全文获取类型
收费全文 | 55898篇 |
免费 | 263篇 |
国内免费 | 549篇 |
专业分类
系统科学 | 1242篇 |
丛书文集 | 190篇 |
教育与普及 | 288篇 |
理论与方法论 | 521篇 |
现状及发展 | 31703篇 |
研究方法 | 863篇 |
综合类 | 19712篇 |
自然研究 | 2191篇 |
出版年
2013年 | 808篇 |
2012年 | 613篇 |
2011年 | 2648篇 |
2009年 | 615篇 |
2008年 | 826篇 |
2007年 | 935篇 |
2006年 | 1026篇 |
2005年 | 1180篇 |
2004年 | 2271篇 |
2003年 | 1931篇 |
2002年 | 1578篇 |
2001年 | 1510篇 |
2000年 | 1052篇 |
1999年 | 1020篇 |
1998年 | 646篇 |
1997年 | 776篇 |
1996年 | 533篇 |
1994年 | 687篇 |
1993年 | 693篇 |
1992年 | 945篇 |
1991年 | 805篇 |
1990年 | 899篇 |
1989年 | 690篇 |
1988年 | 649篇 |
1987年 | 684篇 |
1986年 | 758篇 |
1985年 | 896篇 |
1984年 | 784篇 |
1983年 | 686篇 |
1982年 | 808篇 |
1981年 | 829篇 |
1980年 | 904篇 |
1979年 | 1416篇 |
1978年 | 1251篇 |
1977年 | 1230篇 |
1976年 | 1117篇 |
1975年 | 1079篇 |
1974年 | 929篇 |
1973年 | 1178篇 |
1972年 | 1204篇 |
1971年 | 1241篇 |
1970年 | 1322篇 |
1969年 | 1203篇 |
1968年 | 1184篇 |
1967年 | 1049篇 |
1966年 | 888篇 |
1965年 | 737篇 |
1964年 | 485篇 |
1958年 | 526篇 |
1957年 | 435篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A. Gutnisky P. Glikman M. F. Gimeno A. L. Gimeno 《Cellular and molecular life sciences : CMLS》1982,38(1):116-117
Summary The administration of 15(R)-15-methyl prostaglandin E2 (15(R)-15-M-PGE2) in vivo significantly diminished the uptake of59Fe into blood, spleen, liver, femur and dried intestine of rats, whereas acetylsalicylic acid (ASA) increased the counts significantly. This effect of ASA was counteracted by 15(R)-15-M-PGE2. It is suggested that prostaglandins (PGs) might play an important role in inhibiting iron absorption at the intestinal level.This work was supported by grant No.6638 from CONICET (Argentina). The technical assistance of Mrs María E. Castro and Norma Rizzo is gratefully acknowleged. 相似文献
72.
Summary Host cell reactivation capacity for ozone T3 phage was determined for differentE. coli strains deficient in one or more of the DNA repair mechanisms. The results indicate that DNA polymerase I appears to play a key role in the repair of damage produced on the DNA by ozone while thelexA gene product seems to play a minor one.This research was sponsored by the National Sciences and Engineering Council of Canada. One of us (PLH) acknowledges a scholarship from the NSERCof Canada. 相似文献
73.
Summary The nature of antigen Dd, an antigen present in the extracts of human dandruff which precipitates human sera selectively, and antibodies reacting with it are reported.This work was supported through U.G.C. Grant No. F.23-230/75/SR II. H.K. participated in this study, first as J.R.F. of U.G.C. and then as S.R.F. of I.C.M.R. We are grateful to Dr Baruch S. Blumberg for his invaluable suggestions and to Professor H. Walter for the gift of IgG, IgM and IgA immune sera. 相似文献
74.
We discuss a generalization of the standard notion of probability space and show that the emerging framework, to be called operational probability theory, can be considered as underlying quantal theories. The proposed framework makes special reference to the convex structure of states and to a family of observables which is wider than the familiar set of random variables: it appears as an alternative to the known algebraic approach to quantum probability. 相似文献
75.
A. E. Yassen H. A. Hassan L. S. Kawashti 《Cellular and molecular life sciences : CMLS》1994,50(11-12):1111-1114
A detailed karyotypic analysis of two Egyptian species of bats,Taphozous perforatus andTaphozous nudiventris, was made on the basis of conventional data and G-band patterns. No detectable karyotypic difference was found between the two species (2n=42, F.N. 64). By comparison of G-band patterns, some differences between the two species were seen in the corresponding autosomal pairs. These results are reported for the first time in Egypt. 相似文献
76.
77.
Jacob W. Ulvila 《Journal of forecasting》1985,4(4):377-385
Recent years have seen an increasing cross-fertilization between the fields of decision analysis and forecasting. Decision-analytic models often require forecasts as inputs, and aspects of the Bayesian decision-theoretic framework underlying decision analysis have proved useful to forecasting, particularly in contexts where subjective judgemental inputs are required. This paper describes the use of decision tree analysis for forecasting and illustrates its use for corporate divisional forecasting and planning. A specialized decision-analytic technique, acts as events, is also described and illustrated to forecast a new product's earnings. Conclusions are drawn about the applicability of decision analysis for forecasting. 相似文献
78.
J. W. Faigle H. Stierlin H. Mory T. Winkler H. -P. Kriemler 《Cellular and molecular life sciences : CMLS》1985,41(4):476-478
Summary Indoxyl derivatives were detected as minor products among the urinary metabolites of two trial drugs, a benzodiazepine (GP 55 129) and a benzophenone (CGP 11 952). Their structures were elucidated by NMR and mass spectroscopy. Presumably, metabolites containing potential aldehyde functions react spontaneously with endogenous indoxyl. Such derivatives have not hitherto been encountered in drug metabolism. 相似文献
79.
本文提出了精测安培表内阻的新方法,并将其与其它测量方法进行了比较。 相似文献
80.
本文介绍了在水电工程规划设计时,如何利用三次自然样条插值函数在有限个方案的基础上自动生成无限多个方案,然后采用多目标综合决策模型在其中选择最优方案的一种方法.文中还给出了程序流程,并以某水电站正常蓄水位选择作为实例,对方法进行了验证,结果与专家决策完全吻合. 相似文献