全文获取类型
收费全文 | 5117篇 |
免费 | 763篇 |
国内免费 | 707篇 |
专业分类
化学 | 3618篇 |
晶体学 | 88篇 |
力学 | 323篇 |
综合类 | 107篇 |
数学 | 495篇 |
物理学 | 1956篇 |
出版年
2024年 | 22篇 |
2023年 | 100篇 |
2022年 | 220篇 |
2021年 | 213篇 |
2020年 | 206篇 |
2019年 | 232篇 |
2018年 | 198篇 |
2017年 | 196篇 |
2016年 | 241篇 |
2015年 | 273篇 |
2014年 | 288篇 |
2013年 | 363篇 |
2012年 | 453篇 |
2011年 | 420篇 |
2010年 | 318篇 |
2009年 | 336篇 |
2008年 | 324篇 |
2007年 | 283篇 |
2006年 | 254篇 |
2005年 | 247篇 |
2004年 | 170篇 |
2003年 | 143篇 |
2002年 | 139篇 |
2001年 | 152篇 |
2000年 | 111篇 |
1999年 | 92篇 |
1998年 | 85篇 |
1997年 | 67篇 |
1996年 | 56篇 |
1995年 | 63篇 |
1994年 | 44篇 |
1993年 | 40篇 |
1992年 | 34篇 |
1991年 | 31篇 |
1990年 | 52篇 |
1989年 | 25篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 21篇 |
1985年 | 16篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有6587条查询结果,搜索用时 15 毫秒
211.
Delevoye L Trébosc J Gan Z Montagne L Amoureux JP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(1):94-99
A new decoupling composite pulse sequence is proposed to remove the broadening on spin S=1/2 magic-angle spinning (MAS) spectra arising from the scalar coupling with a quadrupolar nucleus I. It is illustrated on the (31)P spectrum of an aluminophosphate, AlPO(4)-14, which is broadened by the presence of (27)Al/(31)P scalar couplings. The multiple-pulse (MP) sequence has the advantage over the continuous wave (CW) irradiation to efficiently annul the scalar dephasing without reintroducing the dipolar interaction. The MP decoupling sequence is first described in a rotor-synchronised version (RS-MP) where one parameter only needs to be adjusted. It clearly avoids the dipolar recoupling in order to achieve a better resolution than using the CW sequence. In a second improved version, the MP sequence is experimentally studied in the vicinity of the perfect rotor-synchronised conditions. The linewidth at half maximum (FWHM) of 65 Hz using (27)Al CW decoupling decreases to 48 Hz with RS-MP decoupling and to 30 Hz with rotor-asynchronised MP (RA-MP) decoupling. The main phenomena are explained using both experimental results and numerical simulations. 相似文献
212.
Trebosc J Hu B Amoureux JP Gan Z 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(2):220-227
We present several new methods that allow to obtain through-space 2D HETCOR spectra between spin-1/2 and half-integer quadrupolar nuclei in the solid state. These methods use the rotary-resonance concept to create hetero-nuclear coherences through the dipolar interaction instead of scalar coupling into the HMQC and refocused INEPT experiments for spin n/2 (n>1). In opposite to those based on the cross-polarization transfer to quadrupolar nuclei, the methods are very robust and easy to set-up. 相似文献
213.
The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in
leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25–50°C), various concentrations of NaCl (0–250 mM), methyl
viologen (MV, 0–25 μM), SDS (0–1.0%) and NaHSO3 (0–80 μM). Fluorescence emission spectrum of leaves at wavelength regions of 500–800 nm was monitored by excitation at 436 nm.
The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at
436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant
(MV), surfactant (SDS) and simulated SO2 (NaHSO3) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence
spectrum and emission intensity of F685 and F731 depended on the individual treatment. Increase in temperature and concentration of NaHSO3 enhanced fluorescence intensity mainly at F685, while an increase in MV concentration led to a decrease at both F685 and F731. On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the
negative correlation between polarization and fluorescence intensity was found with NaHSO3 treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to
changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed
response to various treatments were discussed. 相似文献
214.
Elastic-inertial focusing has attracted increasing interest in recent years due to the three-dimensional (3D) single-train focusing ability it offers. However, multi-train focusing, instead of single-train focusing, was observed in viscoelastic fluids with low elasticity as a result of the competition between inertia effect and viscoelasticity effect. To address this issue, we employed the secondary flow to facilitate single-train elastic-inertial focusing in low elasticity viscoelastic fluids. A three-section contraction-expansion channel was designed to induce the secondary flow to pinch the multiplex focusing trains into a single one exactly at the channel centerline. After demonstrating the focusing process and mechanism in our device, we systematically explored and discussed the effects of particle diameter, operational flow rate, polymer concentration, and channel dimension on particle focusing performances. Our device enables single-train focusing of particles in viscoelastic fluids with low elasticity, and offers advantages of planar single-layer structure, and sheathless, external-field free operation. 相似文献
215.
Xing Chen Dr. Guoyun Meng Guanming Liao Dr. Florian Rauch Dr. Jiang He Dr. Alexandra Friedrich Prof. Dr. Todd B. Marder Dr. Nan Wang Dr. Pangkuan Chen Prof. Dr. Suning Wang Dr. Xiaodong Yin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(20):6274-6282
A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m−2. These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability. 相似文献
216.
217.
218.
219.
220.
Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification 下载免费PDF全文
Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992,optical parametric chirped pulse amplification(OPCPA)became the most promising method for the amplification of broadband optical pulses.In the meantime,we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers.The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level.Meanwhile,the output pulse duration based on optical parametric amplification has entered the range of fewoptical-cycle field.In this paper,we overview the basic principles,trends in development,and current state of the ultrashort and laser systems based on OPCPA,respectively. 相似文献