全文获取类型
收费全文 | 3579篇 |
免费 | 212篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 55篇 |
综合类 | 2篇 |
化学工业 | 602篇 |
金属工艺 | 71篇 |
机械仪表 | 43篇 |
建筑科学 | 232篇 |
矿业工程 | 27篇 |
能源动力 | 88篇 |
轻工业 | 439篇 |
水利工程 | 27篇 |
石油天然气 | 17篇 |
无线电 | 309篇 |
一般工业技术 | 576篇 |
冶金工业 | 434篇 |
原子能技术 | 30篇 |
自动化技术 | 842篇 |
出版年
2023年 | 36篇 |
2022年 | 33篇 |
2021年 | 104篇 |
2020年 | 73篇 |
2019年 | 105篇 |
2018年 | 132篇 |
2017年 | 118篇 |
2016年 | 152篇 |
2015年 | 113篇 |
2014年 | 153篇 |
2013年 | 245篇 |
2012年 | 209篇 |
2011年 | 238篇 |
2010年 | 178篇 |
2009年 | 175篇 |
2008年 | 205篇 |
2007年 | 181篇 |
2006年 | 156篇 |
2005年 | 127篇 |
2004年 | 122篇 |
2003年 | 89篇 |
2002年 | 114篇 |
2001年 | 44篇 |
2000年 | 47篇 |
1999年 | 44篇 |
1998年 | 73篇 |
1997年 | 55篇 |
1996年 | 51篇 |
1995年 | 34篇 |
1994年 | 38篇 |
1993年 | 33篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 9篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 29篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有3794条查询结果,搜索用时 31 毫秒
141.
Tomáš Brázdil Javier Esparza Stefan Kiefer Antonín Kučera 《Formal Methods in System Design》2013,43(2):124-163
The paper gives a summary of the existing results about algorithmic analysis of probabilistic pushdown automata and their subclasses. 相似文献
142.
Jaroslav Keznikl Tomáš Bureš František Plášil Petr Hnětynka 《Software and Systems Modeling》2014,13(2):843-872
In current software systems, connectors play an important role by encapsulating the communication and coordination logic. Since they share common patterns (elements) depending on characteristics of the connections, the elements can be predefined and reused. A method of connector implementation based on a composition of predefined elements naturally comprises two steps: resolution of the connector architecture, and creation of the actual connector code based on the architecture. However, manual resolution of a connector architecture is very difficult due to the number of factors to be considered. Thus, the challenge is to come up with an automated method, able to address all the important factors. In this paper, we present a method for automated resolution of connector architectures based on constraint solving techniques. We exploit a propositional logic with relational calculus for defining a connector theory, a constraint specification reflecting both the predefined parts and the important resolution factors, and employ a constraint solver to find a suitable connector architecture as a model of the theory. As a proof of the concept, we show how the theory can be captured in the Alloy language and resolved via the Alloy Analyzer. 相似文献
143.
144.
Safety critical railway assets need to be visible from prescribed distances, ensuring safety. Traditional methods for measuring these sighting distances involve manual labour and disruption of rail services. Drawing parallels with other areas, efficiency and cost of such a task can be improved with automation. Hence, in this work, we describe a framework providing such automation, using image frames captured from video equipment as input. Any such framework needs to meet a set of associated challenges, including: determining the image position of decreasing sized assets as they appear farther from the observer, extracting three-dimensional positioning information (relative to motion) from two-dimensional video information and determining when an asset can no longer be seen (i.e. the sighting distance). Results show that the methods included in this framework perform better than a traditional method and information regarding asset-sighting distance is accurately computed. 相似文献
145.
Arne Fallisch Leon Schellhase Jan Fresko Martin Zechmeister Mario Zedda Jens Ohlmann Lukas Zielke Nils Paust Tom Smolinka 《International Journal of Hydrogen Energy》2017,42(19):13544-13553
Hydrogen as a secondary energy carrier promises a large potential as a long term storage for fluctuating renewable energies. In this sense a highly efficient solar hydrogen generation is of great interest especially in southern countries having high solar irradiation. The patented Hydrogen Concentrator (HyCon) concept yields high efficiencies combining multi-junction solar cells with proton exchange (PEM) membrane water electrolysis. In this work, a special PEM electrolysis cell for the HyCon concept was developed and investigated. It is shown that the purpose-made PEM cell shows a high performance using a titanium hybrid fiber sinter function both as a porous transport layer and flow field. The electrolysis cell shows a high performance with 1.83 V at 1 A/cm2 and 24 °C working under natural convection with a commercially available catalyst coated membrane. A theoretical examination predicts a total efficiency for the HyCon module from sunlight to hydrogen of approximately 19.5% according to the higher heating value. 相似文献
146.
147.
Nathaniel A. Riordan Chaturvedi Gogineni Shane R. Johnson Xianfeng Lu Tom Tiedje Ding Ding Yong-Hang Zhang Rafael Fritz Kolja Kolata Sangam Chatterjee Kerstin Volz Stephan W. Koch 《Journal of Materials Science: Materials in Electronics》2012,23(10):1799-1804
Bulk and quantum well GaAs1?xBix/GaAs layers with Bi mole fractions from 0.02 to 0.10 are grown by molecular-beam epitaxy at temperatures ranging from 280 to 320?°C. The samples are characterized using temperature and pump-power dependent photoluminescence measurements covering 8–300?K and 1–250?mW (7–1,800?W/cm2), respectively. The results indicate that there is strong reduction in bandgap energy with the incorporation of small amounts of Bi and that GaAsBi most likely forms a weak type-I band alignment with GaAs. 相似文献
148.
Sets of multiple scalar fields can be used to model many types of variation in data, such as uncertainty in measurements and simulations or time‐dependent behavior of scalar quantities. Many structural properties of such fields can be explained by dependencies between different points in the scalar field. Although these dependencies can be of arbitrary complexity, correlation, i.e., the linear dependency, already provides significant structural information. Existing methods for correlation analysis are usually limited to positive correlation, handle only local dependencies, or use combinatorial approximations to this continuous problem. We present a new approach for computing and visualizing correlated regions in sets of 2‐dimensional scalar fields. This paper describes the following three main contributions: (i) An algorithm for hierarchical correlation clustering resulting in a dendrogram, (ii) a generalization of topological landscapes for dendrogram visualization, and (iii) a new method for incorporating negative correlation values in the clustering and visualization. All steps are designed to preserve the special properties of correlation coefficients. The results are visualized in two linked views, one showing the cluster hierarchy as 2D landscape and the other providing a spatial context in the scalar field's domain. Different coloring and texturing schemes coupled with interactive selection support an exploratory data analysis. 相似文献
149.
This paper aims to investigate the premise that community land trusts (CLTs) offer a method of delivering affordable housing that empowers local communities and provides democratic management of community assets. The paper provides a comparative analysis of CLT developments in England, Scotland and the USA, reviewing the policy and literature to identify two key approaches that underpin CLTs: an approach to property development that emphasises resale restrictions used to preserve housing use for the CLT's target clientele, and an approach to citizen governance that privileges local communities. The paper identifies a variation of practices that underpin the operation of CLTs in each country and uses the advanced developments in Scotland and the USA to illustrate some of the challenges that remain if the CLT sector in England is to continue its recent growth. 相似文献
150.
Stem cells (SCs) perform the task of maintaining tissue homeostasis by both self-renewal and differentiation. While it has been argued that SCs divide asymmetrically, there is also evidence that SCs undergo symmetric division. Symmetric SC division has been speculated to be key for expanding cell numbers in development and regeneration after injury. However, it might lead to uncontrolled growth and malignancies such as cancer. In order to explore the role of symmetric SC division, we propose a mathematical model of the effect of symmetric SC division on the robustness of a population regulated by a serial differentiation cascade and we show that this may lead to extinction of such population. We examine how the extinction likelihood depends on defining characteristics of the population such as the number of intermediate cell compartments. We show that longer differentiation cascades are more prone to extinction than systems with less intermediate compartments. Furthermore, we have analysed the possibility of mixed symmetric and asymmetric cell division against invasions by mutant invaders in order to find optimal architecture. Our results show that more robust populations are those with unfrequent symmetric behaviour. 相似文献