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   314225篇
  免费   2174篇
  国内免费   820篇
化学   138193篇
晶体学   4301篇
力学   18104篇
综合类   3篇
数学   65407篇
物理学   91211篇
  2021年   1516篇
  2020年   1453篇
  2019年   1574篇
  2018年   18544篇
  2017年   19099篇
  2016年   11554篇
  2015年   3472篇
  2014年   3138篇
  2013年   7227篇
  2012年   12522篇
  2011年   26647篇
  2010年   15914篇
  2009年   16331篇
  2008年   21602篇
  2007年   26438篇
  2006年   6415篇
  2005年   13212篇
  2004年   9578篇
  2003年   9480篇
  2002年   6666篇
  2001年   6082篇
  2000年   4658篇
  1999年   3356篇
  1998年   2438篇
  1997年   2450篇
  1996年   2495篇
  1995年   2192篇
  1994年   2138篇
  1993年   1952篇
  1992年   2377篇
  1991年   2487篇
  1990年   2298篇
  1989年   2289篇
  1988年   2277篇
  1987年   2265篇
  1986年   2083篇
  1985年   2559篇
  1984年   2605篇
  1983年   2075篇
  1982年   2103篇
  1981年   1930篇
  1980年   1922篇
  1979年   2210篇
  1978年   2299篇
  1977年   2133篇
  1976年   2083篇
  1975年   1947篇
  1974年   1915篇
  1973年   1998篇
  1972年   1289篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection.  相似文献   
133.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime.  相似文献   
134.
The existence of linear nonstationary optical resonances in a diatomic nanostructural object with a dipole-dipole atomic interaction has been proved. A new solution to the joint system of modified Bloch optical equations and nonlocal field equations is obtained for time intervals much shorter than the times of phase and energy relaxation. Formulas for effective polarizabilities of the object’s atoms, which have a set of dimensional resonances, are derived. The frequencies of these resonances significantly differ from the eigenfrequencies of the object’s atoms, and their properties depend on the interatomic distance, light-pulse duration, initial atomic inversions, and the orientation of the object’s axis relative to the direction of incidence of the external light wave.  相似文献   
135.
The states of a charged particle with a finite free path are determined in the field of a resonant electromagnetic wave. The exact resonance conditions, the modulation and beam instability mechanisms, the charge and current densities (Ohm's law) are obtained for the collisionless beam of resonance particles. Quantum theory of radiation is developed for the resonant adiabatic interaction between a particle and a wave taking into account the interaction with a constant magnetic field induced at the grating surface by the charge and nonresonant waves. The radiation power, the spectrum, and the range of generated frequencies are determined. The results obtained can be used in the plasma and solid-state theories and in electronics.  相似文献   
136.
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed.  相似文献   
137.
138.
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field.  相似文献   
139.
The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-nearest neighbor atoms are calculated for a negatively charged silicon vacancy in the high-spin state in cubic SiC. The calculations are performed within the cluster approach in terms of the density-functional theory (DFT). It is shown that the results of calculations with the use of a 70-atom cluster are in good agreement with experimental data. A detailed consideration is given to spin polarization in the electron subsystem and the applicability of a simple LCAO model that is commonly used in the interpretation of the electron paramagnetic resonance data for semiconductors. The spin density distribution for the defect under investigation is analyzed in terms of localized orbitals.  相似文献   
140.
The European Physical Journal A - The ω-meson photoproduction, γ + p→p + ω, is studied in the framework of a model, containing π-meson exchange in t-channel and...  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