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991.
An approach formulated in terms of conserved variables for the characterisation of propellant combustion in internal ballistics 下载免费PDF全文
R. A. Otón‐Martínez G. Monreal‐González J. R. García‐Cascales F. Vera‐García F. J. S. Velasco F. J. Ramírez‐Fernández 《国际流体数值方法杂志》2015,79(8):394-415
A model formulated in terms of conserved variables is proposed for its use in the study of internal ballistic problems of pyrotechnical mixtures and propellants. It is a transient two‐phase flow model adapted from the non‐conservative Gough model. This conversion is mathematically attractive because of the wide range of numerical methods for this kind of systems that may be applied. We propose the use of the AUSM+, AUSM + up and Rusanov schemes as an efficient alternative for this type of two‐phase problem. A splitting technique is applied, which solves the system of equations in several steps. A second‐order approach based on Monotonic Upstream‐Centred Scheme for Conservation Laws (MUSCL) is also used. Some tests are used to validate the code, namely a shock wave test, a contact discontinuity problem and an internal ballistics problem. In this last case, one‐dimensional numerical results are compared with experimental data of 155‐mm gunshots. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
992.
M. A. Chesta M. E. Ramia S. Jeandrevin C. A. Martín 《Applied Physics A: Materials Science & Processing》2009,97(2):301-307
The present work involves a comprehensive experimental determination of porosity and pore size distribution in rocks from
oil fields formations by deuterium (2H) Nuclear Magnetic Resonance (NMR) and Positronium Annihilation Lifetime Spectroscopy (PALS). Both techniques yield complementary
results; PALS measures the average pore size providing bulk information from which the most abundant pore size can be obtained,
and NMR allows for the determination of the relative pore size distribution accurately. Both techniques give complementary
information to obtain an absolute pore size distribution. 相似文献
993.
A.Martínez Torres 《中国物理C(英文版)》2009,33(12)
We have studied the ππN system and coupled channels by using of the Faddeev equations and two N~* and one △ states, all of them with J~P = 1/2~+, have been found in the formalism as dynamically generated states. In addition, signatures for a new N* resonance with J~P = 1/2~+ are found around an energy of 1920 MeV in the three-body center of mass system. 相似文献
994.
A.?Martínez Torres K.?P.?Khemchandani U.?-G.?Mei?ner E.?Oset 《The European Physical Journal A - Hadrons and Nuclei》2009,41(3):361-368
We provide a series of arguments which support the idea that the peak seen in the \( \gamma\) p \( \rightarrow\) K + \( \Lambda\) reaction around 1920MeV should correspond to the recently predicted state of J P = 1/2+ as a bound state of K \( \bar{{K}}\) N with a mixture of a 0(980)N and f 0(980)N components. At the same time we propose polarization experiments in that reaction as a further test of the prediction, as well as a study of the total cross-section for \( \gamma\) p \( \rightarrow\) K + K - p at energies close to threshold and of dσ/dM inv for invariant masses close to the two-kaon threshold. 相似文献
995.
996.
T. Pinheiro A. Barreiros L. C. Alves M. Neres R. Fleming J. N. Silva P. Filipe R. Silva 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(2):161-164
Skin as a manageable organ can provide direct or indirect information of tissue iron overload resulting from inherited disorders
as hemochromatosis. Patients with hemochromatosis were evaluated at three consecutive phases along the therapy programme.
Nuclear microprobe techniques were used to assess skin iron and Total Reflection X-ray Fluorescence to determine the plasma
iron concentrations. Results showed that iron pools were differently correlated at the three therapy phases. These variations
highlighted the value of skin iron content to assess organ iron deposition and therapy efficacy. Skin iron content can be
used for a better management of patients with iron overload pathologies. 相似文献
997.
Isabel Izquierdo-Barba Edesia Sousa Juan Carlos Doadrio Antonio Luis Doadrio Joaquín Pérez Pariente Africa Martínez Florence Babonneau María Vallet-Regí 《Journal of Sol-Gel Science and Technology》2009,50(3):421-429
Ordered mesoporous materials exhibit potential features to be used as controlled drug delivery systems, including their wide
range of chemical compositions and their outstanding textural and structural properties. Therefore, it is possible to control
the drug release kinetics by tailoring such parameters. In this paper, mesoporous materials such as MCM-48 and SBA-15, which
present different pore sizes (3.7 and 8.8 nm) and structural characteristics (3D-bicontinuous cubic and 2D-hexagonal, respectively)
have been synthesized to evaluate their application as drug delivery system and to determine their influence on release kinetic
of ibuprofen. Moreover, a chemical modification of the SBA-15 mesoporous material with octadecyltrimethoxysilane has also
been performed to study its influence on the release rate of ibuprofen. The structural characteristics (3D cubic and 2D hexagonal
pore system) do not affect the release kinetic profiles of ibuprofen. On the contrary, the pore size affects highly to the
release kinetic profiles from first-order kinetic to zero-order kinetic for MCM-48 and SBA-15, respectively. Moreover, the
importance of surface functionalization was demonstrate through the very fast delivery of ibuprofen from SBA-15 mesoporous
materials functionalized with octadecyl chains. 相似文献
998.
Benito Alcaide Prof. Dr. Pedro Almendros Dr. Teresa Martínez del Campo Elena Soriano Dr. José L. Marco‐Contelles Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(8):1909-1928
Calculating cyclization : Theoretical work directed towards the elucidation of the mechanisms of the gold‐, palladium‐, and lanthanum‐catalyzed oxycyclizations (5‐exo versus 6‐endo versus 7‐endo) of γ‐allenols has been pursued in close relationship with the experimental study (Part 1, accompanying paper) and has corroborated the bench results to provide a complete study of the reactivity of γ‐allenols under different metal‐catalyzed conditions.
999.
Michael F. Brown Karina Martínez‐Mayorga Koji Nakanishi Gilmar F. J. Salgado Andrey V. Struts 《Photochemistry and photobiology》2009,85(2):442-453
Solid‐state NMR spectroscopy gives a powerful avenue for investigating G protein‐coupled receptors and other integral membrane proteins in a native‐like environment. This article reviews the use of solid‐state 2H NMR to study the retinal cofactor of rhodopsin in the dark state as well as the meta I and meta II photointermediates. Site‐specific 2H NMR labels have been introduced into three regions (methyl groups) of retinal that are crucially important for the photochemical function of rhodopsin. Despite its phenomenal stability 2H NMR spectroscopy indicates retinal undergoes rapid fluctuations within the protein binding cavity. The spectral lineshapes reveal the methyl groups spin rapidly about their three‐fold (C3) axes with an order parameter for the off‐axial motion of For the dark state, the 2H NMR structure of 11‐cis‐retinal manifests torsional twisting of both the polyene chain and the β‐ionone ring due to steric interactions of the ligand and the protein. Retinal is accommodated within the rhodopsin binding pocket with a negative pretwist about the C11=C12 double bond. Conformational distortion explains its rapid photochemistry and reveals the trajectory of the 11‐cis to trans isomerization. In addition, 2H NMR has been applied to study the retinylidene dynamics in the dark and light‐activated states. Upon isomerization there are drastic changes in the mobility of all three methyl groups. The relaxation data support an activation mechanism whereby the β‐ionone ring of retinal stays in nearly the same environment, without a large displacement of the ligand. Interactions of the β‐ionone ring and the retinylidene Schiff base with the protein transmit the force of the retinal isomerization. Solid‐state 2H NMR thus provides information about the flow of energy that triggers changes in hydrogen‐bonding networks and helix movements in the activation mechanism of the photoreceptor. 相似文献
1000.