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61.
Xiao-Xiong Gan Dariusz Bugajewski 《Bulletin of the Brazilian Mathematical Society》2011,42(3):415-437
Several kinds of formal Laurent series have been introduced with some restrictions so far. This paper systematically sets
up a natural definition and structure of formal Laurent series without those restrictions, including introducing a multiplication
between formal Laurent series. This paper also provides some results on the algebraic structure of the space of formal Laurent
series, denoted by
\mathbbL\mathbb{L}. By means of the results of the generalized composition of formal power series, we define a composition of a Laurent series
with a formal power series and provide a necessary and sufficient condition for the existence of such compositions. The calculus
about formal Laurent series is also introduced. 相似文献
62.
By swapping entanglements of 3×3-dimensional Bell states, we propose a quantum secure direct communication scheme, whose advantage
is to own the high source capacity. In addition, another light point is that only one set of measuring basis is needed in
this scheme. 相似文献
63.
This paper presents a reconstruction of the three-dimensional velocity field of a turbulent vortex ring by means of Taylor’s
hypothesis. Stereoscopic PIV is used to acquire three velocity component information on a plane. The accuracy of the Taylor’s
hypothesis for this particular flow pattern is first discussed, and the three-dimensional velocity and vorticity information
are then presented. This study also introduces an azimuthally averaging method in order to give a mean structure in cylindrical
coordinates from a single realization and from which turbulent stresses and production can be estimated. The azimuthally averaged
quantities are then compared with the ensemble-averaged results from the previous planar (two-dimensional and stereoscopic)
PIV experiments. 相似文献
64.
David M. Koshy Shucheng Chen Dong Un Lee Michaela Burke Stevens Ahmed M. Abdellah Samuel M. Dull Gan Chen Dennis Nordlund Alessandro Gallo Christopher Hahn Drew C. Higgins Zhenan Bao Thomas F. Jaramillo 《Angewandte Chemie (International ed. in English)》2020,59(10):4043-4050
Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO2 electroreduction (CO2R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO2 reduction (CO2R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO2R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts. 相似文献
65.
Transition metal phosphides (TMPs) are prospective anode materials for lithium-ion batteries (LIBs) due to their high theoretical capacities and low redox voltages. Herein, we report a template directing method to develop a tube-sheath hybrid composing of cobalt phosphide particles encapsulated in metal organic frameworks (MOFs) derived N-doped carbon sheaths (CoxP@NC). The utilization of directing template leads to a homogenous distribution of the subsequently formed cobalt phosphide particles, restrains the aggregation of cobalt phosphides, and thus results in the superb rate capability and cyclability. Contributable to the integrated merits of the interior downsized cobalt phosphide particles and the outer ZIF-67 derived porous carbon sheath, the volume expansion during cycling is effectively suppressed. The CoxP@NC hybrid shows superb electrochemical performance as anode material for LIB, with good reversible capacity of 928 mAh·g?1 after 100 cycles at 0.1 A g?1, and high stability of 526 mAh·g?1 after 600 cycles at 1.0 A g?1. This work provides a route for rational design of MOF derived carbon-based anode material for LIB, which could also be applied as a promising platform in diverse field. 相似文献
66.
The structural, elastic and electronic properties of Ti2SiN were studied by first-principle calculations. The calculated bond lengths of Ti-Si and Ti-C are 2.65 and 2.09 Å, respectively. The results show Ti2SiN is mechanically stable, and its bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio μ and anisotropy factor A are determined to be 182 GPa, 118 GPa, 291 GPa, 0.233 and 1.57, respectively. The calculated electronic structure indicates that Ti2SiN is anisotropic and conductive. 相似文献
67.
Aihuan Dun Jingsong Wei Fuxi Gan 《Applied Physics A: Materials Science & Processing》2011,103(1):139-147
Thermocapillary and chemicapillary effects are known to coexist in a material molten pool when irradiated by a pulse laser.
According to the effects, we fabricate various patterns with different shapes on a Sb2Te3 phase change thin film by precisely adjusting the pulse energy. In this process, the laser power is fixed at 5.0 mW, and
the pulse width is adjusted from 100 ns to 5 ns. The shape of the patterns gradually changes from a dimple-bowl shape, a dome
shape, a “Sombrero” shape to a deep-bowl shape following an increase in the pulse energy, which corresponds to the crystallization-threshold,
bump-threshold, rupture-threshold, and ablation-threshold of the material. The different patterns are the results of the competition
between the thermocapillary and chemicapillary effects in the molten pool, which determine the nature of the flow and lead
to the different patterns in different laser parameters. 相似文献
68.
The optical characteristics of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic, including the electro-optic phase modulation, electric hysteresis property and thermo-optic coefficient, are investigated in detail. Based on this novel ceramic, a polarization independent electro-optic switch by using fiber Sagnac interferometer (FSI) structure is realized. An initial π-shift is introduced into the Sagnac loop to eliminate the effect of the polarization orientation of the incident light on the switch performance. Then an electrically controllable PMNT phase retarder is used to switch the optical signal between the reflection and transmission ports. Some theoretical analyses are given and the switch performances are also discussed, including the thermal characteristic and different switching frequency response. 相似文献
69.
70.
Jijing XuGuijuan Ji Haifeng ZouYanhua Song Shucai Gan 《Journal of magnetism and magnetic materials》2011,323(1):156-161
Sm-substituted barium hexaferrites, Ba3−xSmxCo2Fe24O41 (x=0-0.25), were prepared by a conventional ceramic sintering method. The microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using powder X-ray diffraction, field emission scanning electron microscopy, vector network analyzer and vibrating sample magnetometry. The results reveal that by introducing a relatively small amount of Sm3+ instead of Ba2+ an important modification of both structure and high-frequency electromagnetic properties can be obtained. Doping of Sm3+ suppressed the grain growth and gave rise to a decrease of the grain size. As the Sm content increases, the static magnetic properties continuously increase. The real part and imaginary part of complex permittivity initially increase with Sm content, and then decreases when x>0.10. The imaginary part of complex permeability decreases after Sm3+ is doped. There is no obvious change in the real part of the complex permeability for different Sm contents. The reasons are discussed using electromagnetic theory. 相似文献