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   346251篇
  免费   25084篇
  国内免费   13030篇
电工技术   18734篇
技术理论   57篇
综合类   20491篇
化学工业   58653篇
金属工艺   19331篇
机械仪表   22067篇
建筑科学   26766篇
矿业工程   11450篇
能源动力   10142篇
轻工业   19384篇
水利工程   5482篇
石油天然气   24017篇
武器工业   2700篇
无线电   38034篇
一般工业技术   41241篇
冶金工业   19103篇
原子能技术   3377篇
自动化技术   43336篇
  2024年   1352篇
  2023年   5410篇
  2022年   9278篇
  2021年   13045篇
  2020年   10249篇
  2019年   8355篇
  2018年   9603篇
  2017年   10796篇
  2016年   9632篇
  2015年   12732篇
  2014年   16539篇
  2013年   19870篇
  2012年   20980篇
  2011年   23319篇
  2010年   19973篇
  2009年   19049篇
  2008年   18784篇
  2007年   18046篇
  2006年   18973篇
  2005年   16717篇
  2004年   10818篇
  2003年   9533篇
  2002年   8516篇
  2001年   7813篇
  2000年   8311篇
  1999年   10012篇
  1998年   8438篇
  1997年   7047篇
  1996年   6592篇
  1995年   5530篇
  1994年   4529篇
  1993年   3191篇
  1992年   2584篇
  1991年   2023篇
  1990年   1560篇
  1989年   1273篇
  1988年   1047篇
  1987年   706篇
  1986年   549篇
  1985年   352篇
  1984年   254篇
  1983年   209篇
  1982年   201篇
  1981年   137篇
  1980年   134篇
  1979年   69篇
  1978年   34篇
  1977年   39篇
  1976年   55篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Risks always exist in construction projects and often cause schedule delay or cost overrun. Risk management is a key issue in project management. The first step of risk management is risk identification. It includes the recognition of potential risk event conditions in the project and the clarification of risk responsibilities. We conducted multiple-case studies using a systematic analytical procedure to identify risks in highway projects in Taiwan, to recognize risk allocation by contract clauses, and to analyze the influence of risk allocation on the contractor’s risk handling strategies. The results show that the owner allocates risks by stipulating specific contract clauses into five kinds of risk allocation conditions. If a risk is more controllable by the contractor, the owner has a greater tendency to allocate the risk to the contractor. Risk allocation determines which kinds of risks the contractor would take and influences the contractor’s risk handling decisions. The analysis furthermore indicates that, if the probability of a certain risk event condition is uncontrollable, then with the increasing possibility of taking the risk, the contractor’s tendency of risk handling changes from actively transferring the risk to passively retaining the risk. In contrast, if a risk is controllable and certainly allocated to the contractor, the contractor tends to take the initiative to reduce the impact caused by the risk event rather than retain the risk.  相似文献   
972.
The formation of "sidewall nanowires" on shallow patterned mesa strips with a modulation depth of only 35 nm on GaAs (100) was demonstrated using molecular beam epitaxy. While self-assembled GaAs sidewall nanowire formation is observed near mesa strips running along [011], relatively thinner AlAs/GaAs layers are formed on identical mesa strips running along [01-1]. Cross-sectional atomic force microscopy (XAFM) on (011) and (01-1) and AFM on (100) are used to understand the formation of the different morphology of the nanostructures, depending on the direction of the mesas. The data indicates that anisotropic surface diffusion of adatoms, resulting from the characteristic (2times4) GaAs (100) surface reconstruction, is responsible for the sidewall nanowire formation and for the different morphology observed along different directions  相似文献   
973.
对人力资源会计作了一些粗浅的研究,讨论了有关人力资源会计的确认、计量、核算及信息披露方式等,旨在为我国的人力资源会计研究提供建设性思路。  相似文献   
974.
针对公司在备件采购中存在的质量、价格等问题,探讨了如何使用“定质比价法”这一新的招标采购方法来提高备件质量、降低成本。  相似文献   
975.
The self-assembly of various nanostructures is recently attracting a great deal of research attention. In this paper, we demonstrate that a palladium chloride aqueous solution, mixed with a proper ammonia solution, can produce Tetra-amminepalladous chloride (Pd(NH3)4Cl2·H2O) nanowires. These nanowires can spontaneously form the two-dimensional hexagon-oriented Pd(NH3)4Cl2·H2O arrays on mica surfaces. We can control the length and height of these nanowires by adjusting their deposit time on the mica substrate. This method can be potentially used in making sensors or in making templates to wire and position nanodevices.  相似文献   
976.
Distributed active storage architectures are designed to offload user-level processing to the peripheral from the host servers. In this paper, we report preliminary investigation on performance and fault recovery designs, as impacted by emerging storage interconnect protocols and state-of-the-art storage devices. Empirical results obtained using validated device-level and interconnect data demonstrate the significance of the said parameters on the overall system performance and reliability.  相似文献   
977.
The molten iron allocation problem (MIAP) is to allocate molten iron from blast furnaces to steel-making furnaces. The allocation needs to observe the release times of the molten iron defined by the draining plan of the blast furnaces and the transport time between the iron-making and steel-making stages. Time window constraints for processing the molten iron must be satisfied to avoid freezing. The objective is to find a schedule with minimum total weighted completion time. This objective reflects the practical consideration of improving steel-making efficiency and reducing operation cost caused by the need for reheating. Such a problem can be viewed as a parallel machine scheduling problem with time windows which is known to be NP-hard. In this paper, we first formulate the molten iron allocation problem as an integer programming model and then reformulate it as a set partitioning model by applying the Dantzig–Wolfe decomposition. We solve the problem using a column generation-based branch-and-price algorithm. Since the subproblem of column generation is still NP-hard, we propose a state-space relaxation-based dynamic programming algorithm for the subproblem. Computational experiments demonstrate that the proposed algorithm is capable of solving problems with up to 100 jobs to optimality within a reasonable computation time.  相似文献   
978.
王敦曾 《中国煤炭》2003,29(8):29-32
从矿区建设、采煤技术、煤炭洗选技术和环保、高效先进的煤矿专用设备与自动化控制系统等几个方面介绍了我国煤炭工业取得科研成果,并对这些优秀成果的特点进行了分析。认为我国煤炭工业的科研成果的技术水平在逐年提高,已进入了世界先进行列。  相似文献   
979.
分析了重油催化裂化沉降器结焦的原因,认为反应油气中含有催化剂颗粒以及油气中重组分的冷凝是沉降器结焦的物理原因,而重芳烃、胶质、沥青质的高温缩合则是沉降器结焦的化学因素。因此,防止沉降器结焦的关键是抑制油气重组分的冷凝和减少油气在沉降器内的停留时间。  相似文献   
980.
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