全文获取类型
收费全文 | 6526篇 |
免费 | 110篇 |
国内免费 | 477篇 |
专业分类
化学 | 2662篇 |
晶体学 | 67篇 |
力学 | 394篇 |
综合类 | 10篇 |
数学 | 654篇 |
物理学 | 3326篇 |
出版年
2024年 | 8篇 |
2023年 | 98篇 |
2022年 | 69篇 |
2021年 | 55篇 |
2020年 | 83篇 |
2019年 | 96篇 |
2018年 | 74篇 |
2017年 | 112篇 |
2016年 | 132篇 |
2015年 | 119篇 |
2014年 | 182篇 |
2013年 | 392篇 |
2012年 | 369篇 |
2011年 | 439篇 |
2010年 | 364篇 |
2009年 | 451篇 |
2008年 | 362篇 |
2007年 | 463篇 |
2006年 | 372篇 |
2005年 | 308篇 |
2004年 | 291篇 |
2003年 | 265篇 |
2002年 | 203篇 |
2001年 | 203篇 |
2000年 | 174篇 |
1999年 | 189篇 |
1998年 | 145篇 |
1997年 | 155篇 |
1996年 | 131篇 |
1995年 | 112篇 |
1994年 | 103篇 |
1993年 | 98篇 |
1992年 | 77篇 |
1991年 | 81篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有7113条查询结果,搜索用时 31 毫秒
61.
Scanning probe microscopy characterization of gold-chemisorbed poplar plastocyanin mutants 总被引:1,自引:0,他引:1
L. Andolfi B. Bonanni G. W. Canters M. Ph. Verbeet S. Cannistraro 《Surface science》2003,530(3):181-194
Two poplar plastocyanin mutants adsorbed onto gold electrodes have been characterized at single molecule level by scanning probe microscopy. Immobilization of the two redox metalloprotein mutants on Au(1 1 1) surface was achieved by either a disulphide bridge (PCSS) or a single thiol (PCSH), both the anchoring groups having been introduced by site-directed mutagenesis. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) analysis gives evidence of a stable and robust binding of both mutants to gold. The lateral dimensions, as estimated by STM, and the height above the gold substrate, as evaluated by AFM, of the two mutants well agree with crystallographic sizes. A narrower height distribution is observed for PCSS compared to PCSH, corresponding to a more homogeneous orientation of the former mutant adsorbed onto gold. Major differences between the mutants are observed by electrochemical STM. In particular, the image contrast of adsorbed PCSS is affected by tuning the external electrochemical potential to the redox levels of the mutant, consistent with some involvement of copper active site in the tunneling process. On the contrary, no contrast variation is observed in electrochemical STM of adsorbed PCSH. Moreover, scanning tunneling spectroscopy experiments reveal asymmetric I–V characteristics for single PCSS proteins, reminiscent of a rectifying-like behaviour, whereas an almost symmetric I–V relation is observed for PCSH. 相似文献
62.
Rainer Koch Ralf Becker 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):423-435
After reviewing the presently available quadrature schemes for the discrete ordinates method, the accuracy of different schemes is analyzed and evaluated. It is shown from a comprehensive error analysis that the moment conditions have to satisfied not only for the principal coordinates directions, as it is mostly carried out, but for any arbitrary test direction. Among the schemes with approximately 50 discrete ordinates the DCT-020-2468 quadrature was found to give the best accuracy. The highest accuracy among all schemes is achieved by the LC-11 quadrature which requires 96 discrete ordinates. This scheme is rarely used up to date and deserves more attention for high accuracy predictions. 相似文献
63.
Conventionally, surface roughness is predominantly determined through the use of stylus instruments. However, there are certain limitations involved in the method, particularly when a test specimen, such as a silicon wafer, has a smooth mirror-like surface. Hence, it is necessary to explore alternative non-contact techniques. Light scattering has recently been gaining popularity as an optical technique to provide prompt and precise inspection of surface roughness. In this paper, the total integrated scattering (TIS) model is modified to retrieve parameters on surface micro-topography through light scattering. The applicability of the proposed modified TIS model is studied and compared with an atomic force microscope. Experimental results obtained show that the proposed technique is highly accurate for measuring surface roughness in the nanometer range. 相似文献
64.
Michaël Lejeune Andrea Valsesia Martin Kormunda Pascal Colpo François Rossi 《Surface science》2005,583(1):L142
In this work, chemically and topographically nanopatterned surfaces were produced by a top-down processing approach for biosensing devices. The nanopatterning was the result of the combination of plasma polymerisation (pp) of biofunctional materials and colloidal lithography techniques. The morphological and chemical properties induced by the plasma deposition-etching treatment were characterised by optical method combining ellipsometry and Fourier Transform Infrared spectroscopy studies. This method supported by atomic force microscopy measurements, allowed the full optical characterization of each step of the top-down process. The optical characterization of the end-up nanopatterned samples demonstrated that the chosen process is able to produce well-defined nanostructured surfaces with controlled chemical and morphological properties. 相似文献
65.
66.
Banach frames and atomic decompositions are sequences that have basis-like properties but which need not be bases. In particular, they allow elements of a Banach space to be written as linear combinations of the frame or atomic decomposition elements in a stable manner. In this paper we prove several functional — analytic properties of these decompositions, and show how these properties apply to Gabor and wavelet systems. We first prove that frames and atomic decompositions are stable under small perturbations. This is inspired by corresponding classical perturbation results for bases, including the Paley — Wiener basis stability criteria and the perturbation theorem el kato. We introduce new and weaker conditions which ensure the desired stability. We then prove quality properties of atomic decompositions and consider some consequences for Hilbert frames. Finally, we demonstrate how our results apply in the practical case of Gabor systems in weighted L2 spaces. Such systems can form atomic decompositions for L2w(IR), but cannot form Hilbert frames but L2w(IR) unless the weight is trivial. 相似文献
67.
LIKAITAI HEYINNIAN XIANGYIMIN 《高校应用数学学报(英文版)》1994,9(1):11-30
This paper deals with the inertial manifold and the approximate inertial manifold concepts of the Navier-Stokes equations with nonhomogeneous boundary conditions and inertial algorithm. Furtheremore, we provide the error estimates of the approximate solutions of the Navier-Stokes Equations. 相似文献
68.
D.A. Mazón-Montijo M. Quevedo-López H.N. Alshareef R. Ramírez-Bon 《Applied Surface Science》2007,254(2):499-505
We study the initial growth stages of CdS thin films deposited by an ammonia-free chemical bath deposition process. This ammonia-free process is more environmentally benign because it reduces potential ammonia release to the environment due to its high volatility. Instead of ammonia, sodium citrate was used as the complexing agent. We used atomic force microscopy (AFM), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS) to investigate the morphological and chemical modifications at the substrate surface during the first initial stages of the CdS deposition process. Additionally, X-ray diffraction (XRD) and optical transmission spectroscopy measurements were carried out to compliment the study. XPS results show that the first nucleation centers are composed by Cd(OH)2 which agglomerate in patterns of bands, as demonstrated by AFM results. It is also observed that the conversion to CdS (by anionic exchange) of the first nucleus begins before the substrate surface is completely covered by a homogenous film. 相似文献
69.
We report on first experiments combining quasi-digital highly selective etching and atomic force microscopy (AFM) to examine the interior interfaces of semiconductor heterostructures. Lattice matched (GaIn)As/InP heterostructures grown by metalorganic vapour-phase epitaxy (MOVPE) are taken as a model system to check the capabilities of this new method. Standard selective etchants for different material systems have been optimized in selectivity and etch rate to achieve a quasi-digital etching behaviour. In this way, the real structure of interior interfaces can be determined by AFM. We find a significant difference between the surface of the heterostructure and the interior interfaces. 相似文献
70.
本文考察了以微波等离子体炬(MPT)为光源,电热钽丝环进样时,溶液中共存元素对发射信号的影响。 相似文献