全文获取类型
收费全文 | 187篇 |
免费 | 5篇 |
专业分类
化学 | 125篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 11篇 |
物理学 | 49篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 5篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1887年 | 1篇 |
1882年 | 1篇 |
排序方式: 共有192条查询结果,搜索用时 15 毫秒
181.
Rösener B Rattunde M Moser R Kaspar S Töpper T Manz C Köhler K Wagner J 《Optics letters》2011,36(3):319-321
We demonstrate an optically pumped semiconductor disk laser based on the (AlGaIn)(AsSb) material system, which operates at an emission wavelength of 2.8 μm. Up to 120 mW of output power were obtained in cw operation and more than 500 mW in pulsed mode. The performance of the present laser is discussed in comparison to shorter-wavelength semiconductor disk lasers based on the same materials system. 相似文献
182.
K. Stavenhagen H. Hinneburg M. Thaysen‐Andersen L. Hartmann D. Varón Silva J. Fuchser S. Kaspar E. Rapp P. H. Seeberger D. Kolarich 《Journal of mass spectrometry : JMS》2013,48(6):i-i
Mass spectrometry (MS) is used to quantify the relative distribution of glycans attached to particular protein glycosylation sites (micro‐heterogeneity) and evaluate the molar site occupancy (macro‐heterogeneity) in glycoproteomics. However, the accuracy of MS for such quantitative measurements remains to be clarified. As a key step towards this goal, a panel of related tryptic peptides with and without complex, biantennary, disialylated N‐glycans was chemically synthesised by solid‐phase peptide synthesis. Peptides mimicking those resulting from enzymatic deglycosylation using PNGase F/A and endo D/F/H were synthetically produced, carrying aspartic acid and N‐acetylglucosamine‐linked asparagine residues, respectively, at the glycosylation site. The MS ionisation/detection strengths of these pure, well‐defined and quantified compounds were investigated using various MS ionisation techniques and mass analysers (ESI‐IT, ESI‐Q‐TOF, MALDI‐TOF, ESI/MALDI‐FT‐ICR‐MS). Depending on the ion source/mass analyser, glycopeptides carrying complex‐type N‐glycans exhibited clearly lower signal strengths (10–50% of an unglycosylated peptide) when equimolar amounts were analysed. Less ionisation/detection bias was observed when the glycopeptides were analysed by nano‐ESI and medium‐pressure MALDI. The position of the glycosylation site within the tryptic peptides also influenced the signal response, in particular if detected as singly or doubly charged signals. This is the first study to systematically and quantitatively address and determine MS glycopeptide ionisation/detection strengths to evaluate glycoprotein micro‐heterogeneity and macro‐heterogeneity by label‐free approaches. These data form a much needed knowledge base for accurate quantitative glycoproteomics. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
183.
Inducing Axial Chirality in a “Geländer” Oligomer by Length Mismatch of the Oligomer Strands 下载免费PDF全文
Michel Rickhaus Linda Maria Bannwart Dr. Markus Neuburger Heiko Gsellinger Kaspar Zimmermann Dr. Daniel Häussinger Prof. Dr. Marcel Mayor 《Angewandte Chemie (International ed. in English)》2014,53(52):14587-14591
Helical molecules are not only esthetically appealing due to their structural beauty, they also display unique physical properties as a result of their chirality. We describe herein a new approach to “Geländer” oligomers by interlinking two oligomer strands of different length. To compensate for the dimensional mismatch, the longer oligo(benzyl ether) oligomer wraps around the oligophenyl backbone. The new “Geländer” oligomer 1 was assembled in a sequence of functional‐group transformations and cross‐coupling steps followed by final cyclizations based on nucleophilic substitution reactions, and was fully characterized, including X‐ray diffraction analysis. The isolation of pure enantiomers enabled the racemization process to be studied by circular dichroism spectroscopy. 相似文献
184.
Christian Neis Kaspar Hegetschweiler 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(4):396-399
In the title monohydrated cocrystal, namely 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide–1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol–water (1/1/1), C6H16N3O3+·I−·C6H15N3O3·H2O, the neutral 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (taci) molecule and the monoprotonated 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol cation (Htaci+) both adopt a chair conformation, with the three O atoms in axial and the three N atoms in equatorial positions. The cation, but not the neutral taci unit, exhibits intramolecular O—H...O hydrogen bonding. The entire structure is stabilized by a complex three‐dimensional network of intermolecular hydrogen bonds. The neutral taci entities and the Htaci+ cations are each aligned into chains along [001]. In these chains, two O—H...N interactions generate a ten‐membered ring as the predominant structural motif. The rings consist of vicinal 2‐amino‐1‐hydroxyethylene units of neighbouring molecules, which are paired via centres of inversion. The chains are interconnected into undulating layers parallel to the ac plane, and the layers are further held together by O—H...N hydrogen bonds and additional interactions with the iodide counter‐anions and solvent water molecules. 相似文献
185.
186.
Baumler DJ Hung KF Bose JL Vykhodets BM Cheng CM Jeong KC Kaspar CW 《Applied biochemistry and biotechnology》2006,134(1):15-26
A portion of the cbpA gene from Escherichia coli K-12 encoding a 24 amino acid proton-buffering peptide (Pbp) was cloned via the shuttle vector pJB99 into E. coli JM105 and subsequently into Zymomonas mobilis CP4. Expression of Pbp was confirmed in both JM105 and CP4 by HPLC. Z. mobilis CP4 carrying pJB99-2 (Pbp) exhibited increased acid tolerance (p<0.05) in acidified TSB (HCl [pH 3.0] or acetic acid [pH 3.5]), glycine-HCl buffer (pH 3.0), and sodium acetate-acetic acid
buffer (pH 3.5) in comparison to the parent strain (CP4) and CP4 with pJB99 (control plasmid). Although the expression of
Pbp influenced survival at a low pH, the minimum growth pH was unaffected. Growth of Z. mobilis in the presence of ampicillin also significantly increased acid tolerance by an unknown mechanism. Results from this study
demonstrate that the production of a peptide with a high proportion of basic amino acids can contribute to protection from
low pH and weak organic acids such as acetic acid. 相似文献
187.
Lehaire ML Grundler PV Steinhauser S Marti N Helm L Hegetschweiler K Schibli R Merbach AE 《Inorganic chemistry》2006,45(10):4199-4204
The pH-dependent water-exchange rates of [(CO)2(NO)Re(H2O(cis))2(H2O(trans))]2+ (1) in aqueous media were investigated by means of 17O NMR spectroscopy at 298 K. Because of the low pK(a) value found for 1 (pK(a) = 1.4 +/- 0.3), the water-exchange rate constant k(obs)(H2O(trans/cis)) was analyzed with a two-pathway model in which k(Re)(H2O(trans/cis)) and k(ReOH)(H2O)(trans/cis)) denote the water-exchange rate constants in trans or cis position to the nitrosyl ligand on 1 and on the monohydroxo species [(CO)2(NO)Re(H2O)2(OH)]+ (2), respectively. Whereas the rate constants k(ReOH)(H2O)(trans)) and k(ReOH)(H2O)(cis)) were determined as (4.2 +/- 2) x 10(-3) s(-1) and (5.8 +/- 2) x 10(-4) s(-1), respectively, k(Re)(H2O)(trans)) and k(Re)(H2O)(cis)) were too small to be determined in the presence of the much more reactive species 2. Apart from the water exchange, an unexpectedly fast C identical with 16O --> C identical withO exchange was also observed via NMR and IR spectroscopy. It was found to proceed through 1 and 2, with rate constants k(Re)(CO) and k(ReOH)(CO) of (19 +/- 4) x 10(-3) s(-1) and (4 +/- 3) x 10(-3) s(-1), respectively. On the other hand, N identical with 16O --> N identical with *O exchange was not observed. 相似文献
188.
Alexey Bobrovsky Valery Shibaev Vera Hamplova Miroslav Kaspar Milada Glogarova 《Colloid and polymer science》2010,288(14-15):1375-1384
For the first time, a photochromic azobenzene-containing liquid crystalline (LC) acrylic polymer was used for gelation of low-molar-mass nematic mixture (LMNM). Dissolution of LC polymer in amount of only 2.5 wt.% in LMNM at 120°C (isotropic state) followed by cooling down results in formation of the solid-like photochromic LC gel. Gelation is associated with a phase separation and formation of microsized LC polymer domains, which form a physical “network” containing encapsulated nematic host. Textural changes of mixture during gel formation were analyzed, and absorbance spectra were measured. A special attention was paid to the kinetic study of photoinduced E-Z and Z-E isomerization of azobenzene side groups of polymer in gel. It was shown that ultraviolet (UV)-irradiation and E-Z isomerization processes are accompanied by disruption of H-aggregates of azobenzene moieties and partial dissolution of polymer. 相似文献
189.
Amino acids are important targets for metabolic profiling. For decades, amino acid analysis has been accomplished by either
cation-exchange or reversed-phase liquid chromatography coupled to UV absorbance or fluorescence detection of pre-column or
post-column-derivatized amino acids. Recent years have seen great progress in the development of direct-infusion or hyphenated
mass spectrometry in the analysis of free amino acids in physiological fluids, because mass spectrometry not only matches
optical detection in sensitivity, but also offers superior selectivity. The advent of cryo-probes has also brought NMR spectroscopy
within the detection limits required for the analysis of free amino acids. But there is still room for further improvement,
including expansion of the analyte spectrum, reduction of sample preparation and analysis time, automation, and synthesis
of affordable isotope standards.
Figure Fully automated gas chromatography-mass spectrometry analysis of amino acids. 相似文献
190.