全文获取类型
收费全文 | 3980篇 |
免费 | 637篇 |
国内免费 | 296篇 |
专业分类
化学 | 2370篇 |
晶体学 | 126篇 |
力学 | 200篇 |
综合类 | 26篇 |
数学 | 32篇 |
物理学 | 2159篇 |
出版年
2024年 | 11篇 |
2023年 | 17篇 |
2022年 | 69篇 |
2021年 | 74篇 |
2020年 | 66篇 |
2019年 | 65篇 |
2018年 | 93篇 |
2017年 | 140篇 |
2016年 | 129篇 |
2015年 | 113篇 |
2014年 | 174篇 |
2013年 | 367篇 |
2012年 | 208篇 |
2011年 | 300篇 |
2010年 | 183篇 |
2009年 | 209篇 |
2008年 | 217篇 |
2007年 | 221篇 |
2006年 | 226篇 |
2005年 | 207篇 |
2004年 | 198篇 |
2003年 | 179篇 |
2002年 | 171篇 |
2001年 | 127篇 |
2000年 | 145篇 |
1999年 | 105篇 |
1998年 | 102篇 |
1997年 | 94篇 |
1996年 | 97篇 |
1995年 | 54篇 |
1994年 | 67篇 |
1993年 | 62篇 |
1992年 | 52篇 |
1991年 | 26篇 |
1990年 | 33篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 24篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 35篇 |
1980年 | 31篇 |
1979年 | 57篇 |
1978年 | 31篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有4913条查询结果,搜索用时 0 毫秒
971.
We propose a toy model to describe in the frame of Mode Coupling Theory multiple glass transitions. The model is based on the postulated simple form for static structure factor as a sum of two delta-functions. This form makes it possible to solve the MCT equations in almost analytical way. The phase diagram is governed by two swallow tails resulting from two A4 singularities and includes liquid–glass transition and multiple glasses. The diagram has much in common with those of binary and quasibinary systems. 相似文献
972.
Photoluminescence characteristics and energy transfer between Bi~(3+) and Eu~(3+) in Na_2O–CaO–GeO_2–SiO_2 glass 下载免费PDF全文
We report the photoluminescence(PL) of Eu^3+-doped glass with Bi^3+as a sensitizer. The specific glass system with the strong enhancement of the red emission of Eu3+is obtained by adding a small number of Bi3+ions instead of increasing the Eu^3+ concentration. The emission band of Bi3+overlaps with the excitation band of Eu^3+ and the lifetime decay curves,resulting in a very efficient energy transfer from Bi^3+ to Eu^3+. The probability of energy transfer is strongly dependent on Bi^3+ concentration. In addition, the intensity of 4f–4f transition is much stronger than that of a charge-transfer(CT) band in the excitation spectrum, which indicates that the Na2O–Ca O–Ge O2-Si O2 glass is a suitable red-emitting phosphor with high stability as a candidate for light-emitting diodes(LEDs). 相似文献
973.
CHEN Yan-ping LUO De-li HUANG Bin CHENG Hao TANG Xian-chen LI Qiang LEI Hong-bo CHEN Dan-ping 《光谱学与光谱分析》2021,41(6):1863-1868
采用熔融-淬冷法制备了Tb3+掺杂锂铝硅酸盐闪烁玻璃,用紫外激发光谱、发射光谱及荧光寿命表征了光致发光性能,用X射线和阴极射线激发测试了辐射致发光性能。研究结果表明:低Tb3+掺杂浓度时,随着其浓度增大,Tb3+间的交叉弛豫增加导致了5D3→7Fj跃迁的能量逐渐向5D4→7Fj迁移转变,5D3激发态的荧光寿命和发射强度均明显下降,5D4-7Fj发射强度逐渐增大。较高Tb3+浓度时,其浓度继续增加会提升非辐射比例,是荧光寿命降低和荧光猝灭的最主要原因。比较光致发光和辐照致发光性能,发现随着激发源的能量上升,会增加激发态5D3能级向5D4能级的能量转移,同时,由于玻璃的密度低会导致辐照致发光效率随激发源的能量上升而下降。 相似文献
974.
975.
《中国物理 B》2021,30(6):66301-066301
Dynamics of hydrogen doped Cu_(50) Zr_(50) glass-forming liquids are investigated by using the newly developed modified embedded atomic method(MEAM) potential based on molecular dynamics simulations. We find that the doping of hydrogen atoms slows down the relaxation dynamics, reduces the fragility of supercooled melts, and promotes the occurrence of glass transitions. The dynamic slowdown is suggested to be closely related to the effect of hydrogen atoms on locally ordered structure of melts. With increasing concentration of hydrogen, the five-fold symmetry associated with Cu-and Zr-centered polyhedrons is lowered, on the other hand, the local order featuring metal hydrides is enhanced. The latter dominates the dynamic behaviors of glass-forming liquids, especially for Zr atoms, and results in the dynamic slowdown. 相似文献
976.
《中国物理 B》2021,30(7):76103-076103
It has been a long-standing puzzling problem that some glasses exhibit higher glass transition temperatures(denoting high stability) but lower activation energy for relaxations(denoting low stability). In this paper, the relaxation kinetics of the nanoconfined D-mannitol(DM) glass was studied systematically using a high-precision and high-rate nanocalorimeter.The nanoconfined DM exhibits enhanced thermal stability compared to the free DM. For example, the critical cooling rate for glass formation decreases from 200 K/s to below 1 K/s; the Tg increases by about 20 K–50 K. The relaxation kinetics is analyzed based on the absolute reaction rate theory. It is found that, even though the activation energy E~*decreases,the activation entropy S~*decreases much more for the nanoconfined glass that yields a large activation free energy G~*and higher thermal stability. These results suggest that the activation entropy may provide new insights in understanding the abnormal kinetics of nanoconfined glassy systems. 相似文献
977.
978.
Molecular dynamics simulation is performed to simulate the tension–compression fatigue of notched metallic glasses(MGs), and the notch effect of MGs is explored. The notches will accelerate the accumulation of shear transition zones, leading to faster shear banding around the notches' root causing it to undergo severe plastic deformation. Furthermore, a qualitative investigation of the notched MGs demonstrates that fatigue life gradually becomes shorter with the increase in sharpness until it reaches a critical scale. The fatigue performance of blunt notches is stronger than that of sharp notches. Making the notches blunter can improve the fatigue life of MGs. 相似文献
979.
利用超景深显微镜(OM)、激光拉曼光谱仪(Raman)、X射线荧光光谱仪(XRF)、扫描电子显微镜能谱(SEM-EDS)、色度仪等多种手段,对陕西战国秦墓出土的两种质地、颜色不同的六博棋子进行了综合分析检测。鉴定出蓝色样品为铅钡玻璃,紫色样品为中国紫制品,发现了中国紫在战国时期的新用途。并对比陕西出土的铅钡玻璃制品与两湖、四川地区出土的同时代的铅钡玻璃制品在成分组成上的差异,推测战国时期铅钡玻璃的制作工艺已成熟,可根据器物形制的需求进行不同的成分配比。同时,还发现当时的玻璃制作已有旧料重熔制作新器的现象。在确定中国紫成分的基础上,利用色度计进行色度测试,根据光谱数据,首次为人造硅酸铜钡颜料确定了特征光谱峰,使快速、无损的对人造硅酸铜钡颜料的鉴定识别成为可能。 相似文献
980.