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   117662篇
  免费   16640篇
  国内免费   8558篇
电工技术   8333篇
技术理论   6篇
综合类   11594篇
化学工业   4780篇
金属工艺   1556篇
机械仪表   3972篇
建筑科学   1188篇
矿业工程   1347篇
能源动力   2714篇
轻工业   1081篇
水利工程   421篇
石油天然气   558篇
武器工业   595篇
无线电   30191篇
一般工业技术   7475篇
冶金工业   822篇
原子能技术   368篇
自动化技术   65859篇
  2025年   1147篇
  2024年   4021篇
  2023年   4865篇
  2022年   5621篇
  2021年   6224篇
  2020年   6288篇
  2019年   5173篇
  2018年   5032篇
  2017年   6632篇
  2016年   6865篇
  2015年   6787篇
  2014年   8953篇
  2013年   9022篇
  2012年   11112篇
  2011年   10541篇
  2010年   8475篇
  2009年   8381篇
  2008年   6053篇
  2007年   6221篇
  2006年   4824篇
  2005年   2438篇
  2004年   989篇
  2003年   886篇
  2002年   862篇
  2001年   722篇
  2000年   553篇
  1999年   550篇
  1998年   254篇
  1997年   186篇
  1996年   227篇
  1995年   188篇
  1994年   131篇
  1993年   121篇
  1992年   104篇
  1991年   104篇
  1990年   93篇
  1989年   79篇
  1988年   241篇
  1987年   439篇
  1986年   433篇
  1985年   111篇
  1984年   75篇
  1981年   43篇
  1979年   42篇
  1970年   44篇
  1967年   60篇
  1966年   57篇
  1965年   42篇
  1964年   40篇
  1963年   46篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
As genetic algorithm parameters vary depending on different problem types when applying genetic algorithm to reach global optimum, appropriate design value selection has significant impact on the efficiency of genetic algorithm. However, most users adjust parameters manually based on the reference values of previous literature. Such trial-and-error method is time-consuming, ineffective, and often it could not locate the optimal combination. Therefore, in flowshop scheduling problems, this research anticipates to complete optimal parameter combination design in genetic algorithm using Taguchi experimental design. According to the research results, different ways of producing initial solution have significant influence on this research topic. Consequently, confirmation experiment is conducted using the optimal parameter combination obtained from the research results. It is found that the predicted value of signal-to-noise ratio (S/N ratio) and its actual value exists deviation of 0.238%, indicating repetitiveness and robustness of the obtained parameter combination. Hence, this research method can effectively reduce time spent on parameter design using genetic algorithm and increase efficiency of algorithm.  相似文献   
2.
《IIE Transactions》2007,39(9):879-898
We study an inventory system that consists of two demand classes. The orders in the first class need to be satisfied immediately, whereas the orders in the second class are to be filled in a given demand lead time. The two classes are also of different criticality. For this system, we propose a policy that rations the non-critical orders. Under a one-for-one replenishment policy with backordering and for Poisson demand arrivals for both classes, we first derive expressions for the service levels of both classes. The service level for the critical class is an approximation, whereas the service level for the non-critical class is exact. We then conduct a computational study to show that our approximation works reasonably, the benefits of rationing can be substantial, and the incorporation of demand lead time provides more value when the demand class with demand lead time is the critical class. The research is motivated by the spare parts service system of a major capital equipment manufacturer that faces two types of demand. For this company, the critical down orders need to be satisfied immediately, while the less critical maintenance orders can be satisfied after a fixed demand lead time. We conduct a case study with 64 representative parts and show that significant savings (as much as 14% on inventory on hand) are possible through incorporation of demand lead times and rationing.  相似文献   
3.
《Materials Letters》2007,61(11-12):2259-2261
We report the formation of silver nanoclusters of average size ∼ 1.1 nm in a single step ion-exchanged silica glass. Silver clusters are formed in a glass during ion-exchange by fine-tuning the ion-exchange parameters such as salt composition, temperature and time. Such nanocluster formation during ion-exchange preserves the waveguiding properties of the ion-exchanged surface of the glass making them suitable for nonlinear waveguide device fabrication.  相似文献   
4.
In literature, five different sets of work material constants used in the Johnson–Cook's (J–C) constitutive equation are implemented in a numerical model to describe the behaviour of AISI 316L steel. The aim of this research is to study the effects of five different sets of material constants of the J–C constitutive equation in finite-element modelling of orthogonal cutting of AISI 316L on the experimental and predicted cutting forces, chip morphology, temperature distributions and residual stresses. Several experimental equipments were used to estimate the experimental results, such as piezoelectric dynamometer for cutting forces measurements, thermal imaging system for temperature measurements and X-ray diffraction technique for residual stresses determination on the machined surfaces; while an elastic–viscoplastic FEM formulation was implemented to predict the local and global variables involved in this research. It has been observed that all the considered process output and, in particular the residual stresses are very sensitive to the J–C's material constants.  相似文献   
5.
6.
In this paper, a new methodology is presented for topology optimization of networked embedded systems as they occur in automotive and avionic systems as well as wireless sensor networks. By introducing a model which is (1) suitable for heterogeneous networks with different communication bandwidths, (2) modeling of routing restrictions, and (3) flexible binding of tasks onto processors, current design issues of networked embedded systems can be investigated. On the basis of this model, the presented methodology firstly allocates the required resources which can be communication links as well as computational nodes and secondly binds the functionality onto the nodes and the data dependencies onto the links such that no routing restrictions will be violated or capacities on communication links will be exceeded. Due to the often error-prone communication in networks, we allow for routing each data dependency over multiple routes in the networks. With this strategy, our methodology is able to increase the reliability of the entire system. This reliability analysis is based on Binary Decision Diagrams (BDDs) and is integrated in our multi-objective design space exploration. By applying Evolutionary Algorithms, we are able to consider multiple objectives simultaneously during the optimization process and allow for a subsequent unbiased decision making. An experimental evaluation as well as a demonstration of a case study from the field of automotive electronics will show the applicability of the presented approach.  相似文献   
7.
8.
9.
Branch testing is a well established method for exercising software. JJ-path testing, whilst employed by some practitioners, is less popular, and the testing of JJ-pairs finds few adherents. In this paper an objective, practical study of the cost-effectiveness of these three testing methods is reported. The effectiveness of each method is assessed, in the presence of infeasible paths, not only on its ability to cover the specific structural element of code that it targets, but also on its ability to cover the structural elements targeted by the other two methods – the collateral coverage it achieves. The assessment is based on the results derived from experiments in which each of the three methods is applied to 35 units of program code.  相似文献   
10.
Although the strategic aspects of EDI have been emphasised in the literature, there has been a lack of supporting empirical evidence. This paper describes an empirical study of the adoption and use of EDI in organizations in Germany and the UK. The findings suggest that although companies were motivated by both operational and strategic factors, in practice they have been more successful in realising operational benefits. The findings support an evolutionary view of EDI, where strategic gains are more likely to be found in the later stages of EDI usage. Most of the responding organizations seemed to be in an introductory stage, while some were in an interim stage, where some strategic benefits were being accumulated.  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