全文获取类型
收费全文 | 89793篇 |
免费 | 9466篇 |
国内免费 | 4187篇 |
专业分类
电工技术 | 5620篇 |
技术理论 | 6篇 |
综合类 | 6924篇 |
化学工业 | 18191篇 |
金属工艺 | 3883篇 |
机械仪表 | 5350篇 |
建筑科学 | 10313篇 |
矿业工程 | 1477篇 |
能源动力 | 9326篇 |
轻工业 | 6897篇 |
水利工程 | 1347篇 |
石油天然气 | 3560篇 |
武器工业 | 936篇 |
无线电 | 5695篇 |
一般工业技术 | 9933篇 |
冶金工业 | 3700篇 |
原子能技术 | 1223篇 |
自动化技术 | 9065篇 |
出版年
2024年 | 327篇 |
2023年 | 1591篇 |
2022年 | 2754篇 |
2021年 | 3364篇 |
2020年 | 3385篇 |
2019年 | 3008篇 |
2018年 | 2820篇 |
2017年 | 3194篇 |
2016年 | 3394篇 |
2015年 | 3565篇 |
2014年 | 5447篇 |
2013年 | 5936篇 |
2012年 | 6163篇 |
2011年 | 6835篇 |
2010年 | 5037篇 |
2009年 | 5096篇 |
2008年 | 4621篇 |
2007年 | 5636篇 |
2006年 | 4954篇 |
2005年 | 4415篇 |
2004年 | 3592篇 |
2003年 | 3258篇 |
2002年 | 2633篇 |
2001年 | 2133篇 |
2000年 | 1712篇 |
1999年 | 1411篇 |
1998年 | 1148篇 |
1997年 | 965篇 |
1996年 | 891篇 |
1995年 | 720篇 |
1994年 | 544篇 |
1993年 | 468篇 |
1992年 | 406篇 |
1991年 | 302篇 |
1990年 | 270篇 |
1989年 | 233篇 |
1988年 | 182篇 |
1987年 | 131篇 |
1986年 | 101篇 |
1985年 | 95篇 |
1984年 | 113篇 |
1983年 | 77篇 |
1982年 | 61篇 |
1981年 | 34篇 |
1980年 | 59篇 |
1964年 | 29篇 |
1963年 | 28篇 |
1959年 | 31篇 |
1955年 | 25篇 |
1951年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
1.
2.
《International Journal of Hydrogen Energy》2022,47(75):32031-32038
The activity of catalysts with various sizes was compared in a fixed-bed Fischer–Tropsch reactor under similar operating conditions by determining the deactivation model. Catalyst size had no impact on the type of deactivation model. The smaller catalyst showed a smaller deactivation constant of catalyst (kd) and a lower deactivation rate in the initial stage. The decline in the activities of the catalyst with a mesh size of 40 was lower than the other catalysts, suggesting its higher long-term stability (ass). Larger catalyst sizes led to the fouling of carbon and heavy hydrocarbons, decreasing the specific surface of the catalyst, thus increasing the pore diffusion resistance and further decrementing the catalyst activities. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(80):33955-33965
We report the study of conductive polyaniline (PANI) chain embedded Ti-MOF functionalized with CoS as a cocatalyst for hydrogen evolution reaction (HER) application. The post synthetically modified hybrid photocatalyst PANI/Ti-MOF/CoS greatly influences the redox and e? ? h+ separation process and exhibits an impressive rate of HER (~1322 μmol h?1g?1), suppressing the pristine Ti-MOF (~62 μmol h?1g?1) with apparent quantum yield (AQY) of ~3.2 and transient current response of ~46.4 μA cm?2. In this system, Ti-MOF provides the circulation of Ti3+ and Ti4+ to the reaction of photocatalytic H2 generation, where the additional PANI and CoS amended the performance of H2 production through electron enrichment and thereby improving the stability and integrity of Ti-MOF. The Electrochemical studies demonstrated increased photocurrent by interweaving Ti-MOF crystal with PANI through cation-π interaction thereby enhancing interface connection and then promoting electron transfers. The charge dynamics revealed the initial charge transfer from photoexcited PANI to encapsulated MOF framework to boost the photocatalytic performance of the system. Further, the electron movement at the Ti-MOF/CoS interface is investigated through work function and electrochemical potential of electrons (Fermi level). DFT results demonstrate the importance of CoS in improving the photocatalytic performance of hybrid Ti-MOF catalyst, which leads to superior catalytic behaviour. These results establish that the encapsulation of catalytic active sites inside MOFs with desirable energy band gaps would be an ideal choice for the production of solar fuels. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(89):38043-38054
Aiming at improving the relatively low energy output and energy conversion efficiency of the micro-thermal voltaic (MTPV) system, an innovative heat recirculating micro combustor with pin fins is designed. The effects of pin fins arrangement, hydrogen/air equivalent ratio on the energy output and performance of CHMC, HMCP and HMCI are compared and investigated. The result shows that when the Vin is 6 m/s and Φ is 1.0, the emitter power of CHMC is 72.76W, and that of HCMP and HCMI micro combustor are 75.99W and 76.35W. and the emitter efficiency of CHMC, HCMP and HCMI is 41.93%, 43.26% and 44.01%. HMCI has better energy output capability compared with CHMC and HMCP. Even though, HMCI brings a higher pressure drop, it is within the acceptable range. When the Vin is 6 m/s, the pressure drop from the pin fins only accounts for 26.4% of the total pressure drop for HMCI. Through the study of equivalent ratio, it is found that HMCI has good adaptability in different equivalent ratio range. This work provides new ideas for the development of MTPV system in the future. 相似文献
5.
6.
以智能反射面(intelligent reflecting surface,IRS)辅助的无线携能通信(simultaneous wireless information and power transfer,SWIPT)系统为背景,研究了该系统中基于能效优先的多天线发送端有源波束成形与IRS无源波束成形联合设计与优化方法。以最大化接收端的最小能效为优化目标,构造在发送端功率、接收端能量阈值、IRS相移等多约束下的非线性优化问题,用交替方向乘子法(alternating direction method of multipliers,ADMM)求解。采用Dinkelbach算法转化目标函数,通过奇异值分解(singular value decomposition,SVD)和半定松弛(semi-definite relaxation,SDR)得到发送端有源波束成形向量。采用SDR得到IRS相移矩阵与反射波束成形向量。结果表明,该系统显著降低了系统能量收集(energy harvesting,EH)接收端的能量阈值。当系统总电路功耗为?15 dBm时,所提方案的用户能效为300 KB/J。当IRS反射阵源数与发送天线数均为最大值时,系统可达最大能效。 相似文献
7.
《Ceramics International》2022,48(9):12281-12290
Following the rapid growth of lightning technology, the development of red-emitting phosphors is effective for improving color temperature and color rendering index for w-LEDs devices. Herein, a single phased garnet phosphor with cation and polyhedron substitution modification was firstly prepared. For Mg3Gd2Ge3O12: Bi3+, Eu3+, the intensity has been remarkably improved by about 16% compared to the one without Bi3+ sensitization. The energy transfer mechanism is identified in this work. Based on cation and polyhedron substitution strategies, novel phosphors with different compositions were obtained and further modified the PL properties. With Lu3+ substitution, the bond lengths between Bi3+ ion and anion ligands are decreased and the site symmetry has been strengthened, which leads to a 21 nm blue shift when Lu3+ totally replaced Gd3+ ions. In addition, Lu3+ and [SiO4] substitution strategies both effectively increased symmetric rigid structure, which leads to a significant improvement in thermal stability, indicating the samples own great potential in optical applications This work provides a new insight to synthesis red-emitting phosphors for warm white-LEDs. 相似文献
8.
《Ceramics International》2021,47(19):27217-27229
Herein, an in-depth analysis of the effect of heat treatment at temperatures between 900 and 1500 °C under an Ar atmosphere on the structure as well as strength of Cansas-II SiC fibres was presented. The untreated fibres are composed of β-SiC grains, free carbon layers, as well as a small amount of an amorphous SiCxOy phase. As the heat-treatment temperature was increased to 1400 °C, a significant growth of the β-SiC grains and free carbon layers occurred along with the decomposition of the SiCxOy phase. Moreover, owing to the decomposition of the SiCxOy phase, some nanopores formed on the fibre surface upon heating at 1500 °C. The mean strength of the Cansas-II fibres decreased progressively from 2.78 to 1.20 GPa with an increase in the heat-treatment temperature. The degradation of the fibre strength can be attributed to the growth of critical defects, β-SiC grains, as well as the residual tensile stress. 相似文献
9.
目的建立超高效液相色谱-串联质谱法同时测定糕点中6种常用合成甜味剂的分析方法。方法选用超纯水作为提取溶剂,涡旋和超声提取后,低温离心,取部分上清液加入正己烷除脂,Waters Atlantis■T3色谱柱、甲醇-5 mmol/L甲酸铵(含0.1%甲酸)作为流动相、亲水亲脂平衡型固相萃取柱HLB(hydrophile-lipophile balance)净化。结果6种甜味剂在质量浓度为10~200 ng/mL的曲线范围内呈良好线性关系,相关系数r均大于0.999,平均加标回收率在85.0%-98.2%之间,相对平均偏差(relative standard deviation,RSD)为1.3%~6.7%。结论该方法具有前处理简单、灵敏度高、检测速度快等优点,适合糖精钠、甜蜜素、三氯蔗糖、阿斯巴甜、阿力甜、纽甜的检测,但不适用于安赛蜜的检测。 相似文献