全文获取类型
收费全文 | 51601篇 |
免费 | 6299篇 |
国内免费 | 5007篇 |
专业分类
化学 | 11725篇 |
晶体学 | 1013篇 |
力学 | 11520篇 |
综合类 | 753篇 |
数学 | 23081篇 |
物理学 | 14815篇 |
出版年
2024年 | 78篇 |
2023年 | 525篇 |
2022年 | 780篇 |
2021年 | 1118篇 |
2020年 | 1426篇 |
2019年 | 1269篇 |
2018年 | 1283篇 |
2017年 | 1742篇 |
2016年 | 2011篇 |
2015年 | 1538篇 |
2014年 | 2562篇 |
2013年 | 3849篇 |
2012年 | 2953篇 |
2011年 | 3452篇 |
2010年 | 2941篇 |
2009年 | 3357篇 |
2008年 | 3320篇 |
2007年 | 3331篇 |
2006年 | 3021篇 |
2005年 | 2773篇 |
2004年 | 2444篇 |
2003年 | 2197篇 |
2002年 | 1992篇 |
2001年 | 1670篇 |
2000年 | 1577篇 |
1999年 | 1389篇 |
1998年 | 1315篇 |
1997年 | 1112篇 |
1996年 | 914篇 |
1995年 | 752篇 |
1994年 | 686篇 |
1993年 | 553篇 |
1992年 | 543篇 |
1991年 | 440篇 |
1990年 | 357篇 |
1989年 | 267篇 |
1988年 | 214篇 |
1987年 | 164篇 |
1986年 | 119篇 |
1985年 | 151篇 |
1984年 | 149篇 |
1983年 | 90篇 |
1982年 | 106篇 |
1981年 | 83篇 |
1980年 | 56篇 |
1979年 | 63篇 |
1978年 | 46篇 |
1977年 | 42篇 |
1976年 | 18篇 |
1957年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
42.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
43.
An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
44.
非线性互补问题的一种全局收敛的显式光滑Newton方法 总被引:2,自引:0,他引:2
本针对Po函数非线性互补问题,给出了一种显式光滑Newton方法,该方法将光滑参数μ进行显式迭代而不依赖于Newton方向的搜索过程,并在适当的假设条件下,证明了算法的全局收敛性。 相似文献
45.
电路过渡过程所列方程是微分方程,本文中采用的是方框图模型分析法,即将微分方程的复杂示解分解成最基本的加(减)、乘(除)、积分(微分)、增益等运算,采用VB设计用户界面产进行计算,并给出了一算例。 相似文献
46.
Qi Yongcheng 《数学年刊B辑(英文版)》1998,19(4):499-510
1.IntroductionLet{X.,n21}beasequenceoflidry'swithanondegeneratedistributionfunctionF(x).Supposethereexistsomeconstantsan>0,b.6RandsomeacERsuchthatwhereG.standsforoneoftheextremevaluedistributions:Heretheindex7ERisarealparameter(interpret(1 box)--'/ryase--"for7~0).Theestimationoftheextreme-valueindex7isveryimportantbothintheextremevaluetheoryandinpractice.Manystatistics,suchasHillestimator(forcaseac>0),PickandsestimatorandDekkers-EinmahLdeHaan'smomentestimatorwhicharebasedonafinitesample,… 相似文献
47.
ON A PAIR OF NON-ISOMETRIC ISOSPECTRAL DOMAINS WITH FRACTAL BOUNDARIES AND THE WEYL-BERRY CONJECTURE
ONAPAIROFNONISOMETRICISOSPECTRALDOMAINSWITHFRACTALBOUNDARIESANDTHEWEYLBERRYCONJECTURESLEEMAN,B.D.CHENHUAManuscriptrec... 相似文献
48.
It is proved that for any integerk≥ 54 000, there isN
k
>0 depending onk only such that every even integer ≥N
k
is a sum of two odd prime numbers andk powers of 2.
Project partially supported by RGC Research Grant (No.HKU 7122/97P) and Post-Doctoral Fellowship of the University of Hong
Kong. 相似文献
49.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
50.
1引言CPL(毛细泵两相流回路)能传输较高的热负荷,而且不需要循环泵、阀门等运动部件,重量轻可靠性好;在飞行器热控制方面有很好的应用前景[1]。CPL在恶劣的空间环境中运行,需要防止工作介质出现冷冻,为此,我们已经用解析[2]和数值的方法[3]进行了初步的分析,得到了一些可供工程设计参考应用的结果。另外,在恶劣的空间环境中,如果出现冻结,需要融化起动,热管的安全设计需要研究它的融化特性,以确保热管在空间能正常运行。双倒易边界元方法用Laplace基本解[4],通过对一类偏微分方程两侧进行转化,将它全部转化为纯边界积分… 相似文献