全文获取类型
收费全文 | 11496篇 |
免费 | 1784篇 |
国内免费 | 1704篇 |
专业分类
化学 | 5269篇 |
晶体学 | 84篇 |
力学 | 1983篇 |
综合类 | 10篇 |
数学 | 2067篇 |
物理学 | 5571篇 |
出版年
2024年 | 17篇 |
2023年 | 356篇 |
2022年 | 253篇 |
2021年 | 314篇 |
2020年 | 375篇 |
2019年 | 243篇 |
2018年 | 331篇 |
2017年 | 410篇 |
2016年 | 411篇 |
2015年 | 511篇 |
2014年 | 704篇 |
2013年 | 804篇 |
2012年 | 945篇 |
2011年 | 929篇 |
2010年 | 841篇 |
2009年 | 855篇 |
2008年 | 775篇 |
2007年 | 826篇 |
2006年 | 890篇 |
2005年 | 645篇 |
2004年 | 474篇 |
2003年 | 451篇 |
2002年 | 404篇 |
2001年 | 405篇 |
2000年 | 264篇 |
1999年 | 316篇 |
1998年 | 185篇 |
1997年 | 180篇 |
1996年 | 106篇 |
1995年 | 112篇 |
1994年 | 87篇 |
1993年 | 98篇 |
1992年 | 82篇 |
1991年 | 79篇 |
1990年 | 74篇 |
1989年 | 62篇 |
1988年 | 46篇 |
1987年 | 20篇 |
1986年 | 27篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1971年 | 6篇 |
1957年 | 4篇 |
1945年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
A multicompartment electrolyzer, which has been used for preparative electrophoresis [Z. Liu, Z. Huang, J.-Y. Cong, et al., Sep. Sci. Technol. 31 (1996) 427], is applied for carrying out affinity chromatography in an alternating electric field. The effect of electric field strength on the adsorption and desorption characteristics is experimentally examined with human serum albumin and Blue Sepharose Fast Flow as a model system. It is shown that the existence of an electric field leads to a significant change in the adsorption capacity of the blue dye, which may be used for establishing a preferential adsorption to achieve a high resolution. The adsorption speed increases slightly with respect to the increase of electric field strength, while adsorption capacity in the presence of an electric field is independent of the electric field strength. Different elution behavior is observed as function of adsorption condition and a high recovery of the adsorbed protein is obtained when the adsorption is carried out in the presence of an electric field. 相似文献
992.
The global-in-time existence of non-negative solutions to a parabolic strongly coupled system with mixed Dirichlet–Neumann boundary conditions is shown. The system describes the time evolution of the electron and hole densities in a semiconductor when electron-hole scattering is taken into account. The parabolic equations are coupled to the Poisson equation for the electrostatic potential. Written in the quasi-Fermi potential variables, the diffusion matrix of the parabolic system contains strong cross-diffusion terms and is only positive semi-definite such that the problem is formally of degenerate type. The existence proof is based on the study of a fully discretized version of the system, using a backward Euler scheme and a Galerkin method, on estimates for the free energy, and careful weak compactness arguments. 相似文献
993.
We investigates the effect of Taylor-Grtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Grtler vortex is detected by longitudinal average of velocity fluctuation in the channel and defined as TG fluctuation. It has been found that turbulent diffusion is significant in the Reynolds stress transportation at the suction side of rotating turbulent channel in contrast with the turbulent channel flow without rotation and Taylor-Grtler vortex plays an important role in the turbulent diffusion in Reynolds stress transport. The paper focuses on the low and moderate rotation number, but the effect of the rotation number on the Reynolds stress transport is also reported. 相似文献
994.
This paper presents a family of High‐order finite volume schemes applicable on unstructured grids. The k‐exact reconstruction is performed on every control volume as the primary reconstruction. On a cell of interest, besides the primary reconstruction, additional candidate reconstruction polynomials are provided by means of very simple and efficient ‘secondary’ reconstructions. The weighted average procedure of the WENO scheme is then applied to the primary and secondary reconstructions to ensure the shock‐capturing capability of the scheme. This procedure combines the simplicity of the k‐exact reconstruction with the robustness of the WENO schemes and represents a systematic and unified way to construct High‐order accurate shock capturing schemes. To further improve the efficiency, an efficient problem‐independent shock detector is introduced. Several test cases are presented to demonstrate the accuracy and non‐oscillation property of the proposed schemes. The results show that the proposed schemes can predict the smooth solutions with uniformly High‐order accuracy and can capture the shock waves and contact discontinuities in high resolution. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
995.
The rapid fabrication of inexpensive, efficient optical fiber end-face mirrors by dipping the fiber into a small-volume drop of a molten, low-melting-point metal alloy is described. The technique uses a small (a couple hundred micrometers thick, about 1 mm wide) drop of molten metal to achieve reliable, repeatable adhesion of the metal to the fiber that is not possible with larger volumes. The resulting mirrors have an average reflectance of 65–75% for wavelengths in the telecommunications range of 1300–1600 nm. The efficient and robust nature of the resulting mirrors is demonstrated with a novel end-of-fiber mirrored long-period fiber grating. 相似文献
996.
现代色谱概念的提出,至今已有100多年的历史。1903年俄国植物学家Tswett在华沙自然科学学会生物学会议上发表了题为“一种新型吸附现象及其在生化分析上的应用”的论文。三年后,他将这种方法命名为色谱法(Chromatography),并于1907年的德国生物学术会议上向人们公开展示了采用色谱法提纯的植物色素溶液以及色谱图。一个世纪以来,伴随着科学技术的不断进步,色谱概念和范畴也发生了很大的变化,出现了目前常用的高效液相色谱、气相色谱、薄层色谱、凝胶渗透色谱、纸色谱、毛细管电泳,以及正在迅速发展的多维色谱和微流控芯片等。色谱的应用领域不断拓宽,在医药卫生、环境健康、食品安全、石油化工、有机合成、新能源开发、乃至空间探索等诸多领域发挥了重要的作用。色谱分析与各种有关的联用技术的出现,如色谱-质谱联用,色谱-荧光分析联用等开辟了复杂混合物分析检测的新天地。 相似文献
997.
This paper deals with the existence of positive solution to a strongly coupled system with homogeneous Dirichlet boundary
conditions describing a Schoener’s competitive interaction of two species. Making use of the Schauder fixed point theorem,
a sufficient condition is given for the system to have a coexistence. And true solutions are constructed based on monotone
iterative method. Our results show that this model possesses at least one coexistence state if cross-diffusions and intra-specific
competitions are weak. 相似文献
998.
999.
We numerically study the surface plasmon interference formed by tightly focused higher polarization order axially symmetric polarized beams (ASPBs) based on the vectorial diffraction theory. The definition of ASPBs is stated, and the optical setup for surface plasmon polariton (SPP) excitation and mathematical expressions for interfering SPP fields are proposed. The simulation results show that the interfering SPP fields present a multi-focal spot pattern. In addition, the number of spots is related to the polarization order of the incident beams P as 2×(P-1), indicating potential utilization in near-field multiple optical trapping and near-field imaging and sensing. The unique interfering phenomenon is also explained. 相似文献
1000.