全文获取类型
收费全文 | 12679篇 |
免费 | 32篇 |
国内免费 | 36篇 |
专业分类
系统科学 | 93篇 |
丛书文集 | 205篇 |
教育与普及 | 39篇 |
理论与方法论 | 70篇 |
现状及发展 | 6226篇 |
研究方法 | 554篇 |
综合类 | 5362篇 |
自然研究 | 198篇 |
出版年
2013年 | 121篇 |
2012年 | 209篇 |
2011年 | 365篇 |
2010年 | 87篇 |
2008年 | 221篇 |
2007年 | 240篇 |
2006年 | 251篇 |
2005年 | 275篇 |
2004年 | 222篇 |
2003年 | 230篇 |
2002年 | 239篇 |
2001年 | 310篇 |
2000年 | 308篇 |
1999年 | 204篇 |
1992年 | 193篇 |
1991年 | 165篇 |
1990年 | 162篇 |
1989年 | 161篇 |
1988年 | 167篇 |
1987年 | 169篇 |
1986年 | 177篇 |
1985年 | 242篇 |
1984年 | 165篇 |
1983年 | 153篇 |
1982年 | 114篇 |
1981年 | 136篇 |
1980年 | 158篇 |
1979年 | 408篇 |
1978年 | 306篇 |
1977年 | 344篇 |
1976年 | 245篇 |
1975年 | 247篇 |
1974年 | 370篇 |
1973年 | 318篇 |
1972年 | 335篇 |
1971年 | 345篇 |
1970年 | 474篇 |
1969年 | 417篇 |
1968年 | 438篇 |
1967年 | 388篇 |
1966年 | 332篇 |
1965年 | 251篇 |
1964年 | 107篇 |
1959年 | 129篇 |
1958年 | 221篇 |
1957年 | 180篇 |
1956年 | 170篇 |
1955年 | 137篇 |
1954年 | 135篇 |
1948年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 176 毫秒
21.
Summary The application of diphenylilacetic acid has shown favorable effects on the growth of tobacco plants. Solutions containing 10 p.p.m. and 20 p.p.m. produce, in weight, an almost double growth in treated plants in comparison with the controls. Diphenylilacetic acid can be considered as a growth-promoting substance. The data are not definite. 相似文献
22.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
23.
A. F. McDonagh Y. -M. Pu D. A. Lightner 《Cellular and molecular life sciences : CMLS》1992,48(3):246-248
The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding. 相似文献
24.
25.
A. Fernández-Guasti K. Larsson C. Beyer 《Cellular and molecular life sciences : CMLS》1985,41(11):1414-1416
Summary Intracerebral infusion of (+) bicuculline methiodide, but not of its (–) isomer, in the preoptic area, stimulated masculine sexual behavior in rat as evidenced by a decrease in the number of intromissions preceding ejaculation and a shortening of the ejaculation latency and postejaculatory interval. Data suggest a role of the GABAergic system in mediating masculine sexual behavior.Acknowledgments. Authors wish to thank Ms Elisabeth Wallin for excellent technical assistance and Ms Madelene Kröning for preparing the figures. 相似文献
26.
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
27.
F. Acerbi 《Archive for History of Exact Sciences》2003,57(6):465-502
28.
Contemporary developments in economicmethodology have produced a vibrant agenda ofcompeting positions. These include, amongothers, constructivism, critical realism andrhetoric, with each contributing to the Realistvs. Pragmatism debate in the philosophies of thesocial sciences. A major development in theneo-pragmatist contribution to economicmethodology has been Quine's pragmatic assaulton the dogmas of empiricism, which are nowclearly acknowledged within contemporaryeconomic methodology. This assault isencapsulated in the celebrated Duhem-Quinethesis, which according to a number ofcontemporary leading philosophers of economics,poses a particularly serious methodologicalproblem for economics. This problem, asreflected in Hausman's analysis, consists ofthe inability of economics to learn fromexperience, thereby subverting the capacity totest economic theories. In this paper wedispute this position. Our argument is basedon a combination of Quine's holism with VanFraassen's constructive empiricism, especiallythe latter's analysis of empirical adequacy andhis pragmatic approach to explanation. Theresulting reorientation of economic methodologyrestores the capacity of economics to learnfrom experience and reinstates the imperativeof developing alternatives to orthodoxtheorizing in economics. 相似文献
29.
Coalignment of vimentin intermediate filaments with microtubules depends on kinesin. 总被引:19,自引:0,他引:19
Intermediate filaments in most types of cultured cells coalign with microtubules. Depolymerization of microtubules results in collapse of vimentin and desmin intermediate filaments to the nucleus where they form a perinuclear cap. Collapse can also be induced by microinjection of antibodies against intermediate filament or microtubule proteins. Thus, two filament systems interact with each other. But the molecules mediating this interaction are unknown. One of the candidates for this role is a microtubule motor kinesin. Recent data showed that kinesin is involved in the plus end-directed movement of the membranous organelles along microtubules such as radial extension of lysosomes in macrophages and centrifugal movement of pigment in melanophores. Here we report that injection of the anti-kinesin antibody into human fibroblasts results in the redistribution of intermediate filaments to a tight perinuclear aggregate but had no effect on the distribution of microtubules. Thus, kinesin is involved not only in organelle movement but also in interaction of the two major cytoskeletal systems, intermediate filaments and microtubules. 相似文献
30.
卢武星 《北京师范大学学报(自然科学版)》1994,(4)
1.0MeV208Pb离子在非晶Si中的投影射程RP和射程偏差ΔRP作为注量和温度二者的函数用背散射法进行测定.注量的变化范围为5×1013~7×1014cm-2.注入是在室温和t=-120℃下完成的.由由实验所确定的投影射程,射程偏差与注量或温度无关,并且分别等于295和72.2nm.与TRIM86的计算结果相比较,发现RP的偏离为18%,而ΔRP的偏离为36%.RP和ΔRP二者与注量及温度的无关性,排除了所观察到的与TRIM的矛盾是由于注入期间辐射增强扩散或离子束混合效应而引起的解释。 相似文献