全文获取类型
收费全文 | 611篇 |
免费 | 103篇 |
国内免费 | 144篇 |
专业分类
化学 | 647篇 |
晶体学 | 23篇 |
力学 | 17篇 |
综合类 | 8篇 |
数学 | 34篇 |
物理学 | 129篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 20篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 18篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 39篇 |
2013年 | 61篇 |
2012年 | 54篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 30篇 |
2003年 | 40篇 |
2002年 | 87篇 |
2001年 | 197篇 |
2000年 | 32篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 7篇 |
1959年 | 1篇 |
排序方式: 共有858条查询结果,搜索用时 203 毫秒
741.
本文应用SAXS与微机模型拟合(MCMI)研究了S-LB(S为芪唑盐)薄膜与SA-LB(SA为芪唑盐/花生酸镉)薄膜的微观结构与超分子结构,以及这类LB薄膜凝聚态不稳定的原因.结果指出;第一,从π-A.曲线可知,S与A的脂肪链可以类似于脂肪酸晶胞形成二维类晶系结构;第二,随着分子比R_M=S/A=0到l,S和A之间发生了从分散相至连续相的相逆转;第三,S在二维类晶系中处于不稳定的近似伸直型的高能态构象,然而,哑铃形的芪唑基类似于芪趋向于作倾斜状密堆砌,S的两条脂肪链则倾向于转变为稳定的全反式燕尾形的低能态构象,仅占S分子长约2/3的脂肪链亦降低子S分子间与S-A分子间的凝聚力,这就导致了S连续相的二维类晶系存在大量晶格缺陷,故只能形成4~6层不稳定的Y型LB薄膜;第四,存放一月后,这种不稳定的S连续相的层状超分子结构极易破坏和崩塌. 相似文献
742.
Wei WANG Guang Ming XIA Gui Bao XU Zhi Qiang LIU Qi FANG* State Key Laboratory of Crystal Materials Shandong University Jinan School of Chemistry Chemical Engineering Jinan University Jinan 《中国化学快报》2005,16(1):85-88
Organic molecules that can simultaneously absorb two or more photons in reaching theirexcited states have recently been the subject in various photon-electronic fields. Tomeet the criteria for various nonlinear optical applications, such as three-dimensionaloptical storage1 and up-converted lasing2, molecules with large two-photon absorption(TPA) cross-section σ are required and have been synthesized. These dyes generallybelong to the structural modes of D-π-D, A-π-A3 or D-π-A, where D… 相似文献
743.
Xiwei LIU~* Tianping CHEN~ 《数学年刊B辑(英文版)》2007,28(6):737-746
In this paper,the authors investigate the synchronization of an array of linearly coupled identical dynamical systems with a delayed coupling.Here the coupling matrix can be asymmetric and reducible.Some criteria ensuring delay-independent and delay- dependent global synchronization are derived respectively.It is shown that if the coupling delay is less than a positive threshold,then the coupled network will be synchronized.On the other hand,with the increase of coupling delay,the synchronization stability of the network will be restrained,even eventually de-synchronized. 相似文献
744.
The Existence and Long-Time Behavior of Weak Solution to Bipolar Quantum Drift-Diffusion Model 总被引:1,自引:0,他引:1 下载免费PDF全文
Xiuqing CHEN~* Li CHEN~ 《数学年刊B辑(英文版)》2007,28(6):651-664
The authors study the existence and long-time behavior of weak solutions to the bipolar transient quantum drift-diffusion model,a fourth order parabolic system.Using semi-discretization in time and entropy estimate,the authors get the global existence of nonnegative weak solutions to the one-dimensional model with nonnegative initial and homogenous Neumann(or periodic)boundary conditions.Furthermore,by a logarithmic Sobolev inequality,it is proved that the periodic weak solution exponentially approaches its mean value as time increases to infinity. 相似文献
745.
Yan Jing SU Xiong Hui WEI* Department of Applied Chemistry College of Chemistry Molecular Engineering Peking University Beijing 《中国化学快报》2006,17(5):691-694
Several benzo[c]phenanthridine alkaloids (BPA) were found in plants of Caprifoliaceae, Fumariaceae, Meliaceae, Papaveraceae, and Ruracea families1. BPA represent a group of natural products, exhibiting multiple pharmacological properties and biological ac… 相似文献
746.
Chao Zhan WANG Jiang Feng LIU Xin Du GENG* Institute of Modern Separation Science Key Laboratory of Separation Science in Shanxi Province Northwest University Xi''''an 《中国化学快报》2005,16(3):389-392
Human granulocyte colony-stimulating factor (hG-CSF), a single chain polypeptidecontaining 174 amino acid residues (MW=18,800, pI=6.1), is one of the hemopoieticgrowth factors which plays an important role in stimulating proliferation, differentiation,and functional activation of bloodcells1. It contains a free cysteine at position 17 andtwo intramolecular disulfide bonds, Cys36-Cys42 and Cys64-Cys74, and the two disulfidebonds in G-CSF molecule are both required for its bioactivity2. Wh… 相似文献
747.
Ying Hong WANG Kai Sheng HUANG Mao LIN* Institute of Materia Medica Chinese Academy of Medical Sciences Peking Union Medical College Beijing 《中国化学快报》2000,11(12)
Continuous investigation on oligostilbenes from the lianas of Gnetum hainanense resulted in the isolation of a new rhapontigenin dimer, Gnetuhainin P (1), in addition to the dimers of resveratrol and oxyresveratrol reported previously1. Gnetuhainin P (1) was obtained as a yellowish amorphous powder, [(]25D +6.6 (c 0.092, MeOH). The high resolution FABMS m/z 533.1866 [M+H]+ gave a molecular formula of C30H28O9 (C30H29O9 requires 533.1812), which corresponds to a isorhapontigenin dimer. … 相似文献
748.
Peng DIAO Min GUO Ru Ting TONG* Department of Chemistry Hebei Teacher''''s University Shijiazhuang Department of Traditional Chinese Pharmacy Traditional Chinese Medicine College Hebei Medical University Shijiazhuang 《中国化学快报》2000,11(12)
Interest in the properties of organized monolayers has grown enormously in recent years because these monolayers can provide a means to control the interface at a molecular level1. The self-assemblies of alkanethiols and their derivatives were probably the most intensively studied due to their stability, well-packed structure, ease in preparation, and flexibility in designing the tail group2. The adsorption kinetics of thiol monolayer has been studied by using several techniques, including con… 相似文献
749.
Xiao Mei WANG Qi FANG Chun WANG Guang Yong ZHOU Yan REN Min Hua JIANG* State key laboratory of Crystal Materials Shandong University Jinan 《中国化学快报》2001,(1)
Two-photon absorption (TPA) occurs through the simultaneous absorption of two photons via virtual states in a medium. Materials with large TPA cross section are gaining increasing attention recently due to their potential applications in optical data storage, two-photon up-converted lasing, two-photon-laser scanning fluorescence microscopy, optical power limiting and photodynamic therapy1-3. Numerous organic compounds have been investigated both experimentally and theoretically in order to u… 相似文献
750.
Ya Ping WANG Lu Ling WU Xiang HUANG* College of Chemical Engineering Zhejiang University of Technology Hangzhou Department of Chemistry Zhejiang University Xixi Campus Hangzhou 《中国化学快报》2001,(1)
Conjugated dienes are valuable intermediates in organic chemistry. Many biologically active compounds occurring in nature possess the structural skeleton of conjugated dienes such as chillea amide1 and pelltoine2. Besides, the synthesis of conjugated dienes for use in the Diels-Alder reaction is still an important challenge in organic synthesis. One particularly attractive approach has been the incorporation of heteroatom substituents that can activate the diene3.Recently, we found that β-br… 相似文献