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61.
S. Ciorba F. Fontana G. Ciancaleoni T. Caronna U. Mazzucato A. Spalletti 《Journal of fluorescence》2009,19(5):759-768
The effect of the presence and position of the nitrogen heteroatom on the photobehaviour of a series of symmetric and asymmetric
1,2-diarylethenes, where one or both the one-, two- or three-membered aryl groups, linked to the ethene bridge, contain(s)
nitrogen heteroatoms, has been investigated by fluorimetric and photochemical techniques. The yield of the radiative pathway
is generally reduced with respect to the corresponding hydrocarbons, due to a smaller energy barrier for trans→cis (E→Z) photoisomerization
in the singlet state, which often can be slightly favoured in the aza-compounds. All compounds investigated exist in solution
as mixtures of two or more conformers, which can have different spectral and kinetic properties. Attempts to separate the
intrinsic properties by selective photoexcitation, at a wavelength where the light is mainly absorbed by one conformer, allowed
in some favourable cases the spectra and decay times of the largely prevalent (quasi-pure) conformer to be obtained. In two
cases, the formation of intramolecular (hydrogen-bond-type) interactions between the nitrogen atom and the nearest hydrogen
atom of the ethene bridge (proved by NMR measurements and confirmed by theoretical calculations) were found to stabilize a
specific conformer thus affecting a selective relaxation of the excited molecule. 相似文献
62.
Giovanni Dinelli Antonio Segura Carretero Raffaella Di Silvestro Ilaria Marotti Shaoping Fu Stefano Benedettelli Lisetta Ghiselli Alberto Fernández Gutiérrez 《Journal of chromatography. A》2009,1216(43):7229-7240
An evaluation of the grain functional components of Italian durum wheat cultivars was conducted. The raw material was obtained from the field trial performed in 2006–2007 at the Experimental Farm of the University of Bologna, (Bologna, Italy). The aim of this study was to define the phytochemical profile of ten varieties, comprised of old and modern durum wheat genotypes, including quantitative and qualitative phenolic and flavonoid content (free and bound forms). The results showed that mean values of total phenolic compound and total flavonoid content in old wheat varieties (878.2 ± 19.0 μmol gallic acid equivalent/100 g of grain and 122.6 ± 25.4 μmol catechin equivalent/100 g of grain, respectively) did not differ significantly from those detected in modern genotypes (865.9 ± 128.9 μmol gallic acid equivalent/100 g and 123.5 ± 20.6 μmol catechin equivalent/100 g, respectively). However, the HPLC–ESI-TOF-MS analysis highlighted remarkable differences between modern and old cultivars. The interpretation of the mass spectra allowed the identification of 70 phenolic compounds, including coumarins, phenolic acids, anthocyanins, flavones, isoflavones, proanthocyanidins, stilbenes and lignans. The free extracts of ancient wheat varieties showed the presence of a mean number of phenolic compounds and isomer forms (8.7 ± 2.5 and 7.7 ± 4.7 respectively) significantly higher than in modern genotypes (4.4 ± 2.9 and 2.0 ± 2.4, respectively). A similar trend was observed also for the bound phenolic fraction. Moreover, the phytochemical profiles showed the presence of unique phenolic compounds in both free and bound fractions of some of the investigated wheat genotypes. Results highlighted that investigated old wheat cultivars may offer unique nutraceutical values for their peculiar contents in bioactive phytochemicals, suggesting their uses into a wide range of regular and specialty products naturally enriched with health-promoting compounds. 相似文献
63.
Bartolo Gabriele Raffaella Mancuso Giuseppe Ruffolo Angela Dibenedetto 《Tetrahedron letters》2009,50(52):7330-1772
In the presence of a PdI2-based catalytic system, 1,2-diols undergo an oxidative carbonylation process to afford 5-membered cyclic carbonates in good to excellent yields (84-94%) and with unprecedented catalytic efficiencies for this kind of reaction (up to ca. 190 mol of product per mol of PdI2). Under similar conditions, 6-membered cyclic carbonates are obtained for the first time through a direct catalytic oxidative carbonylation of 1,3-diols (66-74% yields). 相似文献
64.
A. Andreone A. Di Chiara G. Peluso U. Scotti di Uccio F. Tafuri A. Barone G. Pepe F. Fontana 《Il Nuovo Cimento D》1990,12(6):863-868
Summary Some of the main anomalies in conductance characteristics of high-T
C tunnel junctions are considered. Mainly, the extreme, depression of gap structures, the presence of conductance peaks in
corrispondence to the counterelectrode gap, and ?zero-bias anomalies? will be examined. The possibility of application of
the proximity McMillan model to describe the behaviour in conductance of high-T
C junctions is considered. Discussion and preliminary comparison with experimental data on YBCO junctions are also reported. 相似文献
65.
The pressure evolution of the vibrational spectrum of polyethylene was investigated up to 50 GPa along different isotherms by Fourier-transform infrared and Raman spectroscopy and at 0 K by density-functional theory calculations. The infrared data allow for the detection of the orthorhombic Pnam to monoclinic P2(1)∕m phase transition which is characterized by a strong hysteresis both on compression and decompression experiments. However, an upper and lower boundary for the transition pressure are identified. An even more pronounced hysteresis is observed for the higher-pressure transition to the monoclinic A2/m phase. The hysteresis does not allow in this case the determination of a well defined P-T transition line. The ambient structural properties of polyethylene are fully recovered after compression/decompression cycles indicating that the polymer is structurally and chemically stable up to 50 GPa. A phase diagram of polyethylene up to 50 GPa and 650 K is proposed. Analysis of the pressure evolution of the Davydov splittings and of the anomalous intensification with pressure of the IR active wagging mode provides insight about the nature of the intermolecular interactions in crystalline polyethylene. 相似文献
66.
Vincenzo Benessere Raffaella Del Litto Antonella De Roma Francesco Ruffo 《Coordination chemistry reviews》2010,254(5-6):390-401
“Privileged ligands” are chiral auxiliaries of wide applicability in asymmetric catalysis. In the previous decades, their effective three-dimensional structures have often been reproduced by using building blocks from a “chiral pool”, such as the carbohydrates. This strategy has provided unique ligand moieties which combine the performance of “privileged ligands” with increased flexibility and accessibility. This review gives an overview of the research within this field, giving emphasis to the best results obtained with each ligand type. 相似文献
67.
Yves Noel Philippe D'arco Raffaella Demichelis Claudio M. Zicovich‐Wilson Roberto Dovesi 《Journal of computational chemistry》2010,31(4):855-862
Nanotubes can be characterized by a very high point symmetry, comparable or even larger than the one of the most symmetric crystalline systems (cubic, 48 point symmetry operators). For example, N = 2n rototranslation symmetry operators connect the atoms of the (n,0) nanotubes. This symmetry is fully exploited in the CRYSTAL code. As a result, ab initio quantum mechanical large basis set calculations of carbon nanotubes containing more than 150 atoms in the unit cell become very cheap, because the irreducible part of the unit cell reduces to two atoms only. The nanotube symmetry is exploited at three levels in the present implementation. First, for the automatic generation of the nanotube structure (and then of the input file for the SCF calculation) starting from a two‐dimensional structure (in the specific case, graphene). Second, the nanotube symmetry is used for the calculation of the mono‐ and bi‐electronic integrals that enter into the Fock (Kohn‐Sham) matrix definition. Only the irreducible wedge of the Fock matrix is computed, with a saving factor close to N. Finally, the symmetry is exploited for the diagonalization, where each irreducible representation is separately treated. When M atomic orbitals per carbon atom are used, the diagonalization computing time is close to Nt, where t is the time required for the diagonalization of each 2M × 2M matrix. The efficiency and accuracy of the computational scheme is documented. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
68.
Laura Zanetti-Polzi Paolo Marracino Massimiliano Aschi Isabella Daidone Antonella Fontana Francesca Apollonio Micaela Liberti Guglielmo D’Inzeo Andrea Amadei 《Theoretical chemistry accounts》2013,132(11):1-10
A benchmark biochemical reaction is here theoretically investigated by means of a perturbative approach in order to model each reaction step. The reaction is the flavin-indole electron transfer, involving also a spin-state relaxation of the ionic complex. The whole reaction path is modeled and the kinetics of the process is studied. The dipolar interaction between the two radicals is explicitly considered during the dynamic evolution of the system in order to investigate the proper conditions for the triplet-to-singlet transition to occur. 相似文献
69.
Recent developments in microbial inulinases 总被引:15,自引:0,他引:15
Ashok Pandey Carlos R. Soccol Ponniah Selvakumar Vanete T. Soccol Nadia Krieger Jose D. Fontana 《Applied biochemistry and biotechnology》1999,81(1):35-52
Microbial inulinases are an important class of industrial enzymes that have gained much attention recently. Inulinases can
be produced by a host of microorganisms, including fungi, yeast, and bacteria. Among them, however, Aspergillus sp. (filamentous fungus) and Kluyveromyces sp. (diploid yeast) are apparently the preferred choices for commercial applications. Among various substrates (carbon source)
employed for their production, inulin-containing plant materials offer advantages in comparison to pure substrates. Although
submerged fermentation has been universally used as the technique of fermentation, attempts are being made to develop solidstate
fermentation technology also. Inulinases catalyze the hydrolysis of inulin to d-fructose (fructose syrup), which has gained an important place in human diets today. In addition, inulinases are finding
other newer applications. This article reviews more recent developments, especially those made in the past decade, on microbial
inulinases—its production using various microorganisms and substrates. It also describes the characteristics of various forms
of inulinases produced as well as their applications. 相似文献