全文获取类型
收费全文 | 43858篇 |
免费 | 613篇 |
国内免费 | 605篇 |
专业分类
化学 | 19796篇 |
晶体学 | 377篇 |
力学 | 1825篇 |
综合类 | 45篇 |
数学 | 10986篇 |
物理学 | 12047篇 |
出版年
2022年 | 145篇 |
2021年 | 221篇 |
2020年 | 224篇 |
2019年 | 233篇 |
2018年 | 1385篇 |
2017年 | 1613篇 |
2016年 | 1072篇 |
2015年 | 864篇 |
2014年 | 857篇 |
2013年 | 1533篇 |
2012年 | 3754篇 |
2011年 | 3022篇 |
2010年 | 2342篇 |
2009年 | 2053篇 |
2008年 | 1274篇 |
2007年 | 1333篇 |
2006年 | 1168篇 |
2005年 | 4986篇 |
2004年 | 4467篇 |
2003年 | 2891篇 |
2002年 | 1110篇 |
2001年 | 756篇 |
2000年 | 515篇 |
1999年 | 487篇 |
1998年 | 342篇 |
1997年 | 277篇 |
1996年 | 273篇 |
1995年 | 281篇 |
1994年 | 274篇 |
1993年 | 204篇 |
1992年 | 335篇 |
1991年 | 330篇 |
1990年 | 330篇 |
1989年 | 260篇 |
1988年 | 237篇 |
1987年 | 193篇 |
1986年 | 166篇 |
1985年 | 258篇 |
1984年 | 272篇 |
1983年 | 189篇 |
1982年 | 204篇 |
1981年 | 163篇 |
1980年 | 165篇 |
1979年 | 170篇 |
1978年 | 145篇 |
1977年 | 182篇 |
1976年 | 223篇 |
1975年 | 156篇 |
1974年 | 156篇 |
1973年 | 168篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献
92.
In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations. 相似文献
93.
94.
E. Beinrohr M. Németh P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(3):93-99
Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10–9 to 10–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.
One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia 相似文献
95.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献
96.
Deák L. Bottyán L. Major M. Nagy D. L. Spiering H. Szilágyi E. Tanczikó F. 《Hyperfine Interactions》2002,144(1-4):45-52
Hyperfine Interactions - Synchrotron Mössbauer Reflectometry (SMR), the grazing incidence nuclear resonant scattering of synchrotron radiation, can be applied to perform depth-selective phase... 相似文献
97.
复Finsler流形上的Koppelman-Leray-Norguet公式 总被引:1,自引:1,他引:0
利用不变积分核(Berndtsson核),复Finsler度量和联系于Chern-Finsler联络的非线性联络,研究复Finsler流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的积分表示,得到了(p,q)型微分形式的Koppelman-Leray-Norguet公式和■-方程的解.作为应用,利用复Finsler度量和联系于Chern-Finsler联络的非线性联络,给出了Stein流形上具有逐块光滑C~((1))边界的有界域上(p,q)型微分形式的Koppelman- Leray-Norguet公式以及■-方程的解,并且得到了Stein流形上实非退化强拟凸多面体上(p,q)型微分形式的积分表示式和■-方程的解. 相似文献
98.
We introduce and investigate the properties of Hochschild cohomology of algebras in an abelian monoidal category M. We show that the second Hochschild cohomology group of an algebra in M classifies extensions of A up to an equivalence. We characterize algebras of Hochschild dimension 0 (separable algebras), and of Hochschild dimension ≤1 (formally smooth algebras). Several particular cases and applications are included in the last section of the paper. 相似文献
99.
P. Schuurmans J. Wouters P. De Moor N. Severijns W. Vanderpoorten J. Vanhaverbeke L. Vanneste 《Hyperfine Interactions》1992,75(1-4):423-430
Anisotropic α-emission from nuclei in the decay chain from223Ra to207Tl has been observed using low temperature nuclear orientation in combination with high resolution α-detection at 4.2 K. Information
on partial wave amplitudes as well as hyperfine interactions has been extracted. 相似文献
100.