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   442篇
  免费   37篇
电工技术   10篇
化学工业   101篇
金属工艺   6篇
机械仪表   9篇
建筑科学   15篇
矿业工程   2篇
能源动力   14篇
轻工业   61篇
水利工程   14篇
无线电   67篇
一般工业技术   54篇
冶金工业   73篇
原子能技术   2篇
自动化技术   51篇
  2024年   1篇
  2023年   5篇
  2022年   6篇
  2021年   12篇
  2020年   7篇
  2019年   9篇
  2018年   13篇
  2017年   19篇
  2016年   19篇
  2015年   7篇
  2014年   25篇
  2013年   39篇
  2012年   18篇
  2011年   23篇
  2010年   15篇
  2009年   16篇
  2008年   25篇
  2007年   26篇
  2006年   19篇
  2005年   11篇
  2004年   15篇
  2003年   9篇
  2002年   11篇
  2001年   8篇
  2000年   8篇
  1999年   11篇
  1998年   24篇
  1997年   17篇
  1996年   7篇
  1995年   12篇
  1994年   3篇
  1993年   9篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   1篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1981年   1篇
  1980年   2篇
  1979年   3篇
  1977年   1篇
  1976年   1篇
  1975年   3篇
  1972年   2篇
  1971年   1篇
排序方式: 共有479条查询结果,搜索用时 15 毫秒
81.
Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles.  相似文献   
82.
83.
84.
This paper presents the dimensional verification of encapsulations used to package microfluidic devices manufactured using a 3D printer of photopolymerisable resin. This characterisation has been performed by computed tomography (CT) by comparing newly manufactured encapsulations and samples that have been subjected to test conditions. Thus, it has been possible to draw conclusions both on the deviations of the nominal geometry of the encapsulations and on how this might affect their performance. This paper presents a scheme of dimensional verification from the point clouds obtained by CT. Finally, a combined threshold and scale factor correction technique of the tomography images is shown. This method is based on the simultaneous measurement of objective and master parts with known geometry. The results reveal the improvements achievable in the accuracy, given a particular machine configuration. The conclusions facilitate the improvement of the geometric design of these devices regarding their behaviour under test conditions.  相似文献   
85.
86.
This study explored the relationships between eye tracking and traditional usability testing data in the context of analyzing the usability of Algebra Nation?, an online system for learning mathematics used by hundreds of thousands of students. Thirty-five undergraduate students (20 females) completed seven usability tasks in the Algebra Nation? online learning environment. The participants were asked to log in, select an instructor for the instructional video, post a question on the collaborative wall, search for an explanation of a mathematics concept on the wall, find information relating to Karma Points (an incentive for engagement and learning), and watch two instructional videos of varied content difficulty. Participants’ eye movements (fixations and saccades) were simultaneously recorded by an eye tracker. Usability testing software was used to capture all participants’ interactions with the system, task completion time, and task difficulty ratings. Upon finishing the usability tasks, participants completed the System Usability Scale. Important relationships were identified between the eye movement metrics and traditional usability testing metrics such as task difficulty rating and completion time. Eye tracking data were investigated quantitatively using aggregated fixation maps, and qualitative examination was performed on video replay of participants’ fixation behavior. Augmenting the traditional usability testing methods, eye movement analysis provided additional insights regarding revisions to the interface elements associated with these usability tasks.  相似文献   
87.
Product innovation, in particular radical product innovation, is considered to have a positive effect on company success. As a consequence, there is growing interest in the literature on how to foster radical product innovation. Organizational culture is frequently cited as an antecedent. The underlying assumption is that the culture facilitates radical innovation by encouraging employees' innovative behavior. However, empirical research on the mediating role of employees' innovative behavior in the relation between organizational culture and radical product innovation is scarce. The purpose of this paper is to analyze this mediating role using a sample of Spanish firms. Findings show that adhocracy and market cultures are positively related with the degree of radicalness of product innovation and that employees' innovative behavior mediates that relation, but only in the case of the adhocracy culture.  相似文献   
88.
The mobile health (mHealth) and electronic health (eHealth) systems are useful to maintain a correct administration of health information and services. However, it is mandatory to ensure a secure data transmission and in case of a node failure, the system should not fall down. This fact is important because several vital systems could depend on this infrastructure. On the other hand, a cloud does not have infinite computational and storage resources in its infrastructure or would not provide all type of services. For this reason, it is important to establish an interrelation between clouds using communication protocols in order to provide scalability, efficiency, higher service availability and flexibility which allow the use of services, computing and storage resources of other clouds. In this paper, we propose the architecture and its secure protocol that allows exchanging information, data, services, computing and storage resources between all interconnected mHealth clouds. The system is based on a hierarchic architecture of two layers composed by nodes with different roles. The routing algorithm used to establish the connectivity between the nodes is the shortest path first (SPF), but it can be easily changed by any other one. Our architecture is highly scalable and allows adding new nodes and mHealth clouds easily, while it tries to maintain the load of the cloud balanced. Our protocol design includes node discovery, authentication and fault tolerance. We show the protocol operation and the secure system design. Finally we provide the performance results in a controlled test bench.  相似文献   
89.
Exposition of results and complications in 7,162 consecutive sessions with Shockwave Extracorporeal Lithotripsy (SWEL) applied to 3,950 lithiasis located at all levels of the urinary tract. These procedures have been performed without sedation or anaesthesia. Diuresis was not forced during or after treatment with serotherapy, mannitol, or diuretics. Treatment was conducted in an outpatients clinic in all cases. The treatment/lithiasis ratio in this initial series was 1.7. Following therapy, 7.09% of patients treated attended the emergency unit due to colic pain/fever. 3.60% of patients treated required hospitalization due to major complications: subcapsular-retroperitoneal haematoma, 9 cases; ureteral obstruction, 120 cases; septicemia, 22 cases; renal function annulment, 11 cases and death, 2 cases.  相似文献   
90.
BACKGROUND/AIMS: In many centers paracentesis is considered the treatment of choice for tense ascites. However, the mechanism of effective hypovolemia after paracentesis, the main complication associated with this procedure, remains unknown. In the current study, systemic hemodynamics was sequentially studied before and after total paracentesis in 46 patients with cirrhosis and tense ascites. The aim of the study was to assess the mechanism of effective hypovolemia after paracentesis. METHODS: Plasma renin activity and aldosterone, mean arterial pressure, cardiac output (ECO-Doppler) and systemic vascular resistance were measured before, and 3 h, 6 h and 6 days after total paracentesis associated with plasma volume expansion. RESULTS: Effective hypovolemia after paracentesis (defined as 50% increase in plasma renin activity up to a level over 4 ng x m(-1) x h(-1) at the 6th day after paracentesis) occurred in 20 cases [plasma renin activity increased from 8+/-17 to 19+/-2.7 ng x m(-1) x h(-1)]. In the remaining 26 cases no changes in plasma renin activity [8.5+/-2.4 vs. 8.7+/-2.2 ng x m(-1) x h(-1)] were observed. The amounts of ascitic fluid volume removed were similar. Effective hypovolemia after paracentesis was associated with a significant decrease in mean arterial pressure (89+/-2 vs. 81+/-3 mmHg) and systemic vascular resistance [1263+/-67 vs. 1014+/-80 dyn x s(-1) x cm(-5)] 6 days after treatment. In contrast, no significant changes in these parameters were observed in patients not developing this complication. In the whole group of patients a significant inverse relation was observed between changes in plasma renin activity and in systemic vascular resistance (r=0.74;p< 0.001). CONCLUSIONS: These results indicate that effective hypovolemia after paracentesis in cirrhosis is predominantly due to an accentuation of the arteriolar vasodilation already present in these patients.  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