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   1503篇
  免费   65篇
  国内免费   8篇
化学   1003篇
晶体学   14篇
力学   30篇
数学   295篇
物理学   234篇
  2023年   12篇
  2022年   51篇
  2021年   72篇
  2020年   59篇
  2019年   68篇
  2018年   66篇
  2017年   58篇
  2016年   86篇
  2015年   68篇
  2014年   72篇
  2013年   88篇
  2012年   121篇
  2011年   113篇
  2010年   67篇
  2009年   54篇
  2008年   65篇
  2007年   48篇
  2006年   59篇
  2005年   49篇
  2004年   36篇
  2003年   34篇
  2002年   23篇
  2001年   14篇
  2000年   7篇
  1999年   9篇
  1998年   4篇
  1997年   5篇
  1996年   9篇
  1995年   9篇
  1994年   11篇
  1993年   4篇
  1992年   6篇
  1991年   3篇
  1990年   9篇
  1989年   6篇
  1988年   6篇
  1987年   4篇
  1986年   13篇
  1985年   6篇
  1984年   6篇
  1983年   6篇
  1982年   9篇
  1981年   12篇
  1980年   12篇
  1979年   4篇
  1978年   3篇
  1977年   3篇
  1976年   7篇
  1975年   6篇
  1972年   5篇
排序方式: 共有1576条查询结果,搜索用时 15 毫秒
101.
We propose commutation relations for a single mode -deformed para-Bose oscillator. In this new deformation of para-Bose statistics the distribution function has the same form as in the para-Bose statistics. Furthermore, we show analogies between the coherent states of -deformed and q-deformed para-Bose statistics.  相似文献   
102.
We have carried out the study on the isomeric ratios in (γ,p) photonuclear reactions with isotopes 40 92 Zr and 74 183 W in the giant dipole resonance (GDR) region. The targets were irradiated with bremsstrahlungs produced by electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia. Spectra of the irradiated samples were measured with a spectroscopic system consisting of 8192-channel analyzer CANBERRA and high-energy resolution semiconductor detector CANBERRA. The results were discussed and compared with those of other authors. The text was submitted by the authors in English.  相似文献   
103.
Tithonia tagetiflora Desv. (Asteraceae) is a widespread plant in Vietnam, and the species of Tithonia are known as plants containing many biologically active compounds. However, T. tagetiflora's chemical composition remains mostly unknown. Therefore, we now report the structural elucidation of two new sesquiterpene lactones, 8‐angeloyloxy‐2,14‐epoxygermacra‐4,10(1),11(13)‐trien‐6,12‐olide (1) and 6‐angeloyloxy‐1‐hydroxy‐3,4‐epoxygermacra‐9,11(13)‐dien‐8,12‐olide (2), together with three known compounds, including two norisoprenoids, (6S,9S)‐vomifoliol or (6R,9R)‐vomifoliol (3) and (6S,9S)‐roseoside (4), and one glutinane type triterpene, epi‐glutinol (5), from the leaves of T. tagetiflora. Their structures are established by 1D and 2D NMR spectroscopy, as well as ESI‐MS analysis and comparison with literature data. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
104.
Abstract

After a pressure cycle to 30 GPa, benzene transforms to a white solid which can be recovered at ambient. Results obtained from infrared spectroscopy and other physico-chemical methods show that the recovered solid is a highly cross-linked polymer. The molecular structure of benzene is very likely completely altered by the transformation.  相似文献   
105.
Polymers containing hydrolytically labile trialkylsilyl ester side groups were synthesised via a conventional and a controlled radical polymerization. The trialkylsilyl methacrylate monomer unit was chosen for its capacity to hydrolyse into basic, acid or sea water varying the hydrophilic character of the resulting polymer backbone with time. The hydrolysis or saponification reaction of the ester bond of the trialkylsilyl methacrylate was monitored through a 1H NMR study showing the formation of siloxane side-products. Several copolymers and polymer blends were prepared as matrixes for controlled erodible systems. Their capacity to hydrolyse was demonstrated through SEM investigations with selective dissolution of free films containing hydrolysable copolymers and PMMA blends. Well-defined random and diblock copolymers with methyl methacrylate were investigated to show the effect of the microstructure on the erosion properties of the corresponding coatings. Poly(methyl methacrylate-b-tert-butyldimethylsilyl methacrylate) diblock copolymers synthesised through the RAFT process showed a better control of the erosion with a constant erosion rate over a long-time service in sea water at pH = 8.2. In addition, experiments showed that the erosion rate could be modulated by varying the molar proportion of hydrolysable side groups onto the copolymer backbone and the weight amount of copolymers mixed with PMMA in toluene solution.  相似文献   
106.
The monoterpene (−)-isopulegol (7) has been used as a starting material for the total synthesis in eight/nine steps of two sesquiterpenes which were recently isolated from the medicinal plant Fabiana imbricata. Use of this approach has shown that a structure proposed as 3,11-amorphadiene (3) should be revised to that of 4,11-cadinadiene (18) and confirmed the structure proposed for the natural product 4-amorphen-1 1-ol (1).  相似文献   
107.
108.
The seconds living mercury isotopes have been isolated from nuclear reaction products arising in the bombardment of 147Sm target with 40Ar ions at the U-400 cyclotron of JINR-Dubna.  相似文献   
109.
This article shows that finite-dimensional multiplier rules, which are based on the limiting subdifferential, can be proved by Ekeland's variational principle and some basic calculus tools of the generalized differentiation theory introduced by B. S. Mordukhovich. Consequences of a limiting constraint qualification, which yields the normal form of the multiplier rules, stability and calmness of optimization problems, are investigated in detail.  相似文献   
110.
An air-tolerant Cu-catalyzed sulfonylative Hiyama cross-coupling reaction enabling the formation of diaryl sulfones is described. Starting from aryl silanes, DABSO and aryliodides, the reaction tolerates a large variety of polar functional groups (amines, ketones, esters, aldehydes). Control experiments coupled with DFT calculations shed light on the mechanism, characterized by the formation of a Cu(I)-sulfinate intermediate via fast insertion of a SO2 molecule.  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