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   89067篇
  免费   7422篇
  国内免费   3731篇
电工技术   3801篇
技术理论   8篇
综合类   7965篇
化学工业   16232篇
金属工艺   1617篇
机械仪表   2037篇
建筑科学   13412篇
矿业工程   5234篇
能源动力   5229篇
轻工业   5750篇
水利工程   18797篇
石油天然气   7912篇
武器工业   202篇
无线电   1276篇
一般工业技术   4032篇
冶金工业   3476篇
原子能技术   1124篇
自动化技术   2116篇
  2024年   268篇
  2023年   976篇
  2022年   1938篇
  2021年   2379篇
  2020年   2627篇
  2019年   2166篇
  2018年   2109篇
  2017年   2585篇
  2016年   2887篇
  2015年   2865篇
  2014年   5465篇
  2013年   5468篇
  2012年   6733篇
  2011年   6676篇
  2010年   4936篇
  2009年   5176篇
  2008年   4536篇
  2007年   6060篇
  2006年   5644篇
  2005年   5176篇
  2004年   4021篇
  2003年   3677篇
  2002年   3222篇
  2001年   2620篇
  2000年   2172篇
  1999年   1670篇
  1998年   1224篇
  1997年   1005篇
  1996年   763篇
  1995年   691篇
  1994年   509篇
  1993年   386篇
  1992年   307篇
  1991年   239篇
  1990年   176篇
  1989年   187篇
  1988年   117篇
  1987年   128篇
  1986年   96篇
  1985年   95篇
  1984年   89篇
  1983年   53篇
  1982年   28篇
  1981年   9篇
  1980年   16篇
  1979年   17篇
  1978年   3篇
  1977年   8篇
  1976年   5篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
商业智能现在已广泛应用于各个领域,利用商业智能可以对趋势预测做出良好的支持,本文将其中一种常用商业智能的工具——数据仓库技术,应用于小区家庭的用水量预测研究。  相似文献   
992.
本文结合建筑给水系统图的特点,从绘制图例、确定主体管线、添加注释等方面介绍了运用AutoCAD软件进行建筑给排水系统设计图绘制的方法、技巧。  相似文献   
993.
A three‐dimensional oil‐water turbulent flow and oil separation process in a double‐cone liquid‐liquid hydrocyclone (LLHC) is numerically simulated using FLUENT software. The Euler‐Euler approach and Reynolds‐stress model are combined and adopted in this simulation to handle the challenging situation of anisotropic turbulent two‐phase flow with a higher volumetric ratio (over 10%) in the dispersed phase. It is visualized well in the simulation how separation, aggregation and shift of oil and water proceed in the LLHC. The oil separation efficiency is determined based on flow field and phase concentration distribution. The simulation is verified by comparing predicted and measured separation efficiency in the LLHC.  相似文献   
994.
A model is presented for the simulation of water flow, heat flow, and nitrate and ammonium transport. Two approaches are used for modelling plant water uptake as well as for plant nitrogen uptake. Nitrogen transformations are accounted for in a very simple way. This paper focuses mainly on water flow modelling, solute transport, and water uptake. Richards' equation is used to model water flow in layered soil profiles with a great variety of boundary conditions. Solute transport is simulated with either a simple convection dispersion equation or with a two-region physical non-equilibrium model to distinguish between mobile and immobile water and solute exchange between these two regions. A macroscopic sink term is added to Richards' equation to account for plant water uptake. This term can be calculated along two different approaches, one of which is based on the concept of root water potential. The root water potential is then continuously optimized to minimize the difference between the climatic demand and the uptake rate.Simulation results are compared with field data from the Netherlands to illustrate the degree to which the model is able to predict water flow, solute transport and plant water uptake. The root water potential optimization model seems to provide the best prediction of water distribution. In particular the shape of the profile, revealing uptake patterns, is quite well reproduced with this model. Comparison of simulated and observed water content profiles seems also to reveal the presence of preferential pathways. The comparisons show also how predicted solute distributions can be improved by using a two-region approach rather than a simple convection-dispersion model.  相似文献   
995.
The use of an adhesive to bond stainless steel water tubing, allowing stainless steel fittings to be employed, is considered and compared with the more conventional use of compression or capillary copper fittings together with a soft solder. Tests carried out to determine environmental effects on adhesively bonded stainless steel tubing suitable for domestic water supply, and the strengths of these joints, are described. It has been found that acrylic anaerobic adhesives are suitable for bonding tubing carrying cold water, the joints attaining superior strength to the copper-soldered ones; a reasonable degree of flexing can also be tolerated. It would appear that certain selected adhesives may also be used in joints carrying hot water.  相似文献   
996.
阴离子型微乳洗涤剂洗涤过程动力学研究   总被引:2,自引:0,他引:2  
采用微乳手段,将十二烷基硫酸钠(SDS)、癸烷、正丁醇与水制成微乳液。当m(SDS):m(C10H22):m(C4H9OH):m(H2O)=112:96:75:178时形成的微乳液对棉布上由原油形成的污垢的洗涤过程的速率方程为一级,洗涤过程活化能为13.2kJ/mol。30℃浸泡4h洗净度为88%,比用含相同质量分数的表面活性剂溶液的洗涤效果高出37%。  相似文献   
997.
在实验室,采用SBR生化反应器,分别研究了经空气吹脱预处理和未经预处理的新型气化炉煤气洗涤废水经驯化建立的生态系统脱除氨态氮和COD以及脱氮模式的区别,得出以下结论:新型气化炉煤气洗涤废水可采用短程亚硝化型硝化形式直接进行生化处理。  相似文献   
998.
The solubility of many salts in water decreases dramatically with temperature in the vicinity of the critical point of pure water. Examples of these salts are sulfates of sodium, potassium, lithium and sodium carbonate. These salts are usually produced during supercritical water oxidation (SCWO) and contribute to fouling. The solubility of Na2CO3 and Na2SO4 has been determined in pure form and in the presence of each other, for the temperature range relevant to SCWO. The experimental procedure was to pass the salt solution through a tube at constant temperature. After a brief initiation period during which no salt sticks to the tube, the salt above the solubility limit deposited on the tube surface. The solution leaving the section was thus at the solubility limit. A rapid decrease in the salt solubility was observed just above the pseudo-critical temperature. For supercritical conditions, the solubility of each salt in the form of a mixture was quite close to the solubility of pure salt. At the highest fluid density considered (480 kg/m3) the presence of Na2CO3 reduces the solubility of Na2SO4, as might be expected from the “common-ion effect”.  相似文献   
999.
脱水法合成3-羟基丁酸乙酯   总被引:2,自引:0,他引:2  
以3-羟基丁酸和乙醇为原料,在对甲苯磺酸的催化下分别以氧化钙、3A分子筛、无水硫酸镁为脱水剂,采用索氏提取器进行回流脱水合成3-羟基丁酸乙酯。对影响3-羟基丁酸乙酯收率的诸因素进行了考察。试验结果表明:加入脱水剂和带水剂可以显著提高3-羟基丁酸乙酯的收率。当原料配比为:0.1mol 3-羟基丁酸、0.12mol乙醇,0.7175g对甲苯磺酸,带水剂环己烷50mL,脱水剂18.7g氧化钙,反应时间3h时,产品3-羟基丁酸乙酯的收率可达96.6%(质量分数,下同)。  相似文献   
1000.
COD测定方法的研究动态   总被引:3,自引:0,他引:3  
王新  张裕卿 《河北化工》2007,30(1):50-51
从采用不同的氧化剂测定、寻找新的催化剂、样品消解方法的改进、在线监测仪器及与其他综合指标的相关关系等几个方面论述了化学需氧量测定方法的发展与研究现状.  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