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   6845篇
  免费   287篇
  国内免费   223篇
电工技术   226篇
技术理论   1篇
综合类   476篇
化学工业   801篇
金属工艺   68篇
机械仪表   121篇
建筑科学   1321篇
矿业工程   362篇
能源动力   397篇
轻工业   385篇
水利工程   718篇
石油天然气   107篇
武器工业   11篇
无线电   190篇
一般工业技术   260篇
冶金工业   818篇
原子能技术   12篇
自动化技术   1081篇
  2024年   12篇
  2023年   55篇
  2022年   99篇
  2021年   140篇
  2020年   174篇
  2019年   131篇
  2018年   121篇
  2017年   156篇
  2016年   231篇
  2015年   224篇
  2014年   362篇
  2013年   401篇
  2012年   413篇
  2011年   554篇
  2010年   433篇
  2009年   446篇
  2008年   423篇
  2007年   492篇
  2006年   422篇
  2005年   344篇
  2004年   321篇
  2003年   281篇
  2002年   235篇
  2001年   183篇
  2000年   124篇
  1999年   106篇
  1998年   74篇
  1997年   62篇
  1996年   53篇
  1995年   43篇
  1994年   38篇
  1993年   24篇
  1992年   28篇
  1991年   17篇
  1990年   27篇
  1989年   12篇
  1988年   9篇
  1987年   6篇
  1986年   10篇
  1985年   13篇
  1984年   7篇
  1983年   7篇
  1982年   8篇
  1980年   4篇
  1979年   4篇
  1978年   4篇
  1976年   3篇
  1974年   3篇
  1964年   3篇
  1961年   2篇
排序方式: 共有7355条查询结果,搜索用时 15 毫秒
71.
针对炮兵指挥控制系统在作战训练中遇到的问题,在科学地分析了影响效果和相关因素的基础上,依据模糊专家理论的方法和原理,设计了相关的运用决策框架,并提出了运用规则。  相似文献   
72.
机车运用管理是铁路行车组织工作的有机组成部分,铁路运输要围绕列车运行图来进行运行管理,机务管理工作要靠列车运行图牵引动力的机车周转图,机车周转图的完成是机务段各项工作顺利完成的最终目的。要根据本机务段的实际情况制订、安排机车周转图,保证铁路运输的经济和社会效益。探讨了运用管理在机务管理中的应用。  相似文献   
73.
In semi-arid regions, aquifers provide a series of practical advantages that make them preferential sources of water supply. In Spain, groundwater meets about one-fifth of the total water demand and is used to irrigate over one-third of the total irrigated land. This article examines groundwater use in Spain from the perspective of the EU Water Framework Directive. Analysis of different sector uses suggests that core problems (and solutions) related to groundwater lie in agricultural uses and that the Directive's environmental requirements remain distant from reality on the ground, where economic, political and social reasons prevail on legal obligations set by national and supranational authorities.  相似文献   
74.
This paper introduces a new index to test water resource sustainability in regions where groundwater is the main source of water supply. The Spatial Water Use efficiency Index (SWUI) is a geographical information system (GIS) environment index which expresses the ratio of potential available water volume (groundwater recharge minus water needs) to the respective water needs. Its low and/or negative values indicate water stress. SWUI is applied in the island of Crete, Greece, where water needs are mainly covered by groundwater abstractions. The annual water mass balance is estimated using the RIBASIM (River Basin Simulation) model. The total freshwater needs in the Cretan region reach 535 hm3 annually according to the model's simulation. SWUI with values ranging from ? 0.8 to 214.3 has proved to be an important visual tool towards depicting the low efficiency of the east part of the island to cover water demand and a useful decision-making tool in the sustainability evaluation of groundwater aquifers.  相似文献   
75.
以滁州花山水文实验流域为研究对象,研究不同土地利用类型中各种形态的氮随径流流失的特征。基于2012年10月—2013年9月滁州花山水文实验流域氮素实验观测数据,对流域的氮随径流流失的特征进行了分析。结果表明:林地比重较大的集水区域径流中的TN质量浓度和NO-3-N质量浓度较高,农田比重较大的集水区域径流中的NH3-N质量浓度较高;在林地面积比例较大集水区域,TN质量浓度与NO-3-N质量浓度有较好的相关性;而在耕地面积比例较大的集水区域,TN质量浓度与NH3-N质量浓度表现出较好的相关性。对于嵌套子流域,NO-3-N质量浓度沿河道往下游随集水区域的增大和森林覆被比例的减少而呈逐渐递减趋势;在农田非施肥季节,各个月的TN质量浓度空间上自上而下随森林覆被比例的减少而呈逐渐递减趋势,而NH3-N质量浓度变化较小;在施肥季节,TN质量浓度随NH3-N质量浓度的上升而上升。研究还发现:研究区域汪郢左支断面和军事牌断面的集水区域林地比重高达99.92%以上,虽然人类活动较少,但TN质量浓度较高,分别为2.830 mg/L和4.028 mg/L,高于集水区域农田比重较大的竹园沟断面和新坝断面(两断面农田比重分别为39.59%和35.63%),分别是竹园沟断面和新坝断面的1.42~2.51倍、2.02~3.57倍;这一事实与人们通常的认识不一致,值得进一步深入研究。  相似文献   
76.
Research on elderly people's ICT acceptance and use often relies on the technology acceptance model (TAM) framework, but has been mostly limited to task-oriented uses. This article expands approaches in technology acceptance and use by developing a model to explain entertainment-related uses of new media technology by elderly people. On a theoretical level, we expand the TAM perspective by adding concepts that act as barriers and/or facilitators of technology acceptance, namely technophobia, self-efficacy and previous experience and expertise with technology. We develop an expanded TAM by testing the role of these concepts in two studies on entertainment media technology. In Study 1, we investigate behavioural intention to use 3D cinema among N?=?125 German elderly media users (Age 50+). In Study 2, we focus the actual use of a computer game simulation by N?=?115 German and US elderly media users (Age 50+). Findings in both studies point towards the central role of perceived usefulness, here modelled as enjoyment, as the reason for elderly people's use and acceptance of entertainment media technology. Perceived ease of use is seen as a precondition for enjoyment, particularly for interactive media.  相似文献   
77.
The specifics of business intelligence systems compared to operational IS motivate the necessity to research the business intelligence systems acceptance determinants separately. The authors followed an exploratory approach in order to conceptualize a business intelligence acceptance model. Their findings show that in the Business Intelligence Systems context, there is a significant emphasis on organizational factors, such as result demonstrability, social influence, and facilitating conditions with sufficient resources that help build an adequate information culture all substantially influencing the effective acceptance of business intelligence systems.  相似文献   
78.
Abstract

Without prior searching instruction, undergraduate novices wrote structured self-reports during their first session on a Web search engine. Users chose their own topics and followed written instructions that prompted them to describe thoughts and feelings during specified stages of the search: pre-search formulation; search statement formulation; search strategy; and evaluation of results. The sentences in the self-reports were numbered and then coded according to their affective or cognitive function. The affective sentences reveal how users set goals and limit the scope of the cognitive operations. Search acts appear to be governed by an affective filter that organizes incoming information and provides criteria for ranking cognitive relevance to search goal. The cognitive sentences reveal a variety of operations in executing searches. Following the search, students made self-ratings on self-confidence as searchers and satisfaction with the search experience, with explanations of their ratings. Content analysis identified reasons users have for rating self-confidence, stress level, satisfaction, usefulness, and success with future searches.  相似文献   
79.
在综合分析区域水资源特点、水资源承载能力、用水水平与效率及产业结构调整和水价等影响因素的基础上,提出了工业、农业和生活等方面的节水潜力.以提高水资源利用效率和效益为核心,根据我国不同地区的自然特点、水资源条件、经济社会发展和生态环境保护及其对水资源高效利用的要求,研究提出全国节水型社会建设的目标与任务,确定了不同区域用水效率控制红线,制定了全国节水战略与布局,提出了工业、农业和城镇生活等重点领域节水对策措施.按照量水而行、以水定发展的原则,因地制宜确定不同区域节水型社会建设的重点和方向.  相似文献   
80.
The high speed fluid jet for directly or indirectly breaking rock is one of the most effective ways to improve the deep penetration rate.In order to maximize the efficiency of energy use,the flow characteristics of different combinations of high pressure jet nozzles are analyzed through numerical simulations.According to the velocity vectors at the bottom and the bottom hole pressure diagram,the effects of the high pressure nozzle combinations on the flow structure and the penetration rate are analyzed.It is shown that the combination of three vertical edge nozzles is very efficient,but inefficient in cleaning the bottom hole and eroding the wall.The jet velocity is 400 m/s and the radius is 5 mm,with a center nozzle added,the problem can be solved,but the high-pressure fluid displacement would increase.The center nozzle’s jet velocity is 200 m/s and the radius is 8 mm,the combination of two vertical edge nozzles and a center tilt nozzle or that of a vertical edge nozzle and a center tilt nozzle would provide a flow structure favorable for drilling.The angle of inclination is 10o.To take advantage of high pressure jet energy to improve the efficiency of drilling,it is important to select a suitable nozzle combination according real conditions.  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