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   278780篇
  免费   1603篇
  国内免费   802篇
化学   127855篇
晶体学   4139篇
力学   16873篇
综合类   10篇
数学   53272篇
物理学   79036篇
  2021年   1971篇
  2020年   2011篇
  2019年   2569篇
  2018年   13890篇
  2017年   13703篇
  2016年   10755篇
  2015年   3149篇
  2014年   4564篇
  2013年   8860篇
  2012年   10486篇
  2011年   18260篇
  2010年   11941篇
  2009年   12532篇
  2008年   14021篇
  2007年   16093篇
  2006年   6874篇
  2005年   7146篇
  2004年   7092篇
  2003年   7068篇
  2002年   6124篇
  2001年   5828篇
  2000年   4411篇
  1999年   3268篇
  1998年   2878篇
  1997年   2895篇
  1996年   2730篇
  1995年   2322篇
  1994年   2399篇
  1993年   2318篇
  1992年   2572篇
  1991年   2705篇
  1990年   2601篇
  1989年   2679篇
  1988年   2589篇
  1987年   2608篇
  1986年   2469篇
  1985年   3079篇
  1984年   3143篇
  1983年   2632篇
  1982年   2605篇
  1981年   2565篇
  1980年   2380篇
  1979年   2751篇
  1978年   2705篇
  1977年   2888篇
  1976年   2888篇
  1975年   2681篇
  1974年   2613篇
  1973年   2736篇
  1972年   2102篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
Raman scattering in glasses is investigated theoretically. The experimental Raman spectra of glasses exhibit a low-frequency peak (at ~10 cm?1) that, as a rule, is attributed to vibrational modes of nanometer-sized structural units (nanocrystallites). It is established that the elastic moduli of nanocrystallites must necessarily be dependent on their sizes due to the Laplace pressure effect. A theory of the low-frequency peak is constructed using a realistic size distribution function of nanocrystallites with allowance made for the Laplace pressure effect and the dissipation of vibrational energy. Within this theory, the shape of the low-frequency peak and its evolution with temperature can be analyzed quantitatively. The proposed approach offers a physical interpretation of the experimental data and provides insight into the relation of the characteristic nanocrystallite sizes to the elastic moduli and surface tension coefficients of materials.  相似文献   
82.
83.
An experimental apparatus and related procedures for the determination of the effective thermal conductivity of sintered powder-metal plates saturated with distilled water at temperatures in the range 20–150°C are discussed. The apparatus and procedures are applied to two samples of sintered powder-metal plates, one made of nickel 200 and the other of stainless steel 316, with porosities of 28.10 and 46.45%, respectively, and each of nominal dimensions 127 mm × 127 mm × 6.35 mm. The experimental results are compared with corresponding predictions yielded by several correlations available in the literature. The correlations based on experimental data for packed beds of spherical particles and also porous plates made of cold-pressed (but not sintered) particles of angular shapes do not apply well to sintered powder-metal plates. A new correlation, which is based on extensions of ideas contained in earlier works and provides improved predictions, is proposed.  相似文献   
84.
85.
86.
A model of an expanding and rotating universe is constructed in the framework of general relativity. The parameters of the model are compared with the fundamental observables and shown to be in good agreement.Kaluzhsk Branch, N. É. Bauman Moscow State Technical University (MGTU). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 71–77, June, 1993.  相似文献   
87.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure.  相似文献   
88.
Translated from:Problemy Ustoichivosti Stokhasticheskikh Modelei, Trudy Seminara, 1989, pp. 20–26.  相似文献   
89.
90.
The existence of bound states and resonances of the Hamiltonian of a system ofN different quantum lattice particles with nonvanishingN-particle short-range interaction is proved. The dependence of the bound states and the resonances on the coupling constant and the quasimomentum is studied.Samarkand State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 91, No. 1, pp. 51–65, April, 1992.  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