全文获取类型
收费全文 | 440381篇 |
免费 | 3263篇 |
国内免费 | 1135篇 |
专业分类
化学 | 215185篇 |
晶体学 | 6637篇 |
力学 | 23385篇 |
综合类 | 17篇 |
数学 | 60872篇 |
物理学 | 138683篇 |
出版年
2021年 | 2912篇 |
2020年 | 3086篇 |
2019年 | 3649篇 |
2018年 | 11779篇 |
2017年 | 12413篇 |
2016年 | 10301篇 |
2015年 | 4805篇 |
2014年 | 6729篇 |
2013年 | 15879篇 |
2012年 | 16183篇 |
2011年 | 25450篇 |
2010年 | 16785篇 |
2009年 | 17143篇 |
2008年 | 22933篇 |
2007年 | 25724篇 |
2006年 | 13274篇 |
2005年 | 17201篇 |
2004年 | 13679篇 |
2003年 | 12558篇 |
2002年 | 10887篇 |
2001年 | 11109篇 |
2000年 | 8573篇 |
1999年 | 6315篇 |
1998年 | 5125篇 |
1997年 | 5164篇 |
1996年 | 5074篇 |
1995年 | 4400篇 |
1994年 | 4373篇 |
1993年 | 4181篇 |
1992年 | 4736篇 |
1991年 | 4845篇 |
1990年 | 4507篇 |
1989年 | 4556篇 |
1988年 | 4481篇 |
1987年 | 4431篇 |
1986年 | 4220篇 |
1985年 | 5700篇 |
1984年 | 5759篇 |
1983年 | 4767篇 |
1982年 | 4866篇 |
1981年 | 4716篇 |
1980年 | 4504篇 |
1979年 | 4822篇 |
1978年 | 4873篇 |
1977年 | 4957篇 |
1976年 | 4932篇 |
1975年 | 4704篇 |
1974年 | 4539篇 |
1973年 | 4767篇 |
1972年 | 3259篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
53.
54.
55.
D. N. Zaporozhets 《Journal of Mathematical Sciences》2006,137(1):4525-4530
In this note, we find the distibution of the number of real zeros of a random polynomial. We also derive a formula for the
expected number of complex zeros lying in a given domain of the complex plane. Bibliography: 7 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 320, 2004, pp. 69–79. 相似文献
56.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion
for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of
the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23. 相似文献
57.
I. N. Sergeev 《Journal of Mathematical Sciences》2006,135(1):2764-2793
The definition of the characteristic frequencies of zeroes and changes of sign for solutions is given. It is equal to the
upper medium (with respect to the time half-axis) of their number on the half-interval of length π. We also define the main frequencies for a linear homogeneous equation of order n. These main frequencies for an equation with constant coefficients coincide with the absolute values of the imaginary parts
of the roots of the corresponding characteristic polynomial. It is proved that for the second-order equation the main frequencies
are the same for all solutions and that they are stable with respect to uniformly small and infinitely small perturbations
of the coefficients. For the third-order equation they can be different, and for any of the main frequencies an example of
nonstability is given.
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 249–294, 2005. 相似文献
58.
Zarubitskii O. G. Budnik V. G. Omel'chuk A. A. Melekhin V. T. Opanasyuk V. P. Zakharchenko N. F. 《Russian Journal of Applied Chemistry》2002,75(4):558-561
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry. 相似文献
59.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
60.
Allen C. HirshfeldPeter Henselder 《Annals of Physics》2002,302(1):59-77
Deformation quantization, which achieves the passage from classical mechanics to quantum mechanics by the replacement of the pointwise multiplication of functions on phase space by the star product, is a powerful tool for treating systems involving bosonic degrees of freedom, both in quantum mechanics and in quantum field theory. In the present paper we show how these methods may be naturally extended to systems involving fermions. In particular we show how supersymmetric quantum mechanics can be formulated in this approach and consider examples involving both non-relativistic and relativistic systems. 相似文献