全文获取类型
收费全文 | 3097篇 |
免费 | 330篇 |
国内免费 | 296篇 |
专业分类
化学 | 2287篇 |
晶体学 | 40篇 |
力学 | 136篇 |
综合类 | 41篇 |
数学 | 425篇 |
物理学 | 794篇 |
出版年
2024年 | 8篇 |
2023年 | 56篇 |
2022年 | 110篇 |
2021年 | 118篇 |
2020年 | 111篇 |
2019年 | 141篇 |
2018年 | 85篇 |
2017年 | 105篇 |
2016年 | 139篇 |
2015年 | 121篇 |
2014年 | 140篇 |
2013年 | 202篇 |
2012年 | 174篇 |
2011年 | 186篇 |
2010年 | 139篇 |
2009年 | 168篇 |
2008年 | 155篇 |
2007年 | 148篇 |
2006年 | 132篇 |
2005年 | 126篇 |
2004年 | 146篇 |
2003年 | 132篇 |
2002年 | 166篇 |
2001年 | 145篇 |
2000年 | 97篇 |
1999年 | 77篇 |
1998年 | 35篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 26篇 |
1993年 | 17篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 7篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
排序方式: 共有3723条查询结果,搜索用时 15 毫秒
991.
The β-trialkylammonium chloride derivatives of several α,β-unsaturated carbonyl compounds have been shown by infrared spectra to exist in the s-cis and s-trans rotational forms. The equilibrium between these two forms shifts towards the s-cis with the increasing steric requirements of the alkyl substituent linked to carbonyl. The CO and CC stretching frequencies are shifted to higher values as compared with other types of α,β-unsaturated ketones. 相似文献
992.
A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands. 相似文献
993.
Guldi DM Luo C Da Ros T Bosi S Prato M 《Chemical communications (Cambridge, England)》2002,(20):2320-2321
Fulleropyrrolidine- and fulleropyrrolidinium-based donor-acceptor ensembles, C60-Fc, were tested in view of intrinsic reorganisation energies for light-induced electron transfer events; overall, the zwitterionic character of the reduced fulleropyrrolidinium acceptor plays a central role in accelerating charge separation and decelerating charge recombination. 相似文献
994.
995.
Eric Da Silva Cécile F. Rousseau Isabelle Zanella-Cléon Michel Becchi Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):53-59
Electrospray Ionization Mass Spectrometry (ESI/MS) has been used to determine the association constants (KAs) and binding stoichiometries for parent para-Sulphonato-calix[n]arenes and their derivatives with bovine serum albumin (BSA). KA values were determined by titration experiments using a constant concentration of protein. KA measurements were carried out in a methanol–formic acid solution. 5,11,17,23–tetra-Sulphonato-calix[4]arene (1a) and 25-mono-(2-aminoethoxy)-5,11,17,23-tetra-Sulphonato-calix[4]arene (1d) interact strongly with BSA showing 3 non-equivalent binding sites with KA1 = 7.69 × 105 M−1, KA2 = 3.85 × 105 M−1, KA3 = 0.33 × 105 M−1 and KA1 = 1.69 × 105 M−1, KA2 = 2.94 × 105 M−1, KA3 = 0.60 × 105 M−1, respectively. The strength of the interactions between the calixarene and BSA is inversely proportional to the size of macrocyclic
ring: n = 4 > n=6>>n=8. 相似文献
996.
Fen Sun Yan‐Tuan Li Zhi‐Yong Wu Da‐Qi Wang Jian‐Min Dou 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):m60-m62
The structure of the title compound, (C5H12N)4[V10O26(CH3O)2], reveals the presence of four protonated piperidinium cations and a [{V10O26}(OCH3)2]4− polyanion having an embedded centre of inversion. The compound is distinguished by presenting, in contrast with other anionic decavanadates, two methoxy groups bridging the outermost V atoms, and it becomes the first example of this type among reported decavanadates. 相似文献
997.
双电荷离子[C_(12)H_(12)N_2O]~(2+)和[C_(12)H_(12)N_2S]~(2+)的气相单分子分解反应研究任达,贾维平,李智立,刘淑莹(中国科学院长春应用化学研究所,长春,130022)关键词双电荷离子,质量分析离子动能谱,串联质谱,4... 相似文献
998.
S. Carboni A. Da Settimo D. Bertini P. L. Ferrarini O. Livi I. Tonetti 《Journal of heterocyclic chemistry》1975,12(4):743-747
The boron trifluoride-catalyzed rearrangement of the epoxide derived from 3-benzylidene- 7-methyl-2,3-dihydro-1,8-naphthyridin-4-(1H)one (II) is described. The structure of the obtained 8-methyl-4-phenyl-1,2,3,4-tetrahydro-5H-pyrido[2,3,-b]-azepin-3, azepin-3,5-dione (X) has been elucidated with aid of chemical and spectral evidence. 相似文献
999.
Pellarini F Pantarotto D Da Ros T Giangaspero A Tossi A Prato M 《Organic letters》2001,3(12):1845-1848
[see structure]. A fullerene derivative containing a free amino group has been condensed with N-Fmoc-L-glutamic acid alpha-tert-butyl ester to give a C60-functionalized amino acid. The carboxylic end of this amino acid has been deprotected in acidic conditions, and the resulting acid has been used for solid-phase peptide synthesis. The final peptide, cleaved from the resin, was very soluble in water solutions and showed antimicrobial activity against two representative bacteria. 相似文献
1000.
Antonio Da Settimo Anna Maria Marini Giampaolo Primofiore Federico Da Settimo Daniele Bertini 《Journal of heterocyclic chemistry》1998,35(1):57-60
The synthesis of derivatives of two new heterocyclic systems, purino[8,7-b][1,3]benzothiazine and pyrido[3′,2′:5,6][1,3]thiazino[3,2-f]purine, was effected by the Ullmann reaction between 8-mercaptotheophylline or 8-bromotheophylline with the appriopriately substituted benzoic or nicotinic acid, respectively. The 8,8′-dithiobistheophylline is also reported. 相似文献