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   151434篇
  免费   7128篇
  国内免费   3379篇
电工技术   4832篇
技术理论   10篇
综合类   6794篇
化学工业   22792篇
金属工艺   8301篇
机械仪表   7031篇
建筑科学   7571篇
矿业工程   2409篇
能源动力   3040篇
轻工业   8912篇
水利工程   2554篇
石油天然气   4054篇
武器工业   531篇
无线电   17488篇
一般工业技术   24487篇
冶金工业   6008篇
原子能技术   985篇
自动化技术   34142篇
  2024年   525篇
  2023年   1266篇
  2022年   2152篇
  2021年   2925篇
  2020年   2314篇
  2019年   1829篇
  2018年   16222篇
  2017年   15313篇
  2016年   11939篇
  2015年   3321篇
  2014年   3625篇
  2013年   4122篇
  2012年   7412篇
  2011年   13972篇
  2010年   12055篇
  2009年   9168篇
  2008年   10367篇
  2007年   11125篇
  2006年   3412篇
  2005年   4071篇
  2004年   3264篇
  2003年   3051篇
  2002年   2270篇
  2001年   1656篇
  2000年   1871篇
  1999年   2074篇
  1998年   1772篇
  1997年   1433篇
  1996年   1423篇
  1995年   1156篇
  1994年   1021篇
  1993年   705篇
  1992年   556篇
  1991年   416篇
  1990年   339篇
  1989年   308篇
  1988年   228篇
  1987年   155篇
  1986年   110篇
  1985年   81篇
  1984年   61篇
  1983年   41篇
  1982年   52篇
  1968年   45篇
  1966年   44篇
  1965年   48篇
  1958年   38篇
  1957年   36篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
To detect faults in a time-dependent process, we apply a discrete wavelet transform (DWT) to several independently replicated data sets generated by that process. The DWT can capture irregular data patterns such as sharp "jumps" better than the Fourier transform and standard statistical procedures without adding much computational complexity. Our wavelet coefficient selection method effectively balances model parsimony against data reconstruction error. The few selected wavelet coefficients serve as the "reduced-size" data set to facilitate an efficient decision-making method in situations with potentially large-volume data sets. We develop a general procedure to detect process faults based on differences between the reduced-size data sets obtained from the nominal (in-control) process and from a new instance of the target process that must be tested for an out-of-control condition. The distribution of the test statistic is constructed first using normal distribution theory and then with a new resampling procedure called "reversed jackknifing" that does not require any restrictive distributional assumptions. A Monte Carlo study demonstrates the effectiveness of these procedures. Our methods successfully detect process faults for quadrupole mass spectrometry samples collected from a rapid thermal chemical vapor deposition process  相似文献   
42.
43.
44.
45.
46.
The development and test of a PLC control program takes time, increases equipment down-time, and might damage hardware due to program errors. All of these problems can be eliminated if there is a computer simulation system for testing control programs off line. This paper presented a new method, called Direct Sequential Method, for simulating PLCs. This method resolves a ladder logic sequentially by applying a series of logic deductions. This simulation system has been implemented in C and tested successfully.  相似文献   
47.
Recently, Timmermann and Nowak developed algorithms for estimating the means of independent Poisson random variables. The algorithms are based on a multiscale model where certain random variables are assumed to obey a beta-mixture density function. Timmermann and Nowak simplify the density estimation problem by assuming the beta parameters are known and only one mixture parameter is unknown. They use the observed data and the method of moments to estimate the unknown mixture parameter. Taking a different approach, we generate training data from the observed data and compute maximum likelihood estimates of all of the beta-mixture parameters. To assess the improved performance obtained by the proposed modification, we consider a denoising application using Poisson data.  相似文献   
48.
Since most end-of-life electronics equipment contain hazardous materials such as lead solder alloys or lead-impregnated glass, it is important to divert them from landfills. For end-of-life products that are not repairable and do not contain reusable parts, bulk recycling is an alternative to recover base materials. In this paper, we contrast production and recycling planning and distribution decisions, activities, and costs. We reveal that while a traditional production facility connects suppliers and customers, a recycling facility connects both "input" and "output" customers. As a result, decisions in short-term bulk recycling planning include what products to accept, what products to process and reprocess, and what products to carry in inventory. Many recyclers set prices to receive "input" based on experience. For various prices to receive "input", we use a new analytical model to investigate the sensitivity of the short-term bulk recycling planning decisions in products from two different sources: industrial returns versus residential returns. The results of the case study show that different decisions are recommended for the industrial returns versus the residential returns when the total quantity of the incoming products is equal.  相似文献   
49.
In this paper, a new vectorial boundary element method is introduced and applied to the modal analysis of dielectric waveguides with piecewise homogeneous refractive indexes. The procedure, which is free of spurious modes, determines the full field distribution from the longitudinal fields at the refractive index boundaries. Singular kernels are evaluated through series solutions while the electric field discontinuity at corners is accommodated through either a grid refinement technique or a semianalytic approach. Our formalism generates propagation constants and modal field distributions for several representative refractive index profiles with far higher accuracy than standard finite-difference or finite-element procedures.  相似文献   
50.
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