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   5871篇
  免费   125篇
化学   3230篇
晶体学   30篇
力学   128篇
数学   1350篇
物理学   1258篇
  2021年   34篇
  2020年   45篇
  2019年   52篇
  2018年   139篇
  2017年   128篇
  2016年   197篇
  2015年   142篇
  2014年   196篇
  2013年   483篇
  2012年   295篇
  2011年   404篇
  2010年   212篇
  2009年   183篇
  2008年   334篇
  2007年   330篇
  2006年   310篇
  2005年   223篇
  2004年   196篇
  2003年   143篇
  2002年   133篇
  2001年   94篇
  2000年   78篇
  1999年   56篇
  1998年   49篇
  1997年   48篇
  1996年   47篇
  1995年   47篇
  1994年   28篇
  1993年   42篇
  1992年   54篇
  1991年   42篇
  1990年   49篇
  1989年   51篇
  1988年   47篇
  1987年   46篇
  1986年   40篇
  1985年   60篇
  1984年   66篇
  1983年   64篇
  1982年   61篇
  1981年   42篇
  1980年   53篇
  1979年   47篇
  1978年   68篇
  1977年   39篇
  1976年   52篇
  1975年   40篇
  1974年   48篇
  1973年   40篇
  1972年   33篇
排序方式: 共有5996条查询结果,搜索用时 15 毫秒
951.
A clique (resp, independent set) in a graph is strong if it intersects every maximal independent set (resp, every maximal clique). A graph is clique intersect stable set (CIS) if all of its maximal cliques are strong and localizable if it admits a partition of its vertex set into strong cliques. In this paper we prove that a clique C in a vertex-transitive graph Γ is strong if and only if ◂=▸◂⋅▸CI=V(Γ) for every maximal independent set I of Γ. On the basis of this result we prove that a vertex-transitive graph is CIS if and only if it admits a strong clique and a strong independent set. We classify all vertex-transitive graphs of valency at most 4 admitting a strong clique, and give a partial characterization of 5-valent vertex-transitive graphs admitting a strong clique. Our results imply that every vertex-transitive graph of valency at most 5 that admits a strong clique is localizable. We answer an open question by providing an example of a vertex-transitive CIS graph which is not localizable.  相似文献   
952.
Nonlinear Dynamics - The presence of time-varying electromagnetic fields across a neuron cell may cause changes in its electrical characteristics, most notably, in the action potential dynamics....  相似文献   
953.
Ordered mesoporous carbon (OMC) was used as an adsorbent for the removal of pertechnetate (TcO4 ?) anion. The maximum uptake (93 %) of TcO4 ? was obtained after 60 min of contact. The adsorption of TcO4 ? is almost pH-independent in very wide pH region (from 4.0 to 10.0). Maximum K d of 6.6 × 103 cmg?1 was found at pH 2.0. TcO4 ? interacts with carboxylic functional groups present at the surface of the OMC by displacing the OH? ions with TcO4 ? via ion exchange mechanism.  相似文献   
954.
955.
The paper considers a statistical concept of causality in continuous time in the filtered probability spaces which is based on the Granger’s definition of causality. The given causality concept is then applied to the solution of the martingale problem (associated with the stochastic differential equation driven with semimartingales). More precisely, we show that the given causality concept is closely connected to the concept of extremality of measures for the solutions of the martingale problem, for the stopped martingale problem and for the local martingale problem. We also show the equivalence between some models of causality and local uniqueness (for the solutions of the martingale problem).  相似文献   
956.
Central European Journal of Operations Research - In this paper, we analyse the company behaviour in duopoly taking into account the most common strategies, including dominant, reactive,...  相似文献   
957.
Abstract

Medicinal plants play an important role in aquaculture as feed additives. This study aimed to investigate effects of alcoholic extract of acorn on growth performance, body composition, digestive enzymes activity and blood biochemical parameters of rainbow trout (O. mykiss) as a commercially important fish. Five dietary treatments were supplemented: 100, 200, 400 and 600?mg.kg?1 of the extract. Fishes were fed twice per day for 8?weeks, and results showed that acorn extract positively affected all investigated parameters in rainbow trout fishes. Digestive enzymes activity and growth performance were increased, while activity of liver enzymes and cortisol were lowed in comparison to control individuals. Body composition of treated animals was also enhanced. Comparison between treated groups together with integrative biomarker response (IBR) values indicated greatest effects in animals fed with 400 and 600?mg.kg?1 of the extract. Positive effects of the acorn represent promising start point for further studies.  相似文献   
958.
959.
Ambient pressure chemical hydrogenation using p-toluene sulfonyl hydrazide (TSH) via thermal diimide formation (N2H2) permitted reduction of double bonds of poly(myrcene) (poly[Myr]) and poly(farnesene) (poly[Far]). Both pendent and backbone double bonds in poly(Myr) (Mn = 56 kg/mol) and poly(Far) (Mn = 62 kg/mol) synthesized by conventional free radical polymerization were hydrogenated to almost completion. Furthermore, TSH semi-batch addition efficiently hydrogenated double bonds, while avoiding undesired autohydrogenation of diimides that occurred in batch mode. Thermal stability improved for hydrogenated poly(Myr) and poly(Far), where temperature at 10% weight loss (T10%) increased from 188 to 404°C for poly(Myr) and from 310 to 379°C for poly(Far). Tgs of poly(Myr) and poly(Far) also increased by about 10–25°C, indicating increased stiffness after hydrogenation. Finally, viscosities of poly(Myr) and poly(Far) were also increased after hydrogenation, and a greater increase was observed for poly(Myr) (by two orders of magnitude from 102 to 104 Pa s) due to its Mn being much higher than its entanglement molecular weight. Poly(Far) viscosity only increased by 1.5 times after hydrogenation (~104 Pa s), comparable to the poly(Myr) after hydrogenation, suggesting unsaturated poly(Far) was more entangled than unsaturated poly(Myr) because of its longer side chains.  相似文献   
960.
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