全文获取类型
收费全文 | 337401篇 |
免费 | 21173篇 |
国内免费 | 10316篇 |
专业分类
电工技术 | 14500篇 |
技术理论 | 28篇 |
综合类 | 17445篇 |
化学工业 | 54661篇 |
金属工艺 | 18921篇 |
机械仪表 | 18762篇 |
建筑科学 | 21150篇 |
矿业工程 | 8670篇 |
能源动力 | 8537篇 |
轻工业 | 18823篇 |
水利工程 | 5207篇 |
石油天然气 | 17723篇 |
武器工业 | 1772篇 |
无线电 | 38529篇 |
一般工业技术 | 46870篇 |
冶金工业 | 17828篇 |
原子能技术 | 2844篇 |
自动化技术 | 56620篇 |
出版年
2024年 | 1081篇 |
2023年 | 4149篇 |
2022年 | 7207篇 |
2021年 | 10036篇 |
2020年 | 7851篇 |
2019年 | 6663篇 |
2018年 | 20691篇 |
2017年 | 20559篇 |
2016年 | 16613篇 |
2015年 | 10321篇 |
2014年 | 12708篇 |
2013年 | 15386篇 |
2012年 | 18907篇 |
2011年 | 26291篇 |
2010年 | 22827篇 |
2009年 | 19525篇 |
2008年 | 20443篇 |
2007年 | 20791篇 |
2006年 | 13894篇 |
2005年 | 13035篇 |
2004年 | 9332篇 |
2003年 | 8434篇 |
2002年 | 7328篇 |
2001年 | 6114篇 |
2000年 | 6353篇 |
1999年 | 7151篇 |
1998年 | 6390篇 |
1997年 | 5116篇 |
1996年 | 4767篇 |
1995年 | 3941篇 |
1994年 | 3184篇 |
1993年 | 2293篇 |
1992年 | 1783篇 |
1991年 | 1458篇 |
1990年 | 1152篇 |
1989年 | 932篇 |
1988年 | 709篇 |
1987年 | 488篇 |
1986年 | 403篇 |
1985年 | 321篇 |
1984年 | 248篇 |
1983年 | 187篇 |
1982年 | 190篇 |
1981年 | 157篇 |
1980年 | 150篇 |
1979年 | 84篇 |
1978年 | 86篇 |
1977年 | 78篇 |
1976年 | 111篇 |
1955年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Melissa Kurtz 《Journal of Failure Analysis and Prevention》2007,7(3):175-178
Fuel system assemblies used on recreational watercraft failed after a short time in service in a seawater environment. Examination
of the assemblies revealed significant degradation of the polyacetal connectors of the wire subassemblies. Optical and microscopic
evaluations indicated the complete loss of connector material implying decomposition of the resin, along with mud-cracking
and a rough surface morphology signifying chemical attack. An elemental analysis performed on both an intact connector and
degraded connector suggested a potential chemical agent in the form of zinc chloride. At elevated temperatures, concentrated
zinc chloride solutions are known to decompose polyacetal resins. The source of the zinc chloride was established as corrosion
products that resulted during the dezincification of the internal brass connector through exposure to saltwater in the application. 相似文献
993.
994.
In current desktop user interfaces, selection is usually accomplished easily with a mouse or a similar two-dimensional locator. In wearable computing, however, controlling two dimensions simultaneously gets significantly harder: a change in one dimension results easily in an undesired change in the other dimension as well when the user is occupied with a parallel task – such as walking. We present a way to overcome this problem by applying one-dimensional selection for graphical user interfaces in head-worn displays. Our new interaction technique allows a wearable computer user to perform object selection tasks easily and accurately. The technique is based on a visible circle on the screen. The user controls the circle, altering its radius with a one-dimensional valuator. The midpoint of the circle is in the middle of the screen. The object currently on the perimeter of the circle is highlighted and can be selected. Our preliminary usability evaluation, applying our custom evaluation method designed especially for walking users, indicates that the proposed technique is usable also when walking. 相似文献
995.
Hermann Knoflacher 《Sadhana》2007,32(4):293-307
Technological determinism has become a kind of religion for many people since it appears to offer solutions for societal problems
as never before in history. Transport is one of the fascinating technology branches developed during the last 200 years. Effortless
movement over long distances has become possible for car users as long as cheap fossil energy is available. However, the effect
of fast transport on urban structures and society was not taken into account when developing these technical means. Technologists
and economists have used indicators for expected benefits of these fast transport modes without taking into account the real
system effects on society and urban structures. Plausible assumptions and hopes instead of scientific understanding of the
complex system are used in practice. In contradiction to widely held beliefs of transportation planners, there is actually
no growth of mobility if counted in number of trips per person per day, no time saving by increasing speed in the system,
and no real freedom of modal choice. Modal choice is dependent on physical and other structures, the artificial environment
built by urban planners, transport experts and political decisions. The core hypothesis of traditional urban and transport
planning ‘growth of mobility’, ‘travel time saving by increasing speed’ and ‘freedom of modal choice’ are myths and do not
exist in the real urban and transport system. This is the reason why urban planning and transport planning based on traditional
non-scientific assumptions is creating continuously not only more transport problems, but also environmental and social as
well as economic problems all over the world, where these principals are applied. Urban transport planning in Europe, understanding
the transport system and the solutions are presented in this paper. 相似文献
996.
Véronique Baroghel-Bouny Patrick Belin Matthias Maultzsch Dominique Henry 《Materials and Structures》2007,40(8):759-781
Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch
procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi
procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state
diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray
tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone)
and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods
have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus
time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The
possible sources of discrepancy on the results have been analysed. 相似文献
997.
Xiao-Ying Wang Jonathan M. Garibaldi Benjamin Bird Michael W. George 《Applied Intelligence》2007,27(3):237-248
Recently Fourier Transform Infrared (FTIR) spectroscopic imaging has been used as a tool to detect the changes in cellular
composition that may reflect the onset of a disease. This approach has been investigated as a mean of monitoring the change
of the biochemical composition of cells and providing a diagnostic tool for various human cancers and other diseases. The
discrimination between different types of tissue based upon spectroscopic data is often achieved using various multivariate
clustering techniques. However, the number of clusters is a common unknown feature for the clustering methods, such as hierarchical
cluster analysis, k-means and fuzzy c-means. In this study, we apply a FCM based clustering algorithm to obtain the best number
of clusters as given by the minimum validity index value. This often results in an excessive number of clusters being created
due to the complexity of this biochemical system. A novel method to automatically merge clusters was developed to try to address
this problem. Three lymph node tissue sections were examined to evaluate our new method. These results showed that this approach
can merge the clusters which have similar biochemistry. Consequently, the overall algorithm automatically identifies clusters
that accurately match the main tissue types that are independently determined by the clinician. 相似文献
998.
999.
Squeeze-film effects of perforated plates for small amplitude vibration are analyzed through modified Reynolds equation (MRE).
The analytical analysis reckons in most important influential factors: compressibility of the air, border effects, and the
resistance caused by vertical air flow passing through perforated holes. It is found that consideration of air compressibility
is necessary for high operating frequency and small ratio of the plate width to the attenuation length. The analytical results
presented in this paper agree with ANSYS simulation results better than that under the air incompressibility assumption. The
analytical analysis can be used to estimate the squeeze-film effects causing damping and stiffness added to the system. Since
the value of Reynolds number involved in this paper is low (< 1), inertial effects are neglected. 相似文献
1000.
Hua-Chieh Li 《Applicable Algebra in Engineering, Communication and Computing》2007,18(4):313-348
In this paper, we give a general criterion to determine when a complex space-time block code has a ring structure and then
we provide a complete list of complex space-time block codes which have ring structures up to size 4. 相似文献