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   88629篇
  免费   15965篇
  国内免费   184篇
电工技术   1491篇
综合类   77篇
化学工业   27164篇
金属工艺   2610篇
机械仪表   4145篇
建筑科学   2891篇
矿业工程   28篇
能源动力   3142篇
轻工业   10807篇
水利工程   571篇
石油天然气   133篇
武器工业   2篇
无线电   14280篇
一般工业技术   21543篇
冶金工业   5147篇
原子能技术   726篇
自动化技术   10021篇
  2024年   29篇
  2023年   582篇
  2022年   524篇
  2021年   1808篇
  2020年   2420篇
  2019年   4034篇
  2018年   4322篇
  2017年   4508篇
  2016年   5320篇
  2015年   4930篇
  2014年   5686篇
  2013年   7959篇
  2012年   5965篇
  2011年   6399篇
  2010年   5500篇
  2009年   5522篇
  2008年   4978篇
  2007年   4171篇
  2006年   3787篇
  2005年   3199篇
  2004年   2999篇
  2003年   2887篇
  2002年   2635篇
  2001年   2291篇
  2000年   2120篇
  1999年   1503篇
  1998年   1880篇
  1997年   1243篇
  1996年   981篇
  1995年   689篇
  1994年   582篇
  1993年   488篇
  1992年   351篇
  1991年   340篇
  1990年   322篇
  1989年   298篇
  1988年   242篇
  1987年   212篇
  1986年   173篇
  1985年   148篇
  1984年   118篇
  1983年   94篇
  1982年   48篇
  1981年   60篇
  1980年   50篇
  1979年   42篇
  1978年   44篇
  1977年   57篇
  1976年   86篇
  1975年   29篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
131.
132.
133.
Metallurgical and Materials Transactions B - The concentration and chemical bonding state of carbon in direct-reduced iron (DRI) might affect DRI melting temperature and rate. The effects of carbon...  相似文献   
134.
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06  x  0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response.  相似文献   
135.
We present a distribution‐free tabular cumulative sum chart for monitoring the variability of an autocorrelated process. A quantity known as the asymptotic variance parameter is employed as a measure of the variability, and a distribution‐free tabular cumulative sum chart is applied to variance estimates calculated from batches of nonoverlapping samples. The proposed chart is applicable to a stationary process with a general marginal distribution and a general autocorrelation structure. It also determines control limits analytically without trial‐and‐error simulations. The performance of the proposed chart is tested on stationary processes with both normal and nonnormal marginals with various autocorrelation structures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
136.
137.
Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically...  相似文献   
138.
Vegetable soup (VS), a plant-based functional food, has been used as a traditional folk medicine and is attracting attention for its ability to enhance the immune response. β-Glucan, a well-established and effective immunomodulator, has synergistic effects when used in combination with some bioactive compounds. In the present study, we aimed to evaluate the synergistic immunomodulatory effects of the combination of VS and β-glucan on macrophage-mediated immune responses. β-Glucan was demonstrated to synergistically enhance the VS-stimulated immune response, including the production of interleukin-6, tumor necrosis factor-α, and nitric oxide, mainly through the mitogen-activated protein kinase pathway in macrophages. In addition, this combination has the potential for further development in functional foods with immune-enhancing activity.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10068-021-00888-x.  相似文献   
139.
Food Science and Biotechnology - St. Paul’s Wort (Siegesbeckia orientalis L.) confers anti-oxidative, anti-inflammatory, anti-allergic, anti-infertility, and immunosuppressive properties....  相似文献   
140.
This letter presents a small‐sized, high‐power single‐pole double‐throw (SPDT) switch with defected ground structure (DGS) for wireless broadband Internet application. To reduce the circuit size by using a slow‐wave characteristic, the DGS is used for the quarter‐wave (°/4) transmission line of the switch. To secure a high degree of isolation, the switch with DGS is composed of shunt‐connected PIN diodes. It shows an insertion loss of 0.8 dB, an isolation of 50 dB or more, and power capability of at least 50 W at 2.3 GHz. The switch shows very similar performance to the conventional shunt‐type switch, but the circuit size is reduced by about 50% simply with the use of DGS patterns.  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