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   5739篇
  免费   431篇
  国内免费   5篇
电工技术   22篇
综合类   2篇
化学工业   1987篇
金属工艺   50篇
机械仪表   112篇
建筑科学   215篇
矿业工程   10篇
能源动力   154篇
轻工业   1813篇
水利工程   52篇
石油天然气   38篇
无线电   193篇
一般工业技术   705篇
冶金工业   209篇
原子能技术   10篇
自动化技术   603篇
  2024年   19篇
  2023年   92篇
  2022年   352篇
  2021年   398篇
  2020年   214篇
  2019年   236篇
  2018年   244篇
  2017年   250篇
  2016年   279篇
  2015年   207篇
  2014年   305篇
  2013年   454篇
  2012年   413篇
  2011年   444篇
  2010年   340篇
  2009年   334篇
  2008年   283篇
  2007年   256篇
  2006年   183篇
  2005年   141篇
  2004年   117篇
  2003年   94篇
  2002年   88篇
  2001年   46篇
  2000年   49篇
  1999年   54篇
  1998年   51篇
  1997年   44篇
  1996年   36篇
  1995年   17篇
  1994年   18篇
  1993年   16篇
  1992年   10篇
  1991年   8篇
  1990年   5篇
  1989年   21篇
  1988年   7篇
  1987年   11篇
  1986年   6篇
  1985年   7篇
  1984年   7篇
  1983年   2篇
  1982年   3篇
  1981年   1篇
  1980年   4篇
  1978年   4篇
  1977年   2篇
  1976年   3篇
排序方式: 共有6175条查询结果,搜索用时 15 毫秒
991.

In recent years, due to the drastic rise in the number of vehicles and the lack of sufficient infrastructure, traffic jams, air pollution, and fuel consumption have increased in cities. The optimization of timing for traffic lights is one of the solutions for the mentioned problems. Many methods have been introduced to deal with these problems, including reinforcement learning. Although a great number of learning-based methods have been used in traffic signal control, they suffer from poor performance and slow learning convergence. In this paper, a transfer learning-based method for traffic signal control has been proposed. Multi-agent system has also been used for modelling the traffic network and transfer learning has been used to make reinforcement learning agents transfer their experience to each other. Furthermore, a classifier has been utilized to classify the transferred experiences. The results show that using the proposed method leads to a significant improvement on average delay time and convergence time of the learning process.

  相似文献   
992.
The use of pointers presents serious problems for software productivity tools for software understanding, restructuring, and testing. Pointers enable indirect memory accesses through pointer dereferences, as well as indirect procedure calls (e.g., through function pointers in C). Such indirect accesses and calls can be disambiguated with pointer analysis. In this paper we evaluate the precision of one specific pointer analysis (the FA pointer analysis by Zhang et al.) for the purposes of call graph construction for C programs with function pointers. The analysis is incorporated in a production-strength code-browsing tool from Siemens Corporate Research in which the program call graph is used as a primary tool for code understanding.The FA pointer analysis uses an inexpensive, almost-linear, flow- and context-insensitive algorithm. To measure analysis precision, we compare the call graph constructed by this analysis with the most precise call graph obtainable by a large category of existing pointer analyses. Surprisingly, for all our data programs the FA analysis achieves the best possible precision. This result indicates that for the purposes of call graph construction, inexpensive pointer analyses may provide precision comparable to the precision of expensive pointer analyses.  相似文献   
993.
The ultimate strength of structures made of brittle materials—such as microconcrete—strongly depends on microstructural defects, the structure size, and the loading pattern. Probabilistic approaches allow one to take account of such dependencies. By using a Weibull model, cracking of ferrocement panels is analyzed. Provided the behavior of the reinforcement remains elastic, it is shown that the Weibull parameters identified on unreinforced microconcrete samples tested in flexure may be used to predict multiple cracking in ferrocement panels tested in tension. A key aspect of the analysis is related to the understanding and modeling of the stress heterogeneity effect on the local failure probability of unreinforced as well as reinforced microconcrete by the use of a so-called Weibull stress.  相似文献   
994.
We show the culicids collected in the Guajaibón zone, in Havana Province, in order to characterize the present population according to ecological parameters and the possible risk for man. We show that Aedes scapularis is numerically and ecologically dominant over the rest of the species that attack men, as well as the possible indirect influence of culicid populations in crab caves upon human beings.  相似文献   
995.
Although designed as a cross-platform parallel programming model, OpenCL remains mainly used for GPU programming. Nevertheless, a large amount of applications are parallelized, implemented, and eventually optimized in OpenCL. Thus, in this paper, we focus on the potential that these parallel applications have to exploit the performance of multi-core CPUs. Specifically, we analyze the method to systematically reuse and adapt the OpenCL code from GPUs to CPUs. We claim that this work is a necessary step for enabling inter-platform performance portability in OpenCL.  相似文献   
996.
997.
Context: Currently, there is an increasing interest of cosmetic industry on natural extracts. The inclusion of antioxidants in topical formulations can contribute to minimize oxidative stress in the skin, which has been associated with aging. Also, questions of sustainability are leading to the study of new cosmetic ingredients obtained from food by-products. Coffee Silverskin (CS) is a food by-product with established antioxidant activity that has not yet been incorporated into a topical formulation.

Objective: The aim of this study was to evaluate the physical and microbiological stabilities and antioxidant activity of a hand cream formulation containing 2.5% (w/w) of CS extract upon production and after 6 months of shelf-life and in vitro safety/cytotoxicity on skin cell lines after production.

Materials and methods: The in vitro cytotoxicity was evaluated with MTS and LDH assays, at different concentrations, in HaCaT and HFF-1 cells. Formulations were stored at 25?°C/65% RH and 40?°C/75% RH. Physical, microbiological, and antioxidant stabilities were evaluated by centrifugation, viscosity, total colony count, DPPH and total phenolic content (TPC).

Results: The hand cream containing 2.5% (w/w) of CS extract showed stable physical characteristics independently of the storage conditions. The DPPH activity and TPC of the CS formulation were significantly higher compared with those of the base formulation. However, during storage, the antioxidant activity decreases slightly. Microbiological quality was also confirmed. No cytotoxic effects were observed.

Conclusion: It is possible to suggest that this formulation is stable under extreme conditions and safe for topical use.  相似文献   
998.
999.
1000.
Lipolysis, lipid peroxidation, texture and rancid taste were investigated in Serrano hams processed under low, medium and high ripening temperature conditions (RTC) for 15 months. Medium RTC hams showed the highest contents of saturated and monounsaturated free fatty acids (FFAs) from month 5 to 15 and of polyunsaturated FFAs from month 7 to 12. The primary peroxidation index decreased during ripening in all hams, with higher levels for low RTC hams from month 5 onwards. Contrarily, the secondary peroxidation index increased during ripening in all hams, with higher levels for medium RTC hams from month 7 onwards. Texture parameters varied significantly among ham muscles. Shear force increased during ripening in all hams, with higher values for medium RTC hams, whereas cutting force was not influenced by RTC or ripening time. Rancid taste scarcely developed during ripening and was not affected by RTC.  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