全文获取类型
收费全文 | 896篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 518篇 |
晶体学 | 4篇 |
力学 | 32篇 |
数学 | 95篇 |
物理学 | 274篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 14篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 32篇 |
2015年 | 23篇 |
2014年 | 31篇 |
2013年 | 56篇 |
2012年 | 53篇 |
2011年 | 49篇 |
2010年 | 37篇 |
2009年 | 32篇 |
2008年 | 39篇 |
2007年 | 47篇 |
2006年 | 25篇 |
2005年 | 23篇 |
2004年 | 17篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1972年 | 8篇 |
1966年 | 4篇 |
排序方式: 共有923条查询结果,搜索用时 46 毫秒
51.
JPC – Journal of Planar Chromatography – Modern TLC - A sensitive high-performance thin-layer chromatographic (HPTLC) method has been developed for estimation of amentoflavone, an... 相似文献
52.
53.
Steatite mineral rocks, soapstone, have been studied by X-ray diffraction, optical microscopic analysis (modal analysis), electron probe micro analysis and Mössbauer spectroscopy for characterization, mineral percentages and chemical composition. Mössbauer spectra show both, magnetic interactions corresponding to magnetite and doublets corresponding to talc. chlorite, dolomite and tremolite. The temperature dependence of the quadrupole splitting in dolomite has been explained in terms of crystal field interaction. 相似文献
54.
55.
Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO2(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried
out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes.
Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the
dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl.
Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been
discussed. 相似文献
56.
Complexes of CoII with N,N-bis-(3-carboxy-1-oxopropanyl)-1,2-ethylenediamine(L1), N,N-bis-(3-carboxy-1-oxopropanyl)-1,2-phenylenediamine(L2), N,N-bis-(2-carboxy-1-oxophenelenyl)-1,2-phenylenediamine(L3) and N,N-bis-(3-carboxy-1-oxoprop-2-enyl)-1,2-phenylenediamine(L4) have been prepared and characterized by elemental analysis, vibrational spectra, magnetic susceptibility measurements, electronic spectra and thermal studies. Stability constants of the complexes have been evaluated potentiometrically. Vibrational spectra indicate coordination of amide and carboxylate oxygens of the ligands along with two water molecules giving a MO6 weak field octahedral chromophore. Electronic spectra support octahedral geometry around CoII. The [Co(L1)-(H2O)2] · 2H2O complex has the maximum activation energy and [Co(L3)(H2O)2] complex has the minimum activation energy. The order of stability constants of the CoII complexes with various ligands is due to their -donor abilities. 相似文献
57.
Bhaskar Garg Shiou-Ling Lei Shou-Ching Liu Tanuja Bisht Jen-Yu Liu Yong-Chien Ling 《Analytica chimica acta》2012
The time-of-flight secondary ion mass spectrometry (TOF-SIMS) has emerged as a powerful tool for the unswerving detection of biomolecules, in particular, proteins and peptides. To date, there is very little information available on the direct determination of trimethyl/triethyl amines using TOF-SIMS. One major hurdle in this regard is an ultrahigh vacuum system, usually needed in TOF-SIMS, which hampers its usability to trimethyl/triethyl amines owing to their high evaporation rate. We designed an efficient and sensitive protocol for rapid identification and sensitive determination of tertiaryalkyl amines using TOF-SIMS. The amines were derivatized by reaction with 1,4-butane sultone and sulphuric acid sequentially to afford the corresponding sulphonic acidic ionic liquids (ILs). The TOF-SIMS analysis of these task-specific ILs (TSILs) was carried out in both positive and negative polarity. The positive ion mass spectra of TSILs showed sharp fragmented peaks for tertiaryalkyl amines at typical level and up to 10 ppm. The possible mechanism for different fragmentation pathways in positive polarity was discussed. 相似文献
58.
59.
60.
Clickable polyurethanes based on s‐triazine ring containing aromatic diisocyanate bearing pendent alkyne group: Synthesis and postmodification 下载免费PDF全文
Kavita Garg Deepshikha Chatterjee Prakash P. Wadgaonkar 《Journal of polymer science. Part A, Polymer chemistry》2017,55(6):1008-1020
A new s‐triazine ring containing aromatic diisocyanate bearing a pendent alkyne group, namely, 2,4‐bis(4‐isocyanatophenoxy)?6‐(prop‐2‐yn‐1‐yloxy)?1,3,5‐triazine was synthesized and reacted with various diols viz., 1,10‐decanediol, tetraethylene glycol and polyethylene glycols in the presence of dibutyltin dilaurate as the catalyst to obtain a series of linear polyurethanes. The selected polyurethanes possessing pendent alkyne groups were postmodified with chemically diverse azides viz., 1‐(azidomethyl)benzene, 1‐(azidomethyl)pyrene, and methoxy end‐caped poly(ethylene glycol) azide via copper‐catalysed azide‐alkyne Huisgen 1,3‐dipolar cycloaddition. FTIR and 1H NMR spectra indicated quantitative click reaction. UV–vis and fluorescence spectroscopic analysis confirmed complete incorporation of pyrenyl groups indicating the formation of fluorescence active polyurethane by postmodification with 1‐(azidomethyl)pyrene. TG analysis of polyurethanes indicated two stage weight loss and their thermal stability, as judged by T 10 values, was governed by weight percent of urethane linkages. The water contact angle measurements revealed improved wettability with increased content of PEG either in the backbone of polyurethanes or as grafted chains. DLS and TEM studies confirmed that certain polyurethanes possessing PEG segments displayed self‐assembly in aqueous solution, which was further supported by pyrene encapsulation studies using UV–vis spectroscopy. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1008–1020 相似文献