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   572篇
  免费   36篇
  国内免费   5篇
电工技术   3篇
综合类   5篇
化学工业   119篇
金属工艺   8篇
机械仪表   23篇
建筑科学   7篇
能源动力   46篇
轻工业   61篇
水利工程   5篇
石油天然气   11篇
无线电   59篇
一般工业技术   119篇
冶金工业   19篇
原子能技术   2篇
自动化技术   126篇
  2023年   12篇
  2022年   31篇
  2021年   82篇
  2020年   39篇
  2019年   28篇
  2018年   40篇
  2017年   35篇
  2016年   35篇
  2015年   21篇
  2014年   28篇
  2013年   41篇
  2012年   39篇
  2011年   35篇
  2010年   13篇
  2009年   14篇
  2008年   16篇
  2007年   12篇
  2006年   13篇
  2005年   13篇
  2004年   13篇
  2003年   11篇
  2002年   3篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   2篇
  1997年   2篇
  1996年   5篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1991年   4篇
  1990年   2篇
  1988年   3篇
  1986年   2篇
  1981年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有613条查询结果,搜索用时 15 毫秒
101.
We describe a novel two‐photon fluorescence microscopy system capable of producing high‐quality second harmonic generation (SHG) images in thick turbid media by using an innovative detection system. This novel detection system is capable of detecting photons from a very large surface area. This system has proven effective in providing images of thick turbid samples, both biological and artificial. Due to its transmission detection geometry, the system is particularly suitable for detecting SHG signals, which are generally forward directed. In this article, we present comparative data acquired simultaneously on the same sample with the forward and epidetection schemes. Microsc. Res. Tech. 77:368–373, 2014. © 2014 Wiley Periodicals, Inc.  相似文献   
102.
103.
The growth and ordering of C60 molecules on the WO2/W(110) surface have been studied by low-temperature scanning tunnelling microscopy and spectroscopy (STM and STS), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. The results indicate the growth of a well-ordered C60 layer on the WO2/W(110) surface in which the molecules form a close-packed hexagonal structure with a unit cell parameter equal to 0.95 nm. The nucleation of the C60 layer starts at the substrate’s inner step edges. Low-temperature STM of C60 molecules performed at 78 K demonstrates well-resolved molecular orbitals within individual molecules. In the C60 monolayer on the WO2/W(110) surface, the molecules are aligned in one direction due to intermolecular interaction, as shown by the ordered molecular orbitals of individual C60. STS data obtained from the C60 monolayer on the WO2/W(110) surface are in good agreement with DFT calculations.  相似文献   
104.
Poly(ε‐caprolactone) (PCL)‐based thermoreversible networks with self‐healing properties were prepared through Diels–Alder (DA) and retro‐DA reactions. Bis‐ or Tris‐maleimide compounds and a series of copolymer(caprolactone‐diene) PCLXFY (X: degree of polymerization and Y: furan‐average functionality) with Y between 2.4 and 4.9 were used. The successive sequences of formation and dissociation of polycaprolactone networks via DA and retro‐DA reactions were observed repeatedly by dynamic mechanical analyses (DMA) and their gel‐temperatures determined. The cross‐linking densities, thermal properties, and thermal reversibility of the PCLXFY/multimaleimide polymers have been modulated by the structure and functionalities of the used diene and dienophile moieties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   
105.
We proposed an arrayed waveguide granting (AWG) based 10 Gbps full duplex wavelength division multiplexing passive optical network (WDM-PON) utilizing a retum-to-zero differential phase shift keying (R...  相似文献   
106.
Aamir D. Abid 《Combustion and Flame》2009,156(10):1862-17251
A burner-stabilized, stagnation flame technique is introduced. In this technique, a previously developed sampling probe is combined with a water-cooled circular plate such that the combination simultaneously acts as a flow stagnation surface and soot sample probe for mobility particle sizing. The technique allows for a rigorous definition of the boundary conditions of the flame with probe intrusion and enables less ambiguous comparison between experiment and model. Tests on a 16.3% ethylene-23.7% oxygen-argon flame at atmospheric pressure show that with the boundary temperatures of the burner and stagnation surfaces accurately determined, the entire temperature field may be reproduced by pseudo one-dimensional stagnation reacting flow simulation using these temperature values as the input boundary conditions. Soot particle size distribution functions were determined for the burner-stabilized, stagnation flame at several burner-to-stagnation surface separations. It was found that the tubular probe developed earlier perturbs the flow and flame temperature in a way which is better described by a one-dimensional stagnation reacting flow than by a burner-stabilized flame free of probe intrusion.  相似文献   
107.
The synthesis of N‐heteroaryl(trifluoromethyl)hydroxyalkanoic acid esters by solid acid‐catalyzed Friedel–Crafts hydroxyalkylation of indoles and pyrroles with ethyl 3,3,3‐trifluoropyruvate and ethyl 4,4,4‐trifluoroacetoacetate is described. The inexpensive and readily available K‐10 montmorillonite is found to be an efficient catalyst for the synthesis of a wide variety of trifluoromethylated indol‐3‐yl‐ and pyrrol‐2‐yl‐hydroxypropionic and ‐butanoic acid esters. Using a series of substituted indoles and pyrroles the corresponding products were isolated in excellent yield (up to 98%) and 100% selectivity under mild experimental conditions, during very short reaction times. Beyond these, the ease of product isolation, catalyst stability and handling make this process an attractive, environmentally benign alternative for the synthesis of the target compounds.  相似文献   
108.
The advent of healthcare information management systems (HIMSs) continues to produce large volumes of healthcare data for patient care and compliance and regulatory requirements at a global scale. Analysis of this big data allows for boundless potential outcomes for discovering knowledge. Big data analytics (BDA) in healthcare can, for instance, help determine causes of diseases, generate effective diagnoses, enhance QoS guarantees by increasing efficiency of the healthcare delivery and effectiveness and viability of treatments, generate accurate predictions of readmissions, enhance clinical care, and pinpoint opportunities for cost savings. However, BDA implementations in any domain are generally complicated and resource-intensive with a high failure rate and no roadmap or success strategies to guide the practitioners. In this paper, we present a comprehensive roadmap to derive insights from BDA in the healthcare (patient care) domain, based on the results of a systematic literature review. We initially determine big data characteristics for healthcare and then review BDA applications to healthcare in academic research focusing particularly on NoSQL databases. We also identify the limitations and challenges of these applications and justify the potential of NoSQL databases to address these challenges and further enhance BDA healthcare research. We then propose and describe a state-of-the-art BDA architecture called Med-BDA for healthcare domain which solves all current BDA challenges and is based on the latest zeta big data paradigm. We also present success strategies to ensure the working of Med-BDA along with outlining the major benefits of BDA applications to healthcare. Finally, we compare our work with other related literature reviews across twelve hallmark features to justify the novelty and importance of our work. The aforementioned contributions of our work are collectively unique and clearly present a roadmap for clinical administrators, practitioners and professionals to successfully implement BDA initiatives in their organizations.   相似文献   
109.
The objective of this research is to construct a type-II heterojunction interface for effective photoelectrochemical (PEC) water splitting for hydrogen generation. A series of ZnSe/g-C3N4 heterojunctions is prepared by ultrasonication procedure and tested for PEC water splitting for the first time. The successful formation of ZnSe/g-C3N4 is confirmed by phase, morphological and optical analysis. Linear sweep voltammetry of 0.05 ZG (0.05% ZnSe/g-C3N4) showed a six-fold higher photocurrent density of 500 μA than g-C3N4. These results are supported by the Tafel slopes and PL (photoluminescence spectroscopy) studies by showing the smallest slope and lesser electron-hole recombination for 0.05 ZG. Increased lifetime of 107 ms and a higher donor density of 3.6 × 1019 cm?3 for 0.05 ZG is observed. The smallest semicircle for 0.05 ZG in EIS implies the least charge transfer resistance among the prepared heterojunctions. All the results comply with each other showing the successful formation of type-II heterojunction for enhanced PEC water splitting.  相似文献   
110.
Seed micromorphology of 13 species, belonging to four genera of subfamily Alsinoideae (Caryophyllaceae) were investigated with scanning electron microscopy (SEM), in order to assess their diagnostic significance at generic level and provide additional evidence on species delimitation, as well as correct identification and phylogenetic position. Genera and species of subfamily Alsinoideae exhibit great variation in ultrastructure and a high diversity of novel micromorphological characters were observed. Variation in seed shape, color, hilum, anticlinal wall, epidermal cell, cell surface, margins, and quantitative characters as length and width were studied in detail, compared, illustrated, and their taxonomic significant were discussed. Seed shapes of the species were classified as reniform, round, angular, subcircular, subreniform, and elliptical pyriform, with sub‐central, central, basal, and nearly basal hilum. Wavy, irregular, tetragonal, and elongated epidermal cells structure has been observed as an exomorphological character. The present findings show that the micromorphology of subfamily Alsinoideae provides taxonomic information and is helpful to distinguish different species. The results also explained that SEM morphology of seeds provide important data about affinity among taxa and give potential characters in delimitation of members of subfamily Alsinoideae at generic and species level. A principal component analysis allowed to highlight the most outsiders among seed micromorphology with a possible explanation. Taxonomic keys were developed based on micromorphological characters to delimit the species and useful for their quick identification within subfamily Alsinoideae.  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