全文获取类型
收费全文 | 31593篇 |
免费 | 1597篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 331篇 |
综合类 | 60篇 |
化学工业 | 6663篇 |
金属工艺 | 597篇 |
机械仪表 | 574篇 |
建筑科学 | 1882篇 |
矿业工程 | 77篇 |
能源动力 | 872篇 |
轻工业 | 2689篇 |
水利工程 | 295篇 |
石油天然气 | 143篇 |
武器工业 | 3篇 |
无线电 | 2288篇 |
一般工业技术 | 5920篇 |
冶金工业 | 5244篇 |
原子能技术 | 206篇 |
自动化技术 | 5380篇 |
出版年
2023年 | 253篇 |
2022年 | 160篇 |
2021年 | 685篇 |
2020年 | 505篇 |
2019年 | 592篇 |
2018年 | 724篇 |
2017年 | 693篇 |
2016年 | 909篇 |
2015年 | 818篇 |
2014年 | 1034篇 |
2013年 | 1924篇 |
2012年 | 1674篇 |
2011年 | 2126篇 |
2010年 | 1512篇 |
2009年 | 1464篇 |
2008年 | 1765篇 |
2007年 | 1647篇 |
2006年 | 1443篇 |
2005年 | 1231篇 |
2004年 | 1096篇 |
2003年 | 949篇 |
2002年 | 916篇 |
2001年 | 546篇 |
2000年 | 525篇 |
1999年 | 535篇 |
1998年 | 508篇 |
1997年 | 453篇 |
1996年 | 463篇 |
1995年 | 440篇 |
1994年 | 428篇 |
1993年 | 430篇 |
1992年 | 372篇 |
1991年 | 221篇 |
1990年 | 318篇 |
1989年 | 314篇 |
1988年 | 268篇 |
1987年 | 289篇 |
1986年 | 284篇 |
1985年 | 306篇 |
1984年 | 264篇 |
1983年 | 256篇 |
1982年 | 238篇 |
1981年 | 210篇 |
1980年 | 177篇 |
1979年 | 182篇 |
1978年 | 166篇 |
1977年 | 135篇 |
1976年 | 127篇 |
1975年 | 135篇 |
1974年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
Oliver Matthew N. I.; Bernstein Jessey H.; Anderson Kristen G.; Blashfield Roger K.; Roberts Michael C. 《Canadian Metallurgical Quarterly》2004,35(2):141
Do psychology students view their training programs as doing enough to appropriately identify, accommodate, and possibly dismiss students who manifest significant impairment? This study reports the general findings of an exploratory survey distributed to clinical psychology graduate students. Overall, students viewed impairment as a highly sensitive and inadequately addressed issue. Students commonly reported frustration with and concern for impaired colleagues. A few respondents indicated that the terms impaired and problem student were insensitive and that greater attention needed to be given to "impaired" training contexts. Implications regarding formal standards for interpersonal functioning and programmatic supports for students are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
Processing capacity-defined as the relative ability to perform mental work in a unit of time-is a critical construct in cognitive psychology and is central to theories of visual attention. The unambiguous use of the construct, experimentally and theoretically, has been hindered by both conceptual confusions and the use of measures that are at best only coarsely mapped to the construct. However, more than 25 years ago, J. T. Townsend and F. G. Ashby (1978) suggested that the hazard function on the response time (RT) distribution offered a number of conceptual advantages as a measure of capacity. The present study suggests that a set of statistical techniques, well-known outside the cognitive and perceptual literatures, offers the ability to perform hypothesis tests on RT-distribution hazard functions. These techniques are introduced, and their use is illustrated in application to data from the contingent attentional capture paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
Imagination and innovation are among the energy sources the PM industry needs to maintain growth rates. Research in New Jersey shows that binders and lubricants have a role to play in pushing green densities higher… 相似文献
994.
The Treaty of the European Coal and Steel Community (ECSC), which expired in 2002, states in its Article 55 to promote technical and economic research with respect to the production and growing application of coal and steel. The results of funded research projects shall be made available to all representatives and partners concerned. For the European steel industry Article 55 was the basis for building up a steel research programme covering topics from raw materials to steel application and instigated a European network of researchers from the steel industry, research institutes and universities. On the basis of these research and development activities carried out by the ECSC steel research, the iron and steel industry has shown important advances in technology and environmental compatibility. Furthermore, the ECSC steel research has contributed to nearly all important technological developments. The main objective of the ECSC steel Research and Technology Development (RTD) programme was to sustain and develop the Community steel industry's competitiveness. The following report describes fundamental developments and activities within the framework of ECSC research with particular respect to hot metal production in the last 15 years. 相似文献
995.
James S. Davidson Jonathan R. Porter Robert J. Dinan Michael I. Hammons James D. Connell 《Canadian Metallurgical Quarterly》2004,18(2):100-106
The most widely used terrorist tactic is the improvised explosive device, which can range in size from hand-held to truck-size. Most casualties and injuries sustained in such an attack are not caused by the blast itself, but rather by the disintegration and fragmentation of walls, the shattering of windows, and by nonsecured objects propelled at high velocities by the blast. Since 1995, the Air Force Research Laboratory at Tyndall Air Force Base has investigated methods of retrofitting wall structures to better resist blast loads from external explosions. This paper summarizes results from recent tests that involve an innovative use of a sprayed-on polymer to increase blast resistance of unreinforced concrete masonry walls. Test methodology, retrofit materials considered, material properties, mechanisms of effectiveness, and research challenges are discussed. 相似文献
996.
A New Classification of Path-Delay Fault Testability in Terms of Stuck-at Faults 总被引:1,自引:0,他引:1 下载免费PDF全文
SubhashisMajumder BhargabB.Bhattacharya VishwaniD.Agrawal MichaelL.Bushnell 《计算机科学技术学报》2004,19(6):0-0
A new classification of path-delay fault testability in a combinational circuit is presented in terms of testability of stuck-at faults in an equivalent circuit. Earlier results describing correlation of path-delay and stuck-at faults are either incomplete, or use a complex model of equivalent circuit based on timing parameters. It is shown here that a path-delay fault (rising or falling) is testable if and only if certain single or multiple stuck-at fault in the equivalent circuit is testable. Thus, all aspects of path-delay faults related to testability under various classification schemes can be interpreted using the stuck-at fault model alone. The results unify most of the existing concepts and provide a better understanding of path-delay faults in logic circuits. 相似文献
997.
Watershed scale temporal and spatial stability of soil moisture and its role in validating satellite estimates 总被引:2,自引:0,他引:2
Watershed scale soil moisture estimates are necessary to validate current remote sensing products, such as those from the Advanced Microwave Scanning Radiometer (AMSR). Unfortunately, remote sensing technology does not currently resolve the land surface at a scale that is easily observed with ground measurements. One approach to validation is to use existing soil moisture measurement networks and scale these point observations up to the resolution of remote sensing footprints. As part of the Soil Moisture Experiment 2002 (SMEX02), one such soil moisture gaging system in the Walnut Creek Watershed, Iowa, provided robust estimates of the soil moisture average for a watershed throughout the summer of 2002. Twelve in situ soil moisture probes were installed across the watershed. These probes recorded soil moisture at a depth of 5 cm from June 29, 2002 to August 19, 2002. The sampling sites were analyzed for temporal and spatial stability by several measures including mean relative difference, Spearman rank, and correlation coefficient analysis. Representative point measurements were used to estimate the watershed scale (∼25 km) soil moisture average and shown to be accurate indicators with low variance and bias of the watershed scale soil moisture distribution. This work establishes the validity of this approach to provide watershed scale soil moisture estimates in this study region for the purposes of satellite validation with estimation errors as small as 3%. Also, the potential sources of error in this type of analysis are explored. This study is a first step in the implementation of large-scale soil moisture validation using existing networks such as the Soil Climate Analysis Network (SCAN) and several Agricultural Research Service watersheds as a basis for calibrating satellite soil moisture products, for networks design, and designing field experiments. 相似文献
998.
Fuqin Li Thomas J. Jackson Thomas J. Schmugge Michael H. Cosh 《Remote sensing of environment》2004,92(4):521-534
A sequence of five high-resolution satellite-based land surface temperature (Ts) images over a watershed area in Iowa were analyzed. As a part of the SMEX02 field experiment, these land surface temperature images were extracted from Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper (ETM) thermal bands. The radiative transfer model MODTRAN 4.1 was used with atmospheric profile data to atmospherically correct the Landsat data. NDVI derived from Landsat visible and near-infrared bands was used to estimate fractional vegetation cover, which in turn was used to estimate emissivity for Landsat thermal bands. The estimated brightness temperature was compared with concurrent tower based measurements. The mean absolute difference (MAD) between the satellite-based brightness temperature estimates and the tower based brightness temperature was 0.98 °C for Landsat 7 and 1.47 °C for Landsat 5, respectively. Based on these images, the land surface temperature spatial variation and its change with scale are addressed. The scaling properties of the surface temperature are important as they have significant implications for changes in land surface flux estimation between higher-resolution Landsat and regional to global sensors such as MODIS. 相似文献
999.
Wies?aw Ostachowicz Marek Krawczuk Matthew Cartmell Michael Gilchrist 《Computers & Structures》2004,82(6):475-483
The wave propagation model investigated herein is based on the known fact that material discontinuities affect the propagation of elastic waves in solids. The change in certain material characteristics, such as a local change in stiffness or inertia caused by a crack or the presence of material damage, will affect the propagation of transmitted elastic waves and will modify the received signal. Wave frequencies associated with the highest detection sensitivity depend, among other things, on the type of structure, the type of material, and the type of damage. This paper presents a method of wave propagation, which can be further used to detect small delaminations in beam-like structures. The considered beam is modelled by spectral finite elements. 相似文献
1000.
Even as more organizations are moving towards implementing Web-based B2B procurement solutions, they are unsure of the real benefits of the Web. In other words, what is the value of B2B e-procurement to an organization and how to measure this value? What factors affect this value? In this paper, we discuss an evaluation framework to determine the value of B2B e-procurement and the effect of process characteristics on the value. We use an empirical study to highlight the different value created by different procurement types. We then develop a more comprehensive economic model to capture the additional effects of demand volume and process complexity. The integration of theoretical and empirical approaches provides a strong foundation to develop and evaluate useful adoption strategies for B2B e-procurement. 相似文献