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   28883篇
  免费   2968篇
  国内免费   1897篇
电工技术   3302篇
技术理论   2篇
综合类   3134篇
化学工业   3333篇
金属工艺   876篇
机械仪表   1288篇
建筑科学   3317篇
矿业工程   1055篇
能源动力   1112篇
轻工业   1873篇
水利工程   1137篇
石油天然气   2642篇
武器工业   244篇
无线电   2441篇
一般工业技术   3028篇
冶金工业   1391篇
原子能技术   692篇
自动化技术   2881篇
  2024年   45篇
  2023年   338篇
  2022年   653篇
  2021年   1015篇
  2020年   943篇
  2019年   735篇
  2018年   735篇
  2017年   813篇
  2016年   993篇
  2015年   1102篇
  2014年   1725篇
  2013年   1879篇
  2012年   2095篇
  2011年   2395篇
  2010年   1773篇
  2009年   1839篇
  2008年   1697篇
  2007年   1999篇
  2006年   1805篇
  2005年   1533篇
  2004年   1227篇
  2003年   1083篇
  2002年   963篇
  2001年   778篇
  2000年   611篇
  1999年   532篇
  1998年   426篇
  1997年   333篇
  1996年   309篇
  1995年   259篇
  1994年   215篇
  1993年   142篇
  1992年   116篇
  1991年   94篇
  1990年   96篇
  1989年   81篇
  1988年   85篇
  1987年   39篇
  1986年   24篇
  1985年   27篇
  1984年   34篇
  1983年   12篇
  1982年   15篇
  1981年   11篇
  1980年   10篇
  1964年   12篇
  1961年   8篇
  1960年   9篇
  1959年   8篇
  1955年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Background: Recently, it was reported that leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4, also called GPR48) is another receptor for RANKL and was shown to compete with RANK to bind RANKL and suppress canonical RANK signaling during osteoclast differentiation. The critical role of the protein triad RANK–RANKL in osteoclastogenesis has made their binding an important target for the development of drugs against osteoporosis. In this study, point-mutations were introduced in the RANKL protein based on the crystal structure of the RANKL complex and its counterpart receptor RANK, and we investigated whether LGR4 signaling in the absence of the RANK signal could lead to the inhibition of osteoclastogenesis.; Methods: The effects of point-mutated RANKL (mRANKL-MT) on osteoclastogenesis were assessed by tartrate-resistant acid phosphatase (TRAP), resorption pit formation, quantitative real-time polymerase chain reaction (qPCR), western blot, NFATc1 nuclear translocation, micro-CT and histomorphological assay in wild type RANKL (mRANKL-WT)-induced in vitro and in vivo experimental mice model. Results: As a proof of concept, treatment with the mutant RANKL led to the stimulation of GSK-3β phosphorylation, as well as the inhibition of NFATc1 translocation, mRNA expression of TRAP and OSCAR, TRAP activity, and bone resorption, in RANKL-induced mouse models; and Conclusions: The results of our study demonstrate that the mutant RANKL can be used as a therapeutic agent for osteoporosis by inhibiting RANKL-induced osteoclastogenesis via comparative inhibition of RANKL. Moreover, the mutant RANKL was found to lack the toxic side effects of most osteoporosis treatments.  相似文献   
2.
3.
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering.  相似文献   
4.
Images with hazy scene suffer from low-contrast, which reduces the visible quality of the scene, thus making object detection a more challenging task. Low-contrast can result from foggy weather conditions during image acquisition. Dehazing is a process of removal of haze from the photography of a hazy scene. Single-image dehazing based on dark channel priors are well-known techniques in this field. However, the performance of such techniques is limited to priors or constraints. Moreover, this type of method fails when images have sky-region. So, a method is proposed, which can restore the visibility of hazy images. First, a hazy image is divided into blocks of size 32 × 32, then the score of each block is calculated to select a block having the highest score. Atmospheric light is calculated from the selected block. A new color channel is considered to remove atmospheric scattering, obtained channel value and atmospheric light are then used to calculate the transmission map in the second step. Third, radiance is computed using a transmission map and atmospheric light. The illumination scaling factor is adopted to enhance the quality of a dehazed image in the final step. Experiments are performed on six datasets namely, I-HAZE, O-HAZE, BSDS500, FRIDA, RESIDE dataset and natural images from Google. The proposed method is compared against 11 state-of-the-art methods. The performance is analyzed using fourteen quantitative evaluation metrics. All the results demonstrate that the proposed method outperforms 11 state-of-the-art methods in most of the cases.  相似文献   
5.
6.
根据剪切解络-超滤过程中金属离子的动态浓度关系和质量守恒定律,采用CodeBlocks17.12软件编写程序,建立了剪切解络-超滤工艺关键指标预测模型,实现了金属离子浓度、回收率、体积稀释倍数等指标的预测,并用实验加以验证。依次在转速800 r/min、1 400 r/min、3 000 r/min下回收模拟废水中43 μg/L的Co2+、995 μg/L的Ni2+和88 μg/L的La3+,3种金属的回收率均达99.8%以上时,超滤过程体积稀释倍数的预测值分别为7.0、7.5、5.75,实验值分别为7.5、7.25、6.25,可见预测值与实验值基本一致。本模型对研究方案制定和调整有实际指导意义。  相似文献   
7.
为探索生物活性未知的双对苯醌(2,7-dihydroxy-3,6,9-trimethyl-9H-xanthene-1,4,5,8-tetraone,DTXT)的抗氧化活性,并提高其发酵产量,考察DTXT的还原力以及对超氧阴离子自由基、羟自由基、1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基的清除效果,在单因素试验基础上,采用响应面法优化了DTXT产生菌瓶生顶孢霉(Acremonium cavaraeanum)CA022菌株的固体发酵培养基。结果表明:在200 μg/mL质量浓度下,DTXT的还原力与芦丁差异不显著,高于VE和2,6-二叔丁基-4甲基苯酚,对超氧阴离子自由基清除率达到67.00%,对羟自由基清除率达到78.83%,对DPPH自由基清除率达到76.53%。通过响应面试验,得到最佳培养基配方为葡萄糖0.773%、硝酸钠0.185%、H3BO3 0.032%、VB1 100 μg/100 g,在此条件下实际获得的DTXT产量为4 150.8 mg/kg,是优化前产量的(2 864.83 mg/kg)1.45 倍。  相似文献   
8.
9.
Prediction of mode I fracture toughness (KIC) of rock is of significant importance in rock engineering analyses. In this study, linear multiple regression (LMR) and gene expression programming (GEP) methods were used to provide a reliable relationship to determine mode I fracture toughness of rock. The presented model was developed based on 60 datasets taken from the previous literature. To predict fracture parameters, three mechanical parameters of rock mass including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), and elastic modulus (E) have been selected as the input parameters. A cluster of data was collected and divided into two random groups of training and testing datasets. Then, different statistical linear and artificial intelligence based nonlinear analyses were conducted on the training data to provide a reliable prediction model of KIC. These two predictive methods were then evaluated based on the testing data. To evaluate the efficiency of the proposed models for predicting the mode I fracture toughness of rock, various statistical indices including coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) were utilized herein. In the case of testing datasets, the values of R2, RMSE, and MAE for the GEP model were 0.87, 0.188, and 0.156, respectively, while they were 0.74, 0.473, and 0.223, respectively, for the LMR model. The results indicated that the selected GEP model delivered superior performance with a higher R2 value and lower errors.  相似文献   
10.
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