1988年 | 7589篇 |
1987年 | 7639篇 |
1986年 | 7040篇 |
1985年 | 7195篇 |
1984年 | 6018篇 |
1983年 | 5393篇 |
1982年 | 4404篇 |
1981年 | 4260篇 |
1980年 | 3867篇 |
1979年 | 6226篇 |
1978年 | 4982篇 |
1977年 | 4809篇 |
1976年 | 4641篇 |
1975年 | 5000篇 |
1974年 | 5317篇 |
1973年 | 5107篇 |
1972年 | 4758篇 |
1971年 | 4293篇 |
1970年 | 3809篇 |
1969年 | 3800篇 |
1968年 | 3402篇 |
1967年 | 2956篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
W. Leuzinger 《The Biochemical journal》1971,123(2):139-141
By using two methods of titration, the number of active sites in acetylcholinesterase was determined. Either stepwise inhibition of the enzyme by an irreversible inhibitor, namely di-isopropyl phosphorofluoridate, or direct measurement of the concentration of active sites by titration with o-nitrophenyl dimethylcarbamate yielded an equivalent weight of approx. 130000 for an active site in acetylcholinesterase. This indicates two sites per molecule, since the native enzyme has a molecular weight of 260000. 相似文献
943.
W E Berdel P Schick H Sedlmeier U Fink J Rastetter O Messerschmidt 《Radiation research》1983,94(1):166-170
Synthetic lysophospholipids represent a variety of analogs of the naturally occurring 2-lysophosphatidylcholine. Some of these compounds showed significant therapeutic effects on the survival of mice following radiation injury when administered after various doses of whole-body X irradiation. Such therapeutic effects were discernible even when the treatment was given 6 hr after irradiation, and both intravenous and oral application were effective. Intravenous application of 2 X 25 mg/kg lysophospholipid after whole-body X irradiation around the LD50 resulted in significantly higher numbers of surviving animals. The mode of action remains speculative. 相似文献
944.
945.
The histologic properties of pleural adipose organs were studied in 14 newborns. These organs contain milky spots, in which lymphocytes, macrophages and plurivacuolated fat cells are present. The milky spots have a mesothelial covering, persist to the age of 9 months and seem to act as defence devices and a site of fluid exchange. 相似文献
946.
A convenient program for the rapid calculation of sedimentation coefficients in linear salt or sucrose gradients 总被引:4,自引:0,他引:4
C W Dingman 《Analytical biochemistry》1972,49(1):124-133
A program is presented for calculating s20,w values from data obtained by zone sedimentation in linear sucrose or salt gradients in a variety of rotors at temperatures ranging from 0° to 20°C. The program can be either run with the use of high-speed computers or performed with the aid of a small calculator in a reasonably short time. 相似文献
947.
948.
949.
The Importance of Hydrodynamics for Protected and Endangered Biodiversity of Lowland Rivers 总被引:3,自引:3,他引:0
R. J. W. de Nooij W. C. E. P. Verberk H. J. R. Lenders R. S. E. W. Leuven P. H. Nienhuis 《Hydrobiologia》2006,565(1):153-162
This paper examines the relationship between protected and endangered riverine species (target species) and hydrodynamics
in river-floodplain ecosystems, combining ecological and policy-legal aspects of biodiversity conservation in river management.
The importance of different hydrodynamic conditions along a lateral gradient was quantified for various taxonomic groups.
Our results show that (i) target species require ecotopes along the entire hydrodynamic gradient; (ii) different parts of
the hydrodynamic gradient are important to different species, belonging to different taxonomic groups; (iii) in particular
low-dynamic parts are important for many species and (iv) species differ in their specificity for hydrodynamic conditions.
Many species of higher plants, fish and butterflies have a narrow range for hydrodynamics and many species of birds and mammals
use ecotopes along the entire gradient. Even when focussing only on target species, the entire natural hydrodynamic gradient
is important. This means that the riverine species assemblage as a whole can benefit from measures focussing on target species
only. River reconstruction and management should aim at re-establishing the entire hydrodynamic gradient, increasing the spatial
heterogeneity of hydrodynamic conditions. 相似文献
950.