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51.
Dr. Yuriy Rebets Dr. Elke Brötz Niko Manderscheid Dr. Bogdan Tokovenko Dr. Maksym Myronovskyi Prof. Dr. Peter Metz Dr. Lutz Petzke Dr. Andriy Luzhetskyy 《Angewandte Chemie (International ed. in English)》2015,54(7):2280-2284
Pamamycins are macrodiolides of polyketide origin with antibacterial activities. Their biosynthesis has been proposed to utilize succinate as a building block. However, the mechanism of succinate incorporation into a polyketide was unclear. Here, we report identification of a pamamycin biosynthesis gene cluster by aligning genomes of two pamamycin‐producing strains. This unique cluster contains polyketide synthase (PKS) genes encoding seven discrete ketosynthase (KS) enzymes and one acyl‐carrier protein (ACP)‐encoding gene. A cosmid containing the entire set of genes required for pamamycin biosynthesis was successfully expressed in a heterologous host. Genetic and biochemical studies allowed complete delineation of pamamycin biosynthesis. The pathway proceeds through 3‐oxoadipyl‐CoA, a key intermediate in the primary metabolism of the degradation of aromatic compounds. 3‐Oxoadipyl‐CoA could be used as an extender unit in polyketide assembly to facilitate the incorporation of succinate. 相似文献
52.
Konstantinov D Isshiki H Monarkha Y Akimoto H Shirahama K Kono K 《Physical review letters》2007,98(23):235302
Measurements of the dc resistivity of surface-state electrons on liquid helium exposed to microwave radiation are reported. It is shown that the resonant microwave excitation of surface-state electrons is accompanied by a strong increase in their resistivity, which is opposite to the result expected from the previously used two-level model. We show that even a very small fraction of electrons excited to the first excited state and decaying back due to vapor-atom scattering strongly heat the electron system, causing a population of higher subbands. The calculated resistivity change is in good agreement with the observed data. 相似文献
53.
54.
Ksenia V. Ksenofontova Anastasia A. Kerner Alexander A. Ksenofontov Artyom Yu. Shagurin Pavel S. Bocharov Michael M. Lukanov Airat R. Kayumov Darya E. Zhuravleva Zalina I. Iskhakova Evgeniy E. Molchanov Dmitriy A. Merkushev Ilya A. Khodov Yuriy S. Marfin 《Molecules (Basel, Switzerland)》2022,27(22)
A boron-dipyrromethene (BODIPY) derivative reactive towards amino groups of proteins (NHS-Ph-BODIPY) was synthesized. Spectroscopic and photophysical properties of amine-reactive NHS-Ph-BODIPY and its non-reactive precursor (COOH-Ph-BODIPY) in a number of organic solvents were investigated. Both fluorescent dyes were characterized by green absorption (521–532 nm) and fluorescence (538–552 nm) and medium molar absorption coefficients (46,500–118,500 M−1·cm−1) and fluorescence quantum yields (0.32 – 0.73). Solvent polarizability and dipolarity were found to play a crucial role in solvent effects on COOH-Ph-BODIPY and NHS-Ph-BODIPY absorption and emission bands maxima. Quantum-chemical calculations were used to show why solvent polarizability and dipolarity are important as well as to understand how the nature of the substituent affects spectroscopic properties of the fluorescent dyes. NHS-Ph-BODIPY was used for fluorescent labeling of a number of proteins. Conjugation of NHS-Ph-BODIPY with bovine serum albumin (BSA) resulted in bathochromic shifts of absorption and emission bands and noticeable fluorescence quenching (about 1.5 times). It was demonstrated that the sensitivity of BSA detection with NHS-Ph-BODIPY was up to eight times higher than with Coomassie brilliant blue while the sensitivity of PII-like protein PotN (PotN) detection with NHS-Ph-BODIPY and Coomassie brilliant blue was almost the same. On the basis of the molecular docking results, the most probable binding sites of NHS-Ph-BODIPY in BSA and PotN and the corresponding binding free energies were estimated. 相似文献
55.
Yuriy K. Tovbin 《Adsorption》2005,11(3-4):245-257
The equilibrium distribution and the concentration dependence of the local and average self-diffusion coefficients for pure
fluid and binary mixture components in narrow slitlike pores were analyzed. The coefficients were calculated using the lattice
gas model in the quasi-chemical approximation on the assumption of a spherical shape and approximately equal sizes of the
components. For the pure adsorbate, these calculations were compared with molecular dynamics simulations. Both methods gave
similar concentration profile changes and dynamic characteristics of interlayer particle redistributions in strong nonuniform
adsorption fields for dense fluids. A satisfactory agreement was obtained for the temperature dependences of the self-diffusion
coefficients along the pore axis. The influence of the molecule–wall potential and of intermolecular interaction were considered.
The self-diffusion coefficients of the adsorbate were shown to strongly depend on the density of the mixture and the distance
from pore walls. 相似文献
56.
Yuriy Povstenko 《Meccanica》2012,47(1):23-29
The theory of thermoelasticity based on the heat conduction equation with the Caputo time-fractional derivative of order α is used to study thermal stress in an infinite medium with a cylindrical hole. Two types of Neumann boundary conditions are
considered: the constant value of the normal derivative of the temperature and constant heat flux at the surface of a cavity.
The solution is obtained applying Laplace and Weber integral transforms. Numerical results are illustrated graphically. 相似文献
57.
It has been shown that, apart from classical vacancies formed as a result of the thermal fluctuations, a crystal can contain
so-called nonclassical vacancies of nonfluctuation nature. The latter vacancies appear when the temperature exceeds a critical
value T
C
. The factor responsible for their formation is a mechanical instability of an ideal crystal. The temperature T
C
is a second-order phase transition point. The vacancies formed as a result of this phase transition are joined together into
small clusters with sizes of the order of several atoms. The above transition makes a substantial contribution to the premelting
process observed experimentally. 相似文献
58.
59.
60.
Alexander B. Rozhenko Sergiy S. Mykhaylychenko Nadiya V. Pikun Yuriy G. Shermolovich Jerzy Leszczynski 《International journal of quantum chemistry》2014,114(4):241-248
The reactions of perfluoroalkyl thioamides with trimethyl phosphine, trimethyl phosphite, and tris(dimethylamino)phosphine have been analyzed by means of quantum chemical (DFT and MP2) calculations. The reaction seems to proceed via the nucleophilic attack of the electrophilic carbon atom by the phosphorus lone pair with the formation of cyclic or acyclic adducts. The latter releases the thiophosphate molecule forming perfluoroalkylaminocarbene as the short‐lived intermediate. The reaction of the carbene with the second molecule of trialkyl phosphite yields phosphorus ylide. The ylide undergoes a migration of fluorine from carbon to phosphorus. The reactions of perfluoroalkyl thioamides with phosphines and tris(dimethylamino)phosphine probably proceeds differently. Using alkyl thioamides or amides instead of perfluoroalkyl thioamides also makes the reaction less favorable. The only combination of perfluoroalkyl thioamides with trialkyl phosphite fulfills both the kinetic requirements (moderate activation energies and relative energies for intermediates) and the thermodynamic aspects (higher stabilities of the reaction products compared with the starting materials). © 2013 Wiley Periodicals, Inc. 相似文献