全文获取类型
收费全文 | 19332篇 |
免费 | 835篇 |
国内免费 | 142篇 |
专业分类
电工技术 | 335篇 |
综合类 | 32篇 |
化学工业 | 4287篇 |
金属工艺 | 598篇 |
机械仪表 | 636篇 |
建筑科学 | 374篇 |
矿业工程 | 47篇 |
能源动力 | 1373篇 |
轻工业 | 1213篇 |
水利工程 | 150篇 |
石油天然气 | 85篇 |
武器工业 | 1篇 |
无线电 | 2379篇 |
一般工业技术 | 4398篇 |
冶金工业 | 1453篇 |
原子能技术 | 173篇 |
自动化技术 | 2775篇 |
出版年
2024年 | 102篇 |
2023年 | 420篇 |
2022年 | 1002篇 |
2021年 | 1176篇 |
2020年 | 918篇 |
2019年 | 946篇 |
2018年 | 1233篇 |
2017年 | 974篇 |
2016年 | 944篇 |
2015年 | 608篇 |
2014年 | 850篇 |
2013年 | 1542篇 |
2012年 | 907篇 |
2011年 | 1095篇 |
2010年 | 872篇 |
2009年 | 815篇 |
2008年 | 723篇 |
2007年 | 583篇 |
2006年 | 477篇 |
2005年 | 368篇 |
2004年 | 274篇 |
2003年 | 243篇 |
2002年 | 195篇 |
2001年 | 176篇 |
2000年 | 173篇 |
1999年 | 170篇 |
1998年 | 292篇 |
1997年 | 240篇 |
1996年 | 223篇 |
1995年 | 171篇 |
1994年 | 158篇 |
1993年 | 153篇 |
1992年 | 102篇 |
1991年 | 132篇 |
1990年 | 100篇 |
1989年 | 96篇 |
1988年 | 81篇 |
1987年 | 88篇 |
1986年 | 76篇 |
1985年 | 85篇 |
1984年 | 73篇 |
1983年 | 72篇 |
1982年 | 60篇 |
1981年 | 71篇 |
1980年 | 49篇 |
1979年 | 31篇 |
1978年 | 27篇 |
1977年 | 26篇 |
1976年 | 35篇 |
1971年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
Increasing information technology (IT) infrastructure spending and the capability of such projects to provide a platform for a firm to realize value from IT marks their importance. Effective management of IT infrastructure investments includes identification of embedded growth options in the infrastructure, and exercising them in a timely manner. Extant research has recognized that while managers could use real options thinking in IT investment management, managerial bias could affect the timing of option exercise and their realized value. We analyze the effect of time-inconsistent preferences of present-biased managers on the exercise time of real growth options and the realized value using a discrete time option valuation model. The results show that present-biased managers are more likely to exercise options early when the net payoffs are low, the option payoffs have high volatility, and the risk free discount rate is small. In addition, present biased managers are more likely to exercise a growth option early in its life when the project is performing well. We provide implications for practice and IT governance. 相似文献
992.
Rajiv Kumar Sharma Dinesh Kumar Pradeep Kumar 《International journal of systems science》2013,44(6):563-581
The main objective of the article is to permit the reliability analyst's/engineers/managers/practitioners to analyze the failure behavior of a system in a more consistent and logical manner. To this effect, the authors propose a methodological and structured framework, which makes use of both qualitative and quantitative techniques for risk and reliability analysis of the system. The framework has been applied to model and analyze a complex industrial system from a paper mill. In the quantitative framework, after developing the Petrinet model of the system, the fuzzy synthesis of failure and repair data (using fuzzy arithmetic operations) has been done. Various system parameters of managerial importance such as repair time, failure rate, mean time between failures, availability, and expected number of failures are computed to quantify the behavior in terms of fuzzy, crisp and defuzzified values. Further, to improve upon the reliability and maintainability characteristics of the system, in depth qualitative analysis of systems is carried out using failure mode and effect analysis (FMEA) by listing out all possible failure modes, their causes and effect on system performance. To address the limitations of traditional FMEA method based on risky priority number score, a risk ranking approach based on fuzzy and Grey relational analysis is proposed to prioritize failure causes. 相似文献
993.
Jaideep J. Rao Kiran Kumar Ravulapati Tapas K. Das 《International journal of systems science》2013,44(12-13):717-730
Non-cooperative decision-making problems in a decentralized supply chain can be characterized and studied using a stochastic game model. In an earlier paper, the authors developed a methodology that uses machine learning for finding (near) optimal policies for non-zero sum stochastic games, and applied their methodology on an N-retailer and W-warehouse inventory-planning problem. The focus of this paper is on making the methodology more amenable to practical applications by making it completely simulation-based. It is also demonstrated, through numerical example problems, how this methodology can be used to find (near) equilibrium policies, and evaluate short-term rewards of stochastic games. Short-term rewards of stochastic games could be, in many instances, more critical than equilibrium rewards. To our knowledge, no methodology exists in the open literature that can capture the short-term behaviour of non-zero sum stochastic games as examined in this paper. 相似文献
994.
B. Krishna Kumar S. Anbarasu S.R. Anantha Lakshmi 《International journal of systems science》2013,44(1):88-110
A single server queue subject to maintenance of the server and the close down period is considered. We obtain explicit expressions for the transient probabilities of the system size, the server under maintenance state and the close down period. The time-dependent performance measures of the system and the probability density function of the first-passage-time to reach the maintenance state are discussed. The corresponding steady state analysis and key performance measures of the system are also presented. Finally, the effect of various parameters on system performance measures is demonstrated by a numerical example. 相似文献
995.
Pradeep K. Sahoo Sandeep Kumar Ramesh P. Singh 《International journal of remote sensing》2013,34(3):499-518
The Ganga and Yamuna rivers emerge from the Himalayas along two major faults known as the Ganga and Yamuna Tear Faults respectively. The two major strike-slip faults transverse to the Siwalik range are clearly seen in satellite imagery of the Dehradun area. Earthquake records, landslide and recent changes in geomorphological features indicate that the area between the Main Boundary Thrust and the Main Frontal Thrust is tectonically active. An effort has been made to study the tectonic evolution and neotectonism of the Ganga and Yamuna tear faults. Spectral and spatial enhancement techniques have been employed to the digital data of IRS-1B LISS-I to delineate the lineaments and major faults of the area. Based on Mohr's theory, failure criteria and statistical analysis of remotely sensed lineament data, horizontal compressive stress values (SHmax) have been estimated at various sites of the study area. These data are found to be consistent with the published SHmax orientation determined from earthquake focal mechanism solutions. Active faults and lineaments have been extracted from the remotely sensed lineament data. Past earthquake data and depth to basement contour data have been used in an integrated approach with available Geographic Information System (GIS) techniques to reconstruct a present-day regional geodynamic model. Attempts have been made to investigate the genesis of Ganga and Yamuna Tear Faults and possible causes of recent tectonic activities of the area with the help of the proposed geodynamic model. 相似文献
996.
997.
Amit Kumar Dubey Praveen Gupta Subashisa Dutta Bimlesh Kumar 《International journal of remote sensing》2013,34(23):7815-7827
In this study, river stage variation derived from satellite altimetry was used to assess the water level, monthly discharge, and annual water yield at six virtual gauging stations at the braided reaches of the Brahmaputra River. The braided reaches of the river dynamically change their planform, thalweg line, and aggradation or degradation period. Stage records derived from the Envisat satellite of the European Space Agency and Topex/Poseidon of NASA/CNES were used for the period 2002–2010. Spatial interpolation and datum correction were applied on altimetry-derived river stage records before analysis. A correlation and error analysis between the in situ and satellite-altimetry-derived stages was carried out for these stations for both monsoon and non-monsoon seasons. Yearly optical satellite images were used for qualitative assessment of temporal variations in aggradation/degradation phases at the gauging stations. Using the pseudo-rating curve, discharges at two virtual gauging stations were estimated. The results show that the altimetry-estimated discharges are of good agreement with observed discharge for the monsoon months (June–September) as compared with the non-monsoon months (October–May). In order to assess the annual water yield variability, yearly variation in annual water yield from the altimetry data was also estimated and compared to that observed. The estimated annual water yields were 90% accurate. Similarly, the long-term averaged monthly discharge series estimated from satellite altimetry closely follows the temporal trend of that of the observed series. 相似文献
998.
Recent advances in atmospheric remote sensing offer a unique opportunity to compute indirect estimates of air quality, particularly for developing countries that lack adequate spatial–temporal coverage of air pollution monitoring. The present research establishes an empirical relationship between satellite‐based aerosol optical depth (AOD) and ambient particulate matter (PM) in Delhi and its environs. The PM data come from two different sources. Firstly, a field campaign was conducted to monitor airborne particles?2.5 µm and?10 µm in aerodynamic diameter (PM2.5 and PM10 respectively) at 113 spatially dispersed sites from July to December 2003 using photometric samplers. Secondly, data on eight hourly PM10 and total suspended particulate (TSP) matter, collected using gravimetric samplers, from 2000 to 2005 were acquired from the Central Pollution Control Board (CPCB). The aerosol optical depths were estimated from MODIS data, acquired from NASA's Goddard Space Flight Center Earth Sciences Distributed Active Archive Center from 2000 to 2005. Both the PM and AOD data were collocated by time and space: PM mass±150 min of AOD time, and ±2.5 and 5 km radius (separately) of the centroid of the AOD pixel for the 5 and 10 km AOD, respectively. The analysis here shows that PM correlates positively with the 5 km AOD; a 1% change in the AOD explains 0.52%±0.20% and 0.39%±0.15% changes in PM2.5 within 45 and 150 min intervals (of AOD data) respectively. At a coarser spatial resolution, however, the relationship between AOD and PM is relatively weak. But, the relationship turns significantly stronger when monthly estimates are analysed over a span of six years (2000 to 2005), especially for the winter months, which have relatively stable meteorological conditions. 相似文献
999.
Rajib Kumar Panigrahi 《International journal of remote sensing》2013,34(11):3531-3541
Recently, there has been growing interest in dual-polarimetric (dual-Pol) systems, especially in hybrid-Pol mode. In comparison to quad-Pol systems, a dual-Pol system has the advantage of halved average transmitted power and doubled swath coverage. In this article, we present a comparison of information provided by hybrid-Pol and quad-Pol synthetic aperture radar (SAR) data. To be compared, hybrid-Pol data are converted to pseudo-quad-Pol data using compact polarimetric scattering models. We have further compared both configurations based on the information extractable about the scattering process. The scattering contribution of each of the three basic scattering mechanisms, namely single bounce, double bounce and volume scattering, can be evaluated by Freeman and Durden decomposition techniques. Applying such a decomposition technique to quad-Pol and pseudo-quad-Pol data, we evaluate and compare the scattering contribution of each of the three basic scattering mechanisms for clusters of pixels in polarimetric SAR images. 相似文献
1000.
Siddarth Shankar Das Karanam Kishore Kumar Subrata Kumar Das Chandrasekharan Vineeth Tarun Kumar Pant Geetha Ramkumar 《International journal of remote sensing》2013,34(14):4634-4647
Two independent methods for deriving mesopause temperature using meteor radar installed at an equatorial station, Thumba (8.5° N, 76.5° E), are discussed in this article. This meteor radar-derived mesopause temperature is then compared with two different types of spaceborne measurement, namely (i) Sounding the Atmosphere using Broadband Emission Radiometry (SABER) and (ii) the Earth Observing System Microwave Limb Sounder (EOS MLS), and a collocated multi-wavelength dayglow photometer (DGPM). The meteor radar-derived temperature is in fairly good agreement with all the three measurement techniques, with an uncertainty of ±10°. This study focuses on a detailed evaluation and inter-comparison of mesopause temperature derived from different measurement techniques. An attempt is also made to compare the suitability of these observations to study planetary waves and other oscillation activities in the mesospheric region. 相似文献