全文获取类型
收费全文 | 63074篇 |
免费 | 7952篇 |
国内免费 | 4992篇 |
专业分类
电工技术 | 4848篇 |
技术理论 | 10篇 |
综合类 | 7284篇 |
化学工业 | 7622篇 |
金属工艺 | 2263篇 |
机械仪表 | 3150篇 |
建筑科学 | 4359篇 |
矿业工程 | 2120篇 |
能源动力 | 3181篇 |
轻工业 | 3987篇 |
水利工程 | 1430篇 |
石油天然气 | 2414篇 |
武器工业 | 624篇 |
无线电 | 9310篇 |
一般工业技术 | 6433篇 |
冶金工业 | 3427篇 |
原子能技术 | 712篇 |
自动化技术 | 12844篇 |
出版年
2024年 | 275篇 |
2023年 | 1084篇 |
2022年 | 1781篇 |
2021年 | 2017篇 |
2020年 | 2293篇 |
2019年 | 2034篇 |
2018年 | 1829篇 |
2017年 | 2307篇 |
2016年 | 2498篇 |
2015年 | 2668篇 |
2014年 | 4227篇 |
2013年 | 4147篇 |
2012年 | 5091篇 |
2011年 | 5438篇 |
2010年 | 4140篇 |
2009年 | 4156篇 |
2008年 | 3948篇 |
2007年 | 4467篇 |
2006年 | 3870篇 |
2005年 | 3000篇 |
2004年 | 2378篇 |
2003年 | 2195篇 |
2002年 | 1701篇 |
2001年 | 1374篇 |
2000年 | 1215篇 |
1999年 | 986篇 |
1998年 | 855篇 |
1997年 | 715篇 |
1996年 | 623篇 |
1995年 | 517篇 |
1994年 | 447篇 |
1993年 | 327篇 |
1992年 | 317篇 |
1991年 | 241篇 |
1990年 | 161篇 |
1989年 | 132篇 |
1988年 | 108篇 |
1987年 | 68篇 |
1986年 | 54篇 |
1985年 | 53篇 |
1984年 | 41篇 |
1983年 | 33篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1964年 | 8篇 |
1961年 | 8篇 |
1955年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
A 320×240 CMOS image sensor is demonstrated,which is implemented by a standard 0.6 μm 2P2M CMOS process.For reducing the chip area,each 2×2-pixel block shares a sample/hold circuit,analog-to-digital converter and 1-b memory.The 2×2 pixel pitch has an area of 40 μm×40 μm and the fill factor is about 16%.While operating at a low frame rate,the sensor dissipates a very low power by power-management circuit making pixel-level comparators in an idle state.A digital correlated double sampling,which eliminates fixed pattern noise,improves SNR of the sensor, and multiple sampling operations make the sensor have a wide dynamic range. 相似文献
132.
133.
The wettability of the lithium surface by liquid alkali metals Na, K and Rb is investigated for the first time by the sessile drop method in an all-soldered instrument under conditions of a high vacuum. The presence of the temperature threshold of wetting is found in Li–Na and Li–K systems at temperatures of 325°C and 160°C, respectively. A conclusion is drawn that an abrupt decrease in wetting angles in the investigated systems is associated with a marked decrease in the interfacial tension at lithium-lithium, lithium-potassium, and lithium--rubidium interfaces owing to the beginning of a noticeable mutual solubility of the components at relatively high temperatures. 相似文献
134.
Ferdinando Auricchio Lorenza Petrini 《International journal for numerical methods in engineering》2004,61(6):807-836
An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
135.
Abstract: This paper presents a novelty detection-based technique to identify core material properties of honeycombs and cellular structures. A numerical model (finite element) representing full scale and/or reduced size of the cellular solid is used to generate transmissibilities between topological homologous points at cells in different locations. In order to make the procedure robust against noise, these transmissibilities are artificially corrupted. This step is representative of a series of experimentally obtained measurements which automatically return information relating to the size and shape of data noise along with the mean measurement. The next stage, both in this paper and in the proposal for the experimental approach, is to generate several further sets of transmissibilities from the finite element model; the only difference being that the core material properties are altered from the original values. A novelty detection framework is then adopted to find a similarity measure between each of these 'test' transmissibilities and the original set thereby identifying the material properties. Although this work is concerned with identifying only one material property, the methodology extends to identifying several properties. 相似文献
136.
1 Introduction Acquiring knowledge is constantly encountered in the mechanical product evaluation process, such as during setting up evaluation index system and determining evaluation knowledge. The most useful expression form of knowledge is production rule whenever concerning the field knowledge or decision knowledge. How to effectively acquire and express the knowledge becomes the issue that the evaluation work must solve at first. One of an important application of the rough set theory is … 相似文献
137.
138.
A revision algorithm is a learning algorithm that identifies the target concept, starting from an initial concept. Such an algorithm is considered efficient if its complexity (in terms of the resource one is interested in) is polynomial in the syntactic distance between the initial and the target concept, but only polylogarithmic in the number of variables in the universe. We give an efficient revision algorithm in the model of learning with equivalence and membership queries for threshold functions, and some negative results showing, for instance, that threshold functions cannot be revised efficiently from either type of query alone. The algorithms work in a general revision model where both deletion and addition type revision operators are allowed. 相似文献
139.
Y. MURAKAMI K. TAKAHASHI R. KUSUMOTO 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(6):523-531
ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔKIIth. The relationship ΔKIIth > ΔKIth caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack. 相似文献
140.
KMLS型立式砂泵的振动噪声产生原因及解决措施 总被引:1,自引:1,他引:0
针对KMLS型立式砂泵振动、噪声产生原因及其表现特征,提出了解决措施。通过对这些原因的分析研究,可以提供泵设计者和生产者在减少砂泵振动方面采取相应的措施,使KMLS型立式砂泵能更好的服务于用户。 相似文献