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   105744篇
  免费   1573篇
  国内免费   386篇
化学   43849篇
晶体学   987篇
力学   7211篇
数学   35341篇
物理学   20315篇
  2023年   251篇
  2022年   173篇
  2021年   348篇
  2020年   505篇
  2019年   461篇
  2018年   10837篇
  2017年   10654篇
  2016年   7087篇
  2015年   1749篇
  2014年   1221篇
  2013年   2269篇
  2012年   5853篇
  2011年   12502篇
  2010年   6768篇
  2009年   6923篇
  2008年   8360篇
  2007年   10462篇
  2006年   1875篇
  2005年   2775篇
  2004年   2690篇
  2003年   2856篇
  2002年   1816篇
  2001年   880篇
  2000年   820篇
  1999年   550篇
  1998年   474篇
  1997年   352篇
  1996年   527篇
  1995年   332篇
  1994年   290篇
  1993年   358篇
  1992年   285篇
  1991年   213篇
  1990年   189篇
  1989年   177篇
  1988年   177篇
  1987年   175篇
  1986年   172篇
  1985年   223篇
  1984年   181篇
  1983年   153篇
  1982年   148篇
  1981年   135篇
  1980年   122篇
  1979年   136篇
  1978年   115篇
  1977年   91篇
  1976年   93篇
  1975年   86篇
  1973年   106篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
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   
3.
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   
4.
5.
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   
6.
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   
7.
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   
8.
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   
9.
10.
CRANAD-2 is a fluorogenic curcumin derivative used for near-infrared detection and imaging in vivo of amyloid aggregates, which are involved in neurodegenerative diseases. We explore the performance of CRANAD-2 in two super-resolution imaging techniques, namely stimulated emission depletion (STED) and single-molecule localization microscopy (SMLM), with markedly different fluorophore requirements. By conveniently adapting the concentration of CRANAD-2, which transiently binds to amyloid fibrils, we show that it performs well in both techniques, achieving a resolution in the range of 45–55 nm. Correlation of SMLM with atomic force microscopy (AFM) validates the resolution of fine features in the reconstructed super-resolved image. The good performance and versatility of CRANAD-2 provides a powerful tool for near-infrared nanoscopic imaging of amyloids in vitro and in vivo.  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