全文获取类型
收费全文 | 540篇 |
免费 | 19篇 |
国内免费 | 34篇 |
专业分类
化学 | 520篇 |
晶体学 | 4篇 |
力学 | 2篇 |
物理学 | 67篇 |
出版年
2023年 | 10篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 12篇 |
2019年 | 21篇 |
2018年 | 17篇 |
2017年 | 32篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 38篇 |
2011年 | 34篇 |
2010年 | 11篇 |
2009年 | 26篇 |
2008年 | 27篇 |
2007年 | 41篇 |
2006年 | 25篇 |
2005年 | 30篇 |
2004年 | 26篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 17篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有593条查询结果,搜索用时 109 毫秒
121.
122.
The spin-spin proton relaxation times T2 of concentrated sucrose, maltose,D-glucose andL-proline solutions were determined using a Bruker Minispec NMR Spectrometer. Log spin echo amplitude decay curves were also determined and their non-linear nature allowed the proportions of different proton types to be calculated. These were in agreement with the theoretical proportions of ring (non-exchangeable protons), solute hydroxyl protons and water protons in the simple sugar molecules. A deuteration experiment confirmed that only non-exchangeable ring protons remained. 相似文献
123.
硝酸脲中酰胺态氮及总氮含量测定的研究 总被引:2,自引:0,他引:2
对硝酸脲中酰胺态氮及总氮含量进行测定。以甲醛-硫酸法分析硝酸脲中酰胺态氮时,发现酰胺态氮的含量总是与理论值相关差将近1倍。文中解释了造成这一结果的原因。并找到了导致这种结果的定量关系。从反应温度,时间等方面进行多次试验,找到了适宜的分析条件。 相似文献
124.
I. Grosu S. Mager G. Plé R. Martinez M. Horn R. R. Gaviño 《Monatshefte für Chemie / Chemical Monthly》1995,126(8-9):1021-1030
Summary New compounds containing the 2,4,8,10-tetraoxaspiro[5.5]undecanic skeleton, substituted with brominated groups, have been synthesized by a regioselective radicalic bromination reaction. The stereochemistry of the compounds was studied by high resolution NMR methods. The anancomericity or the flipping of the rings was inferred from the conformational analysis. The chirality of the spiranic skeleton was investigated by means of the diastereotopicity of hydrogen and carbon atoms.On leave from Organic Chemistry Department, Babes-Bolyai University, RO-3400 Cluj-Napoca, Romania 相似文献
125.
Richard C. Titmas Thelma S. Angeles Renee Sugasawara Nurredin Aman Michael J. Darsley Gary Blackburn Mark T. Martin 《Applied biochemistry and biotechnology》1994,47(2-3):277-292
Because there are many known C-terminally amidated peptides of biological importance, there is great potential in medicine
and organic synthesis for antibodies that catalyze primary amide bond hydrolysis or formation. We characterized a catalytic
antibody, 13D11, raised to a phosphinate hapten, that hydrolyzed the primary amide of a dansyl-alkylated derivative of (R)-phenylalaninamide
(DNS-(R)F-NH2). At pH 9.0, 13D11 hydrolyzed DNS-(R)F-NH2 with a kcat of 1.65 × 10-7 s-1 (kcat/kuncat = 132) and a Km of 432 μM, and was stereospecifically hapten-inhibited (Ki = 14.0 μM). Control experiments indicated that the catalytic activity was not the result of a contaminating protease. In
accordance with the hapten being a transition-state analog of base hydrolysis, the rate of DNS-(R)F-NH2 hydrolysis increased with hydroxide concentration to an optimum pH of 9.5. Above pH 9.5, activity declined rapidly suggesting
the antibody was inactivated during the long incubation period. This work demonstrates the feasibility of generating catalytic
antibodies to hydrolyze unactivated amide bonds without cofactor assistance. 相似文献
126.
Summary The amide conformers of two compounds and their enantiomers have been separated by liquid chromatography on an 1-acid glycoprotein column. The effects of organic modifier and pH on the separations obtained were investigated. The conformers of one of the compounds were separated micro-preparatively at low temperature on the same column using a D2O-based eluent; D2O had no deleterious effects on the chromatography obtained. Some preliminary competition experiments on one of the amides and a close analogue are presented. 相似文献
127.
Themistoclis Kabanos Spyros P. Perlepes Vaggelis Hondrellis John M. Tsangaris 《Monatshefte für Chemie / Chemical Monthly》1986,117(8-9):955-967
New complexes of the general formulae CoL
2
X·nH2O (X=Cl, Br, I, NCS, NO3 andn=0, 1, 2 or 3), Co2
L
2
X
3·EtOH (X=Cl, Br, I, NCS), Co(DH)X
2 (X=NCS, NO3) and Co(DH)2
X
2 (X=NCS, I) have been prepared, whereLH=N-(2-aminophenyl)pyridine-2-carboxamide andDH=N-(3-aminophenyl)pyridine-2-carboxamide. The compounds were characterized by X-ray powder patterns, conductivity measurements, thermogravimetric analysis, magnetic properties as well as by IR, ligand field and1H-NMR spectroscopy. In the presence of oxygen,LH undergoes a cobalt(III) ion promoted amide hydrogen ionization in thepH region 4–6.
Koordinationsverbindungen von N-(2-aminophenyl)- und N-(3-aminophenyl)pyridin-2-carboxamid mit Cobalt(II) und Cobalt(III). Die Natur der Deprotonierung von Amiden induziert von Cobalt(III) in saurem Medium
Zusammenfassung Neue Komplexe der allgemeinen Formeln CoL 2 X·nH2O (X=Cl, Br, I, NCS, NO3 undn=0, 1, 2, 3), Co2 L 2 X 3·EtOH (X=Cl, Br, I, NCS), Co(DH)X 2 (X=NCS, NO3) und Co(DH)2 X 2 (X=NCS, I) wurden dargestellt mit LH=N-(2-aminophenyl)pyridin-2-carboxamid undDH=N-(3-aminophenyl)pyridin-2-carboxamid. Die Verbindungen wurden mittels Röntgenstrukturanalyse, Leitfähigkeitsmessungen, thermogravimetrischen Analysen, magnetischen Eigenschaften sowie mit IR-, Ligandenfeld- und1H-NMR-Spektroskopie charakterisiert. In Gegenwart von Sauerstoff unterliegtLH einer Cobalt(III)ion-induzierten Amidwasserstoffionisierung impH-Bereich 4–6.相似文献
128.
New N-3 functionalized 3,4-dihydropyrimidine-2(1H)-ones with 1,2,4-oxadiazole group as amide isostere were synthesized in six steps by ionic liquid-phase organic synthesis (IoLiPOS) methodology from ILP bound acetoacetate. The 3,4-dihydropyrimidine-2(1H)-one (3,4-DHPM) core was prepared in the first step by one-pot three-component Biginelli condensation followed by N-alkylation with chloroacetonitrile. Then the nitrile group appended on the 3,4-DHPM heterocycle was quantitatively transformed into amidoxime. Addition of aliphatic carboxylic anhydride or aromatic carboxylic acid to the amidoxime produced the expected 1,2,4-oxadiazole via the O-acylamidoxime intermediate grafted on the ILP bound 3,4-DHPM using two convergent methods. After cleavage by transesterification under mild conditions, the target compounds were obtained in good overall yields. The structures and the purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis. 相似文献
129.
Chandan Singh Ratan Kumar Rai Arvind M. Kayastha Neeraj Sinha 《Magnetic resonance in chemistry : MRC》2016,54(2):132-135
Ultra fast magic angle spinning (MAS) has been a potent method to significantly average out homogeneous/inhomogeneous line broadening in solid‐state nuclear magnetic resonance (ssNMR) spectroscopy. It has given a new direction to ssNMR spectroscopy with its different applications. We present here the first and foremost application of ultra fast MAS (~60 kHz) for ssNMR spectroscopy of intact bone. This methodology helps to comprehend and elucidate the organic content in the intact bone matrix with resolution and sensitivity enhancement. At this MAS speed, amino protons from organic part of intact bone start to appear in 1H NMR spectra. The experimental protocol of ultra‐high speed MAS for intact bone has been entailed with an additional insight achieved at 60 kHz. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
130.
A convenient synthesis of bisamide from aldehyde and amide with BF3 etherate as catalyst was reported. Both aryl and aliphatic bisamides could be prepared with this procedure in high yield at room temperature and the catalyst loading as low as 0.5 mol % was achieved. Fine-tuned solvent was utilized for both rapid conversion and simple isolation. Two CB2 receptor inverse agonists were synthesized with this protocol in high yield. 相似文献