全文获取类型
收费全文 | 26358篇 |
免费 | 4595篇 |
国内免费 | 4947篇 |
专业分类
化学 | 21328篇 |
晶体学 | 527篇 |
力学 | 1201篇 |
综合类 | 367篇 |
数学 | 2591篇 |
物理学 | 9886篇 |
出版年
2024年 | 64篇 |
2023年 | 483篇 |
2022年 | 892篇 |
2021年 | 1085篇 |
2020年 | 1183篇 |
2019年 | 1218篇 |
2018年 | 990篇 |
2017年 | 1039篇 |
2016年 | 1350篇 |
2015年 | 1442篇 |
2014年 | 1802篇 |
2013年 | 2348篇 |
2012年 | 2572篇 |
2011年 | 2696篇 |
2010年 | 2014篇 |
2009年 | 1836篇 |
2008年 | 2103篇 |
2007年 | 1793篇 |
2006年 | 1586篇 |
2005年 | 1266篇 |
2004年 | 1043篇 |
2003年 | 806篇 |
2002年 | 734篇 |
2001年 | 636篇 |
2000年 | 521篇 |
1999年 | 444篇 |
1998年 | 316篇 |
1997年 | 219篇 |
1996年 | 243篇 |
1995年 | 192篇 |
1994年 | 181篇 |
1993年 | 144篇 |
1992年 | 110篇 |
1991年 | 108篇 |
1990年 | 93篇 |
1989年 | 58篇 |
1988年 | 56篇 |
1987年 | 32篇 |
1986年 | 53篇 |
1985年 | 42篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1957年 | 7篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
91.
92.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
93.
A Generalized Optical Logic Element or GOLE is device that performs any of the 16 Boolean logic operations on signals in an optical beam with very fast switching among functions. The advantages of a generalized or universal gate in manufacturing are obvious. Extremely flexible functioning becomes possible if the GOLE functionality is switched in response to earlier computations. Likewise Field Programmable Gate Arrays or FPGAs can be used to fix the GOLE functions, making one of the most powerful and flexible processor units ever designed - called a Field GOLE. Such systems can be made in bulk optics to utilize Spatial Light Modulator or SLM capabilities, but integrated optics on silicon will be the choice for most applications. GOLEs can be generalized in several ways to become Fredkin gates and generalized Fredkin gates. They can also be cascaded similarly to electronic gates. 相似文献
94.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献
95.
物理实验课程考核、评估体系初探 总被引:4,自引:0,他引:4
对物理实验课程考核、评估方法进行了探讨,提出了物理实验课程考核、评估体系及实施细则.重点介绍了体系中的核心部分——正规的物理实验课程考试. 相似文献
96.
97.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
98.
99.
100.