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   381425篇
  免费   33903篇
  国内免费   19252篇
电工技术   24180篇
技术理论   76篇
综合类   48209篇
化学工业   49938篇
金属工艺   15133篇
机械仪表   21025篇
建筑科学   47539篇
矿业工程   19406篇
能源动力   10800篇
轻工业   26380篇
水利工程   16121篇
石油天然气   14818篇
武器工业   3244篇
无线电   27349篇
一般工业技术   31890篇
冶金工业   21541篇
原子能技术   3517篇
自动化技术   53414篇
  2024年   1281篇
  2023年   4293篇
  2022年   9662篇
  2021年   11356篇
  2020年   9979篇
  2019年   8338篇
  2018年   8277篇
  2017年   10154篇
  2016年   12613篇
  2015年   14313篇
  2014年   23296篇
  2013年   21630篇
  2012年   25287篇
  2011年   25994篇
  2010年   20677篇
  2009年   21323篇
  2008年   20060篇
  2007年   26540篇
  2006年   25421篇
  2005年   21941篇
  2004年   18247篇
  2003年   16497篇
  2002年   13378篇
  2001年   11114篇
  2000年   9371篇
  1999年   7460篇
  1998年   5534篇
  1997年   4850篇
  1996年   4376篇
  1995年   3717篇
  1994年   3331篇
  1993年   2428篇
  1992年   2190篇
  1991年   1656篇
  1990年   1454篇
  1989年   1277篇
  1988年   982篇
  1987年   679篇
  1986年   509篇
  1985年   456篇
  1984年   425篇
  1983年   304篇
  1982年   270篇
  1981年   211篇
  1980年   182篇
  1979年   126篇
  1978年   75篇
  1977年   83篇
  1962年   94篇
  1959年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A strategic planning optimization model is proposed for a network of natural gas to liquids (GTL) systems, and it is solved using a rolling horizon strategy. The model formulation determines the strategic and tactical decisions of the GTL supply chain over a long time horizon. The decisions to build new GTL refineries may be made over the span of 30 years and their operations cover the span of 60 years. Multiple capacities of GTL refineries (i.e., 1, 5, 10, 50, and 200 thousand barrels per day) that produce gasoline, diesel, and kerosene commensurate to the United States demand ratio may exist in the network. The parameter inputs include the locations, availabilities, and prices of natural gas in the United States discretized by county, the delivery locations of fuel products, and the transportation costs of every input and output of the refinery, defined for each time period. Formulated as a large-scale mixed-integer linear optimization (MILP) model, the problem is solved using a rolling horizon strategy for tractability. Case studies on the state of Pennsylvania are presented for different planning schemes and their impact on the economic performance of the GTL network is discussed.  相似文献   
82.
In the last few years, more and more complex microsphere models have been proposed to predict the mechanical response of various polymers. Similarly than for microplane models, they consist in deriving a one-dimensional force vs. stretch equation and to integrate it over the unit sphere to obtain a three-dimensional constitutive equation. In this context, the focus of authors is laid on the physics of the one-dimensional relationship, but in most of the case the influence of the integration method on the prediction is not investigated.Here we compare three numerical integration schemes: a classical Gaussian scheme, a method based on a regular geometric meshing of the sphere, and an approach based on spherical harmonics. Depending on the method, the number of integration points may vary from 4 to 983,040! Considering simple quantities, i.e. principal (large) strain invariants, it is shown that the integration method must be carefully chosen. Depending on the quantities retained to described the one-dimensional equation and the required error, the performances of the three methods are discussed. Consequences on stress–strain prediction are illustrated with a directional version of the classical Mooney–Rivlin hyperelastic model. Finally, the paper closes with some advices for the development of new microsphere constitutive equations.  相似文献   
83.
来水利 《云南化工》2019,(7):180-181
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。  相似文献   
84.
85.
86.
With the emergence of distributed ledger technology (DLT), numerous practitioners and researchers have proclaimed its beneficial impact on supply chain transactions in the future. However, the vast majority of DLT initiatives are discontinued after a short period. With the full potential of DLT laying far down the road, especially managers in supply chain management (SCM) seek for short-term cost-saving effects of DLT in order to achieve long-term benefits of DLT in the future. However, the extant research has bypassed grounding long-term as well as short-term effects of DLT on supply chain transaction with empirical data. We address this shortcoming, following an abductive research approach and combining empirical data from a multiple case study design with the corresponding literature. Our study reveals that the effects of DLT on supply chain transactions are two-sided. We found six effects of DLT solutions that have a cost-reducing or cost avoidance impact on supply chain transactions. In addition, we found two effects that change the power distribution between buyers and suppliers in transactions and a single effect that reduces the dependency of supply chain transactions on third parties. While cost-reducing and avoidance as well as dependency-reducing effects are positive effects, the change in power distribution might come with disadvantages. With these findings, the paper provides the first empirical evidence of the impact of DLT on supply chain transactions, which will enable managers to improve their assessment of DLT usage in supply chains.  相似文献   
87.
以电信用户入网协议为切入点,电信用户的携号转网行为应受到《合同法》《消费者权益保护法》等私法规范的保护与限制。该行为引起的格式条款解释、合同终止、违约责任、损失赔偿等问题,不能仅靠《电信条例》等公法规范来调整。应当积极引导广大消费者用户以私法领域相关规定为依据,转变争议解决思维,拓宽纠纷处理途径,合理选择维权手段,以保护自身合法民事权益,与行业监管部门共同推动电信行业有序发展。  相似文献   
88.
This article reviews the four innovation governance approaches (the precautionary principle, responsible innovation, permissionless innovation, and the innovation principle), including definitions, important attributes, and weaknesses found in each approach, and when utilizing an affinity diagram as a tool of analysis, identifies their distinctive characteristics and common relationships. A discussion section summarizes the paper’s findings and offers insights into where there is common relationships for further possible convergence between two innovation governance approaches – responsible innovation and permissionless innovation – that conceptually share substantially more in common than they contrast with each other. For addressing this challenge, the study recommends the following policy proposals: embrace artificial intelligence/machine learning/data analytics for risk management and regulatory adaptability; consider “soft law”as an option to public regulation; and substitute corporate citizenship for corporate social responsibility.  相似文献   
89.
90.
以可编程控制器课程为例,介绍"任务驱动"教学法在教学过程中的具体应用,并探讨了实施过程中存在的问题与解决方法。  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