全文获取类型
收费全文 | 17040篇 |
免费 | 2386篇 |
国内免费 | 1172篇 |
专业分类
化学 | 7502篇 |
晶体学 | 169篇 |
力学 | 721篇 |
综合类 | 72篇 |
数学 | 2443篇 |
物理学 | 9691篇 |
出版年
2024年 | 52篇 |
2023年 | 162篇 |
2022年 | 546篇 |
2021年 | 593篇 |
2020年 | 652篇 |
2019年 | 632篇 |
2018年 | 560篇 |
2017年 | 698篇 |
2016年 | 788篇 |
2015年 | 716篇 |
2014年 | 1150篇 |
2013年 | 1680篇 |
2012年 | 1032篇 |
2011年 | 1079篇 |
2010年 | 834篇 |
2009年 | 987篇 |
2008年 | 1013篇 |
2007年 | 1062篇 |
2006年 | 823篇 |
2005年 | 680篇 |
2004年 | 630篇 |
2003年 | 524篇 |
2002年 | 456篇 |
2001年 | 416篇 |
2000年 | 383篇 |
1999年 | 340篇 |
1998年 | 288篇 |
1997年 | 291篇 |
1996年 | 191篇 |
1995年 | 180篇 |
1994年 | 163篇 |
1993年 | 133篇 |
1992年 | 120篇 |
1991年 | 104篇 |
1990年 | 71篇 |
1989年 | 57篇 |
1988年 | 107篇 |
1987年 | 64篇 |
1986年 | 41篇 |
1985年 | 64篇 |
1984年 | 50篇 |
1983年 | 24篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1973年 | 11篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The paper deals with a singularly perturbed reaction diffusionmodel problem. The focus is on reliable a posteriori error estimatorsfor the H1 seminorm that can be applied to anisotropic finiteelement meshes. A residual error estimator and a local problemerror estimator are proposed and rigorously analysed. They arelocally equivalent, and both bound the error reliably. Threemodifications of these estimators are introduced and discussed. Much attention is given to the performance of the error estimatorin numerical experiments. This helps to identify those estimatorsthat are suitable for practical applications. 相似文献
72.
73.
Taking both the heterogeneous catalytic processes, including the surface formation of particles with excited internal degrees of freedom, and the processes of multicomponent diffusion and heat transfer in the MESOX apparatus fully into account makes it possible to obtain a recombination coefficient and an accommodation coefficient of the oxygen-atoms-on-quartz recombination energy which are in good agreement with the experimental data. The heterogeneous catalysis model constructed can be used effectively for predicting the heat fluxes to the surface of reentry vehicles on their entry into the Earth’s atmosphere. 相似文献
74.
年龄相关的种群扩散系统的最优分布控制 总被引:5,自引:1,他引:4
本文讨论年龄相关的种群扩散系统的最优分布控制 ,证明了最优分布控制的存在性 ,得到了分布控制为最优的充分必要条件及确定最优控制的最优性组 . 相似文献
75.
Michaël Lejeune Andrea Valsesia Martin Kormunda Pascal Colpo François Rossi 《Surface science》2005,583(1):L142
In this work, chemically and topographically nanopatterned surfaces were produced by a top-down processing approach for biosensing devices. The nanopatterning was the result of the combination of plasma polymerisation (pp) of biofunctional materials and colloidal lithography techniques. The morphological and chemical properties induced by the plasma deposition-etching treatment were characterised by optical method combining ellipsometry and Fourier Transform Infrared spectroscopy studies. This method supported by atomic force microscopy measurements, allowed the full optical characterization of each step of the top-down process. The optical characterization of the end-up nanopatterned samples demonstrated that the chosen process is able to produce well-defined nanostructured surfaces with controlled chemical and morphological properties. 相似文献
76.
第二讲合成孔径声纳成像及其研究进展 总被引:1,自引:0,他引:1
文章在介绍了图像声纳的特点、合成孔径声纳(synthetic aperture sonar,SAS)产生背景和发展过程的基础上,对合成孔径声纳的原理、技术难点、成像算法等问题进行了讨论.着重分析了合成孔径声纳成像过程中高分辨率的获取方法、水声信道对成像的影响、多子阵技术及其成像算法、稳定的声纳运动平台和运动监测问题、运动补偿与自聚焦方法等.文章还给出了国内外合成孔径声纳研究的最新进展情况,进而展望了合成孔径声纳的应用前景. 相似文献
77.
L.A. Bakaleynikov E.Yu. Flegontova E. Zolotoyabko 《Journal of Electron Spectroscopy and Related Phenomena》2006
Capabilities of the imaging techniques, in which X-rays are converted to electrons and then the emitted electrons are registered by means of an electron microscope, are analyzed, the focus being on the factors limiting lateral resolution at the stage of electron emission. Bearing in mind the tendency to use harder synchrotron X-rays for some combined X-ray-electron microscopy methods, calculations were made for two significantly different X-ray energies: E = 1.828 keV (K-edge of Si) and E = 11.923 keV (L3-edge of Au). By using Monte Carlo simulations of the electron trajectories beneath the surface of the sample we show that the radius of the spot from which photoelectrons are emitted could be as small as 1 nm. However, when proper account is taken of an entire electron cascade associated with the re-building of electron shells after photoelectron emission, spots more than one order of magnitude larger result, limiting the best lateral resolution to 20–30 nm. 相似文献
78.
THE LARGE TIME BEHAVIOR OF SPECTRAL APPROXIMATION FOR A CLASS OF PSEUDOPARABOLIC VISCOUS DIFFUSION EQUATION 总被引:1,自引:0,他引:1
尚亚东 《数学物理学报(B辑英文版)》2007,27(1):153-168
The asymptotic behavior of the solutions to a class of pseudoparabolic viscous diffusion equation with periodic initial condition is studied by using the spectral method. The semidiscrete Fourier approximate solution of the problem is constructed and the error estiation between spectral approximate solution and exact solution on large time is also obtained. The existence of the approximate attractor AN and the upper semicontinuity d(AN,A)→0 are proved. 相似文献
79.
The ability to quantitatively map the distribution of elements on the micrometer scale and smaller with high sensitivity and isotopic discrimination is unique to ion microscopy. The information contained in ion images can be crucial to the study of the solid state, where chemical heterogeneity is often directly related to observed behavior. The tools of digital image processing allow the extraction of quantitative information from the image data. These techniques coupled with improved instrumentation for the detection of ion images drastically increase the problem solving capabilities of the ion microscope. The use of such methods and instrumentation in the ion microscopic analyses of cell cultures and tissues of biological and biomedical relevance will be discussed. 相似文献
80.
在局部区域上的奇摄动反应扩散方程初始边值问题 总被引:2,自引:2,他引:0
本文是讨论一类在局部区域上的奇摄动反应扩散初始边值问题.利用算子理论和 不动点原理,得到了相应问题解的存在性和唯一性. 相似文献