全文获取类型
收费全文 | 5986篇 |
免费 | 1049篇 |
国内免费 | 613篇 |
专业分类
化学 | 3963篇 |
晶体学 | 57篇 |
力学 | 284篇 |
综合类 | 40篇 |
数学 | 753篇 |
物理学 | 2551篇 |
出版年
2024年 | 12篇 |
2023年 | 142篇 |
2022年 | 169篇 |
2021年 | 211篇 |
2020年 | 251篇 |
2019年 | 209篇 |
2018年 | 194篇 |
2017年 | 182篇 |
2016年 | 302篇 |
2015年 | 255篇 |
2014年 | 323篇 |
2013年 | 392篇 |
2012年 | 501篇 |
2011年 | 574篇 |
2010年 | 363篇 |
2009年 | 344篇 |
2008年 | 368篇 |
2007年 | 347篇 |
2006年 | 347篇 |
2005年 | 276篇 |
2004年 | 209篇 |
2003年 | 186篇 |
2002年 | 205篇 |
2001年 | 161篇 |
2000年 | 135篇 |
1999年 | 163篇 |
1998年 | 134篇 |
1997年 | 118篇 |
1996年 | 111篇 |
1995年 | 74篇 |
1994年 | 56篇 |
1993年 | 55篇 |
1992年 | 47篇 |
1991年 | 60篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 17篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7648条查询结果,搜索用时 93 毫秒
991.
992.
993.
A new nitrosation and oxidation process to synthesize gem-dinitro compounds was accomplished by using nitryl chloride as nitrosation reagent and ozone as oxidizing agent. The main features of the present protocol include the compatibility to substances with high steric hindrance, high yields and mild reaction conditions. A plausible mechanism involving the formation of an intermediate of gem-nitrosonitro compound by means of single electron transfer was also proposed. 相似文献
994.
A colorimetric probe N,N’-bis(2-methoxy-ethyl)-2,3,3-trimethyl-3H-squaraine (MOESQ) with H2O solubility was synthesized to detect Cu2+. MOESQ exhibits good selectivity, high sensitivity and fast UV-Vis response toward Cu2+ over other competing ions in CH3CN. The detection limit of MOESQ for Cu2+ in CH3CN can reach 1.88?×?10?7?molL?1. By adsorbing MOESQ on the chromatography paper, a colorimetric test paper for Cu2+ was prepared, which could detect Cu2+ with the color change from blue to faint yellow even in the limit of detection concentration of 10?6?molL?1. 相似文献
995.
Baichuan Han Jin Sun Kai Chen Zhiyong Chen Minhua Huang Zhenzhong Gao Xianfeng Hou 《Tetrahedron》2018,74(50):7193-7197
A novel fluorescent probe was developed for formaldehyde, which can be synthesized by one-step Buchwald–Hartwig reaction. When hydrazino-group of probe reacted with formaldehyde, hydrophobic reaction product aggregates into nanoparticles and results in the blue fluorescence due to the monomer-excimer effect. With enough sensitivity, high selectivity, good stability in physiological pH range and excellent biocompatibility, this probe can image formaldehyde in living cells. 相似文献
996.
Xinfeng Chen Kui Zhang Huan Yu Long Yu Hongwei Ge Ji Yue Tianxin Hou Abdullah M. Asiri Hadi M. Marwani Suhua Wang 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(3):1011-1019
Herein we report a fluorescent method for sensitive and selective detection of uranyl ions using CdTe quantum dots functionalized with mercaptopropionic acid, which the fluorescence of the quantum dots could be quantitatively quenched through electron transfer mechanism. The detection limit of the method was estimated to be 4 nM, less than the maximum allowed content of 130 nM for uranyl in drinking water defined by the U.S. Environmental Protection Agency. Furthermore, the probe was successfully applied in detection of uranyl ions in real samples, demonstrating its potential practical applications for monitoring of uranyl ions in environment. 相似文献
997.
Journal of Radioanalytical and Nuclear Chemistry - The 110Pd(n,2n)109m,gPd reaction cross-sections and the isomeric cross section ratios (σm/σg) in the neutron energy range of... 相似文献
998.
An efficient, novel and convenient method for the synthesis of modified polyacrylonitrile (PAN) with antibacterial property is reported. The modification of PAN was prepared by a nitrile click chemistry reaction with sodium azide (NaN3) and silver nitrate (AgNO3) as catalyst to yield antibacterial polymeric materials with 5-vinyltetrazole units. The results showed that 5-vinyltetrazole units had coordinated with silver ion (Ag+). Through the electrostatic spinning technology, the post-modification PAN nanofibers (PAN–Ag+ nanofibers) were prepared and the fibers were tested for their antimicrobial properties by the bacterial infection experiment. Afterwards, the antibacterial and stable performance of different proportions of silver ions in PAN nanofibers has been compared. The PAN–Ag+ nanofibers are characterized for mechanical and thermomechanical properties, structural analysis, appearance characteristics, as well as the antibacterial properties. And the nanofibers exhibit marvelous chemical stability according to the thermogravimetric analysis. When at 800 °C, the PAN decomposed about 60%, while the decomposition of the PAN–Ag+s was 40%. Based on the bacterial infection experiment, PAN–Ag+ nanofibers’ antibacterial properties were stronger with the increase of silver ions, such as the number of bacteria clone was smaller and the bacteriostatic ring was larger. Hence, with combination of silver ions, the final polymers show strong antimicrobial properties. 相似文献
999.
近年来,脱羧反应得到了广泛而深入的研究.肉桂酸类化合物的脱羧串联反应也得到了较多的关注.这类反应一般包括两个过程,自由基加成和羧基的脱去,从而在苯环的侧链引入各种各样的官能团.我们在研究过程中发现,在碳酸钾作为碱,过氧叔丁醇作为氧化剂,以二甲基亚砜(DMSO)/水作为混合溶剂条件下(体积比为1:1),肉桂酸类衍生物能够转化成苯丙酮类化合物.通过对反应机理的研究,产物中的甲基来自于过氧叔丁醇,反应经过自由基加成和进一步脱羧得到产物.该反应特点是没有用过渡金属盐作为催化剂,并且是在水相中反应,因此符合绿色化学的发展要求. 相似文献
1000.
本文利用2-氨基吡啶与4-二乙胺基水杨醛反应合成了5-二乙胺基-2-(吡啶-2’-亚氨甲基)苯酚(探针L),对其结构进行了表征。在DMSO/Tris(6:4, v/v, pH =7.4)溶液中,探针L高选择性荧光“关-开”识别Zn2+,在365 nm紫外灯照射下,由无荧光变成蓝色荧光。实验表明,探针L与Zn2+的结合比为1:1,结合常数为2.6×103 L. mol-1,检测限为 9.39×10-7mol/L,pH适用范围为7-11,并可检测水样中的Zn2+。 相似文献