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   1330篇
  免费   152篇
  国内免费   95篇
电工技术   33篇
综合类   129篇
化学工业   116篇
金属工艺   50篇
机械仪表   77篇
建筑科学   81篇
矿业工程   19篇
能源动力   32篇
轻工业   37篇
水利工程   19篇
石油天然气   28篇
武器工业   76篇
无线电   386篇
一般工业技术   111篇
冶金工业   104篇
原子能技术   38篇
自动化技术   241篇
  2024年   2篇
  2023年   20篇
  2022年   36篇
  2021年   61篇
  2020年   28篇
  2019年   29篇
  2018年   27篇
  2017年   35篇
  2016年   63篇
  2015年   64篇
  2014年   71篇
  2013年   87篇
  2012年   100篇
  2011年   138篇
  2010年   84篇
  2009年   91篇
  2008年   75篇
  2007年   102篇
  2006年   91篇
  2005年   54篇
  2004年   59篇
  2003年   43篇
  2002年   41篇
  2001年   26篇
  2000年   22篇
  1999年   23篇
  1998年   22篇
  1997年   11篇
  1996年   18篇
  1995年   13篇
  1994年   6篇
  1993年   4篇
  1992年   4篇
  1991年   5篇
  1990年   3篇
  1989年   4篇
  1988年   3篇
  1987年   5篇
  1986年   1篇
  1985年   1篇
  1977年   2篇
  1975年   1篇
  1957年   1篇
  1954年   1篇
排序方式: 共有1577条查询结果,搜索用时 93 毫秒
11.
Geotechnical characterization of potential lunar sites will be a critical part of the planning and design process. The strategies used to conduct a geotechnical investigation will be dictated by the specific needs of the lunar base, the unique environment of the lunar surface, and general character of the lunar soils and rocks. This paper outlines some of the types of geotechnical information that will be important and identifies some of the more promising strategies which might be used to obtain such information in the lunar environment. Some of the most important geotechnical information for planning and site development will be related to construction in the lunar soil. In addition to construction concerns, geotechnical data for foundation design (or verification of predesigned foundations) will be needed. The geotechnical site‐characterization work should include geophysical techniques, supplemented by conventional mechanical boring and testing only to the degree necessary to correlate geophysical measurements with conventional soil properties and to investigate anomalies. Equipment used for geotechnical site characterization will also serve for mineralogical exploration. Several techniques for geotechnical investigation that may provide very useful information in an expedient manner are described. Geophysical methods include seismic and electromagnetic methods, including seismic surveys that utilize surface waves. Electromagnetic methods such as ground‐penetrating radar are fast, efficient methods for mapping the subsurface, although these techniques do not measure soil characteristics that can readily be correlated with engineering properties. Seismic methods provide information that may correlate with soil strength, compressibility, and excavatability. In‐situ physical testing will likely include penetration testing for direct physical measurement of lunar soil behavior.  相似文献   
12.
Subsurface Characterization at Ground Failure Sites in Adapazari, Turkey   总被引:4,自引:0,他引:4  
Ground failure in Adapazari, Turkey during the 1999 Kocaeli earthquake was severe. Hundreds of structures settled, slid, tilted, and collapsed due in part to liquefaction and ground softening. Ground failure was more severe adjacent to and under buildings. The soils that led to severe building damage were generally low plasticity silts. In this paper, the results of a comprehensive investigation of the soils of Adapazari, which included cone penetration test (CPT) profiles followed by borings with standard penetration tests (SPTs) and soil index tests, are presented. The effects of subsurface conditions on the occurrence of ground failure and its resulting effect on building performance are explored through representative case histories. CPT- and SPT-based liquefaction triggering procedures adequately identified soils that liquefied if the clay-size criterion of the Chinese criteria was disregarded. The CPT was able to identify thin seams of loose liquefiable silt, and the SPT (with retrieved samples) allowed for reliable evaluation of the liquefaction susceptibility of fine-grained soils. A well-documented database of in situ and index testing is now available for incorporating in future CPT- and SPT-based liquefaction triggering correlations.  相似文献   
13.
GEOTHERM is a computer program written in BASIC language to estimate geothermal reservoir temperature using the well-known chemical gèothermometers. The empirical equations used in the program were obtained from the literature. Three different chemical geothermometers are included in the program: Na-K, Na-K-Ca, and silica geothermometers; this gives the user the opportunity not only to select the most reliable geothermometer in estimating subsurface temperature, but also to select the type of geothermometer according to available data. A sample input file of geothermal waters obtained from Iceland has been tested, so as to show the applicability and usefulness of the program.  相似文献   
14.
15.
Beneficial use impairments (BUIs) under the Great Lakes Water Quality Agreement identify environmental issues requiring remedial action within the Great Lakes Areas of Concern (AOCs). We conducted this study to support the assessment of the wildlife component of BUI 3: degradation of fish and wildlife populations. We compared bird and amphibian (frogs and toads) data from the Toronto and Region Conservation Authority’s Terrestrial Long-term Monitoring Program in the Toronto and Region AOC to an adjacent, but otherwise similar, reference watershed, Duffins Creek. Twelve of 13 targets were met within the AOC for forest bird, wetland bird, meadow bird and amphibian populations based on averages of mean annual values at sites within the AOC that were within two standard deviations of averages at sites in the Duffins Creek reference watershed between 2008 and 2017. Even though wildlife populations within the AOC were within the normal range of variability expected from a reference watershed, they were often at lower levels than within the Duffins Creek reference watershed. In addition, forest bird and amphibian populations were negatively affected by urbanization within the AOC and meadow bird indices declined. We conclude that while wildlife populations within the AOC currently meet targets for BUI 3, they continue to be negatively impacted by numerous stressors that are primarily related to past and ongoing urbanization. Thus, continued restoration of wildlife habitat and protection of existing habitat within the AOC is highly recommended.  相似文献   
16.
研究近程防御系统,快速打击威胁目标的控制是整个系统的主要问题。针对敌方空中目标批次较多、运动状态复杂,而我方防御火力有限,对目标进行有效、精确拦截,需要对目标威胁度排序,依次进行打击。为了正确识别对整个目标过程,进行定性和定量的分析判断,提出了一种行之有效的灰色关联分析的变权威胁度分析方法;进行仿真,生成空中多组动态飞行目标,采用上述算法对空中目标有效识别,并对威胁度进行排序,进行打击。实验结果与专家评估后的结果完全一致,并能够准确而快速的在战场做出决策。  相似文献   
17.
Leishmaniasis is one of the most neglected diseases worldwide and is considered a serious public health issue. The current therapeutic options have several disadvantages that make the search for new therapeutics urgent. Gold compounds are emerging as promising candidates based on encouraging in vitro and limited in vivo results for several AuI and AuIII complexes. The antiparasitic mechanisms of these molecules remain only partially understood. However, a few studies have proposed the trypanothione redox system as a target, similar to the mammalian thioredoxin system, pointed out as the main target for several gold compounds with significant antitumor activity. In this review, we present the current status of the investigation and design of gold compounds directed at treating leishmaniasis. In addition, we explore potential targets in Leishmania parasites beyond the trypanothione system, taking into account previous studies and structure modulation performed for gold-based compounds.  相似文献   
18.
由成都建筑材料工业设计研究院有限公司(简称成都院)和中国建材装备有限公司组成联合体总承包的UCC 10 000 t/d熟料水泥生产线,成都院负责提供合同范围内所有的工程设计、核心技术及核心设备、现场管理、人员培训、生产线达标考核,并具体负责实施和完成所有的土建及安装工程。在总承包工程建设的过程管理中,成都院以设计为灵魂,贯彻了"工艺流程顺畅,总图布局合理,系统配置先进可靠,合理节省投资"的设计理念;成都院克服了要求高、工期短、气候条件恶劣、国外施工人员管理难度大、功效低等重重困难,按时、保质保量、安全地完成了土建、安装、调试和试车任务;2007年4月26日,该生产线一次性通过业主的达标考核。我们的经验是:(1)有专业设计院全面介入的工程总承包是项目顺利进行的可靠保证;(2)参与建设的相关单位要相互信任、相互配合、目标一致;(3)工程建设管理科学化、人性化很重要。该项目的成功建设,使成都院总包工程建设的过程管理更加正规化、合理化和科学化。  相似文献   
19.
通过研究多输入多输出(Multiple input and multiple out, MIMO)雷达的角度估计算法,基于收发共址的十字阵MIMO雷达系统,将四元数理论应用到 MIMO雷达角度中,提出了一种新的参数估计算法。通过构造四元数模型,结合增广矩阵束( Matrix enhancement and matrix pencil, MEMP)方法构造增广矩阵,并证明该矩阵的秩 等于目标总数,且不受目标相干性的影响,结合ESPRIT算法实现了对MIMO相干目标的角度估 计。算法无需谱峰搜索,能够实现参数的自动配对,同时降低了运算复杂度。仿真实验进一 步验证了算法的有效性。  相似文献   
20.
采用孪生对靶直流磁控溅射的方法在室温下制备高质量的Ga掺杂ZnO(ZGO)透明导电薄膜,用HCl腐蚀的方法获得满足光散射特性的绒面ZGO薄膜。制备的ZGO样品为具有六角纤锌矿结构的多晶膜,具有(002)方向的择优取向。腐蚀后,绒面ZGO薄膜的晶粒度减小,电阻率基本不变。在可见光范围内,绒面ZGO的反射率比平面ZGO的反射率下降了10%左右。将绒面ZGO薄膜应用于p-i-n型非晶Si薄膜太阳电池中,有效提高了太阳电池性能,使得电池的短路电流提高到17.79 mA/cm2,电池的转换效率增加到7.23%。  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