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   45159篇
  免费   1272篇
  国内免费   31篇
化学   25831篇
晶体学   192篇
力学   930篇
数学   7189篇
物理学   12320篇
  2023年   231篇
  2021年   362篇
  2020年   546篇
  2019年   383篇
  2018年   496篇
  2017年   474篇
  2016年   1118篇
  2015年   962篇
  2014年   1067篇
  2013年   2334篇
  2012年   1850篇
  2011年   2252篇
  2010年   1177篇
  2009年   990篇
  2008年   2109篇
  2007年   2106篇
  2006年   1887篇
  2005年   1678篇
  2004年   1316篇
  2003年   1170篇
  2002年   1078篇
  2001年   918篇
  2000年   805篇
  1999年   571篇
  1998年   512篇
  1997年   509篇
  1996年   635篇
  1995年   564篇
  1994年   575篇
  1993年   664篇
  1992年   584篇
  1991年   458篇
  1990年   483篇
  1989年   423篇
  1988年   431篇
  1987年   443篇
  1986年   393篇
  1985年   595篇
  1984年   599篇
  1983年   519篇
  1982年   563篇
  1981年   559篇
  1980年   506篇
  1979年   488篇
  1978年   503篇
  1977年   490篇
  1976年   430篇
  1975年   411篇
  1974年   402篇
  1973年   389篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Gamma rays of199Au obtained after double neutron capture in197Au were measured at the ILL high flux reactor. A level scheme up to 1770 keV excitation energy is established. The result is compared with IBFM and Boson-Fermion-Symmetry calculations.  相似文献   
52.
53.
54.
55.
In this paper total cross sections for signals and backgrounds of top- and Higgs-production channels in e + e- collisions at a future linear collider are presented. All channels considered are characterized by the emergence of six-particle final states. The calculation takes into account the full set of tree-level amplitudes in each process. Two multi-purpose parton level generators, HELAC/PHEGAS and AMEGIC + + , are used, and their results are found to be in perfect agreement.Received: 26 November 2003, Revised: 15 January 2004, Published online: 3 March 2004  相似文献   
56.
Poly(D ,L ‐lactide) and poly(D ,L ‐lactide‐co‐glycolide) with various composition and with one methacrylate and one carboxylate end group were synthesized and grafted onto poly(vinyl alcohol) (PVA) via the carboxylate group. The graft copolymers were crosslinked via the methacrylate groups using a free radical initiator. The polymer networks were characterized by means of NMR and studied qualitatively by means of IR spectroscopy. The influence of the glycolide content in the polyester grafts and of the number of ester units in the grafts on thermal properties and swellability were studied as well. The high swellability in water is characteristic of all hydrogels. Differential scanning calorimetry (DSC) showed a single glass transition temperature that occurs in the range between 51 and 69 °C. Thermogravimetric analysis (TGA) of the networks showed the main loss in weight in the temperature range between 290 and 370 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4536–4544, 2007  相似文献   
57.
Finding Robust Solutions Using Local Search   总被引:1,自引:0,他引:1  
This paper investigates how a local search metaheuristic for continuous optimisation can be adapted so that it finds broad peaks, corresponding to robust solutions. This is relevant in problems in which uncertain or noisy data is present. When using a genetic or evolutionary algorithm, it is standard practice to perturb solutions once before evaluating them, using noise from a given distribution. This approach however, is not valid when using population-less techniques like local search and other heuristics that use local search. For those algorithms to find robust solutions, each solution needs to be perturbed and evaluated several times, and these evaluations need to be combined into a measure of robustness. In this paper, we examine how many of these evaluations are needed to reliably find a robust solution. We also examine the effect of the parameters of the noise distribution. Using a simple tabu search procedure, the proposed approach is tested on several functions found in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
58.
In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strömbro, J., Gudmundson, P., 2008. Mechano-sorptive creep under compressive loading – a micromechanical model. International Journal of Solids and Structures 45 (9), 2420–2450.]. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.  相似文献   
59.
60.
A new ablation target geometry is presented that was used to produce thin films of La1-xSrxMnO3 grown heteroepitaxially on SrTiO3 by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100 nm. PACS 61.10.-i; 61.18.Bn; 68.47.Gh; 71.27.+a; 81.15.Fg  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