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   39438篇
  免费   4645篇
  国内免费   2400篇
电工技术   4103篇
技术理论   1篇
综合类   3289篇
化学工业   4949篇
金属工艺   1478篇
机械仪表   4034篇
建筑科学   2240篇
矿业工程   1013篇
能源动力   1775篇
轻工业   907篇
水利工程   959篇
石油天然气   1781篇
武器工业   629篇
无线电   4587篇
一般工业技术   3267篇
冶金工业   1061篇
原子能技术   204篇
自动化技术   10206篇
  2024年   48篇
  2023年   657篇
  2022年   1030篇
  2021年   1405篇
  2020年   1443篇
  2019年   1205篇
  2018年   1018篇
  2017年   1329篇
  2016年   1432篇
  2015年   1639篇
  2014年   2504篇
  2013年   2517篇
  2012年   2666篇
  2011年   3272篇
  2010年   2374篇
  2009年   2579篇
  2008年   2450篇
  2007年   2918篇
  2006年   2480篇
  2005年   2160篇
  2004年   1793篇
  2003年   1574篇
  2002年   1232篇
  2001年   1010篇
  2000年   877篇
  1999年   581篇
  1998年   433篇
  1997年   328篇
  1996年   283篇
  1995年   258篇
  1994年   202篇
  1993年   171篇
  1992年   140篇
  1991年   110篇
  1990年   80篇
  1989年   78篇
  1988年   44篇
  1987年   20篇
  1986年   28篇
  1985年   22篇
  1984年   22篇
  1983年   10篇
  1982年   17篇
  1981年   4篇
  1980年   13篇
  1979年   4篇
  1978年   3篇
  1977年   7篇
  1975年   4篇
  1959年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Heparanase (Hpse) is an endo-β-D-glucuronidase capable of cleaving heparan sulfate side chains. Its upregulated expression is implicated in tumor growth, metastasis and angiogenesis, thus making it an attractive target in cancer therapeutics. Currently, a few small molecule inhibitors have been reported to inhibit Hpse, with promising oral administration and pharmacokinetic (PK) properties. In the present study, a ligand-based pharmacophore model was generated from a dataset of well-known active small molecule Hpse inhibitors which were observed to display favorable PK properties. The compounds from the InterBioScreen database of natural (69,034) and synthetic (195,469) molecules were first filtered for their drug-likeness and the pharmacophore model was used to screen the drug-like database. The compounds acquired from screening were subjected to molecular docking with Heparanase, where two molecules used in pharmacophore generation were used as reference. From the docking analysis, 33 compounds displayed higher docking scores than the reference and favorable interactions with the catalytic residues. Complex interactions were further evaluated by molecular dynamics simulations to assess their stability over a period of 50 ns. Furthermore, the binding free energies of the 33 compounds revealed 2 natural and 2 synthetic compounds, with better binding affinities than reference molecules, and were, therefore, deemed as hits. The hit compounds presented from this in silico investigation could act as potent Heparanase inhibitors and further serve as lead scaffolds to develop compounds targeting Heparanase upregulation in cancer.  相似文献   
2.
阿尔兹海默病的疾病进展模型与研究进展   总被引:1,自引:0,他引:1  
阿尔兹海默病(AD)是一种病理机制暂不明确的神经退行性疾病,定量药理学中的疾病进展模型可以通过定量的方法充分描述AD患者疾病发展轨迹。通过模型中引入生物标志物信息,可有助于加深对AD病理机制的研究,辅助并优化临床试验的设计。现已有多种经验性或半机制的AD疾病进展模型报道。本文对此进行了综述,以期为阿尔兹海默病的临床研究和新药研发提供参考。  相似文献   
3.
The ability to trap precise quantities of cells or particles into confined areas has numerous applications for biological purposes. In particular, single cell trapping has received considerable attention because it permits the study of heterogeneity in a population, while trapping larger groups of cells have been used to form aggregates. Among several methods, the use of microwell offers a simple platform to capture cells or particles using hydrodynamic forces. This review examines the use of microwells in both static and microfluidic environments, and the application of microfluidic geometric arrays for trapping. This paper discusses the design and fabrication methods of microwells and compares the trapping and release techniques used in both static and microfluidics‐integrated microwells. Finally, we will summarize novel microfluidic geometric arrays used to capture cells or particles through hydrodynamic trapping.  相似文献   
4.
在电网调度运行的实际生产中,需要综合多个业务系统中的数据,并从中挖掘出有价值的电力运行信息。当前,省地县调度业务多通过调度电话或者邮件联系,同时业务系统分布在不同安全分区,缺乏有效的管理措施。文章阐述了电网省地县调度数据一体化管理平台,其具备提供数据收集、存储、自定义报表、数据加工等功能,使省地县调的纵向数据传输能力得到显著改善。  相似文献   
5.
6.
海上油田大斜度井日益增多,而大斜度井固井质量评价对井控安全、完井射孔、后期老井开窗侧钻等关系重大。随钻声波测井工具不受井斜限制、操作简单,可获得高质量的声波数据资料。本项目将随钻声波测井技术与完井刮管作业相结合,在刮管作业的同时进行固井质量评价,并在渤海油田某区块成功运用,获得很好效果。  相似文献   
7.
双臂机器人系统是当前机器人领域的研究热点,特别是随着单臂机器人在操作能力、控制等方面的局限性不断凸显,最近的研究集中在拥有协调操作能力的冗余双臂机器人。对双臂操作进行分类,然后从双臂协调运动方式、双臂协调控制问题、感知传感器、模仿学习、人机交互五个方面进行分析;综述从运动学、动力学现状入手,分析了双臂协调控制与单臂控制方式在约束关系、运动规划、协调控制方式等方面的不同与发展,结合感知传感器、模仿学习等方法在双臂协调控制中的应用;对人机协作中的交互方式进行了分析,并对双臂机器人的未来研究方向进行了展望。  相似文献   
8.
分析了混合型有源滤波器HAPF(hybrid active power filter)在高压直流系统应用时的稳定性问题,其中HAPF采用H桥级联变换器与LC滤波器组合的方案,对高压直流系统的特征谐波电流进行滤波。为了分析在电网阻抗变化时HAPF出现的谐波谐振现象,对HAPF进行了阻抗建模,基于阻抗模型的分析结果,采用了具有延时补偿功能的谐振调节器对阻抗特性进行修正,并从提高稳定性角度提出了相应的控制参数设计方法。阻抗模型分析结果表明,控制系统延时产生的负阻尼是引发稳定性问题的主要原因,采用改进后的控制方法可以将延时产生的负阻尼修正为正阻尼,能够有效避免谐波谐振。在PSCAD中进行仿真建模,并通过阻抗扫描验证了有源滤波器的阻抗特性。仿真案例证实了控制方法的有效性。  相似文献   
9.
Perfluorosulfonic acid ionomer membranes have been widely used as proton conducting membranes in various electrochemical processes such as polymer electrolyte fuel cells and water electrolysis. While their thermal stability has been studied by thermogravimetry and analysis of low molecular weight products, their decomposition mechanism is little understood. In this study a newly developed methodology of thermal desorption and pyrolysis in combination with direct analysis in real time mass spectrometry is applied for Nafion membrane. An ambient ionization source and a high-resolution time-of-flight mass spectrometer enabled unambiguous assignment of gaseous products. Thermal decomposition is initiated by side chain detachment above 350°C, which leaves carbonyls on the main chain at the locations of the side chains. Perfluoroalkanes are released above 400°C by main chain scission and their further decomposition products dominate above 500 °C. DFT calculation of reaction energies and barrier heights of model compounds support proposed decomposition reactions.  相似文献   
10.
Nepheline precipitation in nuclear waste glasses during vitrification can be detrimental due to the negative effect on chemical durability often associated with its formation. Developing models to accurately predict nepheline precipitation from compositions is important for increasing waste loading since existing models can be overly conservative. In this study, an expanded dataset of 955 glasses, including 352 high-level waste glasses, was compiled from literature data. Previously developed submixture models were refitted using the new dataset, where a misclassification rate of 7.8% was achieved. In addition, nine machine learning (ML) algorithms (k-nearest neighbor, Gaussian process regression, artificial neural network, support vector machine, decision tree, etc.) were applied to evaluate their ability to predict nepheline precipitation from glass compositions. Model accuracy, precision, recall/sensitivity, and F1 scores were systemically compared between different ML algorithms and modeling protocols. Model prediction with an accuracy of ~0.9 (misclassification rate of ~10%) was observed for different algorithms under certain protocols. This study evaluated various ML models to predict nepheline precipitation in waste glasses, highlighting the importance of data preparation and modeling protocol, and their effect on model stability and reproducibility. The results provide insights into applying ML to predict glass properties and suggest areas for future research on modeling nepheline precipitation.  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