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   39937篇
  免费   4214篇
  国内免费   1084篇
电工技术   1215篇
综合类   3013篇
化学工业   11292篇
金属工艺   743篇
机械仪表   1299篇
建筑科学   3239篇
矿业工程   322篇
能源动力   423篇
轻工业   7881篇
水利工程   407篇
石油天然气   483篇
武器工业   230篇
无线电   7864篇
一般工业技术   5102篇
冶金工业   322篇
原子能技术   156篇
自动化技术   1244篇
  2024年   33篇
  2023年   547篇
  2022年   931篇
  2021年   1193篇
  2020年   1206篇
  2019年   945篇
  2018年   871篇
  2017年   1342篇
  2016年   1268篇
  2015年   1470篇
  2014年   2056篇
  2013年   2374篇
  2012年   2920篇
  2011年   2777篇
  2010年   2223篇
  2009年   2324篇
  2008年   2059篇
  2007年   2870篇
  2006年   2814篇
  2005年   2440篇
  2004年   1933篇
  2003年   1601篇
  2002年   1460篇
  2001年   1192篇
  2000年   918篇
  1999年   719篇
  1998年   514篇
  1997年   405篇
  1996年   343篇
  1995年   320篇
  1994年   307篇
  1993年   258篇
  1992年   198篇
  1991年   156篇
  1990年   97篇
  1989年   52篇
  1988年   23篇
  1987年   20篇
  1986年   7篇
  1985年   13篇
  1984年   6篇
  1983年   6篇
  1982年   13篇
  1980年   8篇
  1979年   1篇
  1977年   1篇
  1959年   1篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
1.
Fiber production from inorganic industrial solid wastes is an effective waste management strategy. Because of cost considerations, most enterprises generally use local solid wastes as raw materials to produce fibers. In this study, we explored the feasibility of producing fibers using fly ash and magnesium slag. The results show that the melting temperature of the blends composed of fly ash, magnesium slag, and a small amount of calcined dolomite first decreased and then increased with an increase in acidity coefficient (Mk) from 1.0 to 2.4. The samples could form a eutectic system in the Mk range of 1.4–1.8, and therefore have a relatively low melting temperature in this Mk range. Fly ash could react with magnesium slag and calcined dolomite to form akermanite, gehlenite-magnesium, and anorthite at temperatures close to the melting temperature; therefore, these crystalline phases were the main reaction products formed in the samples with Mk values lower than 1.80. Anorthite reacted further with some Na-containing and Si-containing spieces to produce labradorite. Thus, the content of anorthite and labradorite rapidly increased and they became the major crystal phases in the blend samples with Mk values greater than 1.80. MAS-NMR spectroscopic analysis revealed that the network structure of the melts depended on the ratio of bridging oxygen to non-bridging oxygen; a high ratio of bridging oxygen to non-bridging oxygen could lead to the formation of a dense network structure in the melt. The blends of fly ash and magnesium slag can be used to produce wool fibers and continuous fibers. In addition, the suitable temperature ranges for the production of both types of fibers were determined. The drawing temperature for continuous fiber production depended on the degree of polymerization and structure of the melt.  相似文献   
2.
研究了一种生态多孔纤维棉(EPFC)的生物挂膜性能,并将其应用于脱氮反应器中,考察不同DO水平与装置设计(填充率、孔密度)对脱氮效果的影响。结果表明,EPFC是一种良好的生物挂膜材料。DO含量对反应器脱氮效果影响显著,在ρ(DO)=10~11 mg/L、HRT=5 d时NH4+-N去除率最高97.41%;TN去除率在ρ(DO)=9~10 mg/L、HRT=4 d时最高45.52%。对装置设计进行优化后,发现反应器BR5脱氮效果最好,其填料填充率为2/3、孔密度为5.2个/cm2;优化运行条件为ρ(DO)=9~10 mg/L、HRT=5 d,NH4+-N与TN去除率分别可达98.59%和59.93%。可为EPFC进一步应用于生物脱氮工艺如生物接触氧化法、序批式活性污泥法工艺等提供思路。  相似文献   
3.
新疆准噶尔盆地南缘高探1井于白垩系清水河组测试获日产原油1213 m3/d、天然气32.17×104m3,创整个盆地单井日产量最高纪录,充分证实了南缘油气勘探潜力巨大[1]。为此,2019年,新疆油田在南缘共部署了875 km2三维地震采集项目,采用了井震联合采集技术、井炮源驱动技术、有线仪器+无线节点+有线连续采集技术、宽频单点接收技术、光纤表层调查技术等,高效、高质量完成了野外地震采集,地震资料品质得到了较好的提高,初步形成了适合南缘山前带的地震采集技术,为南缘山前带油气勘探和和下一步增储建产储备了相关的配套技术,该技术也可为国内其它探区山前带地震采集提供借鉴。  相似文献   
4.
为了提高植物蛋白基绿色高分子材料的力学性能和热稳定性能,以棉籽蛋白(CP)为原料,在尿素变性、甘油增塑、双醛淀粉(DAS)交联的基础上,将其与取向排列的天然剑麻长纤维(SF)复合,经热压硫化加工制备得到具有优异性能的棉籽蛋白/剑麻纤维全绿色复合材料。微观结构形貌和性能分析测试表明,复合材料获得改善性能主要归功于:CP基体与SF增强相间形成的紧密界面结合、对剑麻长纤维的预浸渍处理、CP与SF生物大分子间的强氢键作用。考察了不同DAS含量对复合材料力学性能和热稳定性能的影响。拉伸、热重和差示量热分析表明,经20%(质量) DAS交联的复合材料具有最优的拉伸强度(断裂应力7.5 MPa)、模量(杨氏模量93 MPa)、热稳定性(最大分解温度328℃)和玻璃化转变温度(102℃)。  相似文献   
5.
为了提升钢纤维-砂浆界面的黏结性能,采用9种基于硅烷的表面处理剂对钢纤维进行浸渍处理并高温固化成膜;埋置于水泥砂浆圆柱体试块中,开展单根纤维拉拔试验,获得拉拔荷载-位移曲线. 试验结果表明,采用不同的硅烷涂层对钢纤维进行表面改性,可以不同程度地改善钢纤维-砂浆界面的黏结性能;拉拔峰值荷载最高增加5.75倍,拉拔能耗最多增加2.48倍. 硅烷Z6011和Z6020及复合涂层能够较大幅度地提升界面黏结强度,主要增加钢纤维与砂浆界面的化学黏结力;硅烷Z6030和Z6040及复合涂层对界面黏结强度的提升幅度相对较小,主要增加界面滑移摩擦力. 采用扫描电子显微镜(SEM)研究界面黏结性能的提升机理,发现硅烷涂层使得界面过渡区的微观结构更致密,显著提升了钢纤维-砂浆之间的黏结性能.  相似文献   
6.
Cellulose microfibers (CMFs) having surfaces modified with polydopamine (PDPA) and octadecylamine (ODA) were prepared, and their reinforcing abilities for polypropylene (PP) were investigated. The PDPA coating was made via self-polymerization of dopamine (P-CMF), and subsequent alkylation was conducted by the reaction with ODA (OP-CMF). The modified CMFs exhibited improved dispersibility in the PP matrix due to the reduced hydrophilicity. The OP-CMF/PP composite prepared by batch mixing had a higher tensile modulus compared to that for the pure PP and composites with unmodified CMFs. However, excess alkylation lowered the tensile modulus, and the presence of an optimal degree of alkylation was demonstrated. The CMF/PP-IM composites fabricated by injection molding exhibited improved tensile properties compared to those prepared by batch mixing. Both the tensile modulus and yield stress were increased by increasing the CMF content and improved by the surface modification of the CMFs.  相似文献   
7.
为了实现低频振动的高灵敏度测量,设计了一种基于转动支撑梁的新型光纤布拉格光栅加速度计。 通过分析其振动 模型和 MATLAB 数值计算,优化了传感器的结构参数,设计传感器理论灵敏度为 1 725 pm / g,固有频率为 68. 4 Hz。 同时通 过 COMSOL 模拟分析传感器的动态特性,其模拟结果与理论分析吻合。 频响特性和幅值特性实验结果表明光纤光栅加速度 计在加速度 0 ~ 2 g、工作频率 0. 5 ~ 20 Hz 的范围内,传感器加速度特性曲线呈现良好线性关系,灵敏度高达 1 495. 2 pm / g,重 复性良好。 该传感器结构简单紧凑,轴承结构有效减少悬臂梁振动过程中的弹性能耗,可显著提高其灵敏度,能够实现低频 振动信号的探测。  相似文献   
8.
洪帆  宋洁  杜冰  郑环达  郑来久 《精细化工》2021,38(12):2377-2384
细菌纤维素(BC)是微生物生长过程中产生的以葡萄糖为基本骨架的结构性碳水化合物,具有高纯度、高聚合度、高结晶度、高持水性、高抗张强度和良好的机械强度,在功能材料领域显示了巨大的应用潜力.综述了近年来BC合成菌种筛选的研究现状;分析了BC在透气、吸湿排汗、力学性能和染色与脱色性能调控方面的进展情况;重点总结了BC基材料在抗菌、防紫外线、防辐射、防静电、拒水拒油、导电和传感等功能化改性方面的研究进展;最后,指出BC大规模高效成模和成型技术、差异化高功能BC材料制备技术是未来的重点研发方向.  相似文献   
9.
《Ceramics International》2021,47(21):29908-29918
The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn2+ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm−3) electrode with the capacitance of 900 mF cm−2 at a high current density of 10 mA cm−2, lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm−2. These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm−2 (at 10 mA cm−2) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.  相似文献   
10.
An ecofriendly and biodegradable porous structure was prepared from drying aqueous foams based on nano fibrillated cellulose (NFC), extracted from softwood pulp by subcritical water/CO2 treatment (SC-NFC). The primary aim of this work was to use the modified SC-NFC as stabilizer for a water-based Pickering emulsion which upon drying, yielded porous cellulosic materials, a good dye adsorbent. In order to exploit the carboxymethylated SC-NFC (CMSC-NFC, with a degree of substitution of 0.35 and a charge density of 649 μeqv/g) as a stabilizer for water-based Pickering emulsion in subsequent step, an optimized quantity of octyl amine (30 mg/g of SC-NFC) was added to make them partially hydrophobic. A series of dry foam structures were prepared by varying the concentrations of treated CMSC-NFCs and 4 wt% was found to be the optimum concentration to yield foam with high porosity (99%) and low density (0.038 g/cc) along with high compression strength (0.24 MPa), superior to the conventionally extracted NFC. The foams were applied to capture as high as 98% of methylene blue dyes, making them a potential green candidate for treating industrial effluent. In addition, the dye adsorption kinetics and isotherms were found to be well suited with second order kinetics and Langmuir isotherm models.  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