全文获取类型
收费全文 | 9365篇 |
免费 | 80篇 |
国内免费 | 69篇 |
专业分类
系统科学 | 121篇 |
丛书文集 | 94篇 |
教育与普及 | 20篇 |
理论与方法论 | 42篇 |
现状及发展 | 3566篇 |
研究方法 | 660篇 |
综合类 | 4800篇 |
自然研究 | 211篇 |
出版年
2016年 | 61篇 |
2014年 | 62篇 |
2013年 | 83篇 |
2012年 | 215篇 |
2011年 | 473篇 |
2010年 | 96篇 |
2009年 | 73篇 |
2008年 | 277篇 |
2007年 | 333篇 |
2006年 | 264篇 |
2005年 | 253篇 |
2004年 | 356篇 |
2003年 | 257篇 |
2002年 | 288篇 |
2001年 | 312篇 |
2000年 | 307篇 |
1999年 | 229篇 |
1992年 | 128篇 |
1991年 | 130篇 |
1990年 | 120篇 |
1989年 | 108篇 |
1988年 | 109篇 |
1987年 | 121篇 |
1986年 | 116篇 |
1985年 | 162篇 |
1984年 | 127篇 |
1983年 | 103篇 |
1982年 | 88篇 |
1981年 | 116篇 |
1980年 | 111篇 |
1979年 | 253篇 |
1978年 | 203篇 |
1977年 | 185篇 |
1976年 | 139篇 |
1975年 | 163篇 |
1974年 | 214篇 |
1973年 | 177篇 |
1972年 | 194篇 |
1971年 | 219篇 |
1970年 | 276篇 |
1969年 | 211篇 |
1968年 | 189篇 |
1967年 | 211篇 |
1966年 | 181篇 |
1965年 | 145篇 |
1959年 | 53篇 |
1958年 | 105篇 |
1957年 | 76篇 |
1956年 | 74篇 |
1954年 | 74篇 |
排序方式: 共有9514条查询结果,搜索用时 15 毫秒
31.
Jupiter's ring system has previously been described as being composed of a 'bright' narrow ring and an interior, vertically-extended halo. The one image which reveals this morphology most clearly is Voyager 2's parting shot of the Jupiter system, a wide-angle (WA) view of the ring ansa in forward-scattered light (FDS 20693.02). The bright ring is plainly visible, and the halo appears after slight contrast enhancement. By further enhancement of this image we have discovered an additional ring, which is far fainter than either of the (already faint) components previously identified, extending to a radius of 210,000 km. 相似文献
32.
33.
J. R. Martinez N. Cassity S. Barker 《Cellular and molecular life sciences : CMLS》1987,43(9):1013-1015
Summary The -adrenergic agonist isoproterenol and prostaglandins E1 and E2 (but not F2) increased the cAMP content of rat submandibular acini in vitro, but only isoproterenol enhanced ouabain-sensitive86Rb (K) uptake. These findings suggest that cAMP is not involved in the activation of the Na, K pump in salivary cells. 相似文献
34.
M. Kashimata M. Hiramatsu N. Minami Jr N. Minami 《Cellular and molecular life sciences : CMLS》1987,43(2):191-192
Summary An enzyme immunoassay for mouse epidermal growth factor (EGF) involving a liquid phase double-antibody system was developed. The EGF--galactosidase conjugate prepared was stable for at least 8 months. By this method, EGF was detectable at a concentration as low as 20 pg per tube. The concentrations of EGF in various tissues of mice are also presented.This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan. 相似文献
35.
Pineal gland changes of rats exposed to heat 总被引:1,自引:0,他引:1
36.
RNA-DNA hybrids at the cytological level 总被引:37,自引:0,他引:37
37.
Summary Metabolism of 26-hydroxycholesterol to 3-hydroxychol-5-en-24-oic acid and other C24-bile acids has been expected to occur by way of 3-hydroxycholest-5-en-26-oic acid in studies in vitro. 3-Hydroxycholest-5-en-26-oic acid was infused intravenously into bile fistula hamsters and the following C24-bile acids were identified: 3-hydroxychol-5-en-24-oic acid, lithocholic acid, chenodeoxycholic acid, and a small amount of cholic acid. 相似文献
38.
Y. Mamiya H. Sonobe K. Yoshida N. Hara Y. Fujimoto 《Cellular and molecular life sciences : CMLS》1995,51(4):363-367
Ecdysteroids in diapause eggs of the silkworm,Bombyx mori, were analyzed using high-performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). A relatively large amount of an unidentified free ecdysteroid and its phosphoric ester (conjugated form) were detected. These two compounds were isolated by a combination of column chromatography on silicic acid, thin-layer chromatography (TLC), and HPLC using a reverse-phase (RP) column. The purified compounds were identified as 3-epi-22-deoxy-20-hydroxyecdysone (22d20E) and 3-epi-22-deoxy-20-hydroxyecdysone 2-phosphate (22d20E2P) by means of mass spectrometry and nuclear magnetic resonance spectroscopy. to our knowledge, this is the first report of 22d20E and 22d20E2P. 相似文献
39.
Insect motion detectors matched to visual ecology 总被引:1,自引:0,他引:1
To detect motion, primates, birds and insects all use local detectors to correlate signals sampled at one location in the image with those sampled after a delay at adjacent locations. These detectors can adapt to high image velocities by shortening the delay. To investigate whether they use long delays for detecting low velocities, we compared motion-sensitive neurons in ten species of fast-flying insects, some of which encounter low velocities while hovering. Neurons of bee-flies and hawkmoths, which hover, are tuned to lower temporal frequencies than those of butterflies and bumblebees, which do not. Tuning to low frequencies indicates longer delays and extends sensitivity to lower velocities. Hoverflies retain fast temporal tuning but use their high spatial acuity for sensing low-velocity motion. Thus an unexpectedly wide range of spatio-temporal tuning matches motion detection to visual ecology. 相似文献
40.
S. F. Wang J. C. Braekman D. Daloze J. Pasteels P. Soetens N. V. Handjieva P. Kalushkov 《Cellular and molecular life sciences : CMLS》1996,52(6):628-630
The isolation of N-quinaldyl-L-arginine·HCl (1) from the CoccinellidaeSubcoccinella-24-punctata is reported. The structure, first established on the basis of the analysis of the spectral properties of1, has been confirmed by synthesis. The alkaloid is of endogenous origin and markedly deterrent to ants. 相似文献