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   34250篇
  免费   1385篇
  国内免费   37篇
化学   23529篇
晶体学   259篇
力学   628篇
数学   4826篇
物理学   6430篇
  2023年   272篇
  2022年   200篇
  2021年   411篇
  2020年   588篇
  2019年   559篇
  2018年   726篇
  2017年   671篇
  2016年   1322篇
  2015年   1067篇
  2014年   1128篇
  2013年   2242篇
  2012年   2472篇
  2011年   2669篇
  2010年   1535篇
  2009年   1306篇
  2008年   2207篇
  2007年   2167篇
  2006年   1888篇
  2005年   1721篇
  2004年   1369篇
  2003年   1070篇
  2002年   961篇
  2001年   702篇
  2000年   608篇
  1999年   460篇
  1998年   320篇
  1997年   259篇
  1996年   374篇
  1995年   258篇
  1994年   249篇
  1993年   295篇
  1992年   264篇
  1991年   179篇
  1990年   164篇
  1989年   151篇
  1988年   153篇
  1987年   143篇
  1986年   141篇
  1985年   196篇
  1984年   181篇
  1983年   141篇
  1982年   131篇
  1981年   114篇
  1980年   95篇
  1979年   105篇
  1978年   102篇
  1977年   99篇
  1976年   91篇
  1975年   83篇
  1973年   91篇
排序方式: 共有10000条查询结果,搜索用时 18 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.
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.
Kumar  Sanjay  Jiwari  Ram  Mittal  R. C.  Awrejcewicz  Jan 《Nonlinear dynamics》2021,104(1):661-682
Nonlinear Dynamics - In this article, the authors simulate and study dark and bright soliton solutions of 1D and 2D regularized long wave (RLW) models. The RLW model occurred in various fields such...  相似文献   
5.
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   
6.
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.
Numerical Algorithms - In this work, we propose a fractional extension of the one-dimensional nonlinear vibration problem on an elastic string. The fractional problem is governed by a hyperbolic...  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