全文获取类型
收费全文 | 7573篇 |
免费 | 403篇 |
国内免费 | 451篇 |
专业分类
化学 | 1358篇 |
晶体学 | 76篇 |
力学 | 485篇 |
综合类 | 59篇 |
数学 | 4062篇 |
物理学 | 2387篇 |
出版年
2023年 | 45篇 |
2022年 | 105篇 |
2021年 | 86篇 |
2020年 | 101篇 |
2019年 | 118篇 |
2018年 | 92篇 |
2017年 | 121篇 |
2016年 | 109篇 |
2015年 | 109篇 |
2014年 | 168篇 |
2013年 | 506篇 |
2012年 | 236篇 |
2011年 | 333篇 |
2010年 | 356篇 |
2009年 | 816篇 |
2008年 | 811篇 |
2007年 | 671篇 |
2006年 | 628篇 |
2005年 | 378篇 |
2004年 | 273篇 |
2003年 | 303篇 |
2002年 | 298篇 |
2001年 | 251篇 |
2000年 | 203篇 |
1999年 | 203篇 |
1998年 | 214篇 |
1997年 | 142篇 |
1996年 | 107篇 |
1995年 | 79篇 |
1994年 | 92篇 |
1993年 | 47篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 32篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有8427条查询结果,搜索用时 22 毫秒
1.
2.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
4.
5.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
6.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
7.
P. Nithiananthi 《Solid State Communications》2006,137(8):427-430
The binding energies of a hydrogenic donor both in the parabolic and non-parabolic conduction band model within the effective mass approximation have been computed for the low-dimensional semiconducting systems (LDSS) like quantum well, quantum well wire and quantum dot taking GaAs/AlxGa1−xAs systems as an example. It is observed that the effect of non-parabolicity is not effective when the system goes to lower dimensionality. The diamagnetic susceptibility of a hydrogenic donor impurity has also been computed in these LDSS in the infinite barrier model. Since no theoretical or experimental works on the diamagnetic susceptibility of LDSS are available in the literature, as a realistic case the diamagnetic susceptibility has been computed in the finite barrier model (x=0.3) for a quantum well and the results are discussed in the light of semiconductor-metal transition. 相似文献
8.
9.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
10.
Mathematical Notes - 相似文献