全文获取类型
收费全文 | 4661篇 |
免费 | 576篇 |
国内免费 | 517篇 |
专业分类
化学 | 771篇 |
晶体学 | 21篇 |
力学 | 519篇 |
综合类 | 102篇 |
数学 | 3107篇 |
物理学 | 1234篇 |
出版年
2024年 | 8篇 |
2023年 | 48篇 |
2022年 | 66篇 |
2021年 | 82篇 |
2020年 | 110篇 |
2019年 | 123篇 |
2018年 | 107篇 |
2017年 | 157篇 |
2016年 | 158篇 |
2015年 | 139篇 |
2014年 | 237篇 |
2013年 | 387篇 |
2012年 | 252篇 |
2011年 | 277篇 |
2010年 | 215篇 |
2009年 | 286篇 |
2008年 | 310篇 |
2007年 | 317篇 |
2006年 | 295篇 |
2005年 | 274篇 |
2004年 | 213篇 |
2003年 | 224篇 |
2002年 | 243篇 |
2001年 | 182篇 |
2000年 | 157篇 |
1999年 | 145篇 |
1998年 | 134篇 |
1997年 | 127篇 |
1996年 | 103篇 |
1995年 | 61篇 |
1994年 | 50篇 |
1993年 | 34篇 |
1992年 | 42篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 8篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有5754条查询结果,搜索用时 15 毫秒
1.
2.
Mathieu Boiret Anna de Juan Nathalie Gorretta Yves-Michel Ginot Jean-Michel Roger 《Analytica chimica acta》2015
Raman chemical imaging provides chemical and spatial information about pharmaceutical drug product. By using resolution methods on acquired spectra, the objective is to calculate pure spectra and distribution maps of image compounds. With multivariate curve resolution-alternating least squares, constraints are used to improve the performance of the resolution and to decrease the ambiguity linked to the final solution. Non negativity and spatial local rank constraints have been identified as the most powerful constraints to be used. 相似文献
3.
Multivariate curve resolution methods, frequently used in analyzing bilinear data sets, result in ambiguous decomposition in general. Implementing the adequate constraints may lead to reduce the so-called rotational ambiguity drastically, and in the most favorable cases to the unique solution. However, in some special cases, non-negativity constraint as minimal information of the system is a sufficient condition to resolve profiles uniquely. Although, several studies on exploring the uniqueness of the bilinear non-negatively constrained multivariate curve resolution methods have been made in the literature, it has still remained a mysterious question. In 1995, Manne published his profile-based theorems giving the necessary and sufficient conditions of the unique resolution. In this study, a new term, i.e., data-based uniqueness is defined and investigated in details, and a general procedure is suggested for detection of uniquely recovered profile(s) on the basis of data set structure in the abstract space. Close inspection of Borgen plots of these data sets leads to realize the comprehensive information of local rank, and these argumentations furnish a basis for data-based uniqueness theorem. The reported phenomenon and its exploration is a new stage (it can be said fundament) in understanding and describing the bilinear (matrix-type) chemical data in general. 相似文献
4.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
5.
Albo Carlos Cavalheiro 《Applications of Mathematics》2006,51(6):619-628
In the paper we study the equation L
u
= f, where L is a degenerate elliptic operator, with Neumann boundary condition in a bounded open set μ. We prove existence and uniqueness
of solutions in the space H(μ) for the Neumann problem. 相似文献
6.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
7.
8.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
9.
ON THE UNIQUENESS OF THE WEAK SOLUTIONS OF A QUASILINEAR HYPERBOLIC SYSTEM WITH A SINGULAR SOURCE TERM 下载免费PDF全文
This paper is a continuation of the authors'previous paper[1].In this paper the authorsprove,assuming additional conditions on the initial data,some results about the existence anduniqueness of the entropy weak solutions of the Cauchy problem for the singular hyperbolicsystem a_t+(au)_x_2au/x=0,u_t+1/2(a~2+u~2)_x=0,x>0,t≥0. 相似文献
10.