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   31465篇
  免费   4089篇
  国内免费   2106篇
电工技术   4267篇
技术理论   2篇
综合类   3166篇
化学工业   2615篇
金属工艺   1551篇
机械仪表   1467篇
建筑科学   1739篇
矿业工程   1079篇
能源动力   1289篇
轻工业   652篇
水利工程   1418篇
石油天然气   3641篇
武器工业   711篇
无线电   5860篇
一般工业技术   4789篇
冶金工业   536篇
原子能技术   395篇
自动化技术   2483篇
  2024年   161篇
  2023年   472篇
  2022年   911篇
  2021年   1003篇
  2020年   1011篇
  2019年   898篇
  2018年   896篇
  2017年   1069篇
  2016年   1258篇
  2015年   1200篇
  2014年   1745篇
  2013年   1703篇
  2012年   2142篇
  2011年   2497篇
  2010年   1890篇
  2009年   1965篇
  2008年   1795篇
  2007年   2183篇
  2006年   2063篇
  2005年   1617篇
  2004年   1407篇
  2003年   1320篇
  2002年   1004篇
  2001年   827篇
  2000年   841篇
  1999年   682篇
  1998年   573篇
  1997年   464篇
  1996年   396篇
  1995年   343篇
  1994年   294篇
  1993年   264篇
  1992年   219篇
  1991年   145篇
  1990年   126篇
  1989年   91篇
  1988年   63篇
  1987年   35篇
  1986年   18篇
  1985年   12篇
  1984年   17篇
  1983年   5篇
  1982年   12篇
  1981年   3篇
  1980年   5篇
  1979年   6篇
  1978年   2篇
  1976年   3篇
  1974年   1篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
纵横波测井资料在储层评价中的应用   总被引:5,自引:1,他引:4  
将弹性波基础理论,Gasman理论,Biot理论和实验研究结果相结合,探讨了沉积岩地层中速度和弹性模量,弹性模量和孔隙度,剪切模量和孔隙度,速度和孔隙度,孔隙度和Biot系数之间的关系,利用从各种声学测井资料中提取出的P波和S波时差(或速度)定量评价地层孔隙度和骨架物质,辅以泥质指示测井曲线,可以计算地层孔隙度,饱和度,岩性等参数,在M,Krief方法的基础上,采用优化算法寻求适合于任何岩性地层的孔隙度与Biot系数之间的关系式,提高了Biot系数的计算精度,该评价方法有坚实的实验基础和理论基础,评价结果与实验室岩心分析数据吻合。  相似文献   
62.
心电图信号的频域分析   总被引:2,自引:1,他引:1  
提出了一种简便有效的、由心电图(ECG)曲线提取QRS-T复合波的新方法,从而获得P波(当房颤未发生时)或f波(当房颤时);利用功率谱、自相关、互相关等信号处理技术,对它进行了处理和分析,特别是,比较了未房颤时和发生房颤时的相关信息的显著差别。  相似文献   
63.
程立 《西北水电》2002,(2):39-43
结合工程实例,介绍了在物性条件和地质条件复杂地区利用面波勘探技术解决软岩地区第四系覆盖层及其岩埋深的勘探方法。  相似文献   
64.
Filiform corrosion is mainly considered as a cosmetic attack and is undesirable in most applications. The initiation and propagation of the filaments are related to different parameters such as the presence of defects, the permeability of the coating to water and oxygen, the adherence of the paint system and the presence of salts.

The aim of this work is to study the behaviour of painted aluminium samples towards filiform corrosion or delamination. The 6082 Aluminium alloy was selected and the samples were covered with a cataphoretic epoxy primer without lead (PPG Industries France). Prior to the application of the electrocoat, the samples were pre-treated by a commercial Zr/Ti or chromate conversion treatment or simply etched with a commercial acid etching product.

Filiform corrosion was studied by the normalized test (ISO/DIS 4623): painted and scratched samples were inoculated in HCl and exposed in a constant humidity chamber at 40 °C and 82% RH for 3 weeks. After exposure the samples were subjected to a visual and optical microscopic examination.

Electrochemical impedance spectroscopy was used to study the sensitivity to filiform corrosion. The operating mode of this test is similar to the normalized one. The samples were scratched before inoculation for 1 h in HCl and then exposed to the humidity chamber for a maximum of 4 days. The samples were tested by EIS in an acidified 0.1 M Na2SO4 electrolyte solution. The resulting impedance spectra were analyzed with an appropriate equivalent electrical circuit which allows the evaluation of the exposed metallic surface area, directly related to the extent of filiform corrosion or delamination. Different parameters were varied: the exposure time in the humidity chamber; the immersion time in the electrolyte sulphate solution as well as its pH and the coating thickness.  相似文献   

65.
A long thin conducting stripline embedded in a dielectric and centered between two large conducting plates, i.e., the stripline environment, is considered. The stripline is modeled as infinitely long, infinitely thin, and perfectly conducting by first considering a stripline of finite length, thickness, and conductivity in a dielectric layer. Starting from Maxwell's equations and assuming that the current on the stripline is a propagating wave in length direction, asymptotic expressions for the fields inside and in the neighbourhood of the stripline are deduced. These expressions are used to model the stripline in the stripline environment, which leads to a boundary-value problem for the electric potential. This problem is solved by two different approaches, leading to integral equations for the current and for an auxiliary function describing the electric potential. A relation between the current and the auxiliary function is deduced, which is used to obtain asymptotic expressions for current and impedance. Results are compared with a numerical solution of the integral equation for the current and with results in literature.  相似文献   
66.
Interaction of free-surface waves with floating flexible strips   总被引:2,自引:0,他引:2  
The method developed by the author to derive a set of algebaic equations to solve the interaction of free-surface waves with a single floating rigid or flexible two-dimensional platform with small draft is extended to the case that the platform consists of strips with different constant flexural rigidity and mass. The method is based on the application of Green's theorem, with a specific choice of the Green function to arrive at a differential-integral equation along the platform. This equation can be solved exactly by means of superposition of exponential functions, a standard method to solve a set of linear differential equations. After integration with respect to the space coordinate the residue theorem leads to both the dispersion relation along each individual strip and an algebraic equation for the coefficients. Due to very fast convergence with respect to the number of coefficients taken into account the series are truncated. Depending on the water-depth, in each series three to ten terms are taken into account. Results are shown for a structure consisting of several strips that are tightly connected and for disjoint strips. In the latter case the computation of the water level between the strips is also computed. The water level and the reflection and transmission coefficients are not unknowns in the algebraic equation, but are computed afterwards by means of Green's theorem.  相似文献   
67.
花小民 《施工技术》2004,33(5):49-51
通过低应变反射波法与钻孔抽芯 2种检测方法的结果对比分析 ,验证低应变反射波法检测基桩的缺陷及位置的准确性 ,积累波形判别的经验。  相似文献   
68.
提出了一种考虑分布电容的故障测距新算法。该算法基于微分方程描述的线路数学模型,利用单端信息对高压输电线路进行故障测距,保留了解微分方程算法的简单可靠、现实可行、不必考虑衰减直流分量和谐波及电网频率波动影响的特点,同时考虑过渡电阻和分布电容的影响,克服了传统解微分方程法中在经高阻接地故障时测距误差过大和忽略分布电容引起的故障定位不准确的缺点。为了检验算法的精度,进行了大量的动模实验。结果表明,算法原理正确并具有较高的测距精度。  相似文献   
69.
The breakdown processes of oil films under quasi-static loading have been investigated by using a newly developed steel-oil-mercury system. The relationship between the thickness and breakdown ratio of a hexadecane film is represented by a single master curve independently of the indentation speed, indentation load, and temperature. The master curve shows that the breakdown process of hexadecane includes two stages; one is the decrement of the thickness without breakdown and the other is the decrement of the thickness with a drastic progress of breakdown. By solving a small amount of fatty acid in hexadecane, the thickness increases and the breakdown ratio decreases noticeably; a multilayer residual film supporting normal load is formed between two metal surfaces. Experiments at different temperatures reveal a negative relationship between the temperature and thickness of residual film, which indicates that the residual film is organized by physical interaction rather than chemical interaction. At least under a lower concentration, the residual film appears to consist of not only fatty acid molecules but also hexadecane molecules.  相似文献   
70.
裂缝各向异性介质中P-SV转换波正演模拟   总被引:5,自引:1,他引:4  
裂缝介质正演是研究裂缝性油藏的各向异性、裂缝检测方法、裂缝AVO反演等的前提。在裂缝方位各向异性(EDA)介质模型的基础上,重点研究了纵波震源激发的地震波所产生P-SV波的有限差分正演模拟方法。从各向异性单斜对称系统的刚性矩阵推导出的波动方程,可以满足EDA介质模型不同方位角入射的二维差分模拟要求。在有限差分模拟中,采用了普通的Kelly差分格式、二阶各向异性吸收边界条件和一般的纵波震源的解析形式,并应用修正的通量传输校(FCT)方法来消除频散。同时,对纵波震源的解析式进行了技术处理,取得了较好的效果。  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