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   127250篇
  免费   11648篇
  国内免费   4908篇
电工技术   9127篇
技术理论   9篇
综合类   10549篇
化学工业   18398篇
金属工艺   7717篇
机械仪表   8264篇
建筑科学   9481篇
矿业工程   4752篇
能源动力   3880篇
轻工业   10681篇
水利工程   2968篇
石油天然气   6880篇
武器工业   1427篇
无线电   13238篇
一般工业技术   13255篇
冶金工业   5482篇
原子能技术   1861篇
自动化技术   15837篇
  2025年   722篇
  2024年   2861篇
  2023年   2813篇
  2022年   4249篇
  2021年   5540篇
  2020年   4427篇
  2019年   3479篇
  2018年   3558篇
  2017年   3961篇
  2016年   3611篇
  2015年   4896篇
  2014年   6430篇
  2013年   7422篇
  2012年   8677篇
  2011年   9051篇
  2010年   8424篇
  2009年   8007篇
  2008年   8082篇
  2007年   7842篇
  2006年   7194篇
  2005年   6088篇
  2004年   4376篇
  2003年   3373篇
  2002年   2938篇
  2001年   2799篇
  2000年   2560篇
  1999年   2105篇
  1998年   1466篇
  1997年   1225篇
  1996年   1098篇
  1995年   988篇
  1994年   809篇
  1993年   587篇
  1992年   459篇
  1991年   363篇
  1990年   341篇
  1989年   251篇
  1988年   187篇
  1987年   127篇
  1986年   122篇
  1985年   67篇
  1984年   48篇
  1983年   34篇
  1982年   38篇
  1981年   32篇
  1980年   24篇
  1979年   8篇
  1959年   11篇
  1953年   10篇
  1951年   16篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
With the creation of balancing authorities by the North American Reliability Council that span large portions of the North American interconnection, and stringent requirements for real time monitoring of power system evolution, faster and more accurate state estimation algorithms that can efficiently handle systems of very large sizes are needed in the present environment. This paper presents a distributed state estimation algorithm suitable for large-scale power systems. Synchronized phasor measurements are applied to aggregate the voltage phase angles of each decomposed subsystem in the distributed state estimation solution. The aggregated state estimation solution is obtained from the distributed solution using a sensitivity analysis based update at chosen boundary buses. Placement of synchronized phasor measurements in the decomposed subsystems is also investigated in this paper. Test results on the IEEE 118-bus test bed are provided  相似文献   
3.
Flocculation morphology is a new concept that investigates the morphological characteristics of colloidal particles and coagulants in water during the flocculation process, and the influence that these characteristics have on flocculation process efficiency. This paper is a summary of advances in research on this topic over several years. Morphological characteristics of colloids in natural waters and different kinds of hydrolysed coagulants are investigated, and their effect on colloid stability, flocculation kinetics and efficiency is analysed. It is confirmed that the traditional theory has some deviations in coagulation of nonspherical particles, and these deviations are revised by the flocculation morphology model. Flocculation morphology can not only promote research about flocculation theory, but also instruct the production, application and flocculation control. It can be foreseen that more progress will be made in research and application of flocculation morphology in the near future.  相似文献   
4.
Electromigration reliability of interconnect under bidirectional current stress has been studied in a wide frequency range (mHz to 200 MHz). Experimental results show that the AC lifetime rises with the stress current frequency. The current density exponent and the activation energy of AC lifetime are found to be twice that of DC lifetime. Pure AC current stress failure at extremely high current density is believed to result from thermal migration of metal at hot/cold transition points  相似文献   
5.
Z. Jiang  Q. Chen  A. Moser 《Indoor air》1992,2(3):168-179
In order to cumpare the peformance of different supply diffuers of ventilation air, the airflow passern, temperature stratifiation and contaminant dispersion in a furnitured office ventilated by three kinds of air diffuer were numerically investigated. The air diffuers studied in this paper are a quarter-cylinder displacement diffuer on the floor and mixing diffuers (linear and vortex diffuers) on the ceiling. The heat sources in the of-fice are considered to be 50% convective and 50% radiative. The k-? two-equatwn model of turbulence is employed to predict the turbulent diffusion. The results show that the displacement diffuser provides a rather uniform flow field with low velocify in most areas, and the vertical temperature difference from floor to ceiling is as high as 6 K. With the linear diffuser, the air velociry is high, and the temperature is uniform both horizontally and vertically. The air velocity generated by the vortex diffuser is moderate. The distributions of the temperature and the contaminant are rather uniform.  相似文献   
6.
本文针对Beck公式的局限性,对土壤的含水量和^222Rn析出引起的γ辐射剂量率变化进行了修正。通过浙江省576组测量数据的实验拟合,给出了剂量率计算的修正公式。该公式应用到浙江省自身的测量数据上,使计算的总体均值与实测均值仅相差0.8%;每一点位的计算值与实测值相比,平均仅相差3.4%,其比值离散性与实验误差相一致。而Beck公式的计算结果与实测剂量率相比较,以上两项分别偏离+10%和15.2%  相似文献   
7.
We have identified three yeast genes, KES1, HES1 and OSH1, whose products show homology to the human oxysterol binding protein (OSBP). Mutations in these genes resulted in pleiotropic sterol-related phenotypes. These include tryptophan-transport defects and nystatin resistance, shown by double and triple mutants. In addition, mutant combinations showed small but apparently cumulative reductions in membrane ergosterol levels. The three yeast genes are also functionally related as overexpression of HES1 or KES1 alleviated the tryptophan-transport defect in kes1Δ or osh1Δ mutants, respectively. Our study implicates this new yeast gene family in ergosterol synthesis and provides comparative evidence of a role for human OSBP in cholesterol synthesis.  相似文献   
8.
给出了单齿泵削角的优化模型与计算实例,并对理论设计与实验进行了比较分析。  相似文献   
9.
针对3^n阶矩阵的乘法运行,给出了一种分块算法,其乘法运行量比常规的矩阵乘法计算方法和补零的基-2算法都有所减少。  相似文献   
10.
莱钢始建于1970年1月,现控股莱钢股份、鲁银投资两个上市公司及齐鲁证券等25个子公司。莱钢是中国冶金行业首批通过ISO9002质量管理体系、ISO14001环境管理体系和OHSAS18001职业安全健康管理体系国家认证的企业。2005年,莱钢被国家发改委确定为国家第一批循环经济试点单位。  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