全文获取类型
收费全文 | 686篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 496篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 67篇 |
物理学 | 133篇 |
出版年
2023年 | 9篇 |
2022年 | 21篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 56篇 |
2012年 | 48篇 |
2011年 | 53篇 |
2010年 | 32篇 |
2009年 | 30篇 |
2008年 | 40篇 |
2007年 | 33篇 |
2006年 | 39篇 |
2005年 | 34篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有718条查询结果,搜索用时 0 毫秒
661.
B. Muralidhara Rao B. Narayana Biju Mathew K. Subrahmanya Bhat 《Mikrochimica acta》1995,118(1-2):63-68
A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes. 相似文献
662.
663.
Mathew Kallumadil Masaru Tada Masanori Abe Quentin A. Pankhurst 《Journal of magnetism and magnetic materials》2009,321(10):1509-1513
Commercial nanoparticles supplied by Chemicell, Micromod and Bayer-Schering were characterised with regard to their nanocrystalline diameter, hydrodynamic diameter, total iron content and relative ferrous iron content. Additionally, calorimetric measurements were taken using a 900 kHz AC magnetic field of amplitude 5.66 kA/m. It was found that those samples containing relatively high (>18%) ferrous content generated a substantially smaller (12% on average) intrinsic loss power (ILP) than those samples with a lower ferrous content. Two nominally identical Chemicell samples that differed only in their production date showed significantly different ILPs, attributed to a variation in batch-to-batch crystallite sizes. The highest ILP values in the cohort, ca. 3.1 nHm2/kg, were achieved for particles with hydrodynamic diameters of ca. 70 nm and nanocrystalline diameters of ca. 12 nm. These compare favourably with most samples prepared in academic laboratories, although they are not as high as the ca. 23.4 nHm2/kg reported for naturally occurring bacterial magnetosomes. 相似文献
664.
Mathew W.C. Robinson 《Tetrahedron letters》2007,48(27):4727-4731
Mesoporous aluminosilicates are efficient heterogeneous catalysts for both the formation and hydrolysis of a range of acetals under mild conditions and in short reaction times. 相似文献
665.
Stuart W. Prescott Mathew J. Ballard Robert G. Gilbert 《Journal of polymer science. Part A, Polymer chemistry》2005,43(5):1076-1089
A method is presented by which the time‐dependent average termination rate coefficient in an emulsion polymerization may be calculated as an appropriate average of the chain‐length‐dependent termination rate coefficients. The method takes advantage of the fact that the overall termination rate is dominated by terminations between rapidly moving short radicals and much slower long ones. This termination rate coefficient is suitable for use in the Smith–Ewart equations describing the compartmentalization of radicals in an emulsion polymerization. Rate data in emulsion polymerizations can be quantitatively interpreted if the kinetics fall into one of two categories: zero–one (showing compartmentalization; intraparticle termination is not rate‐determining) or pseudo‐bulk (no compartmentalization; intraparticle termination is rate‐determining). The new method can be used to interpret rate data for systems falling between these categories and also can be used to find termination rate coefficients from Monte Carlo simulations of termination kinetics. The latter is especially useful for predicting and understanding kinetics in controlled radical polymerizations in disperse media. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1076–1089, 2005 相似文献
666.
Mathew Perring Ned B Bowden 《Langmuir : the ACS journal of surfaces and colloids》2008,24(18):10480-10487
The first well-defined organic monolayers assembled on polydicyclopentadiene is reported. Commercial grade dicyclopentadiene was polymerized with the Grubbs' second-generation catalyst in a fume hood under ambient conditions at very low monomer to catalyst loadings of 20 000 to 1. This simple method resulted in a polymer that was a hard solid and appeared slightly yellow. Brief exposures of a few seconds of this polymer to Br 2 lead to a surface with approximately half of the olefins brominated as shown by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-infrared (ATR-IR) spectroscopy. The ATR-IR spectroscopy was carried out with the polymer in contact with a Ge hemisphere housed in a GATR accessory from Harrick. This brominated polydicyclopentadiene was immersed in DMF with 4-(trifluoromethyl)benzylamine to assemble a monolayer. The amines displaced Br on the surface to form a monolayer that exposed a CF 3 group on the surface. The surface was extensively studied by XPS using the method described by Tougaard to find the distribution of F within the surface layer. The ratio for the peak area, Ap, to the background height, B, measured 30 eV below the peak maximum was 109.8 eV. This value clearly indicated that F was found only at the surface and was not found within the polymer. A surface coverage of 1.37 amines per nm (2) was estimated and indicated that the monolayer was 28% as dense as a similar monolayer assembled from thiols on gold. Finally, a simple method to pattern these monolayers using soft lithography is described. This work is critically important because it reports the first monolayers on a relatively new and emerging polymer that has many desirable physical characteristics such as high hardness, chemical stability, and ease of forming different shapes. 相似文献
667.
Michael Augustine Sunny Mathew Vincent Mathew 《International Journal of Infrared and Millimeter Waves》2008,29(5):534-544
This paper studies electromagnetic wave propagation in hybrid structures consisting of ferrite and superconducting films.
Dispersion relations for transverse electric mode of propagation are derived. Numerical results are presented for two specific
structures viz. a ferrite/superconductor structure and a ferrite/superconductor/ferrite structure and dependence of propagation
on various structural parameters and frequency are determined. The non-reciprocal nature of propagation is also established. 相似文献
668.
Stereoselective synthesis of highly functionalized tetrahydrofurans via the 1,3-dipolar cycloaddition reaction of acyclic carbonyl ylides to activated alkenes is described. 相似文献
669.
One of the difficulties in analyzing eigenvalue problems that arise in connection with integrable systems is that they are
frequently non-self-adjoint, making it difficult to determine where the spectrum lies. In this paper, we consider the problem
of locating and counting the discrete eigenvalues associated with the Faddeev-Takhtajan eigenvalue problem, for which the
sine-Gordon equation is the isospectral flow. In particular we show that for potentials having either zero topological charge
or topological charge ± 1, and satisfying certain monotonicity conditions, the point spectrum lies on the unit circle and
is simple. Furthermore, we give an exact count of the number of eigenvalues. This result is an analog of that of Klaus and
Shaw for the Zakharov-Shabat eigenvalue problem. We also relate our results, as well as those of Klaus and Shaw, to the Krein
stability theory for J-unitary matrices. In particular we show that the eigenvalue problem associated to the sine-Gordon equation has a J-unitary structure, and under the above conditions the point eigenvalues have a definite Krein signature, and are thus simple
and lie on the unit circle. 相似文献
670.
Hema Tresa Varghese C. Yohannan Panicker V.S. Madhavan Samuel Mathew Jarmila Vinsova Christian Van Alsenoy 《Journal of Raman spectroscopy : JRS》2009,40(9):1211-1223
FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighbouring oxygen atom. The simultaneous IR and Raman activations of the CO stretching mode give the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with similar reported structures. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of CO bond and increases the double bond character of the C N bonds. The first hyperpolarizability, predicted infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non‐linear optics. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献