全文获取类型
收费全文 | 495篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 366篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 49篇 |
物理学 | 81篇 |
出版年
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 41篇 |
2011年 | 40篇 |
2010年 | 13篇 |
2009年 | 7篇 |
2008年 | 33篇 |
2007年 | 30篇 |
2006年 | 43篇 |
2005年 | 24篇 |
2004年 | 26篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1942年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有510条查询结果,搜索用时 15 毫秒
441.
442.
F. Sartorius M. Kranjevi Katharina Heß Dorothy Readhimer R. Stevenson Th. Lindsay G. B. Haven F. J. Zink E. Rupp A. Smits und E. A. Fisher 《Fresenius' Journal of Analytical Chemistry》1937,108(3-4):117-118
Ohne Zusammenfassung 相似文献
443.
Tamas Varga J.F. Mitchell Lindsay G. Arnold Christos D. Malliakas 《Journal of solid state chemistry》2010,183(7):1567-1573
Negative thermal expansion (NTE) materials possess a low-density, open structure that can respond to high pressure conditions, leading to new compounds and/or different physical properties. Here we report that one such NTE material - white, insulating, orthorhombic Sc2W3O12 - transforms into a black compound when treated at 4 GPa and 1400 °C. The high pressure phase, Sc0.67WO4, crystallizes in a defect-rich wolframite-type structure, a dense, monoclinic structure (space group P2/c) containing 1-D chains of edge-sharing WO6 octahedra. The chemical bonding of Sc0.67WO4 vis-à-vis the ambient pressure Sc2W3O12 phase can be understood on the basis of the Sc defect structure. Magnetic susceptibility, resistivity, thermoelectric power and IR spectroscopic measurements suggest that the Sc0.67WO4 sample is a paramagnet whose conductivity is that of a metal in the presence of weak localization and electron-electron interactions. Oxygen vacancies are suggested as a potential mechanism for generating the carriers in this defective wolframite material. 相似文献
444.
Dr. Feng Liang Dr. Shengqing Li Prof. Stuart Lindsay Prof. Peiming Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5998-6007
We have developed a chemical reagent that recognizes all naturally occurring DNA bases, a so called universal reader, for DNA sequencing by recognition tunneling in nanopores. 1 The primary requirements for this type of molecules are the ability to form non‐covalent complexes with individual DNA bases and to generate recognizable electronic signatures under an electrical bias. 1‐H‐imidazole‐2‐carboxamide was designed as such a recognition moiety to interact with the DNA bases through hydrogen bonding. In the present study, we first furnished a synthetic route to 1‐H‐imidazole‐2‐carboxamide containing a short ω‐functionalized alkyl chain at its 4(5) position for its attachment to metal and carbon electrodes. The acid dissociation constants of the imidazole‐2‐carboxamide were then determined by UV spectroscopy. The data show that the 1‐H‐imidazole‐2‐carboxamide exists in a neutral form between pH 6–10. Density functional theory (DFT) and NMR studies indicate that the imidazole ring exists in prototropic tautomers. We propose an intramolecular mechanism for tautomerization of 1‐H‐imidazole‐2‐carboxamide. In addition, the imidazole‐2‐carboxamide can self‐associate to form hydrogen bonded dimers. NMR titration found that naturally occurring nucleosides interacted with 1‐H‐imidazole‐2‐carboxamide through hydrogen bonding in a tendency of dG>dC?dT>dA. These studies are indispensable to assisting us in understanding the molecular recognition that takes place in the nanopore where routinely used analytical tools such as NMR and FTIR cannot be conveniently applied. 相似文献
445.
Zack LN Sun M Bucchino MP Clouthier DJ Ziurys LM 《The journal of physical chemistry. A》2012,116(6):1542-1550
Monomeric ZnOH has been studied for the first time using millimeter and microwave gas-phase spectroscopy. ZnOH is important in surface processes and at the active site of the enzyme carbonic anhydrase. In the millimeter-wave direct-absorption experiments, ZnOH was synthesized by reacting zinc vapor, produced in a Broida-type oven, with water. In the Fourier-transform microwave measurements, ZnOH was produced in a supersonic jet expansion of CH(3)OH and zinc vapor, created by laser ablation. Multiple rotational transitions of six ZnOH isotopologues in their X(2)A' ground states were measured over the frequency range of 22-482 GHz, and splittings due to fine and hyperfine structure were resolved. An asymmetric top pattern was observed in the spectra, showing that ZnOH is bent, indicative of covalent bonding. From these data, spectroscopic constants and an accurate structure were determined. The Zn-O bond length was found to be similar to that in carbonic anhydrase and other model enzyme systems. 相似文献
446.
Cox NM Harding LP Jones JE Pope SJ Rice CR Adams H 《Dalton transactions (Cambridge, England : 2003)》2012,41(5):1568-1573
A new method for assessing the topology of metallosupramolecular assemblies using pyrene-appended ligands is reported. Two potentially tetradentate ligands containing one (L(1)) and two (L(2)) terminal pyrene moieties were synthesised and their complexes with Cu(+) and Cd(2+) were characterised. Photophysical measurements demonstrate that in [Cu(2)(L(1))(2)](2+), [CdL(1)](2+) and [Cu(2)(L(2))(2)](2+) the emission spectra are dominated by monomeric emission but in the cadmium complex of L(2) (where the pyrene units are in close proximity) a quenching of the luminescence coupled with weak emission at 540 nm is indicative of excimer formation. 相似文献
447.
Alexeev D Baxter RL Campopiano DJ Kerbarh O Sawyer L Tomczyk N Watt R Webster SP 《Organic & biomolecular chemistry》2006,4(7):1209-1212
The irreversible inhibition of 8-amino-7-oxononanoate synthase by trifluoroalanine involves decarboxylative defluorination of the inhibitor-PLP aldimine followed by attack of the conjugated imine by the amino group of the active site lysine to afford a covalently bound difluorinated intermediate which can subsequently undergo further HF losses and hydrolysis to afford a 2-(pyridoximine phosphate) acetoyl protein adduct. 相似文献
448.
Herein we present a method to compute d-f mediated exchange coupling in Gd-containing systems with a spin-dependent extended Hückel-tight binding (EHTB) method. EHTB parameters were chosen to exactly reproduce the spin density functional calculation (SDFT) energy gap of the S = 45/2 and 39/2 spin patterns for a model compound, Gd6CoI12(OPH3)6. Comparison between SDFT and EHTB results shows a good match between the spin-pattern energy distribution for the two methods. We applied our EHTB method to the solid-state compound GdB2C2 by considering 6 different variations in the ordering of the 4f7 moments. Calculations indicate that this metallic system should exhibit antiferromagnetic ordering of the 4f7 moments with a magnetic structure consistent with published neutron diffraction results. 相似文献
449.
N-acyl oxazolidinones of simple carboxylic acids and amino acids were observed to undergo successful SmI2-promoted couplings with substituted acrylamides and acrylates, affording a variety of functionalized gamma-ketoamides and -esters with yields attaining 85%. As many of these reductive couplings were previously found to be ineffective employing the corresponding 4-pyridylthio esters, the applicability of this methodology has been substantially improved. The methodology has been adapted to prepare structures related to two potent aspartate protease inhibitors, the renin inhibitor aliskiren, and the gamma-secretase inhibitor L-685,458. Finally, a convenient two-step procedure for the preparation of N-acyl oxazolidinones of N-protected amino acids, which provides consistently good yields of the corresponding imide, has been devised. 相似文献
450.
Eddy MT Ong TC Clark L Teijido O van der Wel PC Garces R Wagner G Rostovtseva TK Griffin RG 《Journal of the American Chemical Society》2012,134(14):6375-6387
We employ a combination of (13)C/(15)N magic angle spinning (MAS) NMR and (2)H NMR to study the structural and functional consequences of different membrane environments on VDAC1 and, conversely, the effect of VDAC1 on the structure of the lipid bilayer. MAS spectra reveal a well-structured VDAC1 in 2D crystals of dimyristoylphosphatidylcholine (DMPC) and diphytanoylphosphatidylcholine (DPhPC), and their temperature dependence suggests that the VDAC structure does not change conformation above and below the lipid phase transition temperature. The same data show that the N-terminus remains structured at both low and high temperatures. Importantly, functional studies based on electrophysiological measurements on these same samples show fully functional channels, even without the presence of Triton X-100 that has been found necessary for in vitro-refolded channels. (2)H solid-state NMR and differential scanning calorimetry were used to investigate the dynamics and phase behavior of the lipids within the VDAC1 2D crystals. (2)H NMR spectra indicate that the presence of protein in DMPC results in a broad lipid phase transition that is shifted from 19 to ~27 °C and show the existence of different lipid populations, consistent with the presence of both annular and bulk lipids in the functionally and structurally homogeneous samples. 相似文献