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   214775篇
  免费   20830篇
  国内免费   11654篇
电工技术   14768篇
技术理论   13篇
综合类   15718篇
化学工业   33249篇
金属工艺   12355篇
机械仪表   14197篇
建筑科学   16774篇
矿业工程   6634篇
能源动力   6505篇
轻工业   16543篇
水利工程   4618篇
石油天然气   11601篇
武器工业   2033篇
无线电   25756篇
一般工业技术   24730篇
冶金工业   9668篇
原子能技术   2650篇
自动化技术   29447篇
  2024年   481篇
  2023年   3745篇
  2022年   6712篇
  2021年   9860篇
  2020年   7475篇
  2019年   5736篇
  2018年   6523篇
  2017年   7272篇
  2016年   6526篇
  2015年   9143篇
  2014年   11328篇
  2013年   13636篇
  2012年   15552篇
  2011年   16266篇
  2010年   14349篇
  2009年   13533篇
  2008年   13247篇
  2007年   12503篇
  2006年   12418篇
  2005年   10491篇
  2004年   7204篇
  2003年   5715篇
  2002年   5169篇
  2001年   4654篇
  2000年   4305篇
  1999年   4398篇
  1998年   3485篇
  1997年   2943篇
  1996年   2716篇
  1995年   2234篇
  1994年   1798篇
  1993年   1330篇
  1992年   1072篇
  1991年   801篇
  1990年   580篇
  1989年   481篇
  1988年   369篇
  1987年   252篇
  1986年   204篇
  1985年   128篇
  1984年   117篇
  1983年   93篇
  1982年   84篇
  1981年   72篇
  1980年   71篇
  1979年   33篇
  1978年   25篇
  1977年   24篇
  1976年   26篇
  1951年   20篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
An increasing number of social media and networking platforms have been widely used. People usually post the online comments to share their own opinions on the networking platforms with social media. Business companies are increasingly seeking effective ways to mine what people think and feel regarding their products and services. How to correctly understand the online customers’ reviews becomes an important issue. This study aims to propose a method with the aspect-oriented Petri nets (AOPN) to improve the examination correctness without changing any process and program. We collect those comments from the online reviews with Scrapy tools, perform sentiment analysis using SnowNLP, and examine the analysis results to improve the correctness. In this paper, we apply our method for a case of the online movie comments. The experimental results have shown that AOPN is helpful for the sentiment analysis and verifying its correctness.  相似文献   
82.
The effects of soybean variety and germination time on structural changes, antinutritional factor content, antioxidant activity of germinated soybean, and on the functional properties of soymilk were comprehensively investigated. The results showed that the antioxidant activity increased with increasing germination time. The content of antinutritional factors decreased with increasing germination time. Soybean varieties with the lowest tannin and trypsin inhibitor content were DN690 and HJ1. Lipoxygenase activity and phytic acid content showed no significant differences among soybean varieties. The content of α-helices and β-turns in soybean protein decreased with increasing germination time, while the content of β-sheets was increased. Soybean protein was progressively broken down into smaller molecular peptides during the germination process. The digestion and content of soluble protein in soymilk increased with germination. In summary, we show that germination is an effective, cheap, and green method that improves the functional properties of soybean and soymilk.  相似文献   
83.
Gao  Zehai  Liu  Yang  Li  Nan  Ma  Kangjie 《Water Resources Management》2022,36(8):2685-2702
Water Resources Management - Urban river not only has the important function in urban hydrological environment, but also is an area for entertainment. Water quality assessment is the core technique...  相似文献   
84.
85.
86.
87.
干河煤矿+80水平三采区皮带巷上部赋存坚硬岩层,围岩压力较大;针对坚硬顶板条件,拟定以强主动支护为主的对策,即采用锚网索喷联合支护技术;应用表明,该巷道围岩变形量不大,验证了该支护技术安全可靠。  相似文献   
88.
针对传统的电弧电路故障检测结果不准确的问题,设计用于电弧检测的SoC系统,并且在55nm工艺下进行流片验证。采用包含两种结构的模数转换器的片上电压源,设计了锁相环以及复位电路,精度最高可达8.67 bit。验证结果表明,本设计可提高电弧检测的准确性。  相似文献   
89.
Natural gas foam can be used for mobility control and channel blocking during natural gas injection for enhanced oil recovery, in which stable foams need to be used at high reservoir temperature, high pressure and high water salinity conditions in field applications. In this study, the performance of methane (CH4) foams stabilized by different types of surfactants was tested using a high pressure and high temperature foam meter for surfactant screening and selection, including anionic surfactant (sodium dodecyl sulfate), non-anionic surfactant (alkyl polyglycoside), zwitterionic surfactant (dodecyl dimethyl betaine) and cationic surfactant (dodecyl trimethyl ammonium chloride), and the results show that CH4-SDS foam has much better performance than that of the other three surfactants. The influences of gas types (CH4, N2, and CO2), surfactant concentration, temperature (up to 110°C), pressure (up to 12.0 MPa), and the presence of polymers as foam stabilizer on foam performance was also evaluated using SDS surfactant. The experimental results show that the stability of CH4 foam is better than that of CO2 foam, while N2 foam is the most stable, and CO2 foam has the largest foam volume, which can be attributed to the strong interactions between CO2 molecules with H2O. The foaming ability and foam stability increase with the increase of the SDS concentration up to 1.0 wt% (0.035 mol/L), but a further increase of the surfactant concentration has a negative effect. The high temperature can greatly reduce the stability of CH4-SDS foam, while the foaming ability and foam stability can be significantly enhanced at high pressure. The addition of a small amount of polyacrylamide as a foam stabilizer can significantly increase the viscosity of the bulk solution and improve the foam stability, and the higher the molecular weight of the polymer, the higher viscosity of the foam liquid film, the better foam performance.  相似文献   
90.
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