全文获取类型
收费全文 | 39173篇 |
免费 | 114篇 |
国内免费 | 169篇 |
专业分类
系统科学 | 238篇 |
丛书文集 | 688篇 |
教育与普及 | 75篇 |
理论与方法论 | 145篇 |
现状及发展 | 17445篇 |
研究方法 | 1641篇 |
综合类 | 18550篇 |
自然研究 | 674篇 |
出版年
2013年 | 292篇 |
2012年 | 589篇 |
2011年 | 1234篇 |
2010年 | 245篇 |
2008年 | 681篇 |
2007年 | 812篇 |
2006年 | 764篇 |
2005年 | 810篇 |
2004年 | 859篇 |
2003年 | 702篇 |
2002年 | 733篇 |
2001年 | 1175篇 |
2000年 | 1107篇 |
1999年 | 777篇 |
1992年 | 734篇 |
1991年 | 558篇 |
1990年 | 610篇 |
1989年 | 566篇 |
1988年 | 540篇 |
1987年 | 562篇 |
1986年 | 604篇 |
1985年 | 768篇 |
1984年 | 578篇 |
1983年 | 494篇 |
1982年 | 415篇 |
1981年 | 444篇 |
1980年 | 543篇 |
1979年 | 1266篇 |
1978年 | 985篇 |
1977年 | 978篇 |
1976年 | 743篇 |
1975年 | 773篇 |
1974年 | 1123篇 |
1973年 | 951篇 |
1972年 | 1022篇 |
1971年 | 1151篇 |
1970年 | 1582篇 |
1969年 | 1185篇 |
1968年 | 1037篇 |
1967年 | 1128篇 |
1966年 | 1008篇 |
1965年 | 742篇 |
1964年 | 223篇 |
1959年 | 394篇 |
1958年 | 742篇 |
1957年 | 525篇 |
1956年 | 429篇 |
1955年 | 357篇 |
1954年 | 401篇 |
1948年 | 292篇 |
排序方式: 共有10000条查询结果,搜索用时 953 毫秒
281.
C. Petter 《Cellular and molecular life sciences : CMLS》1977,33(10):1384-1386
Summary Mouse foetuses were treated by Thalidomide on days 11–12 in order to verify whether the drug would induce blood abnormalities leading to circulatory troubles. About 18% of the treated foetuses showed both severe limb haemorrhages on day 14, and obvious alterations of the nucleated red blood cells of vitelline origin. These blood abnormalities, occurring suddenly during the well-known critical stage of foetal development, could be responsible for circulatory blocks leading to necrosis. 相似文献
282.
Summary Unambiguous assignment of the1H-NMR. resonances due to the hydrogen atoms in the -position of homoserine indicates that the hydrogen which is exchanged and removed in the cystathionine--synthase catalyzed reactions holds the pro-R configuration. 相似文献
283.
Summary Homogenates from T. cruzi epimastigotes produced 3.4 pmoles H2O2/min 106 cells, as detected by the cytochrome c peroxidase assay. Addition of NADH or NADPH increased H2O2 production by a factor of 3 and 5, respectively. When supplemented with NADH and NADPH, the mitochondrial, microsomal, and supernatant fractions produced H2O2, the soluble fraction and the mitochondrial membranes being apparently the main generators of H2O2. The epimastigote homogenates showed cyanide-sensitive superoxide dismutase activity, equivalent to 0.28 g bovine superoxide dismutase per mg homogenate protein.This investigation was supported by grants from Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET) Argentina and the Scientific Office, American States Organization.Career Investigator of CONICET. 相似文献
284.
Non-mendelial female sterility in Drosophila melanogaster: demonstration of an inducer chromosome 4]
A Pélisson 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,284(23):2399-2402
Crosses between two classes of Drosophila melanogaster strains (reactive and inducer) may lead to partially sterile F1 females. This sterility, called S.F. sterility, can be characterized by its physiological features. It appears to be the result of an interaction between two factors: "R" brought into the initial croos by the reactive mother and "I" by chromosomes of the inducer father. Except for chromosome 4, each chromosome of the well known inducer strains may carry the I factor (inducer chromosomes). The present results provide evidence for the presence of an inducer fourth chromosome in the inducer strain Nagasaki. 相似文献
285.
J P Garrec J Jourdan B Blanchard A Hartmann J P Lassalles M Thellier 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,285(5):579-582
The use of the stable isotopes 6 and 7 of lithium, and detection with the ionic analyser, allow the measurement of unidirectional transepithelial Li-fluxes, between "external" and "internal" solutions which both contain 80% Na and 20% Li. Efflux was found to be bigger than influx. An important lag-phase on the curve, reveals the interference of a Li-compartment, with a high capacity, in the epithelium itself. 相似文献
286.
Summary RIA of ecdysones are made on nymphal extracts ofPisaura mirabilis during the intermoulting cycle. The hormone level is low during exuviation and the greatest part of the intermoulting period but increases notably before and after ecdysis. The main hormonal peak or pre-ecdysial peak is due to -ecdysone, characterized by combined TLC/RIA.Acknowledgment. We wish to thank Dr M. Hirn for his help during the manipulations and J. Britton who has translated the text into English. 相似文献
287.
288.
A. R. Jones Carole Murcott D. H. Milton Jennifer Flynn 《Cellular and molecular life sciences : CMLS》1977,33(7):934-935
Summary The male antifertility agent 1-amino-3-chloropropan-2-ol (ACP,I) has been shown to be metabolized to-chlorohydrin (III) and metabolites of-chlorohydrin. This accounts for the similar antifertility and renal toxicity effects of both compounds. 相似文献
289.