全文获取类型
收费全文 | 271149篇 |
免费 | 6265篇 |
国内免费 | 2630篇 |
专业分类
电工技术 | 6621篇 |
综合类 | 2242篇 |
化学工业 | 39723篇 |
金属工艺 | 12393篇 |
机械仪表 | 8926篇 |
建筑科学 | 8510篇 |
矿业工程 | 1442篇 |
能源动力 | 7132篇 |
轻工业 | 26316篇 |
水利工程 | 2418篇 |
石油天然气 | 2886篇 |
武器工业 | 262篇 |
无线电 | 34376篇 |
一般工业技术 | 48271篇 |
冶金工业 | 51293篇 |
原子能技术 | 4224篇 |
自动化技术 | 23009篇 |
出版年
2022年 | 2013篇 |
2021年 | 3218篇 |
2020年 | 2339篇 |
2019年 | 2481篇 |
2018年 | 3411篇 |
2017年 | 3371篇 |
2016年 | 3491篇 |
2015年 | 3416篇 |
2014年 | 4875篇 |
2013年 | 12742篇 |
2012年 | 7492篇 |
2011年 | 9776篇 |
2010年 | 7986篇 |
2009年 | 8589篇 |
2008年 | 9126篇 |
2007年 | 9074篇 |
2006年 | 8391篇 |
2005年 | 7662篇 |
2004年 | 7040篇 |
2003年 | 6839篇 |
2002年 | 6797篇 |
2001年 | 6807篇 |
2000年 | 6234篇 |
1999年 | 6882篇 |
1998年 | 16912篇 |
1997年 | 11886篇 |
1996年 | 9218篇 |
1995年 | 6907篇 |
1994年 | 6094篇 |
1993年 | 5837篇 |
1992年 | 4144篇 |
1991年 | 4070篇 |
1990年 | 3638篇 |
1989年 | 3554篇 |
1988年 | 3471篇 |
1987年 | 2935篇 |
1986年 | 2870篇 |
1985年 | 3416篇 |
1984年 | 3057篇 |
1983年 | 2749篇 |
1982年 | 2554篇 |
1981年 | 2578篇 |
1980年 | 2437篇 |
1979年 | 2272篇 |
1978年 | 2236篇 |
1977年 | 2809篇 |
1976年 | 4173篇 |
1975年 | 1899篇 |
1974年 | 1795篇 |
1973年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
3.
Wireless Personal Communications - Besides anti-malware usage for the eradication of malicious attacks, researchers have developed epidemic models in order to gain more insights into the spread... 相似文献
4.
A. Nakano T. Shimazaki M. Sekiya H. Shiozawa K. Ohtsuka A. Aoyagi T. Iwakiri Z. Mikami M. Sato Y. Sugino K. Kinoshita T. Matsuoka T. Imamura Y. Takayama K. Yamamoto 《International Journal of Hydrogen Energy》2021,46(29):15649-15659
Monitoring the temperature in liquid hydrogen (LH2) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa. 相似文献
5.
Abulyazied Dalia E. Alturki Asma M. Youness Rasha A. Abomostafa H. M. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(10):4077-4092
Journal of Inorganic and Organometallic Polymers and Materials - In this work, a borosilicate glass sample (5SiO2–45B2O3–20Na2O–25CaO–5Ag2O) was added to nano-sized... 相似文献
6.
Jinming Wang Meng Yang Guodong Zou Di Liu Qiuming Peng 《Advanced functional materials》2021,31(21):2101180
Lithium (Li) metal, as an appealing candidate for the next-generation of high-energy-density batteries, is plagued by its safety issue mainly caused by uncontrolled dendrite growth and infinite volume expansion. Developing new materials that can improve the performance of Li-metal anode is one of the urgent tasks. Herein, a new MXene derivative containing pure rutile TiO2 and N-doped carbon prepared by heat-treating MXene under a mixing gas, exhibiting high chemical activity in molten Li, is reported. The lithiation MXene derivative with a hybrid of LiTiO2-Li3N-C and Li offers outstanding electrochemical properties. The symmetrical cell assembling lithiation MXene derivative hybrid anode exhibits an ultra-long cycle lifespan of 2000 h with an overpotential of ≈30 mV at 1 mA cm−2, which overwhelms Li-based anodes reported so far. Additionally, long-term operations of 34, 350, and 500 h at 10 mA cm−2 can be achieved in symmetrical cells at temperatures of −10, 25, and 50 °C, respectively. Both experimental tests and density functional theory calculations confirm that the LiTiO2-Li3N-C skeleton serves as a promising host for Li infusion by alleviating volume variation. Simultaneously, the superlithiophilic interphase of Li3N guides Li deposition along the LiTiO2-Li3N-C skeleton to avoid dendrite growth. 相似文献
7.
Dr. Thomas Le Bihan Dr. Cathryn H. S. Driver Dr. Thomas Ebenhan Dr. Nathalie Le Bris Dr. Jan Rijn Zeevaart Prof. Dr. Raphaël Tripier 《ChemMedChem》2021,16(5):809-821
An improved glucose-chelator-albumin bioconjugate (GluCAB) derivative, GluCAB-2Mal, has been synthesized and studied for in vivo 64Cu-PET/CT imaging in breast cancer mice models together with its first-generation analogue GluCAB-1Mal. The radioligand works on the principle of tumor targeting through the enhanced permeability and retention (EPR) effect with a supportive role played by glucose metabolism. [64Cu]Cu-GluCAB-2Mal (99 % RCP) exhibited high serum stability with immediate binding to serum proteins. In vivo experiments for comparison between tumor targeting of [64Cu]Cu-GluCAB-2Mal and previous-generation [64Cu]Cu-GluCAB-1Mal encompassed microPET/CT imaging and biodistribution analysis in an allograft E0771 breast cancer mouse model. Tumor uptake of [64Cu]Cu-GluCAB-2Mal was clearly evident with twice as much accumulation as compared to its predecessor and a tumor/muscle ratio of up to 5 after 24 h. Further comparison indicated a decrease in liver accumulation for [64Cu]Cu-Glu-CAB-2Mal. 相似文献
8.
目的 为了解决目前三维数据隐藏算法不能兼顾无失真和盲提取的问题,提出一种新的完全无失真的三维网格模型数据隐藏盲算法。方法 首先使用混沌逻辑映射选择嵌入与提取模式,保证数据的安全性。然后利用面元素重排,完全不会造成三维模型失真的性质,通过不同嵌入模式规则对三角面元素进行重排,以嵌入秘密数据。接收端则可根据相应的提取模式规则提取秘密数据。结果 仿真结果与分析表明,该算法不会对三维模型造成任何失真,嵌入容量为每顶点2比特,且能抵抗仿射变换攻击、噪声攻击和平滑攻击等。结论 这种三维数据隐藏盲算法无失真,容量大、安全性高、鲁棒性强,适用于三维载体不容修改的情形,如军事、医学、秘密通信和版权保护等。 相似文献
9.
10.
Bing Huang Meng Wang Guodong Xu Lin Hu Lin Chen Yijie Gu 《Ceramics International》2021,47(6):7700-7710
In this study, La was doped into the lithium layer of Li-rich cathode material and formed a layered-spinel hetero-structure. The morphology, crystal structure, element valence and kinetics of lithium ion migration were studied by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The La doped lithium-rich cathode material exhibited similar initial discharge capacity of 262.8 mAh g?1 at 0.1 C compared with the undoped material, but the discharge capacity retention rate can be obviously improved to 90% after 50 cycles at 1.0 C. Besides that, much better rate capability and Li+ diffusion coefficient were observed. The results revealed that La doping not only stabilized the material structure and reduced the Li/Ni mixing degree, but also induced the generation of spinel phase to provide three-dimensional diffusion channels for lithium ion migration. Moreover, the porous structure of the doped samples also contributed to the remarkable excellent electrochemical performance. All of these factors combined to significantly improve the electrochemical performance of the material. 相似文献