全文获取类型
收费全文 | 474篇 |
免费 | 25篇 |
国内免费 | 12篇 |
专业分类
化学 | 374篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 56篇 |
物理学 | 64篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 27篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 56篇 |
2012年 | 27篇 |
2011年 | 31篇 |
2010年 | 29篇 |
2009年 | 21篇 |
2008年 | 28篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有511条查询结果,搜索用时 31 毫秒
141.
142.
Mina Teicher 《Israel Journal of Mathematics》1987,57(1):49-67
Using combinatorial methods, we classify all birational morphisms blowingm ≦ 5 divisors down to a point. Those which do not factor through the blowing up of a point are treated in the body of the
paper, and the factorizable morphisms are computed in an appendix. The relevance of this classification to the determination
of the nature of the “general” toric morphism is discussed. 相似文献
143.
Nishiwaki N Ogihara T Takami T Tamura M Ariga M 《The Journal of organic chemistry》2004,69(24):8382-8386
beta-Nitroenamines having a formyl group at the beta-position behave as the synthetic equivalent of unstable nitromalonaldehyde, which is a useful synthon for syntheses of versatile nitro compounds. High solubility of the nitroenamines into general organic solvents enables us to conduct reactions in the organic media accompanied by easy experimental manipulations and considerable safety. When nitroenamines are treated with 1,2-bifunctional nucleophiles such as hydrazines, hydroxylamine and glycine ester, nitrated pyrazoles, isoxazole and pyrrole-2-carboxylate were readily prepared. This methodology was also applicable to guanidines and 1,2-diamines, leading to pyrimidines and 1,4-diazepines, respectively. 相似文献
144.
Mina Ouahman Najate Ben Sari-Zizi Guy Guelachvili Claude Alamichel 《Molecular physics》2013,111(6):1477-1488
The 22 K sub-bands, belonging to the v 1 + v ±1 6, v 3 + v ± 5 + 2v 0 6 and v 3 + v ±1 5 + 2v ±2 6 rovibrational bands of monoisotopic CH3 79Br, have been identified. An RMS standard deviation of about 0·020 cm-1 has been achieved by a least squares fit over 619 lines belonging to these 22 sub-bands. For this purpose, a model taking into account (a) anharmonic resonances between (i) v 1 + v ±1 6, and v 3 + v ±1 5 + 2v 0 6, (ii) v 1 + v ±1 6 and v 3 + v ?1 5 + 2v ±2 6 and (iii) v 3 + v ±1 5 + 2v 0 6 and v 2 + 2v 3 + v ±1 5 and (b) Coriolis resonances between the v 2 and v 5 modes, was used. 相似文献
145.
Ali Jebali Seyedhossein Hekmatimoghaddam Aliasghar Behzadi Iraj Rezapor Bahador Haji Mohammadi Tahereh Jasemizad Seyed Ali Yasini Morteza Javadzadeh Asiye Amiri Mansoure Soltani Zeynab Rezaei Najme Sedighi Mina Seyfi Mohammad Rezaei Mehran Sayadi 《Cellulose (London, England)》2013,20(6):2897-2907
In this study, cellulose nanoparticles were prepared by acid hydrolysis, separately conjugated with allicin and lysozyme by a carbodiimide cross-linker, and characterized by scanning electron microscopy, dynamic light scattering, and Fourier transform infrared spectroscopy. Then, their antimicrobial properties were evaluated by the microdilution method and compared with allicin, lysozyme, and nanocellulose alone. The results showed that nanocellulose had few antimicrobial activities, but allicin-conjugated nanocellulose (ACNC) and lysozyme-conjugated nanocellulose (LCNC) had good antifungal and antibacterial effects against standard strains of Candida albicans, Aspergillus niger, Staphylococcus aureus, and Escherichia coli. Noticeably, although allicin and lysozyme had different minimum inhibitory concentrations (MICs) against all strains, the same quantity of MIC50 and MIC90 was observed for both ACNC and LCNC. The authors suggest that both ACNC and LCNC can be used in industries as an antimicrobial agent in food packaging, inside foodstuffs, and in textile materials. 相似文献
146.
147.
Ring‐opening polymerization of cyclic esters by pincer complexes derived from alkaline earth metals 下载免费PDF全文
We report the synthesis and characterization of new Ca(II) and Mg(II) complexes of the type [Ph―PPP]MR (M = Ca, R = N(SiMe3)2 ( 1 ); M = Mg, R = nBu ( 2 )) where Ph―PPP? is a tridentate monoanionic ligand (Ph―PPP―H = bis(2‐diphenylphosphinophenyl)phosphine). Reaction of the opportune metal precursor (Ca[N(SiMe3)2]2.THF2 or MgnBu2) with 1 equiv. of the pro‐ligand Ph―PPP―H produces the corresponding calcium amido ( 1 ) or magnesium butyl ( 2 ) complex in high yield. Solution NMR studies show monomeric and kinetically stable structures for both species. The obtained complexes efficiently mediate the ring‐opening polymerization of ?‐caprolactone showing a turnover frequency of 40 000 h?1. In the presence of a hexogen alcohol, up to 2000 equiv. of monomer are converted by using a low loading of catalyst (5 µmol). Kinetic studies show a first‐order reaction in monomer concentration. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
148.
149.
Ilaria D'auria Mina Mazzeo Daniela Pappalardo Marina Lamberti Claudio Pellecchia 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):403-413
Phosphido‐diphosphine Group 3 metal complexes 1–4 [(o‐C6H4PR2)2P‐M(CH2SiMe3)2; R = Ph, 1 : M = Y, 2 : M = Sc; R = iPr, 3 : M = Y, 4 : M = Sc] are very efficient catalysts for the ring‐opening polymerization (ROP) of cyclic esters such as ε‐caprolactone (ε‐CL), L ‐lactide, and δ‐valerolactone under mild polymerization conditions. In the ROP of ε‐CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (~4 × 104 molCL/molI h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of ε‐CL and L ‐lactide is feasible by combining complexes 1–4 with 5 equiv of 2‐propanol. Polymers with controlled molecular parameters (Mn, end groups) and low polydispersities (Mw/Mn = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ‐valerolactone, complexes 1–4 showed the same activity observed for lactide (L ‐ and D ,L ‐lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac‐β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献