全文获取类型
收费全文 | 490869篇 |
免费 | 5507篇 |
国内免费 | 1451篇 |
专业分类
化学 | 262894篇 |
晶体学 | 7431篇 |
力学 | 22361篇 |
综合类 | 16篇 |
数学 | 56419篇 |
物理学 | 148706篇 |
出版年
2020年 | 3836篇 |
2019年 | 4367篇 |
2018年 | 5449篇 |
2017年 | 5357篇 |
2016年 | 8311篇 |
2015年 | 5351篇 |
2014年 | 8360篇 |
2013年 | 21500篇 |
2012年 | 16614篇 |
2011年 | 20242篇 |
2010年 | 14020篇 |
2009年 | 14176篇 |
2008年 | 18813篇 |
2007年 | 19036篇 |
2006年 | 17783篇 |
2005年 | 16054篇 |
2004年 | 14690篇 |
2003年 | 13219篇 |
2002年 | 13116篇 |
2001年 | 14614篇 |
2000年 | 11113篇 |
1999年 | 8693篇 |
1998年 | 7157篇 |
1997年 | 7067篇 |
1996年 | 6932篇 |
1995年 | 6239篇 |
1994年 | 6121篇 |
1993年 | 5857篇 |
1992年 | 6599篇 |
1991年 | 6611篇 |
1990年 | 6252篇 |
1989年 | 6177篇 |
1988年 | 6346篇 |
1987年 | 6042篇 |
1986年 | 5826篇 |
1985年 | 7972篇 |
1984年 | 8114篇 |
1983年 | 6682篇 |
1982年 | 6999篇 |
1981年 | 6988篇 |
1980年 | 6582篇 |
1979年 | 7044篇 |
1978年 | 7043篇 |
1977年 | 7231篇 |
1976年 | 7178篇 |
1975年 | 6901篇 |
1974年 | 6685篇 |
1973年 | 6935篇 |
1972年 | 4521篇 |
1971年 | 3732篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
S. Venkatesan S. Suresh P. Ramu M. Kandasamy J. Arumugam S. Thambidurai K.M. Prabu N. Pugazhenthiran 《印度化学会志》2022,99(5):100436
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications. 相似文献
42.
Journal of Applied and Industrial Mathematics - We study the problem of optimal location of the ambulance fleet at the base stations. The objective is to minimize the average waiting time for... 相似文献
43.
44.
45.
46.
Haixing Guan Qianwen Zhang Prof. Dr. Patrick J. Walsh Prof. Dr. Jianyou Mao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(13):5210-5215
A unique nickel/organic photoredox co-catalyzed asymmetric reductive cross-coupling between α-chloro esters and aryl iodides is developed. This cross-electrophile coupling reaction employs an organic reductant (Hantzsch ester), whereas most reductive cross-coupling reactions use stoichiometric metals. A diverse array of valuable α-aryl esters is formed under these conditions with high enantioselectivities (up to 94 %) and good yields (up to 88 %). α-Aryl esters represent an important family of nonsteroidal anti-inflammatory drugs. This novel synergistic strategy expands the scope of Ni-catalyzed reductive asymmetric cross-coupling reactions. 相似文献
47.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
48.
Kazakova E. F. Dmitrieva N. E. Zvereva N. L. 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2020,94(2):341-344
Russian Journal of Physical Chemistry A - Rapidly quenched alloys of aluminum with cobalt and zirconium are investigated using a combination of means of physicochemical analysis to study the... 相似文献
49.
International Applied Mechanics - The theorems (statements) on the existence of attractor are proved. A generalized Shilnikov theorem is formulated. In the expression for the saddle of a homoclinic... 相似文献
50.