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   261128篇
  免费   20865篇
  国内免费   10855篇
电工技术   15090篇
技术理论   16篇
综合类   15494篇
化学工业   43909篇
金属工艺   13892篇
机械仪表   15959篇
建筑科学   21169篇
矿业工程   6745篇
能源动力   7325篇
轻工业   16591篇
水利工程   4545篇
石油天然气   13896篇
武器工业   1928篇
无线电   32159篇
一般工业技术   32479篇
冶金工业   13442篇
原子能技术   2759篇
自动化技术   35450篇
  2024年   1127篇
  2023年   4208篇
  2022年   7762篇
  2021年   10471篇
  2020年   7758篇
  2019年   6520篇
  2018年   7038篇
  2017年   8123篇
  2016年   7446篇
  2015年   9860篇
  2014年   12721篇
  2013年   16025篇
  2012年   16242篇
  2011年   18346篇
  2010年   15541篇
  2009年   15310篇
  2008年   14650篇
  2007年   13809篇
  2006年   13922篇
  2005年   12090篇
  2004年   8128篇
  2003年   7024篇
  2002年   6435篇
  2001年   5793篇
  2000年   5772篇
  1999年   6521篇
  1998年   6027篇
  1997年   4952篇
  1996年   4531篇
  1995年   3824篇
  1994年   3166篇
  1993年   2513篇
  1992年   1922篇
  1991年   1476篇
  1990年   1151篇
  1989年   988篇
  1988年   771篇
  1987年   548篇
  1986年   443篇
  1985年   366篇
  1984年   233篇
  1983年   225篇
  1982年   183篇
  1981年   160篇
  1980年   150篇
  1979年   108篇
  1978年   65篇
  1977年   66篇
  1976年   81篇
  1975年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
In optical microscopic measurement of internal blood-vessel diameters, the effect of refraction must be taken into account to ensure accuracy of the result. This effect is discussed and an analytical correction formula derived. Phantom blood vessels with known internal and external diameters were used to test the validity of the correction formula. The errors obtained prior to correction were reduced significantly after correction.  相似文献   
142.
郭晨  刘爱梅  管辉  赵志仁 《水力发电》2005,31(12):89-91
大朝山水电站引水发电系统为地下工程,根据各项安全监测物理量的主要观测成果,对最大观测值分析其对工程的安全影响,为保证其安全运行具有重要意义。为此,分别对大朝山水电站的主要地下建筑物,包括压力引水隧洞、地下厂房、尾水调压室的最大观测值进行了分析研究,并提出了一些建议,有较大的参考价值。  相似文献   
143.
In this paper, two algebraic decoders for the (103, 52, 19) and (113, 57, 15) quadratic residue codes, which have lengths greater than 100, are presented. The results have been verified by software simulation that programs in C++ language have been executed to check possible error patterns of both quadratic residue codes.  相似文献   
144.
A rearrangeable nonblocking 4/spl times/4 thermooptic silicon-on-insulator waveguide switch matrix at 1.55-/spl mu/m integrated spot size converters is designed and fabricated for the first time. The insertion losses and polarization-dependent losses of the four channels are less than 10 and 0.8 dB, respectively. The extinction ratios are larger than 20 dB. The response times are 4.6 /spl mu/s for rising edge and 1.9 /spl mu/s for falling edge.  相似文献   
145.
This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry  相似文献   
146.
文章综述了锂离子电池有机电解液成膜添加剂的作用原理,具体介绍了CO2、SO2、VC化合物、卤化物、有机铜盐以及马来酐等添加剂的研究现状。  相似文献   
147.
本文应用天然气中甲烷、乙烷的碳同位素,甲烷的氢同位素,汞含量及天然气成分等指标,探讨了四川盆地天然气成因分类;并结合地质情况对气源层进行了探讨。  相似文献   
148.
The paper proposes a novel method of forecasting short-term electricity price based on a two-stage hybrid network of self-organised map (SOM) and support-vector machine (SVM). In the first stage, a SOM network is applied to cluster the input-data set into several subsets in an unsupervised manner. Then, a group of SVMs is used to fit the training data of each subset in the second stage in a supervised way. With the trained network, one can predict straightforwardly the next-day hourly electricity prices. To confirm its effectiveness, the proposed model has been trained and tested on the data of historical energy prices from the New England electricity market.  相似文献   
149.
A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism.  相似文献   
150.
The hydration of slag,part 1: reaction models for alkali-activated slag   总被引:3,自引:0,他引:3  
Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products include C–S–H, hydrotalcite, hydrogarnet, AFm phases (C4AH13 and C2ASH8) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C–S–H are determined. The models are validated with a number of experimental investigations reported in literature, yielding good agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase distribution in the hardened AAS paste and the porosity are calculated.  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