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   23079篇
  免费   1990篇
  国内免费   934篇
电工技术   1201篇
综合类   1030篇
化学工业   3749篇
金属工艺   1463篇
机械仪表   1642篇
建筑科学   1269篇
矿业工程   608篇
能源动力   816篇
轻工业   1523篇
水利工程   313篇
石油天然气   972篇
武器工业   115篇
无线电   2971篇
一般工业技术   3589篇
冶金工业   2052篇
原子能技术   184篇
自动化技术   2506篇
  2024年   108篇
  2023年   461篇
  2022年   776篇
  2021年   1111篇
  2020年   826篇
  2019年   678篇
  2018年   820篇
  2017年   776篇
  2016年   802篇
  2015年   914篇
  2014年   1110篇
  2013年   1346篇
  2012年   1446篇
  2011年   1609篇
  2010年   1380篇
  2009年   1353篇
  2008年   1224篇
  2007年   1015篇
  2006年   974篇
  2005年   851篇
  2004年   651篇
  2003年   637篇
  2002年   590篇
  2001年   498篇
  2000年   465篇
  1999年   498篇
  1998年   705篇
  1997年   505篇
  1996年   423篇
  1995年   297篇
  1994年   253篇
  1993年   192篇
  1992年   114篇
  1991年   83篇
  1990年   75篇
  1989年   67篇
  1988年   50篇
  1987年   38篇
  1986年   38篇
  1985年   32篇
  1984年   17篇
  1983年   10篇
  1982年   11篇
  1981年   18篇
  1980年   22篇
  1979年   5篇
  1978年   9篇
  1977年   32篇
  1976年   74篇
  1959年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
利用管式高压反应釜,以四氢萘为溶剂、FeS和S为催化剂,对神府煤进行了加氢液化研究,考察了催化剂、反应温度和反应气氛等因素对煤液化性能和产物组成分布的影响,同时对液化产物进行了红外光谱、元素分析以及酸性含氧官能团等结构表征。结果表明,FeS+S催化神府煤液化的最高四氢呋喃(THF)抽提率和油+气收率分别为69.5%和35.9%;未加催化剂时,神府煤液化THF抽提率和油+气收率都是最低的。  相似文献   
992.
本文通过采用原子吸收法检测分析污泥中的重金属在污泥干化和水泥熟料形成过程中的挥发与固化特性,通过测定各组熟料的f-CaO含量、XRD,研究了污泥掺入对生料易烧性和水泥熟料矿物组成的影响.结果表明:污泥在300℃的低温下干化,Hg的挥发率达到67%,而其它重金属基本不挥发;煅烧过程可以将原料中62.38%的Pb,59.53%的Cr,61.3%的Cd和64.24%的As固化在水泥熟料中;污泥的加入,能够改变水泥熟料的晶格结构,改善水泥生料的易烧性;污泥对水泥熟料的矿物组成影响不大.  相似文献   
993.
A detailed surface characterizations and adsorption mechanism of Cd2+ on chemical activated carbon (CAC) prepared from Garnicia mangostana shell were investigated. The activation is accomplished in self-generating atmosphere using phosphoric acid as activating agent. The characterizations performed are elemental analysis, functional group identification, N2 adsorption isotherm and surface charges. Adsorption mechanism of metal ion was tested using Cd2+ as model ion. CAC achieved BET surface area of 1,498 m2/g with a mixture of micro and mesopores. The point of zero charge is observed to be at pH 2.8 and the optimum pH for Cd2+ adsorption on CAC is 12. The adsorption isotherm followed the Freundlich model, and the adsorption kinetics was explained by pseudo-second order kinetic model. From thermodynamic studies, the adsorption was found to be physical adsorption. X-ray photoelectron spectroscopy (XPS) confirmed the adsorption of Cd2+ onto CAC as +2 oxidation state.  相似文献   
994.
通过蓖麻油与甘油进行酯交换反应制备蓖麻油多元醇,并应用于聚氨酯阻燃硬泡的制备,研究了阻燃剂类型、添加量及蓖麻油多元醇的添加量对聚氨酯硬质泡沫(RPUF)综合性能的影响。结果表明,蓖麻油多元醇的添加量对阻燃RPUF氧指数影响不大,只是添加量大于50%时会导致泡沫收缩:添加不同阻燃剂后发现甲基磷酸二甲酯(DMMP)的阻燃效果好,DMMP合适用量为多元醇组分的20%~30%。  相似文献   
995.
针对气辅成型过程中多个工艺参数的优化配置问题,提出了气辅成型工艺参数径向基函数(RBF)网络预测模型。该模型基于均匀设计思想,以RBF网络为基础,用正交最小二乘训练法对基函数的中心、方差和RBF网络权值进行优化,提高了网络预测模型对气辅成型制品质量指标的预测可靠性。以挂式空调前面板为例,对其进行CAE仿真分析,结果表明,该优化模型可实现对制品质量指标的快速预测,为工艺参数进一步优化奠定了基础。  相似文献   
996.
针对单向纤维增强树脂基复合材料(FRP)压缩强度远低于其拉伸强度的问题,对影响拉挤FRP管轴向压缩承载力的一些因素进行研究,探讨提高拉挤FRP管轴向压缩强度的途径。结果表明,无端部约束情况下增加包裹对提高FRP管承载力效果不明显;端部约束可改变FRP管破坏形式,对提高其承载力效果显著;在端部约束情况下增加包裹也可有效提高FRP管承载力。  相似文献   
997.
DNA and amphiphilic N,N,N‐trimethyl‐N‐hexadecylammonium bromide (THAB) were stoichiometrically mixed together to produce a DNA–lipid complex, which was dissolved in dimethyl sulfoxide (DMSO) at 65°C and then crosslinked with isophorone diisocyanate (IPDI). The obtained organogel swelled reversibly in DMSO, responding to the variation of temperature. Interestingly, we observed that the gel exhibited a temperature‐dependent shape‐memory behavior. Above 65°C, whatever the shape the gel was deformed to, it could retain the new shape as the temperature was decreased to room temperature, while, when the gel was heated to 65°C again, it could recover its initial shape. The shape‐memory characteristic is supposedly originated from the transition between the close‐packed and the destroyed DNA/lipid conformation. The elastic urethane crosslinking bonds between base‐pair sites act as a fixing phase. The gel holds promise in its application as a gentle actuator. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 259–263, 2002  相似文献   
998.
A water‐developable negative photoresist based on the photocrosslinking of N‐phenylamide groups was prepared by the copolymerization of 4‐styrenesulfonic acid sodium salts (SSS) with N‐phenylmethacrylamide (copolymer A) or p‐hydroxy‐N‐phenylmethacrylamide (copolymer B), and its properties such as solubility changes, photochemical reaction, and photoresist characteristics were studied. The copolymer containing a relatively higher amount of SSS units was soluble in water. Solubility changes of the copolymers in the various buffer solutions of pH 4 ~ 11 and in water upon irradiation were observed by the measurement of insoluble fraction. The copolymers were soluble in water before irradiation, whereas they became insoluble upon irradiation with the UV light of 254 nm. The photochemical reaction of the copolymer studied by the UV and IR absorption spectroscopies indicated that a photo‐Fries rearrangement was favored for copolymer A, whereas a photocrosslinking reaction was predominate for copolymer B. Resist properties of the copolymers were studied by measurement of the normalized thickness and by development of the micropattern. Negative tone images with a resolution of 1 μm were obtained with these materials that have a sensitivity (D) of ~ 1100 mJ/cm2 with an aqueous developing process.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1172–1180, 2002  相似文献   
999.
Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, dp, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (Rm) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002  相似文献   
1000.
Viologen–polyaniline (PANI) systems were prepared by PANI being coated onto viologen‐grafted low‐density polyethylene films. PANI in this system could undergo photoinduced doping with ultraviolet irradiation. The electrical stability of the electrically conductive viologen–PANI systems was found to be stable in air, but the conductivity decreased rapidly when the sample was treated in aqueous media of pH > 5 because of the migration of the anions out of PANI into water. However, the conductivity increased by a factor of 2 after treatment in a 1M HCl solution because of the further protonation of PANI by acid. The structural changes of these systems were monitored with ultraviolet–visible absorption spectroscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and resistance measurements. The electrical stability of the viologen–PANI system in water could be enhanced via spin coating with poly(methyl methacrylate) (PMMA) because this layer inhibited the migration of the anions out of the system. The photoinduced doping of PANI could be carried out either before or after the spin coating of PMMA. The advantages and limitations of each method were demonstrated. A PMMA coating with a thickness of approximately 10 μm allowed a significant doping level to be achieved within a short period of irradiation and, at the same time, effectively shielded the film from the effects of the aqueous medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2099–2107, 2002  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