全文获取类型
收费全文 | 888篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
化学 | 656篇 |
晶体学 | 1篇 |
力学 | 25篇 |
数学 | 128篇 |
物理学 | 97篇 |
出版年
2022年 | 21篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 6篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 19篇 |
2013年 | 56篇 |
2012年 | 48篇 |
2011年 | 50篇 |
2010年 | 42篇 |
2009年 | 30篇 |
2008年 | 49篇 |
2007年 | 44篇 |
2006年 | 35篇 |
2005年 | 40篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 28篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有907条查询结果,搜索用时 78 毫秒
61.
Paolo Ferruti Elisabetta Ranucci Amedea Manfredi Nicolò Mauro Elena Ferrari Riccardo Bruni Francesco Colombo Patrizia Mussini Manuela Rossi 《Journal of polymer science. Part A, Polymer chemistry》2012,50(24):5000-5010
Traditional precipitation methods for inorganic micropollutant removal from waters are increasingly being replaced by sorption methods based on both natural and synthetic materials. In this context, two novel effective heavy metal ions absorbers are presented. These resins, LYMA and LMT85, were crosslinked poly(amidoamine)s carrying amine and carboxyl groups in their repeating units. In particular, the LYMA‐repeating unit contains one carboxyl and two amine groups and is a mimic of L ‐lysine, whereas LMT85 contains two amine and five carboxyl groups and is a mimic of EDTA. Both resins were prepared at moderate cost by simple eco‐friendly procedures. The heavy metal ion set adopted as benchmark was Cu2+, Cd2+, Pb2+, Zn2+, Ni2+, and Co2+. LYMA proved selective for Cu2+ and Ni2+, the other ions tested being negligibly absorbed, whereas LMT85 proved capable of rapidly and quantitatively absorbing all the ions tested either singly or in mixed solution. The absorption process was reversible, and the resins were easily regenerated by acidification. The absorption of several metal ions imparted intense coloring to the resins, a feature possibly exploitable for analytical purposes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
62.
Giuseppa Di Bella Patrizia Licata Vito Pellizzeri Hedi Ben Mansour Giacomo Dugo 《Natural product research》2018,32(12):1402-1406
Two species of edible clams Venerupis aurea laeta and Cerastoderma edule glaucum from Ganzirri Lake (Sicily, Italy) were investigated to determine OCP and PCB residues by GC-MS. Thirty-five samples were examined for two years in order to perform: a) their actual contamination; b) the daily dietary exposure of seafood consumers to the pollutants in question. In all the clams analysed in this study, PCB and OCP (4,4′-DDE) residues are always below the limits fixed by law. It seems that there is some seasonality of concentrations observed. In fact the more high concentrations of residues are detected in the hot months, for both species and years. Given the consumption of clams and the values obtained in this study for the two species analysed, it is possible estimate that the average daily dietary intake of NDL-PCB and of 4,4′-DDE for adults is really low. 相似文献
63.
Francesco De Vincentiis Giorgio Bencivenni Dr. Fabio Pesciaioli Andrea Mazzanti Dr. Giuseppe Bartoli Prof. Patrizia Galzerano Dr. Paolo Melchiorre Prof. Dr. 《化学:亚洲杂志》2010,5(7):1652-1656
The first catalytic method for the asymmetric aziridination of cyclic enones is described. The presented organocatalytic strategy is based on the use of an easily available organocatalyst that is able to convert a wide range of cyclic enones into the desired aziridines with very high enantiomeric purity and good chemical yield. Such a method may very well open up new opportunities to stereoselectively prepare complex chiral molecules that possess an indane moiety, a framework that is found in a large number of bioactive and pharmaceutically important molecules 相似文献
64.
Imazosulfuron, 1-(2-chloroimidazo [1,2-a] pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea, is a new sulfonylurea herbicide applied once per growing season. It is highly active at low application levels and is used to control most annual and perennial broad-leaf weeds and some grasses in cereal crop. In this work the degradation of imazosulfuron in four different soils was investigated under aerobic laboratory conditions to evaluate its environmental fate. Test soils were treated with this herbicide in acetonitrile to obtain a final concentration of 0.2 mg kg(-1) (100 g ha(-1)), extracted with methylene chloride and analyzed by reversed-phase liquid chromatography (RP-HPLC) using a C(18) column coupled with UV detection. Recoveries of spiked soils ranged from 84.3 to 99.8% (RDS 0.0-4.9%; n = 4). The limits of quantitation ranged from 0.002 to 0.004 mg kg(-1). Imazosulfuron half-life, t(1/2), was calculated in each of the investigated soil. In aerobic conditions it ranged between 1 and 50 days. 相似文献
65.
The rationale for the extension of the rH-metric standardization and measurements to aqueous-organic solvent mixtures is here introduced, and examples of establishment of the ranges of conventional rH-metric scales as well as primary standards rHs in some typical aqueous-organic solvent mixtures are described. 相似文献
66.
Vistoli G Pedretti A Villa L Testa B 《Journal of the American Chemical Society》2002,124(25):7472-7480
The objective of this study was to determine if and how a solvent influences internal motions in a solute molecule. Acetylcholine was chosen as the object of study given its interesting molecular structure and major biological significance. Molecular dynamics simulations were carried out in the vacuum (10 ns), water (5 ns), methanol (5 ns), and octanol (1.5 ns). Seven clusters of conformers were identified, namely, +g+g, -g-g, +gt, -gt, t+g, t-g, and tt, where the gauche and trans labels refer to the dihedral angles tau(2) and tau(3), respectively. As expected, the relative proportion of these conformational clusters was highly solvent-dependent and corresponded to a progressive loss of conformational freedom with increasing molecular weight of the solvent. More importantly, the conformational clusters were used to calculate instantaneous and median angular velocity (omega and omega(M), respectively) and instantaneous and median angular acceleration (alpha and alpha(M), respectively). Angular velocity and angular acceleration were both found to decrease markedly with increasing molecular weight of the solvent, i.e., vacuum (epsilon = 1) > water > methanol > octanol. The decrease from the vacuum to octanol was approximately 40% for tau(2) and approximately 60% for tau(3). Such solvent-dependent constraints on a solute's internal motions may be biologically and pharmacologically relevant. 相似文献
67.
Lombardi F Tafuri F Ricci F Miletto Granozio F Barone A Testa G Sarnelli E Kirtley JR Tsuei CC 《Physical review letters》2002,89(20):207001
We have measured the angular dependence of the Josephson critical current density (J(C)) in c-axis tilt biepitaxial grain boundary YBa(2)Cu(3)O(7-delta) junctions. We observe for the first time intrinsic d-wave pairing symmetry effects manifested as an oscillatory dependence of J(C) on angle. This intrinsic effect is evident even though spontaneous currents, possibly induced by faceting or barrier impurities, are observed in the grain boundaries. 相似文献
68.
Kolbitsch C Lorenz IH Hörmann C Hinteregger M Löckinger A Moser PL Kremser C Schocke M Felber S Pfeiffer KP Benzer A 《Magnetic resonance imaging》2002,20(7):535-541
Conflicting results reported on the effects of hyperoxia on cerebral hemodynamics have been attributed mainly to methodical and species differences. In the present study contrast-enhanced magnetic resonance imaging (MRI) perfusion measurement was used to analyze the influence of hyperoxia (fraction of inspired oxygen (FiO2) = 1.0) on regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) in awake, normoventilating volunteers (n = 19). Furthermore, the experiment was repeated in 20 volunteers for transcranial Doppler sonography (TCD) measurement of cerebral blood flow velocity in the middle cerebral artery (CBFV(MCA)). When compared to normoxia (FiO2 = 0.21), hyperoxia heterogeneously influenced rCBV (4.95 +/- 0.02 to 12.87 +/- 0.08 mL/100g (FiO2 = 0.21) vs. 4.50 +/- 0.02 to 13.09 +/- 0.09 mL/100g (FiO2 = 1.0). In contrast, hyperoxia diminished rCBF in all regions (68.08 +/- 0.38 to 199.58 +/- 1.58 mL/100g/min (FiO2 = 0.21) vs. 58.63 +/- 0.32 to 175.16 +/- 1.51 mL/100g/min (FiO2 = 1.0)) except in parietal and left frontal gray matter. CBFV(MCA) remained unchanged regardless of the inspired oxygen fraction (62 +/- 9 cm/s (FiO2 = 0.21) vs. 64 +/- 8 cm/s (FiO2 = 1.0)). Finding CBFV(MCA) unchanged during hyperoxia is consistent with the present study's unchanged rCBF in parietal and left frontal gray matter. In these fronto-parietal regions predominantly fed by the middle cerebral artery, the vasoconstrictor effect of oxygen was probably counteracted by increased perfusion of foci of neuronal activity controlling general behavior and arousal. 相似文献
69.
70.
Sharapov SE Alper B Fessey J Hawkes NC Young NP Nazikian R Kramer GJ Borba DN Hacquin S De La Luna E Pinches SD Rapp J Testa D;JET-EFDA contributors 《Physical review letters》2004,93(16):165001
A microwave interferometry technique is applied for the first time for detecting a discrete spectrum of Alfvén cascade (AC) eigenmodes excited with fast ions in reversed magnetic shear plasmas of the Joint European Torus. The interferometry measurements of plasma density perturbations associated with ACs show an unprecedented frequency and time resolution superior to that obtained with external magnetic coils. The measurements of ACs are used for monitoring the evolution of the safety factor and density of rational magnetic surfaces in the region of maximum plasma current. 相似文献