首页 | 官方网站   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   3304篇
  免费   120篇
  国内免费   9篇
工业技术   3433篇
  2023年   21篇
  2022年   32篇
  2021年   69篇
  2020年   41篇
  2019年   37篇
  2018年   72篇
  2017年   68篇
  2016年   111篇
  2015年   74篇
  2014年   102篇
  2013年   139篇
  2012年   149篇
  2011年   196篇
  2010年   113篇
  2009年   159篇
  2008年   146篇
  2007年   130篇
  2006年   135篇
  2005年   110篇
  2004年   110篇
  2003年   66篇
  2002年   83篇
  2001年   51篇
  2000年   60篇
  1999年   61篇
  1998年   80篇
  1997年   74篇
  1996年   66篇
  1995年   66篇
  1994年   56篇
  1993年   48篇
  1992年   38篇
  1991年   35篇
  1990年   29篇
  1989年   26篇
  1988年   24篇
  1987年   24篇
  1986年   18篇
  1985年   36篇
  1984年   27篇
  1983年   37篇
  1982年   28篇
  1981年   31篇
  1980年   30篇
  1979年   23篇
  1978年   20篇
  1977年   26篇
  1976年   36篇
  1974年   15篇
  1968年   13篇
排序方式: 共有3433条查询结果,搜索用时 328 毫秒
991.
The enantiomeric distribution of 3-mercaptohexanol (1) and 3-methylthiohexanol (2) in yellow and purple passion fruits was determined by capillary gas chromatography (GC) using two different chiral stationary phases and a flame photometric detector. The results were confirmed by enantioselective capillary GC combined with mass spectrometric detection.1 shows an enrichment of the (S)-enantiomer, but the enantiomeric purity varies in a wide range. Irrespective from the enantiomeric distribution of1, 2 was detected with high enantiomeric purity in favour of the (S)-enantiomer. Using the method presented the addition of synthetic, racemic2 is easily detected.  相似文献   
992.
We report transverse-field muon-spin-rotation experiments carried out on Tl2Ba2CuO6+ . This system spans the whole overdoped regime, andT c is reduced by excess oxygen doping, which increases the normal-state carrier concentration. In the heavily overdoped regime(0) is found to scale linearly with the superconducting critical temperatureT c , similar to the behavior previously observed for other cuprates in the underdoped regime. However, for the overdoped region one has to explain the reduction of 0, thus the increase of the magnetic penetration depth, in spite of an increasing normal-state carrier concentration. We discuss some possible explanations for this behavior.  相似文献   
993.
Supporting learning using external representations   总被引:1,自引:0,他引:1  
  相似文献   
994.
Phase relations in the ZrO2–LaO1.5 system were studied experimentally in the temperature range from 1673 to 1973 K. X-ray diffraction and scanning electron microscopy were employed to obtain the structural information and the compositions of the tetragonal and pyrochlore (La2Zr2O7) phases. The solubility of LaO1.5 in the tetragonal phase was determined to be very small. The homogeneity range of the pyrochlore phase is estimated to be less than 2 mol% at 1973 K, and less than 1 mol% at 1673 K according to the present work. Based on the experimental results obtained in this work, as well as the available phase diagram and thermodynamic data in literature, a self-consistent thermodynamic assessment was carried out by using the ionic sublattice solution model.  相似文献   
995.
Pervasive Games are innovative game models based on information and communication technologies which merge the real world and the virtual world. The paper describes design and application of a technical platform supporting cross-media communication and comfortable modelling of complex interaction patterns which enables the implementation of pervasive games with mass impact. In an empirical study with 102 students a pervasive game was compared with a conventional case study in respect to the learning process and learning results. It revealed that the game relatively leads to higher energetic activation, more positive emotions, more positive attitudes towards learning content, and more efficient knowledge transfer.  相似文献   
996.
This paper concerns hybrid systems subject to discrete-event supervisory control. It investigates the discrete reachability, where the hybrid system should be moved from a discrete initial state z init into a given discrete goal state z goal by a sequence of discrete inputs. The reachability analysis is carried out in three steps. First, a discrete-event model of the hybrid system is set up. Stochastic automata are used to describe all state sequences which may be generated by the hybrid system. Such a model is called complete. Second, methods for the reachability analysis of stochastic automata are elaborated which concern a weak and a strong condition for reachability. Third, these methods are applied to the hybrid system. It is shown that the reachability of the automaton implies the discrete reachability of the hybrid system, because the model is complete. Therefore, the weak and the strong condition for reachability of the stochastic automaton yield a necessary and a sufficient condition for discrete reachability of the hybrid system.  相似文献   
997.
In Toponomics, the function protein pattern in cells or tissue (the toponome) is imaged and analyzed for applications in toxicology, new drug development and patient-drug-interaction. The most advanced imaging technique is robot-driven multi-parameter fluorescence microscopy. This technique is capable of co-mapping hundreds of proteins and their distribution and assembly in protein clusters across a cell or tissue sample by running cycles of fluorescence tagging with monoclonal antibodies or other affinity reagents, imaging, and bleaching in situ. The imaging results in complex multi-parameter data composed of one slice or a 3D volume per affinity reagent. Biologists are particularly interested in the localization of co-occurring proteins, the frequency of co-occurrence and the distribution of co-occurring proteins across the cell. We present an interactive visual analysis approach for the evaluation of multi-parameter fluorescence microscopy data in toponomics. Multiple, linked views facilitate the definition of features by brushing multiple dimensions. The feature specification result is linked to all views establishing a focus+context visualization in 3D. In a new attribute view, we integrate techniques from graph visualization. Each node in the graph represents an affinity reagent while each edge represents two co-occurring affinity reagent bindings. The graph visualization is enhanced by glyphs which encode specific properties of the binding. The graph view is equipped with brushing facilities. By brushing in the spatial and attribute domain, the biologist achieves a better understanding of the function protein patterns of a cell. Furthermore, an interactive table view is integrated which summarizes unique fluorescence patterns. We discuss our approach with respect to a cell probe containing lymphocytes and a prostate tissue section.  相似文献   
998.
The Oldman River Basin (OMRB), located in southern Alberta (Canada), with an area of 28,200 km2, is mainly forested in its western part and is used for intensive agriculture in its eastern part. The objective of this paper is to estimate the nitrogen (N) budget for the Oldman River Basin as a whole and its sub-basins, and to discuss differences in the N budget between various sub-basins. Better knowledge of the N budget in this watershed may be also utilized for understanding N dynamics in similar watersheds within semi-arid climatic regions. The model used is a mass-balance spreadsheet model that takes into account N inputs and N export through surface water. During the last 120 years, anthropogenic N inputs to the OMRB have increased circa 40 fold. By the end of the 20th century, the OMRB received an annual N input of about 5174 kg N km−2 yr−1, whereas only about 25 kg N km−2 yr−1 were exported via riverine flow. For the sub-basins, annual N inputs ranged from 2516 to 19011 kg N km−2 yr−1, and annual N export via riverine flows varied between 6 and 277 kg N km−2 yr−1. Over 85% of total N inputs to the OMRB are due to anthropogenic activities, including manure (55%), synthetic fertilizer (27%), and N fixation on agricultural lands (4%). Sewage accounted for less than 1%, and N inputs from atmospheric deposition and fixation in forests represented 6 and 8% respectively. Despite increasing anthropogenic N inputs, N export with riverine flow currently accounts for only 1% of the inputs, indicating that most of the N inputs are currently retained in the OMRB or are re-emitted into the atmosphere.  相似文献   
999.
The present study was conducted within the frame of the Sino-German project "Rehabilitation of degraded land ecosystems in the mountainous area of the Southern Shaanxi Province,China".The study deals with the assessment of the potential of oak coppices as well as the evaluation of the socioeconomic conditions in the Shangnan County.The ultimate objective of the study is to provide recommendations on the sustainable management of forest resources,which does not only aim to improve the environmental situation but also to satisfy the demands of the local rural residents.The study was based on 30 samples of oak coppices stands,which were randomly selected within an area of a size of 20 km × 20 km.In each selected stand,the mature stand and understory regeneration were investigated in depth.For the socio-economic survey,175 households from 11 villages were randomly selected.Results revealed that the stocking capacity of the cork oak coppices reaches 120 m3/ha in average at the older age classes(≥25 years) even after frequent timber harvest.High potential for productivity was indicated by the availability of sufficient vigorous individuals at different age classes.In addition,the understory regeneration was sufficient in density(19,000±133 individual/ha) and consisted of diverse valuable native-species(17 species within a survey area of 400 m2).The results of the assessment of the oak coppices provided possibilities for some practices that can be recommended towards sustainable management of such stands.On the other hand,results of the socioeconomic study showed a high degree of acceptance among the local inhabitants(79% of the total households) to change traditional land use,providing an enhancement of their economic situation.  相似文献   
1000.
Energy‐efficient implementation techniques for virtual machines (VMs) have received little attention yet: conventional wisdom claims that VMs have a diametrical effect on energy consumption, and VM‐based applications are therefore short‐lived. In this paper, we argue that bytecode interpretation is affordable if we synthesize VMs specifically for energy efficiency. We present TinyVM, an execution infrastructure that seamlessly integrates with C and nesC/TinyOS‐based programming environments. TinyVM achieves high code density through the use of compressed bytecode as the primary program representation. Compressed bytecode allows rapid application deployment with low communication overhead. TinyVM executes compressed bytecode in place, which eliminates the need for a decompression stage and thereby reduces memory consumption on sensor nodes. Our infrastructure automates the creation of energy‐efficient application‐specific VMs. Applications are partitioned in machine code, bytecode, and VM instruction set extensions. Partitioning is manually controlled and/or fully guided by a discrete optimization problem that produces a partitioning with lowest energy consumption for a given program size limit. We provide experimental results for sensor network benchmarks and for selected applications on various CPU architectures including Atmega128‐based motes and the ARM‐based Intel iMote2. TinyVM has been released under the GNU General Public License. Copyright © 2011 John Wiley & Sons, Ltd.  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-23

京公网安备 11010802026262号