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   14507篇
  免费   209篇
  国内免费   198篇
化学   2239篇
晶体学   71篇
力学   226篇
综合类   115篇
数学   11092篇
物理学   1171篇
  2024年   35篇
  2023年   56篇
  2022年   187篇
  2021年   140篇
  2020年   123篇
  2019年   344篇
  2018年   386篇
  2017年   240篇
  2016年   203篇
  2015年   242篇
  2014年   383篇
  2013年   720篇
  2012年   599篇
  2011年   766篇
  2010年   659篇
  2009年   934篇
  2008年   963篇
  2007年   1011篇
  2006年   779篇
  2005年   572篇
  2004年   509篇
  2003年   404篇
  2002年   340篇
  2001年   319篇
  2000年   359篇
  1999年   400篇
  1998年   320篇
  1997年   281篇
  1996年   253篇
  1995年   269篇
  1994年   271篇
  1993年   246篇
  1992年   197篇
  1991年   135篇
  1990年   145篇
  1989年   135篇
  1988年   103篇
  1987年   103篇
  1986年   83篇
  1985年   85篇
  1984年   88篇
  1983年   38篇
  1982年   88篇
  1981年   69篇
  1980年   78篇
  1979年   51篇
  1978年   72篇
  1977年   52篇
  1976年   41篇
  1975年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
A simple and rapid capillary electrophoretic method was developed for the simultaneous determination of noradrenaline (NA) and dopamine (DA) in Portulaca oleracea L. The buffer solution used in this method was 40 mM tris (hydroxymethyl) aminomethane (Tris)-H3PO4 at pH 2.00 containing 15% methanol. The effects of pH value, organic modifier, and applied voltage were investigated. The linear ranges of NA and DA were 0.5-100 microg/mL (r=0.9952) and 6.25-200 microg/mL (r=0.9992), respectively. The relative standard deviations of the corrected peak area were 6.73% and 4.26%, respectively. NA and DA in Portulaca oleracea L. were simultaneous determined successfully within 5.6 min. In this way, the contents of NA and DA in different parts (stem, leaves, and seeds) of P. oleracea L. and in different extracts of leaves with different solvents (distilled water, 50% methanol, and methanol) were studied.  相似文献   
12.
Simple sugars were isolated from the ethanol extract of Glycyrrhiza glabra L. root. The component composition of the carbohydrate fraction was established using GC-MS (gas-chromatographic separation and mass-spectrometric analysis).  相似文献   
13.
We show that, for the Chebyshev weight function (1–x 2)–1/2, the Cotes numbers for the quadrature rule with nodes at the zeros of the ultraspherical polynomialP n /() are nonnegative if and only if –1/2<1.  相似文献   
14.
15.
In this paper we considered curvature conditions on a Kähler-Einstein surface of general type. In particular we showed that it has negative holomorphic sectional curvature if theL 2-norm of (3C 2 ?C 1 2 )/C 1 2 is sufficiently small, whereC 1 andC 2 are the first and second Chern classes of the surfaces. This generalizes a result of Yau on the uniformization of Kähler-Einstein surfaces of general type and with 3C 2 ?C 1 2 = 0. Also in the process, we obtain a necessary condition in terms of an inequality between Chern numbers for a Kähler-Einstein metric to have negative holomorphic sectional curvature.  相似文献   
16.
For the detection of the rare radioactive isotope41Ca, the possibilities of the earlier-proposed initial-state enrichment by continuous-wave laser radiation are examined. It is shown that the enrichment 1014 of 3d-states of the ion Ca II can be reached. As the method of enriched-state detection, the process of resonant charge exchange is analysed. For a further increase of the selectivity, the repetition of the cycle initial state enrichment plus resonant charge exchange is discussed.  相似文献   
17.
Letx 1, ,x n be real numbers with 1 n x j =0, |x 1 ||x 2 ||x n |, and 1 n f(|x i |)=A>0, wheref is a continuous, strictly increasing function on [0, ) withf(0)=0. Using a generalized Chebycheff inequality (or directly) it is easy to see that an upper bound for |x m | isf –1 (A/(n–m+1)). If (n–m+1) is even, this bound is best possible, but not otherwise. Best upper bounds are obtained in case (n–m+1) is odd provided either (i)f is strictly convex on [0, ), or (ii)f is strictly concave on [0, ). Explicit best bounds are given as examples of (i) and (ii), namely the casesf(x)=x p forp>1 and 0<p<1 respectively.  相似文献   
18.
The differential cross-sections for the emission of M shell fluorescent X-rays from Th by 5·95 keV photons at eight angles ranging from 50° to 120° have been measured. The differential cross-section is found to decrease with increase in the emission angle showing anisotropic spatial distribution of M shell fluorescent X-rays. The present results contradict the predictions of the calculations of Cooper and Zare [1] that the atomic inner shell vacancy states produced in photoionization are not aligned but confirm those of Fluggeet al [2] and Scofield [3] that the vacancy states withJ > 1/2 are aligned. The integral M shell fluorescent emission cross sections have been determined from the measured angular distribution coefficients and compared with theoretical integral cross-sections calculated by using theoretical values of M subshell photoionization cross-sections, fluorescence yields and coster kronig transition probabilities available in literature. The experimental and theoretical values of integral crosssections show a reasonable agreement.  相似文献   
19.
By the application of the coinduction method as well as the Magri method to the ideal of real Hilbert–Schmidt operators we construct the hierarchies of integrable Hamiltonian systems on Banach Lie–Poisson spaces which consist of such types of operators. We also discuss their algebraic and analytic properties and solve them in dimensions, N=2,3,4N=2,3,4.  相似文献   
20.
The quantum group IGL q (N), the inhomogenization of GL q (N), is formulated with -matrices. Theq-deformed universal enveloping algebra is constructed as the algebra of regular functionals in this formulation and contains the partial derivatives of the covariant differential calculus on the quantum space.  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