全文获取类型
收费全文 | 1427篇 |
免费 | 267篇 |
国内免费 | 144篇 |
专业分类
化学 | 955篇 |
晶体学 | 9篇 |
力学 | 144篇 |
综合类 | 27篇 |
数学 | 174篇 |
物理学 | 529篇 |
出版年
2024年 | 6篇 |
2023年 | 40篇 |
2022年 | 67篇 |
2021年 | 47篇 |
2020年 | 68篇 |
2019年 | 59篇 |
2018年 | 37篇 |
2017年 | 40篇 |
2016年 | 71篇 |
2015年 | 67篇 |
2014年 | 79篇 |
2013年 | 99篇 |
2012年 | 133篇 |
2011年 | 119篇 |
2010年 | 93篇 |
2009年 | 94篇 |
2008年 | 93篇 |
2007年 | 77篇 |
2006年 | 87篇 |
2005年 | 45篇 |
2004年 | 54篇 |
2003年 | 40篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 25篇 |
1999年 | 14篇 |
1998年 | 25篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 10篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有1838条查询结果,搜索用时 0 毫秒
991.
利用发射光谱法,研究了圆柱型空心阴极放电条纹的特性.测量了条纹区的发射光谱,在此基础E计算得到r电子激发温度、相对电子密度和电子平均能量的空间分布特性.结果表明条纹区的光强、电子激发温度和电子密度均呈非等幅的周期性变化.与暗纹中心处相比,明纹中心具有较高的电子激发温度和较低的电子密度.由阴极向阳极,明纹中心处的电子激发温度幅值逐渐减小.此外,条纹区的电子激发温度随着电流的增加而增加. 相似文献
992.
993.
H. Tian Y.M. Wang Y. Liu L.X. Guo J.H. Ouyang Y. Zhou D.C. Jia 《Current Applied Physics》2013,13(1):1-6
High infrared emissivity ceramic coatings were prepared on 304 steel by pyrolyzing reactions with poly(hydridomethylsiloxane) (PHMS) and Al/Cr2O3 based mixing powders. The effects of pyrolysis temperature, testing temperature and surface roughness on infrared radiation of polymer derived ceramic coating were systematically investigated. The results indicated that the coating pyrolyzed at 800 °C exhibited a slightly higher infrared emissivity value than that of the coating pyrolyzed at 600 °C, which was attributed to the enhancing photon emission caused by the complete conversion of Al to Al2O3 and PHMS pyrolysis into SiO2, together with the introduction of Cr2O3 based mixing powders. The emissivity value in 3–8 μm waveband of the coating was lower about 0.03 at 600 °C compared with 800 °C testing temperature, while the emissivity value was almost the same in 8–20 μm waveband. The high surface roughness of the coating led to a slightly increasing emissivity due to the enhancing infrared absorbance. 相似文献
994.
Qin Ouyang You-Si Chen Na Zhang Gao-Ming Mo De-Hong Li Qing Yan 《Journal of Macromolecular Science: Physics》2013,52(12):2417-2427
The jet swell effect in the wet spinning of polyacrylonitrile (PAN) fiber was studied by optical microscopy and the jet swell ratio was obtained through directly measuring the diameter of the freely extruded fibers. For reflecting the actual drawing situation of the fibers in the coagulation process, the jet stretches were then corrected from the apparent values to the true values, and their effect on the cross-sectional morphology, internal structure, and orientation of the wet-spun PAN fibers was studied by optical microscopy, scanning electron microscopy, and X-ray diffraction, respectively. The results showed that jet stretch plays an important role in eliminating the adverse effects caused by the jet swell effect and affects the fiber structure; PAN fibers of uniform denier, dense and homogenous structure, and high orientation can only be obtained at a suitable jet stretch. 相似文献
995.
研制了可用于脉冲辐射场中子探测的4He闪烁裂变中子探测器,并对其时间响应进行了理论和实验研究。采用经验公式和蒙特卡罗方法模拟计算了不同厚度裂变靶产生的裂变碎片和不同能量中子产生的反冲4He核在4He气中的飞行时间,并依据卷积原理推导出探测器的时间响应计算公式。计算结果表明,探测器的波形上升时间约为19.5 ns,半高宽约31.0 ns。用ING-103型稠密等离子体聚焦装置(DPF)脉冲中子发生器对探测器的时间响应进行了实验测量,实验结果与理论值基本一致。 相似文献
996.
Zhisheng Wu Guoqing Ouyang Xinyuan Shi Qun Ma Guang Wan Yanjiang Qiao 《Optics and Spectroscopy》2014,117(5):703-709
The previous study mainly focused on the interpretation of the relationship between absorption characteristics and quantitative contribution in each near-infrared (NIR) frequency range. Furthermore, the absorption characteristics of NIR mainly cover overtones and combinations of molecular vibrations such as CH, OH, SH, and NH bonds. And it has been know that NIR wavelengths of C-H bond and O-H bond are assigned to different radio frequencies. This paper was intended to investigate the absorption characteristics of bond C-H and O-H bonds in NIR spectral range. Water and acetone which correspond to O-H and C-H bonds have been selected as typical solvents, as well as solutes. Calibration models were established using partial least square regression (PLS) and multiple linear regression (MLR). The parameter of the model were optimized by different spectral pretreatment methods. The result showed that the model set by Savitzky-Golay smooth (SG) in the spectral region of 810–1100 nm could successfully make accurate predictions. Short wave-NIR region has been discovered as optimum characteristic absorption of C-H and O-H bonds. 相似文献
997.
998.
The Hilbert genus field of the real biquadratic field K=Q(δ~(1/2),d~(1/2)is described by Yue(2010)and Bae and Yue(2011)explicitly in the case=2 or p with p=1 mod 4 a prime and d a squarefree positive integer.In this article,we describe explicitly the Hilbert genus field of the imaginary biquadratic field K=Q(δ~(1/2),d~(1/2)),whereδ=-1,-2 or-p with p=3 mod 4 a prime and d any squarefree integer.This completes the explicit construction of the Hilbert genus field of any biquadratic field which contains an imaginary quadratic subfield of odd class number. 相似文献
999.
Liu HuaChang Ouyang HuaFu Peng Jun Huang Tao Gong KeYun Xu TaoGuang Fu ShiNian 《中国科学:物理学 力学 天文学(英文版)》2011,54(2):231-235
The China Spallation Neutron Source (CSNS) front end incorporates a pre-chopper in the Low Energy Beam Transport line (LEBT) that will remove a 530 ns section of beam at approximately 1 MHz rate, which is the RF frequency of the ring at injection. It’s one of the most critical devices for properly controlling the injecting beam loss. Physical designing of the pre-chopper is carried out, and the RFQ itself is used as the beam dump of the chopper system. In order to examine the reliability of the pre-chopper design, the beam study of a similar chopper system is successfully performed. The results of physical design and experiments are presented.
相似文献1000.
Zidong Xu Yelian Miao Jie Yu Chen Xuejian Jiang Lijun Lin Pingkai Ouyang 《Applied biochemistry and biotechnology》2011,163(1):153-161
Cellulase and xylanase from Trichoderma reesei were immobilized simultaneously on Eudragit L-100, a reversibly soluble polymer. The effects of polymer concentration and
polymer precipitation pH on enzyme activity recovery were investigated at an enzyme complex concentration of 1%. The immobilization
mechanism of cellulase and xylanase on the polymer was discussed. An activity recovery of 75% and 59% was obtained for the
cellulase and the xylanase, respectively, under the condition of a polymer concentration at 2% and a polymer precipitation
pH at 4.0. Most zymoproteins might be connected to the polymer by electrostatic attraction in a medium of pH 4.8. In addition,
the covalent coupling between the zymoproteins and the polymer was demonstrated by the infrared spectrograms. It was suggested
that dehydration–condensation reaction occurred between the zymoproteins and the polymer during the immobilization. 相似文献