全文获取类型
收费全文 | 2594篇 |
免费 | 543篇 |
国内免费 | 305篇 |
专业分类
化学 | 1827篇 |
晶体学 | 29篇 |
力学 | 202篇 |
综合类 | 7篇 |
数学 | 252篇 |
物理学 | 1125篇 |
出版年
2024年 | 9篇 |
2023年 | 64篇 |
2022年 | 114篇 |
2021年 | 114篇 |
2020年 | 113篇 |
2019年 | 110篇 |
2018年 | 112篇 |
2017年 | 93篇 |
2016年 | 146篇 |
2015年 | 134篇 |
2014年 | 145篇 |
2013年 | 183篇 |
2012年 | 277篇 |
2011年 | 293篇 |
2010年 | 185篇 |
2009年 | 137篇 |
2008年 | 151篇 |
2007年 | 161篇 |
2006年 | 140篇 |
2005年 | 91篇 |
2004年 | 77篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 40篇 |
2000年 | 39篇 |
1999年 | 39篇 |
1998年 | 39篇 |
1997年 | 47篇 |
1996年 | 37篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 19篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3442条查询结果,搜索用时 15 毫秒
51.
An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl2-only ACE and BCl3/Cl2ACE,respectively.The mixed radicals of BCl3/Cl2were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl3/Cl2ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode. 相似文献
52.
53.
54.
For decades the research on thin-film growth has attracted considerable attention as these kinds of materials have the potential for a new generation of device application. It is known that the nuclei at the initial stage of the islands are more stable than others and certain atoms are inert while others are active. In this paper, by using kinetic Monte Carlo simulations, we will show that, when a surfactant layer is used to mediate the growth, a counter-intuitive fractal-to-compact island shape transition can be induced by increasing deposition flux or decreasing growth temperature. Specifically, we introduce a reaction-limited aggregation (RLA) theory, where the physical process controlling the island shape transition is the shielding effect of adatoms stuck to the stable islands on the incoming adatoms. Moreover, the origin of a transition from triangular to hexagonal and then to inverted triangular as well as the decay characteristics of three-dimensional islands on the surface and relations of our unique predictions with recent experiments will be discussed. Furthermore, we will present a novel idea to make use of the condensation energy of adatoms to control the island evolution along a special direction. 相似文献
55.
56.
57.
A Phosphorescent Platinum(II) Bipyridyl Supramolecular Polymer Based on Quadruple Hydrogen Bonds 下载免费PDF全文
Fang‐Wei Liu Dr. Li‐Ya Niu Prof. Yong Chen Prof. Vaidhyanathan Ramamurthy Prof. Li‐Zhu Wu Prof. Chen‐Ho Tung Prof. Yu‐Zhe Chen Prof. Qing‐Zheng Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18132-18139
A platinum(II) bipyridyl complex bearing bis‐ureidopyrimidinone (Pt‐bisUPy) has been designed and its self‐assembling behavior has been thoroughly investigated by 1H NMR, DOSY NMR, Ubbelohde viscometry analysis, UV/Vis, and emission spectroscopies. Pt‐bisUPy underwent concentration‐dependent ring‐chain polymerization in apolar solvents. Hydrogen‐bonding interactions play an important role during the formation of the supramolecular polymers. Hydrogen‐bonded supramolecular polymers were transformed to nanoparticles in water through the miniemulsion method. These nanoparticles showed strong π–π excimeric emission. Metal‐metal‐to‐ligand charge transfer (MMLCT) from Pt–Pt interactions was not significant in the emission spectrum. The phosphorescence of the nanoparticle persisted even under aerobic conditions. The triplet state of these phosphorescent nanomaterials were long‐lived and possessed moderate emission quantum yields. Furthermore, the low toxicity of these materials promises a place for them in in vitro and in vivo bioimaging. 相似文献
58.
59.
60.
Shengli Niu Mengqi Liu Chunmei Lu Hui Li Mengjia Huo 《Journal of Thermal Analysis and Calorimetry》2014,115(1):73-79
Potential of carbide slag as transesterification catalyst is validated. Combined with X-ray fluorescence for ingredient determination, X-ray diffraction for textural phase analysis, scanning electron microscope for surface morphology observation and Hammett indicator for basic strength mensuration, thermal event of carbide slag is investigated through thermogravimetric analysis to estimate the potential of this calcium-based industrial waste as transesterification catalyst. Further, kinetic parameters are calculated through model-free method, where the experiments are conducted at temperature heating rates of 5, 10, 15, and 20 K min?1. As for activation energy and reaction order, Vyazovkin method and Avrami theory are respectively mentioned. Meanwhile, catalytic performance of carbide slag is labeled by transesterification efficiency and calcium hydroxide is conditionally mentioned for comparison. In conclusion, potential of carbide slag as transesterification catalyst is adequately validated. 相似文献