全文获取类型
收费全文 | 120085篇 |
免费 | 11168篇 |
国内免费 | 8985篇 |
专业分类
化学 | 45675篇 |
晶体学 | 1362篇 |
力学 | 22977篇 |
综合类 | 1635篇 |
数学 | 34651篇 |
物理学 | 33938篇 |
出版年
2024年 | 189篇 |
2023年 | 1088篇 |
2022年 | 1831篇 |
2021年 | 3253篇 |
2020年 | 3039篇 |
2019年 | 2825篇 |
2018年 | 2586篇 |
2017年 | 3176篇 |
2016年 | 3835篇 |
2015年 | 3415篇 |
2014年 | 4994篇 |
2013年 | 8081篇 |
2012年 | 5736篇 |
2011年 | 6805篇 |
2010年 | 5725篇 |
2009年 | 7053篇 |
2008年 | 7179篇 |
2007年 | 7460篇 |
2006年 | 6467篇 |
2005年 | 5386篇 |
2004年 | 4980篇 |
2003年 | 4696篇 |
2002年 | 6744篇 |
2001年 | 3859篇 |
2000年 | 3332篇 |
1999年 | 2920篇 |
1998年 | 2814篇 |
1997年 | 2300篇 |
1996年 | 2065篇 |
1995年 | 1839篇 |
1994年 | 1658篇 |
1993年 | 1497篇 |
1992年 | 1477篇 |
1991年 | 1071篇 |
1990年 | 938篇 |
1989年 | 734篇 |
1988年 | 660篇 |
1987年 | 536篇 |
1986年 | 474篇 |
1985年 | 605篇 |
1984年 | 511篇 |
1983年 | 292篇 |
1982年 | 525篇 |
1981年 | 631篇 |
1980年 | 555篇 |
1979年 | 611篇 |
1978年 | 493篇 |
1977年 | 370篇 |
1976年 | 315篇 |
1973年 | 198篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
章利用基于三次B样条插值的边界元方法,对振动体外部声辐射问题进行了研究,对CHIEF法及其改进方法作了进一步的改进,提出在加权余量意义下,通过把内部Helmholtz积分方程与其对内点坐标取导后的方程式作线性叠加,在域外构作的一个小体积块上进行积分以形成补充方程,经与表面Helmholtz积分方程相结合,来求解任意频率下的声辐射问题,并以脉动球和摆动球作为算例,说明本提出的方法能够有效地克服在特殊频率处解的非唯一性问题。 相似文献
962.
An initial-value method is given for second-order singularly perturbed boundary-value problems with a boundary layer at one endpoint. The idea is to replace the original two-point boundary value problem by two suitable initial-value problems. The method is very easy to use and to implement. Nontrivial text problems are used to show the feasibility of the given method, its versatility, and its performance in solving linear and nonlinear singularly perturbed problems.This work was supported in part by the Consiglio Nazionale delle Ricerche, Contract No. 86.02108.01, and in part by the Ministero della Pubblica Istruzione. 相似文献
963.
A posteriori error estimators for the Stokes equations 总被引:5,自引:0,他引:5
Summary We present two a posteriori error estimators for the mini-element discretization of the Stokes equations. One is based on a suitable evaluation of the residual of the finite element solution. The other one is based on the solution of suitable local Stokes problems involving the residual of the finite element solution. Both estimators are globally upper and locally lower bounds for the error of the finite element discretization. Numerical examples show their efficiency both in estimating the error and in controlling an automatic, self-adaptive mesh-refinement process. The methods presented here can easily be generalized to the Navier-Stokes equations and to other discretization schemes.This work was accomplished at the Universität Heidelberg with the support of the Deutsche Forschungsgemeinschaft 相似文献
964.
The purpose of this paper is two-fold. First, we introduce a new asymptotic expansion in the exponent for the compound binomial
approximation of the generalized Poisson binomial distribution. The dependence of its accuracy on the symmetry and shifting
of distributions is investigated. Second, for compound binomial and compound Poisson distributions, we present new smoothness
estimates, some of which contain explicit constants. Finally, the ideas used in this paper enable us to prove new precise
bounds in the compound Poisson approximation.
Published in Lietuvos Matematikos Rinkinys, Vol. 46, No. 1, pp. 67–110, January–March, 2006. 相似文献
965.
966.
It is shown that the condition υ > υp (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies
and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to
define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific
response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity
of light in the medium determines the existence of such general lower bound. 相似文献
967.
For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006 相似文献
968.
969.
考虑一类具时滞的 Liénard型方程x+f[x(t) ]x(t) +g[t,x(t-τ(t) ) ]=p(t) =p(t+T) ,利用重合度理论 ,获得了此方程至少存在一个 T周期解的充分条件 相似文献
970.
利用溶胶凝胶法在SiO2Si衬底上沉积高取向的V2O5薄膜,在压强低于2Pa,温度高于400℃的条件下,对V2O5薄膜进行真空烘烤,获得了电阻率变化3个数量级以上、弛豫宽度为62℃的VO2多晶薄膜.以X射线衍射(XRD)、扫描电子显微镜(SEM)图和电阻率转换特性等实验结果为依据,详细分析了溶胶凝胶薄膜在真空烘烤时从V2O5向VO2的转化,它经历了从VnO2n+1(n=2,3,4,6)到VO2的过程.实验证明,根据选择合适的成膜热处理条件和真空烘烤条件是实现溶胶凝胶V2O5结构向VO2结构成功转换的关键
关键词:
溶胶-凝胶法 氧化钒薄膜 VO2膜转换特性 相似文献