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   242619篇
  免费   19695篇
  国内免费   10146篇
电工技术   13731篇
技术理论   24篇
综合类   15548篇
化学工业   40302篇
金属工艺   14211篇
机械仪表   15663篇
建筑科学   18673篇
矿业工程   8004篇
能源动力   6914篇
轻工业   14734篇
水利工程   4008篇
石油天然气   17046篇
武器工业   1855篇
无线电   27079篇
一般工业技术   28710篇
冶金工业   13121篇
原子能技术   2490篇
自动化技术   30347篇
  2024年   839篇
  2023年   3880篇
  2022年   6445篇
  2021年   9855篇
  2020年   7585篇
  2019年   6360篇
  2018年   7175篇
  2017年   8039篇
  2016年   7179篇
  2015年   9624篇
  2014年   12340篇
  2013年   14418篇
  2012年   15606篇
  2011年   16875篇
  2010年   14626篇
  2009年   13774篇
  2008年   13532篇
  2007年   12905篇
  2006年   13270篇
  2005年   11494篇
  2004年   7772篇
  2003年   6568篇
  2002年   5782篇
  2001年   5153篇
  2000年   5640篇
  1999年   6554篇
  1998年   5527篇
  1997年   4498篇
  1996年   4225篇
  1995年   3552篇
  1994年   2850篇
  1993年   2002篇
  1992年   1548篇
  1991年   1222篇
  1990年   931篇
  1989年   733篇
  1988年   534篇
  1987年   342篇
  1986年   270篇
  1985年   194篇
  1984年   135篇
  1983年   104篇
  1982年   121篇
  1981年   99篇
  1980年   78篇
  1979年   39篇
  1978年   26篇
  1977年   21篇
  1976年   36篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively.  相似文献   
85.
86.
87.
88.
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.  相似文献   
89.
This article focuses on the consensus problem of leader-following fractional-order multi-agent systems (MASs) with general linear and Lipschitz nonlinear dynamics. First, the distributed adaptive protocols for linear and nonlinear fractional-order MASs are constructed, respectively. We allow the control coupling gains to be time varying for each agent. Moreover, the adaptive modification schemes for the control gain are designed, which renders smaller control gains and thus requires smaller amplitude on the control input without sacrificing consensus convergence. Second, based on fractional-order Lyapunov stability theorem and Barbalat's lemma, two novel sufficient conditions in terms of linear matrix inequalities are provided to ensure that the leader-following consensus can be obtained in the case for any undirected connected communication graph. Furthermore, we show that the proposed algorithm also works for consensus of agents with intrinsic Lipschitz nonlinear dynamics. As a result, the proposed framework requires no global information and thus can be implemented in a fully distributed manner. Finally, the numerical simulations are given to demonstrate the effectiveness of obtained the theoretical results.  相似文献   
90.
A series of methacrylate-acrylonitrile-butadiene-styrene (MABS) resins was prepared using bulk polymerization. The polarity of the continuous phase and the compatibility of two phases were changed by adjusting the methyl methacrylate (MMA) content, choosing values that were close to styrene-butadiene rubber solubility value. The possibility of controlling the microstructure of the MABS resin by changing the polarity of the components and the compatibility of two phases was assessed. The dynamic mechanical analysis shows that the compatibility of two phases varies with the MMA content. The morphological analysis shows that increasing MMA contents results in a gradual decrease in the sub-inclusion structure with a network skeleton of rubber particles, and that all the particles become solid rubber when the MMA content reaches 75%. The sub-inclusion structure reappears but does not have a network skeleton when the MMA content is 90%. The impact strength and morphological analysis indicate that the solid rubber particles and the sub-inclusion structure with a network skeleton provide excellent toughness, while the sub-inclusion structure without a network skeleton does not. In contrast, the transmittance of the ABS resin first increased and then decreased with increasing MMA content.  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