全文获取类型
收费全文 | 4256篇 |
免费 | 1181篇 |
国内免费 | 442篇 |
专业分类
化学 | 551篇 |
晶体学 | 52篇 |
力学 | 758篇 |
综合类 | 67篇 |
数学 | 1261篇 |
物理学 | 3190篇 |
出版年
2024年 | 13篇 |
2023年 | 52篇 |
2022年 | 73篇 |
2021年 | 79篇 |
2020年 | 143篇 |
2019年 | 89篇 |
2018年 | 120篇 |
2017年 | 156篇 |
2016年 | 194篇 |
2015年 | 151篇 |
2014年 | 257篇 |
2013年 | 330篇 |
2012年 | 249篇 |
2011年 | 278篇 |
2010年 | 241篇 |
2009年 | 275篇 |
2008年 | 345篇 |
2007年 | 291篇 |
2006年 | 264篇 |
2005年 | 276篇 |
2004年 | 246篇 |
2003年 | 246篇 |
2002年 | 222篇 |
2001年 | 174篇 |
2000年 | 173篇 |
1999年 | 130篇 |
1998年 | 131篇 |
1997年 | 121篇 |
1996年 | 99篇 |
1995年 | 76篇 |
1994年 | 55篇 |
1993年 | 67篇 |
1992年 | 45篇 |
1991年 | 39篇 |
1990年 | 26篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 3篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1974年 | 2篇 |
1971年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有5879条查询结果,搜索用时 31 毫秒
91.
本文描述了利用KTP晶体和腔的基波输出镜构成非线性镜实现1.08μmNd:YAP激光器的被动锁模。实验表明,这种新的锁模技术比用染料作可饱和吸收体的被动锁模技术有很多突出的优点,具有很大的发展潜力。实验测得锁模时基波1.08μm输出2.4mJ,二次谐波0.54μm输出0.5mJ(同样条件下的静态输出为2.5mJ),基波脉冲的平均脉宽为40ps。 相似文献
92.
The wavelet and harmonic filtering method suggested by Zalevsky and Ouzieli is introduced in this paper and adopted in our volume holographic image recognition system. This composite filter combines several scaled versions of the cascaded wavelet and harmonic filter, obtaining high discrimination ability and wide dynamic range of rotation and scale deformations. Optical experiments are conducted to demonstrate the validity and practicability of the algorithm. To the best of our knowledge, this is the first report of using this algorithm in a volume holographic system. Moreover, the separate correlation approach proposed in this paper greatly simplifies the manufacturing process and reduces the cost of the system. 相似文献
93.
Infrared (IR)-induced second-harmonic generation in the chalcogenide glasses is observed. A phenomenological approach of IR picosecond non-linear optical (NLO) response in glass is developed for the middle IR spectral range (5–15 μm). The observed effect is explained within the framework of fifth-order NLO susceptibilities. A model that reproduces the basic characteristics of the experimental data, in which the optical non-linearities caused by photoinduced electron–phonon anharmonic interactions, is proposed. The role of the IR-induced phase matching conditions in the observed phenomenon is discussed. 相似文献
94.
95.
Torbjörn Kolsrud 《Journal of Theoretical Probability》1989,2(4):399-418
We derive explicit isomorphism formulas between weighted Dirichlet integrals for harmonic functions and boundary Dirichlet forms. Applications yield results on traces of Markov processes and convergence quasieverywhere of harmonic functions. 相似文献
96.
应用多尺度微扰理论到广义非简谐振子, 得到了一阶经典和量子微扰解. 特别是
我们的量子解在极限条件下能方便地转变为经典解, 并且坐标和动量算符的对易
关系的简化十分自然. 与Taylor级数解相比较, 无论是在经典还是在量子解
中频率移动都出现在各阶振动表达式中, 所以多尺度微扰解是弱耦合非简谐振动的较好解法. 相似文献
97.
Lourdes Callau Marta Giamberini Jos Antonio Reina Ana Mantecn 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):1877-1889
The synthesis of two vinyl‐terminated side‐chain liquid‐crystalline polyethers containing benzylideneaniline moieties as mesogenic cores was approached in two different ways: by chemically modifying poly(epichlorohydrin) with suitable mesogenic acids or by polymerizing analogous glycidyl ester or glycidyl ether derivatives. In all the conditions tested, the first approach led to materials in which the imine group was hydrolyzed. The second approach led to the desired polymers PG2a and PG2b , but only from the glycidyl ether derivatives and when the initiator was the system that combined polyiminophosphazene base t‐Bu‐P4 and 3,5‐di‐t‐butylphenol. These polymers were chemically characterized by IR and 1H and 13C NMR spectroscopies. The estimated degrees of polymerization ranged from 30 to 36. The liquid crystalline behavior of the synthesized polymers was studied by differential scanning calorimetry, polarized optical microscopy (POM) and X‐ray diffraction. Both polymers behave like liquid crystals and exhibited a single mesophase, which was recognized as a smectic C mesophase, probably with a bilayer arrangement, i.e., a smectic C2 mesophase. The crosslinking of both polymers was performed with dicumyl peroxide as initiator, which led to liquid crystalline thermosets. POM and X‐ray diffraction confirmed that the mesophase organization mantained on the crosslinked materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1877–1889, 2006 相似文献
98.
Uwe Bandelow Mindaugas Radziunas Andrei Vladimirov Bernd Hüttl Ronald Kaiser 《Optical and Quantum Electronics》2006,38(4-6):495-512
We study both theoretically and experimentally typical operation regimes of 40 GHz monolithic mode-locked lasers. The underlying
Traveling Wave Equation model reveals quantitative agreement for characteristics of the fundamental mode-locking as pulse
width and repetition frequency tuning, as well as qualitative agreement with the experiments for other dynamic regimes. Especially
the appearance of stable harmonic mode-locking at 80 GHz has been predicted theoretically and confirmed by measurements. Furthermore,
we derive and apply a simplified Delay-Differential-Equation model which guides us to a qualitative analysis of bifurcations
responsible for the appearance and the breakup of different mode-locking regimes. Higher harmonics of mode-locking are predicted
by this model as well. 相似文献
99.
Atsushi Kasue 《Potential Analysis》2006,24(2):137-194
We study spectral convergence of compact Riemannian manifolds or more generally certain Dirichlet spaces, obtaining some compactness
results on harmonic functions and harmonic maps.
Mathematics Subject Classifications (2000) 53C21, 58D17, 58J50.
Atsushi Kasue: Partly supported by the Grant-in-Aid for Scientific Research (B) No. 15340053 of the Japan Society for the
Promotion of Science. 相似文献
100.
Einstein field equations for static anisotropic spheres are solved and exact interior solutions obtained. This paper extends
earlier treatments to include anisotropic models which accommodate a wider variety of physically viable energy densities.
Two classes of solutions are possible. The first class contains the limiting caseμ,∝ r-2 for the energy density which arises in many astrophysical applications. In the second class the singularity at the centre
of the star is not present in the energy density. 相似文献