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   308037篇
  免费   1818篇
  国内免费   662篇
化学   147690篇
晶体学   4506篇
力学   15295篇
综合类   6篇
数学   47042篇
物理学   95978篇
  2020年   2026篇
  2019年   2338篇
  2018年   10992篇
  2017年   11699篇
  2016年   8088篇
  2015年   3146篇
  2014年   4007篇
  2013年   9546篇
  2012年   10984篇
  2011年   19960篇
  2010年   12611篇
  2009年   12658篇
  2008年   17932篇
  2007年   21274篇
  2006年   7967篇
  2005年   13047篇
  2004年   9345篇
  2003年   8960篇
  2002年   6953篇
  2001年   6205篇
  2000年   5090篇
  1999年   3568篇
  1998年   3129篇
  1997年   3100篇
  1996年   3048篇
  1995年   2468篇
  1994年   2548篇
  1993年   2571篇
  1992年   2713篇
  1991年   2763篇
  1990年   2690篇
  1989年   2655篇
  1988年   2590篇
  1987年   2575篇
  1986年   2475篇
  1985年   3160篇
  1984年   3348篇
  1983年   2693篇
  1982年   2965篇
  1981年   2828篇
  1980年   2636篇
  1979年   2858篇
  1978年   2996篇
  1977年   2934篇
  1976年   2936篇
  1975年   2778篇
  1974年   2759篇
  1973年   2954篇
  1972年   1948篇
  1967年   1884篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The 6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this experiment. Up to 105 coincidences were recorded during a second run in 2006.  相似文献   
992.
993.
We describe the relationship between the fuzzy sets and the algebraic hyperstructures. In fact, this paper is a continuation of the ideas presented by Davvaz in (Fuzzy Sets Syst., 117: 477- 484, 2001) and Bhakat and Das in (Fuzzy Sets Syst., 80: 359-368, 1996). The concept of the quasicoincidence of a fuzzy interval value with an interval-valued fuzzy set is introduced and this is a natural generalization of the quasi-coincidence of a fuzzy point in fuzzy sets. By using this new idea, the concept of interval-valued (α,β)-fuzzy sub-hypermodules of a hypermodule is defined. This newly defined interval-valued (α,β)-fuzzy sub-hypermodule is a We shall study such fuzzy sub-hypermodules and sub-hypermodules of a hypermodule. generalization of the usual fuzzy sub-hypermodule. consider the implication-based interval-valued fuzzy  相似文献   
994.
We prove that for any given c, 1 < c < 17/11, almost all natural numbers are representable in the form [x c] + [p c], where x is a natural number and p is a prime.  相似文献   
995.
A six level rate equation system was used to investigate the impact of photodepletion to amplified spontaneous emission (ASE) of intramolecular proton-transfer (IPT) dyes incorporated into polymeric hosts. The model includes the most important transitions for the normal and tautomer form of the molecule as well as intersystem crossing and triplet–triplet transitions. The experimentally observed pulse shape as well as photodepletion phenomena, i.e. a first order exponential decay of the ASE intensity and a shortening in ASE pulse width, have been simulated successfully. Additionally, the model was used to propose an explanation of the unexpected high photodepletion of proton-transfer dyes in solids. The results show that the emission cross section and reabsorption cross section of the tautomer form of the molecule are the most important parameter not only for efficiency but also for photodepletion. The model was tested by comparison with experimental results of 2-(2’-hydroxyphenyl)benzimidazole in polymethylmethacrylate (PMMA), polystyrene (PS) and a 1:1 alternating copolymer matrix PS-co-PMMA. PACS 78.45.th; 42.55.Mv; 42.70.Jk  相似文献   
996.
In this paper we prove four new (infinite) lists of quadratic inequalities, and four cubic inequalities, for the flag f-vectors of 4-polytopes. These extend and supplement the only four currently known non-linear inequalities, which were proved by Bayer in 1987. The new lists of inequalities for flag f-vectors yield new lists of inequalities for f-vectors of 4-polytopes. Using the latter, we managed to improve an estimate discovered by Hoppner and Ziegler concerning upper bounds of f1 in terms of f0 and f3.  相似文献   
997.
998.
999.
1000.
    
  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