全文获取类型
收费全文 | 10686篇 |
免费 | 1954篇 |
国内免费 | 961篇 |
专业分类
化学 | 7016篇 |
晶体学 | 83篇 |
力学 | 671篇 |
综合类 | 85篇 |
数学 | 1199篇 |
物理学 | 4547篇 |
出版年
2024年 | 41篇 |
2023年 | 242篇 |
2022年 | 402篇 |
2021年 | 429篇 |
2020年 | 426篇 |
2019年 | 421篇 |
2018年 | 360篇 |
2017年 | 340篇 |
2016年 | 533篇 |
2015年 | 507篇 |
2014年 | 569篇 |
2013年 | 781篇 |
2012年 | 936篇 |
2011年 | 1016篇 |
2010年 | 637篇 |
2009年 | 665篇 |
2008年 | 662篇 |
2007年 | 570篇 |
2006年 | 524篇 |
2005年 | 437篇 |
2004年 | 340篇 |
2003年 | 281篇 |
2002年 | 256篇 |
2001年 | 207篇 |
2000年 | 217篇 |
1999年 | 204篇 |
1998年 | 212篇 |
1997年 | 191篇 |
1996年 | 149篇 |
1995年 | 195篇 |
1994年 | 166篇 |
1993年 | 125篇 |
1992年 | 101篇 |
1991年 | 85篇 |
1990年 | 90篇 |
1989年 | 64篇 |
1988年 | 43篇 |
1987年 | 33篇 |
1986年 | 35篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Miao W Luo X Wu S Liang Y 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(1-2):413-416
Order-disorder transitions of 9-monolayer Langmuir-Blodgett (LB) films of 7-(2-octadecyloxycarbonylethyl)guanine (ODCG) before and after recognition to cytidine were investigated by Fourier transform infrared (FTIR) spectroscopy. The different order-disorder transitions suggest that molecular recognition between ODCG and cytidine influence these two LB films on the order-disorder process of alkyl tailchain. Cleavage of the multi-hydrogen bonds was also observed by the infrared spectroscopy at elevated temperature. 相似文献
993.
Q.?Zhao H.Z.?Zhang B.?Xiang X.H.?Luo X.C.?Sun D.P.?YuEmail author 《Applied Physics A: Materials Science & Processing》2004,79(8):2033-2036
Selenium dioxide nanowires were fabricated as the co-products of ZnSe nanostructures. The SeO2 nanowires have diameters between 2070 nm and lengths up to several hundred micrometers. The morphology and microstructure of the nanowires were analyzed using TEM, and the growth mechanism of the SeO2 nanowires was explained under the framework of a vapor-solid model, in which structure defects may play a very important role in the nanowire growth. The nanostructured SeO2 materials may find application in both catalytic and biological fields. PACS 81.07.-b; 81.16.-c; 81.07.Nb; 81.05.-t; 68.37.Lp 相似文献
994.
To overcome the complicated and time-consuming difficulties of current models, a new lubrication equation based on boundary velocity slip model for solving the ultra-thin film gas lubrication in hard disk drives is proposed by adopting the nanoscale effect function, N p. The present model is easy to calculate and applicable at nanoscale. The results of numerical calculations indicate that the present model produces a close approximation to that of the exact Boltzmann model. 相似文献
995.
The universal variation pattern of the total energy of various fullerenes including single-walled carbon nanotubes with respect to their extra charge is revealed by the density-functional-theory calculations. The parabolic energy-charge curve with its lowest energy value corresponding to a negatively charged fullerene indicates that these carbon materials have positive electron affinity and are not in the most stable state. The positive electron affinity seems to originate from the pi-electrons and is found to be related to the aggregation property of fullerenes. 相似文献
996.
Xu P Li K Zhao G Zhu SN Du Y Ji SH Zhu YY Ming NB Luo L Li KF Cheah KW 《Optics letters》2004,29(1):95-97
We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%. 相似文献
997.
X.?ZhouEmail author J.?Luo X.?Sun X.?Zeng M.?Zhan S.?Ding M.?Liu 《Applied magnetic resonance》2004,26(3):327-337
Radiation damping is generally observed when a sample with high spin concentration and high gyromagnetic ratio is placed in a high magnetic field. However, we firstly observed liquid-state129Xe radiation damping with laser-enhanced nuclear polarization at low magnetic field in a flow system in which the polarization enhancement factor for the liquid-state129Xe was estimated to be 5000, and, furthermore, theoretically simulated the envelopes of the129Xe free induction decay and spectral lineshape in the presence of both relaxation and radiation damping with different pulse flip angles and ratios ofT 2 * /T rd. The radiation damping time constantT rd of 5 ms was derived on the basis of the simulations. The reasons of depolarization and the further possible improvements were also discussed. 相似文献
998.
A dissipative soliton in an amplifier with a Bragg grating is numerically investigated by direct simulation of Maxwell-Bloch equations. The result of the simulation indicates that a solitary wave can exist in such a medium. However, the pulse shape of the dissipative soliton is asymmetrical because of the gain saturation effect. This gain saturation effect results from the high power of the ultrashort dissipative soliton. The influence of amplifier gain on the solitary wave is also investigated. 相似文献
999.
The backscattered fluorescence of nitrogen from filaments generated by intense ultra-fast Ti:sapphire laser pulses propagating
in air is studied. The backscattered fluorescence from N2 molecules and ions show an exponential increase with increasing filament length, indicating amplified spontaneous emission.
Received: 11 October 2002 / Revised version: 3 December 2002 / Published online: 26 February 2003
RID="*"
ID="*"Corresponding author. Fax: +1-418/6562-623, E-mail: qluo@phy.ulaval.ca 相似文献
1000.
A benzene thermal conversion route has been successfully developed to prepare nanocrystalline indium nitride at 180-200 degrees C by choosing NaNH(2) and In(2)S(3) as novel nitrogen and indium sources. This route has been also extended to the synthesis of other group III nitrides. The product InN was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and infrared spectroscopy (IR). The optical properties of nanocrystalline InN were also recorded by means of UV-vis absorption spectroscopy and photoluminescence (PL) spectroscopy, indicating that the as-prepared sample was within the quantum confinement regime. Finally, the formation mechanism was also investigated. 相似文献