全文获取类型
收费全文 | 2032篇 |
免费 | 547篇 |
国内免费 | 89篇 |
专业分类
化学 | 337篇 |
晶体学 | 11篇 |
力学 | 143篇 |
综合类 | 21篇 |
数学 | 82篇 |
物理学 | 2074篇 |
出版年
2024年 | 5篇 |
2023年 | 23篇 |
2022年 | 63篇 |
2021年 | 60篇 |
2020年 | 72篇 |
2019年 | 49篇 |
2018年 | 47篇 |
2017年 | 79篇 |
2016年 | 88篇 |
2015年 | 70篇 |
2014年 | 156篇 |
2013年 | 146篇 |
2012年 | 135篇 |
2011年 | 145篇 |
2010年 | 109篇 |
2009年 | 124篇 |
2008年 | 149篇 |
2007年 | 147篇 |
2006年 | 146篇 |
2005年 | 108篇 |
2004年 | 120篇 |
2003年 | 77篇 |
2002年 | 70篇 |
2001年 | 70篇 |
2000年 | 73篇 |
1999年 | 56篇 |
1998年 | 54篇 |
1997年 | 40篇 |
1996年 | 35篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2668条查询结果,搜索用时 109 毫秒
101.
102.
理论研究了在激光相位和啁啾调控共同影响下高次谐波光谱的变化。结果表明:当激光相位为0时,一阶啁啾调控使谐波能量延伸。二阶啁啾调控会呈现高强度谐波平台区。当激光相位为0.5π时,一阶啁啾调控可以获得连续平台区,但是强度较弱。在二阶啁啾调控下,谐波能量得到明显增大。通过谐波时频分析给出了不同激光波形下产生高次谐波光谱的原因。 相似文献
103.
A four-level double-ladder atomic system with two upper states coupled to the excited state by a standing-wave trigger field is explored to generate photonic bandgap (PBG) structure. With the assistance of spontaneously generated coherence (SGC) from the two decay pathways, we can obtain single or double fully developed PBG when the trigger field is far away from resonance or resonant. While in the absence of SGC, the atomic medium becomes strong absorptive to the probe field, and therefore the resulting PBGs are severely malformed or even cannot be opened up. Numerical results show that the PBG structure is originated from the third-order cross Kerr nonlinear modulation between the probe and trigger fields. This mechanism differs from the recent schemes based on linear modulation. 相似文献
104.
《Analytical letters》2012,45(10):1743-1756
Abstract Electrolytes were found to have an important influence on the cell constant in electrochemically modulated liquid chromatography. The dependence of cell constant on electrolyte type did not reflect any relation with regard to electrolyte conductivity values. However, electrolytic species of larger ionic sizes result in significantly lower cell constants, and vice versa. It was also found that the cell constant is exponentially dependent on electrolyte concentration, with higher electrolyte concentrations resulting in decreased cell constants. When a potential ramp is applied to the working electrode, a steep change in the potential of the working electrode towards the final potential takes place directly after the application of the potential ramp. The change in the potential of the working electrode then follows an exponential decay isotherm, which depends on both electrolyte type and concentration. 相似文献
105.
Nach Erläuterung der Modulationsüvbertragugsfunktion, einer wichtigen Kenngröβe eines szintigraphischen. Der Übertragungssystems, wird mit ihrer Hilfe ds Auflösungsvermögen von 3″ - und 5″ -Kollimator-Detektor-Systemen verglichen. Die Übertragungsfunktionen werden aus Linienverbreiterungsfunktionen ermittelt. Es wird der Verlauf der Modulationsübertragungs funktionen einzelner Kollimatoren der 3″ - und 5″-Systeme in Abhängigkeit vom Quellen-Kollimator-Abstand diskutiert. Ferner wird die λ/2-Regel benutzt, um Aussagen über die darstellbaren Detailgröβen zu machen, und schlieβlich wird die äquivalente Bandbreite für die einzelnen Modulationsübertragungsfunktionen angegeben. 相似文献
106.
Pierluigi Perrone Silvello Betti Giuseppe Giulio Rutigliano 《Fiber and Integrated Optics》2017,36(4-5):181-195
This article proposes a novel coherent multilevel modulation model that exploits polarization and phase of the field. This model is based on the possibility of coherent systems to use all the four degrees of freedom of the electromagnetic field. The proposed scheme is able, by applying a suitable twisting process to the optical fiber, to physically confine the polarization and the phase of the transmitted field within the phase sphere. In this way, with the same performances of existing systems, the receiver is considerably simplified because there is no longer need of birefringence tracking circuits. 相似文献
107.
Yoshiteru Amemiya Tomohiro Tokunaga Yuichiro Tanushi Shin Yokoyama 《Optical Review》2009,16(3):247-251
Electric-field drive optical modulators using a Si ring resonator were fabricated on silicon-on-insulator (SOI) wafers. The
fabricated resonators consisted of Si waveguides with width and thickness of 1.0 and 0.3 μm, respectively. In order to induce
the linear electro-optic (EO) effect in the Si core layer, the strain was applied by covering the layer with Si3N4 film (0.26 μm thick) deposited by low pressure chemical vapor deposition (LPCVD) at 750 °C. The vertical electric-field was
applied to the Si waveguide through the top and bottom cladding layers, and the optical output from the drop port at the resonance
wavelength was measured. At a wavelength of 1501.6 nm, the optical modulation of 33% was obtained at 200V (electric-field
at the silicon surface ∼3 × 105 V/cm, nearly the breakdown field). The resonance wavelength was shifted toward the short wavelength side by applying both
positive and negative voltages, this shift was explained by carrier concentration modulation. The linear EO effect in the
Si core layer was not observed, presumably because the strain in the Si core layer was too small. 相似文献
108.
Simon M. Vornholt Caroline G. Elliott Cameron M. Rice Dr. Samantha E. Russell Peter J. Kerr Daniel N. Rainer Michal Mazur Dr. Mark R. Warren Dr. Paul S. Wheatley Prof. Russell E. Morris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(33):8537-8546
The size of single crystals of the metal-organic framework CPO-27-Ni was incrementally increased through a series of modulated syntheses. A novel linker modulated synthesis using 2,5-dihydroxyterephthalic acid and the isomeric ligand 4,6-dihydroxyisophthalic acid yielded large single crystals of CPO-27-Ni (∼70 μm). All materials were shown to have high crystallinity and phase purity through powder X-ray diffraction, electron microscopy methods, thermogravimetry, and compositional analysis. For the first time single-crystal structure analyses were carried out on CPO-27-Ni. High BET surface areas and nitric oxide (NO) release efficiencies were recorded for all materials. Large single crystals of CPO-27-Ni showed a prolonged NO release and proved suitable for in situ single-crystal diffraction experiments to follow the NO adsorption. An efficient activation protocol was developed, leading to a dehydrated structure after just 4 h, which subsequently was NO-loaded, leading to a first NO loaded single-crystal structural model of CPO-27-Ni. 相似文献
109.
110.
基于Drude模型研究了异向介质的色散磁导率对调制不稳定性的影响. 结果表明,在反常色散情形,赝五阶非线性在异向介质的负折射区中增大了调制频谱的范围及增益值,这与常规正折射介质中出现的现象正好相反;自陡峭效应在异向介质中有可能为负值,但无论正负,也无论在正折射区还是负折射区,它都抑制调制不稳定性的产生;二阶非线性色散效应在正、负折射区中分别促进和抑制调制不稳定性的产生. 在正常色散情形,由于二阶非线性色散效应的作用,使本来在常规正折射介质中不可能出现的调制不稳定性现象也能出现,这一特性为在正常色散区形成孤 相似文献