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   94983篇
  免费   10536篇
  国内免费   6626篇
电工技术   8151篇
综合类   9679篇
化学工业   10940篇
金属工艺   6117篇
机械仪表   5974篇
建筑科学   6175篇
矿业工程   3938篇
能源动力   2514篇
轻工业   10900篇
水利工程   3053篇
石油天然气   3109篇
武器工业   1603篇
无线电   8311篇
一般工业技术   7039篇
冶金工业   11182篇
原子能技术   1446篇
自动化技术   12014篇
  2024年   624篇
  2023年   1576篇
  2022年   3635篇
  2021年   4602篇
  2020年   3315篇
  2019年   2264篇
  2018年   2443篇
  2017年   2801篇
  2016年   2563篇
  2015年   4073篇
  2014年   4991篇
  2013年   5933篇
  2012年   7468篇
  2011年   7769篇
  2010年   7424篇
  2009年   6791篇
  2008年   6929篇
  2007年   6775篇
  2006年   5788篇
  2005年   4479篇
  2004年   3304篇
  2003年   2235篇
  2002年   1940篇
  2001年   1813篇
  2000年   1483篇
  1999年   749篇
  1998年   2722篇
  1997年   1559篇
  1996年   1003篇
  1995年   582篇
  1994年   489篇
  1993年   541篇
  1992年   111篇
  1991年   116篇
  1990年   119篇
  1989年   114篇
  1988年   92篇
  1987年   81篇
  1986年   75篇
  1985年   53篇
  1983年   17篇
  1982年   40篇
  1981年   41篇
  1980年   72篇
  1979年   17篇
  1977年   158篇
  1976年   283篇
  1975年   13篇
  1959年   36篇
  1951年   15篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
在10 ̄(-5)_eV-20MeV中子能量范围内对天然汞的中子核数据进行评价。评价内容包括总的、弹性、去弹、总非弹、30条分立能级、连续非弹、(n,2n)、(n,3n,)、(n,n'P)、(n,n'α)、(n,P)、(n,α)、(n,d)、(n,t)和(n,γ)截面;次级中子角分布;双微分截面(DDCS);γ射线产生数据等。评价根据有效实验数据(至1993年)和UNF-92 ̄[1]理论计算。评价数据以ENDF/B6格式录入中国评价核数据库CENDL-2.1版(MAT=1800),并提供核工程有关部门使用。  相似文献   
32.
Thromboembolic events frequently complicate the clinical course of patients with inflammatory bowel disease (IBD). Hereditary thrombophilia may contribute to this tendency. Resistance to activated protein C is the most recently described thrombophilic state and may account for up to 40% of patients with thrombophilia. Thirty-seven patients with IBD were studied (mean age 44 years, range 18-82 years). Three patients had a history of thrombotic episodes. The 37 controls included 23 men and 17 women (mean age 48 years, range 16-89 years). Disease activity was assessed using the Harvey Bradshaw index for patients with Crohn's disease and the Truelove and Witts grading system for patients with ulcerative colitis. Levels of fibrinogen, antithrombin III (ATIII), protein C, protein S, activated protein C resistance (APCR), and the presence of a lupus anticoagulant (LA) were determined. Median ATIII levels in patients with IBD were significantly lower than controls (98% vs 106%, P = 0.007), while fibrinogen was elevated (4.2 vs 3.3 g/liter, P = 0.026) despite quiescent disease activity. LA was detected in 7/37 patients in the IBD group compared to 0/37 controls. (chi2 = 5.68, P = 0.017). No significant difference was observed in levels of inherited thrombophilic factors and in particular APCR between IBD patients and controls. In conclusion, the presence of inherited thrombophilic defects, in particular APCR, is uncommon in patients with IBD and does not merit routine screening.  相似文献   
33.
34.
35.
36.
The commercial broiler industry is a modern day agricultural success due to popular consumer demand, healthy flocks, and least cost production. Preventive medicine is the key for economical control of disease in integrated broiler companies, and includes quarantine-eradication, controlled-exposure, and preventive feed medication. Respiratory and enteric diseases present a continuing, potential threat for economic loss. Most exotic and egg-transmitted poultry diseases have been controlled by reduction or eradication policies. Endemic diseases are controlled by mass vaccination and preventive feed medication. Improvements in genetics, housing, equipment, and disease surveillance has allowed continued improvements in disease prevention. Attention to detail and management of risk is crucial to industry success. With fast industry growth and market maturity of the broiler industry, new challenges have risen. These challenges include increased poultry house density, increasing economic pressures, changing industry attitudes, and increased governmental regulations that will strain the continued success of today's control strategies.  相似文献   
37.
STUDY OBJECTIVES: Asymptomatic HIV-infected individuals are increasingly recruited for studies involving invasive procedures such as bronchoscopy. We sought to determine the response to and outcome of a request for a research bronchoscopy in HIV-positive individuals with no respiratory disease, and whether this would adversely affect future decisions to have a medically indicated bronchoscopy. DESIGN AND SETTING: Prospective, semistructured, questionnaire-based study in a London teaching hospital HIV outpatient clinic. PARTICIPANTS: One hundred and seven consecutive HIV-infected eligible individuals. Thirty-one healthy volunteers served as a control group for the subjective response to bronchoscopy. MAIN OUTCOME MEASURES: Subjects' attitudes and responses to requests for bronchoscopy and subsequent behavior when they required medically indicated bronchoscopy. RESULTS: Seventy-five patients (70%) agreed to the procedure in principle, predominantly for altruistic reasons. Thirty-nine subjects underwent bronchoscopy. Five percent found it worse than expected; and 79% agreed to another research bronchoscopy (performed in 11 subjects approximately 2 years later). All patients said they would undergo bronchoscopy again for diagnostic purposes (required in seven during the study). When compared to a healthy volunteer population within the same study, postbronchoscopy symptoms were similar in frequency although somewhat different in nature. Subjects felt that a clear explanation of what was involved enhanced their participation in this research. CONCLUSIONS: Invasive research procedures such as bronchoscopy can be performed and are repeatable in a healthy HIV-infected population. Performance of procedures for research purposes does not appear to adversely affect future health-care decisions.  相似文献   
38.
张敬普  马飞 《计算机与数字工程》2012,40(12):102-104,108
介绍了工作流的应用背景,分析了某校教务系统中采用的工作流技术的原理和设计思想。提出可编辑、管理和监控的工作流模型,并重点介绍了工作流程运行机制。工作流技术使单位内部业务流程自动化,信息流转逐步实现无纸化。利用其图形化定义流程的功能,在办公流程越来越严谨的前提下,办公效率也大幅提高。某校在教务系统中运用了工作流技术,取得了良好的效果。  相似文献   
39.
研究供电系统稳定性优化问题,针对直流分布供电系统中单独设计的功率模块级联后引起整个系统不稳定。由于系统连接,造成系统稳定性下降。为解决上述问题,提出了一种通过测量直流分布供电系统的稳定余度来判断系统稳定性的方法。在分析传统的判定稳定性方法缺点的基础上,根据Middlebrook判据,提出了禁止区域的概念,并进一步简化,推导出测量稳定余度的方法来判断级联系统的稳定性,并在SABER环境下对BOOST供电系统功率因数校正电路的稳定性。实验结果表明,方法能较为简便的判断直流分布供电系统的稳定性,同时对于其它供电系统的稳定性分析均有较好的参考价值。  相似文献   
40.
为提高装备采购效率,分析装备采购过程中诚信问题产生的环节及形成的原因,搭建基于区块链技术装备采购诚信交易机制的基础架构,设计诚信交易机制流程,以实现装备采购活动中企业准入的公平选拨、承制商的自动选择、里程碑拨款的及时准确、信息及时上链促进共同监督等功能,并从智能合约优化、明晰联盟链权限、人才队伍建设3个方面提出需关注的问题.该机制可减少装备采购中不诚信的现象,提高装备采购信息化水平.  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