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971.
Yongbo Bian Jin Guo Changzheng Gao Chunguang Li Hong Li Jia Wang Bin Cui Xiaofeng He Chao Li Na Li Guoqiang Li Qiang Zhang Xueqiang Zhang Jibao Meng Yusheng He 《Physica C: Superconductivity and its Applications》2010,470(15-16):617-621
This paper presents a miniaturized high performance high temperature superconducting (HTS) microwave receiver front-end subsystem, which uses a mini stirling cryocooler to cool a high selective HTS filter and a low noise amplifier (LNA). The HTS filter was miniaturized by using specially designed compact resonators and fabricating with double-sided YBCO films on LAO substrate which has a relatively high permittivity. The LNA was specially designed to work at cryogenic temperature with noise figure of 0.27 dB at 71 K. The mini cryocooler, which is widely used in infrared detectors, has a smaller size (60 mm × 80 mm × 100 mm) and a lighter weight (340 g) than the stirling cryocoolers commonly used in other HTS filter subsystem. The whole front-end subsystem, including a HTS filter, a LNA, a cryocooler and the vacuum chamber, has a size of only φ120 mm × 175 mm and a weight of only 3.3 kg. The microwave devices inside the subsystem are working at 71.8 K with a consumed cooling power of 0.325 W. The center frequency of this subsystem is 925.2 MHz and the bandwidth is 2.7 MHz (which is a fractional bandwidth of 0.2%), with the gain of 19.75 dB at center frequency and the return loss better than ?18.11 dB in the pass band. The stop band rejection is more than 60 dB and the skirt slope is exceeding 120 dB MHz?1. The noise figure of this subsystem is less than 0.8 dB. This front-end subsystem can be used in radars and communication systems conveniently due to it’s compact size and light weight. 相似文献
972.
973.
974.
飞秒物理、飞秒化学和飞秒生物学 总被引:7,自引:0,他引:7
飞秒激光技术因其极高的时间分辨特性而被广泛应用于研究多种材料的超快过程,文章从几个侧面就飞秒技术在物理学,化学及生物学等方面的应用作了介绍,在飞秒物理方面,介绍了飞秒技术在研究半导体量子阱材料,纳米材料的性质及高次谐波产生等方面的研究进展,飞秒化学则主要介绍了飞秒技术在研究光化学反应,光解离过程、键的断裂及结合以及相关的动力学过程的应用;在生物方面,则介绍利用飞秒技术研究光合作用中的能量传递过程,视觉系统中的光致异构化过程以及DNA中的电荷传递及质子传递等过程的研究现状。 相似文献
975.
Lin‐Jian Zhu Jian Wang Tie‐Gang Reng Chun‐Yan Li Dong‐Cai Guo Can‐Cheng Guo 《Journal of Physical Organic Chemistry》2010,23(3):190-194
Six tetraphenylporphyrins (TRPPH2) with different horizontal substituents R (R = H, CH3, OH, F, Cl, Br) were synthesized, and the organic light‐emitting diode (OLED) devices with a general configuration of ITO/TPD/Alq3:2%TRPPH2/Alq3/Al were prepared. The substituted TRPPH2 was used as the host dopant, 4,4‐bis‐(m‐tolyphenylamino)biphenyl (TPD) was used as a hole‐transporting material, and aluminum tris(8‐quinolinolato) (Alq3) was used as an electron‐transporting material. The electroluminescent (EL) properties of these devices were studied to understand the light emitting properties of the substituted TRPPH2. Previous studies have found that the color emitted by the devices was dependent on the TRPPH2 dye concentration. The electronic effect of the horizontal substituents R of TRPPH2 influenced the turn‐on voltage, brightness, and power efficiency of the devices. Also, the electroluminescence performance of the porphyrin‐doped OLED devices depended on the effectual overlaps between the emission of electron‐transporting material and the absorption of the dopants. This means that it is possible to evaluate the electroluminescence performance of the porphyrin‐doped OLED devices based on the emission of electron‐transporting material and the absorption of the dopants. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
976.
Thermal transport property of investigated by molecular Ge34 and d-Ge dynamics and the Slack's equation 下载免费PDF全文
In this study, we evaluate the values of lattice thermal conductivity κL of type Ⅱ Ge clathrate (Ge34) and diamond phase Ge crystal (d-Ce) with the equilibrium molecular dynamics (EMD) method and the Slack's equation. The key parameters of the Slack's equation are derived from the thermodynamic properties obtained from the lattice dynamics (LD) calculations. The empirical Tersoff's potential is used in both EMD and LD simulations. The thermal conductivities of d-Ge calculated by both methods are in accordance with the experimental values. The predictions of the Slack's equation are consistent with the EMD results above 250 K for both Ge34 and d-Ge. In a temperature range of 200-1000 K, the κL value of d-Ge is about several times larger than that of Ge34. 相似文献
977.
Microstructure and strain films using in-plane grazing analysis of GaN epitaxial incidence x-ray diffraction 下载免费PDF全文
This paper investigates the major structural parameters, such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of (100) reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa. 相似文献
978.
<正>Photon quantum statistics of light can be shown by the high-order coherence.The fourth-order coherences of various quantum states including Fock states,coherent states,thermal states and squeezed vacuum states are investigated based on a double Hanbury Brown-Twiss(HBT) scheme.The analytical results are obtained by taking the overall efficiency and background into account. 相似文献
979.
Runwu Peng Lijun Tang Lin Guo Xiaofu Zhang Fangqin Li Zuyan Xu 《Optics & Laser Technology》2010,42(8):1282-1285
A detailed design of a picosecond laser oscillator is made by using optical resonance theory and semiconductor saturable absorber mirror continuous wave mode-locked technology. Mode parameters in the optical resonance including beam sizes on the laser crystal and mode locker are calculated. By theoretical calculations, 3.7 W output power is obtained at a pump power of 11 W and the optical to optical efficiency is 34% in the designed model of picosecond laser. Based on the detailed design, an experiment is proceeded and a picosecond laser oscillator of about 3.5 W output power with 10.6 W pump power is fabricated. The optical to optical efficiency of the laser is 33%, the pulse duration is about 20 ps, and the repetition rate is about 80.3 MHz. The oscillator presents long-term stability in the experiment. 相似文献
980.
X. D. Zhang M. L. Guo C. L. Liu L. A. Zhang W. Y. Zhang Y. Q. Ding Q. Wu X. Feng 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):417-421
A first-principles study has been performed to evaluate the electronic and
optical properties of wurtzite Zn1-xMgxO. Substitutional doping is
considered with Mg concentrations of x = 0, 0.0625, 0.125, 0.1875 and 0.25,
respectively. Mg incorporation can induce band gap widening due to the
decrease of Zn 4s states. The imaginary part of the dielectric function shows
that the optical transition from band edge emission decreases slightly with
increasing Mg contents. The optical band gap also increases from 3.2 to 3.7
eV with increasing Mg contents from 0.0625 to 0.25. The calculated results
suggest that relatively high Mg concentration is necessary for effective
band gap engineering of wurtzite Zn1-xMgxO. 相似文献