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   1035篇
  免费   22篇
电工技术   19篇
化学工业   230篇
金属工艺   27篇
机械仪表   21篇
建筑科学   48篇
矿业工程   23篇
能源动力   12篇
轻工业   107篇
水利工程   20篇
石油天然气   3篇
无线电   73篇
一般工业技术   175篇
冶金工业   145篇
原子能技术   8篇
自动化技术   146篇
  2022年   17篇
  2021年   18篇
  2020年   17篇
  2019年   11篇
  2018年   11篇
  2017年   11篇
  2016年   25篇
  2015年   19篇
  2014年   32篇
  2013年   49篇
  2012年   53篇
  2011年   59篇
  2010年   44篇
  2009年   44篇
  2008年   45篇
  2007年   45篇
  2006年   32篇
  2005年   28篇
  2004年   33篇
  2003年   22篇
  2002年   33篇
  2001年   14篇
  2000年   22篇
  1999年   24篇
  1998年   25篇
  1997年   23篇
  1996年   14篇
  1995年   15篇
  1994年   14篇
  1993年   11篇
  1992年   13篇
  1991年   15篇
  1990年   9篇
  1989年   7篇
  1988年   14篇
  1987年   19篇
  1985年   10篇
  1984年   11篇
  1983年   12篇
  1982年   8篇
  1981年   7篇
  1980年   8篇
  1979年   9篇
  1978年   7篇
  1977年   12篇
  1975年   10篇
  1974年   6篇
  1972年   8篇
  1971年   6篇
  1970年   7篇
排序方式: 共有1057条查询结果,搜索用时 15 毫秒
981.
Different user segments have various requirements and expectations towards the performance of mobile networks. Subscribers having experienced the high quality of UMTS networks desire to maintain high speech quality and excellent data throughput also in areas of missing UMTS but existing GSM coverage. In GSM networks a privileged treatment of UMTS subscribers by means of proper resource allocation provides a substantial quality improvement with respect to standard GSM subscribers. This strategy allows network operators to reduce the performance gap between both network areas experienced by UMTS subscribers. A detailed study on the performance of circuit switched speech and packet data services has been performed based on system level simulations. The results show significant speech quality advantages for users with dual-RAT terminals compared to standard GSM users as well as notably higher data throughput rates.  相似文献   
982.
木材热压过程热量与含湿量传输数学模型初探   总被引:2,自引:0,他引:2  
靖葳  Hubert  P 《木材加工机械》1999,10(3):5-9
木材在热压过程中其内部热量和含湿量的交化,对木材加工质量的影晌很大。本文在理论分析的基础上,建立了合理简化的数学模型,预测热压过程中木材内部的瞬态温度分布,并开发了相应的计算机软件;在其它条件相同的情况下,用该模型对不同含水率的木材求解,得到与实验测量值基本一致的结果。  相似文献   
983.
This paper presents a new and accurate three-dimensional (3-D) reconstruction technique for the scoliotic spine from a pair of planar and conventional (postero-anterior with normal incidence and lateral) calibrated radiographic images. The proposed model uses a priori hierarchical global knowledge, both on the geometric structure of the whole spine and of each vertebra. More precisely, it relies on the specification of two 3-D statistical templates. The first, a rough geometric template on which rigid admissible deformations are defined, is used to ensure a crude registration of the whole spine. An accurate 3-D reconstruction is then performed for each vertebra by a second template on which nonlinear admissible global, as well as local deformations, are defined. Global deformations are modeled using a statistical modal analysis of the pathological deformations observed on a representative scoliotic vertebra population. Local deformations are represented by a first-order Markov process. This unsupervised coarse-to-fine 3-D reconstruction procedure leads to two separate minimization procedures efficiently solved in our application with evolutionary stochastic optimization algorithms. In this context, we compare the results obtained with a classical genetic algorithm (GA) and a recent Exploration Selection (ES) technique. This latter optimization method with the proposed 3-D reconstruction model, is tested on several pairs of biplanar radiographic images with scoliotic deformities. The experiments reported in this paper demonstrate that the discussed method is comparable in terms of accuracy with the classical computed-tomography-scan technique while being unsupervised and while requiring only two radiographic images and a lower amount of radiation for the patient.  相似文献   
984.
Seven issues are discussed in this paper. They are: (a) selection of concepts for functional diagnostic research, (b) methods for classifying personality data, (c) the organization of the levels of personality, (d) the level or locus of diagnosis, (e) the purpose of personality diagnosis, (f) the development of an interpersonal diagnostic system, and (g) the problems of validating multidimensional personality patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
985.
Coordination compounds are of particular interest for the design of new chromophores with large nonlinear optical (NLO) susceptibilities. They offer a wide range of metals with different oxidation states and ligands, which can give rise to tunable electronic properties. Metal ions are excellent templates to build 2D and 3D octupolar NLO-phores. Their associations with functionalized bipyridyl ligands give rise to octahedral and tetrahedral metal complexes with large first-order hyperpolarizabilities. The ability to functionalize these octupoles allows their incorporation into macromolecular architectures such as polymers and metallodendrimers, We also show in this Account two approaches to induce noncentrosymmetry at the macroscopic level, either by supramolecular organization or by the all optical poling procedure.  相似文献   
986.
The nature of the volatile organic compounds that could be at the origin of the characteristic odor of treated wood utility poles was investigated by the study of compositional changes in the chromatographic profiles of fresh-pentachlorophenol (PCP) solvent samples and weathered samples collected from an in-service red pine pole. Over 99 peaks were identified in the chromatogram of the fresh solvent from which a large portion of the C3-, C4-, C5-, C6-alkylbenzene isomers and early eluting n-alkanes was missing from the analysis of weathered samples. Three domains in the chromatographic profile (volatile, semivolatile, and nonvolatile components) were confirmed by assessing the headspace of fresh-PCP solvent samples using direct syringe sampling and solid-phase microextraction. A first level of field validation was achieved using an emission cell for measuring substances emanating from sapwood specimens at different temperatures. The average latent heat of vaporization (deltaHvap) of the PCP-solvent components was estimated at 99.9 kJ/mol from these results. Finally, the analysis of airborne substances at a treating plant and a utility pole storage site confirmed that the C4-, C5-, and C6-alkylbenzene isomers could contribute to the characteristic odor perceived by humans.  相似文献   
987.
A finite element model has been used in order to study the mixing process of species in a 100-microm-wide zigzag microchannel integrating a "Y" inlet junction. The distribution of the concentration was obtained by solving successively the Navier-Stokes equation and the diffusion-convection equation in the steady state form. Because of the large range of Reynolds numbers studied (1 < Re < 800), the 2D diffusion-convection simulations are carried out with high diffusion coefficients. The results illustrated the effects of both flow rate and channel geometry on hydrodynamics and mixing efficiency. Below a critical Reynolds number of approximately 80, the mixing is entirely ensured by molecular diffusion. For higher Reynolds numbers, simulations revealed the mixing contribution of laminar flow recirculations. This effect increases for lower values of diffusion coefficients. Experimental studies on the mixing of species at different flow rates are reported showing the same hydrodynamic tendency.  相似文献   
988.
989.
We present a method to cancel the offset of a Hall sensor and compensate its temperature-dependent drift. We adapt and improve a compensation technique based on a correction using the input voltage. A more accurate compensation for the temperature drift is obtained by an offset calibration at two different temperatures. To decrease the calibration time, we propose a procedure for fast heating of the sensor. It consists of forcing a current pulse through a p-n junction of the sensor. Since the resistance of a forward-biased diode is small, this principle is compatible with low-voltage applications. After correction, the resulting offset is less than two percent of the initial offset over the temperature range −10 to +60°C. The corresponding residual equivalent offset is lower than 250 μT.  相似文献   
990.
From pollutant source to pollutant sink – Novel concepts of solid incineration. Until a few years ago, solid waste incineration plants were considered to be major sources of pollutant emission. Meanwhile, by enhancing the effectiveness of combustion and by integration of modern flue gas cleaning techniques, solid waste incineration now leads with regard to emission reducing engineering measures. Harmful effects on the environment no longer originate in the stacks of these plants. Recently, pollutants enriched in flue gas cleaning products have caused disposal problems. These problems can be solved by concentrating the harmful inorganic constituents, above all mercury and cadmium, to a still higher level through wet chemical extraction and removal of the resulting concentrate from the process. Organic pollutants can be conveniently destroyed by thermal treatment. Despite all the objections there are good chances of using solid waste incineration as a pollutant sink and hence as a tool helping to protect our environment.  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