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   124685篇
  免费   9649篇
  国内免费   4829篇
电工技术   6515篇
技术理论   12篇
综合类   7387篇
化学工业   20227篇
金属工艺   6702篇
机械仪表   7491篇
建筑科学   9522篇
矿业工程   3285篇
能源动力   3547篇
轻工业   8086篇
水利工程   2015篇
石油天然气   6622篇
武器工业   795篇
无线电   15366篇
一般工业技术   15985篇
冶金工业   7434篇
原子能技术   1394篇
自动化技术   16778篇
  2024年   214篇
  2023年   1887篇
  2022年   2658篇
  2021年   4531篇
  2020年   3556篇
  2019年   2929篇
  2018年   3398篇
  2017年   3881篇
  2016年   3384篇
  2015年   4469篇
  2014年   5701篇
  2013年   7190篇
  2012年   7628篇
  2011年   8325篇
  2010年   7194篇
  2009年   7068篇
  2008年   7005篇
  2007年   6507篇
  2006年   6729篇
  2005年   5962篇
  2004年   4093篇
  2003年   3533篇
  2002年   3158篇
  2001年   3016篇
  2000年   3039篇
  1999年   3529篇
  1998年   3342篇
  1997年   2853篇
  1996年   2479篇
  1995年   2059篇
  1994年   1649篇
  1993年   1332篇
  1992年   1005篇
  1991年   760篇
  1990年   636篇
  1989年   526篇
  1988年   406篇
  1987年   315篇
  1986年   216篇
  1985年   193篇
  1984年   117篇
  1983年   95篇
  1982年   104篇
  1981年   94篇
  1980年   65篇
  1979年   46篇
  1978年   37篇
  1977年   53篇
  1976年   72篇
  1975年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
张扬  韩春雷  孙玮琢  鹿瑶  杨笛 《现代导航》2021,12(4):293-296
在现代信息化战争中依据战场态势变化进行合理威胁评估,对实现指挥系统自动化具有重要意义。为了克服传统规则算法评估能力的局限,设计了一种基于深度学习的新型智能威胁评估算法。首先设定了防空威胁评估指标选取原则,在此基础上从多个不同角度出发建立了反映空中目标威胁的指标体系,然后构建深度神经网络模型予以解决。新算法的优点在于威胁评估快速可信、易于实现,且对于不断变化的空情威胁可进行持续更新优化。最后,通过典型作战场景的仿真数据验证了模型的有效性和可行性。  相似文献   
62.
63.
64.
With the evolution of video surveillance systems, the requirement of video storage grows rapidly; in addition, safe guards and forensic officers spend a great deal of time observing surveillance videos to find abnormal events. As most of the scene in the surveillance video are redundant and contains no information needs attention, we propose a video condensation method to summarize the abnormal events in the video by rearranging the moving trajectory and sort them by the degree of anomaly. Our goal is to improve the condensation rate to reduce more storage size, and increase the accuracy in abnormal detection. As the trajectory feature is the key to both goals, in this paper, a new method for feature extraction of moving object trajectory is proposed, and we use the SOINN (Self-Organizing Incremental Neural Network) method to accomplish a high accuracy abnormal detection. In the results, our method is able to shirk the video size to 10% storage size of the original video, and achieves 95% accuracy of abnormal event detection, which shows our method is useful and applicable to the surveillance industry.  相似文献   
65.
66.
Yang  Mengmeng  Chen  Zhaofeng  Liu  Tianlong  Wu  Qiong  Yang  Lixia 《Journal of Porous Materials》2022,29(2):523-530
Journal of Porous Materials - In recent years, oil spills and industrial organic pollutants have caused irreparable damage to the environment and biological ecosystems. Therefore, the treatment of...  相似文献   
67.
68.
The process of cemented carbides manufacturing requires rapid and field elemental analytical techniques to control and evaluate the properties of products. Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is such a potential elemental analytical technique. In this work, a portable LIBS instrument combined with a CF method was developed for the analysis of cemented carbides. Three batches of cemented compact carbides without reference samples were analyzed. Qualitative and quantitative analysis of the samples were achieved by using the portable LIBS instrument combined with CF method. To validate the analysis results, X-ray fluorescence spectrometry (XRF) was used to analyze the samples as well. The results of CF-LIBS agreed well with the results of XRF, with relative errors between ?29.53 and 24.70%. The results demonstrated that the portable LIBS instrument combined with CF method was capable for direct and rapid analysis without any need of standard measurements. Notably, with the portable LIBS instrument combined with CF method, acceptable accuracy could be obtained, which is promising for practical field applications.  相似文献   
69.
吴世超  孙体昌  杨慧芬 《金属矿山》2020,48(11):109-114
以国外某高磷鲕状赤铁矿为研究对象进行脱磷研究,该高磷矿铁品位为55.81%,磷含量为0.72%,铁矿物主要为磁铁矿和赤铁矿,48.61%的磷存在于磷酸盐中,47.22%的磷分布于铁矿物中。研究了脱磷剂用量、秸秆炭用量、还原温度以及还原时间对粉末还原铁指标的影响。结果表明:无脱磷剂碳酸钙时,无法获得合格的指标;在碳酸钙用量为25%,秸秆炭用量为12.5%,还原温度1 200 ℃,还原时间为75 min,还原产品两段磨矿两段磁选的条件下,可获得铁品位、铁回收率以及磷含量分别为94.27%、87.34%以及0.077%的粉末还原铁,该产品可作为电炉炼钢的优质原料。不加添加剂时,部分含磷矿物被还原成单质磷进入到金属铁中,故粉末还原铁磷含量较高,当碳酸钙用量为25%时,含磷矿物的还原受到抑制而保留在脉石相中,可实现降磷目的,而还原时间过长时,磷仍在脉石相中,铁颗粒将部分含磷矿物包裹,磨矿难以分离,导致磷含量升高。  相似文献   
70.
Yang  Ting  Su  Lijun  Wu  Laosheng  Wang  Quanjiu 《Water Resources Management》2020,34(1):51-69

Overland flow is an important hydrological response of catchments to rainstorms and contributes to soil erosion and nutrient loss. The kinematic wave model is known to describe the transformation of rainfall to overland flow. Through this, field studies were conducted on a hillslope to simulate water scouring from upstream with a complex surface condition, which was covered with different sizes and percentages of stones. Existing semi-analytical and numerical models were adopted to describe the overland flow in the field. Results indicate that both semi-analytical and numerical models could be applied to describe the process of overland flow. Furthermore, predicted outflow rates by the semi-analytical and the numerical model showed strong correlation with the field measured outflow rates, respectively (NS?=?(0.926, 0.942, 0.992), RE?=?(5.5%, 4.7%, 1.7%) for the semi-analytical model, and NS?=?(0.817, 0.952, 0.992), RE?=?(5.5%, 5.5%, 2.1%) for the numerical model). Besides, hydraulic parameters (Reynolds number-Re, Froude numbers-Fr, Darcy-Weisbach-f, hydraulic shear stress-τ, stream power-ω, water wave celerity-vw) at any time and distance could be described by the semi-analytical method, and the parameter n/h (an important factor indicating the energy of water and wave flow celerity) could successfully characterize the average hydraulic parameters, and all of the hydraulic parameters are fitted to the expression of y?=?a(n/h)b.

  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