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   560篇
  免费   1篇
  国内免费   2篇
化学   296篇
晶体学   7篇
力学   15篇
数学   34篇
物理学   211篇
  2020年   3篇
  2018年   4篇
  2014年   5篇
  2013年   27篇
  2012年   9篇
  2011年   17篇
  2010年   14篇
  2009年   9篇
  2008年   20篇
  2007年   19篇
  2006年   17篇
  2005年   21篇
  2004年   25篇
  2003年   10篇
  2002年   12篇
  2001年   15篇
  2000年   12篇
  1999年   14篇
  1998年   13篇
  1997年   3篇
  1996年   12篇
  1995年   10篇
  1994年   11篇
  1993年   11篇
  1992年   13篇
  1991年   11篇
  1990年   10篇
  1989年   7篇
  1988年   7篇
  1987年   8篇
  1986年   6篇
  1985年   28篇
  1984年   15篇
  1983年   7篇
  1982年   11篇
  1981年   7篇
  1980年   11篇
  1979年   9篇
  1978年   9篇
  1977年   6篇
  1976年   10篇
  1975年   13篇
  1974年   11篇
  1973年   9篇
  1972年   7篇
  1971年   3篇
  1970年   3篇
  1969年   3篇
  1968年   3篇
  1937年   3篇
排序方式: 共有563条查询结果,搜索用时 0 毫秒
101.
Abstract We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management.  相似文献   
102.
Synchrotron x-ray diffraction is used to compare the misfit strain and composition in a self-organized nanowire array in an InAs/GaSb superlattice with InSb interfacial bonds to a planar InAs/GaSb superlattice with GaAs interfacial bonds. It is found that the morphological instability that occurs in the nanowire array results from the large misfit strain that the InSb interfacial bonds have in the nanowire array. Based on this result, we propose that tailoring the type of interfacial bonds during the epitaxial growth of III-V semiconductor films provides a novel approach for producing the technologically important morphological instability in anomalously thin layers.  相似文献   
103.

Background  

Fully functional HIV-1-specific CD8 and CD4 effector T-cell responses are vital to the containment of viral activity and disease progression. These responses are lacking in HIV-1-infected patients with progressive disease. We attempted to augment fully functional HIV-1-specific CD8 and CD4 effector T-cell responses in patients with advanced chronic HIV-1 infection.  相似文献   
104.
105.
106.
107.
Though molecular simulation of proteins has made notable contributions to the study of protein folding and kinetics, disagreement between simulation and experiment still exists. One of the criticisms levied against simulation is its failure to reproduce cooperative protein folding transitions. This weakness has been attributed to many factors such as a lack of polarizability and adequate capturing of solvent effects. This work, however, investigates how increasing the number of proteins simulated simultaneously can affect the cooperativity of folding transitions--a topic that has received little attention previously. Two proteins are studied in this work: phage T4 lysozyme (Protein Data Bank (PDB) ID: 7LZM) and phage 434 repressor (PDB ID: 1R69). The results show that increasing the number of proteins molecules simulated simultaneously leads to an increase in the macroscopic cooperativity for transitions that are inherently cooperative on the molecular level but has little effect on the cooperativity of other transitions. Taken as a whole, the results identify one area of consideration to improving simulations of protein folding.  相似文献   
108.
We report a new approach to investigating the mechanisms of fast peptide cation-radical dissociations based on an analysis of time-resolved reaction progress by Ehrenfest dynamics, as applied to an Ala-Arg cation-radical model system. Calculations of stationary points on the ground electronic state that were carried out with effective CCSD(T)/6-311++G(3df,2p) could not explain the experimental branching ratios for loss of a hydrogen atom, ammonia, and N–Cα bond dissociation in (AR + 2H)+●. The Ehrenfest dynamics results indicate that the ground and low-lying excited electronic states of (AR + 2H)+● follow different reaction courses in the first 330 femtoseconds after electron attachment. The ground (X) state undergoes competing loss of N-terminal ammonia and isomerization to an aminoketyl radical intermediate that depend on the vibrational energy of the charge-reduced ion. The A and B excited states involve electron capture in the Arg guanidine and carboxyl groups and are non-reactive on the short time scale. The C state is dissociative and progresses to a fast loss of an H atom from the Arg guanidine group. Analogous results were obtained by using the B3LYP and CAM-B3LYP density functionals for the excited state dynamics and including the universal M06-2X functional for ground electronic state calculations. The results of this Ehrenfest dynamics study indicate that reaction pathway branching into the various dissociation channels occurs in the early stages of electron attachment and is primarily determined by the electronic states being accessed. This represents a new paradigm for the discussion of peptide dissociations in electron based methods of mass spectrometry.  相似文献   
109.
Sociology and Social Theory in Agent Based Social Simulation: A Symposium   总被引:2,自引:0,他引:2  
A lengthy and intensive debate about the role of sociology in agent based social simulation dominated the email list simsoc@jiscmail.ac.uk during the autumn of 2000. The debate turned on the importance of models being devised to capture the properties of whole social systems and whether those properties should determine agent behaviour or, conversely, whether the properties of social systems should emerge from the behaviour and interaction of the agents and, if so, how that emergence should be represented. The positions of four of the main protagonists concerned specifically with the modelling issues are reprised and extended in this symposium.  相似文献   
110.
ANKA is a relatively new synchrotron radiation facility at the Forschungszentrum Karlsruhe, a large government research center in the southwest of Germany. The acronym stands for Angstrom Source Karlsruhe. The electron storage ring is 110.4 m in circumference and stores a 2.5 GeV electron beam at a typical current of 200 mA. The facility has been open for users since March 2003.  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