全文获取类型
收费全文 | 11322篇 |
免费 | 313篇 |
国内免费 | 15篇 |
专业分类
化学 | 6682篇 |
晶体学 | 132篇 |
力学 | 215篇 |
数学 | 1914篇 |
物理学 | 2707篇 |
出版年
2022年 | 77篇 |
2021年 | 165篇 |
2020年 | 210篇 |
2019年 | 215篇 |
2018年 | 273篇 |
2017年 | 288篇 |
2016年 | 407篇 |
2015年 | 353篇 |
2014年 | 390篇 |
2013年 | 841篇 |
2012年 | 598篇 |
2011年 | 689篇 |
2010年 | 540篇 |
2009年 | 451篇 |
2008年 | 572篇 |
2007年 | 473篇 |
2006年 | 421篇 |
2005年 | 319篇 |
2004年 | 314篇 |
2003年 | 238篇 |
2002年 | 257篇 |
2001年 | 169篇 |
2000年 | 171篇 |
1999年 | 169篇 |
1998年 | 126篇 |
1997年 | 106篇 |
1996年 | 142篇 |
1995年 | 101篇 |
1994年 | 115篇 |
1993年 | 100篇 |
1992年 | 97篇 |
1991年 | 83篇 |
1990年 | 101篇 |
1989年 | 67篇 |
1988年 | 64篇 |
1987年 | 56篇 |
1985年 | 90篇 |
1984年 | 84篇 |
1983年 | 79篇 |
1982年 | 84篇 |
1981年 | 73篇 |
1980年 | 68篇 |
1979年 | 72篇 |
1978年 | 75篇 |
1977年 | 80篇 |
1976年 | 94篇 |
1975年 | 76篇 |
1974年 | 62篇 |
1973年 | 61篇 |
1972年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
3.
4.
Lubomír Havlk Jan Fbry Margarida Henriques Michal Duek 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(7):623-630
The title structures of KScS2 (potassium scandium sulfide), RbScS2 (rubidium scandium sulfide) and KLnS2 [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS2, RbScS2 and KTbS2) or redetermined. All of them belong to the α‐NaFeO2 structure type in agreement with the ratio of the ionic radii r3+/r+. KScS2, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S2−) and the bond‐valence sums. 相似文献
5.
6.
7.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
8.
Cairns Grant; McIntyre Margaret; Ozdemir Mehmet 《Bulletin London Mathematical Society》1993,25(2):169-176
We prove that the number of vertices of a smooth normal planarcurve is at least 6, if it bounds a surface other than the disk. 相似文献
9.
10.
The presence of copper atoms as continuous networks at the grain boundaries of an aluminium-copper alloy has been considered not preventing the moving of dislocations during creep (or at least partially). The dislocations can bs absorbed by these boundaries and penetrate through them. That leads to changés of shape and structure of grains and also to the sliding of grains against each other. This was deduced from the accelerating increase in the sensitivity of the steady state creep rate to the applied stress of an aluminium 2·8 wt% copper alloy examined at wide range of temperatures (50–350 °C) and applied stresses (7–170 MPa). This rapid increase in the sensitivity parameter of the steady state creep rate occurs in Al-Cu alloys at quite higher ranges of applied stresses and may be attributed mainly to the contribution of the grain boundary movements to the creep strain. 相似文献