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   32816篇
  免费   1656篇
  国内免费   34篇
电工技术   354篇
综合类   59篇
化学工业   7170篇
金属工艺   612篇
机械仪表   583篇
建筑科学   1995篇
矿业工程   79篇
能源动力   903篇
轻工业   2759篇
水利工程   298篇
石油天然气   167篇
武器工业   3篇
无线电   2366篇
一般工业技术   6102篇
冶金工业   5241篇
原子能技术   208篇
自动化技术   5607篇
  2023年   268篇
  2022年   366篇
  2021年   725篇
  2020年   532篇
  2019年   617篇
  2018年   748篇
  2017年   718篇
  2016年   956篇
  2015年   851篇
  2014年   1070篇
  2013年   1983篇
  2012年   1736篇
  2011年   2201篇
  2010年   1578篇
  2009年   1532篇
  2008年   1821篇
  2007年   1703篇
  2006年   1502篇
  2005年   1269篇
  2004年   1137篇
  2003年   972篇
  2002年   941篇
  2001年   557篇
  2000年   539篇
  1999年   546篇
  1998年   505篇
  1997年   466篇
  1996年   468篇
  1995年   447篇
  1994年   436篇
  1993年   435篇
  1992年   394篇
  1991年   233篇
  1990年   324篇
  1989年   324篇
  1988年   277篇
  1987年   297篇
  1986年   287篇
  1985年   314篇
  1984年   274篇
  1983年   258篇
  1982年   241篇
  1981年   210篇
  1980年   178篇
  1979年   182篇
  1978年   168篇
  1977年   136篇
  1976年   122篇
  1975年   136篇
  1974年   111篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
Definition of the problem: Ethical reasoning cannot be enforced. Voluntary understanding is a basic condition for the development of ethical competencies and attitudes. The aim of this survey was to investigate whether the presence of those students who attended our seminars compulsorily would have a negative effect upon the quality of the course. Methods and results: The participants of our small-group seminars in medical ethics were asked to complete a questionnaire on teaching aims, seminar atmosphere, moderation and importance of subjects. One hundred and ninety-two voluntary participants (2001/2) and 293 compulsory participants (2002/3) completed the questionnaire and were statistically compared. There was no significant difference between voluntary and compulsory participants in any of the important items. However, there were considerable differences in some items between male and female participants. Conclusion: We were surprised that there was no difference between the two groups. This leads us to hope that our concept of case-based small-group seminars will prove capable of realising our teaching aims for all students. The difference between male and female participants may have important didactic consequences and will be the subject of further studies.  相似文献   
72.
73.
Michael F. Wilson  Jerry F. Kriz 《Fuel》1985,64(8):1179-1180
In response to an interpretation made by Moore and Akgerman of data taken from a recent publication, previously unexplainable phenomena are accounted for, based on new experimental results. These relate to a thermodynamic equilibrium reaction involving saturation of aromatic hydrocarbons in synthetic crude middle distillates.  相似文献   
74.
Mathematical models have been developed which predict the composition, molecular weight, and melt rheological properties for vinyl chloride/vinyl acetate copolymers of inherent viscosity range 0.4–0.7 dL/g and bound vinyl acetate levels of 3.8–17.4%. The effect of polymer long chain branching on the viscous/elastic moduli ratio is discussed as well as the comparison of Tinius–Olsen melt index measurements vs. mechanical spectrometer results. The reactivity ratio for vinyl chloride/vinyl acetate comonomer pairs was remeasured and found to be significantly different from literature values.  相似文献   
75.
The effects of monomer refluxing on both resin properties and reactor fouling of suspension PVC have been studied in a laboratory-scale 14-L reactor. Process control equations were developed which related the particle properties to the reflux condenser operation by controlling the parameters of (1) the time at which refluxing is begun and (2) the rate profile of heat removal from the condenser. An operating envelope has been developed for laboratory scale operations which optimizes the cycle time of polymerization while minimizing the adverse effects on particle properties. These operating conditions may have application to production scale operations when the proper scaling factors are employed.  相似文献   
76.
A model is presented for the thermal shock damage in plates subjected to a sudden rise in temperature. Spalling is assumed to follow localized buckling caused by the thermally induced compressive stresses above subsurface flaws. The minimum size o flaw required to cause spalling is determined as a function of the material properties of the plate, the temperature rise, the position of the paw, and the time after the thermal shock.  相似文献   
77.
Previous solid state analyses of sintering in Ti4+-doped-commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2O3−TiO3−Na2Ophase diagram at least by 1350°C, a temperature lower than that at which "solid state" studies were conducted. It is suggested that liquid-phase sintering is a much more common occurrence than was realized formerly.  相似文献   
78.
[Correction Notice: An erratum for this article was reported in Vol 55(3) of Journal of Consulting and Clinical Psychology (see record 2008-10745-001). The data presented in Table 2 were incorrect because a row and a column were inadvertently omitted. The corrected Table 2 appears in the erratum.] This study used meta-analysis to study the clinical significance of psychotherapy for symptoms of unipolar depression. The following questions were addressed: How similar is the posttherapy adjustment of depressed adults to that of nondepressed adults? Is this adjustment maintained at follow-up? What dimensions of treatment, therapists, or design are associated with clinical significance? Using the Beck Depression Inventory (BDI), we calculated composite BDI norms from 28 published studies. Sixty effect sizes (from 31 outcome studies utilizing the BDI) were calculated. The results indicated that psychotherapy produces outcomes that have moderate clinical significance and that are well-maintained at follow-up, that individual therapy is associated with greater clinical significance than group treatment, and that type of therapy is not related to improvement. Alternative approaches for operationalizing clinical significance as the return of individuals to normal levels of functioning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
Tested the ability of 4 adult male Sprague-Dawley rats to use odors in discrimination among littermates living as a group. Ss were trained in a Y-maze to discriminate the presence of a littermate from its absence. Results from transfer of training in 3 subsequent testing periods indicated that the animals were capable of distinguishing among individuals when relatedness and familiarity were held constant, that this ability was not due to training, and that performance was based solely on odor cues. Results suggest that laboratory rats exhibit odor sensitivities conmensurate with very complex social processes. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
80.
Gamut mapping deals with the need to adjust a color image to fit into the constrained color gamut of a given rendering medium. A typical use for this tool is the reproduction of a color image prior to its printing, such that it exploits best the given printer/medium color gamut, namely the colors the printer can produce on the given medium. Most of the classical gamut mapping methods involve a pixel-by-pixel mapping and ignore the spatial color configuration. Recently proposed spatial-dependent approaches for gamut mapping are either based on heuristic assumptions or involve a high computational cost. In this paper, we present a new variational approach for space-dependent gamut mapping. Our treatment starts with the presentation of a new measure for the problem, closely related to a recent measure proposed for Retinex. We also link our method to recent measures that attempt to couple spectral and spatial perceptual measures. It is shown that the gamut mapping problem leads to a quadratic programming formulation, guaranteed to have a unique solution if the gamut of the target device is convex. An efficient numerical solution is proposed with promising results.  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