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   42711篇
  免费   1553篇
  国内免费   196篇
化学   22779篇
晶体学   228篇
力学   1226篇
综合类   21篇
数学   7249篇
物理学   12957篇
  2023年   273篇
  2021年   431篇
  2020年   586篇
  2019年   468篇
  2018年   638篇
  2017年   613篇
  2016年   1240篇
  2015年   952篇
  2014年   1115篇
  2013年   2293篇
  2012年   1979篇
  2011年   2134篇
  2010年   1490篇
  2009年   1218篇
  2008年   1984篇
  2007年   1854篇
  2006年   1732篇
  2005年   1549篇
  2004年   1327篇
  2003年   1079篇
  2002年   1007篇
  2001年   913篇
  2000年   745篇
  1999年   532篇
  1998年   473篇
  1997年   452篇
  1996年   554篇
  1995年   475篇
  1994年   510篇
  1993年   520篇
  1992年   565篇
  1991年   399篇
  1990年   410篇
  1989年   368篇
  1988年   340篇
  1987年   344篇
  1986年   322篇
  1985年   517篇
  1984年   499篇
  1983年   418篇
  1982年   432篇
  1981年   442篇
  1980年   431篇
  1979年   411篇
  1978年   406篇
  1977年   402篇
  1976年   375篇
  1975年   368篇
  1974年   354篇
  1973年   292篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We define a multifunction F: XY to be upper (lower) D*-supercontinuous if F +(V) (F (V)) is d*-open in X for every open set V of Y. We obtain some characterizations and several properties concerning upper (lower) D*-supercontinuous multifunctions.   相似文献   
92.
Directed and elliptic flow for the 197Au+197Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4π multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the σ NN and demonstrate the importance of angular momentum conservation in transport codes at low energies.  相似文献   
93.
This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.  相似文献   
94.
95.
96.
97.
The standard method to diagnose and follow-up osteoporosis is the measurement of bone mineral density (BMD) using dual X-ray absorptiometry (DEXA). Manufacturers' manuals of DEXA devices state the intrascanner coefficient of variance is less than 0.01 g/cm2. The aim of this study was to evaluate the in vivo coefficient of variance of a Lunar DPX scanner in male and female healthy adult subjects. Average BMD for females and males were 1.170±0.091 g/cm2 and 1.272±0.115 g/cm2, respectively. Monthly phantom measurements provided and controlled by the manufacturer were 1.243±0.008 g/cm2 (range 1.222 to 1.257) and the coefficient of variance was 0.006. It is concluded that the in vivo coefficient of variance of DEXA devices can slightly be higher than that proposed by the manufacturer. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
98.
Problem fields with one or two generating problems and possibilities of varying existing problems give a good chance for self-activities of students and can be used for reaching different general aims. In this paper some topics concerning quadrilaterals will be presented. I hope they will animate teachers for more problem orientation in mathematics education. First we will reflect about different types of convex and non-convex quadrilaterals and possibilities of ordering them. Then we focus on middle-quadrilaterals and types of quadrilaterals with special middle-quadrilaterals as well as their logical ordering. Finally we investigate the analogies in space to the parallelogram and its sub-types and order them in the “house of parallelepipeds”.  相似文献   
99.
Pre—Separation Axioms in Fuzzifying Topology   总被引:1,自引:0,他引:1  
1  IntroductionYing[5,6 ] introduced and elementally developed so called fuzzifying topology with the semanticmethod of continuous valued L ogic.Shen[7] introduced and studied T0 -,T1-,T2 (Hausdorff) -,T3(regularity) -,T4 (normality) -separation axioms in fuzzifying topology.In [3 ]the concepts of thefamily of fuzzifying pre-open sets,fuzzifying pre-neighbourhood structure of a point and fuzzifyingpre-closure are introduced and studied.It is worth to mention that pre-separation axioms are …  相似文献   
100.
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