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   9152篇
  免费   222篇
  国内免费   13篇
电工技术   117篇
综合类   7篇
化学工业   1536篇
金属工艺   229篇
机械仪表   132篇
建筑科学   455篇
矿业工程   15篇
能源动力   212篇
轻工业   674篇
水利工程   79篇
石油天然气   118篇
武器工业   1篇
无线电   642篇
一般工业技术   1277篇
冶金工业   2710篇
原子能技术   77篇
自动化技术   1106篇
  2021年   77篇
  2020年   78篇
  2019年   87篇
  2018年   98篇
  2017年   98篇
  2016年   107篇
  2015年   100篇
  2014年   116篇
  2013年   473篇
  2012年   263篇
  2011年   335篇
  2010年   243篇
  2009年   262篇
  2008年   325篇
  2007年   329篇
  2006年   280篇
  2005年   283篇
  2004年   241篇
  2003年   225篇
  2002年   247篇
  2001年   150篇
  2000年   156篇
  1999年   214篇
  1998年   395篇
  1997年   291篇
  1996年   249篇
  1995年   178篇
  1994年   186篇
  1993年   193篇
  1992年   141篇
  1991年   109篇
  1990年   132篇
  1989年   141篇
  1988年   124篇
  1987年   136篇
  1986年   131篇
  1985年   175篇
  1984年   177篇
  1983年   120篇
  1982年   108篇
  1981年   131篇
  1980年   91篇
  1979年   128篇
  1978年   97篇
  1977年   123篇
  1976年   130篇
  1975年   90篇
  1974年   82篇
  1973年   92篇
  1972年   74篇
排序方式: 共有9387条查询结果,搜索用时 125 毫秒
991.
992.
Although the European Commission and the Member States of the European Union (EU)1 have promoted a number of policy initiatives to foster the Energy Services Company (ESCO) industry, a recent survey of ESCO businesses in Europe has indicated that major differences exist in the development of the ESCO business among the various countries. In some countries a large number of ESCOs have been successfully operating for a number of years, while in other countries only a few ESCOs have recently started to operate. This difference could be explained by several factors, such as different levels of support offered to ESCOs by national and regional energy authorities, local market structures and rules, and variation in the definitions, roles and activities of ESCOs. This paper reviews and analyses the development and the current status of ESCO industries in the EU and the New Accession Countries. Based on the review and the analysis, a long-term strategy to foster the development of ESCOs in Europe is formulated. The strategic actions recommended build on successful experience in Europe and are proposed with an eye to existing and planned legislative measures, such as the proposed Energy Service Directive and the deployment of the Kyoto flexible mechanisms.  相似文献   
993.
The authors evaluated the adsorption loss of tricyclic antidepressants in analytical procedures with solvent extraction and evaporation. In standard procedures with the use of triple solvent extraction between alkalinized and acidified samples before chromatographic analysis, the adsorption loss was more significant with the demethylated metabolites. As much as 50% adsorption loss can occur; this irreversible loss can be accounted for entirely during the solvent evaporation step. Because of differential adsorption loss among parent drugs, metabolites, and internal standards, the analytical methods usually had wide within-day and day-to-day variations. The authors found that the addition of as little as 0.05% diethylamine to the extract before evaporation completely eliminated the adsorption loss of amitriptyline-nortriptyline, imipramine-desipramine, and doxepin-desmethyldoxepin. with subsequent improvement in procedure performance. This simple modification can be adopted readily by all laboratories that use solvent extraction and subsequent chromatographic analysis of tricyclic antidepressants.  相似文献   
994.
995.
For over 46 years, the American Psychological Association (APA) has sponsored an accreditation system for professional doctoral and internship programs. Throughout its history, national conferences in psychology have consistently supported this accreditation system, at times with reservations. Recently, both academic and professional groups of psychologists have sought a stronger role in this process. The factors leading to APA's accreditation system, its evolution, and the recent major changes enacted in response to the discipline's interests are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
996.
This study was designed to determine whether dextran, gelatin or hydroxyethyl starch-based colloidal resuscitation fluids (CRF) are inhibitory to T lymphocyte activation and mitogenesis in vitro. Isolated peripheral blood lymphocytes from normal donors were activated with mitogen (PHA) and cultured in up to 50% v:v CRF. Dual-label flow cytometry for CD69 and CD25 were used to assess early and full T cell activation responses, respectively, and thymidine incorporation was used to assess mitogenesis. T cell activation and mitogenic responses were not inhibited in the presence of CRF, implying that any systemic immunodepression associated with CRF infusion is not directly related to CRF-mediated impairment of T cell activation.  相似文献   
997.
998.
The design of a log periodic strip grating antenna is described. The 12-element antenna is compact and has a measured power bandwidth of 22%. The antenna elements are mounted on the top of the top layer of a two-layer structure with its feed line located between the two dielectric layers providing electromagnetic coupling. The structure was analyzed using PMESHD, a moment method code for two-layer passive structures. The analysis and measurements are in good agreement. © 1993 John Wiley & Sons. Inc.  相似文献   
999.
OBJECTIVE: To determine the prevalence of fibromyalgia (FM) in schoolchildren according to the 2 stage classification process proposed by the 1990 American College of Rheumatology (ACR) Multicenter Criteria Committee on Fibromyalgia. METHODS: Stage 1: we administered a pain questionnaire to a sample of 548 schoolchildren (264 boys, 284 girls; mean age 11.9 yrs, range 9-15). Stage 2: two rheumatologists examined all children with diffuse pain. Using thumb palpation, they examined 18 fibromyalgia tender points and 3 pairs of controls points followed by dolorimetry. Additionally, a random sample of 79 children with no pain were selected as controls, following the same procedures (thumb palpation and dolorimetry). The Wilcoxon test was used to compare the distribution of tenderness thresholds between FM and non-FM groups. Kappa statistics for multiple raters was used to assess interobserver agreement. RESULTS: Seven children, all girls, fulfilled the ACR diagnostic criteria for FM. Thus, the prevalence of FM in this group of schoolchildren reached only 1.2%. The girls with FM had a mean of 14 tender points, whereas controls (n = 79) had 2.4. Pain thresholds were 3.4 kg in children with FM and 5.1 kg in controls (p = 0.004). CONCLUSION: The prevalence of FM in our study was 5-fold lower than a previous report. This variance may be due to (1) racial and sociocultural differences between populations; and (2) differences in methodological approach. The difficulties of making accurate estimates of FM across different studies are highlighted.  相似文献   
1000.
The inflammatory response after traumatic brain injury (TBI) includes cytokine production, leukocyte infiltration, and microglial activation. Production of nitric oxide by inducible nitric oxide synthase (iNOS) occurs during acute inflammation outside of the CNS and in models of cerebral ischemia, and therefore may contribute to the inflammatory response after TBI. The purpose of this study was to localize and define the time course of iNOS expression after TBI in the immature rat. Immature Wistar rats (age 3.5-4.5 wk) were anesthetized and subjected to percussive trauma to the right parietal cortex. Nontraumatized rats were used as controls (n = 7). At 2, 24, 48, or 168 h (n = 3/group) posttrauma rats were killed by perfusion fixation. Brains were removed, frozen, sectioned, immunostained with antibodies against iNOS and glial fibrillary acidic protein (GFAP, a marker specific for astrocytes), and imaged using fluorescent detection systems. There was no detectable expression of iNOS in control brains. At 2h, minimal cerebrovascular iNOS expression was seen in the peritrauma area. At 24 and 48 h, there was marked peritrauma cerebrovascular iNOS expression that appeared to be restricted to vascular smooth muscle cells and infiltrated leukocytes. Further dual-immunolabeling showed that the leukocytes expressing iNOS were predominantly neutrophils. At 168 h, iNOS expression was no longer detectable. iNOS was not detectable in GFAP-positive cells. The prominent expression of iNOS protein after TBI in cerebrovascular smooth muscle cells and infiltrated neutrophils suggests that iNOS may play a role in cerebrovascular disturbances and secondary brain injury after trauma.  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