全文获取类型
收费全文 | 687篇 |
免费 | 77篇 |
国内免费 | 10篇 |
专业分类
化学 | 552篇 |
晶体学 | 2篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 36篇 |
物理学 | 159篇 |
出版年
2023年 | 9篇 |
2022年 | 32篇 |
2021年 | 33篇 |
2020年 | 45篇 |
2019年 | 37篇 |
2018年 | 18篇 |
2017年 | 34篇 |
2016年 | 31篇 |
2015年 | 34篇 |
2014年 | 36篇 |
2013年 | 47篇 |
2012年 | 38篇 |
2011年 | 50篇 |
2010年 | 29篇 |
2009年 | 50篇 |
2008年 | 42篇 |
2007年 | 40篇 |
2006年 | 33篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有774条查询结果,搜索用时 31 毫秒
81.
In this paper we describe the alloying process of ultra-thin Al layers (below 8 × 1015 Al/cm2) deposited on Ni(1 1 1). For this purpose Auger electron spectroscopy, low energy electron diffraction, and ion beam analysis-channelling measurements have been performed in situ in an ultra-high vacuum chamber. Al deposits formed at low temperature (about 130 K) are strained defective crystalline layers retaining the substrate orientation. Alloying takes place, with very progressive Ni enrichment, in a very broad temperature range between 250 K and 570 K. This feature shows that diffusion of the alloy species is more and more difficult when the Ni concentration increases. At 570 K a crystallographically and chemically ordered Ni3Al phase is formed, and its order continuously improves upon annealing, up to 750 K. We have shown by ion beam methods that this alloy is three-dimensional, extending up to 16 (1 1 1) planes for the thickest deposits. The Ni3Al phase can also be obtained directly by Al deposition at 750 K, but its crystalline quality is lower and the layer is probably formed of grains elongated along 〈1 1 −2〉 directions. The Al content of the thin Ni3Al layers formed mostly dissolves in the bulk above 800 K. However a small amount of Al remains segregated at the Ni crystal surface. 相似文献
82.
Ladislav Nebeský 《Discrete Mathematics》2007,307(16):2067-2073
Let V be a finite nonempty set. In this paper, a road system on V (as a generalization of the set of all geodesics in a connected graph G with V(G)=V) and an intervaloid function on V (as a generalization of the interval function (in the sense of Mulder) of a connected graph G with V(G)=V) are introduced. A natural bijection of the set of all intervaloid functions on V onto the set of all road systems on V is constructed. This bijection enables to deduce an axiomatic characterization of the interval function of a connected graph G from a characterization of the set of all geodesics in G. 相似文献
83.
关于圆形和方形城市工作区道路交通面积的解析与比较 总被引:1,自引:1,他引:0
对于城市规划来讲,事先预测其工作区内所需道路面积,以尽量避免实际交通网络中发生拥挤阻塞,具有重要意义,在本文,我们通过考虑一个城市通勤高峰时期的车辆交通情况,并通过利用走行中的车辆占用道路面积这一概念,基于一个相对现实的模型,从理论上对圆形方形城市工作区推导了所需的道路面积,并将两者加以比较,以发现与其交通网络结构相关的工作区的相对有效形状。 相似文献
84.
Silvia Richter Stepan Kyrsta Jochen Schneider David Hajas Joachim Mayer 《Mikrochimica acta》2006,155(1-2):257-262
Fibre reinforced NiAl offers new possibilities for the development of high strength structural materials of low density applicable
in gas turbines at high operating temperatures. The properties of composite materials are strongly influenced by the strength
of the fibre–matrix interface. In addition, if fibre and matrix differ in their thermal expansion coefficients, a well controlled
interface reaction at high temperature changes is demanded. Therefore, two layers consisting of BN and Hf were embedded between
a sapphire fibre and NiAl and heated at 1350 °C to find a compromise between adhesion and ductility. The control and characterization
of the reaction zone is essential for the development of these new materials. Especially, the characterization of the fibre-coating
interface is a challenge. The different hardness of fibre and coating makes it nearly impossible to use a conventional cross-section
preparation. Further, the small dimension of the reaction zone requires the use of analytical techniques providing high lateral
resolution. In order to accomplish these requirements, a newly developed technique FIB (Focused Ion Beam)-EPMA (Electron Probe
Microanalysis) was combined with XRD (X-ray diffraction). XRD was performed for the identification of the phases. The reaction
zone was exposed by a special FIB preparation technique and examined by surface-sensitive EPMA. This allowed to determine
the spatial distribution of the different phases. 相似文献
85.
von Richthofen Alexander Matsuo Michitaka Karduck Peter Ammann Norbert 《Mikrochimica acta》1994,114(1):511-523
In order to compare thin-film electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) regarding reliability in quantifying chemical compositions of Ti-Al-O-N coatings with depth, a multilayer was prepared on a silicon wafer by using reactive ionized cluster beam deposition technique. Within a total thickness of about 25 nm the composition of the multilayer varied step by step from Ti-Al-O-N at the bottom to Al-O at the top. AES and, as an innovation, EPMA crater edge profiling was applied to measure the composition with depth. For quantification special thin-film EPMA techniques based on Monte Carlo simulations were applied. The chemical binding states of Al and Ti with depth were analysed using a high resolution energy analyser (MAC 3) for the AES investigations working in the direct mode. According to the deposition procedure the concentration profiles of the components varied with depth for both AES and EPMA measurements. AES provided a better depth resolution than EPMA. To get a true calibration of the depth scale an in-situ measurement method like an optical interferometry will be required. Assuming that the relative sensitivity factors are available AES depth profiling delivers concentration profiles with good accuracy. The new EPMA application provided quantitative depth profiles concerning concentration and coverage. For EPMA crater edge profiling the coating needs to be deposited on a foreign substrate because depth distributions of elements being present in both the layer and the substrate cannot be resolved.The combination of AES-depth profiling with EPMA crater edge profiling techniques is a powerful tool to analyse heterostructures quantitatively. 相似文献
86.
The interaction of TL(OH)3, with excess lactic acid indicated the formation of Tl(LA)3 where LA stands for the anion of lactic acid. The structure of the complex was predicted from elemental analyses and IR spectra. The thermal decomposition of the complex using TG, DTG and DTA gave supporting evidence for the predicted structure. The kinetics of thermal decomposition were also studied employing various computational methods. 相似文献
87.
Norris JL Hangauer MJ Porter NA Caprioli RM 《Journal of mass spectrometry : JMS》2005,40(10):1319-1326
Although cleavable detergents were first synthesized a number of years ago, they have only recently been successfully applied to problems involving biological molecules. Recent reports have demonstrated that these compounds are useful for applications involving both 2D PAGE and mass spectrometry. However, most cleavable surfactants have utilized acid-labile functional groups to affect cleavage. In applications where extreme pH is required, acid cleavable detergents have limited usefulness. We report the synthesis of fluoride cleavable silane compounds and photolabile cinnamate esters as cleavable detergents having alternative cleavage chemistries than previously reported cleavable detergents. These compounds were applied to whole cell analysis using MALDI mass spectrometry, and it was demonstrated that their use results in an increase in the number of proteins analyzed by increasing protein solubility. 相似文献
88.
在产业转移背景下,考虑港口服务货运需求与刺激货运需求的双重功效,研究海上丝绸之路沿线产业承接地的港口投资建设问题。首先,在现实交通运输网络中加入虚拟链接构建超级网络,用以刻画制造业的转移、生产和运输过程。其次,建立制造业承接地港口投资决策优化模型,用运输阻抗、地价和工资三个内生变量描述港口投资、产业转移与区域经济之间均衡关系。模型以产业承接地港口收益最大为目标,确定承接地港口的投资规模及费率水平。最后,以斯里兰卡的科伦坡口为例进行数值分析,计算海上丝绸之路沿线港口需求与供给间正向反馈的数量关系及上确界,为优化沿线港口投资实现投资利益最大化提供依据。 相似文献
89.
The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL). The active area leachate has low DOC concentrations (<200 mg l?1) dominated by fulvic acid (FA=160 mg l?1), and produces CH4 dominantly by CO2 reduction (D? excess=20.6‰). Leachate generated in the area of older waste has high DOC (>4770 mg l?1) dominated by FA (4482 mg l?1) and simple fatty acids (acetic=1008 mg l?1 and propionic=608 mg l?1), and produces CH4 by the acetate fermentation pathway (D? excess=9.8‰). CSIA shows an advanced degradation and a progressive accumulation of 13C of fatty acids in leachate from the older area. The enriched 13C value of FA (?20 and?26‰ for the older and active parts, respectively,) and of low molecular weight DOC (?8 and?27‰) as well as of the bulk DOC (?21 and?25‰) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The 13C enrichment of acetate (?12‰) above the 13C of DOC (?21‰) and of propionic acid (?19‰), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8‰) and H2, which produce a more enriched 13C of acetate. In contrast, the 13C of the minor acetate in the active area (?17‰) indicates that CO2-reducing bacteria must be the primary consumers of H2, which has resulted in enriched 13CDIC (10‰) and depleted 13CCH4 (?58‰). 相似文献
90.
Abstract This review article focuses on the analytical capabilities of glow discharge optical emission spectrometry (GD‐OES) and mass spectrometry (GD‐MS) to perform compositional depth profiling (GD‐CDP). The properties of the Grimm‐type glow discharge as well as basic processes of sputtering are described and their influence on the GD as a surface and interface analytical tool are discussed. A series of examples from recent literature ranging from computer hard disks to molecular monolayers on copper substrates are presented to illustrate the excellent depth resolution that can be achieved with GD surface analytical techniques. The conditions for obtaining nanometer or even atomic‐layer depth resolution are discussed. Following this introduction is the possibilities of the technique a selection of applications principally chosen from our laboratories, demonstrating that GD‐OES and GD‐MS can be successfully employed as an analytical tool assisting the development of new materials and coatings. The applications cover common industrial tasks such as heat treatments, studies of diffusion processes at interfaces, and electrochemical depositions for biocompatible material. However, limitations and known artifacts are also discussed. 相似文献