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   1081篇
  免费   11篇
  国内免费   5篇
化学   552篇
晶体学   1篇
力学   14篇
数学   116篇
物理学   414篇
  2022年   7篇
  2021年   7篇
  2020年   9篇
  2019年   10篇
  2018年   6篇
  2016年   8篇
  2015年   8篇
  2014年   14篇
  2013年   48篇
  2012年   45篇
  2011年   42篇
  2010年   34篇
  2009年   26篇
  2008年   44篇
  2007年   37篇
  2006年   59篇
  2005年   54篇
  2004年   43篇
  2003年   39篇
  2002年   37篇
  2001年   31篇
  2000年   36篇
  1999年   21篇
  1998年   21篇
  1997年   13篇
  1996年   28篇
  1995年   18篇
  1994年   21篇
  1993年   29篇
  1992年   28篇
  1991年   12篇
  1990年   14篇
  1989年   9篇
  1988年   17篇
  1987年   13篇
  1986年   9篇
  1985年   12篇
  1984年   16篇
  1983年   8篇
  1982年   15篇
  1981年   6篇
  1980年   12篇
  1979年   7篇
  1978年   11篇
  1977年   6篇
  1976年   10篇
  1975年   14篇
  1973年   8篇
  1972年   6篇
  1968年   6篇
排序方式: 共有1097条查询结果,搜索用时 125 毫秒
91.
There is a need to bring methods to bear on public problems that are inclusive, analytic, and quick. This paper describes the efforts of three pairs of academics working from three different though complementary theoretical foundations and intervention backgrounds (ie ways of working) who set out together to meet this challenge. Each of the three pairs had conducted dozens of interventions that had been regarded as successful or very successful by the client groups in dealing with complex policy and strategic problems. One approach focused on leadership issues and stakeholders, another on negotiating competitive strategic intent with attention to stakeholder responses, and the third on analysis of feedback ramifications in developing policies. This paper describes the 10-year longitudinal research project designed to address the above challenge. The important outcomes are reported: the requisite elements of a general integrated approach and the enduring puzzles and tensions that arose from seeking to design a wide-ranging multi-method approach.  相似文献   
92.
Rayleigh's principle states that the smallest eigenvalue of a regular Sturm-Liouville problem with regular boundary conditions is the minimum value of a certain functional, the so-called Rayleigh quotient, and that this value is attained at the corresponding eigenfunctions only. This can be proved by advanced methods. However, there is an elementary proof, which is presented in this note.  相似文献   
93.
94.
Timothy D. Andersen  Chjan C. Lim 《PAMM》2007,7(1):1101505-1101506
Negative specific heat is a dramatic phenomenon where processes decrease in temperature when adding energy. It has been observed in gravo-thermal collapse of globular clusters. We now report finding this phenomenon in bundles of nearly parallel, periodic, single-sign generalized vortex filaments in the electron magnetohydrodynamic (EMH) model for the unbounded plane under strong magnetic confinement. We derive the specific heat using a steepest descent method and a mean field property. Our derivations show that as temperature increases, the overall size of the system increases exponentially and the energy drops. The implication of negative specific heat is a runaway reaction, resulting in a collapsing inner core surrounded by an expanding halo of filaments. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
95.
We propose an operational degree of polarization in terms of the variance of the Stokes vector minimized over all the directions of the Poincaré sphere. We examine the properties of this second-order definition and carry out its experimental determination. Quantum states with the same standard (first-order) degree of polarization are correctly discriminated by this new measure. We argue that a comprehensive quantum characterization of polarization properties requires a whole hierarchy of higher-order degrees.  相似文献   
96.

We formulate and prove a topological Paley-Wiener theorem for the normalized spherical Laplace transform defined on the rank 1 causal symmetric spaces , for .

  相似文献   

97.
A (p, q, x)-latin rectangle is a rectangular matrix with x symbols in each cell such that each symbol occurs at most p times in each row and at most q times in each column. We exploit the close correspondence between (p, q, x)-latin rectangles and equitable edge-colourings of certain graphs. This paper contains results on existence and various forms of decomposition of such rectangles. In a sequel paper embedding is considered.  相似文献   
98.
99.
For the first time, we demonstrate here functional magnetic resonance imaging (fMRI) using intermolecular multiple-quantum coherences (iMQCs). iMQCs are normally not observed in liquid-state NMR because dipolar interactions between spins average to zero. If the magnetic isotropy of the sample is broken through the use of magnetic field gradients, dipolar couplings can reappear, and hence iMQCs can be observed. Conventional (BOLD) fMRI measures susceptibility variations averaged over each voxel. In the experiment performed here, the sensitivity of iMQCs to frequency variations over mesoscopic and well-defined distances is exploited. We show that iMQC contrast is qualitatively and quantitatively different from BOLD contrast in a visual stimulation task. While the number of activated pixels is smaller in iMQC contrast, the intensity change in some pixels exceeds that of BOLD contrast severalfold.  相似文献   
100.
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