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   16029篇
  免费   2335篇
  国内免费   545篇
化学   2786篇
晶体学   134篇
力学   882篇
综合类   101篇
数学   5889篇
物理学   9117篇
  2024年   54篇
  2023年   393篇
  2022年   665篇
  2021年   703篇
  2020年   756篇
  2019年   458篇
  2018年   626篇
  2017年   894篇
  2016年   887篇
  2015年   929篇
  2014年   1240篇
  2013年   1062篇
  2012年   1346篇
  2011年   1067篇
  2010年   945篇
  2009年   1034篇
  2008年   646篇
  2007年   679篇
  2006年   715篇
  2005年   422篇
  2004年   224篇
  2003年   221篇
  2002年   205篇
  2001年   317篇
  2000年   124篇
  1999年   268篇
  1998年   174篇
  1997年   136篇
  1996年   100篇
  1995年   64篇
  1994年   40篇
  1993年   30篇
  1992年   41篇
  1991年   34篇
  1990年   33篇
  1989年   45篇
  1988年   248篇
  1987年   422篇
  1986年   411篇
  1985年   52篇
  1984年   20篇
  1982年   26篇
  1981年   35篇
  1980年   19篇
  1979年   18篇
  1978年   36篇
  1977年   14篇
  1976年   20篇
  1959年   3篇
  1936年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
An improved, continuous-flow ultrasonic nebulizer equipped with a desolvation system for generating dehydrated aerosol particles prior to their injection into analytical inductively coupled plasmas is described. Results of a critical evaluation of the performance of the nebulizer-desolvation system are also presented. Compared to the commonly used pneumatic nebulizers studied in this work, the ultrasonic version described in this paper provided superior powers of detection, ranging from factors of 5–50, and yielded comparable to superior short and long term reproducibility for dilute acid and high salt content solutions. Clean out times for the ultrasonic nebulizer were marginally longer, by 15–20 s, than those observed for pneumatic nebulizers. “Memory effects” and “desolvation interferences” were generally reducible to negligible proportions through the application of various expediencies discussed in this paper. When substantial changes in concomitant concentrations caused measurable interelement effects, the magnitude of these effects tended to be slightly higher for the ultrasonic system. However, when the samples destined for ultrasonic nebulization were diluted by factors of ~ 10, which corresponds approximately to the superiority of the nebulization efficiency of the ultrasonic nebulizer, the magnitudes of the interelement effects were comparable.  相似文献   
32.
By repeated deposition of several Å of Ni below 100 °C and subsequent annealing to typically 350 °C, thin continuous NiSi2-layers have been grown epitaxially on Si (111). Thicknesses exceeding ∼- 70 Å require a different procedure due to the increasing importance of lateral growth, spoiling the layer quality. We show that MBE at substrate temperatures above 500 °C is not a viable technique to increase the thickness of the ultrathin layers. The reason is found to lie in the insufficient stability of the NiSi2 templates, disintegrating into islands at temperatures above 500 °C. Perfectly smooth layers up to 1000 Å have, however, been grown by a new method in which alternate layers of Ni and Si (typically 1 Å and 4 Å respectively) are deposited onto the initial template at substrate temperatures between 350 °C and 380 °C.  相似文献   
33.
The selective adsorption of blood group antibodies can be realized on immobilized red bloods cells on polycationic supports. Different supports containing dimethyl amino ethyl methacrylate (DMAEMA) has been obtained according to various proceedings : grafting on PVC, bulk polymerization, suspension polymerization.Physical characteristics and specific adsorption yields have been compared.This study has led to perfect specific and performant immunoadsorbents.  相似文献   
34.
35.
《Chemical physics》1986,108(3):417-428
The molcules NSF, NSO, NSCl, HNSF+, HNSO, CH3NSF+, CH3NSO are investigated at the SCF level and partly with inclusion of electron correlation effects. Equilibrium geometries and relative stabilities of isomers and conformers are reported. Structure constants and relative energies are discussed in connection with the molecular electronic structure as characterized by the results of population analyses.  相似文献   
36.
《Chemical physics》1986,101(2):279-289
The phenomenon of laser-induced hole filling (LIHF) is reported and discussed in detail for rhodamine 640, Nd3+, Pr3+ and the mixed system of rhodamine 560 and cresyl violet. Importantly, LIHF does not show any spectral diffusion (i.e. broadening). Possible mechanisms (thermal heating, site reversion and energy transfer) involved in LIHF are discussed and are argued to have insignificant contribution. A tentative model is developed to explain these results. The model basically invokes a connectivity between spatially removed extrinsic (impurity) two-level systems (TLS) via an ensemble of intrinsic (host) TLS (the glassy state). Additionally, a correlation between impurity excitation energies and absolute glassy state energies is imposed.  相似文献   
37.
This paper shows how the notion of ‘relative importance of attributes’ can be defined within the framework of the noncompensatory approach to multiple criteria decision making. The problem of weights then appears as a problem of functional representation of relations. We state some theoretical results concerning this problem and outline a practical decision-aid (Tactic) based on the ideas introduced in the paper.  相似文献   
38.
The paper is concerned with a two-level corporate model. At the lower level, divisions produce for the external market. They require certain technical services. The divisions are coordinated by a central unit at the top level. The central unit must determine the integral plan of technical services i.e. firm-wide optimal make-or-buy decisions, without having complete information on the divisions.We present a decomposition-based planning procedure during which the central unit gathers information to derive an optimal make-or-buy decision while allocating the costs of internal technical services.The model formulation has substantial significance for the real world: A similar organizational structure, information dispersal among subunits and coupling of divisions and departments is commonly observed in existing firms. The resulting planning procedure can be interpreted in terms of planning and budgeting in real organizations.  相似文献   
39.
A problem of the maximization of the ratio of a concave function to a convex function is considered, subject to an upper bound on a single convex constraint function; all these functions are assumed to be differentiable. An incremental algorithm is defined, which solves the problem parametrically for different values of the constraint function by the solution of a set of ordinary first order differential equations. If K is the number of variables in the problem and B(K) is an upper bound—dependent of K —of the time needed to evaluate any function value or any first or second order derivative, the complexity of the algorithm is of the order O[(B(K)K + K)a], where a is the number of integration steps applied in the solution of the differential equations. In particular, a cost-effectiveness resource allocation problem with separable functions is solved numerically in a time of the order O[Ka] if B(K) is independent of K; an example of such a problem is given with analytically solvable differential equations.  相似文献   
40.
《Nuclear Physics A》1986,452(4):573-590
By means of a streamer chamber exposed to the LEAR antiproton beams, the total reaction cross sections, the charged-prong multiplicity distributions and lower limits for the production of negative pions and Ks0 in the p̄-Ne interaction were measured at 19.6, 48.7 and 179.6 MeV. Annihilation was found to be dominant over all other non-elastic p̄-Ne processes. An analysis of Ne and other nuclei data in the frame of the Glauber theory allowed us to determine the ratio between the p̄-n and the p̄-p cross sections. An analysis in the light of INC model predictions allowed us to show up events which can be interpreted as annihilations having occurred deeply inside the nuclei.  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