全文获取类型
收费全文 | 4543篇 |
免费 | 114篇 |
国内免费 | 40篇 |
专业分类
化学 | 3029篇 |
晶体学 | 68篇 |
力学 | 85篇 |
数学 | 743篇 |
物理学 | 772篇 |
出版年
2021年 | 42篇 |
2020年 | 44篇 |
2019年 | 50篇 |
2018年 | 46篇 |
2017年 | 37篇 |
2016年 | 81篇 |
2015年 | 102篇 |
2014年 | 103篇 |
2013年 | 238篇 |
2012年 | 199篇 |
2011年 | 256篇 |
2010年 | 123篇 |
2009年 | 108篇 |
2008年 | 211篇 |
2007年 | 225篇 |
2006年 | 207篇 |
2005年 | 222篇 |
2004年 | 211篇 |
2003年 | 185篇 |
2002年 | 130篇 |
2001年 | 47篇 |
2000年 | 58篇 |
1999年 | 56篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 72篇 |
1995年 | 38篇 |
1994年 | 67篇 |
1993年 | 65篇 |
1992年 | 50篇 |
1991年 | 52篇 |
1990年 | 40篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 50篇 |
1986年 | 45篇 |
1985年 | 71篇 |
1984年 | 71篇 |
1983年 | 47篇 |
1982年 | 57篇 |
1981年 | 57篇 |
1980年 | 45篇 |
1979年 | 71篇 |
1978年 | 63篇 |
1977年 | 71篇 |
1976年 | 48篇 |
1975年 | 54篇 |
1974年 | 49篇 |
1973年 | 40篇 |
1972年 | 41篇 |
排序方式: 共有4697条查询结果,搜索用时 15 毫秒
21.
Xia Yin Weiguang Zhang Qijiao Zhang Jun Fan Chian Sing Lai Edward R. T. Tiekink 《应用有机金属化学》2004,18(3):139-140
The centrosymmetric structure of {Cd[S2CN(CH2Ph)2]2}2 features both bridging and chelating dithiocarbamate ligands so that a square pyramidal S5 coordination geometry results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
22.
Edward Givelberg 《纯数学与应用数学通讯》2004,57(3):283-309
We describe a numerical method to simulate an elastic shell immersed in a viscous incompressible fluid. The method is developed as an extension of the immersed boundary method using shell equations based on the Kirchhoff‐Love and the planar stress hypotheses. A detailed derivation of the shell equations used in the numerical method is presented. This derivation, as well as the numerical method, uses techniques of differential geometry. Our main motivation for developing this method is its use in constructing a comprehensive, three‐dimensional computational model of the cochlea (the inner ear). The central object of study within the cochlea is the basilar membrane, which is immersed in fluid and whose elastic properties rather resemble those of a shell. We apply the method to a specific example, which is a prototype of a piece of the basilar membrane, and study the convergence of the method in this case. Some typical features of cochlear mechanics are already captured in this simple model. In particular, numerical experiments have shown a traveling wave propagating from the base to the apex of the model shell in response to external excitation in the fluid. © 2004 Wiley Periodicals, Inc. 相似文献
23.
Edward S. Fry 《量子光学学报》2006,12(B08):66-67
Since the data show that Bell inequalities are violated experimentally, we must conclude that any hidden variable theory (which correctly predicts experimental data ) will be non-local. But, to conclude that the experimental violations of Bell inequalities show quantum mechanics to be non-local is unjustified. Specifically, the key assumptions required to obtain a Bell inequality are ( 1 ) locality and (2) the assignment of meaningful ( non- negative) probabilities to seemingly physical correlations (Bell expresses these correlations via " hidden variables" ). Since the Bell inequality is violated by experiment, at least one of these assumptions is wrong. The widespread conclusion that locality must be relinquished is valid only if we retain the previously mentioned correlations ( "hidden variables" ). We will demonstrate that the latter are not physical observables - they are not elements of physical reality. 相似文献
24.
25.
Sangcheol Kim Frdric S. Diana Pierre M. Petroff Edward J. Kramer Takeshi Ootsu Tomohide Murase 《Journal of Polymer Science.Polymer Physics》2006,44(22):3227-3233
The encapsulation of the nanocrystalline manganese‐doped zinc sulfide (ZnS:Mn) in poly(styrene‐b‐2vinylpyridine) (PS‐PVP) diblock copolymers is reported. Below the critical micelle concentration in the absence of nanocrystals (NCs), inverse micelles of PS‐PVP were induced by adding ZnS:Mn NCs, the presence of which was confirmed by scanning force microscope and dynamic light scattering. In toluene, a PS‐selective solvent, the less‐soluble PVP blocks preferentially surround the ligand‐coated ZnS:Mn NCs. For PS‐PVP encapsulated ZnS:Mn NCs, the ratio of blue emission to orange emission of ZnS:Mn NCs is dependent on both the concentration of PS‐PVP and the solvent quality. The pyridine of PVP blocks form complexes with the Zn atoms via the nitrogen lone pair and thus the sulfur vacancies are passivated. As a result, the defect‐related blue emission is selectively quenched even when the micelles are not formed. As the concentration of PS‐PVP encapsulating the ZnS:Mn NCs increases, the intensity of blue emission decreases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3227–3233, 2006 相似文献
26.
There are over 100 accreting neutron stars in our galaxy, in which matter (typically H/He) is tidally transferred from a secondary companion to the neutron star. Accretion of this matter perturbs the thermal structure of the interior away from that of an isolated cooling neutron star. In this paper. we review how this accretion induces reactions in the crust of the neutron star that keep the interior hot. If the accretion is intermittent, then the heated surface layers are directly observable when accretion stops. This heating also affects the unstable ignition of light elements in the neutron star envelope. Observations of the neutron star cooling following an accretion outburst can in principle constrain the thermal properties of the crust and core. 相似文献
27.
The performance of high power transistor devices is intimately connected to the substrate thermal conductivity. In this study, the relationship between thermal conductivity and dislocation density is examined using the 3 omega technique and free standing HVPE GaN substrates. Dislocation density is measured using imaging cathodoluminescence. In a low dislocation density regime below 105 cm−2, the thermal conductivity appears to plateau out near 230 W/K m and can be altered by the presence of isotopic defects and point defects. For high dislocation densities the thermal conductivity is severely degraded due to phonon scattering from dislocations. These results are applied to the design of homoepitaxially and heteroepitaxially grown HEMT devices and the efficiency of heat extraction and the influence of lateral heat spreading on device performance are compared. 相似文献
28.
We show that three dimensional Chern-Simons gauge theories with a compact gauge groupG (not necessarily connected or simply connected) can be classified by the integer cohomology groupH
4(BG,Z). In a similar way, possible Wess-Zumino interactions of such a groupG are classified byH
3(G,Z). The relation between three dimensional Chern-Simons gauge theory and two dimensional sigma models involves a certain natural map fromH
4(BG,Z) toH
3(G,Z). We generalize this correspondence to topological spin theories, which are defined on three manifolds with spin structure, and are related to what might be calledZ
2 graded chiral algebras (or chiral superalgebras) in two dimensions. Finally we discuss in some detail the formulation of these topological gauge theories for the special case of a finite group, establishing links with two dimensional (holomorphic) orbifold models. 相似文献
29.
Edward R. T. Tiekink Tomas Kurucsev Bernard F. Hoskins 《Journal of chemical crystallography》1989,19(5):823-839
The preparation, characterization, and X-ray structure analysis of (adeninatoN9)triethylphosphinegold(I) is reported. The crystal structure consists of discrete molecules, the adeninate anion coordinates via the N(9) atom with a Au-N(9) bond distance of 2.057(5) Å and the linear geometry about the Au atom is completed by the P atom of a disordered Et3P ligand; the Au-P(1) bond distance is 2.238(2) Å and the N(9)-Au-P(1) bond angle is 178.8(2)°. The crystals are orthorhombic, space groupPbca, with unit cell dimensionsa=8.528(1),b=17.797(3),c=18.526(2) Å andZ=8. The structure was refined by a full-matrix least-squares procedure to finalR=0.030 andR
w
=0.033 for 1749 reflections withI>2.5a(I). The electronic spectrum of the complex dissolved in water in the near ultraviolet is consistent with essentially separate -electron systems of the adenine and phosphinegold moieties; a conclusion which corroborates the X-ray structural results. 相似文献
30.