全文获取类型
收费全文 | 3104篇 |
免费 | 120篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 36篇 |
综合类 | 6篇 |
化学工业 | 699篇 |
金属工艺 | 112篇 |
机械仪表 | 88篇 |
建筑科学 | 77篇 |
矿业工程 | 3篇 |
能源动力 | 243篇 |
轻工业 | 221篇 |
水利工程 | 19篇 |
石油天然气 | 9篇 |
无线电 | 332篇 |
一般工业技术 | 772篇 |
冶金工业 | 223篇 |
原子能技术 | 16篇 |
自动化技术 | 381篇 |
出版年
2024年 | 13篇 |
2023年 | 56篇 |
2022年 | 98篇 |
2021年 | 149篇 |
2020年 | 102篇 |
2019年 | 104篇 |
2018年 | 144篇 |
2017年 | 127篇 |
2016年 | 107篇 |
2015年 | 68篇 |
2014年 | 123篇 |
2013年 | 232篇 |
2012年 | 157篇 |
2011年 | 213篇 |
2010年 | 126篇 |
2009年 | 131篇 |
2008年 | 126篇 |
2007年 | 112篇 |
2006年 | 80篇 |
2005年 | 83篇 |
2004年 | 59篇 |
2003年 | 62篇 |
2002年 | 60篇 |
2001年 | 34篇 |
2000年 | 38篇 |
1999年 | 35篇 |
1998年 | 42篇 |
1997年 | 35篇 |
1996年 | 38篇 |
1995年 | 40篇 |
1994年 | 36篇 |
1993年 | 29篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 27篇 |
1983年 | 27篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1976年 | 21篇 |
1975年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有3237条查询结果,搜索用时 0 毫秒
121.
122.
Parabolic trough solar collector (PTSC) is one of the most proven technologies for large‐scale solar thermal power generation. Currently, the cost of power generation from PTSC is expensive as compared with conventional power generation. The capital/power generation cost can be reduced by increasing aperture sizes of the collector. However, increase in aperture of the collector leads to higher heat flux on the absorber surface and results in higher thermal gradient. Hence, the analysis of heat distribution from the absorber to heat transfer fluid (HTF) and within the absorber is essential to identify the possibilities of failure of the receiver. In this article, extensive heat transfer analysis (HTA) of the receiver is performed for various aperture diameter of a PTSC using commercially available computational fluid dynamics (CFD) software ANSYS Fluent 19.0. The numerical simulations of the receiver are performed to analyze the temperature distribution around the circumference of the absorber tube as well as along the length of tube, the rate of heat transfer from the absorber tube to the HTF, and heat losses from the receiver for various geometric and operating conditions such as collector aperture diameter, mass flow rate, heat loss coefficient (HLC), HTF, and its inlet temperature. It is observed that temperature gradient around the circumference of the absorber and heat losses from the receiver increases with collector aperture. The temperature gradient around the circumference of the absorber tube wall at 2 m length from the inlet are observed as 11, 37, 48, 74, and 129 K, respectively, for 2.5‐, 5‐, 5.77‐, 7.5‐, and 10‐m aperture diameter of PTSC at mass flow rate of 1.25 kg/s and inlet temperature of 300 K for therminol oil as HTF. To minimize the thermal gradient around the absorber circumference, HTFs with better heat transfer characteristics are explored such as molten salt, liquid sodium, and NaK78. Liquid sodium offers a significant reduction in temperature gradient as compared of other HTFs for all the aperture sizes of the collector. It is found that the temperature gradient around the circumference of the absorber tube wall at a length of 2 m is reduced to 4, 8, 10, 13, and 18 K, respectively, for the above‐mentioned mass flow rate with liquid sodium as HTF. The analyses are also performed for different HTF inlet temperature in order to study the behavior of the receiver. Based on the HTA, it is desired to have larger aperture parabolic trough collector to generate higher temperature from the solar field and reduce the capital cost. To achieve higher temperature and better performance of the receiver, HTF with good thermophysical properties may be preferable to minimize the heat losses and thermal gradient around the circumference of the absorber tube. 相似文献
123.
Singh Dalip Saini Ajay Dhayal Veena Agarwal Dinesh Chandra 《Protection of Metals and Physical Chemistry of Surfaces》2019,55(4):682-688
Protection of Metals and Physical Chemistry of Surfaces - Dense alumina coatings were fabricated over aluminum alloy via dip coating method using oxime-modified aluminum(III) isopropoxide as a... 相似文献
124.
Anand J. Puppala Pinit Ruttanaporamakul Surya Sarat Chandra Congress 《Geotextiles and Geomembranes》2019,47(3):295-305
This paper presents a research study on a bridge site located along US highway 67 over SH 174 in Cleburne, Texas, where bridge approach slabs have experienced more than 0.4 m (17 in.) of settlement within a span of 16 years after construction. Many treatment methods attempted to mitigate this problem had proven to be ineffective. As part of novel rehabilitation works, the top of existing fill soil on the embankment was replaced with lightweight expanded polystyrene (EPS) geofoam blocks to alleviate the approach slab settlements. This paper describes initial design and construction details of the rehabilitation works performed on the embankment system along with a focus on the early performance details. Field monitoring studies were conducted for almost three years to study the bump/settlements under the EPS geofoam embankment system. Short term measured settlement data was analyzed with hyperbolic model to predict the long term settlements. Numerical finite element studies attempted in this study showed that settlements could be reasonably predicted by modeling these geofoam embankments. Based on the monitoring and modeling studies, the effectiveness of utilizing EPS geofoam as an embankment fill material was addressed to mitigate the differential settlements under a bridge approach slab. 相似文献
125.
126.
127.
Singh A. K. Chandra Devesh Kattayat Sandhya Kumar Shalendra Alvi P. A. Rathi Amit 《Semiconductors》2019,53(12):1584-1592
Semiconductors - Compositional variations in GaAs based ternary alloys have exhibited wide range alterations in electronic properties. In the present paper, first-principles study of... 相似文献
128.
Vinod Kumar 《Particulate Science and Technology》2019,37(6):766-776
The effects of SiC, Al2O3, and ZrO2 particles on the characteristics of Al/SiC, Al/Al2O3, and Al/ZrO2 metal matrix composites (MMCs) have been studied in the present research work. The comparison of machining characteristics has been done to analyze the behavior of various reinforced particles with the variation of laser machining variables. The output characteristics such as dross height and kerf deviation have been investigated and compared with each MMCs. SEM and XRD have been used for the investigation of morphological changes in the structure and agglomeration of reinforced particles. The crack and recast layer formation has been examined in the specimens of higher quantity of reinforced particles. It was observed that the MMC material reinforced with SiC particles has shown different behavior as compared to other MMC materials. 相似文献
129.
Water Resources Management - Streamflow forecasting can offer valuable information for optimal management of water resources, flood mitigation, and drought warning. This research aims in evaluating... 相似文献
130.
Ymeti A Greve J Lambeck PV Wink T van Hövell SW Beumer TA Wijn RR Heideman RG Subramaniam V Kanger JS 《Nano letters》2007,7(2):394-397
We report the application of an integrated optical Young interferometer sensor for ultrasensitive, real-time, direct detection of viruses. We have validated the sensor by detecting herpes simplex virus type 1 (HSV-1), but the principle is generally applicable. Detection of HSV-1 virus particles was performed by applying the virus sample onto a sensor surface coated with a specific antibody against HSV-1. The performance of the sensor was tested by monitoring virus samples at clinically relevant concentrations. We show that the Young interferometer sensor can specifically and sensitively detect HSV-1 at very low concentrations (850 particles/mL). We have further demonstrated that the sensor can specifically detect HSV-1 suspended in serum. Extrapolation of the results indicates that the sensitivity of the sensor approaches the detection of a single virus particle binding, yielding a sensor of unprecedented sensitivity with wide applications for viral diagnostics. 相似文献