全文获取类型
收费全文 | 31352篇 |
免费 | 83篇 |
国内免费 | 123篇 |
专业分类
系统科学 | 304篇 |
丛书文集 | 563篇 |
教育与普及 | 99篇 |
理论与方法论 | 97篇 |
现状及发展 | 14629篇 |
研究方法 | 1141篇 |
综合类 | 14426篇 |
自然研究 | 299篇 |
出版年
2012年 | 356篇 |
2011年 | 684篇 |
2009年 | 180篇 |
2008年 | 494篇 |
2007年 | 564篇 |
2006年 | 494篇 |
2005年 | 531篇 |
2004年 | 549篇 |
2003年 | 560篇 |
2002年 | 495篇 |
2001年 | 917篇 |
2000年 | 960篇 |
1999年 | 578篇 |
1994年 | 363篇 |
1992年 | 537篇 |
1991年 | 431篇 |
1990年 | 513篇 |
1989年 | 480篇 |
1988年 | 478篇 |
1987年 | 496篇 |
1986年 | 520篇 |
1985年 | 621篇 |
1984年 | 430篇 |
1983年 | 431篇 |
1982年 | 381篇 |
1981年 | 411篇 |
1980年 | 467篇 |
1979年 | 986篇 |
1978年 | 820篇 |
1977年 | 791篇 |
1976年 | 616篇 |
1975年 | 701篇 |
1974年 | 967篇 |
1973年 | 834篇 |
1972年 | 794篇 |
1971年 | 1022篇 |
1970年 | 1186篇 |
1969年 | 1031篇 |
1968年 | 946篇 |
1967年 | 912篇 |
1966年 | 787篇 |
1965年 | 595篇 |
1964年 | 211篇 |
1959年 | 339篇 |
1958年 | 572篇 |
1957年 | 418篇 |
1956年 | 347篇 |
1955年 | 347篇 |
1954年 | 334篇 |
1948年 | 234篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
P. Gandhi 《Cellular and molecular life sciences : CMLS》1978,34(1):15-15
Summary Incubation of 5,5-7,7-tetramethoxy-8,8-biflavone withAspergillus niger results in the formation of 4,4-dihydroxy-5,5-7,7-tetramethoxy-8,8-biflavan.Part of this work was done at Allahabad University, Chemical Laboratories. 相似文献
152.
Summary
2O,6N-butyryl, 3, 5-cyclic monophosphate (dibu cAMP) when added to fetal rat heart cells in culture inhibits myocyte contraction. This inhibition is 100, 84 and 51% complete when the dibu cAMP concentration used is 2, 0.2 and 0.02 mM, respectively. The potency of dibu cAMP derivatives in myocyte contraction inhibition follows the order, dibu cAMP>
6N-bu cAMP>
2O-bu cAMP=AMP>butyrate. The inhibition caused by the first three chemicals is greater than 70%.The author was a Moss Heart Fellow and acknowledges the technical assistance of Ms Martha Peet. This work was supported in part by the American Heart Association, National Science Foundation and American Cancer Society. 相似文献
153.
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
154.
Summary The effects of L-glutamic acid and of some glutamate analogues have been studied on the central nervous system of the snailHeobania vermiculata, using conventional electrophysiological techniques. The glutamate H-response had the mean equilibrium value of-(57±4) mV and was associated with a Cl– conductance change. The D-response to glutamate application showed an involvement of sodium ions. Aspartate was agonist of glutamate action and displayed similar equilibrium value of the H-response, whereas quisqualate H-response was non-invertible.The authors wish to express their thanks to Prof. A. Curatolo for his continual interest and advice, and to Dr J. Stinnakre for the criticism of the text. 相似文献
155.
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
156.
J P Debeaupuis P Lafont 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(5):431-434
A strain of Aspergillus fumigatus Fres., isolated from sugar-beet draffs, synthesizes in vitro four toxic metabolites which have not yet been described in these fungal species. Toxic effects of the most abundant of these metabolites "fumitoxin A" have been studed on chick embryo. Artemia salina larvae, cell cultures, and on mice. 相似文献
157.
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
158.
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
159.
Daily administration of vitamin D3 (75,000 IU/kg b. wt) for 7 days accelerated Trichinella spiralis cyst calcification in rats with a 14-week-old infection. When disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP) was administered (50 mg/kg b. wt) from 2 days before until 2 days after vitamin D3 treatment, cyst calcification was inhibited. Thus, the ability to inhibit E. spiralis calcification has demonstrated for the first time. 相似文献
160.
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