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   242743篇
  免费   18878篇
  国内免费   9999篇
电工技术   13463篇
技术理论   24篇
综合类   15394篇
化学工业   41210篇
金属工艺   13856篇
机械仪表   15380篇
建筑科学   18513篇
矿业工程   7874篇
能源动力   7058篇
轻工业   14737篇
水利工程   3927篇
石油天然气   17057篇
武器工业   1743篇
无线电   26786篇
一般工业技术   28817篇
冶金工业   13357篇
原子能技术   2456篇
自动化技术   29968篇
  2024年   1032篇
  2023年   3945篇
  2022年   6820篇
  2021年   9558篇
  2020年   7401篇
  2019年   6350篇
  2018年   7073篇
  2017年   7898篇
  2016年   7127篇
  2015年   9409篇
  2014年   11939篇
  2013年   14121篇
  2012年   15150篇
  2011年   16414篇
  2010年   14339篇
  2009年   13543篇
  2008年   13209篇
  2007年   12693篇
  2006年   13132篇
  2005年   11390篇
  2004年   7860篇
  2003年   6933篇
  2002年   6447篇
  2001年   5692篇
  2000年   5854篇
  1999年   6723篇
  1998年   5548篇
  1997年   4588篇
  1996年   4294篇
  1995年   3577篇
  1994年   2848篇
  1993年   2011篇
  1992年   1569篇
  1991年   1253篇
  1990年   952篇
  1989年   766篇
  1988年   548篇
  1987年   345篇
  1986年   284篇
  1985年   207篇
  1984年   141篇
  1983年   117篇
  1982年   131篇
  1981年   103篇
  1980年   75篇
  1979年   38篇
  1978年   28篇
  1977年   24篇
  1976年   36篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry  相似文献   
32.
33.
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x Ho x )TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x Ho x )TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.  相似文献   
34.
We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.  相似文献   
35.
36.
所开发的压水堆核燃料循环分析计算机经济程序包括12个子程序,代表着压水堆整个核燃料循环各种不同的工艺过程。本程序能算出压水堆核电站核燃料循环中燃料费用对发电成本的影响,给出各工艺过程对燃料成本的敏感度分析,并尽可能给出燃料循环中燃料材料及服务的价格数据.  相似文献   
37.
In this study, distribution and history of residual stresses in plaque-like geometries are simulated based on linear thermoviscoelastic model, which helps to understand the mechanics and evolution of the residual stresses in the injection molding process. The numerical calculation of direction, combined with the specified boundary conditions. Results show that the stress variation across the thickness exhibits a high surface tensile value changing to a compressive peak value close to the surface, with the core region experiencing a parabolic tensile peak. Residual stress distribution throughout the thickness is almost same along the flowpath and the final residual stresses value near the gate is lower than the value near the end of flowpath.  相似文献   
38.
Inversion of Rayleigh wave dispersion curves is challenging for most local-search methods due to its high nonlinearity and to its multimodality. In this paper, we implemented and tested a Rayleigh wave dispersion curve inversion scheme based on GPS Positive Basis 2N, a commonly used pattern search algorithm. Incorporating complete poll and complete search strategies based on GPS Positive Basis 2N into the inverse procedure greatly enhances the performance of pattern search algorithms because the two steps can effectively locate the promising areas in the solution space containing the global minima and significantly reduce the computation cost, respectively.The proposed inverse procedure was applied to nonlinear inversion of fundamental-mode Rayleigh wave dispersion curves for a near-surface shear (S)-wave velocity profile. The calculation efficiency and stability of the inversion scheme are tested on three synthetic models and a real example from a roadbed survey in Henan, China. Effects of the number of data points, the reduction of the frequency range of the considered dispersion curve, errors in P-wave velocities and density, the initial S-wave velocity profile as well as the number of layers and their thicknesses on inversion results are also investigated in the present study to further evaluate the performance of the proposed approach.Results demonstrate that pattern search algorithms applied to nonlinear inversion of high-frequency surface wave data should be considered good not only in terms of accuracy but also in terms of the computation effort due to their global and deterministic search process.  相似文献   
39.
宣钢l260m^3高炉大修改造时将炉容扩大到l350m^3,对高炉本体系统设备及冷却系统、自动控制及检测系统进行了全面的改造更新,在炉腹、炉腰及炉身下部高热负荷区域采用铜冷却壁,取消炉身中上部铸铁冷却壁凸台,并采用薄内衬等先进、适用、可靠、成熟的技术。  相似文献   
40.
The Tera-op reliable intelligently adaptive processing system (TRIPS) architecture seeks to deliver system-level configurability to applications and runtime systems. It does so by employing the concept of polymorphism, which permits the runtime system to configure the hardware execution resources to match the mode of execution and demands of the compiler and application.  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