全文获取类型
收费全文 | 68790篇 |
免费 | 297篇 |
国内免费 | 565篇 |
专业分类
系统科学 | 1257篇 |
丛书文集 | 586篇 |
教育与普及 | 288篇 |
理论与方法论 | 537篇 |
现状及发展 | 35575篇 |
研究方法 | 1492篇 |
综合类 | 27726篇 |
自然研究 | 2191篇 |
出版年
2013年 | 819篇 |
2012年 | 807篇 |
2011年 | 2938篇 |
2009年 | 630篇 |
2008年 | 1019篇 |
2007年 | 1230篇 |
2006年 | 1226篇 |
2005年 | 1449篇 |
2004年 | 2624篇 |
2003年 | 2169篇 |
2002年 | 1869篇 |
2001年 | 1860篇 |
2000年 | 1367篇 |
1999年 | 1246篇 |
1998年 | 649篇 |
1997年 | 779篇 |
1994年 | 699篇 |
1993年 | 695篇 |
1992年 | 1201篇 |
1991年 | 974篇 |
1990年 | 1074篇 |
1989年 | 880篇 |
1988年 | 866篇 |
1987年 | 870篇 |
1986年 | 915篇 |
1985年 | 1124篇 |
1984年 | 919篇 |
1983年 | 813篇 |
1982年 | 883篇 |
1981年 | 911篇 |
1980年 | 1018篇 |
1979年 | 1784篇 |
1978年 | 1540篇 |
1977年 | 1537篇 |
1976年 | 1306篇 |
1975年 | 1313篇 |
1974年 | 1378篇 |
1973年 | 1499篇 |
1972年 | 1609篇 |
1971年 | 1702篇 |
1970年 | 1994篇 |
1969年 | 1711篇 |
1968年 | 1618篇 |
1967年 | 1528篇 |
1966年 | 1336篇 |
1965年 | 1041篇 |
1959年 | 581篇 |
1958年 | 915篇 |
1957年 | 700篇 |
1956年 | 577篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
541.
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
542.
Y. Kakiuchi G. M. Hughes T. Arai M. Horimoto Y. Kikuchi T. Koyama 《Cellular and molecular life sciences : CMLS》1981,37(4):376-377
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan. 相似文献
543.
B. Lejczak H. Starzemska P. Mastalerz 《Cellular and molecular life sciences : CMLS》1981,37(5):461-462
Summary Analogues of glutamic acid, -methylglutamic acid and glutamine in which the -or -COOH groups are replaced by PO3H2 or P(O)(OH3)OH functions competitively inhibit rat liver glutamine synthetase. The K1 values are comparable to or lower than KM for L-glutamate.This study was supported by grant R.1.9. 相似文献
544.
R. Lenzhofer C. Cerni I. Fröhlich J. Prager H. Pointner 《Cellular and molecular life sciences : CMLS》1981,37(9):1015-1017
Summary The influence of somatostatin on tumor cell growth was studied in vivo in mice (sarcoma 180 ascites tumor and Lewis lung tumor) and in vitro on nontransformed and polyoma-transformed cell lines. 4 or 20 g/100 g of cyclic somatostatin and 4 g/100 g of linear protamin Zn-bound somatostatin were injected s.c. twice daily in the in vivo study. Cyclic somatostatin (1, 4 or 10 g/ml) was added twice daily to the cell cultures. Somatostatin administration influenced neither the survival of animals nor the growth rate of cultured cell lines. *** DIRECT SUPPORT *** A2025117 00011 相似文献
545.
546.
Summary Food ingestion of male guinea-pigs was restricted to 10 g/day. Total carnitine content of liver of the underfed animals fell to 3.75 moles per liver (46.1% of control). Serum level of total carnitine was 35.0 nmoles/ml (64.4%) in the underfed animals while they developed high ketonemia, 384.2 nmoles/ml (555.2%). In restricted animals the carnitine levels also decreased in the muscles. 相似文献
547.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner. 相似文献
548.
Summary There are wide individual variations in the thermal stability of human plasma dopamine--hydroxylase (DBH). Thermal stability variations have proven of value in biochemical genetic studies of many enzymes. The development of DBH thermolability depends on the exposure of plasma to oxygen. This observation may help to elucidate the biochemical basis of the genetic regulation of DBH.This work was supported in part by NIH grants HL 17487 and NS 11014. 相似文献
549.
Summary Thymidylate synthetase (methylenetetrahydrofolate: 2-deoxyuridine-5-monophosphate C-methyltransferase; EC 2.1.1.45) from neonatal mouse liver has been purified 714-fold by affinity chromatography on aminohexylsepharose bound 10-methyl-5,8-dideazafolate.Supported by grant CA22754, awarded by the National Cancer Institute, DHEW. 相似文献
550.
Summary Growth-promoting alpha-globulin (GPAG), a specific serum protein complex which induces mitotic activity in continually replicating metazoan cells in vitro, was shown in this study to support growth of astrocytes and mesenchymal cells as well as process formation of nerve cells isolated from cerebral hemispheres of chick embryos. 相似文献