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   66678篇
  免费   5429篇
  国内免费   2024篇
电工技术   2813篇
技术理论   2篇
综合类   2522篇
化学工业   12633篇
金属工艺   3549篇
机械仪表   4368篇
建筑科学   3433篇
矿业工程   1280篇
能源动力   2186篇
轻工业   4692篇
水利工程   734篇
石油天然气   2463篇
武器工业   337篇
无线电   9236篇
一般工业技术   10909篇
冶金工业   4087篇
原子能技术   816篇
自动化技术   8071篇
  2024年   182篇
  2023年   1090篇
  2022年   1483篇
  2021年   2806篇
  2020年   2003篇
  2019年   1945篇
  2018年   2198篇
  2017年   2215篇
  2016年   2238篇
  2015年   2515篇
  2014年   3252篇
  2013年   4182篇
  2012年   4349篇
  2011年   5088篇
  2010年   3867篇
  2009年   3871篇
  2008年   3766篇
  2007年   3199篇
  2006年   3150篇
  2005年   2601篇
  2004年   2035篇
  2003年   1850篇
  2002年   1773篇
  2001年   1532篇
  2000年   1426篇
  1999年   1449篇
  1998年   1572篇
  1997年   1181篇
  1996年   1060篇
  1995年   803篇
  1994年   601篇
  1993年   457篇
  1992年   369篇
  1991年   329篇
  1990年   264篇
  1989年   250篇
  1988年   186篇
  1987年   154篇
  1986年   114篇
  1985年   115篇
  1984年   80篇
  1983年   68篇
  1982年   64篇
  1981年   56篇
  1980年   65篇
  1979年   40篇
  1977年   33篇
  1976年   55篇
  1975年   28篇
  1974年   26篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
通过分析A公司在研发项目范围管理中所存在问题,提出研发项目范围管理的方法及其在C产品的应用实例,通过运用研发项目范围管理的工具和方法,改善产品开发流程,从而缩短新产品开发周期,提高响应市场的速度,并提高企业研发项目的管理能力。  相似文献   
42.
43.
Peer-to-Peer Networking and Applications - P2P-TV is a TV system that receives content through a peer-to-peer network. Content is stored in the distributed manner then to be serviced to users, and...  相似文献   
44.
45.
The cover image is based on the Research Article V2O5/RGO/Pt nanocomposite on oxytetracycline degradation and pharmaceutical effluent detoxification by Mohan, H et al., DOI: 10.1002/jctb.6238 .

  相似文献   

46.
47.
The traditional ciphertext policy attribute-based encryption (CP-ABE) has two problems:one is that the access policy must be embedded in the ciphertext and sent, which leads to the disclosure of user爷 s privacy information, the other is that it does not support collaborative decryption, which cannot meet the actual demand of conditional collaborative decryption among multiple users. In order to deal with the above two problems at the same time, a fine-grained cooperative access control scheme with hidden policies (FCAC-HP) is proposed based on the existing CP-ABE schemes combined with blockchain technology. In FCAC-HP scheme, users are grouped by group identifier so that only users within the same group can cooperate. In the data encryption stage, the access policy is encrypted and then embedded in the ciphertext to protect the privacy information of the access policy. In the data access stage, the anonymous attribute matching technology is introduced so that only matched users can decrypt ciphertext data to improve the efficiency of the system. In this process, a smart contract is used to execute the verification algorithm to ensure the credibility of the results. In terms of security, FCAC-HP scheme is based on the prime subgroup discriminative assumption and is proved to be indistinguishable under chosen plaintext attack (CPA) by dual system encryption technology. Experimental verification and analysis show that FCAC-HP scheme improves computational efficiency while implementing complex functions.  相似文献   
48.
While exercise training (ET) is an efficient strategy to manage obesity, it is recommended with a dietary plan to maximize the antiobesity functions owing to a compensational increase in energy intake. Capsiate is a notable bioactive compound for managing obesity owing to its capacity to increase energy expenditure. We aimed to examine whether the antiobesity effects of ET can be further enhanced by capsiate intake (CI) and determine its effects on resting energy expenditure and metabolic molecules. Mice were randomly divided into four groups (n = 8 per group) and fed high-fat diet. Mild-intensity treadmill ET was conducted five times/week; capsiate (10 mg/kg) was orally administered daily. After 8 weeks, resting metabolic rate and metabolic molecules were analyzed. ET with CI additively reduced the abdominal fat rate by 18% and solely upregulated beta-3-adrenoceptors in adipose tissue (p = 0.013) but did not affect the metabolic molecules in skeletal muscles. Surprisingly, CI without ET significantly increased the abdominal fat rate (p = 0.001) and reduced energy expenditure by 9%. Therefore, capsiate could be a candidate compound for maximizing the antiobesity effects of ET by upregulating beta-3-adrenoceptors in adipose tissue, but CI without ET may not be beneficial in managing obesity.  相似文献   
49.
多井评价是建立在单井精细解释对比分析基础上的预测储层及含油气性平面分布规律的技术方法,而常规测井资料无法区分碳酸盐岩岩溶储层,因而利用多井评价结果确定岩溶发育程度在平面上的分布规律就显得十分重要。为此,在岩心标定成像测井的基础上,对四川盆地高石梯—磨溪地区15口井的成像测井岩溶发育特征进行分析,建立了中二叠统茅口组岩溶发育各分带的标准成像图版,利用交会图及直方图分析各分带的常规测井响应特征,在此基础上形成了电成像测井刻度常规测井识别岩溶发育带的新方法。研究结果表明:①高石梯—磨溪地区茅口组岩溶带自上而下可划分为风化壳残积带、垂直渗流岩溶带、水平潜流岩溶带以及受岩溶作用较弱的基岩;②风化壳残积带在成像测井图像显示为"暗—亮—暗"条带状模式,垂直渗流岩溶带为垂直线状与暗色斑状组合模式,水平潜流岩溶带为水平线状—层状与斑状组合模式,基岩整体显示为亮色块状模式偶见线状或斑状特征;③有效储层主要发育在垂直渗流带和水平潜流带的顶部;④该区茅口组岩溶发育主要受裂缝发育控制,而裂缝发育又与断层关系密切。结论认为,该新方法对碳酸盐岩岩溶储层的多井评价具有普遍适用性,为四川盆地中二叠统风险探井的部署提供了技术支撑。  相似文献   
50.
Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna's model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.  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