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   2844篇
  免费   367篇
  国内免费   180篇
化学   285篇
晶体学   6篇
力学   169篇
综合类   22篇
数学   1122篇
物理学   1787篇
  2024年   5篇
  2023年   19篇
  2022年   29篇
  2021年   46篇
  2020年   56篇
  2019年   41篇
  2018年   61篇
  2017年   100篇
  2016年   110篇
  2015年   77篇
  2014年   198篇
  2013年   157篇
  2012年   194篇
  2011年   168篇
  2010年   145篇
  2009年   172篇
  2008年   178篇
  2007年   177篇
  2006年   152篇
  2005年   161篇
  2004年   134篇
  2003年   130篇
  2002年   140篇
  2001年   94篇
  2000年   77篇
  1999年   81篇
  1998年   87篇
  1997年   71篇
  1996年   63篇
  1995年   44篇
  1994年   37篇
  1993年   30篇
  1992年   30篇
  1991年   20篇
  1990年   22篇
  1989年   13篇
  1988年   11篇
  1987年   17篇
  1986年   8篇
  1985年   5篇
  1984年   4篇
  1982年   4篇
  1980年   2篇
  1978年   6篇
  1977年   2篇
  1976年   2篇
  1973年   3篇
  1972年   1篇
  1957年   1篇
  1936年   1篇
排序方式: 共有3391条查询结果,搜索用时 15 毫秒
111.
梯度折射率棒透镜的色差模型   总被引:1,自引:0,他引:1  
张凯  马成义 《光子学报》1998,27(1):81-84
本文提出一个梯度折射率棒透镜(GRIN-RodLens)的色差模型,并运用本模型合理地解释了在色差测量过程发现的各类色差现象.  相似文献   
112.
本文介绍了在YG366高速抛光机上进行的透镜不胶盘单件抛光技术。这一新的抛光方法比弹性成盘法和刚性成盘法有许多优点:它省掉了许多辅助工序,缩短了抛光时间,所以生产周期短,效率高,成本低。同时给出了根据透镜的结构参数进行生产技术准备和评估抛光过程稳定性的公式。最后提出了进一步改进的设想。  相似文献   
113.
M Vxxx R K Murty  N C Das  R P Shukla 《Pramana》1984,22(3-4):213-220
The present paper considers the magnifying power and aberration properties of three different catadioptric magnifying systems useful for application as simple hand-held microfiche readers. These are in the form of a plano-convex lens, a meniscus lens and an achromatic doublet lens and all their outer surfaces have been coated with a semi-reflecting film so that they behave like catadioptric elements. These can be designed to give magnification in the range of 15 × to 25 × with sufficient eye relief. Using such magnifiers, it is possible to read microfiche having frame sizes of 16 × 12 mm and 12 × 9 mm. The cemented achromatic doublet coated on the outer surfaces seems to give a very good image for use in microfiche reader.  相似文献   
114.
The recursive projection algorithm derived in a previous paper is related to several well-known methods of numerical analysis such as the conjugate gradient method, Rosen's method and Henrici's. It is connected with the general interpolation problem, with extrapolation methods, with orthogonal projection on a subspace and with Fourier expansions. Several other connections and applications are presented.  相似文献   
115.
A new programming algorithm for nonlinear constrained optimization problems is proposed. The method is based on the penalty function approach and thereby circumyents the necessity to maintain feasibility at each iteration, but it also behaves much like the gradient projection method. Although only first-order information is used, the algorithm converges asymptotically at a rate which is independent of the magnitude of the penalty term; hence, unlike the simple gradient method, the asymptotic rate of the proposed method is not affected by the ill-conditioning associated with the introduction of the penalty term. It is shown that the asymptotic rate of convergence of the proposed method is identical with that of the gradient projection method.Dedicated to Professor M. R. HestenesThis research was supported by the National Science Foundation, Grant No. GK-16125.  相似文献   
116.
By application of a projection operator technique we derive a formally exact generalization of the nonlinear mean field master equation introduced recently for the study of local fluctuations in a reacting medium. Our starting point is a phenomenological cell master equation. The results of our theory are applicable to the theory of a fluctuating hydrodynamic reacting system. The mean field equation is placed on a firm theoretical foundation by showing it to be the lowest order approximation in an expansion in the dimensionality of the physical space keeping the product of the number of nearest neighbors (an increasing function of dimensionality) and the typical diffusion coefficient constant. A more accurate nonlinear master equation that allows for the correlation and fluctuations in the environment of a given volume element is derived in the form of an augmented mean field equation.Work supported in part by a grant from the National Science Foundation.  相似文献   
117.
In this paper we consider two von Neumann subalgebras and of a type II1 factor . For a map φ on , we define
  相似文献   
118.
We describe the set of values of the parameter for which there exists a Hilbert space H and n partial reflections A 1,...,A n (self-adjoint operators such that A k 3 =Ak or, which is the same, self-adjoint operators whose spectra belong to the set {-1,0,1}) whose sum is equal to the scalar operator I H .  相似文献   
119.
In this paper, we study the existence of the solution of the variational inequality 〈Txξ,yx〉?0 by applying the generalized projection operator , where B is a Banach space with dual space B∗ and by using the well-known FanKKM Theorem.  相似文献   
120.
Let e(x, y, ) be the spectral function and the unit spectral projection operator, with respect to the Laplace–Beltrami operator on a closed Riemannian manifold M. We generalize the one-term asymptotic expansion of e(x, x, ) by Hörmander (Acta Math. 88 (1968), 341–370) to that of x y e(x,y,)| x=y for any multiindices , in a sufficiently small geodesic normal coordinate chart of M. Moreover, we extend the sharp (L 2,L p) (2 p) estimates of by Sogge (J. Funct. Anal. 77 (1988), 123–134; London Math. Soc. Lecture Note Ser. 137, Cambridge University Press, Cambridge, 1989; Vol. 1, pp. 416–422) to the sharp (L 2, Sobolev L p) estimates of .  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