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   393635篇
  免费   13075篇
  国内免费   6552篇
电工技术   12456篇
技术理论   7篇
综合类   7887篇
化学工业   60833篇
金属工艺   19262篇
机械仪表   15336篇
建筑科学   16530篇
矿业工程   4050篇
能源动力   10787篇
轻工业   33510篇
水利工程   4226篇
石油天然气   9814篇
武器工业   879篇
无线电   47310篇
一般工业技术   66534篇
冶金工业   61673篇
原子能技术   5765篇
自动化技术   36403篇
  2023年   2489篇
  2022年   4510篇
  2021年   6659篇
  2020年   4970篇
  2019年   4805篇
  2018年   6155篇
  2017年   6584篇
  2016年   6258篇
  2015年   6940篇
  2014年   9385篇
  2013年   19233篇
  2012年   13776篇
  2011年   17001篇
  2010年   14236篇
  2009年   14810篇
  2008年   15045篇
  2007年   14890篇
  2006年   14314篇
  2005年   12850篇
  2004年   10808篇
  2003年   10278篇
  2002年   10047篇
  2001年   9959篇
  2000年   9426篇
  1999年   10300篇
  1998年   20913篇
  1997年   15202篇
  1996年   12176篇
  1995年   9275篇
  1994年   7958篇
  1993年   7435篇
  1992年   5417篇
  1991年   5154篇
  1990年   4521篇
  1989年   4363篇
  1988年   4115篇
  1987年   3510篇
  1986年   3338篇
  1985年   3851篇
  1984年   3388篇
  1983年   3063篇
  1982年   2894篇
  1981年   2888篇
  1980年   2793篇
  1979年   2602篇
  1978年   2513篇
  1977年   3193篇
  1976年   4744篇
  1975年   2198篇
  1973年   2085篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
数值试井在白6-2井测试资料分析评价中的应用   总被引:1,自引:0,他引:1  
数值试井是在近来发展的一项新的试井解释技术,具有处理非均质,复杂边界油气藏问题的优点,弥补了常规解析试井技术的不足。运用数值试井解释技术,结合动、静态资料,通过对白6-1断块白6-2井测试资料的综合分析评价,确定了储层渗流参数,落实了该气藏的边界情况,为该断块下一步开发提供可靠依据。  相似文献   
72.
Some Insights into MIMO Mutual Information: The High SNR Case   总被引:1,自引:0,他引:1  
We consider mutual information of multiple-input multiple-output (MIMO) wireless channels with complex isotropic Gaussian input in the case where the receiver has perfect channel, knowledge. For arbitrary fading statistics, a mutual information lower bound is decomposed in a sum of three terms involving: a) average SNR; b) channel fading; and c) a term characterizing the "effective rank", or eigenvalue dispersion, of the channel matrix. The decomposition suggests that spatial multiplexing efficiency of a MIMO channel can be characterized by the so-called ellipticity statistic. Distribution functions, means and variances of the random terms in the decomposition for the case of Rayleigh fading are also derived  相似文献   
73.
皖北地区夏季高温多雨,冬季严寒,气候较为恶劣,在该地区宜推广应用SMA混合料铺筑表面层。在进行SMA配合比设计时,必须严格控制原材料的质量,经过精心设计、精心施工,才能修建出一条成功的SMA路面。  相似文献   
74.
A new topology for a photonic signal processor, which overcomes the basic recursive frequency response problem that limits the passband range, is presented. The structure is based on a new multiple-wavelength offset-cavity structure that is cascaded with a series of unbalanced delay line structures. This not only can synthesize a very narrow notch response with good shape factor but also permits a multifold extension of the free spectral range (FSR) and passband width. Results on the interference mitigation filter demonstrate a stopband of 1% of center frequency and a fourfold increase in the FSR and passband width, while also having a very small shape factor, in excellent agreement with predictions.  相似文献   
75.
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned.  相似文献   
76.
Polyvinylalcohol (PVA) polymer gel is a temperature sensitive polymeric gel, with a critical transition temperature (with H2O) of 310 K. At higher than 310 K, this temperature sensitive polymer gel shrinks because of discharging water, whereas at lower temperatures, the gel swelled because of absorbing water. The reversibility of the gel's volume change was confirmed by temperature swing. The adsorption behavior of an organic compound onto the PVA polymer gel in water was tested at various temperatures. The amount of adsorbed organic compound increased remarkably at temperatures higher than about 310 K. Then, it was confirmed that the organic compound in PVA polymer gel could be reversibly adsorbed and desorbed by a temperature change between 293 and 323 K. The mechanism of adsorption of the organic compound onto the PVA polymer gel could be explained by hydration and dehydration of polymer gel.  相似文献   
77.
78.
Radial basis function (RBF) neural networks are used to classify real-life audio radar signals that are collected by a ground surveillance radar mounted on a tank. Currently, a human operator is required to operate the radar system to discern among signals bouncing off tanks, vehicles, planes, and so on. The objective of this project is to investigate the possibility of using a neural network to perform this target recognition task, with the aim of reducing the number of personnel required in a tank. Different signal classification methods in the neural net literature are considered. The first method employs a linear autoregressive (AR) model to extract linear features of the audio data, and then perform classification on these features, i.e, the AR coefficients. AR coefficient estimations based on least squares and higher order statistics are considered in this study. The second approach uses nonlinear predictors to model the audio data and then classifies the signals according to the prediction errors. The real-life audio radar data set used here was collected by an AN/PPS-15 ground surveillance radar and consists of 13 different target classes, which include men marching, a man walking, airplanes, a man crawling, and boats, etc. It is found that each classification method has some classes which are difficult to classify. Overall, the AR feature extraction approach is most effective and has a correct classification rate of 88% for the training data and 67% for data not used for training.  相似文献   
79.
80.
The selector activated sludge (SAS) systems are known to prevent excessive growth of filamentous microorganisms responsible for bulking sludge, but these systems were hardly ever modelled. This study aimed to develop a model capable of predicting rapid substrate removal in the SAS systems. For this purpose, the Activated Sludge Model No. 3 (ASM3) was extended with three processes (adsorption, direct growth on the adsorbed substrate under aerobic or anoxic conditions). The modified ASM3 was tested against the results of batch experiments with the biomass originating from two full-scale SAS systems in Germany. The endogenous biomass was mixed with various readily biodegradable substrates (acetate, peptone, glucose and wastewater) and the utilisation of substrate (expresses as COD) and oxygen uptake rates (OURs) were measured during the experiments. In general, model predictions fitted to the experimental data, but a considerable number of kinetic (5) and stoichiometric (2) parameters needed to be adjusted during model calibration. The simulation results revealed that storage was generally a dominating process compared to direct growth in terms of the adsorbed substrate utilisation. The contribution of storage ranged from 65-71% (Plant A) and 69-92% (Plant B).  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