全文获取类型
收费全文 | 426353篇 |
免费 | 5207篇 |
国内免费 | 1248篇 |
专业分类
化学 | 226104篇 |
晶体学 | 7018篇 |
力学 | 18291篇 |
综合类 | 12篇 |
数学 | 47890篇 |
物理学 | 133493篇 |
出版年
2020年 | 3615篇 |
2019年 | 3913篇 |
2018年 | 4888篇 |
2017年 | 4865篇 |
2016年 | 7557篇 |
2015年 | 4853篇 |
2014年 | 7606篇 |
2013年 | 19195篇 |
2012年 | 14084篇 |
2011年 | 17301篇 |
2010年 | 12052篇 |
2009年 | 11871篇 |
2008年 | 15920篇 |
2007年 | 15712篇 |
2006年 | 14762篇 |
2005年 | 13329篇 |
2004年 | 12117篇 |
2003年 | 10845篇 |
2002年 | 10598篇 |
2001年 | 12439篇 |
2000年 | 9580篇 |
1999年 | 7423篇 |
1998年 | 6073篇 |
1997年 | 5958篇 |
1996年 | 5821篇 |
1995年 | 5347篇 |
1994年 | 5225篇 |
1993年 | 5226篇 |
1992年 | 5849篇 |
1991年 | 5803篇 |
1990年 | 5554篇 |
1989年 | 5473篇 |
1988年 | 5551篇 |
1987年 | 5439篇 |
1986年 | 5135篇 |
1985年 | 6903篇 |
1984年 | 7087篇 |
1983年 | 5640篇 |
1982年 | 5916篇 |
1981年 | 5899篇 |
1980年 | 5579篇 |
1979年 | 5977篇 |
1978年 | 6068篇 |
1977年 | 6129篇 |
1976年 | 5973篇 |
1975年 | 5465篇 |
1974年 | 5474篇 |
1973年 | 5456篇 |
1972年 | 3772篇 |
1968年 | 3231篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
The possibilities and the limitations of 2D NMR for the structural characterization of paramagnetic metalloproteins are reviewed. We survey the general strategies for 2D1H NMR investigations of hyperfine shifted signals. Careful adaptation of classical 2D NMR experiments to fast relaxing systems results in the detection of previously not observed scalar and dipolar connectivities, thus leading to the specific assignment of selected resonances. The approach is of general applicability for paramagnetic metalloproteins. We report here on the application of the application of the method to an iron sulfur protein and a heme protein. In both cases specific assignment of several hyperfine shifted signals, corresponding to active site protons, were obtained; this allowed significant insight into the structure-function relationships of these metalloproteins. 相似文献
942.
943.
As a leading defence equipment company, the Dynamics Divisionof British Aerospace Defence Company (BAeDef(DD)) has experiencedthe worst effects of post-Coldwar defence cuts, a global recession,and a determination by the U.K. Government to achieve greatervalue for money in defence procurement. The major tenet of thisnew approach to defence prwurement was 'eyes on, hands off',promoting a shift of the management of project risks from theMinistry of Defence (MOD) to industry. Initial industry reactionwas sceptical but bxame increasingly compliant as tenderingrequirements included visibility of contractors' risk assessment.This paper describes the risk-assessment methodology createdby BAeDef(DD) to meet these changed conditions. The human and organizational aspects of these developments onrisk have helped create a pro-active risk-management cultureat BAeDef(DD). Continuous assessment of project risks providesthe impetus for wider thinking beyond risk-taking or risk-aversionpreferences, leading to greater realism in planning. Decisionsto implement risk resolution measures require competence incost-benefit analysis. The conditions to foster this new behaviourare better-informed senior management, with the rejection ofbad news eliminated at all levels, and the laying of a pathto becoming a learning company. 相似文献
944.
945.
946.
Methods are proposed for determining the diffusion coefficients of adsorbed molecules and the adsorption isotherms from given concentrations of the solutes in the external solution. The methods are based on a comparison of experimental data with the numerical results produced by a mathematical model of internal-diffusion kinetics of adsorption from a constant bounded volume.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 66, pp. 41–46, 1988. 相似文献
947.
948.
Identification of nonlinear elliptic equations 总被引:1,自引:0,他引:1
An optimization theoretic approach and algorithm for the estimation of state-dependent coefficients in nonlinear elliptic equation is presented. It is based on a splitting method combined with convex analysis techniques. Convergence of the algorithm is established and numerical examples are included.The research of K. Kunisch was supported in part by a grant from the Bundesministerium für Wissenschaft und Forschung, Austria. 相似文献
949.
950.
The magnified cross-section of the LDV probe volume fringe field created on a far screen (image plane) with an imaging lens is examined both analytically and experimentally. It is shown that measurements of the image plane fringe field can be used to quantitatively determine the fringe field existing within the probe volume. Because the fringe spacing in the magnified image is more accessible experimentally, both longitudinal- and lateral-coordinate variations in fringe spacing can be determined, permitting a complete mapping of the fringe field. The detailed knowledge of the fringe field thus obtained allows beam quality, alignment, and fringe uniformity to be evaluated with greater precision than is possible with other techniques.The authors would like to acknowledge C. F. Edwards and R. L. Schmitt for the loan of the beam profiler and for many helpful discussions. This work was performed at the Combustion Research Facility, Sandia National Laboratories, and was supported by the U.S. Department of Energy, Office of Industrial Technologies, Advanced Industrial Concepts Division. 相似文献