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   76098篇
  免费   2424篇
  国内免费   1549篇
化学   48278篇
晶体学   499篇
力学   1454篇
综合类   12篇
数学   14099篇
物理学   15729篇
  2023年   515篇
  2022年   781篇
  2021年   1098篇
  2020年   1143篇
  2019年   1204篇
  2018年   1391篇
  2017年   1312篇
  2016年   2636篇
  2015年   2194篇
  2014年   2304篇
  2013年   4976篇
  2012年   4805篇
  2011年   4828篇
  2010年   3076篇
  2009年   2996篇
  2008年   3990篇
  2007年   3802篇
  2006年   3240篇
  2005年   3321篇
  2004年   3289篇
  2003年   2620篇
  2002年   2365篇
  2001年   1499篇
  2000年   1430篇
  1999年   1046篇
  1998年   888篇
  1997年   797篇
  1996年   922篇
  1995年   690篇
  1994年   732篇
  1993年   725篇
  1992年   693篇
  1991年   585篇
  1990年   632篇
  1989年   526篇
  1988年   533篇
  1987年   472篇
  1986年   498篇
  1985年   686篇
  1984年   667篇
  1983年   513篇
  1982年   507篇
  1981年   524篇
  1980年   440篇
  1979年   435篇
  1978年   419篇
  1977年   380篇
  1976年   401篇
  1975年   381篇
  1974年   395篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
It was studied the tin phase composition of the electrodeposited alloys produced at different temperatures and current densities from an acid chloride/fluoride electrolyte and an acid chloride bath. Mössbauer spectra were consistent with a Ni3Sn4 intermetallic compound, dissolved tin, and a Cu?Sn intermetallic compound formed at the interface of the copper substrate.  相似文献   
132.
A pair of coupled classical oscillators with a general potential and general form of coupling is investigated. For general potentials, the single-frequency solution is shown to be stable for small excitations. For special potentials, such system remains stable for an arbitrary excitation. In both cases, the stability does not depend on the form of coupling. Transition to the instability regime follows from the way how nonlinear potential entrains the energy transfer between the oscillators. Relation between the existence of multi-frequency quasi-periodic or periodic solutions and the instability of single-frequency ones is discussed.  相似文献   
133.
We present a Bayesian theory of object identification. Here, identifying an object means selecting a particular observation from a group of observations (variants), this observation (the regular variant) being characterized by a distributional model. In this sense, object identification means assigning a given model to one of several observations. Often, it is the statistical model of the regular variant, only, that is known. We study an estimator which relies essentially on this model and not on the characteristics of the “irregular” variants. In particular, we investigate under what conditions this variant selector is optimal. It turns out that there is a close relationship with exchangeability and Markovian reversibility. We finally apply our theory to the case of irregular variants generated from the regular variant by a Gaussian linear model.  相似文献   
134.
A new way of expounding analytical properties based on their mutual dependence (complementary and contradictory relationships) and their unequivocal connection with analytical quality facets is presented. To this end, the paper provides answers to the obvious questions that arise in dealing with the subject: why?, how?, when? and where to teach analytical properties in the Analytical Chemistry curriculum?  相似文献   
135.
136.
A simple High performance liquid chromatographic (HPLC) method for the specific determination of the molecular weight and concentration of hyaluronic acid (HA) in complex mixtures has been developed. Hyaluronate-binding proteins isolated from bovine cartilage labelled by 125I or fluoresceinisothiocyanate were used as specific markers. The specific binding affinities of the markers were compared and were found to have association constants of 1.6 x 10(7) M-1 and 1.2 x 10(7) M-1 respectively. The HA levels and molecular weight distributions can be easily determined in the range 10-500 ng/mL in complex mixtures by the use of markers, molecular sieving HPLC columns and appropriate detectors. It has been demonstrated clearly that the method is useful for the highly specific determination of the parameters in complex biological samples such as serum and synovial fluids and is recommended for clinical applications.  相似文献   
137.
138.
We present a solution to the moment problem for effect algebras, concerning mean values of all powers of an observable concentrated on the interval [0, 1] for states from a convex set. We give a solution for particular examples, e.g., for the set of all effect operators. We examine how this problem is related to a socalled E-property. Finally, we give a solution for observables studied in the operational approach to physical theories.  相似文献   
139.
Dislocation motion in the real lattice of alloys is highly complex. In a certain temperature range the dynamic strain ageing phenomena have been reported. In this paper the influence of mobile solute atoms (as obstacles) on the motion of dislocation is analysed. Both processes are assumed to be thermally activated. A new model based on this assumption is proposed. The dislocation velocity and the friction stress (due to solute-dislocation interactions) are calculated. A change in the friction stress caused by solute mobility is discussed.  相似文献   
140.
We consider a sequence of curved rods which consist of isotropic material and which are clamped on the lower base or on both bases. We study the asymptotic behaviour of the stress tensor and displacement under the assumptions of linearized elasticity when the cross‐sectional diameter of the rods tends to zero and the body force is given in the particular form. The analysis covers the case of a non‐smooth limit line of centroids. We show how the body force and the choice of the approximating curved rods can affect the strong convergence and the limit form of the stress tensor for the curved rods clamped on both bases. Copyright © 2006 John Wiley & Sons, Ltd.  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