全文获取类型
收费全文 | 36925篇 |
免费 | 281篇 |
国内免费 | 276篇 |
专业分类
化学 | 14939篇 |
晶体学 | 451篇 |
力学 | 1549篇 |
综合类 | 12篇 |
数学 | 10372篇 |
物理学 | 10159篇 |
出版年
2022年 | 148篇 |
2021年 | 182篇 |
2020年 | 128篇 |
2019年 | 179篇 |
2018年 | 1333篇 |
2017年 | 1592篇 |
2016年 | 967篇 |
2015年 | 762篇 |
2014年 | 752篇 |
2013年 | 1339篇 |
2012年 | 3435篇 |
2011年 | 2679篇 |
2010年 | 2099篇 |
2009年 | 1806篇 |
2008年 | 899篇 |
2007年 | 946篇 |
2006年 | 896篇 |
2005年 | 4671篇 |
2004年 | 4124篇 |
2003年 | 2512篇 |
2002年 | 676篇 |
2001年 | 464篇 |
2000年 | 255篇 |
1999年 | 301篇 |
1998年 | 233篇 |
1997年 | 164篇 |
1996年 | 135篇 |
1995年 | 176篇 |
1994年 | 120篇 |
1993年 | 92篇 |
1992年 | 254篇 |
1991年 | 216篇 |
1990年 | 217篇 |
1989年 | 180篇 |
1988年 | 175篇 |
1987年 | 125篇 |
1986年 | 122篇 |
1985年 | 161篇 |
1984年 | 170篇 |
1983年 | 104篇 |
1982年 | 108篇 |
1981年 | 112篇 |
1980年 | 107篇 |
1979年 | 94篇 |
1978年 | 103篇 |
1977年 | 98篇 |
1976年 | 151篇 |
1975年 | 102篇 |
1974年 | 97篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Srigokul Upadhyayula Vicente Nu?ez Eli M. Espinoza Jillian M. Larsen Duoduo Bao Dewen Shi Jenny T. Mac Bahman Anvari Valentine I. Vullev 《Chemical science》2015,6(4):2237-2251
Cyanine dyes are broadly used for fluorescence imaging and other photonic applications. 3,3′-Diethylthiacyanine (THIA) is a cyanine dye composed of two identical aromatic heterocyclic moieties linked with a single methine, –CH. The torsional degrees of freedom around the methine bonds provide routes for non-radiative decay, responsible for the inherently low fluorescence quantum yields. Using transient absorption spectroscopy, we determined that upon photoexcitation, the excited state relaxes along two parallel pathways producing three excited-state transients that undergo internal conversion to the ground state. The media viscosity impedes the molecular modes of ring rotation and preferentially affects one of the pathways of non-radiative decay, exerting a dominant effect on the emission properties of THIA. Concurrently, the polarity affects the energy of the transients involved in the decay pathways and further modulates the kinetics of non-radiative deactivation. 相似文献
993.
Wiesława Nocuń-Wczelik Artur Łagosz Bartosz Kowalski Marek Gawlicki 《Journal of Thermal Analysis and Calorimetry》2014,118(1):123-131
The calorimetric measurements were applied in testing the wastes collected from different furnaces in electric power plants as materials to be used in civil engineering. The fly ash materials were collected from two power stations based on different brown coal deposits and working with conventional and fluidized bed installation. The reactivity of high calcium fly ash from sub-bituminous coal combustion has been proved in calorimetric, conductometric, chemical shrinkage, and rheological measurements before their practical implementation on larger scale. Highly soluble components of fly ash contribute to the hydration products and structure formation, followed by setting and hardening of fly ash–cement mixture. These results have been the base of research project aimed in the innovative solutions dealing with the management of deposits of wastes generated as a result of coal combustion. The standardization and potential use on larger scale of these materials, necessary from the environmental point of view, seems to be the question of nearest future. 相似文献
994.
A Collaboration M. Makek P. Achenbach C. Ayerbe Gayoso C. Barbieri J. C. Bernauer R. B?hm D. Bosnar A. Denig M. O. Distler I. Fri??i? C. Giusti H. Merkel U. Müller L. Nungesser J. Pochodzalla S. Sanches Majos B. S. Schlimme M. Schwamb Th. Walcher 《The European Physical Journal A - Hadrons and Nuclei》2016,52(9):298
995.
Numerical Algorithms - In this note, we present two new algorithms for the Steinitz Exchange Lemma. They are grounded on a single application of a procedure (finding either a row echelon form or a... 相似文献
996.
Juan Luis Vázquez Ivan Velazco-Cabral Dr. Marcos Flores-Álamo Gleb Turlakov Geraldina Rodríguez Dr. Ivana Moggio Dr. Eduardo Arias Dr. Eduardo Peña-Cabrera Dr. Miguel A. Vázquez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202446
A series of new symmetrical highly substituted BODIPYs 6 a – l was synthesized through a prefunctionalization approach in 35 %–89 % yields from the pyrrole core. This strategy allowed modulation of the substituents at the different positions based on the choice of Fischer's alkynyl carbenes, oxazolones and aldehydes used as precursors. The substituent variation at positions 2, 6, 3 and 5 had the greatest effect on the modulation of their photophysical properties such as absorption (λabs) and emission (λem) wavelengths, extinction coefficient (ϵ), quantum yields (ϕ), Stokes shifts (Δν), fluorescence decay, radiative (krad) and non-radiative (knr) constants and the CIE 1931 coordinates. Theoretical calculations allowed to corroborate the effect of the substituents of meso-position on the modification of the dihedral angles. Cyclic voltammetry studies revealed that the BODIPY series presents similar redox potential behavior, being electrochemically active even in successive cycles, which suggests that transport by diffusion is the dominant process. 相似文献
997.
Dr. Rebecca L. Greenaway Dr. Valentina Santolini Dr. Filip T. Szczypiński Dr. Michael J. Bennison Dr. Marc A. Little Andrew Marsh Dr. Kim E. Jelfs Prof. Andrew I. Cooper 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3718-3722
Molecular dumbbells with organic cage capping units were synthesised via a multi-component imine condensation between a tri-topic amine and di- and tetra-topic aldehydes. This is an example of self-sorting, which can be rationalised by computational modelling. 相似文献
998.
Sara Gil-Guerrero Prof. Manuel Melle-Franco Prof. Ángeles Peña-Gallego Prof. Marcos Mandado 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):16138-16143
The Clar Goblet, the first radical bowtie nanographene proposed by Erich Clar nearly 50 years ago, was recently synthesized. Bowtie nanographenes present quasi-degenerate magnetic ground states, which make them so elusive as unique. A thorough analysis is presented of the spin-state energetics of Clar Goblet and bowtie nanographenes by a battery of existing and novel ab initio procedures ranging from density functional theory to complete active space Hamiltonians. With this, it was proven that π radicals of bowtie nanographenes sit on BP (Benzo[cd]Pyrene) moieties driven by their local aromaticity, a purely chemical concept, which confers global stability to the whole structure. Besides, a novel Pauli energy densities analysis provided a visual intuitive explanation for this preference. These findings allow envisioning that analogous bowtie nanographenes with arbitrary polyradical character are not only feasible at the molecular scale but will share Clar Goblet's peculiar properties. 相似文献
999.
1000.