全文获取类型
收费全文 | 636882篇 |
免费 | 22230篇 |
国内免费 | 13316篇 |
专业分类
化学 | 358797篇 |
晶体学 | 8761篇 |
力学 | 29300篇 |
综合类 | 684篇 |
数学 | 74818篇 |
物理学 | 200068篇 |
出版年
2022年 | 6885篇 |
2021年 | 8252篇 |
2020年 | 8992篇 |
2019年 | 9138篇 |
2018年 | 10417篇 |
2017年 | 9928篇 |
2016年 | 15243篇 |
2015年 | 11353篇 |
2014年 | 15948篇 |
2013年 | 31924篇 |
2012年 | 27587篇 |
2011年 | 32080篇 |
2010年 | 22454篇 |
2009年 | 22119篇 |
2008年 | 27491篇 |
2007年 | 26762篇 |
2006年 | 24955篇 |
2005年 | 22126篇 |
2004年 | 19746篇 |
2003年 | 17088篇 |
2002年 | 16765篇 |
2001年 | 18035篇 |
2000年 | 13950篇 |
1999年 | 11448篇 |
1998年 | 9677篇 |
1997年 | 9191篇 |
1996年 | 8920篇 |
1995年 | 8011篇 |
1994年 | 7836篇 |
1993年 | 7342篇 |
1992年 | 8027篇 |
1991年 | 8018篇 |
1990年 | 7521篇 |
1989年 | 7214篇 |
1988年 | 7111篇 |
1987年 | 6911篇 |
1986年 | 6564篇 |
1985年 | 8321篇 |
1984年 | 8483篇 |
1983年 | 6833篇 |
1982年 | 6996篇 |
1981年 | 6830篇 |
1980年 | 6371篇 |
1979年 | 6870篇 |
1978年 | 7092篇 |
1977年 | 6879篇 |
1976年 | 6873篇 |
1975年 | 6435篇 |
1974年 | 6466篇 |
1973年 | 6411篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
2.
提出用溶胶粒子表面修饰方法,结合溶胶凝胶技术制备无机催化膜.该方法的基本原理是利用合适的金属配合物在胶粒表面的吸附作用,经溶胶凝胶过程,将活性组分结合到无机膜中.实验测定结果表明:(NiEDTA)2-,VO-3,MoO2-4,(Pd(NH3)4)2+,PdCl2-4,PtCl2-6和RhCl3-6可用来修饰AlOOH溶胶.以Pd/γAl2O3催化膜的制备为例,经三次溶胶凝胶过程,可制得无裂缺的厚度为9μm的Pd/γAl2O3催化膜,膜材料的平均孔直径为6nm,Pd被均匀地分布在膜的顶层,其平均粒径为23nm. 相似文献
3.
To investigate local ordering and segregation phenomenon in a Ni91Pt9-alloy after sputtering and annealing a 3D optical atom probe (OAP) has been used. The specimen tips have been prepared from polycrystalline samples. To sputter the samples a separate preparation chamber with a scannable Ar-sputter-gun is connected to the OAP vessel. When necessary, the sample can be electrically heated to induce segregation and cure the altered layer. After a heat treatment of a Ni91 at. %Pt 9 at.% specimen at 1100 K the surface of a (111)-oriented specimen is enriched in platinum by a factor of two in relation to the bulk. The phenomenon of short-range ordering has been investigated on the surface and in the subsurface volume. A 3D reconstruction of this annealed NiPt specimen shows regions with high concentration of platinum that gives an indication at short-range ordering. Uniform sputtering of the tip without a heat treatment induces a decisive depletion of Pt on the surface and the following subatomic layers. The atom-probe results of specimens in thermal equilibrium are in close agreement to further surface sensitive results obtained from Ion Scattering Spectroscopy (ISS) and Auger Electron Spectroscopy (AES). 相似文献
4.
本文是文[1-7]的继续,研究变权综合问题,从确定变权的经验公式入手引出了变权原理,给出了变权的公理化定义,讨论了与之有关的均衡函数及其梯度向量。 相似文献
5.
M. Mirvaliev 《Journal of Mathematical Sciences》1987,38(6):2357-2363
One obtains a formula for the transformation of a vector with a given covariance matrix. The sum of the squares of the components of the transformed vector is equal to a chi-square type quadratic form, constructed with the aid of the initial vector. Taking into account this property, one finds the components of the Pearson statistic, Pearson-Fisher statistic, etc.Translated from Veroyatnostnye Raspredeleniya i Matematicheskaya Statistika, pp. 337–350, 1986. 相似文献
6.
Zi-Cai Li 《Numerical Methods for Partial Differential Equations》1989,5(4):279-295
The nonconforming combination of Ritz-Galerkin and finite difference methods is presented for solving elliptic boundary value problems with singularities. The Ritz-Galerkin method is used in the subdomains including singularities, the finite difference method is used in the rest of the solution domain. Moreover, on the common boundary of two regions where two different methods are used, the continuity conditions are constrained only on the nodes of difference grids. Theoretical analysis and numerical experiments have shown that average errors of numerical solutions and their generalized derivatives can reach the convergence rate O(h2-δ), where h is the mesh spacing of uniform difference grids, and δ is an arbitrarily small, positive number. This convergence rate is better than O(h), obtained by the nonconforming combination of the Ritz-Galerkin and finite element methods. 相似文献
7.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
M. Heusler 《General Relativity and Gravitation》1991,23(2):189-207
The field equations for homogeneous models in an arbitrary number of dimensions form a Hamiltonian system with constraint forces. Due to the monotonic behavior of the determinant of the induced metric, the evolution of the system can be interpreted as the motion of a particle in an explicitly time-dependent potential. Considering vacuum models, we show that this explicit time-dependence can be eliminated. Using the scaling properties of the Ricci tensor we obtain an autonomous system, for which we can also find a Liapunov function in terms of the n-dimensional Ricci curvature. 相似文献
9.
M. Rovinsky 《Selecta Mathematica, New Series》2006,11(3-4):491-522
10.
A detailed analysis is made within perturbative QCD of the decays into gluon jets of P-wave and S-wave quarkonia (JPC = 0++, 1++, 2++, 1+? and 0?+, 1??). For all those states we compute to leading non-trivial order in αs the conventional fraction f(?, δ) of the jet-like hadronic final states, characterized by the back-to-back cone of half angle δ, in which all but a small fraction ? of the total energy is emitted. To the same order we give also the average values of thrust momenta and spherocity distributions. 相似文献