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   456245篇
  免费   5988篇
  国内免费   1379篇
化学   247022篇
晶体学   6653篇
力学   19342篇
综合类   14篇
数学   54063篇
物理学   136518篇
  2021年   3891篇
  2020年   4333篇
  2019年   4748篇
  2018年   6046篇
  2017年   5919篇
  2016年   9178篇
  2015年   5833篇
  2014年   8921篇
  2013年   21291篇
  2012年   16572篇
  2011年   20420篇
  2010年   14131篇
  2009年   13848篇
  2008年   18732篇
  2007年   18676篇
  2006年   17392篇
  2005年   15689篇
  2004年   14501篇
  2003年   12702篇
  2002年   12532篇
  2001年   13727篇
  2000年   10346篇
  1999年   8124篇
  1998年   6803篇
  1997年   6574篇
  1996年   6406篇
  1995年   5715篇
  1994年   5625篇
  1993年   5451篇
  1992年   6057篇
  1991年   6130篇
  1990年   5841篇
  1989年   5673篇
  1988年   5708篇
  1987年   5584篇
  1986年   5296篇
  1985年   6892篇
  1984年   7053篇
  1983年   5573篇
  1982年   5747篇
  1981年   5717篇
  1980年   5256篇
  1979年   5638篇
  1978年   5795篇
  1977年   5682篇
  1976年   5578篇
  1975年   5162篇
  1974年   5119篇
  1973年   5092篇
  1972年   3592篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
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   
952.
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   
953.
954.
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   
955.
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   
956.
957.
958.
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   
959.
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   
960.
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