全文获取类型
收费全文 | 69866篇 |
免费 | 6615篇 |
国内免费 | 3208篇 |
专业分类
电工技术 | 3442篇 |
技术理论 | 1篇 |
综合类 | 3953篇 |
化学工业 | 12346篇 |
金属工艺 | 3650篇 |
机械仪表 | 4405篇 |
建筑科学 | 3880篇 |
矿业工程 | 1318篇 |
能源动力 | 1971篇 |
轻工业 | 7217篇 |
水利工程 | 1217篇 |
石油天然气 | 2024篇 |
武器工业 | 464篇 |
无线电 | 9171篇 |
一般工业技术 | 9928篇 |
冶金工业 | 3467篇 |
原子能技术 | 870篇 |
自动化技术 | 10365篇 |
出版年
2024年 | 298篇 |
2023年 | 1054篇 |
2022年 | 1938篇 |
2021年 | 2665篇 |
2020年 | 1988篇 |
2019年 | 1801篇 |
2018年 | 2181篇 |
2017年 | 2259篇 |
2016年 | 2288篇 |
2015年 | 2713篇 |
2014年 | 3581篇 |
2013年 | 4622篇 |
2012年 | 5124篇 |
2011年 | 5868篇 |
2010年 | 5037篇 |
2009年 | 4995篇 |
2008年 | 4733篇 |
2007年 | 4258篇 |
2006年 | 3865篇 |
2005年 | 3224篇 |
2004年 | 2434篇 |
2003年 | 1967篇 |
2002年 | 1894篇 |
2001年 | 1600篇 |
2000年 | 1261篇 |
1999年 | 1051篇 |
1998年 | 1083篇 |
1997年 | 725篇 |
1996年 | 654篇 |
1995年 | 457篇 |
1994年 | 340篇 |
1993年 | 300篇 |
1992年 | 221篇 |
1991年 | 194篇 |
1990年 | 136篇 |
1989年 | 140篇 |
1988年 | 113篇 |
1987年 | 96篇 |
1986年 | 77篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 39篇 |
1982年 | 47篇 |
1981年 | 28篇 |
1980年 | 36篇 |
1979年 | 24篇 |
1977年 | 32篇 |
1976年 | 46篇 |
1975年 | 26篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
102.
T.J. ChungJ.H. Park C.K. Choi D.-Y. Yoon 《International Journal of Heat and Mass Transfer》2002,45(14):3061-3064
The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system. 相似文献
103.
104.
Propolis collected by bees has many components that possess antifungal, anticancer and antioxidant properties. Cured ground pork meat was treated separately with 0.4% w/w ethanol‐extracted propolis (EEP 0.4%), 0.6% w/w water‐extracted propolis (WEP 0.6%), 0.8% w/w dried residue of ethanol‐extracted propolis (DREEP 0.8%) and 0.1% w/w potassium sorbate (PS 0.1%) and made into sausages. Thiobarbituric acid‐reactive substances (TBARS) were measured in the sausages to assess the effects of storage at 5, 10 and 20 °C after 0, 2 and 4 weeks. After 4 weeks of storage at 5 °C the sausages treated with EEP 0.4%, DREEP 0.8%, WEP 0.6% and PS 0.1% yielded TBARS values which were 50, 59, 35 and 91% respectively of the control value. There was an increase of 0.33 mg MDA kg?1, the lowest of all treatments, in TBARS for the 0.4% w/w EEP‐treated sausages. The curing process will control microbiological spoilage, as will potassium sorbate. © 2002 Society of Chemical Industry 相似文献
105.
Jeong-Hyun Park 《Communications Magazine, IEEE》2002,40(4):38-49
With the advent of IP technologies and the tremendous growth in data traffic, the wireless industry is evolving its core networks toward IP technology. Enabling wireless Internet access is one of the upcoming challenges for mobile radio network operators. The General Packet Radio Service is the packet-switched extension of GSM and was developed to facilitate access to IP-based services better than existing circuit-switched services provided by GSM. We illustrate how a visited mobile subscriber on a GPRS/UMTS network can access his/her home network via the gateway GPRS support node (GGSN). We also propose some implementation ideas on wireless Internet access for a remote mobile subscriber based on a GPRS/UMTS network 相似文献
106.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
107.
比较了几种长距离传动方式的特点与适用场合,重点探讨了实现长距离精密传动的技术要点。结合实际工程,完成了长距离钢带精密传动的应用,并指出张紧机构的设计与应用是钢带实现长距离精密传动的关键。为此文中对钢带传动的典型张紧机构进行了比较,并分析了这几类张紧机构的应用情况,有参考和应用价值。 相似文献
108.
原油中含有大量的高分子有机固相物质,因此,要准确地描述油气体系相平衡,必须对气液固三相相平衡进行研究,在对高分子有机烃类沥青沉降机理有了一定的认识的基础上,提出了大的交互作用系数,可以描述沥青与原油中轻质不相容性的程度。根据对油气烃类混合物体系的一般性认识与提出的沥青组分特征化方法,导出了与之相应的有其自身特殊性的气液沥青三相相平衡物料平衡方程组,用考虑沥青沉降三相闪蒸数值算法,对沥青沉降进行有效的理化模拟计算,此外,结合实例分析,给出了沥青质参考逸度的计算,饱和压力和沉降量的拟合方法。 相似文献
109.
We have investigated the effect of extended dislocations (0.5-3 μm) on charge distribution in GaN epilayer grown by metalorganic chemical vapor deposition on (0001) sapphire using atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM). It has been observed for the surface at the extended dislocations present in undoped GaN film to be negatively charged showing 0.04-0.2 V higher potential relative to regions that contain no dislocations. In addition to the higher potential at the dislocation core, the surrounding surfaces, including the edge of the dislocations, are also negatively charged in a symmetric way around the dislocations revealing crater-shaped higher potential regions (∼0.04 V) relative to surrounding dislocation-free area. The experimental results show that the protrusion-type of dislocation is also negatively charged and its potential is dependent on the size of dislocation. 相似文献
110.
Xuetian Huang Lei Zhang Min Zhang Peida Ye 《Photonics Technology Letters, IEEE》2005,17(7):1423-1425
The performance degradation of differential quadrature phase-shift keying (DQPSK) wavelength-division-multiplexed (WDM) systems due to self-phase modulation (SPM)- and cross-phase modulation (XPM)-induced nonlinear phase noise is evaluated in this letter. The XPM-induced nonlinear phase noise is approximated as Gaussian distribution and summed together with the SPM-induced nonlinear phase noise. We demonstrate that 10-Gb/s systems, whose walkoff length is larger than 40-Gb/s systems', are more sensitive to XPM-induced nonlinear phase noise than 40-Gb/s systems. Furthermore, DQPSK WDM systems show lower tolerance to both SPM- and XPM-induced nonlinear phase noise than differential phase-shift keying WDM systems. 相似文献