全文获取类型
收费全文 | 20615篇 |
免费 | 198篇 |
国内免费 | 390篇 |
专业分类
系统科学 | 526篇 |
丛书文集 | 445篇 |
教育与普及 | 99篇 |
理论与方法论 | 68篇 |
现状及发展 | 6267篇 |
研究方法 | 784篇 |
综合类 | 12493篇 |
自然研究 | 521篇 |
出版年
2021年 | 177篇 |
2016年 | 171篇 |
2015年 | 225篇 |
2014年 | 341篇 |
2013年 | 459篇 |
2012年 | 656篇 |
2011年 | 1181篇 |
2010年 | 517篇 |
2009年 | 530篇 |
2008年 | 744篇 |
2007年 | 808篇 |
2006年 | 734篇 |
2005年 | 656篇 |
2004年 | 475篇 |
2003年 | 362篇 |
2002年 | 362篇 |
2001年 | 546篇 |
2000年 | 614篇 |
1999年 | 449篇 |
1992年 | 304篇 |
1991年 | 262篇 |
1990年 | 262篇 |
1989年 | 239篇 |
1988年 | 215篇 |
1987年 | 227篇 |
1986年 | 205篇 |
1985年 | 246篇 |
1984年 | 235篇 |
1983年 | 159篇 |
1982年 | 172篇 |
1981年 | 157篇 |
1980年 | 199篇 |
1979年 | 445篇 |
1978年 | 340篇 |
1977年 | 367篇 |
1976年 | 264篇 |
1975年 | 322篇 |
1974年 | 446篇 |
1973年 | 379篇 |
1972年 | 360篇 |
1971年 | 422篇 |
1970年 | 484篇 |
1969年 | 425篇 |
1968年 | 407篇 |
1967年 | 442篇 |
1966年 | 384篇 |
1965年 | 301篇 |
1959年 | 155篇 |
1958年 | 231篇 |
1957年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The spontaneous conversion of mammalian cyclic GMP-dependent protein kinase (G-PK) into modulator-dependent protein kinase (type II) (M-PKII) in the absence of cGMP or histone was observed in vitro. The findings, together with similarity in substrate protein specificity, suggest that M-PKII is the catalytic subunit of mammalian G-PK. 相似文献
52.
At ambient temperatures (Ta) of both 8 and 22 degrees C, intraventricular administration of TRH (10-80 microgram) produced a dose-dependent hypothermia in rats. The hypothermia was due to both decreased metabolic heat production and cutaneous vasodilatation. In contrast, at 30 degrees C Ta, TRH increased metabolic heat production (due to behavioral excitation) and led to hyperthermia. 相似文献
53.
Summary Silver-staining has been used to identify the nucleolus organizer regions (NORs) in the bharal. These show homology with sheep, goat, cattle and aoudad. The association of the NORs on both telomeres of chromosome 3 results in a ring chromosome. 相似文献
54.
H. L. Weinberg 《Cellular and molecular life sciences : CMLS》1980,36(5):548-549
Summary The hemolymph volume ofHeliothis zea larvae was determined by the amaranth dye method and found to vary from 28 to 288 l. It averaged 30.6% of b.wt, a value comparable to that obtained with C14 inulin. Amaranth became evenly distributed in the hemocoele in 3–5 min. 相似文献
55.
R. L. Tyson C. -j. Chang J. L. McLaughlin Y. Aynehchi J. M. Cassady 《Cellular and molecular life sciences : CMLS》1981,37(5):441-442
Summary A novel sesquiterpene lactone, 9--hydroxyparthenolide (1) was isolated from a chloroform extract ofAnvillea garcini that was collected in Iran. The structure of1 was assigned on the basis of high field NMR decoupling experiments and other spectroscopic evidence. This -methylene lactone has shown significant activity in both the 9KB cell culture and P388 mouse leukemia test systems.The authors acknowledge the support of contract No. N01-CM-97296 from the National Cancer Institute and the use of the Purdue University Biochemical Magnetic Resonance Laboratory (NIH grant No. RR01077). This is paper 16 in the series Potential Antitumor Agents. 相似文献
56.
57.
58.
Summary The binding of coumarin to serum proteins of the rat has been demonstrated. Of the total bound coumarin (37% of injected dose), 36% was bound to the slow and fast 1 globulins, 11% to the post albumins, 10% to globulin and 9% to albumin. 相似文献
59.
M. D. Adams J. T. Earnhardt B. R. Martin L. S. Harris W. L. Dewey R. K. Razdan 《Cellular and molecular life sciences : CMLS》1977,33(9):1204-1205
Summary Abnormal-8-tetrahydrocannabidiol (ABN-8-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.Acknowledgment. This work was supported by NIDA (grant No. DA-00574-01 and DA-00490) and Virginia Heart Society (grant No. RR-05697) 相似文献