全文获取类型
收费全文 | 23007篇 |
免费 | 112篇 |
国内免费 | 128篇 |
专业分类
系统科学 | 94篇 |
丛书文集 | 257篇 |
教育与普及 | 78篇 |
理论与方法论 | 63篇 |
现状及发展 | 10489篇 |
研究方法 | 905篇 |
综合类 | 11124篇 |
自然研究 | 237篇 |
出版年
2012年 | 272篇 |
2011年 | 504篇 |
2009年 | 145篇 |
2008年 | 384篇 |
2007年 | 425篇 |
2006年 | 365篇 |
2005年 | 383篇 |
2004年 | 501篇 |
2003年 | 384篇 |
2002年 | 381篇 |
2001年 | 664篇 |
2000年 | 688篇 |
1999年 | 486篇 |
1994年 | 331篇 |
1992年 | 348篇 |
1991年 | 325篇 |
1990年 | 360篇 |
1989年 | 320篇 |
1988年 | 340篇 |
1987年 | 371篇 |
1986年 | 380篇 |
1985年 | 456篇 |
1984年 | 331篇 |
1983年 | 330篇 |
1982年 | 286篇 |
1981年 | 302篇 |
1980年 | 333篇 |
1979年 | 722篇 |
1978年 | 588篇 |
1977年 | 544篇 |
1976年 | 428篇 |
1975年 | 514篇 |
1974年 | 651篇 |
1973年 | 561篇 |
1972年 | 588篇 |
1971年 | 741篇 |
1970年 | 842篇 |
1969年 | 712篇 |
1968年 | 696篇 |
1967年 | 641篇 |
1966年 | 574篇 |
1965年 | 417篇 |
1964年 | 165篇 |
1959年 | 216篇 |
1958年 | 417篇 |
1957年 | 324篇 |
1956年 | 266篇 |
1955年 | 239篇 |
1954年 | 257篇 |
1948年 | 211篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
161.
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
162.
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
163.
Summary Epithelial-mesenchymal interaction in the differentiation of duodenal epithelium of fetal rats was investigated by recombination experiments in vitro. The proportion of goblet cells in duodenal epithelium was significantly greater on recombination of developing duodenal epithelium with mesenchyme of the glandular stomach than on recombination with that of the duodenum. Mesenchyme of the glandular stomach or forestomach was better than duodenal mesenchyme in supporting morphogenesis of duodenal epithelium. Treatment of tissues with N-methyl-N-nitro-N-nitrosoguanidine (MNNG) did not affect these tissue interactions.This work was supported by grants-in-aid for cancer research from the Ministry of Education, Science and Culture, Japan.Acknowledgment. The authors wish to express their gratitude to Prof. T. Mizuno of the University of Tokyo for valuable suggestions. 相似文献
164.
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
165.
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
166.
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
167.
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
168.
Summary
-adrenoceptor stimulation by isoprenaline increases the potassium efflux in beating guinea-pig atria. This effect is not mimicked by 8-bromo-cyclic AMP, a cyclic AMP analogue which exerts a positive inotropic effect in this preparation. 相似文献
169.
Summary The karyotype of the pampas fox has 2n=74 and a NF=76. Except forChrysocyon brachyurus, 2n=74 is a common diploid number for the South American Canidae. This number is higher than in theVulpes group and lower than in the group of the typicalCanis. No marker chromosomes are present in the South American Canidae. 相似文献
170.
D. V. Amin R. B. Doctor A. O. Girdhar U. H. Shah 《Cellular and molecular life sciences : CMLS》1980,36(12):1410-1411
Summary Prostaglandin (PG) release was measured from the isolated perfused rabbit heart. The effects of -adrenergic stimulation and blockade suggest that PG synthesis is regulated in part by adrenergic mechanisms. 相似文献