全文获取类型
收费全文 | 451909篇 |
免费 | 13634篇 |
国内免费 | 7548篇 |
专业分类
化学 | 252186篇 |
晶体学 | 6284篇 |
力学 | 21967篇 |
综合类 | 529篇 |
数学 | 51354篇 |
物理学 | 140771篇 |
出版年
2021年 | 4680篇 |
2020年 | 5427篇 |
2019年 | 5592篇 |
2018年 | 6363篇 |
2017年 | 6102篇 |
2016年 | 9310篇 |
2015年 | 6801篇 |
2014年 | 9685篇 |
2013年 | 20529篇 |
2012年 | 17489篇 |
2011年 | 20529篇 |
2010年 | 14357篇 |
2009年 | 14097篇 |
2008年 | 17743篇 |
2007年 | 17611篇 |
2006年 | 16466篇 |
2005年 | 14806篇 |
2004年 | 13067篇 |
2003年 | 11494篇 |
2002年 | 11236篇 |
2001年 | 11942篇 |
2000年 | 9530篇 |
1999年 | 7860篇 |
1998年 | 6851篇 |
1997年 | 6653篇 |
1996年 | 6326篇 |
1995年 | 5824篇 |
1994年 | 5897篇 |
1993年 | 5365篇 |
1992年 | 5933篇 |
1991年 | 5920篇 |
1990年 | 5597篇 |
1989年 | 5415篇 |
1988年 | 5333篇 |
1987年 | 5148篇 |
1986年 | 4865篇 |
1985年 | 6319篇 |
1984年 | 6581篇 |
1983年 | 5495篇 |
1982年 | 5762篇 |
1981年 | 5564篇 |
1980年 | 5452篇 |
1979年 | 5499篇 |
1978年 | 5933篇 |
1977年 | 5750篇 |
1976年 | 5843篇 |
1975年 | 5464篇 |
1974年 | 5565篇 |
1973年 | 5694篇 |
1972年 | 3950篇 |
排序方式: 共有10000条查询结果,搜索用时 327 毫秒
991.
S. Moss de Oliveira P. M. C. de Oliveira F. C. de Sá Barreto 《Journal of statistical physics》1995,78(5-6):1619-1627
Using the finite-size scaling renormalization group, we obtain the two-dimensional flow diagram of the Blume-Capel model forS=1 andS=3/2. In the first case our results are similar to those of mean-field theory, which predicts the existence of first- and second-order transitions with a tricritical point. In the second case, however, our results are different. While we obtain in theS=1 case a phase diagram presenting a multicritical point, the mean-field approach predicts only a second-order transition and a critical endpoint. 相似文献
992.
The 2D Rancieite type manganic acid was prepared by reduction of KMnO4 in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum. 相似文献
993.
G. D. Kartashov 《Journal of Mathematical Sciences》1995,75(1):1389-1393
A point estimator is proposed for certain numerical characteristics of a bivariate normal distribution with parameters that
cannot be observed simultaneously.
Translated fromStatisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 21–28, Perm, 1990. 相似文献
994.
This paper considers a problem of nonlinear programming in which the objective function is the ratio of two linear functions and the constraints define a bounded and connected feasible region. Using a coordinate transformation, this problem is transformed into a simpler one, whose geometric interpretation is of particular significance. The transformation leads to a characterization of some special vertices of the feasible region from both the theoretical and operational points of view. 相似文献
995.
W. A. Rodrigues Jr. Q. A. G. de Souza J. Vaz Jr. P. Lounesto 《International Journal of Theoretical Physics》1996,35(9):1849-1900
In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named the spin-Clifford bundle (SCB). The conditions for the existence of the SCB are studied and are shown to be equivalent to Geroch's theorem concerning the existence of spinor structures in a Lorentzian spacetime. We introduce also the covariant and algebraic Dirac spinor fields and compare these with DHSF, showing that all three kinds of spinor fields contain the same mathematical and physical information. We clarify also the notion of (Crumeyrolle's) amorphous spinors (Dirac-Kähler spinor fields are of this type), showing that they cannot be used to describe fermionic fields. We develop a rigorous theory for the covariant derivatives of Clifford fields (sections of the Clifford bundle, CB) and of Dirac-Hestenes spinor fields. We show how to generalize the original Dirac-Hestenes equation in Minkowski spacetime for the case of RCST. Our results are obtained from a variational principle formulated through the multiform derivative approach to Lagrangian field theory in the Clifford bundle. 相似文献
996.
We propose an effective method of numerical determination of the gradient vector and the Hessian matrix of a quadratic quality
criterion in parametric optimization of continuous-discrete stochastic dynamic control systems based on the application of
adjoint equations.
Translated fromDinamicheskie Sistemy, No. 13, 1994, pp. 20–25. 相似文献
997.
G. Carelli N. Ioli A. Messina A. Moretti S. Schepis F. Strumia 《International Journal of Infrared and Millimeter Waves》1998,19(9):1191-1199
We measured the dependence of the reflectivity of InSb crystals upon temperature in the submillimeter region using monochromatic radiation from an optically pumped far infrared (FIR) laser. The measures allowed us to determine the value of the electron effective mass at low temperatures with radiations of different frequencies. Our measurements extend the results obtained recently on pure crystals with magneto-optical methods to the low temperatures region where only old measures were available. 相似文献
998.
DAndrea A. Tomassini N. Ferrari L. Righini M. Selci S. Bruni M. R. Simeoni G. 《Il Nuovo Cimento D》1995,17(11):1423-1427
Il Nuovo Cimento D - Normalized reflection spectra in GaInAs/GaAs quantum wells are shown for two sets of samples with different alloy concentration (x=9% and 18.5%) and well thickness ranging from... 相似文献
999.
V. G. Osmolovski 《Journal of Mathematical Sciences》1997,84(1):898-910
An existence theorem for the variational problem for the two-phase medium energy functional is proved. Dependence of the solution
on the surface tension coefficient and on the temperature is investigated. Bibliography: 7 titles.
Dedicated to V. A. Solonnikov on his sixtieth anniversary
Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 213, 1994, pp. 131–150.
Translated by S. Yu. Pilyugin. 相似文献
1000.
An iterative method from the class of completely implicit methods (CIM) is proposed for solving the equation of the velocity
potential of elliptical-hyperbolic type. The advantage of the proposed method compared to other CIM schemes is demonstrated
in application to mixed perfect gas flows in a nozzle of a given shape. Accuracy issues, rate of convergence, and various
techniques of ensuring stability in the hyperbolic region are discussed.
Translated from Chislennye Metody v Matematicheskoi Fizike, Published by Moscow University, Moscow, 1996, pp. 39–51. 相似文献