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   12719篇
  免费   971篇
  国内免费   723篇
电工技术   206篇
综合类   964篇
化学工业   2242篇
金属工艺   783篇
机械仪表   359篇
建筑科学   608篇
矿业工程   683篇
能源动力   492篇
轻工业   680篇
水利工程   203篇
石油天然气   4329篇
武器工业   165篇
无线电   394篇
一般工业技术   866篇
冶金工业   497篇
原子能技术   114篇
自动化技术   828篇
  2024年   42篇
  2023年   156篇
  2022年   317篇
  2021年   377篇
  2020年   392篇
  2019年   302篇
  2018年   292篇
  2017年   364篇
  2016年   392篇
  2015年   366篇
  2014年   594篇
  2013年   861篇
  2012年   773篇
  2011年   849篇
  2010年   649篇
  2009年   675篇
  2008年   590篇
  2007年   714篇
  2006年   785篇
  2005年   691篇
  2004年   575篇
  2003年   546篇
  2002年   502篇
  2001年   453篇
  2000年   357篇
  1999年   319篇
  1998年   262篇
  1997年   221篇
  1996年   199篇
  1995年   169篇
  1994年   120篇
  1993年   84篇
  1992年   63篇
  1991年   61篇
  1990年   74篇
  1989年   51篇
  1988年   25篇
  1987年   24篇
  1986年   23篇
  1985年   17篇
  1984年   16篇
  1983年   8篇
  1982年   12篇
  1981年   4篇
  1980年   7篇
  1977年   3篇
  1964年   5篇
  1957年   3篇
  1956年   3篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
炼厂外排污水回用于循环冷却水腐蚀影响因素初探   总被引:3,自引:0,他引:3  
从单因素、多因素和复杂水系考察了炼厂外排污水回用于循环冷却水腐蚀的影响因素,结果表明,碳钢腐蚀的主要影响因素取决于离子特性、氧化膜的形成和溶解氧的扩散等综合协同作用,其中以离子特性的,影响为最大(如:Cl^-、Ca^2 、CO3^2-的腐蚀性较强)。碳钢腐蚀反应又可由以上三种主要影响因素分为三个反应控制区,而当电导率在0.1-2.0mS/cm范围时,其水质属于腐蚀危险高发区。从而也进一步说明水质的低电导率处理,其防腐效果并不理想,相反在高电导率情况下却表现出相对较好的低腐蚀性能。  相似文献   
172.
FOF-18结构与性能的量子化学研究   总被引:1,自引:0,他引:1  
用B3LYP法,在6-31G基组水平上优化了FOF-18的几何构型,得其稳定的几何构型;在振动分析的基础上求得体系的振动频率、IR谱;采用Monte-Carlo方法预估了密度;设计等键等电子反应计算了生成焓;运用Kamlet公式预测爆速、爆压和爆热;将计算性能与CL-20的性能作比较。结果表明,FOF-18整个分子呈N字形,且存在7个强吸收峰,密度2.06g/cm3、生成焓501.03kJ/mol、爆速9411.82m/s、爆压42440.76MPa、爆热6637.46kJ/kg,该化合物的性能与CL-20接近。  相似文献   
173.
L.X. Zhou  F. Wang  J. Zhang 《Fuel》2003,82(13):1579-1586
A unified second-order moment (USM) turbulence-chemistry model is used to simulate methane-air swirling combustion and NO formation for different swirl numbers. The simulation results are compared with those using the EBU-Arrhenius (E-A) combustion model, the simplified PDF model of NO formation in turbulent flows and the corresponding experimental results. The comparison indicates that the USM model is obviously better than the E-A model and the simplified PDF model. The E-A model cannot reasonably simulate the finite-rate kinetics, while the simplified PDF model, using a product of two single-variable PDF's instead of a joint PDF, remarkably under-predicts the NO reaction rate. The USM model gives the best agreement with the experimental results. Predictions show that as the swirl number increases the total NO formation at first decreases and then increases, which is in agreement with the experimental results.  相似文献   
174.
The glass-formation region of the calcia-gallia-silica system was determined. The glasses within this region were measured to have a density of 3 to 4 g/cm3, a refractive index of 1.6 to 1.73, an Abbe number between 35 and 58, a thermal expansion coefficient of 6.5 × 10−7/°C to 11.5 × 10−7/°C, softening temperatures between 730° and 790°C, and a Vickers microhardness of 5.2 to 7.3 GPa. Crystalline phases were identified along the glass-formation boundary. Infrared transmission spectra were used to explain glass structures and their effect on glass properties. The results suggest that the role of calcia in the glass structure is similar to that for calcia in calcium aluminosilicate glasses.  相似文献   
175.
从水泥在水泥-水-粘土系统中水化的特点出发,阐述了湿塑性水泥土的强度形成过程,主要是依赖于水泥石的强度骨架与粘土之间的结构连接。通过实验,研究了几种外加剂对湿塑性水泥土的增强作用及其增强机理,结果表明,外加剂能改善水泥土的水化介质环境和结构粘接,可改善水泥土的稠度和强度。  相似文献   
176.
PET高速纺丝方法及超高速纺丝纤维成形机理   总被引:1,自引:0,他引:1  
综述了 PET高速纺丝热辊法生产工艺 (MG)、冷辊拉伸蒸汽定型法生产工艺 (H 4S)、热管法生产工艺 (TCS)、热管拉伸法生产工艺 (HCS)以及超高速纺丝工艺 (SHSS) ;阐明了超高速纺在纺程上结构的发展与成形机理 ,以及超高速纺纺程上的细颈现象 ,超高速纺的成形机理与高速纺是不同的 ,明显区别在于细颈点的出现  相似文献   
177.
何书美  王素红 《化学世界》2002,43(6):296-297
采用红外光谱、气相色谱 ,X-射线能谱、原子吸收光谱、紫外分光光度法及化学法分析了肥皂霜中脂肪酸盐、硅、磷、碳酸盐等成分。其结果如下 :RCOONa:94.82 %;Si O2 :2 .43%;PO3-4:0 .40 %;Na2 CO3:1 .0 8%、水份及挥发物余量。依据测试结果 ,对肥皂冒霜的原因进行了探讨  相似文献   
178.
The interaction and synergism of some polyoxyethylenated fatty alcohol ether (POE) nonionic surfactants (C12E2, C12E3, C10E5, C10E7, where Cx indicates number of carbon atoms in the chain and Ey indicates number of oxyethylene glycol ethers) with trioxyethylenated dodecyl sulfonate (C12E3S) in mixed monolayer formation at the surface and in mixed micelle formation in aqueous solutions were studied at 25 and 40°C by calculating interaction parameters (βα, βM) from surface tension-concentration data by use of Rosen's equations based on the nonideal solution theory. All the systems investigated adapt reasonably well to the nonideal model, with negative values of βσ and βM (where M means micelle and σ refers to the air-liquid interface) indicating a favorable interaction between the mixed surfactants. Either at a monolayer or in a mixed micelle, the attractive interaction becomes stronger when the alkyl chain in the POE surfactant is longer, i.e., when the POE becomes more hydrophobic. The interaction increases in the order C10E7<C10E5<C12E3, C12E2. For the two C10E n (n= 5,7)/C12E3S systems, as temperature increases from 25 to 40°C, the interaction increases in a mixed micelle, but it decreases in a mixed monolayer. Synergism in mixed micelle formation exists for C12E3S/C10E n mixtures when X1 M , the mole fraction of POE in a mixed micelle, is ≈0.4–0.8, whereas synergism does not occur in the systems of C12E3S/C12E m due to the large difference between CMC1 and CMC2, i.e., large |In(C 1 M /C 2 M )| value (where CMC=critical micelle concentration). The degree of synergism in mixed micelle formation is temperature independent and is 0.23, 0.18, and close to zero for C10E5/C12E3S, C10E7/C12E3S, and C12E m (m=2,3)/C12E3S systems, respectively. Synergism in surface tension reduction effectiveness occurs in C12E3S/C12E2 and C12E3S/C12E3 systems. The mole fractions of POE in the solution phase are 0.302 and 0.333 for the two mixtures at the point of maximum synergism.  相似文献   
179.
Biocompatible composites (Ti, Ta)C x + Ca3(PO4)2 for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca3(PO4)2 mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have little or no influence on the burning velocity U and combustion temperature T c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.   相似文献   
180.
The factors influencing the oxidative stability of different commercial olive oils were evaluated. Comparisons were made of (i) the oxidative stability of commercial olive oils with that of a refined, bleached, and deodorized (RBD) olive oil, and (ii) the antioxidant activity of a mixture of phenolic compounds extracted from virgin olive oil with that of pure compounds andα-tocopherol added to RBD olive oil. The progress of oxidation at 60°C was followed by measuring both the formation (peroxide value, PV) and the decomposition (hexanal and volatiles) of hydroperoxides. The trends in antioxidant activity were different according to whether PV or hexanal were measured. Although the virgin olive oils contained higher levels of phenolic compounds than did the refined and RBD oils, their oxidative stability was significantly decreased by their high initial PV. Phenolic compounds extracted from virgin olive oils increased the oxidative stability of RBD olive oil. On the basis of PV, the phenol extract had the best antioxidant activity at 50 ppm, as gallic acid equivalents, but on the basis of hexanal formation, better antioxidant activity was observed at 100 and 200 ppm.α-Tocopherol behaved as a prooxidant at high concentrations (>250 ppm) on the basis of PV, but was more effective than the other antioxidants in inhibiting hexanal formation in RBD olive oil.o-Diphenols (caffeic acid) and, to a lesser extent, substitutedo-diphenols (ferulic and vanillic acids), showed better antioxidant activity than monophenols (p- ando-coumaric), based on both PV and hexanal formation. This study emphasizes the need to measure at least two oxidation parameters to better evaluate antioxidants and the oxidative stability of olive oils. The antioxidant effectiveness of phenolic compounds in virgin olive oils can be significantly diminished in oils if their initial PV are too high.  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