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   1006篇
  免费   33篇
  国内免费   6篇
电工技术   19篇
技术理论   1篇
综合类   50篇
化学工业   42篇
金属工艺   2篇
机械仪表   14篇
建筑科学   569篇
矿业工程   12篇
能源动力   85篇
轻工业   19篇
水利工程   36篇
石油天然气   6篇
无线电   20篇
一般工业技术   38篇
冶金工业   37篇
原子能技术   9篇
自动化技术   86篇
  2023年   7篇
  2022年   12篇
  2021年   12篇
  2020年   14篇
  2019年   17篇
  2018年   12篇
  2017年   14篇
  2016年   37篇
  2015年   45篇
  2014年   66篇
  2013年   85篇
  2012年   70篇
  2011年   84篇
  2010年   53篇
  2009年   57篇
  2008年   63篇
  2007年   65篇
  2006年   62篇
  2005年   35篇
  2004年   36篇
  2003年   27篇
  2002年   18篇
  2001年   28篇
  2000年   13篇
  1999年   24篇
  1998年   13篇
  1997年   3篇
  1996年   9篇
  1995年   9篇
  1994年   2篇
  1993年   5篇
  1992年   6篇
  1991年   4篇
  1990年   1篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1984年   7篇
  1983年   10篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
排序方式: 共有1045条查询结果,搜索用时 15 毫秒
1.
The constructive analysis of Madrid's old timber-framed collective courtyard buildings, whether demolished, preserved intact, or enlarged, has achieved the dating of relevant case studies. New parameters established in this study set a chronology based on front sector original projects: old (1737–1788), pre-modern (1788–1847) and modern (1847–1892). The on-site inspection and archival research point to ongoing misleading construction in the historic Southern area. Some modern corralas erected on top of pre-existing buildings confirm the initial hypothesis. First dimensioning rules for new façades and the stability required in old ones before adding new storeys, maintaining the original masonry or double-layered system, are discovered. Undated buildings suggest their possible origin a la malicia and a later transformation into transitional corralas. Finally, an analysis of the demolished courtyards narrows down the dating and points to new conjectures in some preserved by showing their uneven layout, old features, and structural discordances in each sector.  相似文献   
2.
WRESTORE (Watershed Restoration Using Spatio-Temporal Optimization of Resources) is a web-based, participatory planning tool that can be used to engage with watershed stakeholder communities, and involve them in using science-based, human-guided, interactive simulation–optimization methods for designing potential conservation practices on their landscape. The underlying optimization algorithms, process simulation models, and interfaces allow users to not only spatially optimize the locations and types of new conservation practices based on quantifiable goals estimated by the dynamic simulation models, but also to include their personal subjective and/or unquantifiable criteria in the location and design of these practices. In this paper, we describe the software, interfaces, and architecture of WRESTORE, provide scenarios for implementing the WRESTORE tool in a watershed community's planning process, and discuss considerations for future developments.  相似文献   
3.
Crocodiles play important roles in many ecosystems, but their populations worldwide are threatened by human exploitation and habitat destruction. We studied ontogenetic changes in habitat use and seasonal activity patterns in a population of Nile crocodiles (Crocodylus niloticus) inhabiting the Lake Albert Delta Wetland System, a Ramsar Site of international importance in Murchison Falls National Park of western Uganda. A total of 186 crocodile observations were made from monthly surveys of five transects during October 2017 to September 2018. Crocodiles exhibited a marginally bi-modal seasonal pattern, with the fewest observations from July to August and October to November, and the highest observations from January to February and April to May. Crocodiles were most frequently encountered along the north shore of the delta, especially on riverbanks with woody vegetation, followed by Cyperus papyrus-Vossia dominated habitats, while crocodiles were infrequently observed on islands and muddy banks. Habitat niche breadth was narrowest in hatchlings and widest in sub-adults, with juveniles and large adults exhibiting intermediate values. Overlap in habitat resource use across size classes was generally high, with the lowest overlap between hatchlings and juveniles, and the highest between large and sub-adult crocodiles. Our study on Nile crocodiles in the Lake Albert delta provides insights into habitat partitioning among different demographic segments of this population that can be utilized to improve its management in one of Africa’s Great Lakes by spatially and temporally focusing conservation efforts on the most used habitats and seasonal aggregations, respectively.  相似文献   
4.
美国西雅图先锋广场历史保护区的形成   总被引:1,自引:0,他引:1  
黄治 《规划师》2004,20(4):91-93
考察美国西雅图先锋广场历史保护区形成的过程,可以看出城市历史文化遗存的保护是经济与历史文化合力作用的结果,公众参与在城市历史文化保护工作中发挥着重要的作用。我国城市经济高速发展,保护与发展的矛盾冲突还没得到很好解决,先锋广场的例子对我们具有一定的参考价值。  相似文献   
5.
介绍了HARSVERT—A06/035型高压变频器的性能及其在新4号高炉冲渣水泵上的应用。  相似文献   
6.
Susceptibility of stone to salt decay is directly related to its microstructural and mechanical characteristics. In the present work, a porous stone from a quarry in Cyprus was examined. Samples of this stone were consolidated and protected with certain conservation materials. The modification of microstructural characteristics of the stone was evaluated by mercury intrusion porosimetry, while its mechanical characteristics were measured by compressive and bending strength tests. From these data, the susceptibility of Cyprus stone to salt (NaCl) decay was estimated. The values of crystallization pressure of NaCl were calculated and compared to the experimentally measured compressive and tensile strength of the stone, in order to examine the probability of stone disruption due to salt crystallization. The development of the phenomenon after coarse pores’ filling with crystals, i.e. crystallization of salts in capillaries or mechanical failure of the stone, was determined by thermodynamic analysis. Additionally, artificial weathering tests of marine salt spray were performed for the evaluation of stone’s durability after the conservation. The treated stone proved to be resistant to salt decay, as it presented ameliorated microstructural and mechanical characteristics, concerning decay due to soluble salt crystallization. The most possible thermodynamic scenario was small pores repletion with crystals, avoiding mechanical failure of the stone.  相似文献   
7.
从分析脱硅的条件出发,引导出新的工艺操作方法、工艺参数和加料方法。用一年的生产实践说明该新工艺操作方法的技术经济效益。  相似文献   
8.
The Crank–Nicolson scheme as well as its modified schemes is widely used in numerical simulations for the nonlinear Schrödinger equation. In this paper, we prove the multisymplecticity and symplecticity of this scheme. Firstly, we reconstruct the scheme by the concatenating method and present the corresponding discrete multisymplectic conservation law. Based on the discrete variational principle, we derive a new variational integrator which is equivalent to the Crank–Nicolson scheme. Therefore, we prove the multisymplecticity again from the Lagrangian framework. Symplecticity comes from the proper discrete Hamiltonian structure and symplectic integration in time. We also analyze this scheme on stability and convergence including the discrete mass conservation law. Numerical experiments are presented to verify the efficiency and invariant-preserving property of this scheme. Comparisons with the multisymplectic Preissmann scheme are made to show the superiority of this scheme.  相似文献   
9.
Selection of strategies that help reduce riverine inputs requires numerical models that accurately quantify hydrologic processes. While numerous models exist, information on how to evaluate and select the most robust models is limited. Toward this end, we developed a comprehensive approach that helps evaluate watershed models in their ability to simulate flow regimes critical to downstream ecosystem services. We demonstrated the method using the Soil and Water Assessment Tool (SWAT), the Hydrological Simulation Program–FORTRAN (HSPF) model, and Distributed Large Basin Runoff Model (DLBRM) applied to the Maumee River Basin (USA). The approach helped in identifying that each model simulated flows within acceptable ranges. However, each was limited in its ability to simulate flows triggered by extreme weather events, owing to algorithms not being optimized for such events and mismatched physiographic watershed conditions. Ultimately, we found HSPF to best predict river flow, whereas SWAT offered the most flexibility for evaluating agricultural management practices.  相似文献   
10.
This paper builds on a prior paper by this author, McGrane (1991). In that paper, ozone is used as the sole means of cooling tower water treatment. The paper discusses water conservation by increased cycles of concentration, greatly increased efficiency through extremely low biological populations, and corrosion data which is compared to ozonated and chemically treated towers.

New in this paper are the results from the combination of a low pressure reverse osmosis system with ozone treatment for cooling tower water. Scale formation has continued to plague cooling towers with high concentrations of calcium in the make-up water. The use of a mineral removal system in cases of extremely hard water has made ozone an attractive alternative to traditional chemicals in many areas.  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