全文获取类型
收费全文 | 1822篇 |
免费 | 130篇 |
国内免费 | 153篇 |
专业分类
化学 | 794篇 |
晶体学 | 7篇 |
力学 | 106篇 |
综合类 | 7篇 |
数学 | 337篇 |
物理学 | 854篇 |
出版年
2024年 | 4篇 |
2023年 | 55篇 |
2022年 | 37篇 |
2021年 | 39篇 |
2020年 | 40篇 |
2019年 | 34篇 |
2018年 | 43篇 |
2017年 | 54篇 |
2016年 | 62篇 |
2015年 | 47篇 |
2014年 | 79篇 |
2013年 | 113篇 |
2012年 | 103篇 |
2011年 | 132篇 |
2010年 | 118篇 |
2009年 | 137篇 |
2008年 | 148篇 |
2007年 | 140篇 |
2006年 | 96篇 |
2005年 | 98篇 |
2004年 | 90篇 |
2003年 | 55篇 |
2002年 | 58篇 |
2001年 | 41篇 |
2000年 | 44篇 |
1999年 | 33篇 |
1998年 | 45篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2105条查询结果,搜索用时 750 毫秒
101.
Danko R. Jocic 《Proceedings of the American Mathematical Society》1999,127(8):2303-2314
For generalized normal derivations, acting on the space of all bounded Hilbert space operators, the following integral representation formulas hold:
and
whenever is a Hilbert-Schmidt class operator and is a Lipschitz class function on Applying this formula, we extend the Fuglede-Putnam theorem concerning commutativity modulo Hilbert-Schmidt class, as well as trace inequalities for covariance matrices of Muir and Wong. Some new monotone matrix functions and norm inequalities are also derived.
102.
Allowing for the interfacial potential distribution it can be shown that the apparent faradaic electron number, napp, of ad-layers of chemically modified electrodes and the surface redox valency, n, relating to the slope of the peak potential/pH response [Huck (2002) J Solid State Electrochem 6:534] are at least identical, having the same thermodynamic origin. napp is calculated from the cyclovoltammetric (CV) peak areas above the interpolated base line. At
for proton-coupled surface redox reactions, the influence of the potential drop of the diffuse double layer disappears because the capacitor of the corresponding equivalent circuit becomes shortened by proton transfer, whereby the otherwise non-integer napp or n values now approach the integer electron numbers, n, of the Nernst equation.
相似文献
Horst HuckEmail: |
103.
An open volume, high isolation, radio frequency surface coil system for pulsed magnetic resonance 总被引:1,自引:1,他引:0
Curto CA Placidi G Sotgiu A Alecci M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(2):353-358
We present an open volume, high isolation, RF system suitable for pulsed NMR and EPR spectrometers with reduced dead time. It comprises a set of three RF surface coils disposed with mutually parallel RF fields and a double-channel receiver (RX). Theoretical and experimental results obtained with a prototype operating at about 100 MHz are reported. Each surface RF coil (diameter 5.5 cm) was tuned to f0 = 100.00 ± 0.01 MHz when isolated. Because of the mutual coupling and the geometry of the RF coils, only two resonances at f1 = 97.94 MHz and f2 = 101.85 MHz were observed. We show they are associated with two different RF field spatial distributions. In continuous mode (CW) operation the isolation between the TX coil and one of the RX coils (single-channel) was about −10 dB. By setting the double-channel RF assembly in subtraction mode the isolation values at f1 or f2 could be optimised to about −75 dB. Following a TX RF pulse (5 μs duration) an exponential decay with time constant of about 600 ns was observed. The isolation with single-channel RX coil was about −11 dB and it increased to about −47 dB with the double-channel RX in subtraction mode. Similar results were obtained with the RF pulse frequency selected to f2 and also with shorter (500 ns) RF pulses. The above geometrical parameters and operating frequency of the RF assembly were selected as a model for potential applications in solid state NMR and in free radical EPR spectroscopy and imaging. 相似文献
104.
Random coil phosphorus chemical shift of deoxyribonucleic acids 总被引:1,自引:0,他引:1
Random coil phosphorus chemical shift has been studied using 16 17-nucleotide DNA sequences. Due to the presence of residual base stacking in these sequences, the temperature and sequence effects were investigated at 50 and 55 degrees C. The phosphorus chemical shifts of random coil DNA sequences have been found to be independent of temperature. Sequence effect analysis shows that the phosphorus chemical shift of a nucleotide in a random coil DNA sequence depends on both its 5'- and 3'-nearest neighbors. A trimer model has been used to establish the random coil 31P chemical shift prediction protocol which shows an accuracy of 0.02 ppm. 相似文献
105.
Edoardo Ballico Changho Keem Seungsuk Park 《Proceedings of the American Mathematical Society》2004,132(11):3153-3158
Let be a smooth projective algebraic curve of genus and an integer with . For all integers we prove the existence of a double covering with a smooth curve of genus and the existence of a degree morphism that does not factor through . By the Castelnuovo-Severi inequality, the result is sharp (except perhaps the bound ).
106.
A four dimensional summability matrix is stronger than convergence in the Pringsheim sense if it sums a divergent double sequence. Presented in this paper are sufficient conditions on a four dimensional matrix transformation which ensure that the summability matrix is stronger than convergence in the Pringsheim sense. Also other sufficient conditions will be presented to ensure the failure of inclusion between two summability matrices.AMS Subject Classification (2000): Primary 40B05. 相似文献
107.
Ezaki T 《Micron (Oxford, England : 1993)》2000,31(6):639-649
It is well known that the major artifact induced by formaldehyde fixation is the masking of tissue antigens due to cross-linking of protein amino acid residues. Recently many antigen retrieval techniques have been devised to unmask the hidden antigen epitopes and recover immunoreactivity. In this study, some practical problems of two common unmasking techniques, i.e. heat-induced epitope retrieval and enzyme digestion have been reviewed in immunostaining of proliferating cell nuclear antigen (PCNA) on formaldehyde-fixed paraffin-embedded sections. As the heating conditions became more severe, false-positive staining and/or nonspecific background staining occurred. Based on the principle of protein inactivation/denaturation and the possible mechanisms of antigen retrieval, it has been suggested that the antigen retrieval itself can also denature proteins in tissues, just as many other protein inactivation processes. Thus, the total magnitude of protein conformational change caused by the overall unmasking procedure is in practice crucial. To prove this hypothesis and to overcome such undesirable drawbacks after antigen retrieval, a new combination technique of a mild heating condition (microwaved at 80°C for 15–20 min) and pepsin digestion was devised. This technique led to a strong specific immunoreactivity of PCNA, without any undesirable false positive or background staining. The procedure was also adapted for double immunostaining of PCNA together with -actin, bromodeoxyuridine, keratin, type IV collagen and vimentin. 相似文献
108.
109.
110.
Most of the recent literature dealing with the modeling of financial assets assumes that the underlying dynamics of equity prices follow a jump process or a Lévy process. This is done to incorporate rare or extreme events not captured by Gaussian models. Of those financial models proposed, the most interesting include the CGMY, KoBoL and FMLS. All of these capture some of the most important characteristics of the dynamics of stock prices. In this article we show that for these particular Lévy processes, the prices of financial derivatives, such as European-style options, satisfy a fractional partial differential equation (FPDE). As an application, we use numerical techniques to price exotic options, in particular barrier options, by solving the corresponding FPDEs derived. 相似文献