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   7556篇
  免费   130篇
  国内免费   88篇
化学   4667篇
晶体学   85篇
力学   166篇
数学   1716篇
物理学   1140篇
  2022年   50篇
  2020年   69篇
  2019年   63篇
  2018年   84篇
  2017年   51篇
  2016年   142篇
  2015年   105篇
  2014年   126篇
  2013年   414篇
  2012年   327篇
  2011年   369篇
  2010年   234篇
  2009年   202篇
  2008年   334篇
  2007年   336篇
  2006年   401篇
  2005年   383篇
  2004年   337篇
  2003年   279篇
  2002年   297篇
  2001年   92篇
  2000年   80篇
  1999年   87篇
  1998年   105篇
  1997年   104篇
  1996年   146篇
  1995年   90篇
  1994年   84篇
  1993年   78篇
  1992年   88篇
  1991年   80篇
  1990年   69篇
  1989年   66篇
  1988年   58篇
  1987年   73篇
  1986年   61篇
  1985年   107篇
  1984年   122篇
  1983年   87篇
  1982年   94篇
  1981年   120篇
  1980年   131篇
  1979年   97篇
  1978年   109篇
  1977年   80篇
  1976年   92篇
  1975年   106篇
  1974年   100篇
  1973年   97篇
  1972年   51篇
排序方式: 共有7774条查询结果,搜索用时 15 毫秒
991.
Lempp  Steffen  McCoy  Charles  Morozov  Andrei  Solomon  Reed 《Order》2002,19(4):343-364
We compare Aut(Q), the classical automorphism group of a countable dense linear order, with Aut c (Q), the group of all computable automorphisms of such an order. They have a number of similarities, including the facts that every element of each group is a commutator and each group has exactly three nontrivial normal subgroups. However, the standard proofs of these facts in Aut(Q) do not work for Aut c (Q). Also, Aut(Q) has three fundamental properties which fail in Aut c (Q): it is divisible, every element is a commutator of itself with some other element, and two elements are conjugate if and only if they have isomorphic orbital structures.  相似文献   
992.
Recent calculations have shown the existence of critical phenomena in general relativity associated with the collapse of wavepackets of massless fields that are near, in parameter space, the onset of black hole formation (the critical point). Two physically distinct systems have been explored: collapse of spherically-symmetric massless scalar field and collapse of vacuum, axisymmetric gravitational waves. Nonlinear effects dominate near the critical point. Black-hole mass serves as an order parameter and has a power-law dependence on critical separation in the supercritical region of parameter space. Remarkably, the values of the critical exponent of the power law are nearly identical in the two systems. The nonlinearity induces the fields to oscillate. Each successive oscillation is an echo, obeying a spatial and temporal scaling relation.  相似文献   
993.
994.
The continuity of the spatial derivatives for solutions of the parabolic Cauchy problem is established down to the initial time under the assumption that the initial data and coefficients are sufficiently smooth.  相似文献   
995.
A simple, inexpensive apparatus is described for estimating the amount of carbon monoxide in air over a range of concentration from 0.01 to 0.1% or higher, with an accuracy of 0.005 to 0.01%. Thc carbon monoxide is oxidised by passing through a layer of Hopcalite catalyst at room temperature, and the rise in temperature of the air stream due to the heat of combustion is measured with a thermometer. About 60% of the theoretically possible temperature rise is actually observed with the apparatus. By means of a calibration chart, the concentration of carbon monoxide present is read as a function of the temperature increase.  相似文献   
996.
997.
Deuterium-labeled polystyrene modified by random distributions of the comonomer p-(1,1,1,3,3,3-hexaflouro-2-hydroxyisopropyl)-α-methyl-styrene [DPS(OH)] has been blended with poly(butyl methacrylate) (PBMA) and studied with small-angle neutron scattering (SANS). Miscibility is induced via hydrogen bonding between the DPS(OH) hydroxyl group and PBMA carbonyl groups. The data suggest that the nature of the miscible-phase structure in these blends differs from that of the usual homopolymer blends at small scattering angles, which we attribute to the short-range site specific nature of the hydrogen bond interaction. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2745–2750, 1998  相似文献   
998.
A general solution to nonsteady coupled magnetohydrodynamic plane Couette flow by the method of Fourier series expansion is presented in this paper. Two particular examples of the utility of the solution are included: 1) an impulsive start of the wall, and 2) a wall velocity proportional to (1 − exp(− αt)). For the case of an impulsive start of the wall it is found that flow is apparently accelerated by the presence of the magnetic field, a situation opposite to that which occurs when no induced magnetic field is allowed.  相似文献   
999.
The title complex crystallizes in the centrosymmetric monoclinic space group C2/c (No. 15) withZ=8. The structure was refined toR=4.49% for those 2745 independent reflections with 2=5–50o and |F |>6(F). Ruthenium-ligand distances are as follows: Ru-P=2.284(2) and 2.286(2) Å, Ru-NO2=2.049(6) Å and Ru-C(Cp)=2.210(10)-2.246(9) Å. Bond lengths within the nitro ligand are N(1)-O(1)=1.226(10) Å and N(1)-O(2)=1.244(10) Å. The methanol of solvation is ordered but is subject to large thermal vibrational motions.  相似文献   
1000.
It is shown that if φ(f)  ∝Rdφ(y) f(y) dy is a Markoff random field and Xα are multiplicative functionals of φ (with E(Xα) = 1) which converge locally in L1, then there exists a locally Markoff random field φ1 such that E(exp(iφ1(f))) = limα E(Xαexp(iφ(φ))). We choose φ to be the two-dimensional generalization of the Ornstein-Uhlenbeck velocity process and take Xα proportional to exp(?λ∝R2 : P(φ(y)) : gα(y) dy), where: P(φ(y)) : is a regularized even degree polynomial in φ(y). It is then proved that for an appropriate choice of gα → 1 and small λ, {Xα} does converge locally in L1 and that the corresponding φ1 is stationary.  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