全文获取类型
收费全文 | 196篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
化学 | 86篇 |
晶体学 | 15篇 |
力学 | 9篇 |
数学 | 45篇 |
物理学 | 44篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 11篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有199条查询结果,搜索用时 156 毫秒
1.
Ejnik JW Todorov TI Mullick FG Squibb K McDiarmid MA Centeno JA 《Analytical and bioanalytical chemistry》2005,382(1):73-79
Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of 235U/238U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uraniums 235U/238U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the 235U/238U ratio. The quantitative analysis was achieved using 233U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized 235U+ and 238U+ into 235UO2+ (m/z=267) and 238UO2+ (m/z=270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the 235U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL–1 urine and an average coefficient of variation (CV) of 1–2% within the sample measurements. The method detection limit for determining 235U/238U ratio was 3.0 pg U mL–1 urine. An additional 21 patient samples were analyzed with no information about medical history. The measured 235U/238U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.The opinions and assertions expressed herein are those of the authors and are not to be construed as official or as representing the views of the Armed Forces Institute of Pathology, the Department of the Army, or the Department of Defense 相似文献
2.
First-second shell interactions in metal binding sites in proteins: a PDB survey and DFT/CDM calculations 总被引:1,自引:0,他引:1
The role of the second shell in the process of metal binding and selectivity in metalloproteins has been elucidated by combining Protein Data Bank (PDB) surveys of Mg, Mn, Ca, and Zn binding sites with density functional theory/continuum dielectric methods (DFT/CDM). Peptide backbone groups were found to be the most common second-shell ligand in Mg, Mn, Ca, and Zn binding sites, followed (in decreasing order) by Asp/Glu, Lys/Arg, Asn/Gln, and Ser/Thr side chains. Aromatic oxygen- or nitrogen-containing side chains (Tyr, His, and Trp) and sulfur-containing side chains (Cys and Met) are seldom found in the second coordination layer. The backbone and Asn/Gln side chain are ubiquitous in the metal second coordination layer as their carbonyl oxygen and amide hydrogen can act as a hydrogen-bond acceptor and donor, respectively, and can therefore partner practically every first-shell ligand. The second most common outer-shell ligand, Asp/Glu, predominantly hydrogen bonds to a metal-bound water or Zn-bound histidine and polarizes the H-O or H-N bond. In certain cases, a second-shell Asp/Glu could affect the protonation state of the metal ligand. It could also energetically stabilize a positively charged metal complex more than a neutral ligand such as the backbone and Asn/Gln side chain. As for the first shell, the second shell is predicted to contribute to the metal selectivity of the binding site by discriminating between metal cations of different ionic radii and coordination geometries. The first-shell-second-shell interaction energies decay rapidly with increasing solvent exposure of the metal binding site. They are less favorable but are of the same order of magnitude as compared to the respective metal-first-shell interaction energies. Altogether, the results indicate that the structure and properties of the second shell are dictated by those of the first layer. The outer shell is apparently designed to stabilize/protect the inner-shell and complement/enhance its properties. 相似文献
3.
Todor Todorov 《Transactions of the American Mathematical Society》1996,348(2):673-689
We prove the existence of solutions for essentially all linear partial differential equations with -coefficients in an algebra of generalized functions, defined in the paper. In particular, we show that H. Lewy's equation has solutions whenever its right-hand side is a classical -function.
4.
Arsenic Speciation in Urine and Blood Reference Materials 总被引:1,自引:0,他引:1
Todor I. Todorov John W. Ejnik Florabel G. Mullick Jose A. Centeno 《Mikrochimica acta》2005,151(3-4):263-268
Acute and chronic exposure to arsenic is a growing problem in the industrialized world. Arsenic is a potent carcinogen and
toxin in humans. In the body, arsenic is metabolized to produce several species, including inorganic forms, such as trivalent
(AsIII) and pentavalent (AsV), and the methylated metabolites such as monomethylarsonic acid, (MMAV), and dimethylarsinic acid (DMAV), in addition to arsenobetaine (AsB) which is ingested and excreted from the body in the same form. Each of these species
has been reported to possess a specific but different degree of toxicity. Thus, not only is the measurement of total As required,
but also quantification of the individual metabolites is necessary to evaluate the toxicity and risk assessment of this element.
There are a large number of reference materials that are used to validate methodology for the analysis of As in blood and
urine, but they are limited to total As concentrations. In this study, the speciation of five arsenic metabolites is reported
in blood and urine from commercial available control materials certified for total arsenic levels. The separation was performed
with an anion exchange column using inductively coupled plasma mass spectrometry as a detector. Baseline separation was achieved
for AsIII, AsV, MMAV, DMAV, and AsB, allowing us to quantify all five species. Excellent agreement between the total arsenic levels and the sum of the
speciated As levels was obtained. 相似文献
5.
Thermoanalytical data on six reagents and on their compounds with Zr(IV) are reported. Except for H acid, all reagents were azopyrazolonic derivatives obtained by synthesis. The purpose of this study was to obtain data on the thermal stabilities of the reagents and their zirconium compounds, and to establish the reagent: zirconium: water combination ratio.
Zusammenfassung Thermoanalytische Daten von 6 Reagenzien und deren Verbindungen mit Zr(IV) werden mitgeteilt. Außer H-Säure waren alle Reagenzien durch Synthese erhaltene Azopyrazolon-Derivate. Zweck der Untersuchung war, Daten über die thermische Stabilität dieser Reagenzien und ihrer Zirkonverbindungen zu erhalten und das Verhältnis Reagens: Zirkon: Wasser festzustellen.
. , , - . , : : .相似文献
6.
T. M. Peev A. V. Krylova N. V. Nefedova T. Stoilova 《Journal of Radioanalytical and Nuclear Chemistry》1986,105(3):157-163
Samples of a catalyst CA-1 for ammonia synthesis were studied. After reduction the samples were treated with CO2 or with a mixture of 1% O2+2.4% H2O+CO2 at temperatures between 600 and 783 K. Mössbauer spectroscopy data indicate that above 600 K carbide phases and magnetite are formed. A probable mechanism for carbide formation is suggested. 相似文献
7.
Todor Gramchev 《Monatshefte für Mathematik》1991,112(2):99-113
We study the weak limits
(t, .)of solutions to semilinear strictly hyperbolic systems and wave equations with initial datau
(0, .) approximating a distribution, 0 <
1. We propose an optimal link between the singularity of and the growth of the nonlinear term in order that
exists. In this way we extend some of the results in [3], [10], [13]. 相似文献
8.
Dr. Todor Baramov Bianca Schmid Ho Ryu Jinhoon Jeong Dr. Karlijn Keijzer Dr. Leonard von Eckardstein Prof. Dr. Mu-Hyun Baik Prof. Dr. Roderich D. Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6955-6962
The E. coli siderophore enterobactin, the strongest FeIII chelator known to date, forms hexacoordinate complexes with SiIV, GeIV, and TiIV. Synthetic protocols have been developed to prepare non-symmetric enterobactin analogues with varying denticities. Various benzoic acid residues were coupled to the macrocyclic lactone to afford a diverse library of ligands. These enterobactin analogues were bound to SiIV, GeIV, and TiIV, and the complexes were investigated through experimental and computational techniques. The binding behavior of the synthesized chelators enabled assessment of the contribution of each of the phenolic hydroxy groups in enterobactin to metal-ion complexation. It was found that at least four O-donors are needed for enterobactin derivatives to act as metal binders. Density functional theory calculations indicate that the strong binding behavior of enterobactin can be ascribed to a diminished translational entropy penalty, a common feature of the chelate effect, coupled with the structural arrangement of the three catechol moieties, which allows the triseryl base to be installed without distorting the preferred local metal-binding geometry of the catecholate ligands. 相似文献
9.
Chesnick IE Todorov TI Centeno JA Newbury DE Small JA Potter K 《Magnetic resonance imaging》2007,25(7):1095-1104
Paramagnetic manganese (II) can be employed as a calcium surrogate to sensitize magnetic resonance microscopy (MRM) to the processing of calcium during bone formation. At high doses, osteoblasts can take up sufficient quantities of manganese, resulting in marked changes in water proton T(1), T(2) and magnetization transfer ratio values compared to those for untreated cells. Accordingly, inductively coupled plasma mass spectrometry (ICP-MS) results confirm that the manganese content of treated cell pellets was 10-fold higher than that for untreated cell pellets. To establish that manganese is processed like calcium and deposited as bone, calvaria from the skull of embryonic chicks were grown in culture medium supplemented with 1 mM MnCl(2) and 3 mM CaCl(2). A banding pattern of high and low T(2) values, consistent with mineral deposits with high and low levels of manganese, was observed radiating from the calvarial ridge. The results of ICP-MS studies confirm that manganese-treated calvaria take up increasing amounts of manganese with time in culture. Finally, elemental mapping studies with electron probe microanalysis confirmed local variations in the manganese content of bone newly deposited on the calvarial surface. This is the first reported use of manganese-enhanced MRM to study the process whereby calcium is taken up by osteoblasts cells and deposited as bone. 相似文献
10.
N. S. Peev 《Crystal Research and Technology》1986,21(3):319-326
Theory of zone recrystallization in the framwork of already known models of normal crystal growth, growth by screw dislocations and by two-dimensional nucleation is discussed. By mathematical treatment, different from Tillers approach, analytical expressions for supersaturation at the crystallisation interface, for superheating at the dissolution interface, growth rate and some other parameters have been obtained for both cases of normal and screw dislocations growth. It is possible to determine the growth mechanism. 相似文献