全文获取类型
收费全文 | 7138篇 |
免费 | 24篇 |
国内免费 | 50篇 |
专业分类
系统科学 | 64篇 |
丛书文集 | 59篇 |
教育与普及 | 15篇 |
理论与方法论 | 68篇 |
现状及发展 | 2841篇 |
研究方法 | 546篇 |
综合类 | 3441篇 |
自然研究 | 178篇 |
出版年
2017年 | 54篇 |
2013年 | 48篇 |
2012年 | 238篇 |
2011年 | 431篇 |
2010年 | 98篇 |
2008年 | 233篇 |
2007年 | 321篇 |
2006年 | 269篇 |
2005年 | 269篇 |
2004年 | 262篇 |
2003年 | 237篇 |
2002年 | 267篇 |
2001年 | 163篇 |
2000年 | 180篇 |
1999年 | 115篇 |
1992年 | 100篇 |
1991年 | 75篇 |
1990年 | 75篇 |
1989年 | 68篇 |
1988年 | 55篇 |
1987年 | 73篇 |
1986年 | 70篇 |
1985年 | 131篇 |
1984年 | 77篇 |
1983年 | 68篇 |
1982年 | 65篇 |
1981年 | 62篇 |
1980年 | 71篇 |
1979年 | 131篇 |
1978年 | 127篇 |
1977年 | 136篇 |
1976年 | 123篇 |
1975年 | 134篇 |
1974年 | 147篇 |
1973年 | 110篇 |
1972年 | 102篇 |
1971年 | 151篇 |
1970年 | 231篇 |
1969年 | 153篇 |
1968年 | 142篇 |
1967年 | 165篇 |
1966年 | 125篇 |
1965年 | 82篇 |
1964年 | 48篇 |
1959年 | 67篇 |
1958年 | 82篇 |
1957年 | 81篇 |
1956年 | 52篇 |
1955年 | 48篇 |
1954年 | 54篇 |
排序方式: 共有7212条查询结果,搜索用时 31 毫秒
991.
E. A. Zeller G. S. Couper S. V. Huprikar A. M. Mellow R. R. Moody 《Cellular and molecular life sciences : CMLS》1976,32(11):1453-1454
Summary The pharmacological action of mescaline on goldfish was studied with the Bitterman-Agranoff shock-avoidance test. In short term experiments with high mescaline doses an increase in learning rates was observed. Similar results were obtained with apomorphine andl-dopa. However, when the fish were exposed to smaller mescaline doses (or to fluphenazine) for 3 days, their ability to avoid electric shock was reduced. Apparently, mescaline induced a release of dopamine which stimulated central dopaminergic systems. Subsequently, MAO destroys the liberated dopamine. Thus, the ensuing dopamine deficit appears to be responsible for the marked changes in behavior in the chronic experiment.This work was supported in part by research grants from the National Eye Institute (EY No. 00313) and the National Institute of Mental Health (MH No. 20020), and by the Sterling Morton Charitable Trust Fund. 相似文献
992.
Summary Arylsulfatase activity has been demonstrated in rat and human parotid and submandibular saliva indicating that oral bacteria are not the only source of salivary sulfatase activity. Activity was also observed in human sweat, tears and in snake venom.Acknowledgments. We extent appreciation to Drs.C. Dawes andK. Abe for assistance in saliva collection, to Dr.K. W. Stewart who provided fresh snake venoms and to Dr.E. T. Pritchard in whose laboratory this study was conducted. Supported by grant Nr. MT 3536 from MRC of Canada. 相似文献
993.
994.
G Béné B Borcard V Graf E Hiltbrand F Noack P Magnin 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,289(16):1275-1277
Dispersion curves of the longitudinal relaxation T1 of protons in healthy amniotic fluid in a meconium solution are distinct at low Larmor frequencies (V0 less than 100 kHz). We are thus able to distinguish these fluids by T1 measurements in this range. 相似文献
995.
We have examined the hot particle problem in terms of the number of irradiated cells and the doses to which they are subjected, assuming both linear and nonlinear dose-response functions typical of those reported in the radiobiological literature. We assess the risk associated with point sources of alpha, beta and gamma activity compared with uniform irradiation, as well as the effects of fractionation of a single particle, and the change in risk if the particle moves. Finally, although the biological data are insufficient for firm estimates, we have tentatively attributed absolute carcinogenic risks in these various situations. 相似文献
996.
997.
G. V. Bykova I. A. Vasilyeva E. A. Gileva 《Cellular and molecular life sciences : CMLS》1978,34(9):1146-1148
Summary Voles from Yakutia and Chukotka were found to differ in the morphology of 3 pairs of autosomes and sex chromosomes, as well as in M3-structure and skull dimensions. This makes their conspecificity doubtful. A variation in short arm lengths of the X- and Y-chromosomes has been discovered. 相似文献
998.
999.
1000.
Structure and conformation of a cyclic tripeptide 总被引:1,自引:0,他引:1