全文获取类型
收费全文 | 1849篇 |
免费 | 71篇 |
国内免费 | 14篇 |
专业分类
化学 | 1160篇 |
晶体学 | 17篇 |
力学 | 34篇 |
数学 | 184篇 |
物理学 | 539篇 |
出版年
2023年 | 19篇 |
2022年 | 48篇 |
2021年 | 49篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 53篇 |
2017年 | 47篇 |
2016年 | 78篇 |
2015年 | 37篇 |
2014年 | 62篇 |
2013年 | 162篇 |
2012年 | 89篇 |
2011年 | 97篇 |
2010年 | 77篇 |
2009年 | 73篇 |
2008年 | 79篇 |
2007年 | 70篇 |
2006年 | 69篇 |
2005年 | 64篇 |
2004年 | 80篇 |
2003年 | 46篇 |
2002年 | 40篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 12篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有1934条查询结果,搜索用时 421 毫秒
161.
Dulić D Pimenov A van der Marel D Broun DM Kamal S Hardy WN Tsvetkov AA Sutjaha IM Liang R Menovsky AA Loidl A Saxena SS 《Physical review letters》2001,86(18):4144-4147
We present microwave and infrared measurements on SmLa0.8Sr0.2CuO4-delta, which are direct evidence for the existence of a transverse optical plasma mode, observed as a peak in the c-axis optical conductivity. This mode appears as a consequence of the existence of two different intrinsic Josephson couplings between the CuO2 layers, one with a Sm2O2 block layer, and the other one with a (La,Sr)2O2-delta block layer. From the frequencies and the intensities of the collective modes we determine the value of the compressibility of the two dimensional electron fluid in the copper oxygen planes. 相似文献
162.
Mrinmay Pal Somnath Bandyopadhyay Palas Biswas Rimlee Debroy M. C. Paul Ranjan Sen Kamal Dasgupta S. K. Bhadra 《Optical and Quantum Electronics》2007,39(14):1231-1243
In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single
stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of
the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed
gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal
power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of
optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating
of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained
within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ±
0.5 dB gain-variation which is an important parameter in optical network system. 相似文献
163.
We present the calculation of envelope of boson and of both low-and high-mass fermion production at the end of inflation when
the coherently oscillating inflatons decay into bosons and fermions. We consider three different models of inflation and use
CWKB technique to calculate the envelope to understand the structure of resonance band formation. We observe that though low-mass
fermion production is not effective in preheating because of Pauli blocking, it is quite probable for high-mass fermion to
take part in pre-heating.
相似文献
164.
165.
Residual stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film-substrate system. The stress measurement instrument was tested for two different kinds of thin film, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrates deposited by RF magnetron sputtering. Residual stress developed in 500 nm thick CN thin films deposited at substrate temperatures in the range 50-550 °C was examined and it was found that stress in CN films decreased from 0.83 to 0.44 GPa compressive with increase of substrate temperature. Residual stress was found to be tensile (121 MPa) for Cu films of thickness 1500 nm deposited at room temperature. 相似文献
166.
In this paper, 10 Gbps optical soliton transmission link using in-line semiconductor optical amplifiers (SOAs) for already installed standard single mode fibers (SMF) at 1.3 μm wavelength has been reported. The pattern effect and the impact of chirp on pulse propagation after amplification have been investigated. The observations are based on modeling and simulation optical soliton transmission link. Optical soliton pulse transmission over distances of the order of several hundreds of kilometers has been shown with and without initial chirp. 相似文献
167.
Paramita Saha Chowdhury 《Journal of luminescence》2007,124(2):327-332
Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO2) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO2-capped nanoparticles. It is found that the average decay time 〈τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO2 and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO2, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency. 相似文献
168.
An experimental and computational investigation into the autoignition of methanol under high‐pressure and low‐to‐intermediate temperature conditions is conducted. The ignition delay results have been obtained using a heated rapid compression machine, over a pressure range of 7–30 bar, a temperature range of 850–1100 K, and an equivalence ratio range of 0.25–2.0. Using kinetic schemes recently reported in the literature for the combustion of methanol, the experimental results are compared to computationally obtained values. The kinetic schemes studied are found to significantly underpredict ignition delays for the conditions investigated. A sensitivity analysis of the computed results to reaction rate constants is also conducted. It is shown that the reaction of methanol with HO2 radical is critical to the predicted values of ignition delays under the current experimental conditions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 175–184, 2011 相似文献
169.
170.
Teruyuki Hakoda Muhammed Alamgir Zaman Chowdhury Akihiko Shimada Koichi Hirota 《Plasma Chemistry and Plasma Processing》2009,29(6):549-557
The decomposition of dimethyl sulfide (DMS) at initial concentrations of 4.5–18.0 ppmv in air was studied under electron-beam
(EB) irradiation. Doses to decompose 90% of input DMS were 2.5 kGy for 4.5 ppmv, 3.4 kGy for 10.6 ppmv, and 3.9 kGy for 18.0 ppmv.
HCOOH, (CH3)2SO, and trace CH3OH and (CH3)2SO2 were produced as irradiation products in addition to CO2 and CO. Application of an O3 decomposition catalyst to an irradiated sample gas led to an enhancement in the oxidation of DMS and its products into CO2 and the decomposition of O3. For 10.6 ppmv DMS/air, the mineralization ratio increased from 41% via only EB irradiation to 100% via the combination treatment
at 6.3 kGy. The yield of CO2 to COx increased from 5.3 to 87.6% by combination with catalytic oxidation. This combination treatment enables the irradiation energy
used to deodorize gas streams containing DMS to be reduced. 相似文献