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   9027篇
  免费   817篇
  国内免费   613篇
电工技术   169篇
综合类   500篇
化学工业   3140篇
金属工艺   731篇
机械仪表   89篇
建筑科学   476篇
矿业工程   267篇
能源动力   274篇
轻工业   2046篇
水利工程   165篇
石油天然气   1022篇
武器工业   54篇
无线电   145篇
一般工业技术   614篇
冶金工业   455篇
原子能技术   178篇
自动化技术   132篇
  2024年   46篇
  2023年   172篇
  2022年   339篇
  2021年   371篇
  2020年   338篇
  2019年   282篇
  2018年   259篇
  2017年   316篇
  2016年   368篇
  2015年   341篇
  2014年   543篇
  2013年   539篇
  2012年   792篇
  2011年   639篇
  2010年   473篇
  2009年   514篇
  2008年   337篇
  2007年   549篇
  2006年   507篇
  2005年   399篇
  2004年   405篇
  2003年   350篇
  2002年   289篇
  2001年   246篇
  2000年   203篇
  1999年   165篇
  1998年   140篇
  1997年   86篇
  1996年   93篇
  1995年   68篇
  1994年   57篇
  1993年   47篇
  1992年   41篇
  1991年   28篇
  1990年   33篇
  1989年   20篇
  1988年   6篇
  1987年   13篇
  1986年   6篇
  1985年   8篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1981年   2篇
  1980年   5篇
  1979年   3篇
  1975年   2篇
  1959年   3篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
This paper examines selected design issues associated with reactor scale-up in the thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. The thermochemical cycle decomposes water into oxygen and hydrogen, through intermediate copper and chlorine compounds. In this paper, emphasis is focused on the hydrogen, oxygen and hydrolysis reactors. A sedimentation cell for copper separation and HCl gas absorption tower are discussed for the thermochemical hydrogen reactor. A molten salt reactor is investigated for decomposition of an intermediate compound, copper oxychloride (CuO·Cl2), into oxygen gas and molten cuprous chloride. Scale-up design issues are examined for handling three phases within the molten salt reactor, i.e., solid copper oxychloride particles, liquid (melting salt) and exiting gas (oxygen). Also, different variations of hydrolysis reactions are compared, including 5, 3 and 2-step Cu–Cl cycles that utilize reactive spray drying, instead of separate drying and hydrolysis processes. The spray drying involves evaporation of aqueous feed by mixing the spray and drying streams. Results are presented for the required capacities of feed materials for the multiphase reactors, steam and heat requirements, and other key design parameters for reactor scale-up to a pilot-scale capacity.  相似文献   
52.
行业标准《原油盐含量测定法(电量法)》(SY/T 0536—2008)中取样方式容易造成油层下部的水醇抽提液夹带油滴或油渍,使盐含量测定结果准确度和精密度变差。通过聚醚砜或聚四氟乙烯滤膜针头过滤器,或用管盖一体的细管预置离心管,分层后用12 cm特制长针头插入并刺穿细管底部膜封方式取样,可有效避免水醇抽提液中油污;同时使用50 mL聚丙烯离心管,使油样取样量增大约5倍,油样代表性提升,相应增大抽提液用量,方便盐含量不同检测方法的选用。  相似文献   
53.
滤波窗口是影响椒盐噪声滤除效果的重要因素。针对自适应中值滤波算法(RAMF)的不足,提出了一种基于窗口的自适应中值滤波算法。该算法分为噪声的检测和滤除两部分。在噪声检测部分,主要通过混合窗口检测出准噪声点,将其用窗口中值代替,而其余信号点保持不变。重复此方法,直至所有的准噪声点处理完毕。然后,在噪声滤除部分,主要根据噪声密度选择合适的最大滤波窗口半径,进而实现噪声滤除。最后,为验证算法的有效性开展了仿真研究,仿真结果表明本算法对椒盐噪声的滤除具有很好的效果,增强了图像的清晰度。  相似文献   
54.
分别以碳酸盐和硝酸盐为前驱体,采用熔盐法在750~1050℃合成了针状的Sr0.5Ba0.5Nb2O6(SBN50)模板晶粒。通过XRD,SEM分析方法,研究了前驱体对SBN50晶粒相结构和微观形貌的影响,并讨论了其形成机理。结果表明:前驱体性质的不同造成熔盐熔点时SrNb2O6数量和形貌的差异,影响最终SBN50晶粒的形貌;SBN50晶粒的生长是二维成核过程。  相似文献   
55.
采用共沉淀–熔盐法制备了M型铁氧体BaFe11.85-2xCoxTixMn0.15O19。运用TGA-DTA、XRD、SEM和矢量网络分析仪,对样品的晶化过程、相组成、显微形貌及微波吸收性能进行了表征。结果表明:Co2+、Ti4+固溶到铁氧体的晶格并取代Fe3+位,有助于提高铁氧体的电、磁损耗。当取代量x为1.2时,微波吸收最强,制得的样品的吸波频率在8.2~12.4 GHz范围内,tanδe、tanδμ的最大值分别为:9.0,6.8。  相似文献   
56.
以BH—G/K玻璃为基体,以添加Al2O3粉的DM—308玻璃为表层区研制出与金属外壳封接的双层玻坯。分析了Al2O3粒度及添加量对熟坯致密化和线收缩率的影响。结果表明,表层区使用添加质量分数为20%和30%0.5μm粒径Al2O3粉的DM—308玻璃可以实现熟坯的匹配收缩,用于UP2113—14外壳熔封。电镀后外壳气密性、绝缘电阻均有数量级提高,玻璃沿引线上爬高度只为BH—G/K玻璃的1/3,显著降低外壳盐雾试验后引线根部易锈蚀和引线受力后绝缘子开裂的风险。  相似文献   
57.
Membrane decorated with biocides is an effective way to suppress biofilm growth. However, their immediate biocidal effect usually suffers from a significant decline due to the irreversible consumption of the biocides. Here, a smart nanofiltration membrane is reported with rechargeable antibacterial capability that is fabricated by a facile interfacial polymerization via 3-aminophenylboronic acid and trimesoyl chloride on a polysulfone substrate. Biocides bearing diol groups can be grafted onto the membrane surface under neutral/alkaline condition and then released from the surface under acidic environment, due to the pH-responsive feature of boronate ester complexes. The resultant membrane exhibits integrated properties of fast bacterial inactivating efficiency, rechargeable antibacterial capability, and impressive stability. In addition, the achieved membrane shows remarkable separation efficiency to dye/monovalent salt system. The successful fabrication of the membrane with rechargeable anti-bacterial property provides new insights into the development of pH-responsive and sustainable antibacterial membranes.  相似文献   
58.
Mg batteries as the most typical multivalent batteries are attracting increasing attention because of resource abundance, high volumetric energy density, and smooth plating/stripping of Mg anodes. However, current limitations for the progress of Mg batteries come from the lack of high voltage electrolytes and fast Mg‐insertable structure prototypes. In order to improve their energy or power density, hybrid systems combining Li‐driven cathode reaction with Mg anode process appear to be a potential solution by bypassing the aforementioned limitations. Here, FeS x (x = 1 or 2) is employed as conversion cathode with 2–4 electron transfers to achieve a maximum energy density close to 400 Wh kg?1, which is comparable with that of Li‐ion batteries but without serious dendrite growth and polysulphide dissolution. In situ formation of solid electrolyte interfaces on both sulfide and Mg electrodes is likely responsible for long‐life cycling and suppression of S‐species passivation at Mg anodes. Without any decoration on the cathode, electrolyte additive, or anode protection, a reversible capacity of more than 200 mAh g?1 is still preserved for Mg/FeS2 after 200 cycles.  相似文献   
59.
The glaciogenic Al Khlata Formation (Late Carboniferous – Early Permian) contains important reservoir and seal intervals in oil fields in southern Oman. Here we describe a 3D regional geological model of the Al Khlata Formation and the underlying Misfar Group in a 1750 km2 area in the Eastern Flank of the South Oman Salt Basin. The Misfar Group (Devonian‐Carboniferous?) was included in the model because it also contains glaciogenic facies in the study area. The 3D model is based on wireline logs from 42 wells, palynological zonation in 31 wells, cores from three wells, and a 2011 3D seismic dataset from which three horizons (top‐Huqf, top‐Rahab Shale and top‐Gharif) were interpreted throughout the study area. The combined Al Khlata and Misfar interval varies in thickness in the area from 20 to 730 m over relatively short distances. These large variations in thickness were due to the creation of accommodation in mini‐basins resulting from the removal of underlying Infracambrian salt at the basin margin. In places, some of the available accommodation was occupied by Cambrian sandstones of the Nimr Group and Haima Supergroup, influencing the location and thickness of the Al Khlata mini‐basins. These local depocentres vary in scale, shape and orientation relative to the present‐day salt edge: some are ovoid in plan‐view, others more linear and parallel to the salt edge, and one takes the form of a narrow graben almost perpendicular to the salt edge. By the Early Permian, towards the end of Al Khlata time, deposits become more blanket‐like and uniform, indicating an external or more regional control on base level. Four key lithofacies have been distinguished from wireline logs and were populated zone‐by‐zone through the geological model: sandstone (reservoir), shale (seal), and sandy and silty diamictite. Sandstones are most common towards the base of the Misfar – Al Khlata interval and shales towards the top. The Rahab Shale (Early Permian) at the top of the Al Khlata Formation forms an important seal for oil fields in South Oman, often in combination with seals in overlying intervals. The Rahab Shale was the first widespread seal to be deposited which may have trapped oil migrating from the South Oman Salt Basin during the Palaeozoic. The most common lithofacies in the Misfar – Al Khlata interval in the modelled area is diamictite (60%), which is normally considered to be a waste‐rock lithology. However thick silty diamictites of sufficient extent can seal hydrocarbon accumulations, and some sandy diamictites have the potential to be unconventional reservoir rocks. Even after 50 years of exploration and production of oil from the Al Khlata Formation, there remains potential for further discoveries and overlooked pay zones due to its heterogeneous character and the occurrence of intra‐formational seals.  相似文献   
60.
通过新型聚合物LH-3500与孤岛油田现用及油田现有性能最优的聚合物在孤岛油田污水中进行的耐温抗盐性能评价,发现结构优化后的LH-3500的溶解性、耐温抗盐性及抗稀释性综合评价结果最优;而且浓度为1500mg/L的LH-3500的粘度即可与浓度为2300mg/L的现场注聚用的聚合物A和聚合物B的粘度相当;可以采用污水配制并大大减少聚合物用量。其在孤岛油田推广使用势必会带来巨大的经济效益和环境效益。  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