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   9533篇
  免费   619篇
  国内免费   108篇
电工技术   28篇
综合类   108篇
化学工业   2041篇
金属工艺   169篇
机械仪表   143篇
建筑科学   165篇
矿业工程   121篇
能源动力   547篇
轻工业   4220篇
水利工程   162篇
石油天然气   312篇
武器工业   1篇
无线电   313篇
一般工业技术   963篇
冶金工业   146篇
原子能技术   58篇
自动化技术   763篇
  2024年   73篇
  2023年   423篇
  2022年   659篇
  2021年   567篇
  2020年   504篇
  2019年   386篇
  2018年   318篇
  2017年   467篇
  2016年   511篇
  2015年   518篇
  2014年   624篇
  2013年   546篇
  2012年   611篇
  2011年   597篇
  2010年   432篇
  2009年   401篇
  2008年   171篇
  2007年   324篇
  2006年   251篇
  2005年   199篇
  2004年   90篇
  2003年   138篇
  2002年   173篇
  2001年   137篇
  2000年   83篇
  1999年   105篇
  1998年   103篇
  1997年   67篇
  1996年   80篇
  1995年   40篇
  1994年   34篇
  1993年   31篇
  1992年   26篇
  1991年   27篇
  1990年   22篇
  1989年   25篇
  1988年   60篇
  1987年   141篇
  1986年   108篇
  1985年   43篇
  1984年   23篇
  1983年   21篇
  1982年   12篇
  1981年   15篇
  1980年   10篇
  1979年   15篇
  1978年   18篇
  1976年   9篇
  1975年   5篇
  1972年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
借鉴生物神经内分泌免疫系统的协同进化机制,基于细胞因子网络平台提出了Web服务的合成方法.在细胞因子网络调控下的生物实体代理Web服务,构成为一个带有条件的米兰机单元,Web服务的合成可以转换为米兰机进化过程.生物实体通过消息匹配和条件约束形成细胞因子网络,Web服务的合成通过生物实体细胞因子网络支持.在服务协同进化过程中可以动态调整其合成的服务,完成服务的动态自组织合成和管理等工作.仿真结果表明该方法在环境动态变化时具有适应性.  相似文献   
62.
Crop yield is a key element in rural development and an indicator of national food security. A method that could estimate crop yield over large hilly areas would be highly desirable. Methods including high spatial resolution satellite imagery have the potential to achieve this objective. This paper describes a method of integrating QuickBird imagery with a production efficiency model (PEM) to estimate crop yield in Zhonglianchuan, a hilly area on Loess Plateau, China. In the PEM model, crop yield is a function of the photosynthetic active radiation (PAR), fraction of absorbed photosynthetically active radiation (fAPAR) and light-use efficiency (LUE). Based on the high spatial resolution QuickBird imagery, a land cover classification is used to attribute a class-specific LUE. The fAPAR is related to spectral vegetation indices (SVI), which can be derived from the satellite images. The LUE, fAPAR and incident PAR data were combined to estimate the crop yield. Farmer-reported crop yield data in 80 representative plots were used to validate the model output. The results indicated QuickBird imagery can improve the accuracy of predicted results relative to the Landsat TM image. The predicted yield approximated well with the data reported by the farmers (r2 = 0.86; n = 80). The spatial distributions of crop yield derived here also offers valuable information to manage agricultural production and understand ecosystem functioning.  相似文献   
63.
Brownfield redevelopment (BR) is an ongoing issue for governments, communities, and consultants around the world. It is also an increasingly popular research topic in several academic fields. Strategic decision support that is now available for BR is surveyed and assessed. Then a dominance-based rough-set approach is developed and used to classify cities facing BR issues according to the level of two characteristics, BR effectiveness and BR future needs. The data for the classification are based on the widely available results of a survey of US cities. The unique features of the method are its reduced requirement for preference information, its ability to handle missing information effectively, and the easily understood linguistic decision rules that it generates, based on a training classification provided by experts. The resulting classification should be a valuable aid to cities and governments as they plan their BR projects and budgets.  相似文献   
64.
Wilson's disease (WD) is characterized by excessive accumulation of intracellular copper in liver and extrahepatic tissues, leading to significant oxidative stress and tissue damage. To date, several diagnostic biomarkers for WD such as serum ceruloplasmin, serum or urine copper levels and copper content in liver have been identified. However, these biomarkers may not be convincing for the diagnosis in some WD patients. To identify additional novel diagnostic biomarkers, we compared the serum protein profiles of asymptomatic childhood WD patients (n=20), without neurologic manifestation or liver cirrhosis, with normal controls (n=13). Fourteen spots, five up‐regulated and nine down‐regulated (>2‐fold), were differentially expressed in WD patients in comparison to normal control on 2‐DE. Among them, three spots were down‐regulated in both male and female WD. MS/MS analysis revealed that the three spots were complement component C3, complement factor B and alpha‐2 macroglobulin. By comparative proteome analysis, complement component C3, complement factor B and alpha‐2 macroglobulin, which are related to oxidative stress and inflammation, turned out to be good candidates for novel diagnostic biomarkers for early stages of WD.  相似文献   
65.
Nonvolatile field‐effect transistor (FET) memories containing transition metal dichalcogenide (TMD) nanosheets have been recently developed with great interest by utilizing some of the intriguing photoelectronic properties of TMDs. The TMD nanosheets are, however, employed as semiconducting channels in most of the memories, and only a few works address their function as floating gates. Here, a floating‐gate organic‐FET memory with an all‐in‐one floating‐gate/tunneling layer of the solution‐processed TMD nanosheets is demonstrated. Molybdenum disulfide (MoS2) is efficiently liquid‐exfoliated by amine‐terminated polystyrene with a controlled amount of MoS2 nanosheets in an all‐in‐one floating‐gate/tunneling layer, allowing for systematic investigation of concentration‐dependent charge‐trapping and detrapping properties of MoS2 nanosheets. At an optimized condition, the nonvolatile memory exhibits memory performances with an ON/OFF ratio greater than 104, a program/erase endurance cycle over 400 times, and data retention longer than 7 × 103 s. All‐in‐one floating‐gate/tunneling layers containing molybdenum diselenide and tungsten disulfide are also developed. Furthermore, a mechanically‐flexible TMD memory on a plastic substrate shows a performance comparable with that on a hard substrate, and the memory properties are rarely altered after outer‐bending events over 500 times at the bending radius of 4.0 mm.  相似文献   
66.
Microfluidic systems have become a superior platform for explorations of fascinating fluidic physics at microscale as well as applications in biomedical devices, chemical reactions, drug delivery, etc. Exploitations of this platform are built upon the fundamental techniques of flow visualizations. However, the currently employed fluorescent materials for microfluidic visualization are far from satisfaction, which severely hinders their widespread applications. Here fluorescent carbon nanodots are documented as a game‐changer, applicable in versatile fluidic environment for the visualization in microfluidics with unprecedented advantages. One of the fastest fluorescent imaging speeds up to 2500 frames per second under a normal contionous wave (CW) laser line is achieved by adopting carbon nanodots in microfluidics. Besides better visualizations of the fluid or interface, fluorescent carbon nanodots‐based microparticles enable quantitative studies of high speed dynamics in fluids at microscale with a more than 90% lower cost, which is inaccessible by traditionally adopted fluorescent dye based seeding particles. The findings hold profound influences to microfluidic investigations and may even lead to revolutionary changes to the relevant industries.  相似文献   
67.
Aggregation induced emission (AIE) has attracted considerable interest for the development of fluorescence probes. However, controlling the bioconjugation and cellular labeling of AIE dots is a challenging problem. Here, this study reports a general approach for preparing small and bioconjugated AIE dots for specific labeling of cellular targets. The strategy is based on the synthesis of oxetane‐substituted AIEgens to generate compact and ultrastable AIE dots via photo‐crosslinking. A small amount of polymer enriched with oxetane groups is cocondensed with most of the AIEgens to functionalize the nanodot surface for subsequent streptavidin bioconjugation. Due to their small sizes, good stability, and surface functionalization, the cell‐surface markers and subcellular structures are specifically labeled by the AIE dot bioconjugates. Remarkably, stimulated emission depletion imaging with AIE dots is achieved for the first time, and the spatial resolution is significantly enhanced to ≈95 nm. This study provides a general approach for small functional molecules for preparing small sized and ultrastable nanodots.  相似文献   
68.
The issues of hydrogen generation and storage have hindered the widespread use and commercialization of hydrogen fuel cell vehicles.It is thus highly attractive,but the design and development of highly active non-noble-metal catalysts for on-demand hydrogen release from alkaline NaBH4 solution under mild conditions remains a key challenge.Herein,we describe the use of CoP nanowire array integrated on a Ti mesh (CoP NA/Ti) as a three-dimensional (3D) monolithic catalyst for efficient hydrolytic dehydrogenation of NaBH4 in basic solutions.The CoP NA/Ti works as an on/off switch for on-demand hydrogen generation at a rate of 6,500 mL/(min.g) and a low activation energy of 41 kJ/mol.It is highly robust for repeated usage after recycling,without sacrificing catalytic performance.Remarkably,this catalyst also performs efficiently for the hydrolysis of NH3BH3.  相似文献   
69.
70.
《工程(英文)》2017,3(5):731-737
Due to increasing safety concerns regarding human consumption of fish products, an increasing number of medicinal chemicals are prohibited from use in aquaculture. As a result, Chinese herbal medicines are being increasingly used, coining the use of the term “green medicine.” Research shows that Chinese herbal medicines have many beneficial effects on fish, including growth promotion, enhancement of disease resistance, and improvement in meat quality. Many effective ingredients have been discovered in Chinese herbal medicines, which function to promote feed intake, improve meat flavor, and increase digestive enzyme activity. They also regulate and participate in processes that improve the specific and non-specific immunity of fish; however, the composition of Chinese herbal medicines is very complex and it is often difficult to identify the effective ingredients. This article reviews the latest research and application progress in Chinese herbal medicines regarding growth and feed utilization, immunity and disease resistance, and the meat quality of cultured fish. It also discusses research on the chemical constituents of classical Chinese medicinal herbs and problems with the application of Chinese herbal medicines in fish culture. This article concludes by proposing that future studies on Chinese herbal medicines should focus on how to cheaply refine and extract the effective ingredients in classical Chinese medicinal herbs, as well as how to use them efficiently in aquaculture.  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