全文获取类型
收费全文 | 7885篇 |
免费 | 570篇 |
国内免费 | 824篇 |
专业分类
化学 | 1576篇 |
晶体学 | 33篇 |
力学 | 979篇 |
综合类 | 89篇 |
数学 | 4290篇 |
物理学 | 2312篇 |
出版年
2024年 | 13篇 |
2023年 | 118篇 |
2022年 | 171篇 |
2021年 | 167篇 |
2020年 | 242篇 |
2019年 | 220篇 |
2018年 | 205篇 |
2017年 | 245篇 |
2016年 | 244篇 |
2015年 | 214篇 |
2014年 | 319篇 |
2013年 | 556篇 |
2012年 | 348篇 |
2011年 | 471篇 |
2010年 | 400篇 |
2009年 | 583篇 |
2008年 | 506篇 |
2007年 | 557篇 |
2006年 | 529篇 |
2005年 | 418篇 |
2004年 | 354篇 |
2003年 | 351篇 |
2002年 | 260篇 |
2001年 | 231篇 |
2000年 | 228篇 |
1999年 | 198篇 |
1998年 | 237篇 |
1997年 | 180篇 |
1996年 | 157篇 |
1995年 | 85篇 |
1994年 | 63篇 |
1993年 | 45篇 |
1992年 | 56篇 |
1991年 | 45篇 |
1990年 | 30篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有9279条查询结果,搜索用时 31 毫秒
1.
《Mendeleev Communications》2022,32(4):534-536
Correlation times and diffusion coefficients of water molecules were measured for the first time by 1H spin relaxation and pulsed field gradient NMR in Li+, Na+ and Cs+ ionic forms of Nafion 117 membrane. Hydration numbers of Li+, Na+ and Cs+ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules. 相似文献
2.
3.
An efficient edge based data structure has been developed in order to implement an unstructured vertex based finite volume algorithm for the Reynolds-averaged Navier–Stokes equations on hybrid meshes. In the present approach, the data structure is tailored to meet the requirements of the vertex based algorithm by considering data access patterns and cache efficiency. The required data are packed and allocated in a way that they are close to each other in the physical memory. Therefore, the proposed data structure increases cache performance and improves computation time. As a result, the explicit flow solver indicates a significant speed up compared to other open-source solvers in terms of CPU time. A fully implicit version has also been implemented based on the PETSc library in order to improve the robustness of the algorithm. The resulting algebraic equations due to the compressible Navier–Stokes and the one equation Spalart–Allmaras turbulence equations are solved in a monolithic manner using the restricted additive Schwarz preconditioner combined with the FGMRES Krylov subspace algorithm. In order to further improve the computational accuracy, the multiscale metric based anisotropic mesh refinement library PyAMG is used for mesh adaptation. The numerical algorithm is validated for the classical benchmark problems such as the transonic turbulent flow around a supercritical RAE2822 airfoil and DLR-F6 wing-body-nacelle-pylon configuration. The efficiency of the data structure is demonstrated by achieving up to an order of magnitude speed up in CPU times. 相似文献
4.
5.
G. Peruginelli 《代数通讯》2018,46(11):4724-4738
We classify the maximal subrings of the ring of n×n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring. 相似文献
6.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
7.
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
8.
9.
10.