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951.
A series of first principles calculations have been carried out to study structural, electronic properties of BaSxSe1−x alloys. We have used the local density as well as the generalized gradient approximations for the exchange-correlation potential. The structural properties of these materials, in particular the composition dependence to the lattice constant and bulk modulus, are found to be linear. It is also found linear relationship between theoretical band gaps and 1/a2 (where a is lattice constant). 相似文献
952.
We report microstructure evolution in as-spun Fe78Si9B13 ribbons under various wheel speeds (s), which was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). With decreasing s, the volume fraction of the residual amorphous phase (Va) in the as-spun ribbons decreases gradually, and the total exothermic heat of the crystallization in the DSC curves also decreases, but the ratio of the exothermic heat of the second crystallization to the first one is on the contrary. α-Fe is found in the ribbon with s of 32.9 m/s, while α-Fe, eutectic α-Fe+Fe2B, and Fe3Si phases are found in ribbons with s of 25.6 and 18.3 m/s. The phase precipitating behavior in cooling processes is well consistent with the annealing process in the literatures. 相似文献
953.
F. Yang Z. Wang Y. Zhou F. Li J. Xu Y. Xu X. Cheng Y. Lu Y. Bo Q. Peng D. Cui X. Zhang X. Wang Y. Zhu Z. Xu 《Applied physics. B, Lasers and optics》2009,96(2-3):415-422
We have presented theoretical and experimental investigations of nanosecond (ns) deep-ultraviolet (DUV) 177.3 nm radiation by means of second harmonic generation (SHG) from a frequency-tripled Nd:YAG laser (355 nm, 49 ns and 10 kHz) in KBe2BO3F2 (KBBF) nonlinear crystal for the first time. A DUV KBBF-SHG numerical model, accounting for linear absorption, pump depletion, beam spatial birefringent walk-off and diffraction, is performed in the Gaussian approximation of spatial and temporal profiles. In the experiment, a maximum average output power of 14.1 mW at 177.3 nm was obtained. The dependence of 177.3 nm output power on the 355 nm pump power was simulated. The calculated results are in good agreement with the measured data. We used the model further to investigate the optical conversion efficiency, pulse width, beam spatial intensity profile and beam quality factor of the generated 177.3 nm light, in particular the effect of beam birefringent walk-off. 相似文献
954.
H. Wang S.R. Foltyn L. Civale B. Maiorov Q.X. Jia 《Physica C: Superconductivity and its Applications》2009,469(23-24):2033-2036
Numerous experimental results have suggested that the Jc of YBa2Cu3O7 (YBCO) films is significantly higher near the film–substrate interface than in the remainder of the film. We previously proposed that this effect is due to interfacial pinning enhancement caused by stress and the resulting misfit dislocations at the heteroepitaxial interface. To test this hypothesis we have used a non-superconducting PrBa2Cu3O7?δ (PrBCO) buffer layer to minimize the lattice mismatch with YBCO. We find that the PrBCO layers lower Jc of the 0.4 μm YBCO films in a predictable way, and that, if sufficiently thick (~0.5 μm), they eliminate interfacial enhancement altogether. Our interpretation of this result is that the defects responsible for interfacial enhancement of flux pinning originate at the bottom of the non-superconducting PrBCO layer, which screens the pinning centers from vortices in YBCO. This result demonstrates that the pinning enhancement arises from stress at the film–substrate interface. 相似文献
955.
The definition of quasi-local mass for a bounded space-like region Ω in space-time is essential in several major unsettled problems in general relativity. The quasi-local mass is expected to be a type of flux integral on the boundary two-surface \({\Sigma=\partial \Omega}\) and should be independent of whichever space-like region \({\Sigma}\) bounds. An important idea which is related to the Hamiltonian formulation of general relativity is to consider a reference surface in a flat ambient space with the same first fundamental form and derive the quasi-local mass from the difference of the extrinsic geometries. This approach has been taken by Brown-York [4,5] and Liu-Yau [16,17] (see also related works [3,6,9,12,14,15,28,32]) to define such notions using the isometric embedding theorem into the Euclidean three space. However, there exist surfaces in the Minkowski space whose quasilocal mass is strictly positive [19]. It appears that the momentum information needs to be accounted for to reconcile the difference. In order to fully capture this information, we use isometric embeddings into the Minkowski space as references. In this article, we first prove an existence and uniqueness theorem for such isometric embeddings. We then solve the boundary value problem for Jang’s [13] equation as a procedure to recognize such a surface in the Minkowski space. In doing so, we discover a new expression of quasi-local mass for a large class of “admissible” surfaces (see Theorem A and Remark 1.1). The new mass is positive when the ambient space-time satisfies the dominant energy condition and vanishes on surfaces in the Minkowski space. It also has the nice asymptotic behavior at spatial infinity and null infinity. Some of these results were announced in [29]. 相似文献
956.
This review deals with the high-throughput field in surface catalysis and adsorption. Special focus is placed on advanced
methods for knowledge discovery such as density functional theory (DFT) simulations. An inventory of successful cases on several
elements in Group I-B and VIII is reported, including the relevant data and knowledge management, which are very important
in chemical industry, fuel cell, and environment protection, for both scientific and economical reasons.
相似文献
957.
Di-You Jiang R. S. Wu S. S. Li Z. S. Wang 《International Journal of Theoretical Physics》2009,48(8):2297-2304
Two schemes, introducing the projective operator and the auxiliary qubit respectively, for controlled dense coding are investigated
by using a three-qubit symmetric state with entanglement, where the supervisor (Cliff) can control an average amount of information
transmitted from the sender (Alice) to the receiver (Bob) by adjusting the measurement angle θ. We show that the results for the average amounts of information are unique from the different two schemes. The schemes may
be extended to many-qubit systems. 相似文献
958.
Dehua Wang Kaiyun Huang Shenglu Lin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):699-706
The ionization of Rydberg hydrogen atoms near a metal surface at different scaled energies above the classical saddle point
energy has been discussed by using the semiclassical method. The results show that the atoms ionize by emitting a train of
electron pulses. In order to reveal the chaotic and escape dynamical properties of this system in detail, the sensitive dependence
of the ionization rate upon the scaled energy is discussed. As the scaled energy is close to the saddle point energy, the
ionization process of the hydrogen atom is nearly the same as the case of hydrogen atom in an electric field. There is only
a single pulse of electrons, with an exponentially decaying tail. With the increase of the scaled energy, the ionization rates
are similar to the case of the hydrogen atom in parallel electric and magnetic field, a series of electron pulses appear in
the ionization process. This is caused by classical chaos, which occurs for the metal surface. Our studies also suggest that
the metal surface can play the role of both the electric and the magnetic fields. Our theoretical analysis will be useful
for guiding experimental studies of the ionization of atoms near the metal surface. 相似文献
959.
Bin Dong BaoSheng Cao ZhiQing Feng XingJun Wang ChengRen Li RuiNian Hua 《中国科学G辑(英文版)》2009,52(7):1043-1046
The Er3+-Yb3+ codoped Al2O3 nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The
green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions
of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes
predominant after annealing. The mixture of (Er,Yb)3Al5O12 and α-(Al,Er,Yb)2O3 phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of 4I11/2+a photon→4F7/2 and ET (III) of 2F5/2(Yb3+)+4I11/2(Er3+)→2F7/2(Yb3+)+4F7/2(Er3+) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The
results have proved that arc discharge synthesis is a new promising preparation technology for optical materials.
Supported by National Natural Science Foundation of China (Grant No. 10804015), the Scientific Research Foundation for Doctor
of Liaoning Province (Grant No. 20071095), and the Educational Committee Foundation of Liaoning Province (Grant No. 2008123) 相似文献
960.
Han Wang Christoph Junghans Kurt Kremer 《The European physical journal. E, Soft matter》2009,28(2):221-229
We employ the inverse Boltzmann method to coarse-grain three commonly used three-site water models (TIP3P, SPC and SPC/E)
where one molecule is replaced with one coarse-grained particle with isotropic two-body interactions only. The shape of the
coarse-grained potentials is dominated by the ratio of two lengths, which can be rationalized by the geometric constraints
of the water clusters. It is shown that for simple two-body potentials either the radial distribution function or the geometrical
packing can be optimized. In a similar way, as needed for multiscale methods, either the pressure or the compressibility can
be fitted to the all atom liquid. In total, a speed-up by a factor of about 50 in computational time can be reached by this
coarse-graining procedure. 相似文献