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991.
992.
The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiOn/SrTiO3 superlattices 下载免费PDF全文
We have performed the first-principles calculation to investigate the origins of ferroelectricities and different po- larization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. Ow- ing to the decline of internal electric field in SrTiO3 (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are en- hanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3. 相似文献
993.
小孔阵列衍射特性与应用 总被引:1,自引:4,他引:1
以单色标量波衍射理论为基础,研究了均匀平面波从不同角度入射小孔阵列的衍射特性。运用单孔衍射理论,同时考虑相邻小孔间衍射光强的相互影响,建立了小孔阵列衍射的理论模型和光强分布的数值积分式,小孔为硬边小孔。利用Matlab对500 nm波长的平面波入射微小方孔阵列衍射图样进行了计算机仿真,得到了不同几何参量下平面波从不同角度入射时的衍射图样的一维和二维光强分布图,并将仿真结果用于微型数字式太阳敏感器的光学系统中的结构参量设计和图像处理中的参量确定。太阳敏感器的成像实验结果表明,小孔阵列衍射光强分布图的仿真结果正确、太阳敏感器光学系统参量设计合理。小孔阵列衍射理论为太阳敏感器的光学系统设计和图像处理提供了可靠的理论基础。 相似文献
994.
以MEH-PPV(聚[2-甲氧基-5-(2′-乙基己氧基-对苯乙烯)])和Alq3作为发光层, 成功制备出ITO/SiO2/MEH-PPV/SiO2/Al结构和ITO/SiO2/Alq3 /SiO2/Al结构的固态阴极射线器件。通过分析SSCL光谱,认为这些高速电子激发有机材料后形成Frenkel激子。当器件两个电极之间加的电压比较低时,有机薄膜层的场强也比较低,这些激子被解离的概率很小,从而产生的是激子发光的长波发射;当器件两个电极之间加的电压比较高时,有机薄膜层的场强很高, 在有机层形成的激子大部分被解离, 解离后的电子直接跃迁至LUMO(lowest unoccupancied molecular orbit),这些电子弛豫后从LUMO能级到HOMO(highest occupancied molecular orbit )能级直接辐射跃迁, 接着重新复合发光,从而产生短波发射。制作的固态阴极射线器件可以实现全色发光, 提高发光效率和加强蓝光发射。作者可以预期所研制出的这种SSCL器件必将引发平板显示领域一场新的革命性变革。 相似文献
995.
We study three-body entanglement induced by spontaneous
emission in a three two-level atoms system by using the entanglement
tensor approach. The results show that the amount of entanglement
is strongly dependent on the initial state of the system and the species
of atoms. The three-body entanglement is the result of the coherent
superposition of the two-body entanglements. The larger the
two-body entanglement is, the stronger the three-body entanglement
is. On the other hand, if there exists a great difference in three two-body entanglement measures,
the three-body entanglement is very weak.
We also find that the maximum of the two-body entanglement
obtained with nonidentical atoms is greater than that obtained
with identical atoms via adjusting the difference in atomic frequency. 相似文献
996.
Compared with direct ablation, confined ablation provides an effective way
to obtain a large target momentum and a high coupling coefficient. By using
a transparent glass layer to cover the target surface, the coupling
coefficient is enhanced by an order of magnitude. With the increase of the gap
width between the target surface and the cover layer, the coupling
coefficient exponentially decreases. It is found that the coupling
coefficient is also related to the thickness of the cover layer. 相似文献
997.
Effects of initial frequency chirp on the linear propagation characteristics of the exponential optical pulse 总被引:6,自引:0,他引:6 下载免费PDF全文
In this paper, the linear propagation characteristics of the exponential optical
pulse with initial linear and nonlinear frequency chirp are numerically studied in a
single mode fibre for \be2<0. It can be found that the temporal full width at
half maximum and time-bandwidth product of exponential pulse monotonically increase
with the increase of propagation distance and decrease with the increase of linear
chirp C for C<0.5, go through an initial decreasing stage near \zeta=1, then
increase with the increase of propagation distance and linear chirp C for
C\geq0.5. The broadening of pulses with negative chirp is faster than that with
positive chirp. The exponential pulse with linear chirp gradually evolves into a
near-Gaussian pulse. The effect of nonlinear chirp on waveform of the pulse is much
greater than that of linear chirp. The temporal waveform breaking of exponential
pulse with nonlinear chirp is first observed in linear propagation. Furthermore, the
expressions of the spectral width and time-bandwidth product of the exponential
optical pulse with the frequency chirp are given by use of the numerical analysis
method. 相似文献
998.
M. Gai 《Physics of Atomic Nuclei》2006,69(11):1805-1811
The Standard Solar Model (BP04) predicts a total 8B neutrino flux that is 17.2% larger than that measured in the salt phase of the SNO detector (and if it is significant, it
will indicate oscillation to sterile neutrinos). Hence, it is important to examine in detail the uncertainties (and values)
of inputs to the BP04. Currently, the largest fractional uncertainty is due to the new evaluation of the surface composition
of the Sun. We examine the nuclear input on the formation of solar 8B [S
17(0)] and demonstrate that it is still quite uncertain due to the ill-known slope of the measured astrophysical cross section
factor and thus illdefined extrapolation to zero energy. This yields an additional reasonable uncertainty due to extrapolation
of
−3.0
+0.0
eV b (
−14%
+0%
). Since a large discrepancy exists between measured as well as predicted slopes, the value of S
17(0) is dependent on the choice of data and theory used to extrapolate S
17(0). This situation must be alleviated by new measurement(s). The “world average” is driven by the Seattle result owing to
the very small quoted uncertainty, which we, however, demonstrate to be an overestimated accuracy. We propose more realistic
error bars for the Seattle results based on the published Seattle data.
The text was submitted by the author in English. 相似文献
999.
实验研究了电压敏感染料di-4-ANEPPS在家兔心肌组织中的吸收光谱和荧光光谱特性。结果表明,含染料组织的光吸收普遍大于对照组,在450~550 nm波段吸收谱差异更明显;染料在心室组织中的最大吸收峰为(479.75±0.44) nm。通过测量含染料心脏不同部位的荧光光谱,首次发现心室组织、心房组织和主动脉的最大荧光峰位有一定差异,其相对荧光强度则与染料的分布浓度有关。根据三维和二维荧光光谱分别确定了含染料心房和心室组织的最佳荧光激发波长和荧光测定波长。利用心房和心室组织的静息电位差,在不同波长激发光下测量了染料的荧光光谱移动,确定了光标测量实验的最佳激发光和相应荧光检测波长范围。这些研究结果为心脏光学标测系统的设计提供了理论依据。 相似文献
1000.