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   147100篇
  免费   14240篇
  国内免费   9169篇
电工技术   11797篇
技术理论   2篇
综合类   18149篇
化学工业   16474篇
金属工艺   6324篇
机械仪表   10635篇
建筑科学   18254篇
矿业工程   6646篇
能源动力   4902篇
轻工业   8278篇
水利工程   6515篇
石油天然气   6364篇
武器工业   2013篇
无线电   10193篇
一般工业技术   18665篇
冶金工业   5742篇
原子能技术   2335篇
自动化技术   17221篇
  2024年   604篇
  2023年   1692篇
  2022年   3292篇
  2021年   3839篇
  2020年   4366篇
  2019年   3797篇
  2018年   3654篇
  2017年   4639篇
  2016年   5165篇
  2015年   5381篇
  2014年   8780篇
  2013年   8426篇
  2012年   11166篇
  2011年   11372篇
  2010年   8829篇
  2009年   9190篇
  2008年   8549篇
  2007年   10617篇
  2006年   9282篇
  2005年   7799篇
  2004年   6425篇
  2003年   5541篇
  2002年   4595篇
  2001年   3828篇
  2000年   3383篇
  1999年   2908篇
  1998年   2308篇
  1997年   2013篇
  1996年   1697篇
  1995年   1524篇
  1994年   1283篇
  1993年   946篇
  1992年   834篇
  1991年   587篇
  1990年   480篇
  1989年   488篇
  1988年   344篇
  1987年   201篇
  1986年   161篇
  1985年   72篇
  1984年   72篇
  1983年   37篇
  1982年   45篇
  1981年   58篇
  1980年   31篇
  1979年   39篇
  1978年   19篇
  1977年   16篇
  1975年   18篇
  1959年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
闩体的刚度和强度必须满足设计要求。用有限元法对复杂结构件进行力学性能分析是非常有效的方法。采用ANSYS软件对闩体进行了刚度和强度分析,得出了有用的结论,可供相关设计借鉴。  相似文献   
62.
固定床吸附器透过曲线参数优化方法   总被引:3,自引:1,他引:2  
开发了一种固定床吸附器透过曲线参数估值的优化方法,用Basic语言编制了运算程序,并在普及型286微机上考核了该法的可靠性,相对误差在1%以下,运算机时7.5min。  相似文献   
63.
Individual yeast cells can be successfully isolated and recultured on plates with a new isolation method making use of optical trapping with infrared laser light. The cells can be selected on morphological criteria by high resolution microscopy. The isolation device is constructed from two coverslips separated by spacers, in which selected cells are transferred to a plastic capillary, using the optical trap. To test the procedure, selection experiments were done with a mixture of two Saccharomyces cerevisiae strains, distinguishable both in fluorescence microscopy and on agar plates. These experiments showed that only selected cells were isolated, and close to 100% of the isolated stationary-phase cells formed colonies on agar plates, indicating a high recovery. A lower recovery was obtained with exponential-phase cells, possibly because of a higher sensitivity to laser irradiation. Applications for this method may include the isolation of mutants with altered morphology and the isolation of subpopulations of yeast cultures, for their separate investigation or for the initiation of pure cultures.  相似文献   
64.
Solar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to ensure the accuracy of energy monitoring in a photovoltaic system. While treating a system monitoring equipment as a black box. the author has developed the method of calibrating an energy-integrating function. At first for various input waveforms, the relationship between sampling intervals and quasi-integration outputs have been examined by trapezoidal rule. In the numerical simulation the phases of the sampling clock also are considered Then it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy-integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between both outputs can uniquely give the sampling interval being inspected. Conditions to ensure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. Practical calibrating procedures also are proposed for the integrating function of PV system monitoring.  相似文献   
65.
密集平行束孔落矿的底盘漏斗采矿方案的特点是:用密集严行束孔落矿;凿岩与出矿水平合二为一;实行“掘井、劈漏、落矿三位一体”的回采工艺。该方案结构简单、采切比低、工人劳动强度低,适于开采缓倾斜顶底围岩不稳固的中厚以上矿体。  相似文献   
66.
An experimental-numerical method for measuring dynamic crack propagating velocities under stress wave loading is established in this paper. The experiments of the three-point bend specimen are done on the improved Hopkinson bar. Deflection of loading point, dynamic load and instantaneous crack length are measured, then crack propagating velocities are calculated. Experiments on 40Cr steel show that the results given by this method have a good agreement with that obtained by the resistance fracture gage method. Therefore this method is feasible for measuring crack propagating velocities under high loading rate and will have wide application.  相似文献   
67.
Distortion as a result of the quenching process is predominantly due to the thermal gradient and phase transformations within the component. Compared with traditional liquid quenching, the thermal boundary conditions during gas quenching are relatively simple to control. By adjusting the gas-quenching furnace pressure, the flow speed, or the spray nozzle configuration, the heat-transfer coefficients can be designed in terms of both the component geometry and the quenching time. The purpose of this research is to apply the optimization methodology to design the gas-quenching process. The design objective is to minimize the distortion caused by quenching. Constraints on the average surface hardness, and its distribution and residual stress are imposed. The heat-transfer coefficients are used as design variables. DEFORM-HT is used to predict material response during quenching. The response surface method is used to obtain the analytical models of the objective function and constraints in terms of the design variables. Once the response surfaces of the objective and constraints are obtained, they are used to search for the optimum heat-transfer coefficients. This process is then used instead of the finite-element analysis. A one-gear blank case study is used to demonstrate the optimization scheme.  相似文献   
68.
萃取预分离法分离富铕中钇矿新工艺   总被引:2,自引:0,他引:2  
采用一种新的串级萃取方式--萃取预分离法分离富铕中钇矿的新工艺.原料首先流入十几的三出口预先粗分离工艺,其萃余液La~Gd(TbDy)直接流入Nd/Sm工艺;中间出口流入(Gd)Tb~HoY(Er)Gd~Dy/Ho~LuY细分离工艺;出口负载有机相(Ho)Er~LuY流入Gd~Dy/Ho~LuY的洗涤段.结果表明,新工艺的粗分离工艺将占原料约70%的La~Gd(TbDy)预分离掉,使流入Gd~Dy/Ho~LuY工艺的稀土量减少约70%;由于Gd~Dy/Ho~LuY分组的萃余液GdTbDy含Ho2O3小于0.03%,省去原工艺的GdTbDy/HoY分离;新工艺的处理能力提高30%,酸碱消耗减少20%以上,贵重稀土元素Eu和Tb的存槽量大大减少.  相似文献   
69.
溶液法制备高接枝率HDPE-g-MAH   总被引:7,自引:0,他引:7  
用溶液法制备了HDPE -g -MAH,并讨论了单体、引发剂用量、反应温度、反应时间、投料方式等因素对产物接枝率的影响。  相似文献   
70.
水性聚氨酯材料配方设计技巧   总被引:1,自引:1,他引:1  
介绍了优选法的0.618法和分数法,对其进行改进创新和原理证明,并应用于生产涂料配方设计中。  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