全文获取类型
收费全文 | 449篇 |
免费 | 77篇 |
国内免费 | 9篇 |
专业分类
化学 | 84篇 |
晶体学 | 2篇 |
力学 | 12篇 |
综合类 | 1篇 |
数学 | 3篇 |
物理学 | 433篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 12篇 |
2009年 | 61篇 |
2008年 | 56篇 |
2007年 | 45篇 |
2006年 | 41篇 |
2005年 | 36篇 |
2004年 | 3篇 |
2003年 | 28篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 33篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有535条查询结果,搜索用时 15 毫秒
91.
CO和NO吸附或两者竞争吸附在Pt/Al2O3,Re/Al2O3和Pt-Re/Al2O3催化剂上的红外光谱可以给出Pt和Re的表面结构信息.本文研究的催化剂为低金属载量的Pt/Al2O3,Re/Al2O3和工业型Pt-Re/Al2O3,其中Pt含量0.22%,Re含量0.43%(质量分数).实验结果表明,用NO与CO双分子竞争吸附的红外光谱实验方法可分别表征还原态Pt-Re/Al2O3重整催化剂上Pt表面和Re表面,并视需要可对Pt表面和Re表面进行半定量分析.在还原态工业型Pt-Re/Al2O3重整催化剂表面上,没有明显迹象表明有Pt-Re合金形成. 相似文献
92.
本文介绍了催化加氢制备4-氨基二苯胺反应液的反相高效液相色谱分析的新方法。探讨了流动相组成对原料,溶剂和产物分离的影响;日内和日间的各3次测定,其相对标准偏差均≤1.70%,4-氨基二苯胺的回收率为97.8%~103.7%。 相似文献
93.
Alexander I. Vodchits Valery P. Kozich Valentin A. Orlovich 《Optics Communications》2006,260(1):307-310
Optical parametric amplification of multi-frequency seed pulses generated in a mixture of compressed hydrogen and methane by stimulated Raman scattering of 1 ps, 1 kHz laser pulses at 395.8 nm has been studied. Efficient generation of spectrally narrow ultrashort pulses with a spatial distribution close to the Gaussian profile of the pump beam was obtained in the visible and near infrared ranges. 相似文献
94.
The content and the three dimensional distribution of impurities play an important role in the production process of high
purity rhenium powder (99.99% purity grade) and for its further use as alloying and coating agent in high temperature applications.
In this paper the characterization of raw Re granulate, Re powder, cleaned by heat treatment, Re coatings, produced by most
common preparation methods (PVD and VPS) and PM Re by means of SIMS is presented. The analysis of the three dimensional distribution
of trace elements is performed by 3D SIMS. The quantification of carbon, which was not possible with other analytical techniques
as a result of the high volatility of Re2O7 until now, has been carried out by SIMS depth profile analysis. It is discussed if internal standards, produced by introduction
of defined amounts of carbon soot to the Re powder lead to useful results. 相似文献
95.
Simultaneous determination of ginsenoside Rg1, Re and notoginsenoside R1 in human plasma by LC‐MS/MS and its application in a pharmacokinetic study in Chinese volunteers 下载免费PDF全文
Xiqian Zhang Rujun Ma Xiaojuan Liu Xuehua Jiang Ling Wang 《Biomedical chromatography : BMC》2016,30(12):1915-1921
A rapid and sensitive liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method has been developed and validated for simultaneous quantification of ginsenosides Rg1, Re and notoginsenoside R1 in human plasma. Chromatography was performed on Capcell Pak C18 MG II column using a binary gradient using mobile phase A (5 mm ammonium formate solution) and B (methanol, containing 5 mm ammonium formate) at a flow rate of 0.3 mL/min. The entire chromatographic run time was 3.2 min. Quantification was achieved using multiple reaction monitoring in positive mode using API 3000. This method was validated in terms of specificity, linearity, precision, accuracy, matrix effect and stability. The calibration curves were linear in the concentration range of 0.020–5.00 ng/mL for ginsenosides Rg1, Re and notoginsenoside R1. The lower limit of quantification (LLOQ) of this method was 0.020 ng/mL. The intra‐run and inter‐run precision values were within 12.31% for ginsenoside Rg1, 14.13% for ginsenoside Re and 11.46% for notoginsenoside R1 at their LLOQ levels. The samples were stable under all tested conditions. This method was successfully applied to study the pharmacokinetics of ginsenoside Rg1 and notoginsenoside R1 in 24 healthy volunteers following oral administration of 200 mg Sanqi Tongshu Enteric‐Pellets Capsule. 相似文献
96.
T. Hornung R. Meier D. Zeidler K.-L. Kompa D. Proch M. Motzkus 《Applied physics. B, Lasers and optics》2000,71(3):277-284
This paper reports two pump–probe experiments in sodium where dynamically tailored ultrashort pulses from a Ti:Sapphire-pumped
optical parametric amplifier were employed. The first study focuses on the one-photon Na(3s→3p) transition to derive sensitive
criteria which judge the performance of a frequency-domain pulse shaper using a spatial light modulator. On the basis of the
interpretation, follow-up experiments are suggested to test their cogency. The second experiment uses coherent quantum control
by placing an appropriate phase distribution on the incident beam to enhance or cancel the transition probability in the nonresonant
two-photon process Na(3s→→5s). Ignorant of the “ideal” phase function, an evolutionary algorithm which uses a feedback derived
from the experiment performs the optimization and produces the desired bright or dark pulses within a few minutes. Attention
is given to the role of resonant 3s→3p transitions excited by the spectral wings of the pump pulse. Different parametrizations
of the phase distribution have been examined. Two of these produced solutions which had not previously been predicted by theory
still meet the objective of the experiment. The study represents the first successful application of a feedback-organized
self-learning algorithm to the design of dark pulses.
Received: 3 November 1999 / Published online: 5 July 2000 相似文献
97.
Hydroxylamine synthesis by oxygen insertion into ReNH2 bond via Baeyer–Villiger oxidation: a Theoretical study 下载免费PDF全文
A novel scheme has been proposed by computational methods (B3LYP and CCSD(T)) to produce hydroxylamine under normal experimental conditions using [O3Re‐(NH2)] and H2O2 under basic conditions. This particular reaction may proceed similar to Baeyer–Villiger oxidation and μ‐peroxo type pathways to insert oxygen into the Re?NH2 bond to yield NH2OH; nevertheless, Baeyer–Villiger type oxidation is seems to be more viable. The calculated energy barriers further revealed that the introduction of different solvent medium does not affect significantly the energies of intermediates and transition state molecules. The calculated Gibbs free energies show that this reaction is perhaps viable experimentally to produce NH2OH from the our choice of reagents. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
98.
An actively mode-locked fiber ring laser based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is demonstrated to operate stably with a simple configuration. By forward injecting an easily-generated external pulse train, the mode-locked fiber laser can generate an optical-pulse sequence with pulsewidth about 6 ps and average output power about 7.9 mW. The output pulses show an ultra-low RMS jitter about 70.7 fs measured by a RF spectrum analyzer. The use of the proposed forward-injection configuration can realize the repetition-rate tunability from 1 to 15 GHz for the generated optical-pulse sequences. By employing a wavelength-tunable optical band-pass filter in the laser cavity, the operation wavelength of the designed SOA-based actively mode-locked fiber laser can be tuned continuously in a wide span between 1528 and 1565 nm. The parameters of external-injection optical pulses are studied experimentally to optimize the mode-locked fiber laser. 相似文献
99.
By analyzing the potential energy surface, the shape phase diagram and the energy spectrum of the nucleus in U(5) symmetry in the IBM, we propose that the U(5) symmetry with parameters (A+B)<0 may be a model to describe the rotation driven vibrational to axially rotational phase transition along the yrast line. With such a model, we have described successfully the observed rotation driven shape phase transition along the yrast line and proposed some other empirical evidences. 相似文献
100.
A.O. Evans E.S. Paul A.J. Boston H.J. Chantler C.J. Chiara M. Devlin A.M. Fletcher D.B. Fossan D.R. LaFosse G.J. Lane I.Y. Lee A.O. Macchiavelli P.J. Nolan D.G. Sarantites J.M. Sears A.T. Semple J.F. Smith K. Starosta C. Vaman A.V. Afanasjev I. Ragnarsson 《Physics letters. [Part B]》2006
Three strongly coupled sequences have been established in 110,112Te up to high spins. They are interpreted in terms of deformed structures built on proton 1-particle–1-hole excitations that reach termination at I∼40?. This is the first observation of smooth terminating dipole structures in this mass region. Lifetime measurements have allowed the extraction of experimental B(M1;I→I−1) and B(E2;I→I−2) reduced transition rates for one of the dipole bands in 110Te. The results support the deformed interpretation. 相似文献