全文获取类型
收费全文 | 22504篇 |
免费 | 2747篇 |
国内免费 | 4673篇 |
专业分类
化学 | 16088篇 |
晶体学 | 351篇 |
力学 | 1386篇 |
综合类 | 377篇 |
数学 | 2955篇 |
物理学 | 8767篇 |
出版年
2024年 | 51篇 |
2023年 | 223篇 |
2022年 | 488篇 |
2021年 | 487篇 |
2020年 | 586篇 |
2019年 | 590篇 |
2018年 | 479篇 |
2017年 | 538篇 |
2016年 | 751篇 |
2015年 | 842篇 |
2014年 | 911篇 |
2013年 | 1326篇 |
2012年 | 1333篇 |
2011年 | 2472篇 |
2010年 | 1688篇 |
2009年 | 1600篇 |
2008年 | 1262篇 |
2007年 | 1109篇 |
2006年 | 1148篇 |
2005年 | 1210篇 |
2004年 | 1916篇 |
2003年 | 1245篇 |
2002年 | 1224篇 |
2001年 | 980篇 |
2000年 | 620篇 |
1999年 | 516篇 |
1998年 | 432篇 |
1997年 | 352篇 |
1996年 | 246篇 |
1995年 | 246篇 |
1994年 | 218篇 |
1993年 | 534篇 |
1992年 | 590篇 |
1991年 | 384篇 |
1990年 | 369篇 |
1989年 | 359篇 |
1988年 | 128篇 |
1987年 | 48篇 |
1986年 | 61篇 |
1985年 | 61篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1982年 | 30篇 |
1981年 | 14篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
YUAN Mengjia WANG Xia CHEN Long ZHANG Mingxing HE Linwei MA Fuyin LIU Wei WANG Shuao 《高等学校化学研究》2021,37(3):679-685
As a rising star among porous solid materials, covalent organic frameworks(COFs) with excellent properties including but not limit to facilely controllable structure, high porosity, and multi-chemical functionality represent significant potential for efficient 127Xe/85Kr capture and separation. In this study, through tuning the length of the organic ligands, two-dimensional(2D) COF mate-rials with identical connection group but different pore properties, denoted as ATFG-COF and TpPa-COF with AA-stacking model and TpBD-COF with AB-stacking model were synthesized and tested for Kr and Xe adsorption for the first time. Adsorption measurements indicate that the narrower pore apertures and higher porosity are conducive for COF materials to capture Xe and Kr. Furthermore, the Henry's constant, isosteric heat of adsorption(Qst), and ideal adsorbed solution theory(IAST) selectivity of ATFG-COF, the pore size of which is closest to the kinetic diameter of the Xe atom(0.41 nm) among 2D COF materials, were carried out based on the single component sorption isotherms. The results illustrate that the high isosteric heat values of Xe/Kr adsorption on ATFG-COF are 25 and 16 kJ/mol at room temperature, respectively. Henry's law predicts that the selectivity factor of Xe to Kr is 6.07, consistent with the adsorption selectivity(ca. 6) calculated based on the IAST. 相似文献
72.
73.
利用G98及GAMESS从头计算程序的RHF/6-31方法,对β-榄香烯的全部振动基频作了计算,并与实测红外光谱做了对比,归属了它们的振动模式,讨论了它们的特征基频,并对理论计算的振动频率进行了标度校正。 相似文献
74.
Shengkai Li Zhaotian Zhu Xinqi Cai Minghui Song Shen Wang Qing Hao Long Chen Zhuo Chen 《中国化学》2021,(6):1491-1497
Main observation and conclusion
Surface-enhanced Raman spectroscopy(SERS)-based bioanalytical technique involves the interaction of SERS-active substrate with c... 相似文献
75.
76.
提出了一种原子荧光光谱法间接测定中草药中铜含量的方法。在弱酸性介质中,CuI与HgI42-反应生成稳定的Cu2HgI4,经异戊醇萃取分离后,通过用原子荧光光谱法测定有机相中剩余的汞量,间接换算成铜含量。铜的质量浓度在0.01~0.1mg.L-1范围内与荧光强度呈线性关系,方法的检出限(3S/N)为3.5μg.L-1。方法用于国家标准物质黄芪(GSB-19)、茶叶(GSB-7)和柑橘叶(GSB-11)的分析,测定值与认定值相符,测定值的相对标准偏差(n=9)在0.8%~2.4%之间。 相似文献
77.
78.
Commercial CaO was modified simply with benzyl bromide. The modified CaO had good water resistance, and characterization by FTIR and TG revealed the modifier was chemically bonded to the CaO surface. Commercial CaO and CaO modified with benzyl bromide were investigated as catalysts for the Henry reaction between benzaldehyde and nitromethane. It was found that the catalytic activity of the modified CaO was greatly improved, with high conversion of benzaldehyde to the (E)-phenyl nitroolefin and 1-phenyl-2-nitroethanol, and with different selectivity from commercial CaO. The effect of modification and reaction conditions on yield, selectivity, and mechanism were studied thoroughly. 相似文献
79.
YU GuoLiang GU JianZhong HOU Long LI ZhenYu WANG YanZhao ZHANG YiYun 《中国科学:物理学 力学 天文学(英文版)》2013,(9):1735-1739
The frequency distribution of different ingredients in-ray spectra,e.g.,photo-peak,fluctuations of counts and Compton region,is separately analyzed.After wavelet transform of-ray spectra,the wavelet coefficients of a photo-peak increase with transforming scales and these coefficients show direct proportion with intensity of peak at determinate scale.A novel algorithm based on wavelet transform is proposed and studied.The results indicate that most of the photo-peaks in multi-spectra can be determined accurately,the-rays energy and intensity of the peak can also be determined.This method has the prospect of being applied in on-line multi-spectra analysis in such fields as radioprotection and nuclear safety monitoring. 相似文献
80.
ZHONG XiChun TANG PengFei GAO BeiBei MIN JiXiong LIU ZhongWu ZHENG ZhiGang ZENG DeChang YU HongYa QIU WanQi 《中国科学:物理学 力学 天文学(英文版)》2013,(6):1096-1099
The magnetic properties and magnetocaloric effects of amorphous and crystalline Gd55Co35Ni10 ribbons are investigated.A main phase with a Ho 12 Co 7-type monoclinic structure(space group P21/c) and a minor phase with a Ho4Co3-type hexagonal structure(space group P63/m) are obtained for crystalline ribbon after annealing.The amorphous ribbons order ferromagnetically and undergo a second-order transition at 192 K.For crystalline Gd55Co35Ni10 ribbons,two magnetic phase transitions occur at 158 and 214 K,respectively.The peak value of-△SM under a field change of 0-5 T is 6.5 J/kg K at 192 K for amorphous Gd55Co35Ni10 ribbons.A relatively large magnetic entropy change(~5.0 J/kg K) under a field change of 0-5 T for the crystalline Gd55Co35Ni10 ribbons is obtained in the temperature interval range of 154-214 K.The large platform of magnetic entropy change and the negligible thermal/magnetic hysteresis loss mean the crystalline Gd55Co35Ni10 compound can satisfy the requirement of the Ericsson-type refrigerator working in the temperature range from 154K to 214K. 相似文献