全文获取类型
收费全文 | 31032篇 |
免费 | 86篇 |
国内免费 | 151篇 |
专业分类
系统科学 | 119篇 |
丛书文集 | 289篇 |
教育与普及 | 101篇 |
理论与方法论 | 88篇 |
现状及发展 | 13948篇 |
研究方法 | 1237篇 |
综合类 | 15146篇 |
自然研究 | 341篇 |
出版年
2013年 | 218篇 |
2012年 | 407篇 |
2011年 | 710篇 |
2008年 | 525篇 |
2007年 | 592篇 |
2006年 | 577篇 |
2005年 | 587篇 |
2004年 | 609篇 |
2003年 | 576篇 |
2002年 | 534篇 |
2001年 | 967篇 |
2000年 | 967篇 |
1999年 | 617篇 |
1994年 | 365篇 |
1992年 | 566篇 |
1991年 | 436篇 |
1990年 | 530篇 |
1989年 | 468篇 |
1988年 | 459篇 |
1987年 | 521篇 |
1986年 | 530篇 |
1985年 | 656篇 |
1984年 | 453篇 |
1983年 | 453篇 |
1982年 | 408篇 |
1981年 | 396篇 |
1980年 | 418篇 |
1979年 | 1002篇 |
1978年 | 791篇 |
1977年 | 725篇 |
1976年 | 613篇 |
1975年 | 686篇 |
1974年 | 845篇 |
1973年 | 747篇 |
1972年 | 720篇 |
1971年 | 904篇 |
1970年 | 1095篇 |
1969年 | 904篇 |
1968年 | 925篇 |
1967年 | 805篇 |
1966年 | 729篇 |
1965年 | 536篇 |
1964年 | 201篇 |
1959年 | 294篇 |
1958年 | 531篇 |
1957年 | 383篇 |
1956年 | 336篇 |
1955年 | 321篇 |
1954年 | 322篇 |
1948年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
H. Kemona J. Prokopowicz N. Wotosowicz 《Cellular and molecular life sciences : CMLS》1978,34(2):257-257
Summary It has been shown that there is a higher count of blood platelets and thrombopoietic activity of plasma in women than men. 相似文献
192.
Summary 5-bromo-2-deoxyuridine (BUdR) removal from liver DNA in newborn and young adult rats has been demonstrated: it forms the basis of a reliable method to measure DNA repair in tissues provided with detectable DNA synthetic activity.This work was supported by a grant from Consiglio Nazionale delle Ricerche, Rome, and Donazione Teston, Bologna, Italy. 相似文献
193.
Summary 2 populations of rat fleas,Xenopsylla astia, collected from (A) Bombay and (B) Trivandrum, were found to differ in chromosome number as follows; (A) 2n=10 in both sexes; (B) 2n=18 (male) and 20 (female). Preliminary observations have further shown that the 2 populations differ in certain morphological characters and that their reciprocal hybrids are sterile in the male and partially sterile in the female sex.Acknowledgments. We wish to express our deepest gratitude to Dr Robert E. Lewis, Professor of Entomology, Iowa State University, USA, for confirming our identification of the 2 samples of rat fleas. We are indebted to Dr N.R. Prabhoo, Reader in Zoology, University of Kerala, Trivandrum, for his advice and helpful suggestions. We are also indebted to Prof. K.M. Alexander, for encouragement and providing facilities. Financial help of the University Grants Commission, India, to one of us (C.T.) is also gratefully acknowledged. 相似文献
194.
Summary The seedling growth ofBrassica campestris var.varuna, has been studied, as affected by water-stress and gibberellin treatments. A boost in the net GA response due to water-stress, has been observed. Thus presence of GA can overcome the water-stress effects.Publication No. 26 from Dept of Biosciences, Himachal Pradesh University, Simla. Authors are grateful to CSIR, New Delhi, for JRF to SB. 相似文献
195.
Summary A 2-dimensional thin-layer method has been developed for the separation on cellulose of adenine and guanine derivatives. Using incubated rat cerebral cortex slices it was shown that noradrenaline and acetylcholine stirnulated cAMP and cGMP production respectively but glutamate and -aminobutyric acid stimulated production of both cyclic nucleotides. 相似文献
196.
Z. Ben-Ishay F. Reichert S. Sharon 《Cellular and molecular life sciences : CMLS》1978,34(10):1369-1370
Summary Eradication of replicating bone marrow cells of rat by means of combined administration of single doses of hydroxyurea and vinblastin is followed within 9–10 h by an inflow of lymphoid cells of extramedullary origin in the range of 13,200,000/femur. The rat bone marrow with a high content of lymphoid cells was previously shown to be concentrated in stem cells. The factor(s) which convey the information of decrease of replicating marrow cells to extramedullary sites is at present unknown.Acknowledgment. This study was supported by a grant from the Chief Scientist Office, Ministry of Health, Israel.Hydroxyurea for this investigation was given as a gift by the Squibb Institute of Medical Research, Princeton, N.J. USA, to which the authors are indebted. 相似文献
197.
Summary The effects of time and various doses of testosterone on the responsiveness of lactate dehydrogenase of pituitary of 7-, 38- and 78-week-old rats were studied. The activity of the enzyme increases in 78-week-old rats. Castration decreases the enzyme activity at all ages. Maximum increase in the enzyme activity is seen with 50 and 100 g of testosterone 4 h after administration of hormone to castrated rats. No further time and dose-dependent effect is observed. The magnitude of increase for the enzyme is higher at the age of 38 weeks and decreases in 78-week-old rats.To whom all correspondence should be addressed. The authors are grateful to Professor M.S. Kanungo, Biochemistry Laboratory, Department of Zoology, Banaras Hindu University for the suggestions and encouragement. K.V.G. thanks the PL-480 for a research fellowship. 相似文献
198.
M Debray-Sachs M Dy H Aurengo B Descamps 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(2):249-252
CBA Mice were immunized by two intraperitoneal injections of 30 X 10(6) DBA/2 or C57BL/6 spleen cells at days--12 and--2. Peritoneal cell population was obtained at day zero by washing the peritoneal cavity of Mice. Adherent cells were then separated using a 2 hrs. incubation in "Falcon" plates followed by washing. This macrophage-rich peritoneal cell population was found nonspecifically cytotoxic against 51Cr labeled tumoral target cells: P815 X DBA/2 mastocytoma cells, EL4 X C57BL/L lymphoma cells and spontaneous lymphoma AKR cells (same H--2k as CBA). This adherent peritoneal cell cytoxicity was demonstrated after 24 hrs. incubation with the target cells. It was found in nonspecific combination as well as when using target cells syngeneic to the donor. These findings suggest that adherent peritoneal cell cytotoxicity could be at least partly due to macrophages and result from factor (s) released by sensitized lymphocytes in vivo in the same way as has been previously demonstrated in vitro. 相似文献
199.
M M Beljanski P Bourgarel M S Beljanski 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(24):1825-1828
Under well defined conditions ribosomal RNAs purified from Escherichia coli can be degraded by ribonuclease U2 giving rise to RNA fragments of 60--70 nucleotides. In vitro, these fragments are efficiently transcribed into a complementary DNA by DNA polymerase RNA dependent, partially purified from extracts of E. coli. In vivo, "RNA-fragments-U2" inhibit the development of plant tumors. 相似文献
200.
The glycoprotein CEA (carcinoembryonic antigen) carries carbohydrate groups, which react with the plant lectins from Agaricus bisporus, Arachis hypogaea (peanut), with Tridacnin from invertebrate clams and with the anti-A lectins from snails. Accordingly, it has cryptantigenic structures, which correspond to the T or T-like antigen, the Tridacnin receptor and to the so called A-like antigen. 相似文献