全文获取类型
收费全文 | 8378篇 |
免费 | 411篇 |
国内免费 | 384篇 |
专业分类
化学 | 4425篇 |
晶体学 | 202篇 |
力学 | 173篇 |
综合类 | 38篇 |
数学 | 2520篇 |
物理学 | 1815篇 |
出版年
2023年 | 27篇 |
2022年 | 70篇 |
2021年 | 76篇 |
2020年 | 128篇 |
2019年 | 158篇 |
2018年 | 142篇 |
2017年 | 164篇 |
2016年 | 167篇 |
2015年 | 133篇 |
2014年 | 198篇 |
2013年 | 300篇 |
2012年 | 213篇 |
2011年 | 405篇 |
2010年 | 310篇 |
2009年 | 539篇 |
2008年 | 434篇 |
2007年 | 470篇 |
2006年 | 406篇 |
2005年 | 423篇 |
2004年 | 550篇 |
2003年 | 468篇 |
2002年 | 425篇 |
2001年 | 330篇 |
2000年 | 298篇 |
1999年 | 204篇 |
1998年 | 176篇 |
1997年 | 181篇 |
1996年 | 213篇 |
1995年 | 165篇 |
1994年 | 211篇 |
1993年 | 163篇 |
1992年 | 141篇 |
1991年 | 79篇 |
1990年 | 62篇 |
1989年 | 63篇 |
1988年 | 53篇 |
1987年 | 71篇 |
1986年 | 56篇 |
1985年 | 48篇 |
1984年 | 46篇 |
1983年 | 17篇 |
1982年 | 40篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 68篇 |
1978年 | 52篇 |
1977年 | 53篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有9173条查询结果,搜索用时 390 毫秒
951.
P. Wolf G. Staffelbach A. Roux L. Gicquel T. Poinsot V. Moureau 《Comptes Rendus Mecanique》2009,337(6-7):385-394
Increasingly stringent regulations and the need to tackle rising fuel prices have placed great emphasis on the design of aeronautical gas turbines, which are unfortunately more and more prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. In this article, full annular Large Eddy Simulations (LES) of two helicopter combustors, which differ only on the swirlers' design, are performed. In both computations, LES captures self-established rotating azimuthal modes. However, the two cases exhibit different thermo-acoustic responses and the resulting limit-cycles are different. With the first design, a self-excited strong instability develops, leading to pulsating flames and local flashback. In the second case, the flames are much less affected by the azimuthal mode and remain stable, allowing an acceptable operation. Hence, this study highlights the potential of LES for discriminating injection system designs. To cite this article: P. Wolf et al., C. R. Mecanique 337 (2009). 相似文献
952.
Windows95环境中转速测量和直流电机转速控制方法 总被引:1,自引:1,他引:0
介绍在Windows95环境中用Visual Basic5.0编写转速测量和直流电机转速控制方法的过程。 相似文献
953.
Within the collective coordinate approach to chiral soliton models we suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave-functions while the charge operators maintain a symmetric structure. Sizable symmetry breaking in the wave-functions is required to reproduce the observed spacing in the spectrum of the
baryons. The matrix elements of the flavor symmetric charge operators nevertheless yield gA/gV ratios for hyperon beta-decay which agree with the empirical data approximately as well as the successful F&D parameterization of the Cabibbo scheme. Demanding the strangeness component in the nucleon to vanish in the two flavor limit of the model, determines the structure of the singlet axial charge operator and yields the various quark flavor components of the axial charge of the Λ-hyperon. The suggested picture gains support from calculations in a realistic model using pion and vector meson degrees of freedom to build up the soliton. 相似文献
954.
We propose a novel approach for solving polynomial programs over compact domains with equality constraints. By means of a generic transformation, we show that existing solution schemes for the, typically simpler, problem without equalities can be used to address the problem with equalities. 相似文献
955.
The rotary motion of the F0 part of the F0F1-ATPase motor that synthesizes the ATP molecules used by the intracellular stepping motors, such as kinesins, is modeled within a stochastically fluctuating medium via the application of the Langevin dynamics wherein the random intramembrane fluctuations are represented by a white noise. We have investigated the influence of an applied electric field and an applied electric current on this rotary motion, and the subsequent production rate of the ATP molecules. It is seen that the application of a field, or a current, changes both the elastic behavior of the cell membrane and the transmembrane potential. These changes in turn transform the dynamics of the F0 part of the motor. We have found that at low fields, the role of transmembrane potential becomes significant in the production rate of the ATP molecules, whereas at high fields the changes induced in the surface tension of the membrane also contribute to the production rate of the ATP. 相似文献
956.
Eric Sundberg 《Discrete Mathematics》2008,308(15):3308-3314
A positional game is essentially a generalization of tic-tac-toe played on a hypergraph (V,F). A pivotal result in the study of positional games is the Erd?s-Selfridge theorem, which gives simple criteria for the existence of a Breaker's winning strategy on a hypergraph F. It has been shown that the Erd?s-Selfridge theorem can be tight and that numerous extremal systems exist for that theorem. We focus on a generalization of the Erd?s-Selfridge theorem proven by Beck for biased (p:q) games, which we call the (p:q)-Erd?s-Selfridge theorem. We show that for pn-uniform hypergraphs there is a unique extremal system for the (p:q)-Erd?s-Selfridge theorem (q?2) when Maker must win in exactly n turns (i.e., as quickly as possible). 相似文献
957.
958.
Polymeric melaminium sulfate [(LH2)2(SO4)2]n has been synthesized by reaction of melamine L with sulfuric acid in aqueous solution. The compound was characterized by elemental analysis, 1H NMR, ESI MS and a single crystal X‐ray diffraction analysis. The architecture of the assembly formed is based on hydrogen bonded dimers of diprotonated melaminium cations (LH2)2+ which are linked by a hydrogen bonded network with sulfate ions forming 2D sheets. A 3D polymeric structure results from the presence of mutual hydrogen bonds between sulfate ions and melaminium cations in different sheets. Significant π‐π stacking is also present between the aromatic cations in this supramolecular arrangement. 相似文献
959.
960.
José Angel Brito Helena Teruel Stéphane Massou Montserrat Gómez 《Magnetic resonance in chemistry : MRC》2009,47(7):573-577
Oxomolybdenum(VI) complexes containing diverse ligands from an electronic and topological point of view have been analysed by means of 95Mo NMR in solution with the purpose of using this technique as a tool to study their coordination chemistry and reactivity. The relationship between the electronic density on the metal tuned by the electron‐donor ability of the coordinated ligands and the 95Mo chemical shift has been proved for mono‐ and bimetallic complexes showing a hexa‐ or hepta‐coordination around the metal centre. The different origins of the signal broadening (associated either to the symmetry of the metallic polyhedron or to the presence of isomers or to the ligand de‐coordination) have been also considered to rationalise the obtained data. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献