全文获取类型
收费全文 | 11702篇 |
免费 | 1001篇 |
国内免费 | 826篇 |
专业分类
化学 | 1765篇 |
晶体学 | 29篇 |
力学 | 745篇 |
综合类 | 130篇 |
数学 | 9087篇 |
物理学 | 1773篇 |
出版年
2024年 | 23篇 |
2023年 | 106篇 |
2022年 | 143篇 |
2021年 | 201篇 |
2020年 | 310篇 |
2019年 | 332篇 |
2018年 | 291篇 |
2017年 | 314篇 |
2016年 | 362篇 |
2015年 | 286篇 |
2014年 | 519篇 |
2013年 | 1078篇 |
2012年 | 554篇 |
2011年 | 591篇 |
2010年 | 509篇 |
2009年 | 701篇 |
2008年 | 671篇 |
2007年 | 754篇 |
2006年 | 664篇 |
2005年 | 572篇 |
2004年 | 528篇 |
2003年 | 516篇 |
2002年 | 481篇 |
2001年 | 387篇 |
2000年 | 403篇 |
1999年 | 364篇 |
1998年 | 310篇 |
1997年 | 307篇 |
1996年 | 193篇 |
1995年 | 132篇 |
1994年 | 127篇 |
1993年 | 70篇 |
1992年 | 99篇 |
1991年 | 49篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 51篇 |
1984年 | 61篇 |
1983年 | 29篇 |
1982年 | 42篇 |
1981年 | 44篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 18篇 |
1977年 | 24篇 |
1976年 | 23篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Crosslinked poly(ethylene oxide) containing siloxanes fabricated through thiol‐ene photochemistry 下载免费PDF全文
Victor A. Kusuma Elliot A. Roth William P. Clafshenkel Steven S. Klara Xu Zhou Surendar R. Venna Erik Albenze David R. Luebke Meagan S. Mauter Richard R. Koepsel Alan J. Russell David Hopkinson Hunaid B. Nulwala 《Journal of polymer science. Part A, Polymer chemistry》2015,53(13):1548-1557
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557 相似文献
3.
4.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
5.
In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the differential quadrature (DQ) method. The vorticity‐stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 104 to 106 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are critical to the patterns of flow and thermal fields. The present study suggests that a critical aspect ratio may exist at high Rayleigh number to distinguish the flow and thermal patterns. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
6.
本文对具有有限时滞的泛函微分方程建立了关于依照两种测度的实际稳定性的Razumikhin型判定定理,其中未采用通常的辅助函数,且可运用多个含有状态变量x的部分变元的Lyapunov函数,得出部分变远实际稳定性的判定定理,从而改进了已有的结果。 相似文献
7.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
8.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
9.
10.
李永祥 《数学物理学报(A辑)》2003,23(2):245-252
该文讨论四阶常微分方程边值问题u^(4)(t)=f(t,u,u″), t∈[0,1],u(0)=u(1)=u″(0)=u″(1)=0解的存在性, 其中f(t,u,v):[0,1]×R×R→R为Carathéodory函数. 在不限制f关于u,v的增长阶, 不假定f关于u,v的单调性的一般情形下, 用上下解方法获得了解的存在性结果,并讨论了单调迭代求解的有效性. 相似文献