全文获取类型
收费全文 | 247653篇 |
免费 | 3852篇 |
国内免费 | 2097篇 |
专业分类
化学 | 133471篇 |
晶体学 | 3136篇 |
力学 | 10279篇 |
综合类 | 15篇 |
数学 | 29446篇 |
物理学 | 77255篇 |
出版年
2021年 | 2479篇 |
2020年 | 2561篇 |
2019年 | 2792篇 |
2018年 | 3567篇 |
2017年 | 3440篇 |
2016年 | 5420篇 |
2015年 | 3631篇 |
2014年 | 5053篇 |
2013年 | 12187篇 |
2012年 | 10470篇 |
2011年 | 12285篇 |
2010年 | 8097篇 |
2009年 | 8041篇 |
2008年 | 10752篇 |
2007年 | 10850篇 |
2006年 | 10105篇 |
2005年 | 9210篇 |
2004年 | 8741篇 |
2003年 | 7347篇 |
2002年 | 7113篇 |
2001年 | 7354篇 |
2000年 | 5694篇 |
1999年 | 4410篇 |
1998年 | 3553篇 |
1997年 | 3472篇 |
1996年 | 3326篇 |
1995年 | 2997篇 |
1994年 | 2813篇 |
1993年 | 2672篇 |
1992年 | 2976篇 |
1991年 | 2843篇 |
1990年 | 2755篇 |
1989年 | 2519篇 |
1988年 | 2573篇 |
1987年 | 2569篇 |
1986年 | 2399篇 |
1985年 | 3210篇 |
1984年 | 3424篇 |
1983年 | 2776篇 |
1982年 | 2945篇 |
1981年 | 2887篇 |
1980年 | 2728篇 |
1979年 | 2821篇 |
1978年 | 2904篇 |
1977年 | 2910篇 |
1976年 | 2960篇 |
1975年 | 2751篇 |
1974年 | 2715篇 |
1973年 | 2847篇 |
1972年 | 1795篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
981.
We study the structure of the most common type of Riemannian submersions, namely those whose fibers are given by the orbits
of an isometric group action on a Riemannian manifold. Special emphasis is given to the case where the ambient space has nonnegative
curvature.
The first author was supported by research grant MTM2004-04794-MEC. Most of this work was done during a visit of the second
author to Madrid, financed in part by funds of the aforementioned grant. 相似文献
982.
983.
E. D. Aluker A. G. Krechetov A. Yu. Mitrofanov A. S. Pashpekin 《Russian Journal of Physical Chemistry B, Focus on Physics》2007,1(6):570-572
A new method for studying the kinetics of the expansion of explosion products based on measuring the time elapsed from explosion initiation to the short-circuiting of the discharge gap by the products was proposed. It was revealed that, at the initial stage of expansion of the silver azide explosion products, they move with uniform acceleration, a behavior suggestive that, during this period, the exothermic reaction 2N3 → 3N2 occurs. 相似文献
984.
在(NH4)3VS4/CuI/Py反应体系中合成了新化合物 [VS4Cu6(Py)8I3]并测定其晶体结构。该化合物(C40H40N8Cu6I3S4V)属正交晶系, 空间群为Fdd2, 晶胞参数为: a = 29.924(6), b = 13.475(3), c = 25.853(5) , V = 10425(4) ?, Dc = 2.006 g/cm3, Mr = 1573.92, Z = 8, (MoK) = 4.546 mm-1, F(000) = 6048。结构由直接法解出, 用全矩阵最小二乘法修正, 最终偏离因子R = 0.023, wR = 0.069。簇合物分子是由6个带端基配体的Cu沿着四面体单元VS4的6条SS边配位而成, 6个Cu排列成了1个八面体, V基本位于八面体的中心, 整个分子具有C2对称性。 相似文献
985.
986.
D. A. Davydov S. Z. Nazarova A. A. Valeeva A. A. Rempel 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(5):677-680
The order-disorder phase transition in vanadium monoxide of substoichiometric compositions VOy has been studied for the first time in situ by the Faraday method with a pendulum magnetic balance of the Domenically type. A minimum is found on the temperature dependence of the magnetic susceptibility of vanadium monoxide of different compositions at a temperature of about 700 K. X-ray diffraction analysis performed before and after measuring the magnetic susceptibility confirmed the change in the structure of vanadium monoxide and the possibility of atom-vacancy processes upon cooling and heating of the samples. 相似文献
987.
Márcio D. Lima Mônica J. de Andrade Viera Skákalová Felipe Nobre Carlos P. Bergmann Siegmar Roth 《固体物理学:研究快报》2007,1(4):165-167
A method for the production of transparent carbon nanotube networks (CNTNs) over transparent substrates was developed. In this method, CNTNs were grown directly in the target surface by applying the catalyst in specific zones of the substrate through lithographic techniques. The networks can be also transferred from the original substrate to other surfaces. The newly grown carbon nanotubes have a very high aspect ratio (>50000). Thus far, networks with an optical transmittance of 94% at 550 nm and a surface resistivity of 3.6 kΩ/sq have been produced. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
988.
P. Thomsen-Schmidt K. Hasche G. Ulm K. Herrmann M. Krumrey G. Ade J. Stümpel I. Busch S. Schädlich A. Schindler W. Frank D. Hirsch M. Procop U. Beck 《Applied Physics A: Materials Science & Processing》2004,78(5):645-649
High-accuracy film thickness measurements in the range below 100 nm can be made by various complex methods like spectral ellipsometry (SE), scanning force microscopy (SFM), grazing incidence X-ray reflectometry (GIXR), or X-ray fluorescence analysis (XRF). The measurement results achieved with these methods are based on different interactions between the film and the probe. A key question in nanotechnology is how to achieve consistent results on a level of uncertainty below one nanometre with different techniques.Two different types of thickness standards are realised. Metal film standards for X-ray techniques in the thickness range 10 to 50 nm are calibrated by GIXR with monochromatised synchrotron radiation of 8048 eV. The results obtained at four different facilities show excellent agreement. SiO2 on Si standards for SE and SFM in the thickness range 6 to 1000 nm are calibrated by GIXR with monochromatised synchrotron radiation of 1841 eV and with a metrological SFM. Consistent results within the combined uncertainties are obtained with the two methods. Surfaces and interfaces of both types of standards are additionally investigated by transmission electron microscopy (TEM). PACS 61.10.Kw; 68.55.Jk; 06.20.Fn; 06.60.Mr; 07.79.Lh 相似文献
989.
Manufacturing cell formation using similarity coefficients and a parallel genetic TSP algorithm: Formulation and comparison 总被引:2,自引:0,他引:2
J. BalakrishnanP. D. Jog 《Mathematical and Computer Modelling》1995,21(12):61-73
Many algorithms have been proposed to form manufacturing cells from component routings. However, many of these do not have the capability of solving large problems. We propose a procedure using similarity coefficients and a parallel genetic implementation of a TSP algorithm that is capable of solving large problems of up to 1000 parts and 1000 machines. In addition, we also compare our procedure with many existing procedures using nine well-known problems from the literature.
The results show that the proposed procedure compares well with the existing procedures and should be useful to practitioners and researchers. 相似文献
990.
This note outlines an algorithm for solving the complex ‘matrix Procrustes problem’. This is a least‐squares approximation over the cone of positive semi‐definite Hermitian matrices, which has a number of applications in the areas of Optimization, Signal Processing and Control. The work generalizes the method of Allwright (SIAM J. Control Optim. 1988; 26 (3):537–556), who obtained a numerical solution to the real‐valued version of the problem. It is shown that, subject to an appropriate rank assumption, the complex problem can be formulated in a real setting using a matrix‐dilation technique, for which the method of Allwright is applicable. However, this transformation results in an over‐parametrization of the problem and, therefore, convergence to the optimal solution is slow. Here, an alternative algorithm is developed for solving the complex problem, which exploits fully the special structure of the dilated matrix. The advantages of the modified algorithm are demonstrated via a numerical example. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献