全文获取类型
收费全文 | 1164篇 |
免费 | 53篇 |
国内免费 | 12篇 |
专业分类
化学 | 758篇 |
晶体学 | 4篇 |
力学 | 59篇 |
数学 | 233篇 |
物理学 | 175篇 |
出版年
2023年 | 14篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 44篇 |
2015年 | 46篇 |
2014年 | 31篇 |
2013年 | 54篇 |
2012年 | 77篇 |
2011年 | 90篇 |
2010年 | 54篇 |
2009年 | 49篇 |
2008年 | 64篇 |
2007年 | 72篇 |
2006年 | 70篇 |
2005年 | 72篇 |
2004年 | 74篇 |
2003年 | 48篇 |
2002年 | 31篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1909年 | 4篇 |
1908年 | 3篇 |
1899年 | 2篇 |
排序方式: 共有1229条查询结果,搜索用时 15 毫秒
951.
[chemical structure: see text]. Two natural products have been synthesized using a ZnCl2-mediated benzylic coupling reaction. Both are potent inhibitors of the GTPase activity of FtsZ, a highly conserved protein that is essential for bacterial cytokinesis. 相似文献
952.
Amination of halobenzenes, which proceeds via the benzyne intermediate (1), has been studied using quantum chemical methods. The computational data are in agreement with experimentally observed trends in reactivity and provide a qualitative explanation for the observed hydrogen isotope effects. To investigate if this is a viable way to isolate the pentazolate anion (2), the reactivities of the halobenzenes have been compared to phenylpentazole (3). The reaction energetics for phenylpentazole become favorable after complexation with Zn(2+). 相似文献
953.
We have simulated the HOONO vibrational overtone spectrum with use of a local mode Hamiltonian that includes the OH-stretching, OOH-bending, and NOOH-torsional modes and coupling between all three modes. The local mode parameters and the dipole moment function are calculated with coupled-cluster ab initio theory and an augmented Dunning-type triple-zeta basis set. We investigate the accuracy of the local mode parameters obtained from two different potential-energy fitting routines, as well as the sensitivity of these parameters to the basis set employed. We compare our simulated spectra to previously published action spectra in the first and second OH-stretching overtone regions. In addition we have recorded the spectrum in the OH-stretch and OOH-bend combination region around 7700 cm-1 and we also compare to this. Our simulated spectrum is in qualitative agreement with experiment in the first and second OH-stretching overtone and in the stretch-bend regions. 相似文献
954.
David Fuchs Charlotte Gabel-Jensen Henrik Jensen Kasper D. Rand Stig Pedersen-Bjergaard Steen Honoré Hansen Nickolaj Jacob Petersen 《Analytica chimica acta》2016
A fully integrated and automated electromembrane extraction LC-MS (EME-LC-MS) system has been developed and characterized. Hyphenation of a flow–flow EME probe to LC-MS was accomplished by using an in-built 10-port switching valve of the LC-MS system. The 10-port switching valve decoupled the high pressure of the UHPLC-system from the low pressure required for operation of the EME-probe by automated switching between a sample extraction/analysis and a sample load position. In the sample load position the extracted analytes were loaded into a HPLC sample loop. By switching the valve to the sample extraction/analysis position the setup allowed simultaneous analysis of previously loaded analytes while extracting a new sample. Performance of the system was characterized with respect to precision and linearity (RSD < 2.5%, R2: 0.998) and the setup was applied for studying the in-vitro metabolism of methadone by rat liver microsomes. As the metabolic reaction proceeded, methadone and its metabolites were extracted and analyzed in parallel by LC-MS using either isocratic or gradient elution. Compared to a conventional in-vitro metabolism analysis based on protein precipitation followed by LC-MS analysis the fully automated EME-LC-MS system offers a significant time saving and in addition demonstrates increased sensitivity as the analytes were automatically enriched during the extraction process. The experiment revealed 6 to 16 times higher S/N ratios of the EME-LC-MS method compared to protein precipitation followed by LC-MS and thus concomitantly lower LOD and LOQ. The setup integrates a complete analytical workflow of rapid extraction, enrichment, separation and detection of analytes in a fully automated manner. These attributes make the developed system a powerful alternative approach for a wide range of analytical applications. 相似文献
955.
Irene Osada Henrik de Vries Prof. Dr. Bruno Scrosati Prof. Dr. Stefano Passerini 《Angewandte Chemie (International ed. in English)》2016,55(2):500-513
The advent of solid‐state polymer electrolytes for application in lithium batteries took place more than four decades ago when the ability of polyethylene oxide (PEO) to dissolve suitable lithium salts was demonstrated. Since then, many modifications of this basic system have been proposed and tested, involving the addition of conventional, carbonate‐based electrolytes, low molecular weight polymers, ceramic fillers, and others. This Review focuses on ternary polymer electrolytes, that is, ion‐conducting systems consisting of a polymer incorporating two salts, one bearing the lithium cation and the other introducing additional anions capable of plasticizing the polymer chains. Assessing the state of the research field of solid‐state, ternary polymer electrolytes, while giving background on the whole field of polymer electrolytes, this Review is expected to stimulate new thoughts and ideas on the challenges and opportunities of lithium‐metal batteries. 相似文献
956.
Carl Henrik Grbitz David S. Wragg Ingrid Marie Bergh Bakke Christian Fleischer Gaute Grnnevik Maria Mykland Yoomin Park Kristian Wiedicke Trovik Halvard Serigstad Brd Edgar Vestheim Sundsli 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(7):536-543
Racemates of hydrophobic amino acids with linear side chains are known to undergo a unique series of solid‐state phase transitions that involve sliding of molecular bilayers upon heating or cooling. Recently, this behaviour was shown to extend also to quasiracemates of two different amino acids with opposite handedness [Görbitz & Karen (2015). J. Phys. Chem. B, 119 , 4975–4984]. Previous investigations are here extended to an l ‐2‐aminobutyric acid–d ‐methionine (1/1) co‐crystal, C4H9NO2·C5H11NO2S. The significant difference in size between the –CH2CH3 and –CH2CH2SCH3 side chains leads to extensive disorder at room temperature, which is essentially resolved after a phase transition at 229 K to an unprecedented triclinic form where all four d ‐methionine molecules in the asymmetric unit have different side‐chain conformations and all three side‐chain rotamers are used for the four partner l ‐2‐aminobutyric acid molecules. 相似文献
957.
Difference between Extra‐ and Intracellular T1 Values of Carboxylic Acids Affects the Quantitative Analysis of Cellular Kinetics by Hyperpolarized NMR 下载免费PDF全文
Dr. Magnus Karlsson Dr. Pernille Rose Jensen Prof. Jan Henrik Ardenkjær‐Larsen Dr. Mathilde H. Lerche 《Angewandte Chemie (International ed. in English)》2016,55(43):13567-13570
Incomplete knowledge of the longitudinal relaxation time constant (T1) leads to incorrect assumptions in quantitative kinetic models of cellular systems, studied by hyperpolarized real‐time NMR. Using an assay that measures the intracellular signal of small carboxylic acids in living cells, the intracellular T1 of the carboxylic acid moiety of acetate, keto‐isocaproate, pyruvate, and butyrate was determined. The intracellular T1 is shown to be up to four‐fold shorter than the extracellular T1. Such a large difference in T1 values between the inside and the outside of the cell has significant influence on the quantification of intracellular metabolic activity. It is expected that the significantly shorter T1 value of the carboxylic moieties inside cells is a result of macromolecular crowding. An artificial cytosol has been prepared and applied to predict the T1 of other carboxylic acids. We demonstrate the value of this prediction tool. 相似文献
958.
Carl Henrik Grbitz Lars Male Hartviksen 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):o171-o176
The crystal structures of the four dipeptides l ‐seryl‐l ‐asparagine monohydrate, C7H13N3O5·H2O, l ‐seryl‐l ‐tyrosine monohydrate, C12H16N2O5·H2O, l ‐tryptophanyl‐l ‐serine monohydrate, C14H17N3O4·H2O, and l ‐tyrosyl‐l ‐tryptophan monohydrate, C20H21N3O4·H2O, are dominated by extensive hydrogen‐bonding networks that include cocrystallized solvent water molecules. Side‐chain conformations are discussed on the basis of previous observations in dipeptides. These four dipeptide structures greatly expand our knowledge on dipeptides incorporating polar residues such as serine, asparagine, threonine, tyrosine and tryptophan. 相似文献
959.
Salmi T Hänninen V Garden AL Kjaergaard HG Tennyson J Halonen L 《The journal of physical chemistry. A》2008,112(28):6305-6312
The O-H stretching vibrational overtone spectrum of the water dimer has been calculated with the dimer modeled as two individually vibrating monomer units. Vibrational term values and absorption intensities have been obtained variationally with a computed dipole moment surface and an internal coordinate Hamiltonian, which consists of exact kinetic energy operators within the Born-Oppenheimer approximation of the monomer units. Three-dimensional ab initio potential energy and dipole moment surfaces have been calculated using the internal coordinates of the monomer units using the coupled cluster method including single, double, and perturbative triple excitations [CCSD(T)] with the augmented correlation consistent valence triple zeta basis set (aug-cc-pVTZ). The augmented correlation consistent valence quadruple zeta basis set (aug-cc-pVQZ), counterpoise correction, basis set extrapolation to the complete basis set limit, relativistic corrections, and core and valence electron correlations effects have been included in one-dimensional potential energy surface cuts. The aim is both to investigate the level of ab initio and vibrational calculations necessary to produce accurate results when compared with experiment and to aid the detection of the water dimer under atmospheric conditions. 相似文献
960.
René Holm Rune A. Hartvig Henrik V. Nicolajsen Peter Westh Jesper Østergaard 《Journal of inclusion phenomena and macrocyclic chemistry》2008,61(1-2):161-169
The complexation of seven bile salts, present in the small intestine of rat, dog and man, (taurocholate, tauro-β-muricholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate and glycochenodeoxycholate) with γ-cyclodextrin and the chemically modified 2-hydroxypropyl-γ-cyclodextrin, was studied using affinity capillary electrophoresis (ACE). The cyclodextrins (CDs) were investigated due to their use in drug formulation as excipients for solubilisation of poorly soluble drugs and drug candidates. Using mobility shift ACE, the bile salt cyclodextrin interactions were characterized demonstrating 1:1 binding stoichiometry with stability constants ranging from 2 × 103 to 8 × 104 M?1. The binding constants showed a systematic dependence on the number and position of hydroxyl groups on the steroid skeleton and the stability constants were in general higher for complexation with the native cyclodextrin than with the modified cyclodextrin. Based upon the size of the complexation constants, it was suggested that the interaction between the CDs and the bile salts takes place at the C and D ring of the steroid skeleton. The complexation of bile salts with the γ-cyclodextrins may compete with drug-γ-cyclodextrin complex formation and, thus, potentially affect drug absorption and efficacy. 相似文献