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   6450篇
  免费   227篇
  国内免费   510篇
化学   3270篇
晶体学   95篇
力学   245篇
综合类   52篇
数学   1379篇
物理学   2146篇
  2023年   54篇
  2022年   120篇
  2021年   124篇
  2020年   109篇
  2019年   151篇
  2018年   114篇
  2017年   159篇
  2016年   162篇
  2015年   110篇
  2014年   207篇
  2013年   430篇
  2012年   262篇
  2011年   323篇
  2010年   231篇
  2009年   413篇
  2008年   391篇
  2007年   386篇
  2006年   359篇
  2005年   280篇
  2004年   237篇
  2003年   223篇
  2002年   249篇
  2001年   188篇
  2000年   174篇
  1999年   161篇
  1998年   135篇
  1997年   149篇
  1996年   92篇
  1995年   72篇
  1994年   84篇
  1993年   64篇
  1992年   79篇
  1991年   48篇
  1990年   32篇
  1989年   35篇
  1988年   88篇
  1987年   36篇
  1986年   16篇
  1985年   76篇
  1984年   94篇
  1983年   44篇
  1982年   79篇
  1981年   91篇
  1980年   52篇
  1979年   48篇
  1978年   49篇
  1977年   31篇
  1976年   20篇
  1974年   15篇
  1973年   18篇
排序方式: 共有7187条查询结果,搜索用时 15 毫秒
61.
62.
本文通过对傅里叶变换红外光谱(FTIR)技术研究证明了磷酰化氨基酸可以知聚成肽,并由此说明了在仿生化成肽反应过程中,磷(酰化)起着十分重要的作用,同时了说明了FTIR技术为仿生化的过程研究提供了新的研究方法。  相似文献   
63.
A study of the normal modes of vibration and their dispersion in polyadenylic acid based on the Urey–Bradley force field is reported. It gives a better interpretation of FTIR spectra as compared with the valence force field. Characteristic features of dispersion curves such as regions of high density‐of‐states, repulsion, and character mixing of dispersive modes are discussed. Predictive valuzes of heat capacity as a function of temperature are reported.  相似文献   
64.
Let be a compact set with interior G. Let L 1 (G,dx), >0 dx-a.e. on G, and m:=dx. Let A=(a ij ) be symmetric, and globally uniformly strictly elliptic on G. Let be such that ; f, , is closable in L 2 (G,m) with closure ( r ,D( r )). The latter is fulfilled if satisfies the Hamza type condition, or i L 1 loc (G,dx), 1id. Conservative, non-symmetric diffusion processes X t related to the extension of a generalized Dirichlet form where satisfies are constructed and analyzed. If G is a bounded Lipschitz domain, H 1,1 (G), and a ij D( r ), a Skorokhod decomposition for X t is given. This happens through a local time that is uniquely associated to the smooth measure 1{ Tr ()>0} d, where Tr denotes the trace and the surface measure on G.This research has been financially supported by TMR grant HPMF-CT-2000-00942 of the European Union. Mathematics Subject Classification (2000): 60J60, 60J55, 31C15, 31C25, 35J25  相似文献   
65.
New goodness-of-fit tests, based on bootstrap estimated expectations of probability integral transformed order statistics, are derived for the location-scale model. The resulting test statistics are location and scale invariant, and are sensitive to discrepancies at the tails of the hypothesized distribution. The limiting null distributions of the test statistics are derived in terms of functionals of a certain Gaussian process, and the tests are shown to be consistent against a broad family of alternatives. Critical points for all sample sizes are provided for tests of normality. A simulation study shows that the proposed tests are more powerful than established tests such as Shapiro-Wilk, Cramér-von Mises and Anderson-Darling, for a wide range of alternative distributions.  相似文献   
66.
The most momentous requirement a quantum theory of gravity must satisfy is Background Independence, necessitating in particular an ab initio derivation of the arena all non-gravitational physics takes place in, namely spacetime. Using the background field technique, this requirement translates into the condition of an unbroken split-symmetry connecting the (quantized) metric fluctuations to the (classical) background metric. If the regularization scheme used violates split-symmetry during the quantization process it is mandatory to restore it in the end at the level of observable physics. In this paper we present a detailed investigation of split-symmetry breaking and restoration within the Effective Average Action (EAA) approach to Quantum Einstein Gravity (QEG) with a special emphasis on the Asymptotic Safety conjecture. In particular we demonstrate for the first time in a non-trivial setting that the two key requirements of Background Independence and Asymptotic Safety can be satisfied simultaneously. Carefully disentangling fluctuation and background fields, we employ a ‘bi-metric’ ansatz for the EAA and project the flow generated by its functional renormalization group equation on a truncated theory space spanned by two separate Einstein–Hilbert actions for the dynamical and the background metric, respectively. A new powerful method is used to derive the corresponding renormalization group (RG) equations for the Newton- and cosmological constant, both in the dynamical and the background sector. We classify and analyze their solutions in detail, determine their fixed point structure, and identify an attractor mechanism which turns out instrumental in the split-symmetry restoration. We show that there exists a subset of RG trajectories which are both asymptotically safe and split-symmetry restoring: In the ultraviolet they emanate from a non-Gaussian fixed point, and in the infrared they loose all symmetry violating contributions inflicted on them by the non-invariant functional RG equation. As an application, we compute the scale dependent spectral dimension which governs the fractal properties of the effective QEG spacetimes at the bi-metric level. Earlier tests of the Asymptotic Safety conjecture almost exclusively employed ‘single-metric truncations’ which are blind towards the difference between quantum and background fields. We explore in detail under which conditions they can be reliable, and we discuss how the single-metric based picture of Asymptotic Safety needs to be revised in the light of the new results. We shall conclude that the next generation of truncations for quantitatively precise predictions (of critical exponents, for instance) is bound to be of the bi-metric type.  相似文献   
67.
The five lowest doubly excited deformational vibrational bands ν4 + ν6, 2ν6, ν3 + ν4, ν3 + ν6, and 2ν3 of PH2D have been recorded for the first time using a Bruker 120 HR interferometer with a resolution 0.0033 cm−1 and analysed. Some transitions belonging to a very weak band 2ν4 have been also assigned. From the fit 24 and 86, respectively, diagonal and resonance interaction parameters were obtained which reproduce 1089 upper energy levels obtained from more than 4600 assigned transitions with the rms deviation of 0.00059 cm−1.  相似文献   
68.
Some Hardy-type integral inequalities in general measure spaces, where the corresponding Hardy operator is replaced by a more general Volterra type integral operator with kernel , are considered. The equivalence of such inequalities on the cones of non-negative respective non-increasing functions are established and applied.

  相似文献   

69.
In this paper, we study conditions under which Schrodinger type operators with a matrix potential is separated and Schrodinger equation has a unique solution in the weighted space L2,k(Rn)l, where l is any natural number and k ε C1(Rn) is a positive function  相似文献   
70.
This article is essentially devoted to a brief historical introduction to Euler's formula for polyhedra, topology, theory of graphs and networks with many examples from the real-world. Celebrated Königsberg seven-bridge problem and some of the basic properties of graphs and networks for some understanding of the macroscopic behaviour of real physical systems are included. We also mention some important and modern applications of graph theory or network problems from transportation to telecommunications. Graphs or networks are effectively used as powerful tools in industrial, electrical and civil engineering, communication networks in the planning of business and industry. Graph theory and combinatorics can be used to understand the changes that occur in many large and complex scientific, technical and medical systems. With the advent of fast large computers and the ubiquitous Internet consisting of a very large network of computers, large-scale complex optimization problems can be modelled in terms of graphs or networks and then solved by algorithms available in graph theory. Many large and more complex combinatorial problems dealing with the possible arrangements of situations of various kinds, and computing the number and properties of such arrangements can be formulated in terms of networks. The Knight's tour problem, Hamilton's tour problem, problem of magic squares, the Euler Graeco-Latin squares problem and their modern developments in the twentieth century are also included.  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