全文获取类型
收费全文 | 20328篇 |
免费 | 2494篇 |
国内免费 | 1516篇 |
专业分类
化学 | 6485篇 |
晶体学 | 101篇 |
力学 | 4252篇 |
综合类 | 232篇 |
数学 | 10256篇 |
物理学 | 3012篇 |
出版年
2024年 | 10篇 |
2023年 | 170篇 |
2022年 | 254篇 |
2021年 | 410篇 |
2020年 | 620篇 |
2019年 | 544篇 |
2018年 | 519篇 |
2017年 | 618篇 |
2016年 | 837篇 |
2015年 | 671篇 |
2014年 | 1007篇 |
2013年 | 1747篇 |
2012年 | 1167篇 |
2011年 | 1243篇 |
2010年 | 1077篇 |
2009年 | 1248篇 |
2008年 | 1247篇 |
2007年 | 1292篇 |
2006年 | 1105篇 |
2005年 | 1051篇 |
2004年 | 875篇 |
2003年 | 892篇 |
2002年 | 768篇 |
2001年 | 693篇 |
2000年 | 608篇 |
1999年 | 577篇 |
1998年 | 501篇 |
1997年 | 466篇 |
1996年 | 291篇 |
1995年 | 297篇 |
1994年 | 248篇 |
1993年 | 187篇 |
1992年 | 203篇 |
1991年 | 172篇 |
1990年 | 105篇 |
1989年 | 85篇 |
1988年 | 66篇 |
1987年 | 64篇 |
1986年 | 57篇 |
1985年 | 76篇 |
1984年 | 50篇 |
1983年 | 43篇 |
1982年 | 38篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 29篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1975年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
1.
2.
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
3.
4.
5.
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
6.
The indentation technique is widely used in measuring the mechanical properties of soft matter at the microscale or nanoscale,but still faces challenges by these unique properties as well as the consequent strong surface adhesion, including the strong nonlinear effect, unclear judgment of the contact point, difficulties in estimating the contact area, and the risk of the indenter piercing the sample. Here we propose a two-step method to solve these problems: lay a hard film on a soft matter, and obtain the viscoelastic properties of this soft matter through the indentation response of this composite structure. We first establish a theoretical indentation model of the hard film-soft substrate system based on the theory of plates, elastic-viscoelastic correspondence principle and Boltzmann superposition principle. To verify the correctness of this method, we measure the mechanical properties of the methyl vinyl silicone rubber(MVSR) covered by a Cu nanofilm. Finally, we test the effectiveness and error sensitivity of this method with the finite element method(FEM). The results show that our method can accurately measure the mechanical properties of soft matter, while effectively circumventing the problems of the traditional indentation technique. 相似文献
7.
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
8.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated. 相似文献
9.
miRNA (miR)-155 is a potential biomarker for breast cancers. We aimed at developing a nanosensor for miR-155 detection by integrating hybridization chain reaction (HCR) and silver nanoclusters (AgNCs). HCR serves as an enzyme-free and isothermal amplification method, whereas AgNCs provide a built-in fluorogenic detection probe that could simplify the downstream analysis. The two components were integrated by adding a nucleation sequence of AgNCs to the hairpin of HCR. The working principle was based on the influence of microenvironment towards the hosted AgNCs, whereby unfolding of hairpin upon HCR has manipulated the distance between the hosted AgNCs and cytosine-rich toehold region of hairpin. As such, the dominant emission of AgNCs changed from red to yellow in the absence and presence of miR-155, enabling a ratiometric measurement of miR with high sensitivity. The limit of detection (LOD) of our HCR-AgNCs nanosensor is 1.13 fM in buffered solution. We have also tested the assay in diluted serum samples, with comparable LOD of 1.58 fM obtained. This shows the great promise of our HCR-AgNCs nanosensor for clinical application. 相似文献
10.
Hui Li Jian Liu Juan Zhao Huiting He Dr. Dabo Jiang Prof. Steven Robert Kirk Prof. Qiong Xu Dr. Xianxiang Liu Prof. Dulin Yin 《ChemistryOpen》2021,10(4):477-485
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss. 相似文献