全文获取类型
收费全文 | 262篇 |
免费 | 251篇 |
国内免费 | 33篇 |
专业分类
化学 | 29篇 |
晶体学 | 1篇 |
数学 | 28篇 |
物理学 | 488篇 |
出版年
2024年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 3篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 14篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 28篇 |
2005年 | 33篇 |
2004年 | 48篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 21篇 |
2000年 | 34篇 |
1999年 | 29篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有546条查询结果,搜索用时 15 毫秒
1.
高效液相色谱-串联质谱法同时测定食品中五种黄色化工染料 总被引:5,自引:0,他引:5
采用高效液相色谱-串联质谱法(HPLC-MS/MS)建立了食品中非法添加的碱性橙、碱性嫩黄、酸性橙I、酸性橙II和酸性黄36这5种黄色工业染料的定量定性分析方法。使用Agilent ODS C18分离柱(50 mm×2.0 mm, 1.8 μm),以5 mmol/L乙酸铵水溶液(0.1%甲酸)-乙腈(3:2, v/v)为流动相,流速为0.3 mL/min。采用电喷雾离子化源,以多反应监测(MRM)方式分别在正、负离子模式下进行检测。在最佳检测条件下,得到了较宽的线性范围和较低的定量检出限。碱性橙和碱性嫩黄的线性范围均为5.0~80.0 mg/L;酸性橙I、酸性橙II及酸性黄36的线性范围均为10.0~160.0 μg/L。食品中碱性橙、碱性嫩黄、酸性橙I、酸性橙II及酸性黄36的定量限分别为20、20、40、40、40 ng/g。该方法重现性较好,保留时间和峰面积的相对标准偏差分别不大于0.50%和2.14%。本研究还测定了鸡肉、豆制品和黄鱼中添加的5种化工染料,回收率在79.8%~95.2%之间,结果令人满意。 相似文献
2.
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
3.
Laser wakefield accelerators(LWFAs)are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators.It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones.The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators.To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams.A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled.Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA,as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs. 相似文献
4.
A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated.A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier.After the amplified pulses pass through the LBO crystal,the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA).The 850-nm chirped signal light gain from the stretcher is 1.5×10 4 in the first-stage OPA while it is 120 in the second-stage OPA.The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8×10 6. 相似文献
5.
Surface-enhanced resonance Raman scattering (SERRS) of
Rhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied.
Based on the great enhancement of the Raman signal and the quench of the
fluorescence, the SERRS spectra of R6G were recorded for the samples of dye
colloidal solution with different concentrations. Spectral inhomogeneity
behaviours from single molecules in the dried sample films were observed with
complementary evidences, such as spectral polarization, spectral diffusion,
intensity fluctuation of vibrational lines and even ``breathing' of the
molecules. Sequential spectra observed from a liquid sample with an average of
0.3 dye molecules in the probed volume exhibited the expected Poisson
distribution for actually measuring 0, 1 or 2 molecules. Difference between
the SERRS spectra of R6G excited by linearly and circularly polarized light
were experimentally measured. 相似文献
6.
Study on the interaction of intense femtosecond laser pulses with nanometre-sized hydrogen clusters 下载免费PDF全文
The interaction of intense femtosecond laser pulses with hydrogen clusters
has been experimentally studied. The hydrogen clusters were produced from
expansion of high-pressure hydrogen gas (backed up to 8\tm106Pa) into vacuum
through a conical nozzle cryogenically cooled by liquid nitrogen. The
average size of hydrogen clusters was estimated by Rayleigh scattering
measurement and the maximum proton energy of up to 4.2keV has been obtained
from the Coulomb explosion of hydrogen clusters under 2×1016 W/cm2 laser irradiation. Dependence of the maximum proton energy on cluster size and laser intensity was
investigated, indicating the correlation between the laser intensity and the
cluster size. The maximum proton energy is found to be directly proportional
to the laser intensity, which is consistent with the theoretical prediction. 相似文献
7.
8.
高度有序的二氧化钛纳米管阵列的制备及其光催化活性的研究 总被引:1,自引:0,他引:1
采用电化学阳极氧化法在钛表面构筑了一种结构有序、微米级的TiO2纳米管阵列膜层. 考察了制备电压、氧化时间、溶液搅拌等实验参数对TiO2纳米管阵列形貌和尺寸的影响. 应用SEM和XRD对膜层的形貌和晶型进行了分析和表征, 并通过TiO2纳米管阵列膜对甲基橙的光催化降解, 研究了TiO2纳米管阵列膜层结构与光催化活性的关系. 结果表明: 阳极电压和溶液搅拌对制备TiO2纳米管阵列的结构起到关键的作用. 控制20 V电压制备的TiO2纳米管阵列膜, 管长达2.6~3.3 μm, 经500 ℃热处理后具有最高的光催化活性, 其光催化性能明显优于一般的TiO2纳米颗粒膜. 相似文献
9.
Accurate determination of the absolute phase and temporal-pulse phase of few-cycle laser pulses 下载免费PDF全文
A Fourier analysis method is used to accurately determine not
only the absolute phase but also the temporal-pulse phase of an
isolated few-cycle (chirped) laser pulse. This method is
independent of the pulse shape and can fully characterize the
light wave even though only a few samples per optical cycle are
available. It paves the way for investigating the absolute
phase-dependent extreme nonlinear optics, and the evolutions of
the absolute phase and the temporal-pulse phase of few-cycle
laser pulses. 相似文献
10.
Characteristics of ultrafast K line hard x—ray source from femtosecond terawatt laser—produced plasma 下载免费PDF全文
Theoretical studies and analytical scalings were carried out to find the optimized laser parameters and target conditions so that ultrashort hard x-ray pulses and high x-ray power could be achieved.The dependence of laser intensity and wavelength on the yield of K-shell x-ray emission was studied.We propose an optimal design for a foil target for producing high-yield hard x-ray pulses of customizing duration. 相似文献