全文获取类型
收费全文 | 29878篇 |
免费 | 5069篇 |
国内免费 | 3697篇 |
专业分类
化学 | 17655篇 |
晶体学 | 254篇 |
力学 | 2345篇 |
综合类 | 231篇 |
数学 | 5079篇 |
物理学 | 13080篇 |
出版年
2024年 | 93篇 |
2023年 | 413篇 |
2022年 | 852篇 |
2021年 | 943篇 |
2020年 | 1312篇 |
2019年 | 1063篇 |
2018年 | 988篇 |
2017年 | 1014篇 |
2016年 | 1314篇 |
2015年 | 1221篇 |
2014年 | 1643篇 |
2013年 | 2670篇 |
2012年 | 1668篇 |
2011年 | 1808篇 |
2010年 | 1512篇 |
2009年 | 1815篇 |
2008年 | 1896篇 |
2007年 | 1883篇 |
2006年 | 1781篇 |
2005年 | 1466篇 |
2004年 | 1333篇 |
2003年 | 1245篇 |
2002年 | 1023篇 |
2001年 | 917篇 |
2000年 | 875篇 |
1999年 | 789篇 |
1998年 | 675篇 |
1997年 | 615篇 |
1996年 | 460篇 |
1995年 | 404篇 |
1994年 | 345篇 |
1993年 | 286篇 |
1992年 | 263篇 |
1991年 | 245篇 |
1990年 | 153篇 |
1989年 | 131篇 |
1988年 | 140篇 |
1987年 | 131篇 |
1986年 | 106篇 |
1985年 | 168篇 |
1984年 | 157篇 |
1983年 | 87篇 |
1982年 | 140篇 |
1981年 | 138篇 |
1980年 | 97篇 |
1979年 | 89篇 |
1978年 | 67篇 |
1977年 | 62篇 |
1976年 | 36篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
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
62.
We analyze the effect of co-segregation on the mobility of grain boundaries within the framework of the impurity drag theory originally proposed by Cahn and Lücke and Stüwe for an ideal solution. The new derivation extends this model to the case where there are two types of impurities (or three components in the alloy). Since the resultant expression for the boundary mobility is complicated, numerical solutions were obtained for several cases to show how co-segregation affects the boundary mobility. Depending on the relative diffusivities of the two impurities which are both attracted to the boundary, the mobility may either increase or decrease with increasing concentration of one of the impurities. When one of the impurities is attracted to the boundary and the other repelled from the boundary, increasing the concentration of the attractive impurity can lead to a sharp decrease in the boundary mobility. 相似文献
63.
光纤的能量传输特性及应用 总被引:5,自引:0,他引:5
着重分析了影响光纤传输能量以及光纤传输中造成能量损耗的因素。这些因素主要包括光纤材料、构造、光纤的折射率分布、光纤的长度和芯径、光纤的数值孔径和热效应以及耦合等。同时 ,结合激光二极管点火的实例 ,分析探讨了其背景和应用价值。结论是 :为了尽可能减少能量损耗、提高光纤输出的激光功率和激光功率密度 ,应当选取合适的激光工作波长、较小的光纤长度、较小的芯径和较小的数值孔径 ,应采用渐变折射率分布光纤 ,应减少弯曲与耦合 相似文献
64.
D. Yafaev 《Proceedings Mathematical Sciences》2002,112(1):245-255
We find an explicit function approximating at high energies the kernel of the scattering matrix with arbitrary accuracy. Moreover,
the same function gives all diagonal singularities of the kernel of the scattering matrix in the angular variables.
This paper is dedicated to Jean-Michel Combes on the occasion of his sixtieth birthday. 相似文献
65.
强流脉冲电子束在材料中的能量沉积剖面、能量沉积系数和束流传输系数受其入射角的影响很大,理论计算了0.5~2.0MeV的电子束以不同的入射角在Al材料中的能量沉积剖面和能量沉积系数,并且还计算了0.4~1.4MeV电子束以不同入射角穿透不同厚度C靶的束流传输系数。计算结果表明,随着入射角的增大,靶材表面层单位质量中沉积的能量增大,电子在靶材料中穿透深度减小,能量沉积系数减小,相应的束流传输系数也减小;能量为0.5~2.0MeV的电子束当入射角在60°~70°时在材料表面层单位质量中沉积的能量较大。 相似文献
66.
F. F. Maia Jr. J. A. K. Freire G. A. Farias V. N. Freire E. F. da Silva Jr. 《Applied Surface Science》2002,190(1-4):247-251
The excitonic properties of a ZnSe/ZnSxSe1−x strained quantum well (QW) are calculated taking into account interface effects. Numerical results obtained with ZnS0.18Se0.82/ZnSe QWs show that graded interfaces can be responsible for a strong broadening of excitonic spectra. 相似文献
67.
We consider Markov processes built from pasting together pieces of strong Markov processes which are killed at a position
dependent rate and connected via a transition kernel. We give necessary and sufficient conditions for local absolute continuity
of probability laws for such processes on a suitable path space and derive an explicit formula for the corresponding likelihood
ratio process. The main tool is the consideration of the process between successive jumps – what we call ‘elementary experiments’
– and criteria for absolute continuity of laws of the process there. We apply our results to systems of branching diffusions
with interactions and immigrations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
68.
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
69.
Guido Wauters Jacques Dewaele Carlo Vandecasteele Richard Dams 《Mikrochimica acta》1989,98(4-6):157-162
Proton activation analysis was used for the determination of cadmium and lead in three sediment reference materials. The method is based on the111,112Cd(p, xn)111 In and the206,207,208Pb(p, xn)206Bi reactions.111In and206Bi were chemically separated by anion exchange. The results obtained were taken into account for the certification of the materials and are in the excellent agreement with the certified values. 相似文献
70.
Basic principles of the generalized lattice model of multicomponent condensed systems are formulated. Short-range parts of interatomic interactions are taken into account by means of the geometric constraints method. Long-range parts of the interactions are taken into account in mean field approximation. The expression for Helmholtz free energy is obtained. A system of integral equations for the equilibrium distributions of components is derived. The asymptotic properties of its solutions are investigated. Moment expansion of interatomic interactions and localization of integral terms in free energy is obtained. A Ginzburg–Landau-like functional of free energy is derived. 相似文献