全文获取类型
收费全文 | 10067篇 |
免费 | 1833篇 |
国内免费 | 1376篇 |
专业分类
化学 | 5431篇 |
晶体学 | 382篇 |
力学 | 1149篇 |
综合类 | 136篇 |
数学 | 235篇 |
物理学 | 5943篇 |
出版年
2024年 | 22篇 |
2023年 | 68篇 |
2022年 | 255篇 |
2021年 | 300篇 |
2020年 | 271篇 |
2019年 | 260篇 |
2018年 | 296篇 |
2017年 | 425篇 |
2016年 | 482篇 |
2015年 | 385篇 |
2014年 | 544篇 |
2013年 | 899篇 |
2012年 | 685篇 |
2011年 | 655篇 |
2010年 | 601篇 |
2009年 | 642篇 |
2008年 | 585篇 |
2007年 | 672篇 |
2006年 | 601篇 |
2005年 | 529篇 |
2004年 | 511篇 |
2003年 | 443篇 |
2002年 | 377篇 |
2001年 | 334篇 |
2000年 | 323篇 |
1999年 | 319篇 |
1998年 | 243篇 |
1997年 | 205篇 |
1996年 | 193篇 |
1995年 | 159篇 |
1994年 | 137篇 |
1993年 | 155篇 |
1992年 | 125篇 |
1991年 | 72篇 |
1990年 | 71篇 |
1989年 | 68篇 |
1988年 | 85篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
为了解D-和L-丙氨酸单晶晶格在极低温下是否存在磁手性相变,在2-20 K下改变磁场强度(0,1,3,5T)测定其比热.实验结果表明比热和温度之间的函数关系很好地符合C(T)=aT3+b/T2方程,其中aT3项为晶格声子的贡献,可由公式CV=(12/5)π4R(T/ΘD)3来描述(ΘD为德拜温度),b/T2项为磁场对比热的贡献.实验发现,在2-20 K范围内D-和L-丙氨酸单晶在不同磁场强度下均存在Boson峰(在Cp/T3-T曲线中表现为一个最大值).磁的贡献导致D-和L-丙氨酸单晶的四条Cp/T3-T曲线在2-12 K时不重合,且在12-20 K时消失,此即Schottky反常.零磁场下,D-和L-丙氨酸的Boson峰分别为9.44和10.86 K;德拜温度分别为151.5和152.7 K.结合磁场强度1 T下的直流磁化率测定,发现在温度低于5 K时,D-和L-丙氨酸单晶有相反的磁化率行为,反映了核自旋和电子自旋弱相互作用的手性表现. 相似文献
962.
N. Kumar V. Sharma N. Padha N. M. Shah M. S. Desai C. J. Panchal I. Yu. Protsenko 《Crystal Research and Technology》2010,45(1):53-58
Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (Ts) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all Ts. With the increase of Ts the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different Ts. The activation energy for films deposited at different Ts was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
963.
964.
965.
基于固体的熔化和凝固实验的传统做法,结合现代测量技术对其进行了改进,对晶体海波和非晶体石蜡的熔化和凝固进行了全程监控,取得了很好的实验效果并节省了实验时间,提高了实验的准确性. 相似文献
966.
967.
We developed a new radiation parameterization of hydrofluorocarbons (HFCs), using the correlated k-distribution method and the high-resolution transmission molecular absorption (HITRAN) 2004 database. We examined the instantaneous and stratospheric adjusted radiative efficiencies of HFCs for clear-sky and all-sky conditions. We also calculated the radiative forcing of HFCs from preindustrial times to the present and for future scenarios given by the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios (SRES, in short). Global warming potential and global temperature potential were then examined and compared on the basis of the calculated radiative efficiencies. Finally, we discuss surface temperature changes due to various HFC emissions. 相似文献
968.
Travis J. Moore Darron P. Cundick Dale R. Tree Larry L. Baxter 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(12):1978-1986
The spectral emittance of deposits left by bituminous and sub-bituminous coals under oxidizing conditions have been measured in situ. Pulverized coal is injected into a down-fired entrained-flow reactor. Ash accumulates on a probe in the reactor effluent and radiation emitted by the ash layer is recorded using a Fourier transform infrared (FTIR) spectrometer. Values for the spectral emissive power emitted by the ash and the surface temperature of the ash are extracted from these data. These results are then used to calculate the spectral emittance of the deposit. The spectral emittances of ash deposits formed by burning Illinois #6 (bituminous) coal and Powder River Basin (sub-bituminous) coal were measured between 3000 and 500 wavenumbers. The spectral emittance of the deposit left by the bituminous coal has a constant value of approximately 0.46 between 3000 and 2400 wavenumbers. Between 2200 and 1200 wavenumbers, the spectral emittance of the deposit increases from approximately 0.47 to approximately 0.61. Between 1200 and 500 wavenumbers, the spectral emittance is relatively constant at 0.61. The spectral emittance of the deposit left by the sub-bituminous coal is also relatively constant between 3000 and 2400 wavenumbers at a value of 0.29. Between 2200 and 500 wavenumbers, the spectral emittance of deposits from the sub-bituminous coal increases from approximately 0.29 to 0.55. Differences between these spectral emittance measurements and those measured ex situ illustrate the importance of making in situ measurements. Band emittances were calculated using the measured spectral emittances, and band emittances of the deposits are reported as functions of temperature. 相似文献
969.
Spectral broadening of the fluorescence of a Nd/Cr:YAG ceramic at the 1064 nm lasing wavelength was observed, and the amplification properties at a high temperature were investigated by considering cross-relaxation. These ceramics are promising for use as a solid-laser material pumped with solar or lamp light. It has been found that whenever the temperature of a laser medium is high and a spectral shift occurs, a high small-signal gain remains owing to the broad spectral band and the cross-relaxation. This optical property is remarkably different from that of a Nd:YAG laser. For a conventional Nd:YAG laser, the bandwidth at 1064 nm is 0.45 nm, and a reduction in small-signal gain occurs at a temperature of 373 K because the spectral peak shift is 0.005 nm/K. However, for the Nd/Cr:YAG ceramic, the bandwidths are 1.2 and 1.9 nm in the case of 0.1% Cr ion doping and 3% Cr ion doping, respectively, owing to the existence of excited Cr ions and the shortening of the effective Nd ion coherence time. It is prospected that the laser medium can be used at a high temperature of 600 K. 相似文献
970.
A Sagnac interferometer with a long-period fiber grating (LPG) inscribed in the polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for simultaneous measurement of strain and temperature. Due to the different responses of the LPG and the Sagnac interferometer to strain and temperature, simultaneous measurement can be achieved by monitoring the wavelength shifts and the intensity changes of a resonance dip of the sensor setup. The experimental results show that the achieved sensitivities to strain and temperature are 6.4 × 10− 3 dB/με and 0.65 nm/°C, respectively. 相似文献