全文获取类型
收费全文 | 49800篇 |
免费 | 116篇 |
国内免费 | 206篇 |
专业分类
系统科学 | 269篇 |
丛书文集 | 1078篇 |
教育与普及 | 107篇 |
理论与方法论 | 281篇 |
现状及发展 | 22759篇 |
研究方法 | 1897篇 |
综合类 | 23039篇 |
自然研究 | 692篇 |
出版年
2013年 | 385篇 |
2012年 | 654篇 |
2011年 | 1380篇 |
2010年 | 285篇 |
2008年 | 860篇 |
2007年 | 915篇 |
2006年 | 942篇 |
2005年 | 919篇 |
2004年 | 873篇 |
2003年 | 860篇 |
2002年 | 882篇 |
2001年 | 1447篇 |
2000年 | 1336篇 |
1999年 | 915篇 |
1992年 | 884篇 |
1991年 | 704篇 |
1990年 | 760篇 |
1989年 | 780篇 |
1988年 | 751篇 |
1987年 | 806篇 |
1986年 | 776篇 |
1985年 | 944篇 |
1984年 | 744篇 |
1983年 | 637篇 |
1982年 | 568篇 |
1981年 | 580篇 |
1980年 | 744篇 |
1979年 | 1537篇 |
1978年 | 1331篇 |
1977年 | 1313篇 |
1976年 | 997篇 |
1975年 | 1065篇 |
1974年 | 1482篇 |
1973年 | 1291篇 |
1972年 | 1342篇 |
1971年 | 1576篇 |
1970年 | 2048篇 |
1969年 | 1546篇 |
1968年 | 1514篇 |
1967年 | 1540篇 |
1966年 | 1304篇 |
1965年 | 940篇 |
1964年 | 275篇 |
1959年 | 535篇 |
1958年 | 870篇 |
1957年 | 656篇 |
1956年 | 561篇 |
1955年 | 488篇 |
1954年 | 545篇 |
1948年 | 326篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
331.
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
332.
Summary The female: male sex ratio in litters born to C57 black mice immunized with male spleen preparations is 21 and males were stillborn. In additionDrosophila busckii males are H-Y antigen positive. It is argued that H-Y is the primary testicular determinant and that this role is evolutionarily ancient. 相似文献
333.
Summary Natural cell-mediated cytotoxicity of normal murine Peyer's patch cells against Ehrlich ascites carcinoma was found in a short-term51Cr release assay. Peyer's patch and lymph node cells showed natural cytotoxicity at approximately the same level.Acknowledgments. This work was supported by grant No. 10.5 from the Polish Academy of Sciences. 相似文献
334.
Summary Amylase, - and -glucosidase, - and -galactosidase, -fructosidase, trypsin, aminotripeptidase, leucine-aminopeptidase, prolinase, prolidase glycyl-L-leucine dipeptidase and glycylglycine dipeptidase are present in the 3rd instar larvae ofChilo auricilius.Dr Kishan Singh, Indian Institute of Sugarcane Research, Lucknow, is gratefully acknowledged for providing necessary facilities. 相似文献
335.
J. Kędziora M. Soszyński G. Bartosz H. Witas W. Leyko 《Cellular and molecular life sciences : CMLS》1980,36(8):926-927
Summary A statistically significant decrease of prealbumin and statistically significant increases of alpha2-macroglobulin and IgA were found in blood plasma of patients with Down's syndrome using quantitative crossed immunoelectrophoresis.We are indebted to Prof. T.C. Bøg-Hansen, University of Copenhagen, for the helpful discussion of our results. 相似文献
336.
W. D. MacRae G. F. Q. Chan Chi-Kit Wat G. H. N. Towers J. Lam 《Cellular and molecular life sciences : CMLS》1980,36(9):1096-1097
Summary -Terthienyl and 5 polyacetylenes were examined for chromosome damaging activity using Syrian hamster cells. None of these naturally occurring compounds induced sister chromatid exchanges and neither -terthienyl nor phenylheptatriyne induced chromosome aberrations.The authors wish to thank the National Science and Engineering Research Council for financial support of this research. 相似文献
337.
Summary The effects of selected -agonists and -antagonists on theophylline-induced lipolysis were investigate in isolated hamster white fat cells 2-Agonists (tramazoline, clonidine) inhibited theophylline-induced lipolysis while an 2-agonist (methoxamine) was without any effect. The inhibitory effect of 2-agonists was suppressed by yohimbine (2-antagonist), whereas 2-antagonists were inefficient. This result implies that the -adrenergic receptor of hamster fat cells is of the 2-type, although located postsynaptically.Acknowledgments. This work was supported by grants from CNRS (ERA 412) and DGRST (grant No. 787 1078). We thank M. Dauzats for excellent technical assistance. We thank Prof. H. Schmitt for tramazoline and AR-C 239 and for helpful discussion. 相似文献
338.
Summary Prostaglandins (PGs) E2, F2, and I2 were examined for their effects on the electrical and mechanical activities of isolated rat, rabbit and guinea-pig hearts. All PGs produced dysrhythmias in rat hearts at low concentrations only, while higher concentrations were antiarrhythmic. Guinea-pig hearts were less responsive while rabbit hearts were completely resistant.We thank the Manitoba Heart Foundation for financial support and Dr J. Pike (Upjohn, Kalamazoo, MI, USA) for gifts of prostaglandins. Dr M. Karmazyn is a Fellow of the Canadian Heart Foundation. 相似文献
339.
Summary After a dose of 3.0 Gy in the peak position of the pion depth-dose curve, the ratios between observed chromosome aberration yields under conditions of oxygenation and of anoxia were obtained for lymphocytes exposed at 3 depths in a plastic phantom. These ratios were 3.7, 1.9 and 1.3 in the plateau, peak and post-peak positions, respectively, suggesting a corresponding decrease in the oxygen enhancement ratio.Acknowledgments. We wish to thank Dr D.H. Reading, Mr M.A. Hynes and Mr W. Spinks for their assistance at the Rutherford Laboratory's -II beam line. This work was partly supported by Euratom Contract 171-76-1 BIO-UK. 相似文献
340.
C. R. Pace-Asciak N. S. Edwards M. C. Carrara 《Cellular and molecular life sciences : CMLS》1980,36(6):635-637
Summary Tritium-labelled PGF2 was administered i.v. into rats of varying ages (2, 4, 6 weeks and adult). Urine was collected and assayed for radioactive products by thin-layer-chromatography. Results showed a distinctly different urinary profile between the 2-week-old and the adult rat. While the urinary pattern from the 2-week-old rat gave a single less polar product than PGF2, the pattern from the adult rat gave products more polar than PGF2. Urine from the 4- and 6-week-old rats gave a mixture of these types of products. These results indicate that some prostaglandin catabolic pathway (likely the -oxidative system) is activated in vivo within the 4–6-week postnatal period in the rat.Supported by a grant (MT-4181) to C.P.-A. from the Medical Research Council of Canada.This study is in partial fulfillment of the requirements for a Ph.D. degree in the Department of Pharmacology, University of Toronto. 相似文献