全文获取类型
收费全文 | 680篇 |
免费 | 14篇 |
国内免费 | 2篇 |
专业分类
化学工业 | 32篇 |
金属工艺 | 1篇 |
机械仪表 | 19篇 |
建筑科学 | 31篇 |
能源动力 | 32篇 |
轻工业 | 38篇 |
水利工程 | 5篇 |
无线电 | 49篇 |
一般工业技术 | 106篇 |
冶金工业 | 277篇 |
原子能技术 | 7篇 |
自动化技术 | 99篇 |
出版年
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 35篇 |
2012年 | 21篇 |
2011年 | 22篇 |
2010年 | 25篇 |
2009年 | 23篇 |
2008年 | 26篇 |
2007年 | 26篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 19篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 22篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 3篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 16篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1972年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
1.
2.
3.
AbstractAustralian cities have observed a “consensus turn” expressed as broad public support of greater accessibility and public transport provision as revealed in metropolitan strategic plans. In contrast large-scale road projects proposed to traverse the inner-city of three major Australian cities reveals an ongoing and deep-seated attachment by some to car-based travel in Australian urban transport planning. Comparative case studies of these three road projects in Melbourne, Sydney and Perth explores the impact that an antagonistic relationship between the state and community has on the culture of transport planning. Through observational insights, policy and media analysis and interviews with community groups, we show that this antagonistic planning culture arises when there is a fracture between metropolitan strategic plan-making and project planning, and when clear channels of communication and deliberation are undermined. 相似文献
4.
Chuang MT Fu JS Jang CJ Chan CC Ni PC Lee CT 《The Science of the total environment》2008,406(1-2):168-179
Aerosol is frequently transported by a southward high-pressure system from the Asian Continent to Taiwan and had been recorded a 100% increase in mass level compared to non-event days from 2002 to 2005. During this time period, PM2.5 sulfate was found to increase as high as 155% on event days as compared to non-event days. In this study, Asian emission estimations, Taiwan Emission Database System (TEDS), and meteorological simulation results from the fifth-generation Mesoscale Model (MM5) were used as inputs for the Community Multiscale Air Quality (CMAQ) model to simulate a long-range transport of PM2.5 event in a southward high-pressure system from the Asian Continent to Taiwan. The simulation on aerosol mass level and the associated aerosol components were found within a reasonable accuracy. During the transport process, the percentage of semi-volatile PM2.5 organic carbon in PM2.5 plume only slightly decreased from 22-24% in Shanghai to 21% near Taiwan. However, the percentage of PM2.5 nitrate in PM2.5 decreased from 16-25% to 1%. In contrast, the percentage of PM2.5 sulfate in PM2.5 increased from 16-19% to 35%. It is interesting to note that the percentage of PM2.5 ammonium and PM2.5 elemental carbon in PM2.5 remained nearly constant. Simulation results revealed that transported pollutants dominate the air quality in Taipei when the southward high-pressure system moved to Taiwan. Such condition demonstrates the dynamic chemical transformation of pollutants during the transport process from continental origin over the sea area and to the downwind land. 相似文献
5.
6.
Vandana Gupta Mingwei Gong S. Dharmaraja Carey Williamson 《International Journal of Communication Systems》2011,24(5):647-665
This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
We demonstrate a wavelength tunable optical excitation source for coherent Raman scattering (CRS) spectroscopy based on a single femtosecond fiber laser. Electrically controlled wavelength tuning of Stokes optical pulses was achieved with soliton self frequency shift in an optical fiber, and linear frequency chirping was applied to both the pump and the Stokes waves to significantly improve the spectral resolution. The coherent anti-Stokes Raman scattering (CARS) spectrum of cyclohexane was measured and vibrational resonant Raman peaks separated by 70?cm(-1) were clearly resolved. Single laser-based tunable excitation may greatly simplify CRS measurements and extend the practicality of CRS microscopy. 相似文献
8.
9.
Mehran Seyed-Ahmadi Blake Erb Carey J. Simonson Robert W. Besant 《International Journal of Heat and Mass Transfer》2009,52(25-26):6012-6020
Part І of this paper [17] developed and verified the numerical model for simultaneous heat and moisture transfer in the run-around membrane energy exchanger (RAMEE) system to determine the transient behavior of the system under different initial and operating conditions.This paper presents the transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio. Also the system quasi-steady state operating conditions are predicted as the system approaches its asymptotic operating condition. The transient responses are predicted with changes in various parameters. These include: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the storage volume ratio and the initial salt solution concentration have significant impacts on the transient response of the system and heat transfer between the RAMEE system and the surrounding environment can change the system quasi-steady conditions substantially. 相似文献
10.
Arvin Farid Akram N. Alshawabkeh Carey M. Rappaport 《Canadian Metallurgical Quarterly》2009,135(9):1209-1218
This paper explains and evaluates the potential and limitations of conducting cross-well radar (CWR) in sandy soils. Implementing the experiment and data collection in the absence of any scattering object, and in the presence of an acrylic plate [a representative of dielectric objects, such as dense nonaqueous phase liquid (DNAPL) pools, etc.], as a contrasting object in a water-saturated soil is also studied. To be able to image the signature of any object, more than one pair of receiving and transmitting antennas are required. The paper describes a method to achieve repeatable, reliable, and reproducible laboratory results for different transmitter-receiver combinations. Different practical methods were evaluated for collecting multiple-depth data. Similarity of the corresponding results and problems involved in each method are studied and presented. The data show that the frequency response of a saturated coarse-grained soil is smooth due to the continuous and dominant nature of water in saturated soils. The repeatability and potential symmetry of patterns across some borehole axes provide a valuable tool for validation of experimental results. The potential asymmetry across other borehole axes is used as a tool to evaluate the strength of the perturbation on the electromagnetic field due to hidden objects and to evaluate the feasibility of detecting dielectric objects (such as DNAPL pools, etc.) using CWR. The experimental simulation of this paper models a real-life problem in a smaller scale, in a controlled laboratory environment, and within homogeneous soils that are uniformly dry or fully water saturated, with a uniform dielectric property contrast between the inclusion and background. The soil in the field will not be as homogeneous and uniform. The scaling process takes into consideration that as the size is scaled down; the frequency needs to be scaled up. It is noteworthy that this scaling process needs to be extensively studied and validated for future extension of the models to real-field applications. For example, to extend the outcome of this work to the real field, the geometry (antenna size, their separation and inclusion size) needs to be scaled up back to the field size, while soil grains will not. Therefore, soil, water, and air coupling effects and interactions observed at the laboratory scale do not scale up in the field, and may have different unforeseen effects that require extensive study. 相似文献