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   2873篇
  免费   149篇
  国内免费   1篇
电工技术   12篇
综合类   3篇
化学工业   743篇
金属工艺   31篇
机械仪表   16篇
建筑科学   132篇
矿业工程   4篇
能源动力   47篇
轻工业   489篇
水利工程   32篇
石油天然气   19篇
武器工业   1篇
无线电   137篇
一般工业技术   485篇
冶金工业   503篇
原子能技术   17篇
自动化技术   352篇
  2024年   15篇
  2023年   26篇
  2022年   78篇
  2021年   122篇
  2020年   66篇
  2019年   47篇
  2018年   59篇
  2017年   88篇
  2016年   86篇
  2015年   85篇
  2014年   109篇
  2013年   157篇
  2012年   162篇
  2011年   195篇
  2010年   148篇
  2009年   129篇
  2008年   160篇
  2007年   159篇
  2006年   144篇
  2005年   102篇
  2004年   87篇
  2003年   85篇
  2002年   67篇
  2001年   54篇
  2000年   33篇
  1999年   51篇
  1998年   47篇
  1997年   46篇
  1996年   39篇
  1995年   26篇
  1994年   35篇
  1993年   37篇
  1992年   29篇
  1991年   19篇
  1990年   28篇
  1989年   22篇
  1988年   20篇
  1987年   21篇
  1986年   17篇
  1985年   21篇
  1984年   8篇
  1983年   16篇
  1982年   9篇
  1980年   14篇
  1979年   6篇
  1978年   5篇
  1977年   10篇
  1974年   7篇
  1973年   4篇
  1960年   5篇
排序方式: 共有3023条查询结果,搜索用时 15 毫秒
51.
Multimedia Tools and Applications - Improving the ability to interact through voice with a robot is still a challenge especially in real environments where multiple speakers coexist. This work has...  相似文献   
52.
53.
Materials design principles of ancient fish armour   总被引:1,自引:0,他引:1  
Knowledge of the structure-property-function relationships of dermal scales of armoured fish could enable pathways to improved bioinspired human body armour, and may provide clues to the evolutionary origins of mineralized tissues. Here, we present a multiscale experimental and computational approach that reveals the materials design principles present within individual ganoid scales from the 'living fossil' Polypterus senegalus. This fish belongs to the ancient family Polypteridae, which first appeared 96 million years ago during the Cretaceous period and still retains many of their characteristics. The mechanistic origins of penetration resistance (approximating a biting attack) were investigated and found to include the juxtaposition of multiple distinct reinforcing composite layers that each undergo their own unique deformation mechanisms, a unique spatial functional form of mechanical properties with regions of differing levels of gradation within and between material layers, and layers with an undetectable gradation, load-dependent effective material properties, circumferential surface cracking, orthogonal microcracking in laminated sublayers and geometrically corrugated junctions between layers.  相似文献   
54.
Sample pretreatment is the most important procedure to remove the matrix for interfacing with mass spectrometry (MS). Additionally, for the samples with low concentration, the process of preconcentration is required before MS analysis. We have newly developed a solid-phase extraction stationary phase based on C60-fullerene covalently bound to silica for purification of biomolecules of different characteristics. Silica particles of different porosity are modified with aminopropyl linker and then covalently bound to C60-fullerenoacetic acid or C60-epoxyfullerenes. The developed materials have been successfully applied as an alternative to commercially available reversed-phase materials for solid-phase extraction. C60-fullerene silica is able to retain small and hydrophilic molecules like phosphopeptides, which can be easily lost by reversed-phase sorbents. The novel materials are applied for desalting and preconcentration of proteins and peptides, especially phosphopeptides. In addition, the C60-fullerene silica is applied for the solid-phase extraction of selected flavonoids with recoveries of approximately 99%. The recoveries are compared with the commercially available solid-phase extraction materials.  相似文献   
55.
The influence of the composition and the relative humidity on the properties of pharmaceutical compacts prepared from mixtures of three excipients and three super-disintegrants was evaluated. Various amounts of super-disintegrant and different conditions of relative humidity during the storage were used to study mechanistically the disintegration process and to connect it to compact's mechanical properties. Three point single beam test was used to measure tensile strength and Young's modulus of compacts containing various amount of disintegrant and stored under various relative humidity. The presence of moisture within pharmaceutical compacts containing a disintegrant influences drastically their mechanical properties. Then, the results are related to micro-cracks visualized by MEB.  相似文献   
56.
Bone and cartilage generation by three-dimensional scaffolds is one of the promising techniques in tissue engineering. One approach is to generate histologically and functionally normal tissue by delivering healthy cells in biocompatible scaffolds. These scaffolds provide the necessary support for cells to proliferate and maintain their differentiated function, and their architecture defines the ultimate shape. Rapid prototyping (RP) is a technology by which a complex 3-dimensional (3D) structure can be produced indirectly from computer aided design (CAD). The present study aims at developing a 3D organic-inorganic composite scaffold with defined internal architecture by a RP method utilizing a 3D printer to produce wax molds. The composite scaffolds consisting of chitosan and hydroxyapatite were prepared using soluble wax molds. The behaviour and response of MC3T3-E1 pre-osteoblast cells on the scaffolds was studied. During a culture period of two and three weeks, cell proliferation and in-growth were observed by phase contrast light microscopy, histological staining and electron microscopy. The Giemsa and G?m?ri staining of the cells cultured on scaffolds showed that the cells proliferated not only on the surface, but also filled the micro pores of the scaffolds and produced extracellular matrix within the pores. The electron micrographs showed that the cells covering the surface of the struts were flattened and grew from the periphery into the middle region of the pores.  相似文献   
57.
INTRODUCTION: Medical diagnostic tests are evaluated based on measures of sensitivity (Sn), specificity (Sp), and likelihood ratios (LR). These procedures are limited in the event of a biased gold standard or missing data. Interpretations of these measures are frequently inappropriate. PURPOSE: The Rasch measurement model (RMM) was examined as a method to provide evidence of diagnostic test utility in order to overcome the limitations of Sn, Sp, and LR. METHODS: Patients suspected of a knee ligament tear (n = 825) were studied, by evaluating four diagnostic tests. The RMM probability estimates for each test were compared to estimates of Sn, Sp, and LR. RESULTS: The RMM provided probability estimates for the diagnosis that were comparable to likelihood ratios. These probability estimates correlated with the estimates of Sn, Sp, and LR. The RMM estimates were not affected by missing data. DISCUSSION: The RMM may provide an alternative means to study the utility of medical diagnostic tests to estimate the probability of disease presence/absence.  相似文献   
58.
Microsystem Technologies - State-of-the-art neurosurgery intervention relies heavily on information from tissue imaging taken at a pre-operative stage. However, the data retrieved prior to...  相似文献   
59.
It has been demonstrated that object-oriented frameworks can bring all kinds of advantages to application developers. To gain the advantages, application developers have to follow the framework-based development process. One step of the process is to integrate new components for framework extension. This is defined as a framework extension task in this work. In this task, application developers have to (1) retrieve examples, (2) acquire necessary documents, which are defined as the documents containing example adaptation information, and (3) adapt examples. Currently, acquiring necessary documents requires a lot of time because it is achieved through manually searching the Internet. Although there are many approaches to correctly acquiring those documents, the focus is never on time reduction. To satisfy the new criterion, we find the following challenging issues: (1) the dynamics of the valid document version, and (2) the uncertainty of the relevant necessary documents. The first issue is that the valid document version varies according to the framework version under which the retrieved example is workable. The second one is that the relevant necessary documents cannot be decided until a specific necessary document is specified. To resolve those two issues, a Self-adaptive Document link provision system, named SeaDoc, is provided in this work. SeaDoc resolves the dynamics by dynamically constructing document links with the corresponding valid document version. SeaDoc also resolves the uncertainty by adaptively selecting highly relevant document links. The experimental results show that SeaDoc reduces the time by 73 and 83 % compared with other two approaches.  相似文献   
60.
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