全文获取类型
收费全文 | 27772篇 |
免费 | 51篇 |
国内免费 | 125篇 |
专业分类
系统科学 | 216篇 |
丛书文集 | 489篇 |
教育与普及 | 79篇 |
理论与方法论 | 162篇 |
现状及发展 | 12399篇 |
研究方法 | 1293篇 |
综合类 | 12891篇 |
自然研究 | 419篇 |
出版年
2013年 | 220篇 |
2012年 | 456篇 |
2011年 | 879篇 |
2010年 | 184篇 |
2009年 | 149篇 |
2008年 | 491篇 |
2007年 | 555篇 |
2006年 | 574篇 |
2005年 | 587篇 |
2004年 | 572篇 |
2003年 | 558篇 |
2002年 | 602篇 |
2001年 | 926篇 |
2000年 | 837篇 |
1999年 | 551篇 |
1992年 | 477篇 |
1991年 | 389篇 |
1990年 | 404篇 |
1989年 | 392篇 |
1988年 | 380篇 |
1987年 | 415篇 |
1986年 | 431篇 |
1985年 | 514篇 |
1984年 | 394篇 |
1983年 | 339篇 |
1982年 | 277篇 |
1981年 | 295篇 |
1980年 | 375篇 |
1979年 | 888篇 |
1978年 | 683篇 |
1977年 | 681篇 |
1976年 | 517篇 |
1975年 | 562篇 |
1974年 | 807篇 |
1973年 | 697篇 |
1972年 | 721篇 |
1971年 | 798篇 |
1970年 | 1066篇 |
1969年 | 799篇 |
1968年 | 730篇 |
1967年 | 790篇 |
1966年 | 688篇 |
1965年 | 490篇 |
1959年 | 267篇 |
1958年 | 463篇 |
1957年 | 357篇 |
1956年 | 318篇 |
1955年 | 266篇 |
1954年 | 282篇 |
1948年 | 220篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
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
133.
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
134.
M. Marušić Nikša Allegretti F. Čulo 《Cellular and molecular life sciences : CMLS》1978,34(10):1355-1356
Summary Cyclophosphamide given to rats 2 or 5 days after an injection of Yoshida ascites sarcoma cured approximately the same proportion of animals, but the resistance to a subsequent tumor challenge was found only in rats treated with the drug 5 days after tumor injection. 相似文献
135.
C Torrossian 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(9):693-696
The oxygen consumption of "hibernating" ants shows a grouping effect translated by a significant decrease in the level of oxygen consumption as a function of grouping effect. The general relation between oxygen consumption and the living body mass is the same, if the living material belongs to a single animal, or a social community of ants. 相似文献
136.
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
137.
At ambient temperatures (Ta) of both 8 and 22 degrees C, intraventricular administration of TRH (10-80 microgram) produced a dose-dependent hypothermia in rats. The hypothermia was due to both decreased metabolic heat production and cutaneous vasodilatation. In contrast, at 30 degrees C Ta, TRH increased metabolic heat production (due to behavioral excitation) and led to hyperthermia. 相似文献
138.
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
139.
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
140.
Comparison of white pock (h) mutants of monkeypox virus with parental monkeypox and with variola-like viruses isolated from animals 总被引:5,自引:0,他引:5
Monkeypox mutants arising spontaneously or after serial, high multiplicity passage were characterized phenotypically and by restriction endonuclease mapping. Some resemble "whitepox" and variola viruses in several of the markers tested but all are distinguishable phenotypically from these. None resembles "whitepox" viruses in genome structure although near-terminal deletions or symmetrical, terminal rearrangements, relative to parental monkeypox, occurred. "Whitepox" viruses isolated from animals closely resemble variola in both phenotype and genome structure. 相似文献