全文获取类型
收费全文 | 43212篇 |
免费 | 11799篇 |
国内免费 | 1435篇 |
专业分类
化学 | 43198篇 |
晶体学 | 357篇 |
力学 | 552篇 |
综合类 | 1篇 |
数学 | 2398篇 |
物理学 | 2773篇 |
无线电 | 7167篇 |
出版年
2022年 | 33篇 |
2021年 | 196篇 |
2020年 | 1790篇 |
2019年 | 3210篇 |
2018年 | 1462篇 |
2017年 | 1039篇 |
2016年 | 4008篇 |
2015年 | 4089篇 |
2014年 | 4070篇 |
2013年 | 4648篇 |
2012年 | 3484篇 |
2011年 | 2704篇 |
2010年 | 3249篇 |
2009年 | 3226篇 |
2008年 | 2785篇 |
2007年 | 2197篇 |
2006年 | 1853篇 |
2005年 | 1988篇 |
2004年 | 1718篇 |
2003年 | 1595篇 |
2002年 | 2244篇 |
2001年 | 1466篇 |
2000年 | 1389篇 |
1999年 | 411篇 |
1998年 | 95篇 |
1997年 | 94篇 |
1996年 | 87篇 |
1995年 | 42篇 |
1994年 | 48篇 |
1993年 | 45篇 |
1992年 | 29篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 40篇 |
1988年 | 46篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 65篇 |
1984年 | 71篇 |
1983年 | 40篇 |
1982年 | 69篇 |
1981年 | 62篇 |
1980年 | 57篇 |
1979年 | 53篇 |
1978年 | 64篇 |
1977年 | 56篇 |
1976年 | 42篇 |
1975年 | 47篇 |
1974年 | 35篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Philip B. Burt 《Foundations of Physics》1993,23(6):965-968
Several interesting and important quantum field theories must contain the coupling constant in the boundary conditions. The theories considered include quantum electrodynamics of spin-1/2 fermions and gauge field theories. 相似文献
62.
63.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
64.
Philip B. Lukins 《Chemical physics letters》1991,180(6):551-555
Measurements of the magneto-optical Cotton—Mouton effect at 632.8 nm of O2(3Σ) over a range of temperature (≈299–464 K) and pressure (up to 613 kPa) are reported and analysed. The study enables a useful comparison to be made of data obtained under different conditions by the two groups that have undertaken systematic measurements of this effect. Agreement between the experimental results and also the derived molecular properties is found to be satisfactory. 相似文献
65.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
66.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
67.
The carrier sense multiple access with collision detection (CSMA-CD) protocol cannot be applied directly to radio channels because of the difficulty in sensing remote carrier in the presence of local transmission. Only recently, a new protocol called the CSMA with timesplit collision detection (CSMA-TCD) was introduced to overcome this problem on radio channels. This paper presents an extension of the CSMA-TCD protocol, called CSMA-TCD with multitone tree search (CSMA-TCD-MTTS). In CSMA-TCD, a preamble is transmitted before data transmission. For CSMA-TCD-MTTS, the preamble is modulated with one out ofN tones. In case of a collision, a resolution algorithm splits the terminals involved into anN -degree tree according to the tone chosen. This paper presents the throughput and approximate delay analysis of the CSMA-TCD-MTTS protocol. 相似文献
68.
69.
H.‐C. Su F.‐C. Fang T.‐Y. Hwu H.‐H. Hsieh H.‐F. Chen G.‐H. Lee S.‐M. Peng K.‐T. Wong C.‐C. Wu 《Advanced functional materials》2007,17(6):1019-1027
Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)2sb]PF6 and [Ir(dFppy)2 sb]PF6 in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)2sb]PF6 and [Ir(dFppy)2sb]PF6 achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W–1) at 2.5 V, and 7.1 % and 26.2 lm W–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells. 相似文献