全文获取类型
收费全文 | 468088篇 |
免费 | 40208篇 |
国内免费 | 22217篇 |
专业分类
电工技术 | 29115篇 |
技术理论 | 54篇 |
综合类 | 34259篇 |
化学工业 | 75773篇 |
金属工艺 | 27350篇 |
机械仪表 | 30064篇 |
建筑科学 | 37240篇 |
矿业工程 | 15786篇 |
能源动力 | 13140篇 |
轻工业 | 31453篇 |
水利工程 | 9325篇 |
石油天然气 | 29694篇 |
武器工业 | 4037篇 |
无线电 | 51837篇 |
一般工业技术 | 50617篇 |
冶金工业 | 23590篇 |
原子能技术 | 5101篇 |
自动化技术 | 62078篇 |
出版年
2024年 | 1998篇 |
2023年 | 7256篇 |
2022年 | 13462篇 |
2021年 | 18844篇 |
2020年 | 14301篇 |
2019年 | 11538篇 |
2018年 | 13197篇 |
2017年 | 14866篇 |
2016年 | 13468篇 |
2015年 | 18781篇 |
2014年 | 23863篇 |
2013年 | 28296篇 |
2012年 | 31179篇 |
2011年 | 34174篇 |
2010年 | 30473篇 |
2009年 | 28574篇 |
2008年 | 27901篇 |
2007年 | 26440篇 |
2006年 | 26169篇 |
2005年 | 22673篇 |
2004年 | 15482篇 |
2003年 | 13715篇 |
2002年 | 13135篇 |
2001年 | 11446篇 |
2000年 | 10798篇 |
1999年 | 11409篇 |
1998年 | 8617篇 |
1997年 | 7358篇 |
1996年 | 7024篇 |
1995年 | 5765篇 |
1994年 | 4629篇 |
1993年 | 3172篇 |
1992年 | 2483篇 |
1991年 | 1895篇 |
1990年 | 1467篇 |
1989年 | 1181篇 |
1988年 | 1009篇 |
1987年 | 628篇 |
1986年 | 482篇 |
1985年 | 300篇 |
1984年 | 250篇 |
1983年 | 185篇 |
1982年 | 158篇 |
1981年 | 98篇 |
1980年 | 131篇 |
1979年 | 61篇 |
1978年 | 21篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1959年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 50 毫秒
91.
Wireless Networks - In such mobile platforms as ships and aircraft, the detection and reconnaissance devices are near to the communication facilities. When working at the same time, they will... 相似文献
92.
Xiao-Lei Qiu Zi-Rui Fan Yang-Yang Liu Ding-Fu Wang Shi-Xin Wang Chun-Xia Li 《International journal of molecular sciences》2021,22(8)
A self-nanoemulsifying drug delivery system (SNEDDS) was developed to enhance the absorption of heparin after oral administration, in which heparin was compounded with phospholipids to achieve better fat solubility in the form of heparin-phospholipid (HEP-Pc) complex. HEP-Pc complex was prepared using the solvent evaporation method, which increased the solubility of heparin in n-octanol. The successful preparation of HEP-Pc complex was confirmed by differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR) spectroscopy, NMR, and SEM. A heparin lipid microemulsion (HEP-LM) was prepared by high-pressure homogenization and characterized. HEP-LM can enhance the absorption of heparin after oral administration, significantly prolong activated partial thromboplastin time (APTT) and thrombin time (TT) in mice, and reduce fibrinogen (FIB) content. All these outcomes indicate that HEP-LM has great potential as an oral heparin formulation. 相似文献
93.
Mitigating gibbsite particle cracking and breakage during industrial alumina production can increase the quality of smelter grade alumina product by reducing the ultrafine particle content. Therefore, it is essential to investigate the particle cracking during static calcination and the breakage of calcined gibbsite particles under external force. In this work, we investigated the impact of the calcination ramping rate and the crystallite size on gibbsite particle cracking during static calcination. A slow ramping rate and a large pristine crystallite size tend to increase particle cracking. Apart from the study of particle cracking behaviour, we also investigated the breakage of calcined gibbsite particle under external force. Cracks on the particle surface can initiate breakage within the crystallite and along the grain boundary under external force. The breakage within crystallite occurs as the cleavage of the crystallite, while the breakage along the grain boundary leads to the shedding of a whole crystallite. We further explored the factors influencing the strength of calcined gibbsite particles. With increasing calcination temperature, the strength of particle increases when gibbsite converts to boehmite, and then decreases when boehmite converts into amorphous alumina. Particles containing smaller crystallites and calcined with fast ramping rates exhibit higher resistance to breakage. 相似文献
94.
Wireless Networks - TCP latency is critical to the performance of Web services. However, packet loss greatly impairs the TCP performance due to its poor loss recovery mechanisms. Recent work FUSO... 相似文献
95.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献
96.
在液化天然气(LNG)接收站工程设计建设过程中,火炬系统的设计是保证LNG接收站安全生产的必要条件。以国内某LNG接收站为例,分析了LNG蒸发气(BOG)产生的因素和机理,及6种工况组合下火炬排放量的计算方法。结果表明:在工况1条件下与实际生产情况吻合良好,其对应的火炬气排放量约为142.7 t/h。在此基础上确定了:BOG支管管径为DN600,BOG总管的管径为DN900;被分离液滴的直径不大于600μm;火炬分液罐尺寸为?2.5 m×8.0 m;电加热器的功率为195 kW;火炬形式为封闭式地面火炬。研究结果可为今后LNG接收站项目火炬系统的处理能力及设备配置提供理论指导。 相似文献
97.
在80 MHz~1 GHz频段,单个功率管输出功率能达到100 W以上,为研制输出功率400 W的功率放大器,文中设计了四路功率合成器。该合成器需要实现功率容量大、工作频带宽、体积小的设计目标。在功率容量方面,文中采用悬置带状线结构,其功率容量远远大于微带线结构;在工作频带方面,采用切比雪夫九节阻抗变换器,将工作带宽拓宽为80 MHz~1 GHz;在体积方面,文中合成器的功率合成部分采用Y型节级联实现四路功率合成,阻抗变换部分采用切比雪夫阻抗变换器进行阻抗变换,该结构相较于磁环巴伦功率合成器,不但具有损耗小、平坦度高的优点,而且通过将阻抗变换器设计成曲折的形状,进一步缩小了合成器体积。仿真与实测结果显示该合成器在80 MHz~1 GHz范围内还具有较高的平坦度,合成效率可达90%以上。 相似文献
98.
Nan Wu Xiaodong Li Mu Zhang Yi Ren Qi Zhu Haijun Peng Hongqiang Ru Xudong Sun 《Journal of the European Ceramic Society》2021,41(4):2898-2907
Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd2O3-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd2O3-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd2O3 and MgO (93 and 78 nm, respectively) and high density. 相似文献
99.
100.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics. 相似文献