全文获取类型
收费全文 | 291398篇 |
免费 | 2578篇 |
国内免费 | 771篇 |
专业分类
化学 | 157838篇 |
晶体学 | 4281篇 |
力学 | 12517篇 |
综合类 | 9篇 |
数学 | 33786篇 |
物理学 | 86316篇 |
出版年
2020年 | 2348篇 |
2019年 | 2601篇 |
2018年 | 3339篇 |
2017年 | 3302篇 |
2016年 | 4936篇 |
2015年 | 3078篇 |
2014年 | 4748篇 |
2013年 | 11960篇 |
2012年 | 9143篇 |
2011年 | 11266篇 |
2010年 | 7781篇 |
2009年 | 7578篇 |
2008年 | 10486篇 |
2007年 | 10732篇 |
2006年 | 10067篇 |
2005年 | 9229篇 |
2004年 | 8422篇 |
2003年 | 7586篇 |
2002年 | 7441篇 |
2001年 | 7664篇 |
2000年 | 5943篇 |
1999年 | 4612篇 |
1998年 | 4142篇 |
1997年 | 4140篇 |
1996年 | 3931篇 |
1995年 | 3552篇 |
1994年 | 3752篇 |
1993年 | 3444篇 |
1992年 | 3891篇 |
1991年 | 3902篇 |
1990年 | 3794篇 |
1989年 | 3697篇 |
1988年 | 3813篇 |
1987年 | 3660篇 |
1986年 | 3478篇 |
1985年 | 4652篇 |
1984年 | 4961篇 |
1983年 | 4091篇 |
1982年 | 4353篇 |
1981年 | 4249篇 |
1980年 | 4218篇 |
1979年 | 4187篇 |
1978年 | 4496篇 |
1977年 | 4385篇 |
1976年 | 4441篇 |
1975年 | 4097篇 |
1974年 | 4129篇 |
1973年 | 4291篇 |
1972年 | 2983篇 |
1971年 | 2461篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
D. N. Karimov E. A. Krivandina Z. I. Zhmurova B. P. Sobolev V. A. Bezhanov S. P. Chernov G. M. Shapochkin 《Crystallography Reports》2006,51(6):1009-1015
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region. 相似文献
62.
63.
The semi‐iterative method (SIM) is applied to the hyper‐power (HP) iteration, and necessary and sufficient conditions are given for the convergence of the semi‐iterative–hyper‐power (SIM–HP) iteration. The root convergence rate is computed for both the HP and SIM–HP methods, and the quotient convergence rate is given for the HP iteration. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
64.
A mixed problem is considered for a system of partial differential equations modeling the process of adsorption dynamics. An existence and uniqueness theorem is proved for this problem, and the solution properties are investigated. The inverse problem is posed, involving the determination of the system coefficient given additional information about the solution. A uniqueness theorem is proved for the solution of the inverse problem.__________Translated from Prikladnaya Matematika i Informatika, No. 16, pp. 5 – 14, 2004. 相似文献
65.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
66.
Molecular electroactive monolayers have been produced from vinylferrocene (VFC) via light-assisted surface anchoring to H-terminated n- and p-Si(1 0 0) wafers prepared via wet chemistry, in a controlled atmosphere. The resulting Si-C bound hybrids have been characterized by means of XPS and AFM. Their performance as semiconductor functionalized electrodes and their surface composition have been followed by combining electrochemical and XPS measurements on the same samples, before and after use in an electrochemical cell. White-light photoactivated anchoring at short (1 h) exposure times has resulted in a mild route, with a very limited impact on the initial quality of the silicon substrate. In fact, the functionalized Si surface results negligibly oxidized, and the C/Fe atomic ratio is close to the value expected for the pure molecular species. The VFC/Si hybrids can be described as (η5-C5H5)Fe2+(η5-C5H4)-CH2-CH2-Si species, on the basis of XPS results. Electrochemical methods have been applied in order to investigate the role played by a robust, covalent Si-C anchoring mode towards substrate-molecule electronic communication, a crucial issue for a perspective development of molecular electronics devices. The response found from cyclic voltammograms for p-Si(1 0 0) functionalized electrodes, run in the dark and under illumination, has shown that the electron transfer is not limited by the number of charge carriers, confirming the occurrence of electron transfer via the Si valence band. The hybrids have shown a noticeable electrochemical stability and reversibility under cyclic voltammetry (cv), and the trend in peak current intensity vs. the scan rate was linear. The molecule-Si bond is preserved even after thousands of voltammetric cycles, although the surface coverage, evaluated from cv and XPS, decreases in the same sequence. An increasingly larger surface concentration of Fe3+ at the expenses of Fe2+ redox centers has been found at increasing number of cv’s, experimentally associated with the growth of silicon oxide. Surface SiO− groups from deprotonated silanol termination, induced by the electrochemical treatments, are proposed as the associated counterions for the Fe3+ species. They could be responsible for the observed decrease in the electron transfer rate constant with electrode ageing. 相似文献
67.
We describe in detail fundamental properties of continuity modules of various orders in the spaces L
p of functions defined on a finite segment. We establish some general estimates of seminorms in terms of continuity modules with the best known constants. An example of application of these results to the best approximations is considered. Bibliography: 32 titles. 相似文献
68.
Porous road surfaces offer an effective means of reducing the generation and propagation of noise from road traffic. However, the porosity of these surfaces can deteriorate over time, leading to a reduction in their noise reducing properties. Efficient methods are therefore required for monitoring this performance. Existing techniques for performing in-situ measurements of acoustic absorption are unsuitable for use within the traffic stream. Static measurements using time domain Maximum Length Sequence (MLS) based techniques have been demonstrated to offer advantages over traditional techniques, presenting the opportunity for measurements under dynamic conditions. This paper describes the design of a system for carrying out dynamic MLS-based measurements. Results are presented which demonstrate that stable dynamic measurements can be carried out at speeds of up to 30 km/h. 相似文献
69.
H. Moers H. Klewe-Nebenius G. Pfennig und H. J. Ache 《Fresenius' Journal of Analytical Chemistry》1987,329(2-3):361-366
Summary The adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS. 相似文献
70.