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   346775篇
  免费   5568篇
  国内免费   1090篇
化学   190871篇
晶体学   4278篇
力学   13567篇
综合类   8篇
数学   43569篇
物理学   101140篇
  2021年   2056篇
  2020年   2561篇
  2019年   2463篇
  2018年   2786篇
  2017年   2632篇
  2016年   5254篇
  2015年   4383篇
  2014年   5507篇
  2013年   16344篇
  2012年   12969篇
  2011年   15423篇
  2010年   9629篇
  2009年   9357篇
  2008年   14091篇
  2007年   14152篇
  2006年   13580篇
  2005年   12616篇
  2004年   11252篇
  2003年   9850篇
  2002年   9581篇
  2001年   10646篇
  2000年   8322篇
  1999年   6540篇
  1998年   5220篇
  1997年   5031篇
  1996年   5170篇
  1995年   4653篇
  1994年   4467篇
  1993年   4265篇
  1992年   4787篇
  1991年   4560篇
  1990年   4304篇
  1989年   4057篇
  1988年   4350篇
  1987年   4003篇
  1986年   3906篇
  1985年   5604篇
  1984年   5647篇
  1983年   4583篇
  1982年   4965篇
  1981年   4958篇
  1980年   4652篇
  1979年   4774篇
  1978年   4778篇
  1977年   4748篇
  1976年   4719篇
  1975年   4603篇
  1974年   4475篇
  1973年   4640篇
  1972年   2634篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
991.
The rotational spectra of three low-energy conformers of thiodiglycol (TDG) (HOCH2CH2SCH2CH2OH) have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To determine the likely conformational structures with ab initio approach, conformational structures of 2-(ethylthio)ethanol (HOEES) (CH3CH2SCH2CH2OH) were used as starting points together with the consideration of possible intramolecular hydrogen bonding in TDG. Three lower-energy conformers have been found for TDG at the MP2=Full/6311G** level and ab initio results agree nicely with experimentally determined rotational constants. In addition, Stark measurements were performed for two of the three conformers for dipole moment determinations, adding to our confidence of the conformational structure matches between experimental observations and ab initio calculations. Of the three lower-energy conformers, one displays a compact folded-like structure with strong hydrogen bonding between the two hydroxyl groups and the central sulfide atom. Two other conformers have relatively open chain-like structures with hydrogen bonding between each of the hydroxyl groups to the central sulfur atom, of which one has pure b-type dipole moment according to the ab initio results.  相似文献   
992.
Positions and intensities for 453 spectral lines in 12 rovibrational bands of 12C16O2 have been determined between 3700 and 3750 cm−1. At three temperatures (294, 500, and 698 K) eight spectra have been recorded at a pressure around 5 mbar and for an absorption path of about 190 cm−1 using a Bomen DA3 Fourier transform spectrometer (4 × 10−3 cm−1 resolution). Some of the measured positions and intensities can be compared with recent experimental results that validate the experimental set-up and the data analysis procedure. The results are also compared with the values listed in the HITRAN 2000 database. If the agreement is generally good, discrepancies are observed for three hot bands.  相似文献   
993.
In bricklayers' model, which is a generalization of the misanthrope processes, we show that a nontrivial class of product distributions is closed under the time-evolution of the process. This class also includes measures fitting to shock data of the limiting PDE. In particular, we show that shocks of this type with discontinuity of size one perform ordinary nearest neighbor random walks only interacting, in an attractive way, via their jump rates. Our results are related to those of Belitsky and Schütz(4) on the simple exclusion process, although we do not use quantum formalism as they do. The structures we find are described from a fixed position. Similar ones were found in Balázs,(2) valak as seen from the random position of the second class particle.  相似文献   
994.
995.
A suitable derivative of Einstein's equations in the framework of the teleparallel equivalent of general relativity (TEGR) yields a continuity equation for the gravitational energy‐momentum. In particular, the time derivative of the total gravitational energy is given by the sum of the total fluxes of gravitational and matter fields energy. We carry out a detailed analysis of the continuity equation in the context of Bondi and Vaidya's metrics. In the former space‐time the flux of gravitational energy is given by the well known expression in terms of the square of the news function. It is known that the energy definition in the realm of the TEGR yields the ADM (Arnowitt‐Deser‐Misner) energy for appropriate boundary conditions. Here we show that the same energy definition also describes the Bondi energy. The analysis of the continuity equation in Vaidya's space‐time shows that the variation of the total gravitational energy is determined by the energy flux of matter only.  相似文献   
996.
Photoinduced optical and second-order non-linear optical effects in the interfaces separating In2O3–SiON (O/N ratio equals 1) films doped with A1, Sn and glass substrates were investigated using the photoinduced optical second harmonic generation. The photoinduced effective second-order optical susceptibility deff (at λ=1.76 μm) shows a good correlation with the linear optical susceptibility, particularly with the shift of the absorption edge. The maximal response of the photoinduced optical response signal was observed for the pump–probe delaying time of 34 ps. The performed experimental measurements indicate that the observed effects are mainly caused by the interface potential gradients on the border glass–In2O3–SiON film and by additional polarization due to insertion of the Al and Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigation of thin semiconducting interfacial layers and simultaneously such films may be used as materials for non-linear optical devices.  相似文献   
997.
998.
The rate-dependent effects in metallic ferromagnetic materials with magnetization processes attributed to domain-walls motion were studied. The experimental method for eddy-current relaxation time determination was proposed. Some discrepancies between the data and theoretical predictions were observed and discussed. The origin of these discrepancies is accounted for by the decrease of viscous-type relaxation process as the rate of change of averaged magnetization is approaching zero.  相似文献   
999.
Simple Entanglement Measure for Multipartite Pure States   总被引:3,自引:0,他引:3  
A simple entanglement measure for multipartite pure states is formulated based on the partial entropy of a series of reduced density matrices. Use of the proposed new measure to distinguish disentangled, partially entangled, and maximally entangled multipartite pure states is illustrated.  相似文献   
1000.
Using two different types of the laddering equations realized simultaneously by the associated Gegenbauer functions, we show that all quantum states corresponding to the motion of a free particle on AdS 2 and S 2 are splitted into infinite direct sums of infinite-and finite-dimensional Hilbert subspaces which represent Lie algebras u(1, 1) and u(2) with infinite- and finite-fold degeneracies, respectively. In addition, it is shown that the representation bases of Lie algebras with rank 1, i.e., gl(2, C), realize the representation of nonunitary parasupersymmetry algebra of arbitrary order. The realization of the representation of parasupersymmetry algebra by the Hilbert subspaces which describe the motion of a free particle on AdS 2 and S 2 with the dynamical symmetry groups U(1, 1) and U(2) are concluded as well.  相似文献   
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