全文获取类型
收费全文 | 1110篇 |
免费 | 33篇 |
国内免费 | 6篇 |
专业分类
化学 | 744篇 |
晶体学 | 4篇 |
力学 | 21篇 |
数学 | 225篇 |
物理学 | 155篇 |
出版年
2023年 | 12篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 13篇 |
2019年 | 37篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 38篇 |
2015年 | 44篇 |
2014年 | 42篇 |
2013年 | 86篇 |
2012年 | 61篇 |
2011年 | 68篇 |
2010年 | 50篇 |
2009年 | 53篇 |
2008年 | 62篇 |
2007年 | 74篇 |
2006年 | 41篇 |
2005年 | 31篇 |
2004年 | 36篇 |
2003年 | 30篇 |
2002年 | 36篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 10篇 |
1955年 | 2篇 |
1931年 | 2篇 |
排序方式: 共有1149条查询结果,搜索用时 15 毫秒
191.
Johannes Oschwald Dr. David Reger Dr. Stefan Frühwald Vera Warmbrunn Prof. Dr. Andreas Görling Prof. Dr. Norbert Jux Prof. Dr. Thomas Drewello 《Chemphyschem》2023,24(21):e202300496
Gas-phase complexes of [n]helicenes with n=6, 7 and 8 and the silver(I) cation are generated utilizing electrospray ionization mass spectrometry (ESI-MS). Besides the well-established [1 : 1] helicene/Ag+-complex in which the helicene provides a tweezer-like surrounding for the Ag+, there is also a [2 : 1] complex formed. Density functional theory (DFT) calculations in conjunction with energy-resolved collision-induced dissociation (ER-CID) experiments reveal that the second helicene attaches via π-π stacking to the first helicene, which is part of the pre-formed [1 : 1] tweezer complex with Ag+. For polycyclic aromatic hydrocarbons (PAHs) of planar structure, the [2 : 1] complex with silver(I) is typically structured as an Ag+-bound dimer in which the Ag+ would bind to both PAHs as the central metal ion (PAH–Ag+–PAH). For helicenes, the Ag+-bound dimer is of similar thermochemical stability as the π-π stacked dimer, however, it is kinetically inaccessible. Coronene (Cor) is investigated in comparison to the helicenes as an essentially planar PAH. In analogy to the π-π stacked dimer of the helicenes, the Cor−Ag+−Cor−Cor complex is also observed. Competition experiments using [n]helicene mixtures reveal that the tweezer complexes of Ag+ are preferably formed with the larger helicenes, with n=6 being entirely ignored as the host for Ag+ in the presence of n=7 or 8. 相似文献
192.
Vera Dugandžić Izabella Jolan Hidi Karina Weber Dana Cialla-May Jürgen Popp 《Analytica chimica acta》2016
Herein we report a novel strategy for the in situ synthesis of the silver colloids for LoC-SERS applications. Silver nanoparticles are obtained in a segmented flow based glass microfluidic chip by the reduction of silver ions with hydrazine in ammonium hydroxide solution. Citrate ions are used as protecting agents. The synthesized nanoparticles are characterized by UV-VIS spectroscopy, SEM and TEM imaging. The SERS performance of the in situ synthesized nanoparticles is tested by using adenine as a test analyte right after the colloid synthesis. Reproducibility is tested by repeating the measurements three times at independent days applying the same measurement conditions. In comparison with nanoparticles synthesized in a conventional strategy i.e. in a large batch, chip synthesized nanoparticles show a better day-to-day and long-term reproducibility, lower detection limits and broader working ranges. The great advantage offered by the in situ synthesized colloids combined with the already proven potential of LoC-SERS for bioanalytics, raises the possibility of the employment of LoC-SERS as a fast and sensitive analytic tool in a plethora of applications. 相似文献
193.
Richard M. Laine Joseph C. Furgal Phi Doan David Pan Vera Popova Xingwen Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(3):1077-1081
The direct depolymerization of SiO2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Simet, followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)4. Thus, 2‐methyl‐2,4‐pentanediol, 2,2,4‐trimethyl‐1,3‐pentanediol, or ethylene glycol (EGH2) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H2O and distillable spirocyclic alkoxysilanes [bis(2‐methyl‐2,4‐pentanediolato) silicate, bis(2,2,4‐trimethyl‐1,3‐pentanediolato) silicate or Si(eg)2 polymer with 5–98 % conversion, as governed by surface area/crystallinity. Si(eg)2 or bis(2‐methyl‐2,4‐pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)4 in 60 % yield, thus providing inexpensive routes to high‐purity precipitated or fumed silica and compounds with single Si−C bonds. 相似文献
194.
Stanislav K. Filatov Maria G. Krzhizhanovskaya Rimma S. Bubnova Andrey P. Shablinskii Olga L. Belousova Vera A. Firsova 《Structural chemistry》2016,27(6):1663-1671
Thermal expansion of four strontium borates has been studied by high-temperature powder X-ray diffraction. Strong anisotropy of thermal expansion is observed for the structures of Sr3B2O6 (0D) and SrB2O4 (1D) based on triangles BO3 only: The high expansion occurs perpendicular to the BO3 plane, i.e. along the direction of the less strong bonds in the crystal structure. The monoclinic Sr2B16O26 (3D) borate expands dramatically due to shear deformations in monoclinic plane: Monoclinic β′ angle changes significantly because it is not fixed by symmetry. In contrast to these borates, SrB4O7 (3D) borate built up from tetrahedra only expands almost isotropically. Average value of volume expansion is 36 × 10?6 K?1 for studied Sr-borates. Tendency of slight decrease in the volume thermal expansion and sharp decrease in the melting points is observed with an increase in B2O3 content as a result of the degree of polymerization increase. As the B2O3 content grows in Sr-borates, the structural complexity increases in the SrO–B2O3 system due to more complex anionic structure. Inverse “melting temperature decrease—structural complexity increase” correlation is revealed. 相似文献
195.
Direct Identification of Protein–Protein Interactions by Single‐Molecule Force Spectroscopy
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Andrés M. Vera Dr. Mariano Carrión‐Vázquez 《Angewandte Chemie (International ed. in English)》2016,55(45):13970-13973
Single‐molecule force spectroscopy based on atomic force microscopy (AFM‐SMFS) has allowed the measurement of the intermolecular forces involved in protein‐protein interactions at the molecular level. While intramolecular interactions are routinely identified directly by the use of polyprotein fingerprinting, there is a lack of a general method to directly identify single‐molecule intermolecular unbinding events. Here, we have developed an internally controlled strategy to measure protein–protein interactions by AFM‐SMFS that allows the direct identification of dissociation force peaks while ensuring single‐molecule conditions. Single‐molecule identification is assured by polyprotein fingerprinting while the intermolecular interaction is reported by a characteristic increase in contour length released after bond rupture. The latter is due to the exposure to force of a third protein that covalently connects the interacting pair. We demonstrate this strategy with a cohesin–dockerin interaction. 相似文献
196.
A mild, photoactivated 1,3-dipolar cycloaddition procedure was successfully developed for the synthesis of polysubstituted pyrazolines. This procedure involved the in situ generation of the reactive nitrile imine dipoles using a hand-held UV lamp at 302 nm, followed by spontaneous cycloaddition with a broad range of 1,3-dipolarophiles with excellent solvent compatibility, functional group tolerance, regioselectivity, and yield. 相似文献
197.
198.
Khozikov V Kosobokova O Citver G Tyshko G Gavrilov DN Gudkov G Gorfinkel V 《Electrophoresis》2007,28(3):317-321
A novel, nondamaging method for experimental characterization of the formation and propagation of high-resistivity zones in CE, based on the measurement of time-dependent Joule heating on the outer capillary surface is proposed. The method detects propagation of resistive regions in capillaries in real time and allows the estimation of their velocity and resistance. The presented experimental data are in agreement with the results of the computer simulation as well as with previous data on the subject. The proposed method is useful for the development of new polymers as well as for the refinement and optimization of new CE protocols. 相似文献
199.
Silva R Boldt S Costa VM Carmo H Carvalho M Carvalho F Bastos Mde L Lemos-Amado F Remião F 《Biomedical chromatography : BMC》2007,21(7):670-679
The sustained high release of catecholamines to circulation is a deleterious condition that may induce toxicity, which seems to be partially related to the products formed by oxidation of catecholamines that can be further conjugated with glutathione (GSH). The aim of the present study was to develop a method for the determination of GSH adducts of adrenaline in biological samples. Two position isomers of the glutathion-S-yl-adrenaline were synthesized and characterized by HPLC using diode array, coulometric and mass detectors. A method for the extraction of these adducts from human plasma was also developed, based on adsorption to activated alumina, which showed adequate recoveries and proved to be crucial in removing interferences from plasma. The selectivity, precision and linearity of the method were all within the accepted values for these parameters. Furthermore, the sensitivity of this method allows the detection of adduct amounts that are within the range of the expected concentrations for these adducts under certain pathophysiological conditions and/or drug treatments. In conclusion, the development of this method allows the direct analysis of GSH adducts of adrenaline in human plasma, providing a valuable tool for the study of the catecholamine oxidation process and its related toxicity. 相似文献
200.
Characterization of the protein profile of the whey fraction from a milk sample taken from an individual donkey belonging to the 'Ragusana' species of the East of Sicily is reported. Direct RP-HPLC/electrospray ionization (ESI)-MS analysis of the whey fraction allowed the detection of some unknown components, together with the identification of already known whey proteins. Matrix-assisted laser desorption/ionization (MALDI)-TOF/MS and RP-HPLC/ESI-MS/MS analysis of the enzymatic digests of the unknown components resulted the identification and characterization of (1) two beta-casein fragments; (2) the sequence of donkey's serum albumin; and (3) the oxidized methionine forms of lysozyme B and alpha-lactoalbumin. One of the two beta-casein fragments corresponds to the sequence Val(176)-Arg(189) of the horse's beta-casein. The second one corresponds the C-terminal sequence Tyr(199)-Val(226) of the horse's beta-casein, with four amino acid substitutions (Q --> R(203), L/I --> P(206), F --> L(210) and P --> A(219)). Both fragments, reasonably arising by endogenous proteases cleavage of the donkey's beta-casein, could be potential biologically active peptides. Direct mass spectrometric sequence characterization of the detected donkey's serum albumin reveals the presence of the amino acid substitution Val --> Ile at position 497 with respect to the cDNA deduced sequence. The oxidized forms of lysozyme B and alpha-lactoalbumin are selectively oxidized at methionine 79 and methionine 90, respectively. 相似文献