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   85938篇
  免费   6247篇
  国内免费   2915篇
电工技术   4352篇
技术理论   9篇
综合类   4644篇
化学工业   15325篇
金属工艺   4436篇
机械仪表   5235篇
建筑科学   7004篇
矿业工程   1967篇
能源动力   2501篇
轻工业   4900篇
水利工程   1437篇
石油天然气   4462篇
武器工业   489篇
无线电   10404篇
一般工业技术   11234篇
冶金工业   4611篇
原子能技术   832篇
自动化技术   11258篇
  2024年   247篇
  2023年   1263篇
  2022年   2066篇
  2021年   3049篇
  2020年   2296篇
  2019年   1994篇
  2018年   2223篇
  2017年   2477篇
  2016年   2325篇
  2015年   2925篇
  2014年   4002篇
  2013年   5061篇
  2012年   5254篇
  2011年   5537篇
  2010年   4906篇
  2009年   4727篇
  2008年   4466篇
  2007年   4408篇
  2006年   4652篇
  2005年   4136篇
  2004年   2789篇
  2003年   2503篇
  2002年   2201篇
  2001年   2027篇
  2000年   2290篇
  1999年   2567篇
  1998年   2389篇
  1997年   1880篇
  1996年   1740篇
  1995年   1444篇
  1994年   1212篇
  1993年   878篇
  1992年   653篇
  1991年   538篇
  1990年   404篇
  1989年   365篇
  1988年   312篇
  1987年   168篇
  1986年   154篇
  1985年   104篇
  1984年   91篇
  1983年   60篇
  1982年   57篇
  1981年   51篇
  1980年   37篇
  1979年   32篇
  1978年   13篇
  1977年   33篇
  1976年   16篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
新型合成聚合物重金属离子吸附剂及其吸附性能   总被引:6,自引:0,他引:6  
阐述了新型聚合物重金属离子吸附剂的合成与改性及其对水溶液中Cd(Ⅱ)、Pb(Ⅱ)、Cu(Ⅱ)、Hg(Ⅱ)等重金属离子的吸附性能。这些聚合物重金属离子吸附剂对低浓度的重金属离子表现出了较好的吸附能力,其中聚合物吸附剂PGHyFeO—COOH对mg/L级的Pb(Ⅱ)、Cd(Ⅱ)、Hg(Ⅱ)的最大吸附量分别为211.4mg/g、155.0mg/g、147.2mg/g。这些吸附剂的吸附速度也较快,平衡吸附时间一般在60min左右,有的甚至只有几分钟。新型聚合物重金属离子吸附剂在水处理工业中具有广阔的应用前景。  相似文献   
992.
垂直矩形窄缝通道内气液两相流型的研究   总被引:1,自引:1,他引:1       下载免费PDF全文
思勤  王会军 《化工学报》1990,41(6):745-753
本文研究了矩形窄缝通道内气液两相流的流型.用目测和摄影方法得到气液两相向上并流的流型.用x-y函数记录仪测得各种流型下的压差频谱图.作出了以1/X_(tt)~G_t和j_(?)~Re为坐标的流型图.作者还用Lockbart-Martinelli方法计算了矩形通道内气液两相流的压降,并与实测值进行了比较.  相似文献   
993.
Experimental values of the Flory–Huggins parameter, χ, between polymers and solvents, are frequently used to determine the solubility parameters of the polymers. A method using nonlinear curve fitting of RTχ/V was compared to the linear regression method commonly used. It was found that the formulas for the solubility parameter were the same, but the linear method produced a slightly different entropy term. The nonlinear method gave a lower correlation coefficient and wider confidence intervals and was more effective at distinguishing systems than the linear model. The effect of the deviation of probes in the solubility parameter model is discussed. Using probes with low solubility parameters to measure the polymer solubility parameter gave wider confidence intervals. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2894–2902, 2004  相似文献   
994.
Vulcanizates of blends of ethylene–propylene–diene rubber and polyamide copolymers were prepared by reactive compatibilization. A reactive route was employed for compatibilizing these blends with the addition of chlorinated polyethylene (CPE). The influence of the compatibilizers, crosslinking agents, blend compositions, and addition modes of the compatibilizers on the mechanical properties of the blends was investigated. The morphologies of the blends were determined with scanning electron microscopy. The addition of CPE was found to reduce the particle size of the dispersed phase remarkably. The stability of the blends with compatibilizers was measured by high‐temperature thermal aging. The mechanical properties were examined by stress–strain measurements and dynamic mechanical thermal measurements; the addition of polyamide copolymers caused significant improvements in the tensile properties of these blends.© 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1727–1736, 2003  相似文献   
995.
本工作采用热压工艺,以Y_2O_3为烧结添加剂,在1850℃下制备TiC_p-AIN复合材料。结果表明:复合材料的密度、抗折强度、断裂韧性受第二相TiC_p的影响,通过合理工艺因素选择,可以使复合材料的抗折强度和断裂韧性比基体AIN材料分别提高40%,80%,达到438MPa,5.59MPa·m ̄(1/2)。由XRD内应力分析和TEM显微结构测试结果可知,复合材料性能改善原因在于高弹性用量的TiC引入以及AIN和TiC热膨胀系数不匹配导致的残余内应力。  相似文献   
996.
甲酸甲酯合成与转化的催化技术   总被引:3,自引:0,他引:3  
本文评述了甲酸甲酯(MF)合成与转化的催化技术,展示了从MF出发发展C_1化学的可能途径,在MF的合成方面详细地分析了从甲醇出发的羰化法、脱氢法和氧化法催化技术,简介了我们的有关研究工作。  相似文献   
997.
The coal partial gasification catalyzed by limestone, sodium carbonate and dolomite was studied using a bench-scale atmospheric fluidized bed in the presence of air and steam at 900 °C. The effects of limestone, sodium carbonate and dolomite on composition, heating value, gas yield of product gas and carbon conversion in the catalytic coal partial gasification have been examined. The experimental results show that the catalysts can effectively improve the gas quality, the heating value and the gas yield of product gas and carbon conversion. The catalytic effect of sodium carbonate is better than that of limestone and dolomite. The increase of limestone loading can enhance the quality of product gas, such as the content of combustible gas, the high heating value and the gas yield, during coal partial gasification. This work was presented at the 6 th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.  相似文献   
998.
The surface compositions of a series of polystyrene‐b‐polydimethylsiloxane (PS‐b‐PDMS) and polystyrene‐g‐polydimethylsiloxane (PS‐g‐PDMS) copolymers were investigated using ATR‐FTIR and XPS technique. The results showed that enrichment of PDMS soft segments occurred on the surface of the block copolymers as well as on that of graft copolymers. And the magnitude order of the enrichment was as follows: PS‐b‐PDMS > PS‐g‐PDMS, which was attributed to the facilitating of the movement of the PDMS segments in PS‐b‐PDMS copolymer. Meanwhile, the solvent type and the contact medium had influence on the accumulation of PDMS on the surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006  相似文献   
999.
A novel mechanism to form binary polymer blends is through phase separation by spinodal decomposition in the unstable region of the phase diagram. The present work investigates the effects of thermally‐induced phase separation by spinodal decomposition on the morphology development of liquid crystalline polymer/polycarbonate blends. Moreover, a thermodynamic binary phase diagram is obtained using a twin‐screw extruder at various processing melt temperatures. Differential scanning calorimetry and scanning electron microscopy were used to study the miscibility of the blends and the resulting morphology. A thermodynamic binary phase diagram exhibiting a lower critical solution temperature was obtained. The droplet size distribution of the blend was also obtained and discussed in light of the Cahn‐Hilliard theory.  相似文献   
1000.
李文应用裂解色谱法对丙烯酸酯等物质的共聚物与共混物进行了鉴定。  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