全文获取类型
收费全文 | 24970篇 |
免费 | 3325篇 |
国内免费 | 1814篇 |
专业分类
电工技术 | 2191篇 |
综合类 | 2351篇 |
化学工业 | 3617篇 |
金属工艺 | 1362篇 |
机械仪表 | 1699篇 |
建筑科学 | 2036篇 |
矿业工程 | 671篇 |
能源动力 | 775篇 |
轻工业 | 2697篇 |
水利工程 | 663篇 |
石油天然气 | 730篇 |
武器工业 | 433篇 |
无线电 | 2955篇 |
一般工业技术 | 2657篇 |
冶金工业 | 727篇 |
原子能技术 | 452篇 |
自动化技术 | 4093篇 |
出版年
2024年 | 56篇 |
2023年 | 339篇 |
2022年 | 804篇 |
2021年 | 1188篇 |
2020年 | 813篇 |
2019年 | 671篇 |
2018年 | 681篇 |
2017年 | 757篇 |
2016年 | 751篇 |
2015年 | 967篇 |
2014年 | 1366篇 |
2013年 | 1661篇 |
2012年 | 2021篇 |
2011年 | 2084篇 |
2010年 | 1975篇 |
2009年 | 1933篇 |
2008年 | 1932篇 |
2007年 | 1912篇 |
2006年 | 1628篇 |
2005年 | 1445篇 |
2004年 | 1060篇 |
2003年 | 776篇 |
2002年 | 794篇 |
2001年 | 775篇 |
2000年 | 520篇 |
1999年 | 303篇 |
1998年 | 161篇 |
1997年 | 132篇 |
1996年 | 81篇 |
1995年 | 92篇 |
1994年 | 77篇 |
1993年 | 65篇 |
1992年 | 52篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 37篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1973年 | 3篇 |
1959年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Strength of Materials - In order to study the failure process of a large-scale spherical bearing, the finite element simulation method was used to establish the full-scale finite element model of... 相似文献
3.
为稳定掺入高吸水树脂(SAP)水泥基材料的流动性能,采用反相悬浮聚合法制备了多孔型聚丙烯酸/丙烯酰胺SAP.利用扫描电子显微镜(SEM)观测SAP的微观形貌,通过傅里叶红外光谱(FTIR)分析SAP的分子结构,用“茶袋法”测试SAP的吸液性能,并通过流动度试验研究了非多孔型及多孔型SAP对水泥净浆流动度经时变化的影响.结果表明:多孔型SAP具有微米级连通孔结构,能够有效促进吸水速率,达到吸水平衡只需1 min内;当通过额外引水保持水泥净浆初始流动度相同时,多孔型SAP的掺入对水泥净浆流动度的经时损失影响最小. 相似文献
4.
鞠雪艳 《中国炼油与石油化工》2022,24(2):14-22
Conversion of LCO (light cycle oil) to BTX (benzene, toluene, and xylene) is an economically valuable method for refineries. However, this approach still faces difficulties as the main reactions are not clearly understood. Here we study the detailed hydrocracking pathway of typical reactants, 1-methylnaphthalene and tetralin, through molecular simulations and experiments to improve our understanding of the conversion process of LCO to BTX. Molecular simulations demonstrate that the rate-determining step is the isomerization pathway of six-membered ring to five-membered ring in tetralin as its activation energy (ΔEa) is the highest among all the reactions and the order of ΔEa of reactions is isomerization > ring-opening ≈ side-chain cleavage. The results of experiments show that with the increase in reaction depth, i.e., through a high temperature (350 – 370 °C) and low LHSV (4.5 – 6.0 h−1), isomerization, ring-opening, and side-chain cleavage reactions occurred, thus improving the selectivity and yield of alkyl aromatics. 相似文献
5.
6.
7.
Imbalance vibration is a typical failure mode of rotational machines and has significant negative effects on the effii-ciency,accuracy,and service life of equipment.To automatically reduce the imbalance vibration during the opera-tional process,different types of active balancing actuators have been designed and widely applied in actual produc-tion.However,the existing electromagnetic-ring active balancing actuator is designed based on an axial excitation structure which can cause structural instability and has low electromagnetic driving efficiency.In this paper,a novel radial excitation structure and the working principle of an electromagnetic-ring active balancing actuator with a combined driving strategy are presented in detail.Then,based on a finite element model,the performance param-eters of the actuator are analyzed,and reasonable design parameters are obtained.Self-locking torque measurements and comparative static and dynamic experiments are performed to validate the self-locking torque and driving effi-ciency of the actuator.The results indicate that this novel active balancing actuator has sufficient self-locking torque,achieves normal step rotation at 2000 r/min,and reduces the driving voltage by 12.5%.The proposed novel balancing actuator using radial excitation and a combination of permanent magnets and soft-iron blocks has improved electro-magnetic efficiency and a more stable and compact structure. 相似文献
8.
Xuepeng Ni Zhe Cui Ning Jiang Huifang Chen Qilin Wu Anqi Ju Meifang Zhu 《材料科学技术学报》2021,77(18):169-177
The electrode materials with high pseudocapacitance can enhance the rate capability and cycling stabil-ity of lithium-ion storage devices.Herein,we fabricated MoS2 nanoflowers with ultra-large interlayer spacing on N-doped hollow multi-nanochannel carbon nanofibers(F2-MoS2/NHMCFs)as freestanding binder-free anodes for lithium-ion batteries(LIBs).The ultra-large interlayer spacing(0.78~1.11 nm)of MoS2 nanoflowers can not only reduce the internal resistance,but also increase accessible active sur-face area,which ensures the fast Li+intercalation and deintercalation.The NHMCFs with hollow and multi-nanochannel structure can accommodate the large internal strain and volume change during lithi-ation/delithiation process,it is beneficial to improving the cycling stability of LIBs.Benefiting from the above combined structure merits,the F2-MoS2/NHMCFs electrodes deliver a high rate capability 832 mA h g-1 at 10 A g-1 and ultralong cycling stability with 99.29 and 91.60%capacity retention at 10 A g-1 after 1000 and 2000 cycles,respectively.It is one of the largest capacities and best cycling stability at 10 A g-1 ever reported to date,indicating the freestanding F2-MoS2/NHMCFs electrodes have potential applications in high power density LIBs. 相似文献
9.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
10.
For the fluctuation of CFCC caused by environmental noise is the main reason for the low accuracy of keystroke detection,the spatial characteristics of adjacent between CFCC were studied,and the spatial gradient structure of CFCC based on points was established.On this basis,the effect of CFCC spatial gradient on keystroke content recognition and the selection of precise neighborhood points were studied on training and testing.Finally,a high-robustness keystroke recognition algorithm based on acoustic signals was constructed.Extensive experiments in different environments demonstrate that the proposed CFCC spatial gradient sound feature achieves great performance and the recognition accuracy is 96.15%. 相似文献