全文获取类型
收费全文 | 4434篇 |
免费 | 749篇 |
国内免费 | 430篇 |
专业分类
化学 | 1084篇 |
晶体学 | 60篇 |
力学 | 339篇 |
综合类 | 66篇 |
数学 | 1800篇 |
物理学 | 2264篇 |
出版年
2024年 | 13篇 |
2023年 | 53篇 |
2022年 | 100篇 |
2021年 | 114篇 |
2020年 | 129篇 |
2019年 | 135篇 |
2018年 | 143篇 |
2017年 | 174篇 |
2016年 | 185篇 |
2015年 | 142篇 |
2014年 | 236篇 |
2013年 | 415篇 |
2012年 | 229篇 |
2011年 | 230篇 |
2010年 | 239篇 |
2009年 | 237篇 |
2008年 | 281篇 |
2007年 | 280篇 |
2006年 | 257篇 |
2005年 | 267篇 |
2004年 | 218篇 |
2003年 | 192篇 |
2002年 | 192篇 |
2001年 | 147篇 |
2000年 | 152篇 |
1999年 | 130篇 |
1998年 | 121篇 |
1997年 | 94篇 |
1996年 | 95篇 |
1995年 | 70篇 |
1994年 | 68篇 |
1993年 | 39篇 |
1992年 | 37篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有5613条查询结果,搜索用时 15 毫秒
11.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
12.
13.
High temperature GaN layers have been grown on Si (1 1 1) substrate by metalorganic vapor phase epitaxy (MOVPE). AlN was used as a buffer layer and studied as a function of thickness and growth temperature. The growth was monitored by in situ laser reflectometry. High resolution X-ray diffraction (HRXRD) revealed that optimized monocrystalline GaN was obtained for a 40 nm AlN grown at 1080 °C. This is in good agreement with the results of morphological study by scanning electron microscopy (SEM) and also confirmed by atomic force microscopy (AFM) observations. The best morphology of AlN with columnar structure and lower rms surface roughness is greatly advantageous to the coalescence of the GaN epilayer. Symmetric and asymmetric GaN reflections were combined for twist and stress measurements in monocrystalline GaN. It was found that mosaicity and biaxial tensile stress are still high in 1.7 μm GaN. Curvature radius measurement was also done and correlated to the cracks observations over the GaN surface. 相似文献
14.
R. Jayakumar Y.‐S. Lee S. Nanjundan 《Journal of polymer science. Part A, Polymer chemistry》2003,41(18):2865-2878
The calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HEEP)2 and poly(ethylene glycol) (PEG300 or PEG400) with di‐n‐butyltin dilaurate as a catalyst. A series of calcium‐containing PUEs of different compositions were synthesized with Ca(HEEP)2/PEG300 (or PEG400)/diisocyanate (HMDI or TDI) molar ratios of 2:2:4, 3:1:4, and 1:3:4 so that the coating properties of the PUEs could be studied. Blank PUEs without calcium‐containing ionic diols were also prepared by the reaction of PEG300 or PEG400 with HMDI or TDI. The PUEs were well characterized by Fourier transform infrared, 1H and 13C NMR, solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as top coats on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, such as the tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2865–2878, 2003 相似文献
15.
Letters in Mathematical Physics - 相似文献
16.
选用新方法合成了2-碘—N-甲基苯磺酰胺,通过^1H NMR,^13C NMR,^13C DEPT NMR(Distortionless Enhancement by Polarization Transfer NMR)和MS确证的其结构。 相似文献
17.
M. I. Gil' 《Proceedings of the American Mathematical Society》2003,131(12):3737-3746
A linear operator in a separable Hilbert space is called a quasinormal one if it is a sum of a normal operator and a compact one. In the paper, bounds for the spectrum of quasinormal operators are established. In addition, the lower estimate for the spectral radius is derived. Under some restrictions, that estimate improves the well-known results. Applications to integral operators and matrices are discussed. Our results are new even in the finite-dimensional case.
18.
Comment on “A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map“
Comment on a recent paper on Commun. Theor. Phys. (Beijing, China) 38 (2002) pp. 523-528. 相似文献
19.
Wuqing Ning 《Journal of Mathematical Analysis and Applications》2007,327(2):1396-1419
In this paper, an algorithm is established to reconstruct an eigenvalue problem from the given data satisfying certain conditions. These conditions are proved to be not only necessary but also sufficient for the given data to coincide with the spectral characteristics corresponding to the reconstructed eigenvalue problem. 相似文献
20.
Laurent Bruneau 《Reports on Mathematical Physics》2004,54(2):169-199
We study Pauli-Fierz Hamiltonians-self-adjoint operators describing a small quantum system interacting with a bosonic field. Using quadratic form techniques, we extend the results of Dereziński-Gérard and Gérard about the self-adjointness, the location of the essential spectrum and the existence of a ground state to a large class of Pauli-Fierz Hamiltonians. 相似文献