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   232503篇
  免费   2275篇
  国内免费   798篇
化学   116732篇
晶体学   3777篇
力学   10763篇
综合类   1篇
数学   25524篇
物理学   78779篇
  2020年   1795篇
  2019年   2049篇
  2018年   2735篇
  2017年   2657篇
  2016年   3929篇
  2015年   2396篇
  2014年   3986篇
  2013年   10090篇
  2012年   7556篇
  2011年   9422篇
  2010年   6705篇
  2009年   6639篇
  2008年   8718篇
  2007年   8751篇
  2006年   8279篇
  2005年   7504篇
  2004年   6927篇
  2003年   6114篇
  2002年   6066篇
  2001年   7095篇
  2000年   5376篇
  1999年   4239篇
  1998年   3565篇
  1997年   3473篇
  1996年   3297篇
  1995年   3010篇
  1994年   2959篇
  1993年   3049篇
  1992年   3156篇
  1991年   3333篇
  1990年   3085篇
  1989年   3027篇
  1988年   3067篇
  1987年   2957篇
  1986年   2804篇
  1985年   3813篇
  1984年   4009篇
  1983年   3200篇
  1982年   3414篇
  1981年   3340篇
  1980年   3182篇
  1979年   3292篇
  1978年   3383篇
  1977年   3319篇
  1976年   3428篇
  1975年   3110篇
  1974年   3123篇
  1973年   3171篇
  1972年   2213篇
  1971年   1836篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field  $ F $ which possess a “unital” matrix subalgebra  $...  相似文献   
103.
Journal of Applied Spectroscopy - The temperature dependence of the refractive indices of K2SO4 with copper impurity was investigated. It was found that introduction of the copper impurity leads to...  相似文献   
104.
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase.  相似文献   
105.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
106.
107.
An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
108.
The paper discusses the applicability of quasi-crystalline approximation to describing the thermal motion of water molecules in their normal and supercooled states. The problem is subjected to the critical analysis of experimental data on incoherent scattering of slow neutrons based on theories developed by Singwi-Sjolander [1] and Oskotsky [2] modified to duly take into account the limited applicability range of diffusion approximation. The applicability conditions of quasi-crystalline approximation are shown to be consistently satisfied only when water is in supercooled state and within a narrow temperature range above the melting temperature.  相似文献   
109.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity. PACS 47.80.Jk, 47.40.Ki, 47.60.+i  相似文献   
110.
The semiclassical theory of proximity effects predicts a gap E g~?D/L 2 in the excitation spectrum of a long diffusive superconductor/normal-metal/superconductor (SNS) junction. Mesoscopic fluctuations lead to anomalously localized states in the normal part of the junction.As a result, a nonzero, yet exponentially small, density of states (DOS) appears at energies below E g. In the framework of the supermatrix nonlinear σ model, these prelocalized states are due to the instanton configurations with broken supersymmetry. The exact result for the DOS near the semiclassical threshold is found, provided the dimensionless conductance of the normal part G N is large. The case of poorly transparent interfaces between the normal and superconductive regions is also considered. In this limit, the total number of subgap states may be large.  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