全文获取类型
收费全文 | 108636篇 |
免费 | 17313篇 |
国内免费 | 12792篇 |
专业分类
化学 | 76163篇 |
晶体学 | 1190篇 |
力学 | 6187篇 |
综合类 | 749篇 |
数学 | 13264篇 |
物理学 | 41188篇 |
出版年
2024年 | 364篇 |
2023年 | 2134篇 |
2022年 | 3795篇 |
2021年 | 4107篇 |
2020年 | 4323篇 |
2019年 | 4123篇 |
2018年 | 3847篇 |
2017年 | 3484篇 |
2016年 | 5215篇 |
2015年 | 5136篇 |
2014年 | 6294篇 |
2013年 | 8126篇 |
2012年 | 9647篇 |
2011年 | 9884篇 |
2010年 | 6931篇 |
2009年 | 6653篇 |
2008年 | 7020篇 |
2007年 | 6280篇 |
2006年 | 5843篇 |
2005年 | 4913篇 |
2004年 | 3822篇 |
2003年 | 3104篇 |
2002年 | 2892篇 |
2001年 | 2424篇 |
2000年 | 2105篇 |
1999年 | 2179篇 |
1998年 | 1838篇 |
1997年 | 1639篇 |
1996年 | 1600篇 |
1995年 | 1424篇 |
1994年 | 1300篇 |
1993年 | 1053篇 |
1992年 | 948篇 |
1991年 | 823篇 |
1990年 | 678篇 |
1989年 | 527篇 |
1988年 | 390篇 |
1987年 | 348篇 |
1986年 | 347篇 |
1985年 | 282篇 |
1984年 | 197篇 |
1983年 | 167篇 |
1982年 | 136篇 |
1981年 | 86篇 |
1980年 | 67篇 |
1979年 | 29篇 |
1978年 | 24篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1957年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
971.
In this paper, we describe a facile and rapid method for preparing In2S3 nanoparticles via ultrasound dispersion. This method allows us to prepare In2S3 nanoparticles from bulk indium and sulfur with ease and without using expensive agents and in a short time. The possible growing mechanism of the In2S3 nanoparticles was presented. In addition, we provide detailed characterizations including TEM, XRD, TG-DTA, and XPS to study the shape, composition and structure of In2S3 nanoparticles. We also studied the tribology property of In2S3 nanoparticles made using this novel recipe. 相似文献
972.
F. Yang Z. Wang Y. Zhou F. Li J. Xu Y. Xu X. Cheng Y. Lu Y. Bo Q. Peng D. Cui X. Zhang X. Wang Y. Zhu Z. Xu 《Applied physics. B, Lasers and optics》2009,96(2-3):415-422
We have presented theoretical and experimental investigations of nanosecond (ns) deep-ultraviolet (DUV) 177.3 nm radiation by means of second harmonic generation (SHG) from a frequency-tripled Nd:YAG laser (355 nm, 49 ns and 10 kHz) in KBe2BO3F2 (KBBF) nonlinear crystal for the first time. A DUV KBBF-SHG numerical model, accounting for linear absorption, pump depletion, beam spatial birefringent walk-off and diffraction, is performed in the Gaussian approximation of spatial and temporal profiles. In the experiment, a maximum average output power of 14.1 mW at 177.3 nm was obtained. The dependence of 177.3 nm output power on the 355 nm pump power was simulated. The calculated results are in good agreement with the measured data. We used the model further to investigate the optical conversion efficiency, pulse width, beam spatial intensity profile and beam quality factor of the generated 177.3 nm light, in particular the effect of beam birefringent walk-off. 相似文献
973.
We report low temperature scanning tunneling microscopy and spectroscopy on graphene flakes supported on a graphite substrate. The experiments demonstrate that graphite is exceptionally well suited as a substrate for graphene because it offers support without disturbing the intrinsic properties of the charge carriers. The degree of coupling of a graphene flake to the substrate was recognized and characterized from the appearance of an anomalous Landau level sequence in the presence of a perpendicular magnetic field. By following the evolution of the Landau level spectra along the surface, we identified graphene flakes that are decoupled or very weakly coupled to the substrate. From the Landau level sequence in this flake, we extract the local Fermi velocity and energy of the Dirac point and find extremely weak spatial variation of these quantities confirming the high quality and non invasive nature of the graphite substrate. 相似文献
974.
C.Y. Zhang H.Z. Guo H. Yuan C. Lu L. Li J. Gao 《Solid State Communications》2009,149(29-30):1193-1196
We report a detailed experimental study of the fluctuations of acoustoelectric (AE) current induced by surface acoustic waves in a shallow-etched quantum point contact defined in a GaAs/AlxGa1?xAs heterostructure at 1.7 K. We observe that current fluctuations between two AE current plateaus are more obvious than those at the plateaus. Switching the metastable states of the impurities is considered as the physical origin of the current fluctuations. 相似文献
975.
X.P. Chen M.Y. Li Q. Liu Z. Han 《Physica C: Superconductivity and its Applications》2009,469(2-3):116-119
Effect of the evolution of the secondary phases in the first sintering process on the microstructure and critical current density of Bi-2223/Ag tapes has been studied. The amount and grain size of secondary phases were characterized by XRD and SEM/EDS. It has been found that both the microstructure and critical current of the fully reacted tapes depended strongly on the secondary phases formed in the first sintering process. The (Ca,Sr)2CuO3 and (Ca,Sr)14Cu24O41 phases were easily formed and to be stable at higher temperature, however, at lower temperature, the CuO particles appeared easily and keeping stable with dwelling time. The best conversion to Bi-2223, together with the lowest amount of the total secondary phases was achieved when samples treated at 830 °C in 8.5% O2. Samples with the lowest amount and minimum size of secondary phase produced in the first sintering process will obtain the best performance of the fully reacted tapes. The optimum sintering parameters are obtained by controlling the evolution of the secondary phases during the first sintering process. 相似文献
976.
Di-You Jiang R. S. Wu S. S. Li Z. S. Wang 《International Journal of Theoretical Physics》2009,48(8):2297-2304
Two schemes, introducing the projective operator and the auxiliary qubit respectively, for controlled dense coding are investigated
by using a three-qubit symmetric state with entanglement, where the supervisor (Cliff) can control an average amount of information
transmitted from the sender (Alice) to the receiver (Bob) by adjusting the measurement angle θ. We show that the results for the average amounts of information are unique from the different two schemes. The schemes may
be extended to many-qubit systems. 相似文献
977.
Yongzheng Zhu Yanling Cao Juan Ding Zhihui Li Junsong Liu Yuanbin Chi 《Applied Physics A: Materials Science & Processing》2009,94(4):731-734
A non-close-packed three-dimensional photonic crystal of titania hollow spheres has been fabricated. The fabricated process
is based on the silica template technique, thermal sintering, and the sol–gel process. The band-structure calculations and
optical measurements both indicate that a quasi-full three-dimensional photonic bandgap located at the visible wavelength
has been presented between the eighth and ninth bands. This indicates that the non-close-packed structure of titania hollow
spheres was easier to open the complete photonic bandgaps than other face-centered cubic structures made by self-assembling
methods at the visible region. 相似文献
978.
Using the finite-difference time-domain (FDTD) method, we simulate the coupling between a gold nanorod and gold nanoparticles
with different plasmonic resonant frequencies/volumes as well as that between the nanorod and a dielectric nanosphere. The
influences of coupling with different nanoparticles on the excitation of a forbidden longitudinal surface plasmon mode of
the nanorod under normal incidence are investigated. It is found that the cause of this excitation is the broken symmetry
of the local electric field experienced by the nanorod resulting from the charge pileup on the other nanoparticle. This result
is valuable for understanding the near-field optical characterization of plasmonic metal nanoparticles.
Supported by the National Natural Science Foundation of China (Grant Nos. 10821062 and 10804004), the National Basic Research
Program of China (Grant No. 2007CB307001), and the Specialized Research Fund for the Doctoral Program of Higher Education
(Grant No. 200800011023)
Contributed by GONG QiHuang 相似文献
979.
Bin Dong BaoSheng Cao ZhiQing Feng XingJun Wang ChengRen Li RuiNian Hua 《中国科学G辑(英文版)》2009,52(7):1043-1046
The Er3+-Yb3+ codoped Al2O3 nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The
green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions
of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes
predominant after annealing. The mixture of (Er,Yb)3Al5O12 and α-(Al,Er,Yb)2O3 phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of 4I11/2+a photon→4F7/2 and ET (III) of 2F5/2(Yb3+)+4I11/2(Er3+)→2F7/2(Yb3+)+4F7/2(Er3+) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The
results have proved that arc discharge synthesis is a new promising preparation technology for optical materials.
Supported by National Natural Science Foundation of China (Grant No. 10804015), the Scientific Research Foundation for Doctor
of Liaoning Province (Grant No. 20071095), and the Educational Committee Foundation of Liaoning Province (Grant No. 2008123) 相似文献
980.