全文获取类型
收费全文 | 82809篇 |
免费 | 6525篇 |
国内免费 | 7792篇 |
专业分类
化学 | 30216篇 |
晶体学 | 356篇 |
力学 | 7625篇 |
综合类 | 1515篇 |
数学 | 33397篇 |
物理学 | 24017篇 |
出版年
2023年 | 686篇 |
2022年 | 977篇 |
2021年 | 1491篇 |
2020年 | 1687篇 |
2019年 | 1932篇 |
2018年 | 1637篇 |
2017年 | 1963篇 |
2016年 | 2290篇 |
2015年 | 1971篇 |
2014年 | 2975篇 |
2013年 | 5597篇 |
2012年 | 3336篇 |
2011年 | 3863篇 |
2010年 | 3340篇 |
2009年 | 4589篇 |
2008年 | 5103篇 |
2007年 | 5333篇 |
2006年 | 4957篇 |
2005年 | 4229篇 |
2004年 | 3909篇 |
2003年 | 3925篇 |
2002年 | 3626篇 |
2001年 | 3031篇 |
2000年 | 2959篇 |
1999年 | 2604篇 |
1998年 | 2450篇 |
1997年 | 1996篇 |
1996年 | 1684篇 |
1995年 | 1619篇 |
1994年 | 1457篇 |
1993年 | 1254篇 |
1992年 | 1195篇 |
1991年 | 931篇 |
1990年 | 756篇 |
1989年 | 650篇 |
1988年 | 590篇 |
1987年 | 459篇 |
1986年 | 408篇 |
1985年 | 473篇 |
1984年 | 452篇 |
1983年 | 225篇 |
1982年 | 362篇 |
1981年 | 418篇 |
1980年 | 320篇 |
1979年 | 309篇 |
1978年 | 236篇 |
1977年 | 219篇 |
1976年 | 164篇 |
1974年 | 111篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Lehmer序列中的平方数 总被引:4,自引:1,他引:3
设V_n(R,Q)表示参数为R和Q的Lehmer伴随序列,如果R和Q为互素奇数且D=R-4Q>0,我们找出了满足Q_n(R,Q)或nQ_n(R,Q)是平方数的所有奇数n,这里Q_n(R,Q)R~(1/2)=V_n(R,Q)。 相似文献
992.
F. Despa R. S. Berry 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):37-40
Interpretive theoretical tools prove valuable in guiding
the analysis of experiments in the realm of atomic clusters.
Here, we review basic elements of an analytic approach that
makes it possible to find and visualize the effective
electrostatic potential and Coulomb correlations in multicenter
problems. To illustrate the utility of these concepts we apply
them to exploring molecular-doped metallic clusters. This study
is aiming at a systematic, visual assessment of changes induced
in screening, Coulomb correlation and effective potential by
varying the charge of the electronegative impurity and its
position in the cluster cage. 相似文献
993.
矩阵的合同、相似与二次型 总被引:1,自引:0,他引:1
王芳珍 《新疆大学学报(理工版)》2004,21(3):244-245
矩阵的合同关系、相似关系都是等价关系,它们虽然不同。但又有联系.对称矩阵是这两个知识点的交汇点。即两个实对称矩阵合同当且仅当它们相似.进一步得到二次型可以通过一个正交变换化为标准型。这一理论是高等代数教科书的重要内容。然而.现行的教科书对该理论的证明至少涉及到二次型、线性空间、线性变换和欧氏空间的内容.本文利用欧氏空间的正交性质给出这一理论新的简洁证明。以供教学参考之用。 相似文献
994.
995.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献
996.
Simone Calogero 《Journal of Differential Equations》2004,204(2):323-338
The Nordström-Vlasov system is a Lorentz invariant model for a self-gravitating collisionless gas. We establish suitable a priori bounds on the solutions of this system, which together with energy estimates and the smoothing effect of “momentum averaging” yield the existence of global weak solutions to the corresponding initial value problem. In the process we improve the continuation criterion for classical solutions which was derived recently. The weak solutions are shown to preserve mass. 相似文献
997.
A program to compute many functions dependent on the electron density ρ(r) from the results of ab initio molecular calculations is presented. The program allows the generation of different one-, two-, and three-dimensional grids for further graphical representation or numerical analysis. Other options like extracting separate atom contributions to the function computed or locating maximum and minimum values are also implemented. A number of illustrative applications regarding different ρ(r)-dependent functions are presented and the performance and portability of the program is discussed. 相似文献
998.
TorstenLinB 《计算数学(英文版)》2003,21(4):401-410
We consider a singularly perturbed semilinear convection-diffusion problem with a boundary layer of attractive turning-point type. It is shown that its solution can be decomposed into a regular solution component and a layer component. This decomposi-tion is used to analyse the convergence of an upwinded finite difference scheme on Shishkin meshes. 相似文献
999.
用无限阶Toeplitz矩阵求常系数微分方程的级数解 总被引:1,自引:0,他引:1
无限阶Toeplitz矩阵的属于0的特征向量可递推地求得,可表示常系数齐次微分方程的解.用它的逆可求得常系数非齐次微分方程的特解. 相似文献
1000.
Yi Liu David D. Díaz Adrian A. Accurso K. Barry Sharpless Valery V. Fokin M. G. Finn 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5182-5189
1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007 相似文献