全文获取类型
收费全文 | 4696篇 |
免费 | 149篇 |
国内免费 | 16篇 |
专业分类
化学 | 2954篇 |
晶体学 | 15篇 |
力学 | 246篇 |
数学 | 831篇 |
物理学 | 815篇 |
出版年
2023年 | 51篇 |
2022年 | 143篇 |
2021年 | 134篇 |
2020年 | 111篇 |
2019年 | 100篇 |
2018年 | 88篇 |
2017年 | 92篇 |
2016年 | 189篇 |
2015年 | 153篇 |
2014年 | 144篇 |
2013年 | 252篇 |
2012年 | 264篇 |
2011年 | 295篇 |
2010年 | 179篇 |
2009年 | 150篇 |
2008年 | 289篇 |
2007年 | 273篇 |
2006年 | 224篇 |
2005年 | 240篇 |
2004年 | 167篇 |
2003年 | 159篇 |
2002年 | 120篇 |
2001年 | 54篇 |
2000年 | 49篇 |
1999年 | 48篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 52篇 |
1995年 | 45篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 31篇 |
1987年 | 44篇 |
1986年 | 25篇 |
1985年 | 40篇 |
1984年 | 43篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 28篇 |
1975年 | 15篇 |
1974年 | 14篇 |
1858年 | 11篇 |
排序方式: 共有4861条查询结果,搜索用时 15 毫秒
61.
A convenient route to new 3-quinolinonyl-pyrazoles and isoxazoles is described through cyclization of 3-[(E)-3-(dimethylamino)-2-propenoyl]-4-hydroxy-1-methyl-2(1H)-quinolinone. The phototoxicity as well as the cytotoxic activities of the title compounds are evaluated against leukemia- and adenocarcinoma-derived cell lines in comparison to the normal human keratinocytes. 相似文献
62.
Carlo Bruno Eleonora Ussano Gianni Barucca Davide Vanossi Giovanni Valenti Edward A. Jackson Andrea Goldoni Lucio Litti Simona Fermani Luca Pasquali Moreno Meneghetti Claudio Fontanesi Lawrence T. Scott Francesco Paolucci Massimo Marcaccio 《Chemical science》2021,12(23):8048
The presence of non-hexagonal rings in the honeycomb carbon arrangement of graphene produces rippled graphene layers with valuable chemical and physical properties. In principle, a bottom-up approach to introducing distortion from planarity of a graphene sheet can be achieved by careful insertion of curved polyaromatic hydrocarbons during the growth of the lattice. Corannulene, the archetype of such non-planar polyaromatic hydrocarbons, can act as an ideal wrinkling motif in 2D carbon nanostructures. Herein we report an electrochemical bottom-up method to obtain egg-box shaped nanographene structures through a polycondensation of corannulene that produces a new conducting layered material. Characterization of this new polymeric material by electrochemistry, spectroscopy, electron microscopy (SEM and TEM), scanning probe microscopy, and laser desorption-ionization time of flight mass spectrometry provides strong evidence that the anodic polymerization of corannulene, combined with electrochemically induced oxidative cyclodehydrogenations (Scholl reactions), leads to polycorannulene with a wavy graphene-like structure.A bottom-up synthesis of wavy graphene structures obtained through an anodic polymerization process, combined with an electrochemically triggered oxidative cyclodehydrogenation, of the bowl-shaped polyaromatic hydrocarbon corannulene. 相似文献
63.
Giovannelli Tommaso Liuzzi Giampaolo Lucidi Stefano Rinaldi Francesco 《Computational Optimization and Applications》2022,82(2):293-327
Computational Optimization and Applications - In this paper, mixed-integer nonsmooth constrained optimization problems are considered, where objective/constraint functions are available only as the... 相似文献
64.
Francesco Cubadda 《Russian Chemical Bulletin》1995,44(2):388-390
Information Congresses, Conferences, Symposia, Workshops, and Seminars in the Field of Chemical Sciences held with Participation of the Russian Academy of Sciences
The XXXV International IUPAC Symposium on macromolecular chemistry (MACROACRON-94) 相似文献65.
Summary We consider a (possibly) vector-valued function u: RN, Rn, minimizing the integral
, 2-2/(n*1)<p<2, whereD
i
u=u/x
i
or some more general functional retaining the same behaviour, we prove higher integrability for Du: D1 u,..., Dn–1 u Lp/(p-1) and Dnu L2; this result allows us to get existence of second weak derivatives: D(D1 u),...,D(Dn–1u)L2 and D(Dn u) L
p.This work has been supported by MURST and GNAFA-CNR. 相似文献
66.
67.
68.
69.
The application of hydrolases in organic solvents for synthetic purposes is a procedure routinely adopted in organic chemistry, especially for the preparation of chiral building blocks. Numerous studies have shed light on several aspects of the mechanism of hydrolase action in low-water environments. Procedures suitable to improve the catalytic efficiency of enzymes and productivity of the synthetic processes have been reported. These fundamental and applied investigations have made hydrolase-catalyzed reactions in organic solvents of industrial interest. In this article we describe and discuss various approaches adopted to optimize the performance of hydrolases in organic media, with special emphasis on the formulation of the biocatalysts which, under proper conditions, can display an activity equal to that displayed in aqueous buffers. 相似文献
70.
Photodegradation of Polychlorinated Dibenzo-p-dioxins in Liquid Samples by Near UV Light Irradiation
Photodegradation of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) in hexane solution was studied under controlled near-UV light exposure in the spectral region from 325 to 269 nm. GC-MS was used to detect the amount of unreacted dioxin and to characterize the relevant degradation products. Irradiation experiments carried out at a constant light energy (700 mJ) showed that the percentage of 1,2,3,4-TCDD left in the solution after irradiation changed from about 55 to 75%, with a minimum of 55% at 310 nm. Further irradiation experiments carried out at two wavelengths, namely 310 and 269 nm, and light energy ranging from 0 to 4000 mJ, showed that the photodegradation reaction of the TCDD always followed a pseudo-first-order kinetic, with a rate constant of 8 × 10−4and 5 × 10−4mJ−1, respectively. These experiments also showed that trichloro- and dichloro-dibenzo-p-dioxins were produced with less than 15% of the initial quantity of TCDD, leading to the conclusion that the dechlorination process is a minor photolysis pathway. 相似文献