全文获取类型
收费全文 | 39758篇 |
免费 | 4407篇 |
国内免费 | 1702篇 |
出版年
2024年 | 41篇 |
2023年 | 257篇 |
2022年 | 651篇 |
2021年 | 1338篇 |
2020年 | 929篇 |
2019年 | 1125篇 |
2018年 | 1207篇 |
2017年 | 947篇 |
2016年 | 1341篇 |
2015年 | 1782篇 |
2014年 | 2149篇 |
2013年 | 2384篇 |
2012年 | 2633篇 |
2011年 | 2627篇 |
2010年 | 1585篇 |
2009年 | 1493篇 |
2008年 | 1760篇 |
2007年 | 1624篇 |
2006年 | 1471篇 |
2005年 | 1269篇 |
2004年 | 1053篇 |
2003年 | 1020篇 |
2002年 | 904篇 |
2001年 | 2554篇 |
2000年 | 2392篇 |
1999年 | 1781篇 |
1998年 | 611篇 |
1997年 | 612篇 |
1996年 | 555篇 |
1995年 | 522篇 |
1994年 | 410篇 |
1993年 | 332篇 |
1992年 | 864篇 |
1991年 | 688篇 |
1990年 | 602篇 |
1989年 | 463篇 |
1988年 | 354篇 |
1987年 | 278篇 |
1986年 | 210篇 |
1985年 | 170篇 |
1984年 | 102篇 |
1983年 | 80篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 28篇 |
1976年 | 30篇 |
1973年 | 30篇 |
1970年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
A comparative analysis of photosynthetic characteristics of hulless barley at two altitudes on the Tibetan Plateau 总被引:1,自引:0,他引:1
To determine the photosynthetic characteristics of C3 plants and their sensitivity to CO2 at different altitudes on the Tibetan Plateau, hulless barley (Hordeum vulgare L. ssp. vulgare) was grown at altitudes of 4,333 m and 3,688 m. Using gas-exchange measurements, photosynthetic parameters were simulated,
including the maximum net photosynthesis (P
max) and the apparent quantum efficiency (α). Plants growing at higher altitude had higher net photosynthetic rates (P
N), photosynthesis parameters (P
max and α) and sensitivities to CO2 enhancement than plants growing at lower altitude on the Tibetan Plateau. The enhancements of P
N, P
max, and α for plants growing at higher altitude, corresponding with 10 μmol(CO2) mol−1 increments, were approximately 0.20∼0.45%, 0.05∼0.20% and 0.12∼0.36% greater, respectively, than for plants growing at lower
altitude, respectively, where CO2 levels rose from 10 to 170 μmol(CO2) mol−1. Therefore, on the Tibetan Plateau, the changes in the photosynthetic capacities and the photosynthetic sensitivities to
CO2 observed in the C3 plants grown above 3,688 m are likely to increase with altitude despite the decreasing CO2 partial pressure. 相似文献
84.
85.
Effect of propionate and pyruvate on citrulline synthesis and ATP content in rat liver mitochondria.
L Cathelineau F P Petit F X Coudé P P Kamoun 《Biochemical and biophysical research communications》1979,90(1):327-332
Propionate inhibits citrullinogenesis when succinate (plus rotenone) or glutamate are the oxidizable substrates used. Propionate decreases the intramitochondrial concentration of carbamylphosphate by decreasing the ATP content. When the energy supply for citrullinogenesis is provided by an influx of exogenous ATP, propionate is no longer an inhibitor. Pyruvate inhibits citrullinogenesis with glutamate but not with succinate (plus rotenone) as oxidizable substrates. Propionate and pyruvate deplete mitochondrial ATP but probably by different mechanisms. 相似文献
86.
87.
88.
89.
The bioinorganic complexes of europium with N-acetyl-DL-alanine, N-acetyl-DL-valine, and DL-alanyl-DL-alanine have been synthesized and the M?ssbauer spectra at room temperature have been measured for these solid state complexes. The M?ssbauer parameters indicate that the water molecules in these complexes are not directly linked to the central europium ion and are outside the coordination sphere of europium and biological ligands, and that the chemical bond between the europium ion and the ligands may be predominantly ionic in character, with the possibility of partial covalent contribution. 相似文献
90.