全文获取类型
收费全文 | 631篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 355篇 |
晶体学 | 7篇 |
力学 | 11篇 |
数学 | 84篇 |
物理学 | 186篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 26篇 |
2012年 | 33篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 34篇 |
2007年 | 28篇 |
2006年 | 32篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 3篇 |
1975年 | 13篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1972年 | 11篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1968年 | 6篇 |
排序方式: 共有643条查询结果,搜索用时 15 毫秒
101.
O'Dell LA Gunawidjaja PN Holland MA Mountjoy G Pickup DM Newport RJ Smith ME 《Solid state nuclear magnetic resonance》2008,33(1-2):16-24
The HfO2-SiO2 system is attracting interest as a possible new dielectric material in semiconductor devices. Knowledge of the location of hafnium within the silica network and the effect hafnium has on the structure will be central to the successful use of this material system in this application. Here, sol-gel techniques have been used to manufacture (HfO2)x(SiO2)1-x samples (x=0.1, 0.2 and 0.4, each heat treated at 250, 500 and 750 degrees C) and these have been characterised by magic angle spinning (MAS) NMR (1H, 13C, 17 O, 29Si), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. 29Si MAS NMR showed that increasing the hafnia content decreases the connectivity of the silicate network, i.e. increases the range of differently connected SiO4 (Qn) units with more having increased numbers of non-bridging oxygens (i.e. lower n). FTIR and 17 O MAS NMR showed unequivocally that the x=0.4 sample phase-separated at higher temperatures, while in the x=0.1 sample the hafnium was homogeneously mixed into the SiO2 phase without any phase separation. 相似文献
102.
103.
Jason P. Holland Melanie Gut Simon Klingler Rachael Fay Amaury Guillou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(1):33-48
The ability to modify biologically active molecules such as antibodies with drug molecules, fluorophores or radionuclides is crucial in drug discovery and target identification. Classic chemistry used for protein functionalisation relies almost exclusively on thermochemically mediated reactions. Our recent experiments have begun to explore the use of photochemistry to effect rapid and efficient protein functionalisation. This article introduces some of the principles and objectives of using photochemically activated reagents for protein ligation. The concept of simultaneous photoradiosynthesis of radiolabelled antibodies for use in molecular imaging is introduced as a working example. Notably, the goal of producing functionalised proteins in the absence of pre-association (non-covalent ligand-protein binding) introduces requirements that are distinct from the more regular use of photoactive groups in photoaffinity labelling. With this in mind, the chemistry of thirteen different classes of photoactivatable reagents that react through the formation of intermediate carbenes, electrophiles, dienes, or radicals, is assessed. 相似文献
104.
High‐Frequency Fe–H Vibrations in a Bridging Hydride Complex Characterized by NRVS and DFT
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Vladimir Pelmenschikov Dr. Leland B. Gee Dr. Hongxin Wang Dr. K. Cory MacLeod Sean F. McWilliams Dr. Kazimer L. Skubi Prof. Dr. Stephen P. Cramer Prof. Dr. Patrick L. Holland 《Angewandte Chemie (International ed. in English)》2018,57(30):9367-9371
High‐spin iron species with bridging hydrides have been detected in species trapped during nitrogenase catalysis, but there are few general methods of evaluating Fe?H bonds in high‐spin multinuclear iron systems. An 57Fe nuclear resonance vibrational spectroscopy (NRVS) study on an Fe(μ‐H)2Fe model complex reveals Fe?H stretching vibrations for bridging hydrides at frequencies greater than 1200 cm?1. These isotope‐sensitive vibrational bands are not evident in infrared (IR) spectra, showing the power of NRVS for identifying hydrides in this high‐spin iron system. Complementary density functional theory (DFT) calculations elucidate the normal modes of the rhomboidal iron hydride core. 相似文献
105.
This paper describes the use of the terephthalate dosimeter to measure the threshold and extent of cavitation arising from medical ultrasound sources at high frequencies. Significant hydroxyl radical production was noted from a physiotherapy source and low level activity was also detected when using a pulsed, diagnostic type transducer system. The effect of sound intensity and the type of field is described. The possibility of using polymer degradation to monitor the cavitation is also discussed. 相似文献
106.
A. Juliard J. Ledrut E. B. Holland G. M. Gilligan H. F. Bradley M. G. Roeder S. G. Clarke und B. S. Evans 《Fresenius' Journal of Analytical Chemistry》1930,79(5-6):205-207
Ohne Zusammenfassung 相似文献
107.
Cadmium phosphate glasses, of general formula xCdO(1−x)P2O5 (0.25?x?0.6), have been prepared by melting in alumina crucibles, with resulting dissolution of up to 6.4 mol% Al2O3. The local structure in these glasses has been studied using 31P, 27Al and 113Cd nuclear magnetic resonance. The distribution of [PO4]Qn species as a function of composition has been shown to follow the simple binary model. The rate of change of the chemical shift of the 31P species in the Q2 environment depends on the bond order, which in turn reflects the extent of double bonding between phosphorus and oxygen. 相似文献
108.
109.
Hindered beta-aminoarylphosphines show promise as bidentate ligands for metal centers, but their reported synthesis requires heating at high temperatures for several days. Herein are reported conditions by which the two steps composing this synthesis, Buchwald-Hartwig amination and nucleophilic phosphorylation reactions, may both be completed in less than 3 h using microwave irradiation. The effects of several parameters on the outcome of the amination reaction are discussed, as are some indications of the scope within which each of these microwave protocols is effective. 相似文献
110.
Holland JP Barnard PJ Collison D Dilworth JR Edge R Green JC McInnes EJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(19):5890-5907
Detailed chemical, spectroelectrochemical and computational studies have been used to investigate the mechanism of hypoxia selectivity of a range of copper radiopharmaceuticals. A revised mechanism involving a delicate balance between cellular uptake, intracellular reduction, reoxidation, protonation and ligand dissociation is proposed. This mechanism accounts for observed differences in the reported cellular uptake and washout of related copper bis(thiosemicarbazonato) complexes. Three copper and zinc complexes have been characterised by X-ray crystallography and the redox chemistry of a series of copper complexes has been investigated by using electronic absorption and EPR spectroelectrochemistry. Time-dependent density functional theory (TD-DFT) calculations have also been used to probe the electronic structures of intermediate species and assign the electronic absorption spectra. DFT calculations also show that one-electron oxidation is ligand-based, leading to the formation of cationic triplet species. In the absence of protons, metal-centred one-electron reduction gives the reduced anionic copper(I) species, [CuIATSM](-), and for the first time it is shown that molecular oxygen can reoxidise this anion to give the neutral, lipophilic parent complexes, which can wash out of cells. The electrochemistry is pH dependent and in the presence of stronger acids both chemical and electrochemical reduction leads to quantitative and rapid dissociation of copper(I) ions from the mono- or diprotonated complexes, [CuIATSMH] and [Cu(I)ATSMH2]+. In addition, a range of protonated intermediate species have been identified at lower acid concentrations. The one-electron reduction potential, rate of reoxidation of the copper(I) anionic species and ease of protonation are dependent on the structure of the ligand, which also governs their observed behaviour in vivo. 相似文献