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   460863篇
  免费   6473篇
  国内免费   1242篇
化学   247693篇
晶体学   5538篇
力学   19392篇
综合类   14篇
数学   55705篇
物理学   140236篇
  2021年   3930篇
  2020年   4563篇
  2019年   4809篇
  2018年   6214篇
  2017年   6106篇
  2016年   9626篇
  2015年   6225篇
  2014年   9311篇
  2013年   21866篇
  2012年   16919篇
  2011年   20756篇
  2010年   14323篇
  2009年   14031篇
  2008年   19048篇
  2007年   18918篇
  2006年   17460篇
  2005年   15617篇
  2004年   14389篇
  2003年   12609篇
  2002年   12405篇
  2001年   13901篇
  2000年   10510篇
  1999年   8215篇
  1998年   6814篇
  1997年   6127篇
  1996年   5987篇
  1995年   5666篇
  1994年   5645篇
  1993年   5502篇
  1992年   6069篇
  1991年   6049篇
  1990年   5836篇
  1989年   5594篇
  1988年   5641篇
  1987年   5529篇
  1986年   5198篇
  1985年   6876篇
  1984年   6974篇
  1983年   5579篇
  1982年   5669篇
  1981年   5646篇
  1980年   5209篇
  1979年   5602篇
  1978年   5772篇
  1977年   5657篇
  1976年   5561篇
  1975年   5148篇
  1974年   5099篇
  1973年   5112篇
  1972年   3562篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Plasma Chemistry and Plasma Processing - Nonequilibrium nitrogen dissociation-recombination kinetics in the boundary layer and on the surface of a solid body during hypersonic flow. the subsequent...  相似文献   
992.
We study the conjugate boundary-value problem with boundary conditions whose orders can be as large as the order of the differential equation or larger. We construct the Green's function of the problem over the entire space when the separating surface is a hyperplane, and we describe its properties. Bibliography: 6 titles.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 30, 1989, pp. 20–24.  相似文献   
993.
994.
Barium ferrite particulates prepared by a salt-melt method   总被引:1,自引:0,他引:1  
Barium ferrite particulates have been prepared by coprecipitation and calcination in a flux of NaCl-KCl. It was found that a flux containing more than 30 wt% KCl tends to seriously deteriorate the magnetic properties of resultant perticulates. The flux with 10 wt% KCl or less showed promising results. A Ba(CoZr)0.75Fe10.5O19 particulate showed the best properties, i.e., a saturation magnetization of 68.5, a squareness ratio of 0.49, and a coercivity of 1280 Oe, when calcined in NaCl at 900°C for 4 h.  相似文献   
995.
We discuss the possible new electroweak interactions which may be generated by the Higgs sector at the scale of theZ mass. For this purpose, we give a set ofSU(2)×U(1) gauge invariant operators constructed in terms ofW, Z, γ and Higgs fields which in the unitary gauge describe all possible γWW andZWW anomalous couplings. The dimension of these operators varies from 6 to 12. This fact allows us to consider various scenaria for the manifestations of the New Physics. We conclude that the underlying dynamics induced by the Higgs sector can be tested through a model-independent amplitude analysis of gauge boson pair production at LEP2 and future colliders.  相似文献   
996.
997.
998.
Many biological and medical studies have as a response of interest the time to occurrence of some event, such as the occurrence of a particular symptom or disease, remission, relapse, death due to some specific disease, or simply death. In this paper we study the problem of assessing the effect of potential risk factors on the outcome event of interest through a parametric or semi-parametric frailty model where the lifetimes have a reason to be considered dependent. This dependence may arise because of multiple endpoints within the same individual or because, when studying a single endpoint, there are natural groupings between study subjects. The objective of this paper is to extend both parametric and semi-parametric approaches to regression analysis in which the lifetimes of individuals in a group are effected by the same random frailty which follows a positive stable distribution. Some comparisons of the properties of this frailty distribution with other frailty distributions are made and an example which assesses the effect of a treatment in a litter-matched tumorigenesis study is presented.  相似文献   
999.
High resolution Fourier transform spectra of deuterated hydrogen sulfide have been recorded in the region 2400-3000 cm−1. Rotational structures of the ν1 + ν2, ν2 + ν3 bands of D232S, of the ν3 and ν1 + ν2 bands of HD32S, and of the ν1 + ν2 band of HD34S were analyzed. Band centers and rotational, centrifugal distortion, and resonance parameters were obtained, which reproduce the initial values of the upper energy levels within a mean accuracy of 1.39 × 10−4 cm−1 for the states (110) and (011) of D232S, 1.61 × 10−4 cm−1 and 1.82 × 10−4 cm−1 for the states (001) and (110) of HD32S, and 2.09 × 10−4 cm−1 for the state (110) of HD34S, respectively.  相似文献   
1000.
Summary Benzoylacetone isonicotinoyl hydrazone has been prepared in two forms: yellow (BzH2) and white (BzH2·H2O). Analytical, t.g.a., i.r. and n.m.r. results showed the yellow form to be a mixture of keto-enol tautomers, whereas the white form is a mixture of cis-trans enol tautomers. Complexes MBz (M = Ni, Cu, Zn and Pd), CoBz·H2O and Cd(BzH)2 have been isolated and characterized by physicochemical techniques.  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