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   29350篇
  免费   3554篇
  国内免费   1527篇
电工技术   2554篇
技术理论   1篇
综合类   3085篇
化学工业   3685篇
金属工艺   890篇
机械仪表   1251篇
建筑科学   3301篇
矿业工程   1088篇
能源动力   995篇
轻工业   1469篇
水利工程   1063篇
石油天然气   1304篇
武器工业   373篇
无线电   3131篇
一般工业技术   2022篇
冶金工业   2375篇
原子能技术   250篇
自动化技术   5594篇
  2024年   121篇
  2023年   436篇
  2022年   702篇
  2021年   846篇
  2020年   922篇
  2019年   857篇
  2018年   752篇
  2017年   984篇
  2016年   1185篇
  2015年   1191篇
  2014年   1774篇
  2013年   1627篇
  2012年   1854篇
  2011年   2062篇
  2010年   1595篇
  2009年   1728篇
  2008年   1681篇
  2007年   1839篇
  2006年   1749篇
  2005年   1484篇
  2004年   1209篇
  2003年   1143篇
  2002年   1022篇
  2001年   892篇
  2000年   679篇
  1999年   530篇
  1998年   368篇
  1997年   307篇
  1996年   244篇
  1995年   226篇
  1994年   227篇
  1993年   157篇
  1992年   127篇
  1991年   82篇
  1990年   107篇
  1989年   72篇
  1988年   62篇
  1987年   40篇
  1986年   38篇
  1985年   141篇
  1984年   245篇
  1983年   287篇
  1982年   205篇
  1981年   309篇
  1980年   120篇
  1979年   43篇
  1978年   39篇
  1977年   14篇
  1975年   22篇
  1974年   24篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
31.
Presents the citation, biography, and selected bibliography for R. Chris Fraley, one of the 2007 recipients of the American Psychological Association's Award for Distinguished Scientific Early Career Contributions to Psychology (individual differences). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
32.
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
33.
陈志华 《电力学报》2004,19(3):253-255
每个国定的经济能不能持续发展 ;能不能在激烈的国际竞争中始终不衰 ;关键在于这个国家能不能开发人力资源 ;占领人力资源、用好人力资源。  相似文献   
34.
The price of SO2 permits and the volume of trading under the US Acid Rain Program have been lower than expected. This can be explained by the creation and distribution of more permits than were initially authorized, by the sale of permits by high cost abaters who are subject to more stringent local emission constraints or who have irreversibly invested in high cost abatement technologies and by the deregulation of the natural gas and railroad industries which, in combination with incentives for cost-cutting under the new market approach to SO2 control, has lowered marginal costs of abatement curves and made them more uniform across powerplants. The low price of permits and low trading volume are evidence that market approaches to pollution control can be more cost-effective than command and control regulations. The effect of public policies and technological changes on the allowance market are usefully examined in the context of an ideal market, in which the equilibrium price of allowances equals the marginal cost of abatement of individual powerplants. Using recent data from Coggins and Swinton (1996), we are able to explain the current price of permits with some accuracy.  相似文献   
35.
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.  相似文献   
36.
由进口电性能仪配上自制的高温系统,计算机自动采集数据,配置成一套高低温电性参数测定装置,该装置的特点是,升温快,炉体小巧,炉芯可更换盛液氮装置,屏蔽良好,等温区长,温工及参数测量精确可靠。  相似文献   
37.
张家桂 《控制与决策》1994,9(6):459-463
本文提出励磁电流可自动控制的他励式双高调速系统设计方案。系统在提升特别是在下放重物时,具有较硬的机械性;在负载10-100%的变化范围内,可实现最大偏差Δnmax/nmin100%≤10%,调速范围D≥10;在满载运行条件下,可节约电能80%以上。  相似文献   
38.
A semi-analytic boundary element method for parabolic problems   总被引:1,自引:0,他引:1  
A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems.  相似文献   
39.
An efficient method is described for sensitivity analysis of nonlinear initial value problems, which may include algebraic equations as well as ordinary differential equations.The linearity of the sensitivity equations is utilized to solve them directly via the local Jacobian of the state equations. The method is implemented with the implicit integrator DASSL and is demonstrated on a stiff industrial reaction model.  相似文献   
40.
[Correction Notice: An erratum for this article was reported in Vol 20(2) of Canadian Journal of Behavioural Science Revue canadienne des Sciences du comportement (see record 2007-09831-001). The abstract accompanying the original article was incorrect; the correct abstract (in French) is presented in the erratum.] We know little about individuals who are declared unfit to stand trial and/or not guilty by reason of insanity. The few existing studies are characterized by methodological weaknesses, notably by short follow-up periods and a lack of external validity. The present investigation, which aims to evaluate and explain readmissions that occurred during a seven- to nine-year period, corrects only some of these weaknesses. Sixty-one per cent of the subjects were rehospitalized during the period of study. It proved difficult to identify the factors associated with readmission. However, males with a diagnosis of schizophrenia and who had committed violent crimes were found the most likely to be readmitted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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