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   21270篇
  免费   2375篇
  国内免费   1185篇
电工技术   730篇
技术理论   1篇
综合类   1885篇
化学工业   4702篇
金属工艺   1329篇
机械仪表   832篇
建筑科学   3023篇
矿业工程   1880篇
能源动力   690篇
轻工业   915篇
水利工程   1120篇
石油天然气   2480篇
武器工业   127篇
无线电   718篇
一般工业技术   1701篇
冶金工业   1513篇
原子能技术   336篇
自动化技术   848篇
  2024年   97篇
  2023年   278篇
  2022年   603篇
  2021年   729篇
  2020年   837篇
  2019年   721篇
  2018年   638篇
  2017年   763篇
  2016年   846篇
  2015年   911篇
  2014年   1307篇
  2013年   1358篇
  2012年   1642篇
  2011年   1609篇
  2010年   1247篇
  2009年   1345篇
  2008年   1111篇
  2007年   1358篇
  2006年   1254篇
  2005年   1014篇
  2004年   845篇
  2003年   743篇
  2002年   605篇
  2001年   505篇
  2000年   433篇
  1999年   384篇
  1998年   295篇
  1997年   257篇
  1996年   221篇
  1995年   178篇
  1994年   139篇
  1993年   82篇
  1992年   103篇
  1991年   77篇
  1990年   65篇
  1989年   49篇
  1988年   22篇
  1987年   40篇
  1986年   25篇
  1985年   23篇
  1984年   27篇
  1983年   14篇
  1982年   8篇
  1981年   9篇
  1980年   5篇
  1979年   2篇
  1976年   2篇
  1975年   1篇
  1964年   1篇
  1959年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.  相似文献   
2.
In this article, two novel kinds of focusing elements as reflectors are analyzed and compared. One is the grooved Fresnel zone plate reflector with continuous phase‐correcting. The other called subzone paraboloid reflector, has the profile that consists of a series of paraboloids. Their diffraction efficiencies and bandwidths are described. The two elements still preserve the advantages of Fresnel zone plates, namely, low profile, high efficiency, and simple fabrication. Two dual‐reflector antennas using the proposed focusing elements as the main reflectors are simulated and the results show that these antennas have good radiation performances. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:101–108, 2015.  相似文献   
3.
新汶矿业集团经过探索和实践,研究运用了差异互补式全掩护支护技术、掩护支架自牵引联动装置工艺、矿车运输、滑移运输多用轨道、自动找正装车平台、液控调整装置等新技术、新工艺,做到了液压支架综合流程快速回撤,实现了高效化、连贯化安全回撤,取得了良好的经济效益。  相似文献   
4.
Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m2, respectively.  相似文献   
5.
埋地油气管道通过永冻土地带时,由于管内介质与周围的冻土发生了热力作用,使冰土解冻,在管道周围形成融化圈。文章分析了永冻土的特点,建立了永冻土地带土壤传热数学模型:融化圈内外传热方程、管道向土壤和土壤表面向大气所放热量的守恒关系、融化圈界面处土壤温度、相变界面处固相变为液相的传热条件。还建立了埋地管道模型,并以穿过永冻土地带土壤的输油管道为例,分析并计算了各种应力的最大值所在的位置和大小,提出了在永冻土地带减小管道热力变形的措施。  相似文献   
6.
吴建国  杜东兴 《冶金能源》1997,16(2):8-10,24
对菱镁矿在固体燃料燃烧过程中的固硫特性进行了理论研究,所得结论对进一步将菱镁矿作为固体燃料燃烧过程中的固硫剂具有非常重要的意义。  相似文献   
7.
砂砾岩储集层含油性解释方法   总被引:15,自引:4,他引:11  
LJ地区砂砾岩地层具有岩石结构复杂,储集层非均质性强,稠油和稀油并存的特点,利用测井资料解释含油性难度很大,以地层测试资料为依据,综合利用多种测井信息,提取反映含油性变化的测井特征参数;应用测井参数交会法和测井相分析法建立有效,快速识别稠油,油层和水层的标准,测井相分析法消除了用测井单参数和两参数交会解释含油性存在的多解性,提高子解释结果的成功率,用编制的解释软件处理了LJ地区58口井的资料,解释结果与试油资料对比吻合程度较高,为砂岩储层含油性解释提供了一种有效,快速的方法,为该区先导性试验提供了可靠的依据。  相似文献   
8.
在对白水头地区低阻油层的地质特征、物性特征及成因环境进行了分析研究后 ,应用测井曲线特征集法 ,把白水头油田常规油气层、低阻油气层、油水同层、水层等看成是独立的地质事件 ,建立了它们与测井曲线特征之间的对应关系 ,利用这种关系对未知地质事件进行了预测划分。最后根据所建模型定量计算储层各种参数 ,收到了良好的地质效果 ,表明测井曲线特征集法对于识别多成因的低阻油层是一种有效方法  相似文献   
9.
Soil moisture status in the root zone is an important component of the water cycle at all spatial scales (e.g., point, field, catchment, watershed, and region). In this study, the spatio-temporal evolution of root zone soil moisture of the Walnut Gulch Experimental Watershed (WGEW) in Arizona was investigated during the Soil Moisture Experiment 2004 (SMEX04). Root zone soil moisture was estimated via assimilation of aircraft-based remotely sensed surface soil moisture into a distributed Soil-Water-Atmosphere-Plant (SWAP) model. An ensemble square root filter (EnSRF) based on a Kalman filtering scheme was used for assimilating the aircraft-based soil moisture observations at a spatial resolution of 800 m × 800 m. The SWAP model inputs were derived from the SSURGO soil database, LAI (Leaf Area Index) data from SMEX04 database, and data from meteorological stations/rain gauges at the WGEW. Model predictions are presented in terms of temporal evolution of soil moisture probability density function at various depths across the WGEW. The assimilation of the remotely sensed surface soil moisture observations had limited influence on the profile soil moisture. More specifically, root zone soil moisture depended mostly on the soil type. Modeled soil moisture profile estimates were compared to field measurements made periodically during the experiment at the ground based soil moisture stations in the watershed. Comparisons showed that the ground-based soil moisture observations at various depths were within ± 1 standard deviation of the modeled profile soil moisture. Density plots of root zone soil moisture at various depths in the WGEW exhibited multi-modal variations due to the uneven distribution of precipitation and the heterogeneity of soil types and soil layers across the watershed.  相似文献   
10.
This paper presents a demonstration of a methodology for fault removal during software development. The methodology encompasses the entire development history, from system and software requirements generation to system test. Thus it considers not only the faults during software testing after formal configuration controls have been invoked, but also the faults discovered prior to that phase: during system and software requirements generation, preliminary design, detailed design and code and unit testing. The agents for fault discovery used in verification and validation are called activities, techniques and tools (AT & Ts) in this paper, each having a certain maximum potential or capability for fault discovery. The AT & Ts considered include the usual specification review activities, and also certain tools not normally applied in ‘standard’ software development, such as automated requirements aids. Application of the methodology yields numbers of residual faults as of each phase of development, including those remaining to be discovered during operations and maintenance. Some previous experience and data on residual faults correspond to these results, indicating that the methodology and choice of parameters are reasonable. The methodology also allows one to calculate a relative loss due to delay in fault discovery, which, as is well known, rises rapidly when faults are not discovered during the phase in which they are generated.  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