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   3186篇
  免费   209篇
  国内免费   306篇
化学   217篇
晶体学   3篇
力学   142篇
综合类   51篇
数学   2640篇
物理学   648篇
  2024年   5篇
  2023年   24篇
  2022年   37篇
  2021年   50篇
  2020年   65篇
  2019年   68篇
  2018年   84篇
  2017年   84篇
  2016年   107篇
  2015年   63篇
  2014年   162篇
  2013年   256篇
  2012年   125篇
  2011年   184篇
  2010年   165篇
  2009年   170篇
  2008年   244篇
  2007年   215篇
  2006年   200篇
  2005年   171篇
  2004年   144篇
  2003年   148篇
  2002年   152篇
  2001年   110篇
  2000年   100篇
  1999年   101篇
  1998年   104篇
  1997年   68篇
  1996年   59篇
  1995年   39篇
  1994年   32篇
  1993年   23篇
  1992年   17篇
  1991年   6篇
  1990年   19篇
  1989年   12篇
  1988年   11篇
  1987年   3篇
  1986年   9篇
  1985年   13篇
  1984年   10篇
  1983年   3篇
  1982年   7篇
  1981年   6篇
  1980年   4篇
  1979年   4篇
  1978年   4篇
  1976年   5篇
  1973年   3篇
  1936年   2篇
排序方式: 共有3701条查询结果,搜索用时 20 毫秒
81.
1 INTRODUCTION Bauxite porcelain is a novel “K2O–Al2O3–SiO2” system ceramic by using sintered bauxite, clay and potash feldspar and albite as the main raw materials with the Al2O3’s content of 50%~60(massfraction). Compared to the traditional“K2O–Al2O3–SiO2” feldspar porcelain by using quartz, bolus alb and potash feldspar and albite as the main raw materials, the bauxite porcelain possesses such advantages as high mechanical strength, excellent electrical insula- tion prop…  相似文献   
82.
Based on the X-ray scattering intensity theory and using the approximate expression for the atomic scattering factor, the correction factors for three crystalline peaks and an amorphous peak of Nylon 1212 were calculated and the formula of degree of crystallinity of Nylon 1212 was derived by a graphic multipeak resolution method. The degree of crystallinity calculated from the WAXD method is compatible with those obtained by density and calorimetry methods.  相似文献   
83.
A new approximate formula for temperature integral is proposed. The linear dependence of the new fomula on x has been established. Combining this linear dependence and integration-by-parts, new equation for the evaluation of kinetic parameters has been obtained from the above dependence. The validity of this equation has been tested with data from numerical calculating. And its deviation from the values calculated by Simpson's numerical integrating was discussed. Compared with several published approximate formulae, this new one is much superior to all other approximations and is the most suitable solution for the evaluation of kinetic parameters from TG experiments. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
84.
Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble “mystery boxes”. Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field.  相似文献   
85.
The title compound has been synthesized and characterized crystallographically. It is a co-crystal consisting of two different neutral zinc(Ⅱ) complexes with Hbpbm (Hbpbm = 4-bromo-2-(benzimidazol-2-yl)phenol) and Hnpbm (Hnpbm = 2-(1-butylbenzimidazol-2-yl)phenol).One is a monomeric mixed-ligand complex of [Zn(bpbm)(npbm)] 1 and the other a dimer of[Zn2(npbm)4] 2 with their ratio of 2:1. Thus the overall formula for the title compound is 21·2.Adjacent 1 and 2 are connected to each other by intermolecular hydrogen bonding interactions in the lattice. The crystal data: monoclinic, space group P21/c, a= 15.0141(12), b = 20.9941(17), c =18.4686(15) (A), β = 97.445(2)°, V= 5772.4(8) (A)3, Mr= 2429.68, Z = 2, Dc = 1.398 g/cm3,μ = 1.579mm-1, F(000) = 2504, R = 0.0637 and wR = 0.1771 for 6464 observed reflections (I> 2σ(Ⅰ)). The geometrical structure for 1 has also been theoretically optimized and compared with the experimental one.  相似文献   
86.
A fundamental principle of queueing theory isL=W (Little's law), which states that the time-average or expected time-stationary number of customers in a system is equal to the product of the arrival rate and the customer-average or expected customer-stationary time each customer spends in the system. This principle is now well known and frequently applied. However, in recent years there have been extensions, such as H=G and the continuous, distributional, ordinal and central-limit-theorem versions, which show that theL=W relation, when viewed properly, has much more power than was previously realized. Moreover, connections have been established between H=G and other fundamental relations, such as the rate conservation law and PASTA (Poisson arrivals see time averages), which show that there is a much greater unity in the overall theory than was previously realized. This paper provides a review.This paper is dedicated to the memory of our colleague Professor Peter Franken (1937–1989), who contributed greatly to the subject of this paper and to queueing theory more generally.  相似文献   
87.
The paper describes the structure of a new space of generalized Wiener functionals, , called the Wiener algebra, or space of Wiener distributions, and demonstrates its use in the white noise analysis. The concepts of derivatives and integrals for multi-time parameter generalized stochastic process:N are introduced, and a derivative version of Itô's lemma is proved. The algebraic structure of and its lattice of subspaces is elaborated, and within this framework a generalized version of the Malliavin calculus is presented.  相似文献   
88.
In this paper we describe a new technique for generating iteration formulas — of arbitrary order — for determining a zero (assumed simple) of a functionf, assumed analytic in a region containing the zero. The 1/p Padé Approximant (p0) to the functiong(t)f(z) is formed wherez=w+t, using the Taylor series forf at the pointw, an approxination to the zero off. The value oft for which the 1/p Padé Approximant vanishes provides the basis of iteration formulas of orderp+2.Some known iteration formulas, e.g., Newton-Raphson's, Halley's and Kiss's of order of convergence two, three and four, are directly obtained by settingp=0,1 and 2, respectively.  相似文献   
89.
We prove a generalization of the Kibble–Slepian formula (for Hermite polynomials) and its unitary analogue involving the 2D Hermite polynomials recently proved in [16]. We derive integral representations for the 2D Hermite polynomials which are of independent interest. Several new generating functions for 2D q-Hermite polynomials will also be given.  相似文献   
90.
Recently there has been a renewed interest in asymptotic Euler–MacLaurin formulas, because of their applications to spectral theory of differential operators. Using elementary means, we recover such formulas for compactly supported smooth functions on intervals, polygons, and three-dimensional polytopes, where the coefficients in the asymptotic expansion are sums of differential operators involving only derivatives of the function in directions normal to the faces of the polytope. Our formulas apply to wedges of any dimension.  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