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   36587篇
  免费   1412篇
  国内免费   45篇
化学   24907篇
晶体学   288篇
力学   690篇
数学   5294篇
物理学   6865篇
  2023年   284篇
  2022年   204篇
  2021年   416篇
  2020年   585篇
  2019年   547篇
  2018年   780篇
  2017年   713篇
  2016年   1357篇
  2015年   1115篇
  2014年   1123篇
  2013年   2322篇
  2012年   2594篇
  2011年   2759篇
  2010年   1627篇
  2009年   1334篇
  2008年   2297篇
  2007年   2274篇
  2006年   2018篇
  2005年   1817篇
  2004年   1481篇
  2003年   1102篇
  2002年   1015篇
  2001年   754篇
  2000年   667篇
  1999年   486篇
  1998年   371篇
  1997年   276篇
  1996年   409篇
  1995年   270篇
  1994年   281篇
  1993年   313篇
  1992年   289篇
  1991年   218篇
  1990年   195篇
  1989年   188篇
  1988年   167篇
  1987年   170篇
  1986年   163篇
  1985年   217篇
  1984年   187篇
  1983年   152篇
  1982年   139篇
  1981年   148篇
  1980年   103篇
  1979年   135篇
  1978年   117篇
  1977年   104篇
  1976年   119篇
  1975年   100篇
  1973年   117篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
1.
Applications of Mathematics - Proper traffic simulation of electric vehicles, which draw energy from overhead wires, requires adequate modeling of traction infrastructure. Such vehicles include...  相似文献   
2.
Set-Valued and Variational Analysis - R. Tyrell Rockafellar and his collaborators introduced, in a series of works, new regression modeling methods based on the notion of superquantile (or...  相似文献   
3.
Archiv der Mathematik - In this note, we introduce a criterion to detect vanishing of essential algebras of a Green biset functor by means of morphisms. We introduce the inflation morphism and...  相似文献   
4.
Set-Valued and Variational Analysis - The production correspondence associated with a technology maps every input vector into the set of output vectors that may be obtained by means of those...  相似文献   
5.
6.
Central European Journal of Operations Research - The paper deals with the analysis of the empirical distribution of returns of selected market indices of developed and developing markets in...  相似文献   
7.
Cedrela genus, a member of the Meliaceae family, presents both chemical characteristics associated with and those that distinguish it from the rest of its members. The presence of triterpenes and limonoids is the characteristic of the Meliaceae family, but the class and type of these chemical constituents are distinctive for each genus. Cedrela includes cycloartane, ursane, oleanane, tirucallane, butyrospermane, and apotirucallane triterpenes, and its limonoids belongs to six class and nine types, known as class Ia-type havanensines, class Ib-type delevoyin, class II-type gedunin, class IIIb-type andirobin, class IIIg-type mexicanolide, class IVa-type evoludone, class Va-type obacunol, class V-type limonin, and class VIII. Each of these structural arrangements includes specific traits, defined by their biosynthetic origin, which can be established by means of structural elucidation techniques, particularly 1H and 13C NMR, which assisted by 2D NMR techniques, allowing to deduce their structures unequivocally. The constant presence of these skeletal arrangements in Cedrela ensures that they are its chemophenetic markers and their recurrence is an important criterion for their identity. This review is a compilation of the occurrence of triterpenes and limonoids in Cedrela genus, detailing their biosynthetic association and collecting and organizing their NMR data, with the purpose of facilitating its location, analysis, and use in the phytochemical study of species from this genus.  相似文献   
8.
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.  相似文献   
9.
Journal of Solid State Electrochemistry - A study of poly(3-hexylthiophene) (P3HT) thin films by spin-coating process, deposited on conducting glass substrates of fluorine-doped tin oxide (FTO), is...  相似文献   
10.
Journal of Analytical Chemistry - Polycyclic aromatic hydrocarbons (PAHs) can be extremely hazardous to human health due to their carcinogenicity and toxicity. Following mother exposure, a part of...  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