全文获取类型
收费全文 | 569篇 |
免费 | 27篇 |
国内免费 | 10篇 |
专业分类
化学 | 248篇 |
力学 | 23篇 |
数学 | 21篇 |
物理学 | 314篇 |
出版年
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 22篇 |
2014年 | 36篇 |
2013年 | 33篇 |
2012年 | 29篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 33篇 |
2008年 | 54篇 |
2007年 | 43篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 29篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有606条查询结果,搜索用时 15 毫秒
521.
Wolfgang Vautz Bertram Bödeker Jörg Ingo Baumbach Sabine Bader Michael Westhoff Thorsten Perl 《International Journal for Ion Mobility Spectrometry》2009,12(2):47-57
Ion mobility spectrometry is increasingly in demand for medical applications and its potential for implementation in food
quality and safety or process control suggest rising use of instruments in this field as well. All those samples are commonly
extremely complex and mostly humid mixtures. Therefore, pre-separation techniques have to be applied. As ion mobility spectrometers
with gas-chromatographic pre-separation acquire a huge amount of data, effective data processing and automated evaluation
by comparison of detected peak pattern with data bases have to be utilised. This requires accurate on-line calibration of
the instruments to guarantee reproducible results, in particular with respect to identification of an analyte by determination
of its ion mobility and retention time. To reduce environmental and instrumental influence, the reduced ion mobility is used.
It is derived from the drift time normalised to electric field, length of the drift region and to temperature and pressure
of the drift gas (traditional method). All data required for this normalisation are afflicted with a particular error and
thus leading to a deviation of the calculated ion mobility value. Furthermore, this traditional method enables a calculation
of the reduced ion mobility only after the measurement. To avoid those errors and to enable on-line calibration of ion mobility,
an instrument specific factor is implemented generally representing all relevant variables. This factor can be determined
from an initial measurement of few spectra and can thereafter be applied on the following measurement. The application of
this approach obtained reproducible reduced ion mobility values for positive and negative ions over a broad drift time range
and for common variation of ambient conditions as well for varying instrument conditions such as electric fields respectively
drift times and in different drift gases. Moreover, the reduced ion mobility is available already during the measurements
with a significantly higher reliability and accuracy which was increased to a factor of 5 compared to the traditional ion
mobility determination and enables an on-line identification of analytes for the first time. 相似文献
522.
523.
Evan D. Hudspeth Danielle Cleveland Kathleen L. Batchler Phuong A. Nguyen Tracey L. Feaser Lauren E. Quattrochi 《光谱学快报》2013,46(1):99-115
We have evaluated a small portable Raman instrument on loan from B&W Tek, Inc., and have determined that it can successfully be used in the classroom both as a visual aid for teaching the fundamentals of Raman spectroscopy and for a variety of undergraduate experiments as a normal component of an instrumental analysis class. Having portable Raman instrumentation would allow the instructor to demonstrate the principles of Raman spectroscopy, as well as the concepts of calibration curves, blank subtraction, detection limits, and regression analysis. Both qualitative and quantitative types of experiments were done for solid Tylenol tablets, aqueous solutions of isopropyl alcohol, dimethyl sulfoxide, methanol, and ethanol, and gaseous CO2 and N2O4. Additionally, surface‐enhanced resonance Raman spectra of Rhodamine 6G were obtained using a chloride ion–activated silver colloid. Spectra from the B&W Tek, Inc., instrument were comparable to literature Raman spectra. 相似文献
524.
Danielle Cleveland Matthew Carlson Evan D. Hudspeth Lauren E. Quattrochi Kathleen L. Batchler Shrimati A. Balram 《光谱学快报》2013,46(6):903-924
Raman spectroscopy has steadily gained popularity as a powerful tool in both the analytical lab and the undergraduate classroom. The technique is attractive because it allows for rapid, nondestructive qualitative or quantitative analyses of many analytes with little or no sample preparation requirements. The introduction of less expensive, smaller, and more powerful diode laser excitation sources and the recent availability of rugged, red‐sensitive, charge‐coupled device–based miniature modular spectrometers has prompted the integration of Raman spectroscopy into the undergraduate curriculum. We have evaluated the analytical utility of a small, portable Raman instrument for the qualitative and quantitative analyses of two “real” samples. The experiments in this paper were designed to be used as a laboratory component for undergraduate education and include the quantification of ethanol in consumer alcoholic beverages and the qualitative identification of marine diesel fuels that had been spilled on surface waters. In the case of the liquor samples, the ethanol concentration in colorless, odorless alcoholic beverages could be determined very rapidly, but colored and heavily scented liquors proved more difficult and required pretreatment with activated carbon to remove fluorescence that masked the Raman signal. Similarly, a high‐intensity fluorescence background was observed to mask characteristic Raman bands of the diesel fuels. Some reduction in the intensity of the fluorescence was observed after carbon pretreatment of the fuels. The set of undergraduate experiments described in this paper treat the concepts of quantitative and qualitative analysis using portable instrumentation, instrumental calibration by the standard addition and external curve methods, and method development for the analysis of real consumer and environmental samples. 相似文献
525.
Statistical evaluation of an analytical GC/MS method for the determination of long chain fatty acids
In-depth evaluation of an analytical method to detect and quantify long chain fatty acids (C8-C16) at trace level concentrations (25-1000 μg/l) is presented. The method requires derivatization of the acids with methanolic boron trifluoride, separation, and detection by gas chromatography-mass spectrometry. The calibration experiments passed all the tested performance criteria such as linearity, homoscedasticity, and ruggedness. The detection limits and related quantities were computed by applying the method detection limit, and the calibration line approximation. The values obtained by applying the latter approach were more reliable and consistent with the actual statistical theory of detection decisions and yielded the following concentrations: C8, 87.6 μg/l; C10, 45.2 μg/l; C11, 39.9 μg/l; C12, 37.7 μg/l; C14, 41.4 μg/l and C16, 40.6 μg/l. Two different gas-liquid chromatographic columns were tested and similar results achieved, which shows the ruggedness of the method. 相似文献
526.
The performance of twelve laboratories with previously established proficiency in the determination of the mineral oil content in a fresh water sediment is described. The summation parameter total petrol hydrocarbon (TPH) is defined according to ISO 16703:2004 with regard to the sample preparation to be applied, the flame ionisation detection (FID) and the boiling range of C10–C40 to be integrated. Comprehensive tests of homogeneity and stability have been carried out on the candidate material using appropriate models. The outcome of the study served as the basis for the certification of the candidate reference material as ERM-CC015a. The certified mass fraction is 1,820±130mgkg−1and traceability was established by using an appropriate calibration standard certified for the mass fraction of C10–C40. The interlaboratory scatter of measurement results in this exercise can largely be explained by the variability of the individual calibrations based on this common calibration standard. 相似文献
527.
Here we investigate whether the deformation observed in an experiment in which the porcine circumflex coronary artery is subjected
to inflation at constant length included in the class,
,
,
. We find that this is not the case and discuss its implications in the study of the mechanics of this artery. Moreover, we
identify and quantify the uncertainty in the value of the invariants of the left Cauchy–Green tensor inferred from the 2D
motion of markers affixed to the surface of the test specimen, and suggest that 3D tracking of markers is needed due to inherent
bending and twisting induced by pressurization in vitro. 相似文献
528.
K. Hugenberg 《Progress in Particle and Nuclear Physics》2010,64(2):288-290
The KArlsruher TRItium Neutrino experiment KATRIN aims to determine the mass of the electron antineutrino with a sensitivity of 0.2 eV/c2 on m(νe) at 90% confidence level by measuring the kinematics of the tritium beta decay with a spectrometer of MAC-E filter-type. To investigate the properties of the spectrometer, electron sources with special properties are needed. A pulsed UV LED photoelectron source with angular selectivity has been developed for this purpose. The principle has been successfully tested during measurements at the spectrometer of the Mainz neutrino mass experiment. 相似文献
529.
《Analytical letters》2012,45(16):2640-2651
An ensemble multivariate calibration algorithm, termed as MISEPLS, is proposed. In MISEPLS, when constructing a member model, the variables that have mutual information (MI) with the response less than a threshold are eliminated; thus, the modeling can be performed in a subset of original variables and some problems arising from multi-collinearity can be avoided. Through experiments on three near-infrared (NIR) spectroscopic datasets from the food industry, MISEPLS proves to be superior to the single-model full-spectrum PLS and MIPLS (PLS combined with MI-induced variable selection). MISEPLS can improve the accuracy and robustness of a calibration model, without increasing its complexity. 相似文献
530.
Jesús Villa María AraizaDaniel Alaniz Rumen IvanovMarvin Ortiz 《Optics and Lasers in Engineering》2012,50(2):256-261
In this work we present a phase to (x,y,z)-coordinates transformation method for the calibration of a fringe projection profilometer. Our technique is divided in two parts: (1) phase to z transformation (for axial calibration) based on the typical polynomial fitting which uses a flat plane placed at several z positions to measure the phase of the projected fringes. (2) Phase to x and y transformation (for transverse calibration) based on the use of a crossed gratings pattern and a Fourier phase measurement method to determine x and y coordinates at several z positions. As will be shown the use of the crossed gratings pattern and the Fourier phase measurement method for transverse calibration is advantageous in several aspects: an unique image can give us x and y information at once. It provides x and y coordinates at each pixel in the image avoiding the use of interpolation methods. We present some experimental results and explain the viability of the proposed technique. 相似文献