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   215519篇
  免费   1564篇
  国内免费   630篇
化学   117923篇
晶体学   3270篇
力学   8349篇
综合类   6篇
数学   23379篇
物理学   64786篇
  2020年   1970篇
  2019年   2264篇
  2018年   3206篇
  2017年   3113篇
  2016年   4267篇
  2015年   2372篇
  2014年   3820篇
  2013年   9264篇
  2012年   6893篇
  2011年   8435篇
  2010年   6072篇
  2009年   5922篇
  2008年   8137篇
  2007年   8209篇
  2006年   7631篇
  2005年   6938篇
  2004年   6168篇
  2003年   5642篇
  2002年   5498篇
  2001年   5939篇
  2000年   4685篇
  1999年   3471篇
  1998年   3012篇
  1997年   3036篇
  1996年   2825篇
  1995年   2321篇
  1994年   2420篇
  1993年   2454篇
  1992年   2597篇
  1991年   2660篇
  1990年   2562篇
  1989年   2539篇
  1988年   2465篇
  1987年   2438篇
  1986年   2357篇
  1985年   3038篇
  1984年   3194篇
  1983年   2561篇
  1982年   2828篇
  1981年   2705篇
  1980年   2505篇
  1979年   2720篇
  1978年   2835篇
  1977年   2858篇
  1976年   2834篇
  1975年   2689篇
  1974年   2667篇
  1973年   2811篇
  1972年   1875篇
  1967年   1830篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
In the present paper, the main probabilistic characteristics (the mathematical expectation, variance, and correlation function) of the amount of harmful substances in anthropogenic formations are calculated under the stationary conditions when the stream of these substances is a recurrent stream of events.  相似文献   
222.
223.
An isotopic effect in the widths of giant dipole resonances is established on the basis of an analysis of the latest systematics of photoabsorption cross sections for nuclei containing 12 to 65 nucleons. This effect arises owing to isospin splitting of a giant resonance and is enhanced by its configuration splitting.  相似文献   
224.
The size of an ionistor capacitor structure is found to change during its charging and discharging. The specific feature of this effect that distinguishes it from other known effects of changing sizes under electric and magnetic fields (the piezoelectric effect and striction) is the complete hysteresis; i.e., the size reached under the exposure remains unchanged after the field is turned off.  相似文献   
225.
N. Elgun  E. A. Davis 《Journal of Non》2003,330(1-3):226-233
Hydrogenated amorphous GaP films have been prepared by reactive rf sputtering. Infrared spectroscopy, optical transmission and reflection, photothermal deflection spectroscopy and dc conductivity have been studied to investigate the local bonding configurations, the optical absorption edges and the temperature dependence of the conductivity as a function of hydrogen content. The results are discussed and compared with the effects of hydrogenation on amorphous Si.  相似文献   
226.
227.
We prove the Thom isomorphism theorem for the K-theory of bundles with fibers equal to a projective module over a C*-algebra for the action of a compact Lie group both on this algebra and on the total space. Bibliography: 12 titles.  相似文献   
228.
A nuclear-reactor experiment on the search for the emission of neutral pions from the neutron-induced fission of 235U nuclei has been carried out. To this end, an experimental setup for searching for the emission of π0 mesons with high sensitivity to this process has been designed and produced. This setup consisted of two Cherenkov total-absorption spectrometers for the detection and measurements of the energy of two gamma-ray photons from π 0-meson decay. The spectrometers were placed at the exits of two coaxial horizontal experimental channels. To protect the detectors from low-energy β and γ rays and neutron fluxes, 3.5-m-long water filters were situated in the channels. To reject the cosmic background, large-area scintillation counters operating in the anticoincidence mode were placed over each spectrometer. The energy and time resolution of the spectrometers, as well as the efficiency of detecting charged particles by scintillation counters, were tested on the secondary electron beam of the Tomsk electron synchrotron Sirius. Runs of measurements of the effect on the operating reactor (duration of 805 h) were alternated with runs of measurements of background on the stopped reactor (duration of 403 h). Statistical processing of the experimental results yields an upper limit of ≤5.3×10 ?12 with a 90% confidence level for the probability of the emission of neutral pions from the neutron-induced fission of 235U nuclei. This result and results of other works carried out with sources of spontaneously fissioning 252Cf nuclei show that the probabilities of the emission of π0 mesons from spontaneous fission and fission induced by fission-spectrum neutrons are equal to each other.  相似文献   
229.
Two additional types of light scattering in continuous media are considered. One is the cross photoelastic scattering from density fluctuations caused by thermodynamic temperature fluctuations and the other is the cross thermorefractive scattering from temperature fluctuations caused by density fluctuations, which manifest themselves in propagation of elastic sound waves. Expressions for the light scattering coefficients for these two types of scattering are obtained. The integral intensities of scattered light are shown to be comparable with the well-known integral intensities of light scattering by fluctuations of density (pressure) and temperature (entropy) for some substances.  相似文献   
230.
Nonuniform distributions of the order parameter in a film of an incommensurate ferroelectric whose free energy expansion does not contain Lifshitz invariants are considered. An equation describing the order parameter distribution over the film thickness is derived in the approximation of slowly varying amplitudes. The effect of film thickness and surface properties on the temperature of transition to the incommensurate phase is analyzed.  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