全文获取类型
收费全文 | 143篇 |
免费 | 17篇 |
专业分类
化学 | 140篇 |
力学 | 1篇 |
数学 | 9篇 |
物理学 | 10篇 |
出版年
2023年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 27篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有160条查询结果,搜索用时 109 毫秒
101.
102.
Montoya-Mayor R Fernández-Espinosa AJ Ternero-Rodríguez M 《Analytical and bioanalytical chemistry》2011,399(6):2031-2041
In this study a new method of principal component (PC) analysis, sequential PC analysis (SPCA), is proposed and assessed on
real samples. The aim was to identify the atmospheric emission sources of soluble compounds in rainwater samples, and the
sample collection was performed with an automatic sampler. Anions and cations were separated and quantified by ion chromatography,
whereas trace metals and metalloids were determined by inductively coupled plasma mass spectrometry. SPCA results showed eight
interfering PCs and ten significant PCs. The interfering cases originated from different atmospheric sources, such as resuspended
crustal particles, marine aerosols, urban traffic and a fertilizer factory. The significant PCs explained 84.6% of the total
variance; 28.1% accounted for the main contribution, which was resuspended industrial soil from a fertilizer factory containing
NO2-, NH4+, NO3-, SO42-, F-, Al, K+, Mn, Sb and Ca2+ as indicators of the fertilizer factory. Another important source (15.0%) was found for Na+, Mg2+, K+, Cl- and SO42-, which represents the marine influence from south and southwest directions. Emissions of Ba2+, Pb, Sr2+, Sb and Mo, which represent a traffic source deposited in soils, were identified as another abundant contribution (12.1%)
to the rainwater composition. Other important contributions to the rainwater samples that were identified through SPCA included
the following: different urban emissions (Cu, As, Cd, Zn, Mo and Co, 18.1%), emissions from vegetation (HCOO-, 7.7%) and emissions from industrial combustion processes (Ni, V 15.6%). The application of SPCA proved to be a useful tool
to identify the complete information on rainwater samples as indicators of urban air pollution in a city influenced mainly
by vehicle traffic emissions and resuspended polluted soils. 相似文献
103.
Ortiz RP Osuna RM Hernandez V Navarrete JT Vercelli B Zotti G Sumerin VV Balenkova ES Nenajdenko VG 《The journal of physical chemistry. A》2007,111(5):841-851
The synthesis, structure, and electronic properties of a novel cross-conjugated 10H-bisthienodithiocin-10-dicyanoethylene are reported. The X-ray single-crystal structure of the compound reveals a nonplanar conformation. The FT-IR and FT-Raman spectra of the compound show a great resemblance, which is a spectroscopic observation common to many push-pull systems. The UV-vis spectrum in CHCl3 displays a strong absorption at 370 nm accompanied by a shoulder at 430 nm so that the optical gap is 2.88 eV. On the other hand, the electrochemical gap amounts to 2.38 V. DFT and TDDFT quantum chemical calculations, at the B3LYP/6-31G** level, have been also performed to (i) determine the minimum-energy molecular structure, (ii) gain knowledge about the equilibrium atomic charges distribution, the topologies, and absolute energies of the frontier molecular orbitals around the gap and about the molecular vibrations which give rise to the most outstanding Raman bands experimentally evidenced, and (iii) to analyze the nature of the vertical one-electron excitations associated to the strongest UV-vis absorptions. 相似文献
104.
In this study, the reaction mechanism of toluene 1,2-epoxide/2-methyloxepin with OH radical was studied by means of quantum chemical computations performed using B3LYP/6-31G(d,p), B3LYP/6-311G(2df,2p), and BHandHLYP/6-31G(d,p) methods. Ground state, intermediate, and transition states were determined. The results indicated that the 2-methyloxepin, A, isomer is more stable, by 2.4 kcal/mol, than toluene 1,2-epoxide, B. Two reaction pathways were studied, RP-A and RP-B, corresponding to the reaction of OH with toluene 1,2-epoxide and 2-methyloxepin, respectively. The localization of a pre-reactive complex for RP-A is crucial for the accurate estimation of the rate constant, k=1.0x10(-10) cm3 molecule(-1) s(-1), which is in good agreement with that determined experimentally, whereas for RP-B the rate constant is 1.3x10(-14) cm3 molecule(-1) s(-1). Under atmospheric conditions, both pathways yield 6-oxohepta-2,4-dienal as a main product, and from the energetic and kinetic results it was found that RP-A is the preferred pathway. The study of the oxide/oxepin mechanism is relevant because, aside from its relatively high concentration in the troposphere, this compound has carcinogenic and mutagenic properties. 相似文献
105.
Mechanostability of the Single‐Electron‐Transfer Complexes of Anabaena Ferredoxin–NADP+ Reductase
下载免费PDF全文
Dr. Carlos Marcuello Dr. Rocío de Miguel Dr. Marta Martínez‐Júlvez Prof. Dr. Carlos Gómez‐Moreno Dr. Anabel Lostao 《Chemphyschem》2015,16(15):3161-3169
The complexes formed between the flavoenzyme ferredoxin–NADP+ reductase (FNR; NADP+=nicotinamide adenine dinucleotide phosphate) and its redox protein partners, ferredoxin (Fd) and flavodoxin (Fld), have been analysed by using dynamic force spectroscopy through AFM. A strategy is developed to immobilise proteins on a substrate and AFM tip to optimise the recognition ability. The differences in the recognition efficiency regarding a random attachment procedure, together with nanomechanical results, show two binding models for these systems. The interaction of the reductase with the natural electron donor, Fd, is threefold stronger and its lifetime is longer and more specific than that with the substitute under iron‐deficient conditions, Fld. The higher bond probability and two possible dissociation pathways in Fld binding to FNR are probably due to the nature of this complex, which is closer to a dynamic ensemble model. This is in contrast with the one‐step dissociation kinetics that has been observed and a specific interaction described for the FNR:Fd complex. 相似文献
106.
Rocío Aguilar-Martínez M. Milagros Gómez-Gómez 《International journal of environmental analytical chemistry》2013,93(11):1100-1116
Several field trials have been carried out to assess the performance of the passive sampler Chemcatcher as aquatic monitoring technology for inorganic mercury and the organotin pollutants monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in different types of waters across ten locations in Europe. Two version of the sampler were used. One for mercury that consists on 47?mm Empore? disks of iminodiacetic chelating groups as the receiving phase overlaid by a diffusion membrane of polyethersulphone; and other for organotin compounds comprising a C18 disk and a cellulose acetate membrane. Both membranes were held in a disposable polycarbonate body. The two samplers were calibrated in the laboratory in a previous work to estimate the pollutant concentration. For field sampling, the samplers were deployed for 14 days. In parallel spot samples were periodically collected during the deployment period for comparison purposes. No significant biofouling on the samplers was observed for the locations monitored. In general, water concentrations estimated by Chemcatcher were lower than those found in spot water samples due to the device only collected the soluble bioavailable fraction of target pollutants. However, the pre-concentration capability of Chemcatcher allowed the determination of the tested pollutants at levels where spot sampling fails, even in difficult water bodies such as sewage treatment plants. These advantages lead to consider this emerging methodology as a complementary tool to traditional spot sampling. 相似文献
107.
de Carvalho Braga Denis Fernando Mello Luis Rocşoreanu Carmen Sterpu Mihaela 《Nonlinear dynamics》2010,62(4):989-1000
Nonlinear Dynamics - On a versal deformation of the Bautin bifurcation it is possible to find dynamical systems that undergo Hopf or non-hyperbolic limit cycle bifurcations. Our paper concerns a... 相似文献
108.
Alonso B Borrego-Varillas R Sola ÍJ Varela Ó Villamarín A Collados MV Román JS Bueno JM Roso L 《Optics letters》2011,36(19):3867-3869
The energy scaling up of pulse postcompression is still an open issue. In this work we analyze the use of astigmatic focusing to improve the output pulses in a filamentation based postcompression setup. Unlike spherical conditions, astigmatic focusing enhances the output energy and the spectral broadening of the filament. This is due to the increase of critical power, allowing a considerable improvement of the postcompression energy and stability in a simple way. We demonstrated compression from FWHM 100 fs, 10 nm, 3 mJ input pulses to 13 fs, 142 nm, near 1 mJ pulses. 相似文献
109.
García-Villalba R Pacchiarotta T Carrasco-Pancorbo A Segura-Carretero A Fernández-Gutiérrez A Deelder AM Mayboroda OA 《Journal of chromatography. A》2011,1218(7):959-971
A new analytical approach based on gas chromatography coupled to atmospheric pressure chemical ionization-time of flight mass spectrometry was evaluated for its applicability for the analysis of phenolic compounds from extra-virgin olive oil. Both chromatographic and MS parameters were optimized in order to improve the sensitivity and to maximize the number of phenolic compounds detected. We performed a complete analytical validation of the method with respect to its linearity, sensitivity, precision, accuracy and possible matrix effects. The LODs ranged from 0.13 to 1.05ppm for the different tested compounds depending on their properties. The RSDs for repeatability test did not exceed 6.07% and the accuracy ranged from 95.4% to 101.5%. To demonstrate the feasibility of our method for analysis of real samples, we analyzed the extracts of three different commercial extra-virgin olive oils. We have identified unequivocally a number of phenolic compounds and obtained quantitative information for 21 of them. In general, our results show that GC-APCI-TOF MS is a flexible platform which can be considered as an interesting tool for screening, structural assignment and quantitative determination of phenolic compounds from virgin olive oil. 相似文献
110.
Using molecular dynamics experiments, we analyze equilibrium and dynamical characteristics related to the solvation of excess protons in water-acetone mixtures. Our approach is based on the implementation of an extended valence-bond Hamiltonian, which incorporates translocation of the excess charge between neighboring water molecules. Different mixtures have been analyzed, starting from the pure water case down to solutions with a water molar fraction x(w) = 0.25. In all cases, we have verified that the structure of the first solvation shell of the H(3)O(+) moiety remains practically unchanged, compared to the one observed in pure water. This shell is composed by three water molecules acting as hydrogen bond acceptors, with no evidence of hydrogen bond donor-like connectivity. Moreover, the increment in the acetone concentration leads to a gradual stabilization of Eigen-like [H(3)O[middle dot](H(2)O)(3)](+) configurations, in detriment of Zundel-like [H[middle dot](H(2)O)(2)](+) ones. Rates of proton transfer and proton diffusion coefficients have been recorded at various water-acetone relative concentrations. In both cases, we have found a transition region, in the vicinity of x(w) ~ 0.8, where the concentration dependences of the two magnitudes change at a quantitative level. A crude estimate shows that, at this tagged concentration, the volumes "occupied" by the two solvents become comparable. The origins of this transition separating water-rich from acetone-rich realms is rationalized in terms of modifications operated in the nearby, second solvation shell, which in the latter solutions, normally includes at least, one acetone molecule. Our results would suggest that one possible mechanism controlling the proton transfer in acetone-rich solutions is the exchange of one of these tagged acetone molecules, by nearby water ones. This exchange would give rise to Zundel-like structures, exhibiting a symmetric, first solvation shell composed exclusively by water molecules, and would facilitate the transfer between neighboring water molecules along the resonant complex. 相似文献