全文获取类型
收费全文 | 2808篇 |
免费 | 291篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 69篇 |
综合类 | 183篇 |
化学工业 | 339篇 |
金属工艺 | 60篇 |
机械仪表 | 242篇 |
建筑科学 | 207篇 |
矿业工程 | 45篇 |
能源动力 | 436篇 |
轻工业 | 150篇 |
水利工程 | 8篇 |
石油天然气 | 97篇 |
武器工业 | 8篇 |
无线电 | 70篇 |
一般工业技术 | 1127篇 |
冶金工业 | 51篇 |
原子能技术 | 4篇 |
自动化技术 | 45篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 49篇 |
2021年 | 57篇 |
2020年 | 76篇 |
2019年 | 55篇 |
2018年 | 64篇 |
2017年 | 60篇 |
2016年 | 83篇 |
2015年 | 97篇 |
2014年 | 171篇 |
2013年 | 152篇 |
2012年 | 189篇 |
2011年 | 197篇 |
2010年 | 154篇 |
2009年 | 178篇 |
2008年 | 142篇 |
2007年 | 186篇 |
2006年 | 171篇 |
2005年 | 158篇 |
2004年 | 145篇 |
2003年 | 151篇 |
2002年 | 87篇 |
2001年 | 90篇 |
2000年 | 67篇 |
1999年 | 48篇 |
1998年 | 48篇 |
1997年 | 24篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1979年 | 1篇 |
排序方式: 共有3141条查询结果,搜索用时 31 毫秒
1.
针对在高太阳辐射地区,柴油车驾驶室内使用车载空调会增加车辆发动机的耗油量、降低柴油车经济效益的问题,搭建了一套由发动机尾气余热驱动的吸附式车载空调系统。系统由填充有氯化钙/氯化锰/硫化膨胀石墨复合吸附剂的吸附床、蒸发器、冷凝器、储液罐和阀门组成,使用氨作为制冷剂,利用车辆在行驶时接触到的自然风为吸附床冷却,在发动机尾气余热的驱动下,为驾驶室内提供连续的制冷效果。结合仿真和实验测试,对所设计系统的制冷性能进行了分析,仿真结果表明,系统最优循环时间为45 min,系统的理论平均制冷功率可达3.5 kW以上,系统COP处于0.2~0.25之间。实验结果表明,在230℃的尾气温度条件下,系统能产生3 kW的平均制冷量。在40℃环境温度条件下,系统在蒸发器进出口处的平均温差为6.5℃,平均制冷量为3.2 kW。 相似文献
2.
3.
Mauro D. Santos Ivonne Delgadillo Jorge A. Saraiva 《International Journal of Food Science & Technology》2020,55(3):1171-1179
Hyperbaric storage (HS) was evaluated as a new food preservation methodology at room temperature (RT) for beef and pork meat, both minced and in pieces, and compared to refrigeration (RF) storage. The meat samples were stored at 50, 75 and 100 MPa and variable RT up to 60 days. HS at 75 and 100 MPa could not only inhibit microbial growth but also inactivate microorganisms. Regarding physicochemical analyses, an overall equal to better pH maintenance in HS samples was achieved, and similar colour differences between HS and RF were observed. Generally, similarities in moisture content and drip loss between HS (mostly 75 and 100 MPa) and RF were detected (tendency for lower values in the former and higher values in the latter for the higher pressure level). Protein solubility revealed a decrease of sarcoplasmic protein values during storage with a pressure level dependency in some samples. 相似文献
4.
Imad Hussain S.N. Khan Eun Ji Kim So Eun Jeon Bon Heun Koo 《Ceramics International》2018,44(3):2892-2899
A systematic study focusing on the effect of Niobium (Nb) doping on the structural, magnetic and magnetocaloric properties of Ba2FeMoO6 samples is presented here. The samples of interest Ba2FeMo1?xNbxO6 (0 ≤ x ≤ 0.4) were prepared using the solid state reaction method and were confirmed to possess a cubic structure with Fm-3m space group using the X-ray diffraction analysis and Rietveld refinement. A second order of ferromagnetic phase transition was recorded in both the pure as well as the Nb doped samples using the temperature dependent magnetization and Arrott plots analysis. The pristine Ba2FeMoO6 (BFMO) sample indicated a spontaneous magnetization (34.6 emu/g at 100 K) with a relatively sharp magnetic transition at the Curie temperature (TC) of 315 K as compared to the doped samples. A magnetic entropy change of 0.93 Jkg?1K?1 at an applied magnetic field of 2.5 T was measured for the pure BFMO sample. The doped BFMO samples with Mo partially substituted by Nb however, were observed to effectively modify the TC accompanied by a decrease in magnetization. The results investigated in this work suggest that the magnetic and magnetocaloric properties of the BFMO can be tailored by controlled Nb doping which is of significant importance in order to realize the numerous potential applications of the material in the magnetic refrigeration technology. 相似文献
5.
《低温学》2015
The design procedure of an active magnetic regenerator (AMR) operating between liquid nitrogen temperature and liquid hydrogen temperature is discussed with the selected magnetic refrigerants. Selected magnetic refrigerants (GdNi2, Dy0.85Er0.15Al2, Dy0.5Er0.5Al2, and Gd0.1Dy0.9Ni2) that have different transition temperatures are layered in an AMR to widen the temperature span. The optimum volume fraction of the layered refrigerants for the maximum COP with minimum volume is designed in a two-stage active magnetic regenerative refrigerator (AMRR) using one dimensional numerical simulation. The entropy generation in each stage of the AMR is calculated by the numerical simulation to optimize the proposed design. The main sources of the entropy generation in the AMR are pressure drop, convection and conduction heat transfers in the AMR. However, the entropy generation by the convective heat transfer is mostly dominant in the optimized cases. In this paper, the design parameters and the operating conditions such as the distribution of the selected refrigerants in the layered AMR, the intermediate temperature between two stages and the mass flow rate of heat transfer fluid are specifically determined to maximize the performance of the AMR. The proposed design method will facilitate the construction of AMR systems with various magnetic refrigerants and conditions such as AMR size, operating temperature range, and magnetic field variation. 相似文献
6.
Effect of biodegradable film (lyophilised alga Fucus spiralis and sorbic acid) on quality properties of refrigerated megrim (Lepidorhombus whiffiagonis) 下载免费PDF全文
Bibiana García‐Soto José M. Miranda Ana Rodríguez‐Bernaldo de Quirós Raquel Sendón Ana V. Rodríguez‐Martínez Jorge Barros‐Velázquez Santiago P. Aubourg 《International Journal of Food Science & Technology》2015,50(8):1891-1900
The effect of replacing the on‐board currently employed polyethylene film by a novel type of environmentally friendly packaging was studied. For it, a polylactic acid (PLA) biodegradable film including lyophilised alga Fucus spiralis and sorbic acid was applied during megrim (Lepidorhombus whiffiagonis) refrigeration and its effect on fish quality loss was evaluated. Thus, sensory assessment showed that samples wrapped up with PLA film including 8% alga and 1% sorbic acid were still acceptable on day 11, while control fish specimens (kept under polyethylene film) were rejected at that time. Under such biodegradable film condition, a preservative effect was also implied according to chemical indices assessment related to microbial activity (trimethylamine–N) and lipid oxidation development (peroxide and fluorescent compounds formation); additionally, lower mean numbers for different microbiological groups (aerobes, Enterobacteriaceae and psychrotrophs) were detected. This result provides a promising replacement strategy to enhance refrigerated fish quality and reduce the waste material content. 相似文献
7.
8.
To evaluate the performance of the ejector-expansion refrigeration cycle (EERC) using zeotropic mixtures, a numerical study is conducted. A constant-pressure two-phase ejector model for zeotropic mixtures is established. The effects of both the fluid composition and the working conditions are investigated. Mixture R134a/R143a is selected as the working and the simulation results reveal that, the cycle COP increases first and then decreases as MFt (the mass fraction of R134a) increases in the researched condition. The COP gets a maximum value of 4.18 with MFt of 0.9 and yields a minimum value of 3.66 with MFt of 0.5. With mixture 0.9/0.1, the COP improvement reaches a maximum value of 10.47%. This improvement rises at high condensing temperature or low evaporating temperature. The exergy analysis shows that the compressor and ejector contribute the most exergy destruction, and the cycle exergy efficiency achieves a maximum value with MFt of 0.7. 相似文献
9.
用水溶液挤压法制备了24个CaCl2/ENG成型混合吸附剂样品,利用目前闪光扩散法测量导热系数最先进的仪器——LFA447激光导热仪对样品进行了导热系数的测试。研究表明:挤压法制备的样品垂直于压力方向上的导热系数高于平行于压力方向上的,大约是其1.1~1.2倍,具有各向异性;在一定范围内,随着固化密度的增加导热系数不断增加,随着氯化钙和膨胀石墨质量比的减小导热系数也不断增大;在氯化钙和ENG的质量比为2∶1,固化密度从600kg/m3增加到700kg/m3的过程中导热系数增加得最为明显,固化密度和膨胀石墨的含量对成型吸附剂样品的导热系数的影响有耦合作用。 相似文献
10.