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   353866篇
  免费   31048篇
  国内免费   18645篇
电工技术   41674篇
技术理论   59篇
综合类   47352篇
化学工业   36463篇
金属工艺   12333篇
机械仪表   18736篇
建筑科学   46700篇
矿业工程   18288篇
能源动力   11072篇
轻工业   17745篇
水利工程   17821篇
石油天然气   14896篇
武器工业   3183篇
无线电   26807篇
一般工业技术   24175篇
冶金工业   18819篇
原子能技术   3840篇
自动化技术   43596篇
  2024年   1205篇
  2023年   3583篇
  2022年   6949篇
  2021年   8281篇
  2020年   8967篇
  2019年   7455篇
  2018年   7153篇
  2017年   9008篇
  2016年   10298篇
  2015年   11786篇
  2014年   21429篇
  2013年   18966篇
  2012年   24146篇
  2011年   25773篇
  2010年   20129篇
  2009年   21239篇
  2008年   20000篇
  2007年   25486篇
  2006年   24017篇
  2005年   20491篇
  2004年   17226篇
  2003年   15467篇
  2002年   12641篇
  2001年   10739篇
  2000年   9023篇
  1999年   7299篇
  1998年   5455篇
  1997年   4654篇
  1996年   4294篇
  1995年   3629篇
  1994年   3284篇
  1993年   2457篇
  1992年   2110篇
  1991年   1585篇
  1990年   1391篇
  1989年   1216篇
  1988年   969篇
  1987年   662篇
  1986年   498篇
  1985年   411篇
  1984年   387篇
  1983年   277篇
  1982年   248篇
  1981年   191篇
  1980年   156篇
  1979年   123篇
  1978年   72篇
  1977年   79篇
  1976年   61篇
  1975年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Personal exposure in a displacement ventilated room is examined. The stratified flow and the considerable concentration gradients necessitate an improvement of the widely used fully mixing compartmental approach. The exposure of a seated and a standing person in proportion to the stratification height is examined by means of full-scale measurements. A breathing thermal manikin is used to simulate a person. It is found that the flow in the boundary layer around a person is able to a great extent to entrain and transport air from below the breathing zone. In the case of non-passive, heated contaminant sources, this entrainment improves the indoor air quality. Measurements of exposure due to a passive contaminant source show a significant dependence on the flow field as well as on the contaminant source location. Poor system performance is found in the case of a passive contaminant released in the lower part of the room close to the occupant. A personal exposure model for displacement ventilated rooms is proposed. The model takes the influence of gradients and the human thermal boundary layer into account. Two new quantities describing the interaction between a person and the ventilation are defined.  相似文献   
172.
173.
控制pH4-6,用锌粉还原氯化除汞上清液中的汞(Ⅱ)离子,取置换后液加入过量的硝酸银标准溶液,以硫酸铁铵溶液作指示剂,用硫氰酸钾标准滴定溶液滴定来测定氯量。该方法的检出限:0.25mg/100mL,回收率:98%-101%。  相似文献   
174.
李振琪 《中国水利》2007,(23):42-43
隆德县在大水沟农村饮水工程建设管理中,科学规划,优化设计方案,完善政策措施,创新管理体制和运行机制,尤其是用水户全过程参与工程建设管理、实行“两部制”水价、实施工程定期检查养护制度、建立工程管理单位目标责任考核制度、执行水费统一管理和提留统筹费等一系列做法.确保了国家投资效益的充分发挥和工程的可持续利用.  相似文献   
175.
This paper presents a single lossless inductive snubber‐assisted ZCS‐PFM series resonant DC‐DC power converter with a high‐frequency high‐voltage transformer link for industrial‐use high‐power magnetron drive. The current flowing through the active power switches rises gradually at a turned‐on transient state with the aid of a single lossless snubber inductor, and ZCS turn‐on commutation based on overlapping current can be achieved via the wide range pulse frequency modulation control scheme. The high‐frequency high‐voltage transformer primary side resonant current always becomes continuous operation mode, by electromagnetic loose coupling design of the high‐frequency high‐voltage transformer and the magnetizing inductance of the high‐frequency high‐voltage transformer. As a result, this high‐voltage power converter circuit for the magnetron can achieve a complete zero current soft switching under the condition of broad width gate voltage signals. Furthermore, this high‐voltage DC‐DC power converter circuit can regulate the output power from zero to full over audible frequency range via the two resonant frequency circuit design. Its operating performances are evaluated and discussed on the basis of the power loss analysis simulation and the experimental results from a practical point of view. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 79–87, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20126  相似文献   
176.
The purpose of this study was to analyze the symbolization of colors as cultural codes, based on costume colors. In order to study the significance of colors in cultural changes, we carried out a quantitative analysis and interpreted it from the perspective of cultural semiotics. The range of this study was focused on Korean costume colors, over diverse diachronic stages of Korean culture. For this study 1535 color samples were collected, measured with a spectrophotometer, and analyzed quantitatively according their diachronic stages of origin. As a result, red, blue, and yellow were found to be the most frequently used colors during the Chosun Dynasty, a period based on Confucianism. These colors acted as cultural codes with cultural significance. During the Modern times pink, light blue, and black increased in frequency and represented the reception of western culture, the changing sex role of women in society, and utilitarianism. In these days, neutral colors and grayish tones of all colors are the most significant colors of high frequency. The use of such colors is closely related to industrialization, mechanization, functionalism, and the changes of women's sex roles in the societies. They are used as cultural codes, especially to emphasize a rational and masculine image rather than a feminine image. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 71–79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20290  相似文献   
177.
A study has been made on the effects of loading scheme and conditions restricting macroscopic strain on the work-hardening kinetics and strain accumulation in the solid state in sintering materials with bimodal pore size distributions. Active loading intensifies the reduction in the small pores. The greatest effect comes from combining sintering with hydrostatic compression. At the same time, kinematic constraints (partial or complete adhesion in surfaces) substantially retards the shrinkage of large pores, which means that the porous structure can be controlled. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 10–15, May–June, 2006.  相似文献   
178.
射线层析技术中的算法探讨   总被引:1,自引:0,他引:1  
周兵  朱介寿 《石油物探》1992,31(2):16-22
  相似文献   
179.
基于斜坡的工程地质测绘和实验室分析,总结了研究地段区域滑坡规律,引入粘弹性基础板的弯曲破坏原理,对该地段斜坡破坏机制进行分析。从岩体本身的质量和岩体在地球内外营力作用下所表现的自稳性两方面考虑,采用两级模糊综合评判理论对测区进行斜坡稳定性工程地质单元划分,并利用刚体平衡理论验证模糊评判结果。  相似文献   
180.
介绍了造成铁路油槽车底油收不尽的原因,一是节约意识差;二是设备设施陈旧或维护不够;三是操作不当。提出了增强节约意识,挖掘设备潜力,采用合理的吸油方法的对策。  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