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   26304篇
  免费   4477篇
  国内免费   2605篇
化学   17232篇
晶体学   198篇
力学   1915篇
综合类   201篇
数学   3522篇
物理学   10318篇
  2024年   25篇
  2023年   574篇
  2022年   642篇
  2021年   782篇
  2020年   1098篇
  2019年   1020篇
  2018年   901篇
  2017年   881篇
  2016年   1216篇
  2015年   1155篇
  2014年   1447篇
  2013年   1946篇
  2012年   2352篇
  2011年   2465篇
  2010年   1647篇
  2009年   1600篇
  2008年   1748篇
  2007年   1507篇
  2006年   1384篇
  2005年   1168篇
  2004年   862篇
  2003年   682篇
  2002年   579篇
  2001年   477篇
  2000年   497篇
  1999年   603篇
  1998年   495篇
  1997年   506篇
  1996年   479篇
  1995年   458篇
  1994年   384篇
  1993年   333篇
  1992年   270篇
  1991年   244篇
  1990年   232篇
  1989年   185篇
  1988年   135篇
  1987年   92篇
  1986年   79篇
  1985年   74篇
  1984年   49篇
  1983年   36篇
  1982年   42篇
  1981年   17篇
  1980年   6篇
  1979年   2篇
  1976年   1篇
  1959年   1篇
  1957年   7篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
1.

In this paper, a power penalty approximation method is proposed for solving a mixed quasilinear elliptic complementarity problem. The mixed complementarity problem is first reformulated as a double obstacle quasilinear elliptic variational inequality problem. A nonlinear elliptic partial differential equation is then defined to approximate the resulting variational inequality by using a power penalty approach. The existence and uniqueness of the solution to the partial differential penalty equation are proved. It is shown that, under some mild assumptions, the sequence of solutions to the penalty equations converges to the unique solution of the variational inequality problem as the penalty parameter tends to infinity. The error estimates of the convergence of this penalty approach are also derived. At last, numerical experimental results are presented to show that the power penalty approximation method is efficient and robust.

  相似文献   
2.
Pan  Nana  Fan  Jishan  Zhou  Yong 《Applications of Mathematics》2021,66(3):373-382
Applications of Mathematics - We prove a regularity criterion for a nonhomogeneous incompressible Ginzburg-Landau-Navier-Stokes system with the Coulomb gauge in ?3. It is proved that if the...  相似文献   
3.
A *-ring R is called a nil *-clean ring if every element of R is a sum of a projection and a nilpotent.Nil *-clean rings are the *-version of nil-clean rings introduced by Diesl.This paper is about the nil *-clean property of rings with emphasis on matrix rings.We show that a *-ring R is nil *-clean if and only if J(R) is nil and R/J(R) is nil*-clean.For a 2-primal *-ring R,with the induced involution given by (aij)* =(a*ij)T,the nil *-clean property of Mn(R) is completely reduced to that of Mn(Z2).Consequently,Mn(R) is not a nil *-clean ring for n =3,4,and M2(R) is a nil *-clean ring if and only if J(R) is nil,R/J(R) is a Boolean ring and a*-a ∈ J(R) for all a ∈ R.  相似文献   
4.
It remains a great challenge to realize direct manipulation of a nitrogen-vacancy(NV) spin at the single-quantum level with a microwave(MW) cavity. As an alternative, a hybrid system with the spin–phonon–photon triple interactions mediated by a squeezed cantilever-type harmonic resonator is proposed. According to the general mechanical parametric amplification of this in-between phonon mode, the direct spin–phonon and photon–phonon couplings are both exponentially enhanced, which can even further improve the coherent manipulation of a single NV spin and MW photon with a higher efficiency. In view of this triple system with enhanced couplings and the additional sideband adjustable designs, this scheme may provide a more efficient phonon-mediated platform to bridge or manipulate the MW quantum and a single electron spin coherently. It is also hoped to evoke wider applications in the areas of quantum state transfer and preparation,ultrasensitive detection and quantum nondestructive measurement, etc.  相似文献   
5.
本文选用混杂的B3LYP密度泛函理论方法,在Lanl2dz水平上,对5,15-二(二茂铁基)-卟啉酞菁钇[Por(Fc)2]Y(Pc)的结构进行了优化,结果表明,5,15-二(二茂铁基)-卟啉酞菁钇呈现出三明治型构型,卟啉环与酞菁环呈穹型围绕在金属钇原子周围。对分子内主要的键长与键角进行了理论计算,通过频率计算,得到了5,15-二(二茂铁基)-卟啉酞菁钇[Por(Fc)2]Y(Pc)的红外光谱图,与实验所得的红外光谱图进行比对,将理论计算和实验所得的光谱主要振动峰进行了线性回归拟合,相关系数为0.992,标准偏差为16.96。理论计算与实验所获得的红外光谱图基本一致,说明本文所选用的DFT理论计算方法是可行的。通过GaussView软件对5,15-二(二茂铁基)-卟啉酞菁钇的红外谱带简正振动模式进行了指认。此外,分析讨论了5,15-二(二茂铁基)-卟啉酞菁钇[Por(Fc)2]Y(Pc)的分子静电势,确定了极大值与极小值的位置。对于研究5,15-二(二茂铁基)-卟啉酞菁钇分子的性质,提供了相应的理论基础。  相似文献   
6.
We simulate the polarization manipulation of bright-dark vector bisolitons at 1-μm wavelength regime.Through changing the pulse parameters,different kinds of pulse shapes and optical spectra are generated in output orthogonal polarization directions.When the input vector bisoliton is polarization-locked with 1064 nm central wavelength,“1+1”fundamental dark-dark and“2+1”pseudo-high-order bright-dark group-velocity-locked vector solitons can be achieved through changing the projection angle.When the input vector bisoliton is group-velocity-locked with 1063 nm and 1065 nm central wavelengths,“2+1”and“2+2”pseudo-high-order bright-dark group-velocity-locked vector solitons,bright-dark group-velocity-locked vector solitons with chirp-like temporal oscillations are generated.Our simulation results can provide beneficial conduct for polarization manipulation of vector multi-solitons,and have promising applications in quantum information register,optical communications,nanophotonics,and all-optical switching.  相似文献   
7.
Zhou  Jiuru 《Archiv der Mathematik》2021,116(6):693-706

In this paper, we study vanishing and splitting results on a complete smooth metric measure space \((M^n,g,\mathrm {e}^{-f}\mathrm {d}v)\) with various negative m-Bakry-Émery Ricci curvature lower bounds in terms of the first eigenvalue \(\lambda _1(\Delta _f)\) of the weighted Laplacian \(\Delta _f\), i.e., \(\mathrm {Ric}_{m,n}\ge -a\lambda _1(\Delta _f)-b\) for \(0<a\le \dfrac{m}{m-1}, b\ge 0\). In particular, we consider three main cases for different a and b with or without conditions on \(\lambda _1(\Delta _f)\). These results are extensions of Dung and Vieira, and weighted generalizations of Li-Wang, Dung-Sung, and Vieira.

  相似文献   
8.
Designs, Codes and Cryptography - Large sets of combinatorial designs has always been a fascinating topic in design theory. These designs form a partition of the whole space into combinatorial...  相似文献   
9.
Zhou  Yan  Yan  Xiang-Ping  Zhang  Cun-Hua 《Nonlinear dynamics》2021,105(4):3731-3747
Nonlinear Dynamics - This article considers a reaction–diffusion predator–prey model with schooling behavior both in predator and prey species and subject to the homogeneous Neumann...  相似文献   
10.
Xiu  Chunbo  Zhou  Ruxia  Zhao  Shaoda  Xu  Guowei 《Nonlinear dynamics》2021,104(1):789-805
Nonlinear Dynamics - In order to enhance the chaotic degree of cellular neural network (CNN), the memristive characteristic is combined in CNN, and a five-dimensional memristive CNN hyperchaotic...  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