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   737篇
  免费   13篇
  国内免费   2篇
化学   398篇
晶体学   9篇
力学   71篇
数学   113篇
物理学   161篇
  2022年   5篇
  2021年   8篇
  2020年   7篇
  2018年   10篇
  2017年   6篇
  2016年   11篇
  2015年   9篇
  2014年   13篇
  2013年   64篇
  2012年   24篇
  2011年   33篇
  2010年   15篇
  2009年   19篇
  2008年   22篇
  2007年   33篇
  2006年   24篇
  2005年   21篇
  2004年   21篇
  2003年   9篇
  2002年   23篇
  2001年   10篇
  2000年   11篇
  1999年   18篇
  1998年   9篇
  1997年   5篇
  1996年   15篇
  1995年   10篇
  1994年   10篇
  1993年   11篇
  1992年   13篇
  1991年   8篇
  1990年   10篇
  1989年   11篇
  1988年   8篇
  1987年   10篇
  1986年   10篇
  1985年   15篇
  1984年   15篇
  1983年   15篇
  1982年   10篇
  1981年   9篇
  1980年   9篇
  1979年   11篇
  1977年   8篇
  1976年   18篇
  1975年   15篇
  1974年   13篇
  1973年   11篇
  1972年   5篇
  1971年   10篇
排序方式: 共有752条查询结果,搜索用时 31 毫秒
71.
Positive-mode atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS n ) was tested for the differentiation of regioisomeric aromatic ketocarboxylic acids. Each analyte forms exclusively an abundant protonated molecule upon ionization via positive-mode APCI in a commercial linear quadrupole ion trap (LQIT) mass spectrometer. Energy-resolved collision-activated dissociation (CAD) experiments carried out on the protonated analytes revealed fragmentation patterns that varied based on the location of the functional groups. Unambiguous differentiation between the regioisomers was achieved in each case by observing different fragmentation patterns, different relative abundances of ion-molecule reaction products, or different relative abundances of fragment ions formed at different collision energies. The mechanisms of some of the reactions were examined by H/D exchange reactions and molecular orbital calculations.  相似文献   
72.
Functional biopolymer nanoparticles or microparticles can be formed by heat treatment of globular protein-ionic polysaccharide electrostatic complexes under appropriate solution conditions. These biopolymer particles can be used as encapsulation and delivery systems, fat mimetics, lightening agents, or texture modifiers. This review highlights recent progress in the design and fabrication of biopolymer particles based on heating globular protein-ionic polysaccharide complexes above the thermal denaturation temperature of the proteins. The influence of biopolymer type, protein-polysaccharide ratio, pH, ionic strength, and thermal history on the characteristics of the biopolymer particles formed is reviewed. Our current understanding of the underlying physicochemical mechanisms of particle formation and properties is given. The information provided in this review should facilitate the rational design of biopolymer particles with specific physicochemical and functional attributes, as well as stimulate further research in identifying the physicochemical origin of particle formation.  相似文献   
73.
This review covers selected surfactant ligands that undergo a change in aggregate morphology upon coordination of a metal ion, with a particular focus on coordination-induced micelle-to-vesicle transitions. The surfactants include microbially produced amphiphilic siderophores, as well as synthetic amphiphilic ligands. The mechanism of the metal-induced phase change is considered in light of the coordination chemistry of the metal ions, the nature of the ligands, and changes in molecular geometry that result from metal coordination. Of particular interest are biologically produced amphiphiles that coordinate transition metal ions and amphiphilic ligands of relevance to bioinorganic chemistry.  相似文献   
74.
The addition of H(2) across a transition metal-borane bond is reported for the first time providing a mechanism for recharging borane functional groups to borohydride.  相似文献   
75.
76.
77.
Using Monte Carlo simulations, we have found that there is a surprising non-monotonic dependence of a polymer's diffusion coefficient upon the degree of disorder of the surrounding environment. Starting with a two-dimensional periodic lattice of obstacles, we randomly displace obstacles to create a quenched gel system with a tunable degree of disorder. Very small displacements increase the diffusion coefficient of polymers since they increase the width of the tube through which the polymer chains reptate. As we displace the obstacles further, however, entropic trapping is observed and the diffusion coefficient of the polymer decreases dramatically. This is a striking example of the delicate balance between entropic and frictional effects for a polymer diffusing in a dense system.  相似文献   
78.
In this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles. The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases, and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles.  相似文献   
79.
Microlens arrays and microoptical components in general are integral components in a wide range of high-tech products. The ability to fabricate such elements cheaply and with a high degree of accuracy is vital for the development of the next generation of optics-based technologies. There are currently a wide range of microoptical element fabrication technologies. These techniques all have advantages and disadvantages and no one technique is yet sufficient to meet all possible application criteria. One method that has been examined recently is the ink-jet deposition method. This method applies well-established ink-jet printer technology and is thus one possible candidate for large-scale fabrication of inexpensive components. The lenses fabricated using this method are normally found to have spherical profiles. In this paper, we examine the possibility of modifying the profile of these spherical lenses using an applied electric field (E-field). We note that the resulting aspheric lenses have a wide number of applications. These include beam shaping and power transfer applications including fiber coupling. In this paper we describe initial experiments involving single lenses. The single lenses produced using applied E-Fields differ significantly from lenses produced with no applied E-field.  相似文献   
80.

Background  

The neuronal endoplasmic reticulum (ER) is an extensive, complex endomembrane system, containing Ca2+ pumps, and Ca2+ channels that permit it to act as a dynamic calcium store. Currently, there is controversy over the continuity of the ER in neurones, how this intersects with calcium signalling and the possibility of physical compartmentalisation. Unfortunately, available probes of ER structure such as vital dyes are limited by their membrane specificity. The introduction of ER-targeted GFP plasmids has been a considerable step forward, but these are difficult to express in neurones through conventional transfection approaches. To circumvent such problems we have engineered a novel ER-targeted GFP construct, termed pIN-KDEL, into a 3rd generation replication-defective, self-inactivating lentiviral vector system capable of mediating gene transduction in diverse dividing and post-mitotic mammalian cells, including neurones.  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