全文获取类型
收费全文 | 636篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 358篇 |
晶体学 | 7篇 |
力学 | 11篇 |
数学 | 85篇 |
物理学 | 186篇 |
出版年
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 13篇 |
2013年 | 26篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 18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 | 9篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 6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 | 7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647条查询结果,搜索用时 0 毫秒
111.
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
112.
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
113.
Cowley RE Elhaïk J Eckert NA Brennessel WW Bill E Holland PL 《Journal of the American Chemical Society》2008,130(19):6074-6075
This communication reports the first examples of transition metal complexes containing an RNNNNNNR 2- ligand. Addition of 1-azidoadamantane to the diiron(I) synthon LRFeNNFeL R (L R = HC[C(R)N(2,6- iPr 2C 6H 3)] 2; R = methyl, tert-butyl) leads to the diiron complexes L RFe(mu-eta2:eta2-AdN6Ad)FeLR, which are surprisingly thermally stable. Magnetic, M?ssbauer, and crystallographic data are consistent with pairs of high-spin iron(II) ions antiferromagnetically coupled through a dianionic AdN6Ad 2- bridge. 相似文献
114.
The applicability of dual injection CE for affinity selection of biopolymers that contain multiple binding sites is demonstrated. The efficient analysis of biomolecules such as carbohydrates and proteins, as well as pharmaceuticals by CE requires the reduction or elimination of nonspecific interactions with the capillary surface. Phospholipids are integral components of cell membranes and aqueous phospholipid liquid crystals adopt a bilayer structure on fused-silica. This phospholipid surface does not interact significantly with the following biomolecules: serum albumin, the 96-110 heparin binding domain of amyloid precursor protein (APP), polydisperse glycosaminoglycans, and variable chain-length oligosaccharides. Pharmaceuticals including five anionic nonsteroidal anti-inflammatory drugs, three cationic analgesics, and two cationic beta-blockers, also show minimal interaction with the surface. In addition, the use of a phospholipid coating suppresses EOF, which enables reversed-polarity separations, dual opposite injection CE, affinity screening via CE by dual opposite injection, and serial target-ligand injections. 相似文献
115.
The reaction of K2PtCl4 with an excess of 1-methyluracilate (1-MeU) in water at 60 degrees C leads to the formation of two major products, K2[Pt(1-MeU-N3)4].10H2O (1) and trans-K[Pt(1-MeU-N3)2(1-MeU-C5)(H2O)].3H2O (2). Addition of CuCl2 to an aqueous solution of 2 yields the mixed-metal complex trans-[PtCl(1-MeU-N3,O4)2(1-MeU-C5,O4)Cu(H2O)].H2O (4). Single-crystal X-ray analysis was carried out for 1 and 4. In both compounds, the heterometals (K+ in 1 and Cu2+ in 4) are bonded to exocyclic oxygens atoms of the 1-MeU ligands, giving rise to intermetallic distances of 3.386(2) and 3.528(2) A in 1 and 2.458(1) A in 4. The shortness of the Pt-Cu separation in 4 is consistent with a dative bond between PtII and CuII. The aqua ligand in 2 is readily substituted by a series of other ligands (e.g., 1-MeC, 9-MeGH, and CN-), as demonstrated by 1H NMR spectroscopy, with 3J(195Pt-1H(6)) coupling constants being sensitive indicators. Acid-base equilibria of 1 and 2 have been studied in detail and reveal some unexpected features: 1 has a relatively high basicity, with protonation starting below pH 5, and first and second pKa values being ca. 3.4 and 0.4, respectively. These pKa values are markedly higher than those of related neutral 2:1 or cationic 1:1 complexes and are attributed to both charge effects (-2 charge of 1) and a favorable stabilization of oxygen-protonated species by the arrangement of four exocyclic oxygen groups of 1-MeU ligands at either sides of the platinum coordination planes. Whereas in 2, H+ affinities of the three uracil ligands are in the normal range, there is a surprisingly low acidity of N(3)H of the C5-bonded uracil with a pKa of approximately 12.2, which compares with 9.75 for free 1-methyluracil. This implies that the C5-bonded PtII does not induce the typical acidifying effect of a PtII metal entity when bonded to a ring nitrogen atom of a neutral nucleobase. Rather, the effect is qualitatively similar to that of a metal ion bonded to N3 of an anionic 1-MeU ligand, which likewise increases its overall basicity as compared to neutral 1-MeUH. 相似文献
116.
S. Oberholzer M. Henny C. Strunk C. Schnenberger T. Heinzel K. Ensslin M. Holland 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
We realized an equivalent Hanbury Brown and Twiss experiment for a beam of electrons in a two-dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter which is used to partition the incident beam into transmitted and reflected partial beams. The current fluctuations in the reflected and transmitted beam are fully anticorrelated demonstrating that fermions tend to exclude each other (anti-bunching). If the occupation probability of the incident beam is lowered by an additional gate, the anticorrelation is reduced and disappears in the classical limit of a highly diluted beam. 相似文献
117.
118.
Takaoki Koyanagi Dr. Geoffray Leriche Alvin Yep David Onofrei Prof. Gregory P. Holland Prof. Michael Mayer Prof. Jerry Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8074-8077
This paper examines the effects of four different polar headgroups on small‐ion membrane permeability from liposomes comprised of Archaea‐inspired glycerolmonoalkyl glycerol tetraether (GMGT) lipids. We found that the membrane‐leakage rate across GMGT lipid membranes varied by a factor of ≤1.6 as a function of headgroup structure. However, the leakage rates of small ions across membranes comprised of commercial bilayer‐forming 1‐palmitoyl‐2‐oleoyl‐sn‐glycerol (PO) lipids varied by as much as 32‐fold within the same series of headgroups. These results demonstrate that membrane leakage from GMGT lipids is less influenced by headgroup structure, making it possible to tailor the structure of the polar headgroups on GMGT lipids while retaining predictable leakage properties of membranes comprised of these tethered lipids. 相似文献
119.
This article discusses the formation and detailed materials characterisation of nickel silicide thin films. Nickel silicide thin films have been formed by thermally reacting electron beam evaporated thin films of nickel with silicon. The nickel silicide thin films have been analysed using Auger electron spectroscopy (AES) depth profiles, secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy (RBS). The AES depth profile shows a uniform NiSi film, with a composition of 49-50% nickel and 51-50% silicon. No oxygen contamination either on the surface or at the silicide-silicon interface was observed. The SIMS depth profile confirms the existence of a uniform film, with no traces of oxygen contamination. RBS results indicate a nickel silicide layer of 114 nm, with the simulated spectra in close agreement with the experimental data. Atomic force microscopy and transmission electron microscopy have been used to study the morphology of the nickel silicide thin films. The average grain size and average surface roughness of these films was found to be 30-50 and 0.67 nm, respectively. The film surface has also been studied using Kikuchi patterns obtained by electron backscatter detection. 相似文献
120.
Michael K. Holland Joseph V. Cordaro 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):555-563
Minimizing plutonium measurement uncertainty is essential to nuclear material control and international safeguards. In 2005,
the International Organization for Standardization (ISO) published ISO 12183 “Controlled-potential coulometric assay of plutonium,”
2nd edition. ISO 12183:2005 recommends a target of ±0.01% for the mass of original sample in the aliquot because it is a critical
assay variable. Mass measurements in radiological containment were evaluated and uncertainties estimated. The uncertainty
estimate for the mass measurement also includes uncertainty in correcting for buoyancy effects from air acting as a fluid
and from decreased pressure of heated air from the specific heat of the plutonium isotopes. 相似文献