全文获取类型
收费全文 | 38551篇 |
免费 | 9689篇 |
国内免费 | 1444篇 |
专业分类
化学 | 43202篇 |
晶体学 | 348篇 |
力学 | 575篇 |
综合类 | 18篇 |
数学 | 2503篇 |
物理学 | 3038篇 |
出版年
2023年 | 41篇 |
2022年 | 43篇 |
2021年 | 213篇 |
2020年 | 1283篇 |
2019年 | 2634篇 |
2018年 | 1056篇 |
2017年 | 667篇 |
2016年 | 3430篇 |
2015年 | 3581篇 |
2014年 | 3493篇 |
2013年 | 4235篇 |
2012年 | 3167篇 |
2011年 | 2395篇 |
2010年 | 2931篇 |
2009年 | 2924篇 |
2008年 | 2572篇 |
2007年 | 1950篇 |
2006年 | 1648篇 |
2005年 | 1809篇 |
2004年 | 1593篇 |
2003年 | 1449篇 |
2002年 | 2091篇 |
2001年 | 1421篇 |
2000年 | 1357篇 |
1999年 | 409篇 |
1998年 | 105篇 |
1997年 | 75篇 |
1996年 | 97篇 |
1995年 | 63篇 |
1994年 | 65篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 41篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 24篇 |
1985年 | 67篇 |
1984年 | 41篇 |
1983年 | 42篇 |
1982年 | 38篇 |
1981年 | 53篇 |
1980年 | 43篇 |
1979年 | 33篇 |
1978年 | 35篇 |
1977年 | 35篇 |
1976年 | 26篇 |
1975年 | 29篇 |
1974年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
191.
192.
193.
194.
195.
196.
197.
198.
We continue the investigation of locally testable codes, i.e., error‐correcting codes for which membership of a given word in the code can be tested probabilistically by examining it in very few locations. We give two general results on local testability: First, motivated by the recently proposed notion of robust probabilistically checkable proofs, we introduce the notion of robust local testability of codes. We relate this notion to a product of codes introduced by Tanner and show a very simple composition lemma for this notion. Next, we show that codes built by tensor products can be tested robustly and somewhat locally by applying a variant of a test and proof technique introduced by Raz and Safra in the context of testing low‐degree multivariate polynomials (which are a special case of tensor codes). Combining these two results gives us a generic construction of codes of inverse polynomial rate that are testable with poly‐logarithmically many queries. We note that these locally testable tensor codes can be obtained from any linear error correcting code with good distance. Previous results on local testability, albeit much stronger quantitatively, rely heavily on algebraic properties of the underlying codes. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
199.
Wei‐Ling Wang Jian‐Wei Xu Yee‐Hing Lai 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4154-4164
Bipyridinophane–fluorene conjugated copolymers have been synthesized via Suzuki and Heck coupling reactions from 5,8‐dibromo‐2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane and suitable fluorene precursors. Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P7 ) exhibits large absorption and emission redshifts of 20 and 34 nm, respectively, with respect to its planar reference polymer Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐1,4‐(2,5‐dimethylbenzene)] ( P11 ), which bears the same polymer backbone as P7 . These spectral shifts originate from intramolecular aromatic C? H/π interactions, which are evidenced by ultraviolet–visible and 1H NMR spectra as well as X‐ray single‐crystal structural analysis. However, the effect of the intramolecular aromatic C? H/π interactions on the spectral shift in poly[9,9‐dihexylfluorene‐2,7‐yleneethynylene‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P10 ) is much weaker. Most interestingly, the quenching behaviors of these two conjugated polymers are largely dependent on the polymer backbone. For example, the fluorescence of P7 is efficiently quenched by Cu2+, Co2+, Ni2+, Zn2+, Mn2+, and Ag+ ions. In contrast, only Cu2+, Co2+, and Ni2+ ions can partially quench the fluorescence of P10 , but much less efficiently than the fluorescence of P7 . The static Stern–Volmer quenching constants of Cu2+, Co2+, and Ni2+ ions toward P7 are of the order of 106 M?1, being 1300, 2500, and 37,300 times larger than those of P10 , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4154–4164, 2006 相似文献
200.
The theory of asymptotic speeds of spread and monotone traveling waves is established for a class of monotone discrete and continuous‐time semiflows and is applied to a functional differential equation with diffusion, a time‐delayed lattice population model and a reaction‐diffusion equation in an infinite cylinder. © 2005 Wiley Periodicals, Inc. 相似文献