首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   69171篇
  免费   6255篇
  国内免费   4816篇
化学   22683篇
晶体学   564篇
力学   6929篇
综合类   857篇
数学   23672篇
物理学   25537篇
  2024年   95篇
  2023年   558篇
  2022年   1120篇
  2021年   1373篇
  2020年   1506篇
  2019年   1562篇
  2018年   1414篇
  2017年   1737篇
  2016年   1950篇
  2015年   1464篇
  2014年   2435篇
  2013年   4559篇
  2012年   2927篇
  2011年   3115篇
  2010年   2685篇
  2009年   3882篇
  2008年   4275篇
  2007年   4763篇
  2006年   4098篇
  2005年   3474篇
  2004年   2950篇
  2003年   3225篇
  2002年   3547篇
  2001年   2794篇
  2000年   2621篇
  1999年   2326篇
  1998年   2120篇
  1997年   1418篇
  1996年   1240篇
  1995年   1078篇
  1994年   1075篇
  1993年   832篇
  1992年   872篇
  1991年   603篇
  1990年   563篇
  1989年   424篇
  1988年   383篇
  1987年   385篇
  1986年   331篇
  1985年   341篇
  1984年   336篇
  1983年   186篇
  1982年   269篇
  1981年   253篇
  1980年   174篇
  1979年   206篇
  1978年   182篇
  1977年   164篇
  1976年   108篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
In the periodic table the position of each atom follows the ‘aufbau’ principle of the individual electron shells. The resulting intrinsic periodicity of atomic properties determines the overall behavior of atoms in two-dimensional (2D) bonding and structure formation. Insight into the type and strength of bonding is the key in the discovery of innovative 2D materials. The primary features of 2D bonding and the ensuing monolayer structures of the main-group II–VI elements result from the number of valence electrons and the change of atom size, which determine the type of hybridization. The results reveal the tight connection between strength of bonding and bond length in 2D networks. The predictive power of the periodic table reveals general rules of bonding, the bonding-structure relationship, and allows an assessment of published data of 2D materials.  相似文献   
3.
4.
We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution { u , p } of the Navier–Stokes equation such that | ? j u ( t , x ) | = O ( | x | 1 ? n ? j ) and | ? j p ( t , x ) | = O ( | x | ? n ? j ) ( j = 0 , 1 , ) uniformly in t R as | x | . Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described.  相似文献   
5.
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   
6.
《Mendeleev Communications》2022,32(4):507-509
We report on the synthesis of new Ru(bpy)2(phen) catalyst for the oscillatory Belousov–Zhabotinsky chemical reaction and on the preparation of novel Ru(bpy)2(phen)-based self-oscillating gels. The synthesized gels exhibit high-amplitude autonomous mechanical oscillations when the Belousov–Zhabotinsky reaction proceeds inside these gels  相似文献   
7.
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   
8.
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   
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.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号