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   48812篇
  免费   6742篇
  国内免费   2447篇
电工技术   3209篇
技术理论   1篇
综合类   5575篇
化学工业   8274篇
金属工艺   2807篇
机械仪表   2741篇
建筑科学   2275篇
矿业工程   4559篇
能源动力   1796篇
轻工业   6900篇
水利工程   975篇
石油天然气   2629篇
武器工业   377篇
无线电   3749篇
一般工业技术   3148篇
冶金工业   1810篇
原子能技术   121篇
自动化技术   7055篇
  2024年   119篇
  2023年   1293篇
  2022年   2079篇
  2021年   2290篇
  2020年   2592篇
  2019年   1774篇
  2018年   1565篇
  2017年   1435篇
  2016年   1819篇
  2015年   2120篇
  2014年   3745篇
  2013年   4257篇
  2012年   6622篇
  2011年   6208篇
  2010年   4019篇
  2009年   4383篇
  2008年   2490篇
  2007年   3268篇
  2006年   2622篇
  2005年   1030篇
  2004年   364篇
  2003年   290篇
  2002年   284篇
  2001年   224篇
  2000年   286篇
  1999年   245篇
  1998年   134篇
  1997年   87篇
  1996年   71篇
  1995年   45篇
  1994年   49篇
  1993年   44篇
  1992年   41篇
  1991年   29篇
  1990年   6篇
  1989年   7篇
  1988年   13篇
  1987年   7篇
  1986年   10篇
  1985年   5篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   4篇
  1976年   2篇
  1959年   1篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
为了避免过度使用天然砂石材料做为沥青混合料的骨料以及符合绿色发展的战略方针,采用固体废弃物铁尾矿来代替砂石材料来制备一种新型的铁尾矿沥青混合料。采用质谱仪对所选用铁尾矿进行化学成分分析,并对不同铁尾矿掺量作用下沥青混合料的针入度、锥入度、软化点、延度、粘度以及老化耐久性等方面进行了研究。研究结果表明:铁尾矿沥青混合料的较佳制备温度选定为180℃;综合经济效益和有效性确定铁尾矿的较佳掺量为30%;相对老化后的铁尾矿沥青材料而言,在同一铁尾矿掺量作用下两种不同沥青混合料老化前的针入度和延度均出现了降低的趋势,但是在同一铁尾矿掺量作用下两种不同沥青混合料老化前的软化点却出现了增大的趋势。综合分析得到:温度为180℃以及铁尾矿掺量为30%制备的沥青混合料可以满足公路的路用要求。所有沥青试样的光谱变化规律基本一致,说明了掺入铁尾矿改性沥青的结构与未掺入铁尾矿沥青的结构基本一致;但是随着铁尾矿掺量的增大,沥青的FT-IR光谱在同一波数作用下却呈现出不断减小的变化趋势,说明了铁尾矿可以有效改善沥青的物理性能。   相似文献   
2.
In the present era of machines and edge-cutting technologies, still document frauds persist. They are done intuitively by using almost identical inks, that it becomes challenging to detect them—this demands an approach that efficiently investigates the document and leaves it intact. Hyperspectral imaging is one such a type of approach that captures the images from hundreds to thousands of spectral bands and analyzes the images through their spectral and spatial features, which is not possible by conventional imaging. Deep learning is an edge-cutting technology known for solving critical problems in various domains. Utilizing supervised learning imposes constraints on its usage in real scenarios, as the inks used in forgery are not known prior. Therefore, it is beneficial to use unsupervised learning. An unsupervised feature extraction through a Convolutional Autoencoder (CAE) followed by Logistic Regression (LR) for classification is proposed (CAE-LR). Feature extraction is evolved around spectral bands, spatial patches, and spectral-spatial patches. We inspected the impact of spectral, spatial, and spectral-spatial features by mixing inks in equal and unequal proportion using CAE-LR on the UWA writing ink hyperspectral images dataset for blue and black inks. Hyperspectral images are captured at multiple correlated spectral bands, resulting in information redundancy handled by restoring certain principal components. The proposed approach is compared with eight state-of-art approaches used by the researchers. The results depicted that by using the combination of spectral and spatial patches, the classification accuracy enhanced by 4.85% for black inks and 0.13% for blue inks compared to state-of-art results. In the present scenario, the primary area concern is to identify and detect the almost similar inks used in document forgery, are efficiently managed by the proposed approach.  相似文献   
3.
4.
Zhang  Qi  Wang  Yujing  Zhang  Xueling  Song  Jun  Li  Yinlei  Wu  Xuehong  Yuan  Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after...  相似文献   
5.
Higher alcohols synthesis (HAS) from syngas (CO/H2) has attracted widespread attention, while the low selectivity and poor stability of the catalysts mainly stumbled its industrial application. In the work, Ni–Co alloy nanoparticles (NPs) derived from Co1-xNixAl2O4 loaded on the SiO2 with large specific surface area were prepared; and during reaction, the highly dispersed Ni–Co alloys were self-optimized to Ni–Co alloy@Co–Co2C. Importantly, Ni–Co alloy@Co–Co2C can be regenerated through oxidation - reduction - self-optimization process. Characteristic results indicated that the structural liberalization during the reaction process inhibited the loss of Ni, regulated and balanced the dual active sites of the catalyst and the Ni–Co alloys were regenerated after the re-oxidation and re-reduction process. The optimized catalyst exhibited excellent catalytic performance, including a high total selectivity to alcohols of 39.3% and an excellent catalytic stability at 250 °C, 3.5 MPa (H2/CO = 2) and a space velocity of 6000 mL (gcat h)?1. In addition, the Ni–Co alloy@Co–Co2C catalyst after stability test could recover its original catalytic performance after re-oxidation and re-reduction. The renewable characteristics and superior catalytic performance of Ni–Co alloy@Co–Co2C made the catalyst to be one of the potential industrial catalysts for HAS.  相似文献   
6.
This study aimed to determine the main bioactive components of Cornus officinalis vinegar (COV) and assess the effects of COV on the body weight (BW) and hepatic steatosis in a nonalcoholic fatty liver disease (NAFLD) mouse model. Seven-week-old KM female mice were divided into five treatment groups: (1) Normal control (NC) group, (2) high fat diet (HFD) group, (3) low concentration treatment group (3.5% COV), (4) medium concentration treatment group (5.0% COV), and (5) high concentration treatment group (6.5% COV). Mice in the NC group were fed with a normal chow diet, and those in the other four groups were fed with a HFD known for causing obesity for 10 weeks. Then, mice in the three COV treatment groups were orally administered with COV once a day for 6 weeks. Results showed that the contents of loganin and morroniside in COV reached 16.82 and 51.17 µg/ml, respectively, and COV also contained multiple organic acids. COV significantly reduced BW, abdominal fat weight, liver weight, and the levels of glucose, triglyceride, and low-density lipoprotein cholesterol of serum and increased the levels of high-density lipoprotein cholesterol of serum (< 0.05). COV also improved the liver function and anti-oxidant activity of liver (< 0.05). COV treatments increased the interleukin-10 expression and reduced the tumor necrosis factor-α expression in the liver tissue of NAFLD mice (< 0.05). Histopathological observation revealed that COV suppressed hepatic lipid accumulation and steatosis. The results suggest that COV may contribute to the alleviation of NAFLD and obesity.  相似文献   
7.
In this study, microbes were isolated from the rice slurry of a fermented rice cake to obtain lactic acid bacteria and yeast species. These species were identified using microbial physiology and gene sequence analyses. As the growth of the lactic acid bacterial strain R-2b and the yeast J-3a strains were found to be the best, a composite starter comprising these microbes was used for the preparation of fermented rice cakes. Based on single factor and orthogonal experiments, when the proportion of Lactobacillus plantarum, Saccharomyces cerevisiae, and Candida humilis was 1:3:6, the optimal fermentation conditions were addition of sugar and starter amounts of 20% and 6%, respectively, a fermentation temperature of 32 °C, and fermentation time of 8 h. The fermented rice cake with this optimum ratio had the most abundant volatile components and qualified physicochemical and microbial indexes. Additionally, the overall quality was better than that of commercially available products.  相似文献   
8.
通过调研现场情况以及检测煤泥特性,探寻一种实用性强、方法简单的新工艺来替代劳累的人工和繁琐的机械清淤,解决现实问题。针对实际情况开发清仓新工艺,介绍了该工艺的技术路线选择、设计依据以及实际应用效果。该新工艺具有降低清仓时间、减轻工人劳动强度、设备操作简单、实用性强等特点。  相似文献   
9.
李鹏  王先科 《中州煤炭》2022,(9):276-278
为了方便煤炭的运输,某矿使用了矿用履带式搬运车。履带运输车解决了轮式运输车在恶劣道路条件下不能行走的问题,这种履带车是一种新型的运输工具,其特点是体积小、转弯灵活、动力强大,可在不受场地限制的情况下轻松通过狭窄的地方,能有效解决山区、土壤、陡坡等恶劣条件下物料的运输问题,适合普通运输车辆无法通行的地方。介绍了矿用履带式搬运车的主要结构以及工作原理,并给出了实际应用中应注意的事项。  相似文献   
10.
Photocatalytic water splitting has become a promising technology to solve environmental pollution and energy shortage. Exploring stable and efficient photocatalysts are highly desired. Herein, we propose novel low-dimensional InSbS3 semiconductors with good stability based on density functional theory. Such InSbS3 structures could be obtained from their bulk crystal by suitable exfoliation methods. Our calculations indicate that two-dimensional (2D) and one-dimensional (1D) InSbS3 nanostructures have moderate band gaps (2.54 and 1.97 eV, respectively) and suitable band edge alignments, which represents sufficient redox capacity for photocatalytic water splitting. 2D InSbS3 monolayer possesses oxygen evolution reaction (OER) activity and 1D InSbS3 single-nanochain possesses hydrogen evolution reaction (HER) activity under acidic conditions. Interestingly, two edge electron states can be introduced when the dimension of InSbS3 is reduced from 2D to 1D and the new electron states can exist in arbitrary-width nanoribbons, which can effectively promote the process of HER. Moreover, InSbS3 monolayer and single-nanochain also exhibit large solar-to-hydrogen efficiency, high carrier mobility, and excellent optical absorption properties, which can facilitate the process of photocatalytic reactions. Our findings can stimulate the synthesis and applications of low-dimensional InSbS3 semiconductors for overall water splitting.  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