全文获取类型
收费全文 | 424篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
化学 | 309篇 |
力学 | 30篇 |
综合类 | 2篇 |
数学 | 3篇 |
物理学 | 92篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 60篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 21篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1968年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有436条查询结果,搜索用时 15 毫秒
91.
D.R. Symes J. Osterhoff R. Fustlin M. Maurer A.C. Bernstein A.S. Moore E.T. Gumbrell A.D. Edens R.A. Smith T. Ditmire 《High Energy Density Physics》2007,3(3-4):353-357
To study hydrodynamic behavior on thin shell high Mach number blast waves, experiments have been performed in which spatially tailored shock waves have been launched in a gas of clusters using an intense 35 fs laser pulse. The target medium was first modified by destroying clusters in specific locations using a spatially modulated laser focus. Under subsequent intense laser irradiation, the efficient absorption properties of the remaining clustered regions compared to those regions with no clusters led to a pattern of hot and cold plasma resulting in a cylindrical blast wave with a periodic modulation imprinted on the shock front. This technique may provide a method for studying thin shell instabilities in strongly radiative blast waves. 相似文献
92.
Junhua Tong Liang Zhao Huihui Li Chenglin Wu Xu Han Jiang Wang Hong Liu 《Tetrahedron》2018,74(27):3755-3760
Asymmetric construction of β,β-diaryl substituted glycine bearing two contiguous chiral centers remains a significant challenge. Herein, the application of the para-quinone methides (p-QMs) and Ni(II)- complex of glycine via 1,6-conjugate addition to achieve asymmetric synthesis of β,β-diaryl substituted glycine has been explored successfully. This protocol features operational simplicity, high diastereoselectivity, and recyclable chiral ligand, which provides a versatile approach to the synthesis of highly enantiopure β,β-diaryl substituted glycine. 相似文献
93.
R. Taylor 《Journal of Molecular Structure》1981,73(1):125-136
The room temperature distribution of O-H ? O hydrogen bond geometries has been predicted by a Monte Carlo calculation, with an empirical potential energy function for the hydrogen bond. The results are compared with a recent survey of hydrogen bonds in carbohydrate crystal structures. The calculated and observed distributions of the O-H ? O angle have mean values of 165.5° and 167.1° respectively. Both the theoretical and experimental results suggest that short O ? H hydrogen bonds tend to be more linear than long O ? H bonds. The distribution of hydrogen bonding within the lone pair plane of the acceptor oxygen atom is predicted to be broader than the distribution perpendicular to this plane, in agreement with the experimental data. The empirical hydrogen bond function, in conjunction with the molecular mechanics program MMI, has also been used to predict the geometries of inter-residue hydrogen bonds in five disaccharides. The O ? H distances and O-H ? O angles are reproduced with r.m.s. deviations of 0.06 Å and 9° respectively. 相似文献
94.
The molecular structure of allyl silane has been studied by gas-phase electron diffraction. The experimental radial distribution curve has only four prominent peaks, resulting in serious resolution problems in the structure determination. A single conformer whose dimensions resemble those of related molecules fits the diffraction data. The torsion angle φsiccc is102 ± 1°, measured from the conformation having Si-C and CC eclipsed. 相似文献
95.
In the U.S., all clinical laboratory testing is regulated by the Clinical Laboratory Improvement Amendments (CLIA) (). The CLIA link test quality and adherence to a body of testing regulations intended to ensure accurate, reliable, and timely patient test results. The goal of the CLIA legislation was to ensure a minimum, fundamental level of quality. In the context of “NEXUS,” quality must “go beyond getting the ‘right’ answer on the ‘right’ patient that can be interpreted against ‘right’ reference values. CLIA regulations with specific minimum, performance requirements, or safeguards, are designed to prevent testing errors. The US Institute of Medicine found that testing processes fail as a result of human error, lack of documentation, and lack of test management. In the latest (2004) interpretations of CLIA regulations, the minimum quality control requirement continues to be analyzing at least two external, liquid quality control materials per test per day. In 1995, we proposed that the responsibility for achieving quality test results shifts from the sole purview of the laboratory director to an “alliance” of laboratory professionals, manufacturers, and regulators. The EQC (equivalent quality control) concept as proposed is a positive step in achieving this alliance. With the obvious lack of scientific and statistical robustness, EQC falls far short of ensuring quality. Achieving the “NEXUS Vision” for quality laboratory testing will not come solely from laboratory professionals. The NEXUS is about how to ensure the full-quality assessment of the testing process – pre-analytical, analytical, and post-analytical.Presented at the 10th Conference Quality in the Spotlight, March 2005, Antwerp, Belgium. 相似文献
96.
Magnus Holmgren Thomas Svensson Erland Johnson Klas Johansson 《Accreditation and quality assurance》2005,10(5):208-213
This paper presents the experiences of calculation and reporting uncertainty of measurement in fatigue testing. Six Nordic laboratories performed fatigue tests on steel specimens. The laboratories also reported their results concerning uncertainty of measurement and how they calculated it. The results show large differences in the way the uncertainties of measurement were calculated and reported. No laboratory included the most significant uncertainty source, bending stress (due to misalignment of the testing machine, incorrect specimens and/or incorrectly mounted specimens), when calculating the uncertainty of measurement. Several laboratories did not calculate the uncertainty of measurement in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM) [1]. 相似文献
97.
《Comptes Rendus Chimie》2019,22(8):574-584
Microwave-assisted extraction (MAE) at atmospheric pressure has been demonstrated as an efficient technology for the extraction of polymeric hemicelluloses from spruce sawdust. This technology was shown to be more efficient than conventional extraction. MAE leads to a high solubilization of wood and a selective extraction of hemicellulose polymers with high molecular weights. To optimize MAE, different treatment powers (125–573 W) of presoaked spruce sawdust in water and 1 M sodium hydroxide solution for a period of 60 min were tested. The yield of hemicellulose extraction increased with the microwave power in both mediums, but with a clear advantage for presoaked samples in basic medium. The characterization of extracted hemicelluloses has shown high extraction selectivity depending on the medium of impregnation of sawdust before MAE: High-molecular-mass acetylated galactoglucomannans (Mw ∼ 41 kDa) were isolated after presoaking in water and higher molecular mass arabinoglucoronoxylans (Mw ∼ 66 kDa) in basic medium. 相似文献
98.
1H NMR spectra of 1,3-butadieneiron tricarbonyl oriented in a nematic liquid crystal solvent have been analysed and used to derive the structure of the proton skeleton, which is found to be non-planar. The distance of the anti protons from the plane defined by the remaining four protons is 0.77 ± 0.06 ±. 相似文献
99.
Continuous-wave and Fourier transform NMR absorption spectra have been recorded for pure γ-AIOOH at room temperature and 130K. The well-resolved doublet lineshape shows that there are proton pairs (intrapair separation Å), the presence of which has not previously been recognized. A structural model based on the occupation of two sites consistent with the space group Cmcm is proposed. 相似文献
100.
Irina Lutinger 《Accreditation and quality assurance》2002,7(11):494-497
As laboratories continue to downsize, commercialize and become more businesslike in today’s managed care environment, their
present and future success will greatly depend on the efficiency and flexibility of their laboratory information system (LIS).
Today, LIS is a primary tool for managing business and communication. Laboratories that hope to remain competitive in today’s
dynamic health care must continue to implement new and innovative approaches with their LISs.
Received: 26 July 2002 Accepted: 6 August 2002
Presented at the European Conference on Quality in the Spotlight in Medical Laboratories, 7–9 October 2001, Antwerp, Belgium 相似文献