全文获取类型
收费全文 | 221526篇 |
免费 | 2724篇 |
国内免费 | 1327篇 |
专业分类
化学 | 123156篇 |
晶体学 | 3234篇 |
力学 | 8901篇 |
综合类 | 61篇 |
数学 | 24429篇 |
物理学 | 65796篇 |
出版年
2020年 | 1763篇 |
2019年 | 1908篇 |
2018年 | 2489篇 |
2017年 | 2531篇 |
2016年 | 3668篇 |
2015年 | 2448篇 |
2014年 | 3556篇 |
2013年 | 8913篇 |
2012年 | 7724篇 |
2011年 | 9441篇 |
2010年 | 6679篇 |
2009年 | 6475篇 |
2008年 | 8820篇 |
2007年 | 8932篇 |
2006年 | 8414篇 |
2005年 | 7731篇 |
2004年 | 6894篇 |
2003年 | 6066篇 |
2002年 | 6005篇 |
2001年 | 6710篇 |
2000年 | 5079篇 |
1999年 | 3670篇 |
1998年 | 3047篇 |
1997年 | 3018篇 |
1996年 | 3017篇 |
1995年 | 2620篇 |
1994年 | 2721篇 |
1993年 | 2586篇 |
1992年 | 2835篇 |
1991年 | 2894篇 |
1990年 | 2707篇 |
1989年 | 2625篇 |
1988年 | 2558篇 |
1987年 | 2498篇 |
1986年 | 2525篇 |
1985年 | 3304篇 |
1984年 | 3364篇 |
1983年 | 2810篇 |
1982年 | 3054篇 |
1981年 | 2818篇 |
1980年 | 2613篇 |
1979年 | 2795篇 |
1978年 | 3001篇 |
1977年 | 3038篇 |
1976年 | 3062篇 |
1975年 | 2795篇 |
1974年 | 2912篇 |
1973年 | 2962篇 |
1972年 | 2326篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
The complextrans-[PtCl2 (Me2PhP)(cis-2,4-dimethylpyrrolidine)] has been characterized by X-ray crystallography. It crystallizes in the monoclinic space group P 22/c witha=8.762(3),b=16.034(5),c=12.600(4)Å,=93.43(3)° andZ=4. The structure was solved by heavy atom method and refined toR=0.052 for 3251 observed counter reflections. The coordination sphere of the Pt atom is square-planar with a geometry very similar to that of the studied complexes of the type trans-[PtCl2(R3P)L] whereL is either one of the possible isomers of theC,C-dimethylpyrrolidine or the unsubstituted pyrrolidine. In the present complex the puckered five-membered ring of the dimethylpyrrolidine ligand assumes an envelope conformation with the maximum puckering at the N atom. 相似文献
982.
LetS
(1)
(n, Q) denote the maximum module of exponential sums for polynomials of degree n over the Galois fieldF
Q
. In a previous paper the transition to the multiple exponential sums allowed us to obtain a good lower bound of the valueS
(1)
(n, Q), which coincides with Weil's bound whenn = q
(m-1)/2 + 1, whereq, m are odd andm 3. Here the same approach is used for the estimation of the valueS
(d)
(n, Q), which corresponds to polynomials(x
d
) overF
Q
, whered is any divisor ofq – 1. 相似文献
983.
We construct functions Mα which are piecewise homogeneous polynomials on the (d+1)-dimensional torus Ud+1. These functions possess complete symmetry with respect to the independent variables. The symmetry and homogeneous relations
for these functions are exploited to obtain a recurrence relation and explicit representations. Furthermore, we show that
, where ω=e12x/k, 0≤jt≤k−1, are linearly independent. By restricting Mα to Ud, we obtain the complex analogue of polynomial box splines on a (d+1)-direction mesh on Ud, which is a multivariate analogue of B-splines on the circle studied by I.J. Schoenberg[8]. 相似文献
984.
985.
Two different relaxed problems associated with a problem of optimal control theory, governed by an ODE, are considered: the first is obtained by Young's methods and the second by semicontinuity arguments. A formula which relates the two relaxed functionals to each other is given. 相似文献
986.
Ramez L. Sami 《Archive for Mathematical Logic》1989,28(3):149-154
From the hypothesis that all Turing closed games are determined we prove: (1) the Continuum Hypothesis and (2) every subset of 1 is constructible from a real. 相似文献
987.
We consider the problem of finding maximal flows with respect to capacities which are linear functions of a parametert [0,T]. Since this problem is a special case of a parametric linear program the classichorizontal approach can be applied in which optimal solutions are computed for successive subintervals of [0,T]. We discuss an alternative algorithm which approximates in each iteration the optimal solution for allt [0,T]. Thisvertical algorithm is a labeling type algorithm where the flow variables are piecewise linear functions. Flow augmentations are done alongconditional flow augmenting paths which can be found by modified path algorithms. The vertical algorithm can be used to solve the parametric flow problem optimally as well as to compute a good approximation for allt if the computation of the optimal solution turns out to be too time consuming.Partially supported by NSF Grants ECS-8412926 and INT-8521433, and NATO Grant RG 85/0240. 相似文献
988.
L. Desvillettes 《Communications in Mathematical Physics》1989,123(4):687-702
We give a lower bound of the entropy dissipation rate of Ka, Boltzmann and Fokker-Planck-Landau equations. We apply this estimate to the problem of the speed of convergence to equilibrium in large time for the Boltzmann equation. 相似文献
989.
The performance of a combined CARS/LDA instrument capable of measuring temperature and two velocity components with a time coincidence of about 4 s is evaluated in a turbulent premixed propane-air Bunsen-burner flame. Measurements near the base of the flame exhibit negative axial correlations, indicative of normal gradient transport; those near the flame tip show strong positive axial correlations, indicative of transport counter to the temperature gradient. The radial correlations are positive both in the reaction zone and in the plume. An analysis of temperature data from measurements made (1) independent of and (2) coincidental with LDA measurements indicates that the CARS/LDA instrument provides a density-weighted velocity, temperature, and velocity temperature correlation due to the density variations in the flame. 相似文献
990.