全文获取类型
收费全文 | 70788篇 |
免费 | 5342篇 |
国内免费 | 6755篇 |
专业分类
化学 | 26451篇 |
晶体学 | 290篇 |
力学 | 6889篇 |
综合类 | 1250篇 |
数学 | 26002篇 |
物理学 | 22003篇 |
出版年
2023年 | 591篇 |
2022年 | 1180篇 |
2021年 | 1316篇 |
2020年 | 1390篇 |
2019年 | 1679篇 |
2018年 | 1334篇 |
2017年 | 1574篇 |
2016年 | 1814篇 |
2015年 | 1645篇 |
2014年 | 2384篇 |
2013年 | 4532篇 |
2012年 | 2740篇 |
2011年 | 3162篇 |
2010年 | 2714篇 |
2009年 | 3839篇 |
2008年 | 4255篇 |
2007年 | 4491篇 |
2006年 | 4215篇 |
2005年 | 3588篇 |
2004年 | 3301篇 |
2003年 | 3343篇 |
2002年 | 3074篇 |
2001年 | 2607篇 |
2000年 | 2528篇 |
1999年 | 2260篇 |
1998年 | 2105篇 |
1997年 | 1739篇 |
1996年 | 1548篇 |
1995年 | 1398篇 |
1994年 | 1303篇 |
1993年 | 1117篇 |
1992年 | 1086篇 |
1991年 | 843篇 |
1990年 | 692篇 |
1989年 | 604篇 |
1988年 | 552篇 |
1987年 | 437篇 |
1986年 | 376篇 |
1985年 | 432篇 |
1984年 | 434篇 |
1983年 | 212篇 |
1982年 | 348篇 |
1981年 | 407篇 |
1980年 | 304篇 |
1979年 | 295篇 |
1978年 | 220篇 |
1977年 | 209篇 |
1976年 | 155篇 |
1974年 | 111篇 |
1973年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
171.
通过用毛细管测量纯水表面张力系数实验,得到管内径d与接触角θ的相对误差之间的关系曲线,由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差,并简单地讨论了实验的理想状态与实际情况的差别. 相似文献
172.
The structure, harmonic frequencies, and nonresonance Raman intensities for porphin, tetraazaporphin (TAP), and three of its isotopomers are calculated by the density-functional theory of B3LYP/6-31G(d). Scaling of force constants for porphin in nonredundant natural coordinates is performed. The scaling factors obtained were used to predict the force field and normal modes of TAP and three of its isotopomers. Two alternative methods are used to carry out reliable assignment of the TAP frequencies: wavenumber-linear scaling method and frequency-shift method. There is good agreement between the frequencies predicted within the framework of the three methods used. The conservativeness of the out-of-plane B
2g
- and B
3g
-modes for porphin and TAP is examined. The Raman spectrum for TAP is simulated. A refinement of the assignment of the experimental frequencies for TAP of even symmetry types on the basis of the calculations performed is made. 相似文献
173.
Based on the beam coherence-polarization (BCP) matrix, the polarization property of coherent and incoherent Gaussian beam combinations is studied in detail. The general expressions for the degree of polarization P of the resulting beam in case of incoherent and coherent combinations are derived. It is shown that P is dependent on the incoherent or coherent combination, propagation distance, separation, azimuth of the polarization plane and numbers of beamlets in general. The irradiance distribution of the resulting beam for the coherent cases depends on the azimuth of the polarization plane of beamlets. However, for the incoherent case it does not. 相似文献
174.
175.
XiWenHE HongShengGUO YuMeiJIA 《中国化学快报》2003,14(9):979-982
In order to obtain mechanically stable membrane for practical application, the imprinted polymer was synthesized in the pores of polyfluoromembrane, the binding and transport ability of the membrane were studied. 相似文献
176.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
177.
研究了Banach空间中非线性混合型微分-积分方程初值问题u′=f(t,u,Tu,Su),u(0)=x0的整体解,完全没有要求f的任何增性,利用Mnch不动点定理和比较结果得到了初值问题整体解的存在性和唯一解,并且给出了一致收敛于唯一解的迭代序列,改进推广和统一了已有的许多结果. 相似文献
178.
Ab initio calculations showed that the tetrachlorodibenzo-para-dioxin radical cations (TCDD RCs) with a planar structure have two steady states with asymmetric dioxin cycles. The activation barriers between these states are up to 2 kcal/mole, so that the RCs may be regarded as being structurally nonrigid within the dioxin cycle. The 2,3,7,8-TCDD RC is more stable than the 1,4,6,9-TCDD RC, the energy difference being 5.2 kcal/mole. The adiabatic ionization potential of 2,3,7,8-TCDD (7.54 eV) is 0.1 eV smaller than the corresponding potential of 1,4,6,9-TCDD. These factors account for the increased hemoproteide affinity and hence increased biological activity of 2,3,7,8-TCDD. 相似文献
179.
Grishin D. F. Semyonycheva L. L. Telegina E. V. Smirnov A. S. Nevodchikov V. I. 《Russian Chemical Bulletin》2003,52(2):505-507
Organometallic compounds Cp2TiCl2, (EtC5H4)2NbCl2, and (PriC5H4)2WCl2 were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed. 相似文献
180.
A thermodynamic approach with internal variables using Lagrange formalism. Part I: General framework 总被引:1,自引:0,他引:1
Rachid Rahouadj Jean-Franois Ganghoffer Christian Cunat 《Mechanics Research Communications》2003,30(2):109-117
We present some reflections on the application of the Lagrangian formalism for continuous media locally uniform subjected to internal irreversible evolutions. The Lagrangian density, defined as the time derivative of a non-equilibrium thermodynamic potential, [Thermodynamics of Relaxation Processes using Internal variables within a Lagrange-formalism. P. Germain’s Anniversary Volume 2000. Contiuum Thermomechanics: the Art and Science of Modeling Matter’s Behaviour, 2000], contains all the symmetry properties of the system. The generalised Lagrange co-ordinates correspond to the state and internal variables of the time derivative of the generalised Gibbs potential. The latter being used within the framework of the De Donder’s method, must also account for the memory effect of the physical medium.This first part is devoted to the thermodynamic framework called the distribution of non-linear relaxations approach (DNLR) developed by C. Cunat on the basis of the generalised Gibbs’ relation. 相似文献