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   159594篇
  免费   7951篇
  国内免费   4072篇
电工技术   5510篇
技术理论   7篇
综合类   7273篇
化学工业   23829篇
金属工艺   9257篇
机械仪表   8123篇
建筑科学   8003篇
矿业工程   3215篇
能源动力   3505篇
轻工业   8975篇
水利工程   2864篇
石油天然气   4582篇
武器工业   707篇
无线电   17657篇
一般工业技术   25323篇
冶金工业   6512篇
原子能技术   1269篇
自动化技术   35006篇
  2024年   368篇
  2023年   1399篇
  2022年   2349篇
  2021年   3315篇
  2020年   2493篇
  2019年   2200篇
  2018年   16591篇
  2017年   15737篇
  2016年   12197篇
  2015年   3792篇
  2014年   4262篇
  2013年   4984篇
  2012年   8423篇
  2011年   14872篇
  2010年   13069篇
  2009年   10113篇
  2008年   11155篇
  2007年   11887篇
  2006年   4122篇
  2005年   4638篇
  2004年   3629篇
  2003年   3460篇
  2002年   2924篇
  2001年   2158篇
  2000年   1900篇
  1999年   1803篇
  1998年   1316篇
  1997年   1067篇
  1996年   1005篇
  1995年   839篇
  1994年   670篇
  1993年   541篇
  1992年   422篇
  1991年   311篇
  1990年   203篇
  1989年   157篇
  1988年   185篇
  1987年   94篇
  1986年   92篇
  1985年   49篇
  1984年   39篇
  1968年   44篇
  1966年   42篇
  1965年   46篇
  1959年   36篇
  1958年   38篇
  1957年   37篇
  1956年   36篇
  1955年   66篇
  1954年   72篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Evaluation of kinetic distribution and behaviors of nanoparticles in vivo provides crucial clues into their roles in living organisms. Extracellular vesicles are evolutionary conserved nanoparticles, known to play important biological functions in intercellular, inter‐species, and inter‐kingdom communication. In this study, the first kinetic analysis of the biodistribution of outer membrane vesicles (OMVs)—bacterial extracellular vesicles—with immune‐modulatory functions is performed. OMVs, injected intraperitoneally, spread to the whole mouse body and accumulate in the liver, lung, spleen, and kidney within 3 h of administration. As an early systemic inflammation response, increased levels of TNF‐α and IL‐6 are observed in serum and bronchoalveolar lavage fluid. In addition, the number of leukocytes and platelets in the blood is decreased. OMVs and cytokine concentrations, as well as body temperature are gradually decreased 6 h after OMV injection, in concomitance with the formation of eye exudates, and of an increase in ICAM‐1 levels in the lung. Following OMV elimination, most of the inflammatory signs are reverted, 12 h post‐injection. However, leukocytes in bronchoalveolar lavage fluid are increased as a late reaction. Taken together, these results suggest that OMVs are effective mediators of long distance communication in vivo.  相似文献   
5.
Cases of isolated hepatic tuberculosis (TB) are rare. The diagnosis is often delayed or missed because of nonspecific symptoms and laboratory findings. Besides, the disease is extremely rare even in a country where TB is an alarming public health problem. This report demonstrates the difficulty in correctly diagnosing local hepatic TB. We report the case of a 62‐year‐old male patient with end‐stage renal disease treated with hemodialysis, who developed 2 months of abdominal distension and general anorexia, with hyperechoic hepatic lesions on ultrasound. Computed tomography suspected multiple liver tumors. The liver biopsy finally led to the diagnosis of TB of the liver without other involvements. We conclude that isolated hepatic TB is one of the rare forms of extrapulmonary TB in dialysis patients. A greater awareness of this rare clinical entity may prevent needless surgical interventions.  相似文献   
6.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms.  相似文献   
7.
刘喜武  董宁  刘宇巍 《石油物探》2015,(2):210-217,225
由于尺度的限制,利用地震方法进行裂缝参数定量表征一直是地球科学的难题。基于裂缝性孔隙介质动态等效理论的频变AVAZ反演方法给出了研究思路。首先介绍了裂缝性孔隙介质的等效介质理论研究进展,分析比较了各种裂缝性储层岩石静态等效介质模型和动态等效介质模型;然后给出了基于Chapman模型的裂缝参数和渗透率定量表征的正问题数学模型以及反演问题求解的方法和策略,以及基于模型数据的数值计算结果;最后讨论了频变AVAZ反演方法目前存在的问题和进一步研究方向。  相似文献   
8.
9.
In order to predict the wearing of stellite alloys,the related methods of rare metals data processing were discussed. The method of opposite degree(OD) algorithm was put forward to predict the wearing of stellite alloys.OD algorithm is based on prior numerical data, posterior numerical data and the opposite degree between numerical forecast data. To compare the performance of predicted results based on different algorithms, the back propagation(BP) and radial basis function(RBF) neural network methods were introduced. Predicted results show that the relative error of OD algorithm is smaller than those of BP and RBF neural network methods. OD algorithm is an effective method to predict the wearing of stellite alloys and it can be applied in practice.  相似文献   
10.
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