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991.
992.
采用图像诊断方法对高能环形电子束形状及空间尺寸进行了研究,以高能脉冲环形电子束轰击高Z靶材料产生脉冲X射线,X射线经过X射线增感屏转换为可见光,用单次图像采集系统获取可见光的积分图像。为满足诊断所需的空间分辨和系统灵敏度,通过理论计算确立了靶的材料、厚度及X射线增感屏的型号和厚度等参数。根据测试环境,设计了系统的现场安装结构,系统基本满足测试要求。分析从实验中获取的图像,可知环形电子束的内径为36.5 mm,环厚为1 mm,环形不均匀,水平方向电子束强。 相似文献
993.
Wei Huang Mohamed Pourkashanian Lin Ma Derek B. Ingham Shi Bin Luo Zhen Guo Wang 《显形杂志》2011,14(1):63-74
Abstract
As effective devices to extend the fuel residence time in supersonic flow and prolong the duration time for hypersonic vehicles cruising in the near-space with power, the backward-facing step and the cavity are widely employed in hypersonic airbreathing propulsive systems as flameholders. The two-dimensional coupled implicit RANS equations, the standard k-ε turbulence model, and the finite-rate/eddy-dissipation reaction model have been used to generate the flow field structures in the scramjet combustors with the backward-facing step and the cavity flameholders. The flameholding mechanism in the combustor has been investigated by comparing the flow field in the corner region of the backward-facing step with that around the cavity flameholder. The obtained results show that the numerical simulation results are in good agreement with the experimental data, and the different grid scales make only a slight difference to the numerical results. The vortices formed in the corner region of the backward-facing step, in the cavity and upstream of the fuel injector make a large difference to the enhancement of the mixing between the fuel and the free airstream, and they can prolong the residence time of the mixture and improve the combustion efficiency in the supersonic flow. The size of the recirculation zone in the scramjet combustor partially depends on the distance between the injection and the leading edge of the cavity. Further, the shock waves in the scramjet combustor with the cavity flameholder are much stronger than those that occur in the scramjet combustor with the backward-facing step, and this causes a large increase in the static pressure along the walls of the combustor. 相似文献994.
Highly stable and spherical silver nanoparticles, stabilized by methoxycarbonyl-terminated hyperbranched poly(amine-ester)
(HPAE-COOCH3), were synthesized in water with reducing AgNO3/HPAE-COOCH3 using two methods, viz. NaBH4 and ultraviolet irradiation. HPAE-COOCH3 was found to play a key role in the formation of nanoparticles. UV–visible absorption, Transmission electron microscopic
(TEM), and Fourier transform infrared spectroscopy (FT-IR) had been used to study the structure and characterization of the
silver nanoparticles. The absorption peaks of the silver nanoparticles appear at ~420 nm in UV–visible absorption spectra;
average particle size reduced by NaBH4 is ~30 nm, which is ~10 and ~15 nm, respectively, when ultraviolet irradiation time is 12 and 24 h. FT-IR spectra confirm
that there is strong interaction between silver nanoparticles and HPAE-COOCH3. And silver nanoparticles/HPAE-COOCH3 aqueous solution can keep stable for more than 3 months. 相似文献
995.
996.
Haishan Liu Hui Luo Mingxing Luo Liucheng Wang 《The European Physical Journal C - Particles and Fields》2011,71(11):1793
This paper starts with a self-contained discussion of the so-called Akulov–Volkov action SAV\mathcal{S}_{\mathrm{AV}}, which is traditionally taken to be the leading-order action of the Goldstino field. Explicit expressions for SAV\mathcal{S}_{\mathrm{AV}} and its chiral version SAVch\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} are presented. We then turn to the issue on how these actions are related to the leading-order action SNL\mathcal{S}_{\mathrm{NL}} proposed in the newly proposed constrained superfield formalism. We show that SNL\mathcal{S}_{\mathrm{NL}} may yield SAV/SAVch\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} or a totally different action SKS\mathcal{S}_{\mathrm{KS}}, depending on how the auxiliary field in the former is integrated out. However, SKS\mathcal{S}_{\mathrm{KS}} and SAV/SAVch\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} always yield the same S-matrix elements, as one would have expected from general considerations in quantum field theory. 相似文献
997.
X. X. Jin J. G. Du G. Jiang X. Luo X. W. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,64(2-3):323-329
Using density functional theory (DFT) with valence basis set LANL2TZ to study the relative stabilities and electronic properties of the most stable structures of Nb n V(0,?±1) (n = 1?6) clusters. The ground state structures of Nb n V (0,?±1) keep the similar geometric structure as the host Nb n clusters. The doping of vanadium atom enhances the chemical activities of Nb n clusters. The Nb3V and Nb6V are more stable than other clusters. The average binding energy of charged systems (Nb n V+ and Nb n V? clusters) are generally larger than neutral Nb n V clusters natural population analysis shows that there are charge transfers from niobium to vanadium atoms in the small Nb1?4V, however, for larger clusters (Nb5V and Nb6V), the charge transfers are from vanadium to niobium atoms. The vertical and adiabatic ionization potentials (VIP and AIP) are estimated and the vertical one is more close to experimental results. 相似文献
998.
The security of the quantum secret key plays a critical role in quantum communications.Thus far,one problem that still exists in existing protocols is the leakage of the length of the secret key.In this letter,based on variable quantum encoding algorithms,we propose a secure quantum key distribution scheme,which can overcome the security problem involving the leakage of the secret key.Security analysis shows that the proposed scheme is both secure and effective. 相似文献
999.
Electric field-induced stress birefringence in layered composites PbZr1-xTixO3/Polycarbonate 下载免费PDF全文
Electro-optical composites based on the product of electro-strictive and elasto-optical effects are developed.Layered composites of PbZr 1 x Ti x O 3 and polycarbonate are synthesised.Their electro-optical properties are studied.The nominal transverse electro-optical coefficient of the composite is observed to be about 3.6 times larger than that of LiNbO 3.Experiments and theoretical analyses show that the electro-optical effect of the composite has a strong ’size effect’.With the ratio of thickness/length decreasing or the width of elasto-optical phase increasing,the half-wave electric field intensity increases but the transverse electro-optical coefficient decreases for the layered composite. 相似文献
1000.
A low specific on-resistance (R S,on) silicon-on-insulator (SOI) trench MOSFET (metal-oxide-semiconductor-field-effect-transistor) with a reduced cell pitch is proposed.The lateral MOSFET features multiple trenches:two oxide trenches in the drift region and a trench gate extended to the buried oxide (BOX) (SOI MT MOSFET).Firstly,the oxide trenches increase the average electric field strength along the x direction due to lower permittivity of oxide compared with that of Si;secondly,the oxide trenches cause multiple-directional depletion,which improves the electric field distribution and enhances the reduced surface field (RESURF) effect in the SOI layer.Both of them result in a high breakdown voltage (BV).Thirdly,the oxide trenches cause the drift region to be folded in the vertical direction,leading to a shortened cell pitch and a reduced R S,on.Fourthly,the trench gate extended to the BOX further reduces R S,on,owing to the electron accumulation layer.The BV of the MT MOSFET increases from 309 V for a conventional SOI lateral double diffused metal-oxide semiconductor (LDMOS) to 632 V at the same half cell pitch of 21.5 μm,and R S,on decreases from 419 m · cm 2 to 36.6 m · cm 2.The proposed structure can also help to dramatically reduce the cell pitch at the same breakdown voltage. 相似文献