全文获取类型
收费全文 | 84096篇 |
免费 | 6028篇 |
国内免费 | 5895篇 |
专业分类
化学 | 27229篇 |
晶体学 | 485篇 |
力学 | 6929篇 |
综合类 | 910篇 |
数学 | 34563篇 |
物理学 | 25903篇 |
出版年
2024年 | 118篇 |
2023年 | 778篇 |
2022年 | 1362篇 |
2021年 | 1676篇 |
2020年 | 1917篇 |
2019年 | 2028篇 |
2018年 | 1863篇 |
2017年 | 2057篇 |
2016年 | 2269篇 |
2015年 | 1827篇 |
2014年 | 3033篇 |
2013年 | 6157篇 |
2012年 | 3348篇 |
2011年 | 3926篇 |
2010年 | 3312篇 |
2009年 | 4954篇 |
2008年 | 5169篇 |
2007年 | 5689篇 |
2006年 | 4879篇 |
2005年 | 3927篇 |
2004年 | 3404篇 |
2003年 | 3607篇 |
2002年 | 3966篇 |
2001年 | 3015篇 |
2000年 | 2912篇 |
1999年 | 2564篇 |
1998年 | 2369篇 |
1997年 | 1695篇 |
1996年 | 1392篇 |
1995年 | 1144篇 |
1994年 | 1164篇 |
1993年 | 876篇 |
1992年 | 973篇 |
1991年 | 653篇 |
1990年 | 599篇 |
1989年 | 458篇 |
1988年 | 428篇 |
1987年 | 403篇 |
1986年 | 363篇 |
1985年 | 359篇 |
1984年 | 411篇 |
1983年 | 224篇 |
1982年 | 347篇 |
1981年 | 420篇 |
1980年 | 373篇 |
1979年 | 374篇 |
1978年 | 342篇 |
1977年 | 261篇 |
1976年 | 221篇 |
1973年 | 141篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
1.
2.
深挖高职院校公选课“生活中的化学”的育人元素,精心设计教学内容,运用课堂主题辩论、趣味生活实验的设计与展示、探秘生活中的化学等理论知识传授与课内外实践相结合的教学方式,实现全过程育人,充分展现了公选课在立德树人方面的价值。 相似文献
3.
《Indagationes Mathematicae》2021,32(1):55-85
We show that the differential structure of the orbit space of a proper action of a Lie group on a smooth manifold is weakly reflexive. This implies that the orbit space is a differentiable space in the sense of Smith, which ensures that the orbit space has an exterior algebra of differential forms, that satisfies Smith’s version of de Rham’s theorem. Because the orbit space is a locally closed subcartesian space, it has vector fields and their flows. 相似文献
4.
M. Amar D. Andreucci R. Gianni C. Timofte 《Journal of Mathematical Analysis and Applications》2021,493(2):124533
We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation. 相似文献
5.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献
6.
Bifurcation analysis of visual angle model with anticipated time and stabilizing driving behavior 下载免费PDF全文
Xueyi Guan 《中国物理 B》2022,31(7):70507-070507
In the light of the visual angle model (VAM), an improved car-following model considering driver's visual angle, anticipated time and stabilizing driving behavior is proposed so as to investigate how the driver's behavior factors affect the stability of the traffic flow. Based on the model, linear stability analysis is performed together with bifurcation analysis, whose corresponding stability condition is highly fit to the results of the linear analysis. Furthermore, the time-dependent Ginzburg-Landau (TDGL) equation and the modified Korteweg-de Vries (mKdV) equation are derived by nonlinear analysis, and we obtain the relationship of the two equations through the comparison. Finally, parameter calibration and numerical simulation are conducted to verify the validity of the theoretical analysis, whose results are highly consistent with the theoretical analysis. 相似文献
7.
Chemical bonding in representative astrophysically relevant neutral,cation, and anion HCnH chains 下载免费PDF全文
Ioan Baldea 《中国物理 B》2022,31(12):123101-123101
Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from ab initio computations for representative members of the astrophysically relevant neutral and charged HC2k/2k+1H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes, e.g., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC2k/2k+1H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study. 相似文献
8.
9.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献
10.