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   2558篇
  免费   103篇
  国内免费   7篇
化学   1976篇
晶体学   7篇
力学   34篇
数学   342篇
物理学   309篇
  2023年   16篇
  2022年   19篇
  2021年   32篇
  2020年   51篇
  2019年   56篇
  2018年   26篇
  2017年   32篇
  2016年   77篇
  2015年   84篇
  2014年   89篇
  2013年   138篇
  2012年   142篇
  2011年   178篇
  2010年   119篇
  2009年   85篇
  2008年   148篇
  2007年   158篇
  2006年   131篇
  2005年   125篇
  2004年   118篇
  2003年   85篇
  2002年   91篇
  2001年   50篇
  2000年   47篇
  1999年   36篇
  1998年   49篇
  1997年   39篇
  1996年   34篇
  1995年   48篇
  1994年   44篇
  1993年   46篇
  1992年   27篇
  1991年   33篇
  1990年   23篇
  1989年   20篇
  1988年   12篇
  1987年   14篇
  1986年   10篇
  1985年   21篇
  1984年   19篇
  1983年   11篇
  1982年   7篇
  1981年   8篇
  1980年   12篇
  1979年   7篇
  1978年   10篇
  1977年   11篇
  1975年   4篇
  1973年   12篇
  1972年   3篇
排序方式: 共有2668条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
This experiment investigates the effect of images of differently colored sports cars on the loudness of a simultaneously perceived car sound. Still images of a sports car, colored in red, light green, blue, and dark green, were displayed to subjects during a magnitude estimation task. The sound of an accelerating sports car was used as a stimulus. Statistical analysis suggests that the color of the visual stimulus may have a small influence on loudness judgments. The observed loudness differences are generally equivalent to a change in sound level of about 1 dB, with maximum individual differences of up to 3 dB.  相似文献   
55.
56.
57.
The use of a common set of basis functions for design and analysis is the main paradigm of isogeometric analysis. The characteristics of the commonly used non-uniform rational B-splines (NURBS) surfaces require methods to handle non-conforming meshes to attain an efficient computational framework. The isogeometric mortar method uses constrained approximation spaces to enforce a coupling of deformations at the interface between patches in a weak manner. This method neither requires additional degrees of freedom nor the choice of empirical parameters. The main drawback of the standard isogeometric mortar approach is the non-local support of the mortar basis functions along the interface. This yields a large number of nodes per element for elements adjacent to the interface. Thus, the computational costs increase significantly for mesh refinement. This issue is remedied by the use of dual basis functions for the mortar method, which is referred to as dual mortar method. In this contribution several choices for the dual basis functions for B-splines are proposed and compared. A special focus is set on the support of the dual basis functions and on the support of the resulting mortar basis functions. Numerical examples show the influence of the choice for the dual basis functions on the accuracy of the global stress distribution, on the fulfillment of the interface conditions and on numerical efficiency. The use of approximate dual basis functions is shown to be competitive to computations of conforming meshes in terms of accuracy and efficiency. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
58.
Summary. We derive globally convergent multigrid methods for discrete elliptic variational inequalities of the second kind as obtained from the approximation of related continuous problems by piecewise linear finite elements. The coarse grid corrections are computed from certain obstacle problems. The actual constraints are fixed by the preceding nonlinear fine grid smoothing. This new approach allows the implementation as a classical V-cycle and preserves the usual multigrid efficiency. We give estimates for the asymptotic convergence rates. The numerical results indicate a significant improvement as compared with previous multigrid approaches. Received March 26, 1994 / Revised version received September 22, 1994  相似文献   
59.
Ternary Thallium Indium Sulfides: A Summary Combined thermal and X-Ray analyses in the ternary system Thallium—Indium—Sulfur show, that the two binary sections Tl2S? In2S3 and TlS? InS contain ternary compounds with unique crystal structures. The chemical formulas of these ternary solids are TlIn5S8, TlIn3S5, TlInS2 and Tl3InS3 for the section Tl2S? In2S3 and TlIn5S6 as well as Tl3In5S8 (metastable high temperature phase) for the section TlS? InS respectively. With TlIn5S7 an additional ternary solid could be detected, which is located outside the two sections. It is derived from the binary mixed valence compound In6S7 by complete substitution of In+ by Tl+. The following ionic formulations make the mixed valence character of the ternary Thallium—Indium-Sulfides reasonable: TlIn5S8 = Tl+(In3+)5(S2?)8, TlIn3S5 = Tl+ (In3+)3(S2?)5, TlInS2 = Tl+In3+(S2?)2, Tl3InS3 = (Tl+)3In3+ · (S2?)3, TlIn5S6 = Tl+([In2]4+)2In3+ (S2?)6, Tl3In5S8 = 4 × [(Tl+)0,75 · (In+)0,25In3+(S2?)2], TlIn5S7 = Tl+[In2]4+ (In3+)3(S2?)7. All compounds contain Tl+-ions in a characteristic “lone pair coordination” of S2? ions. Indium atoms however occur with the oxidation numbers +2 (formal, In2 dumb bells with covalent In? In bonding) and +3 (with In3+ in tetrahedral and octahedral coordination of S2?). Chemical preparation, crystal chemistry and general properties of the ternary solids are discussed, summarized and compared to each other.  相似文献   
60.
An important class of red fluorescent proteins (RFPs) feature a 2-iminomethyl-5-(4-hydroxybenzylidene)imidazolinone chromophore. Among these proteins, eqFP611 has the chromophore in a coplanar trans orientation, whereas the cis isomer is preferred by other RFPs such as DsRed and its variants. In the photoactivatable protein asFP595, the chromophore can even be switched from the nonfluorescent trans to the fluorescent cis state by light. By using X-ray crystallography, we have determined the structure of dimeric eqFP611 at high resolution (up to 1.1 A). In the far-red emitting eqFP611 variant d2RFP630, which carries an additional Asn143Ser mutation, the chromophore resides predominantly (approximately 80%) in the cis isomeric state, and in RFP639, which has Asn143Ser and Ser158Cys mutations, the chromophore is found completely in the cis form. The pronounced red shift of excitation and emission maxima of RFP639 can thus unambiguously be assigned to trans-cis isomerization of the chromophore. Among RFPs, eqFP611 is thus unique because its chromophore is highly fluorescent in both the cis and trans isomeric forms.  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