全文获取类型
收费全文 | 258篇 |
免费 | 116篇 |
国内免费 | 26篇 |
专业分类
化学 | 71篇 |
力学 | 5篇 |
数学 | 16篇 |
物理学 | 308篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 1篇 |
2011年 | 25篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2007年 | 3篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 14篇 |
1999年 | 36篇 |
1998年 | 44篇 |
1997年 | 33篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 70篇 |
1992年 | 46篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
311.
312.
通过测量、分析CuCl_2的激光诱导荧光并与氧碘化学激光器光腔中红光辐射的傅里叶变换光谱比较,认为红光辐射体是CuCl_2。 相似文献
313.
P. Decowski E. A. Bakkum P. Box K. A. Griffioen R. Kamermans R. J. Meijer 《Zeitschrift für Physik A Hadrons and Nuclei》1987,326(2):235-236
High resolution positron spectroscopy in U-U collisions at bombarding energies of 5.6 MeV/u, the lowest energy studied until now as well as of 5.9 MeV/u, reveals similar multiple structures between 220 keV and 385 keV superimposed on the induced and nuclear continua. 相似文献
314.
315.
建立色散介质3维真实人体模型,用色散介质时域有限差分((FD)2TD)方法计算了强电磁脉冲(EMP)对人体的作用。结果表明,电磁脉冲对人体的透入主要决定于脉冲前沿,受脉冲宽度的影响较小;透入体内的脉冲,相对辐照脉冲显著变窄;人体吸收的电磁能没有明显受到辐照脉冲能注量的影响;虽然人体从单个脉冲吸收的能量远低于用比吸收能定义的安全标准,但这种剂量的照射在离体培养的人肝细胞(L-02)上却产生了明显的生物学效应,这意味着比吸收能难以作为人员安全评估标准。 相似文献
316.
The Ni catalysts supported on γ-Al2O3 were synthesized by an impregnation method.Their catalytic performance in methane dry reforming was investigated.The reforming reactions were carried out in a microreactor using a CO2:CH4 feed ratio of 1:1,a F/W = 2640 ml/(h·g),reaction temperatures between 500-850 ?C,and at atmospheric pressure.The influence of Ca,Ce,and Zr promoters on catalyst stability,coke deposition,and the H2/CO ratio were also studied.Effluents were analyzed using an online gas chromatograph equ... 相似文献
317.
新型热释电多功能能量卡计测量系统 总被引:1,自引:1,他引:1
简要介绍了新型热释电多功能能量卡计测量系统的结构、工作原理和系统的特点。给出了用该系统监测强激光打靶时的能量平衡率、能量吸收系数及受激拉曼散射(SRS)角分布测量的部分实验结果。尤其是测得的1060nm强激光打靶后产生的SRS光在0°~15°区域内的实验点和角分布情况在国内外尚属首批数据。 相似文献
318.
Claire J Beddows Matthew R Box Christopher Butters Nicholas Carr Michael Green Monika Kursawe Mary F Mahon 《Journal of organometallic chemistry》1998,550(1-2)
Reaction of cis-[Mo(NCMe)2(CO)2(η5-L)][BF4] (L=C5H5 or C5Me5) with 1-acetoxybuta-1,3-diene gives the cationic complexes [Mo{η4-syn-s-cis-CH2CHCHCH(OAc)}(CO)2(η5-L)][BF4], which, on reaction with aqueous NaHCO3/CH2Cl2, afford good yields of the anti-aldehyde substituted complexes [Mo{η3-exo-anti-CH2CHCH(CHO)}(CO)2(η5-L)] 2 (L=C5Me5), 4 (L=C5H5)]. The corresponding η5-indenyl substituted complex 5 was prepared by protonation (HBF4·OEt2) of [Mo(η3-C3H5)(CO)2(η5-C9H7)] followed by addition of CH2=CHCH=CH(OAc) and hydrolysis (aq. NaHCO3/CH2Cl2). An X-ray crystallographic study of complex 2 confirmed the structure and showed that there is a contribution from a zwitterionic form involving donation of electron density from the molybdenum to the aldehyde carbonyl group. Treatment of 2 and 4, in methanol solution, with NaBH4 afforded the alcohols [Mo{η3-exo-anti-CH2CHCHCH2(OH)}(CO)2(η5-L)] [6 (L=C5H5), 8 (L=C5Me5)]; however, prolonged (30 h) reaction with NaBH4/MeOH surprisingly gave good yields of the methoxy-substituted complexes [Mo{η3-exo-anti-CH2CHCHCH2(OMe)}(CO)2(η5-L)] [7 (L=C5H5), 9 (L=C5Me5)], the structure of 7 being confirmed by single crystal X-ray crystallography. This methoxylation reaction can be explained by coordination of the hydroxyl group present in 6 and 8 onto B2H6 to form the potential leaving group HOBH3−, which on ionisation affords [Mo(η4-exo-buta-1-3-diene)(CO)2(η5-L)]+ which is captured by reaction with OMe−. Complex 8 is also formed in good yield on reaction of 2 with HBF4·OEt2 followed by treatment of the resulting cation [Mo{η4-exo-s-cis-syn-CH2CHCHCH(OH)}(CO)2(η5-C5Me5)][BF4] with Na[BH3CN]. Reaction of 4 with the Grignard reagents MeMgI, EtMgBr or PhMgCl afforded moderate yields of the alcohols [Mo{η3-exo-anti-CH2CHCHCH(OH)R}(CO)2(η5-C5H5)] [11 (R=Me), 12 (R=Et), 13 (R=Ph)]. Similarly, treatment of 2 with MeLi gave the corresponding alcohol 14. An attempt to carry out the Oppenauer oxidation [Al(OPr′)3/Me2CO] of 11 resulted in an elimination reaction and the formation of the η3-s-pentadienyl complex [Mo{η3-exo-anti-CH2CHCH(CHCH2)}(CO)2(η5-C5H5)], which was structurally identified by X-ray crystallography. Interestingly, oxidation of 6 with [Bu4nN][RuO4]/morpholine-N-oxide affords the aldehyde complex, 4 in good yield. Finally, reaction of 11 with [NO][BF4] followed by addition of Na2CO3 affords the fur-3-ene complex [Mo{η2-
(H)Me}(CO)(NO)(η5-C5H5)]. 相似文献
319.
Joseph C. Calabrese 《有机化学》1993,(2)
The mechanism of decarboxylative cyclization of allylic cyclic carbamates 1 leading to 2-substituted △~3-piperidines and-pyrrolidines, as well as its applications to the total synthesis of (--)codonopsine, are described. 相似文献
320.
In this study a mathematical model of a small scale single pellet for the oxidative coupling of methane(OCM)over titanite pervoskite is developed.The method is based on a computational fluid dynamics(CFD)code which known as Fluent may be adopted to model the reactions that take place inside the porous catalyst pellet.The steady state single pellet model is coupled with a kinetic model and the intra-pellet concentration profiles of species are provided.Subsequent to achieving this goal,a nonlinear reaction network consisting of nine catalytic reactions and one gas phase reaction as an external program is successfully implemented to CFD-code as a reaction term in solving the equations.This study is based on the experimental design which is conducted in a differential reactor with a Sn/BaTiO3 catalyst(7-8 mesh) at atmospheric pressure,GHSV of 12000 h-1,ratio of methane to oxygen of 2,and three different temperatures of 1023,1048 and 1073 K.The modeling results such as selectivity and conversion at the pellet exit are in good agreement with the experimental data.Therefore,it is suggested that to achieve high yield in OCM process the modeling of the single pellet should be considered as the heart of catalytic fixed bed reactor. 相似文献