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   331363篇
  免费   5514篇
  国内免费   820篇
电工技术   6583篇
综合类   775篇
化学工业   49663篇
金属工艺   11000篇
机械仪表   9331篇
建筑科学   8506篇
矿业工程   990篇
能源动力   9015篇
轻工业   33884篇
水利工程   2712篇
石油天然气   3776篇
武器工业   18篇
无线电   41002篇
一般工业技术   62855篇
冶金工业   62290篇
原子能技术   5593篇
自动化技术   29704篇
  2021年   2810篇
  2020年   2094篇
  2019年   2523篇
  2018年   4403篇
  2017年   4143篇
  2016年   4326篇
  2015年   3238篇
  2014年   5249篇
  2013年   15824篇
  2012年   8516篇
  2011年   11291篇
  2010年   8888篇
  2009年   10066篇
  2008年   10661篇
  2007年   10573篇
  2006年   9210篇
  2005年   8466篇
  2004年   8166篇
  2003年   7892篇
  2002年   7677篇
  2001年   7817篇
  2000年   7460篇
  1999年   7908篇
  1998年   19381篇
  1997年   13897篇
  1996年   10857篇
  1995年   8337篇
  1994年   7547篇
  1993年   7180篇
  1992年   5361篇
  1991年   5125篇
  1990年   4993篇
  1989年   4805篇
  1988年   4703篇
  1987年   3945篇
  1986年   4046篇
  1985年   4815篇
  1984年   4367篇
  1983年   4086篇
  1982年   3634篇
  1981年   3837篇
  1980年   3534篇
  1979年   3449篇
  1978年   3254篇
  1977年   3939篇
  1976年   5171篇
  1975年   2806篇
  1974年   2685篇
  1973年   2726篇
  1972年   2225篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
In this paper, we report on the indoor concentrations from a suite of full-scale outdoor tracer-gas point releases conducted in the downtown area of Oklahoma City in 2003. A point release experiment consisted of releases of sulfur hexafluoride (SF6) in multiple buildings and from different outdoor locations. From the measurements, we are able to estimate the concentration variations indoors for a building operating under “typical” operating conditions. The mean indoor spatial coefficients of variation are 30% to 45% from a daytime outdoor release are around 80% during an outdoor evening release. Having estimates of the spatial coefficient of variation provides stakeholders, including first responders, with the likely range of concentrations in the building when little is known about the building characteristics and operating behavior, such as developing urban-scale hazard and consequence analyses. We show differences in indoor measurements at different distances to the release points, floors of the building, and heating, ventilation, and air conditioning system (HVAC) operation. We also show estimates at different time resolutions. The statistics show that in the studied medium to large commercial buildings, spatial differences would result in peak indoor concentrations in certain parts of the buildings that may be substantially higher than the building average. To our knowledge, very few tracer gas measurements have been conducted in buildings of this scope, particularly with measurements on multiple floors and within a floor. The resulting estimates of spatial variability provide a unique opportunity for hazard assessment, and comparison to multi-zone models.  相似文献   
53.
The diagnosis and treatment of prostate cancer (PCa) is a major health-care concern worldwide. This cancer can manifest itself in many distinct forms and the transition from clinically indolent PCa to the more invasive aggressive form remains poorly understood. It is now universally accepted that glycan expression patterns change with the cellular modifications that accompany the onset of tumorigenesis. The aim of this study was to investigate if differential glycosylation patterns could distinguish between indolent, significant, and aggressive PCa. Whole serum N-glycan profiling was carried out on 117 prostate cancer patients’ serum using our automated, high-throughput analysis platform for glycan-profiling which utilizes ultra-performance liquid chromatography (UPLC) to obtain high resolution separation of N-linked glycans released from the serum glycoproteins. We observed increases in hybrid, oligomannose, and biantennary digalactosylated monosialylated glycans (M5A1G1S1, M8, and A2G2S1), bisecting glycans (A2B, A2(6)BG1) and monoantennary glycans (A1), and decreases in triantennary trigalactosylated trisialylated glycans with and without core fucose (A3G3S3 and FA3G3S3) with PCa progression from indolent through significant and aggressive disease. These changes give us an insight into the disease pathogenesis and identify potential biomarkers for monitoring the PCa progression, however these need further confirmation studies.  相似文献   
54.
55.
56.
57.
Twin screw granulation (TSG) is a new process of interest to the pharmaceutical community that can continuously wet granulate powders, doing so at lower liquid concentrations and with better product consistency than found by a high shear batch mixer. A considerable body of research has evolved over the short time since this process was introduced but generally with little comparison of results. A certain degree of confidence has been developed through these studies related to how process variables and many attributes of machinery configuration will affect granulation but some major challenges still lay ahead related to scalability, variations in the processing regimes related to degree of channel fill and the impact of wetting and granulation of complex powder formulations. This review examines the current literature for wet granulation processes studied in twin screw extrusion machinery, summarizing the influences of operational and system parameters affecting granule properties as well as strives to provide some practical observations to newly interested users of the technique.  相似文献   
58.
  Qing  Xu  Bin  Yu  Yang  Zhan  Wei  Zhao  Yu  Zheng  Jun  Ji  Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability...  相似文献   
59.
60.
Russian Engineering Research - Attention focuses on the heat propagation in metal polycrystals where the grain or subgrain size affects the strengthening—as a result of surface plastic...  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