全文获取类型
收费全文 | 587篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
化学 | 385篇 |
晶体学 | 3篇 |
力学 | 12篇 |
数学 | 100篇 |
物理学 | 110篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 17篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 27篇 |
2013年 | 29篇 |
2012年 | 38篇 |
2011年 | 38篇 |
2010年 | 22篇 |
2009年 | 22篇 |
2008年 | 35篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 33篇 |
2004年 | 31篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 13篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1921年 | 1篇 |
排序方式: 共有610条查询结果,搜索用时 15 毫秒
61.
Enrico Sanjust Raffaello Pompei Antonio Rescigno Augusto Rinaldi Maoro Ballero 《Applied biochemistry and biotechnology》1991,31(3):223-235
Four species of Pleurotus were adapted to grow on olive milling wastewater, and in certain conditions produced high yield of fruit bodies. Some biochemical transformations were observed in the olive milling wastewater owing to the growth of Pleurotus. In particular, the fungi actively excreted large amounts of laccase in the medium, and at the same time the concentration of phenolics and other toxic compounds significantly decreased, as revealed by HPLC analysis and toxicity tests on standard cultures of human cell lines. 相似文献
62.
Dividing a complex reaction involving a hypervalent iodine reagent into three limiting mechanisms by ab initio molecular dynamics 下载免费PDF全文
Oliver Sala Hans Peter Lüthi Antonio Togni Marcella Iannuzzi Jürg Hutter 《Journal of computational chemistry》2015,36(11):785-794
The electrophilic N‐trifluoromethylation of MeCN with a hypervalent iodine reagent to form a nitrilium ion, that is rapidly trapped by an azole nucleophile, is thought to occur via reductive elimination (RE). A recent study showed that, depending on the solvent representation, the SN2 is favoured to a different extent over the RE. However, there is a discriminative solvent effect present, which calls for a statistical mechanics approach to fully account for the entropic contributions. In this study, we perform metadynamic simulations for two trifluoromethylation reactions (with N‐ and S‐nucleophiles), showing that the RE mechanism is always favoured in MeCN solution. These computations also indicate that a radical mechanism (single electron transfer) may play an important role. The computational protocol based on accelerated molecular dynamics for the exploration of the free energy surface is transferable and will be applied to similar reactions to investigate other electrophiles on the reagent. Based on the activation parameters determined, this approach also gives insight into the mechanistic details of the trifluoromethylation and shows that these commonly known mechanisms mark the limits within which the reaction proceeds. © 2015 Wiley Periodicals, Inc. 相似文献
63.
Explicit generators for high-order (r>1) scalar and vector finite element spaces generally used in numerical electromagnetism are presented and classical degrees of freedom, the so-called moments, revisited. Properties of these generators on simplicial meshes are investigated, and a general technique to restore duality between moments and generators is proposed. Algebraic and exponential optimal h- and r-error rates are numerically validated for high-order edge elements on the problem of Maxwell’s eigenvalues in a square domain. 相似文献
64.
Geisberger G Paulus S Carraro M Bonchio M Patzke GR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4619-4625
Chitosan and its derivates continue to attract considerable research interest as effective drug carriers with good biocompatibility and high cellular uptake rates. We used these versatile features to tap the considerable biomedical potential of polyoxometalates (POMs) through their encapsulation into a carboxymethyl chitosan (CMC) matrix. The nanocapsules were prepared by ionic gelification with Ca(2+); their size distribution ranges from 60 to 150 nm. Because [Co(4)(H(2)O)(2)(PW(9)O(34))(2)](10-) is well known for its manifold properties, such as antiviral activity, it was selected as a model POM. The resulting composites were characterised with a wide range of analytical methods, which pointed to quantitative encapsulation of intact POMs within the CMC matrix. We studied the biocompatibility of the POM/CMC nanocomposites on HeLa cells through MTT and proliferation assays. Even after prolonged incubation times at high concentrations, the composites did not display cytotoxicity, thereby drastically reducing the side effects of the pristine POMs. This opens up new avenues for designing novel inorganic drug prototypes from bioactive POMs. 相似文献
65.
Badaloni E Barbarino M Cabri W D'Acquarica I Forte M Gasparrini F Giorgi F Pierini M Simone P Ursini O Villani C 《Journal of chromatography. A》2011,1218(25):3862-3875
New monolithic HPLC columns were prepared by γ-radiation-triggered polymerization of hexyl methacrylate and ethylene glycol dimethacrylate monomers in the presence of porogenic solvents. Polymerization was carried out directly within capillary (250-200 μm I.D.) and nano (100-75 μm I.D.) fused-silica tubes yielding highly efficient columns for cap(nano)-LC applications. The columns were applied in the complete separation of core (H2A, H2B, H3, and H4) and linker (H1) histones under gradient elution with UV and/or electrospray ionization (ESI) ion trap mass spectrometry (MS) detections. Large selectivity towards H1, H2A-1, H2A-2, H2B, H3-1, H3-2 and H4 histones and complete separation were obtained within 8 min time windows, using fast gradients and very high linear flow velocities, up to 11 mm/s for high throughput applications. The method developed was the basis of a simple and efficient protocol for the evaluation of post-translational modifications (PTMs) of histones from NCI-H460 human non-small-cell lung cancer (NSCLC) and HCT-116 human colorectal carcinoma cells. The study was extended to monitoring the level of histone acetylation after inhibition of Histone DeACetylase (HDAC) enzymes with suberoylanilide hydroxamic acid (SAHA), the first HDAC inhibitor approved by the FDA for cancer therapy. Attractive features of our cap(nano)-LC/MS approach are the short analysis time, the minute amount of sample required to complete the whole procedure and the stability of the polymethacrylate-based columns. A lab-made software package ClustMass was ad hoc developed and used to elaborate deconvoluted mass spectral data (aligning, averaging, clustering) and calculate the potency of HDAC inhibitors, expressed through a Relative half maximal Inhibitory Concentration parameter, namely R_IC(50) and an averaged acetylation degree. 相似文献
66.
Giuseppina Castronuovo Marcella Niccoli 《Journal of Thermal Analysis and Calorimetry》2011,103(2):641-646
The formation of complexes of parent and alkylated cyclodextrins (CDs) with 1-heptanol and 1-octanol has been studied calorimetrically
at 298 K in water and in concentrated aqueous solutions of urea. The forces involved in the association process are discussed
in the light of the signs and values of the thermodynamic parameters obtained: association enthalpy, binding constant, Gibbs
free energy, and entropy. It was inferred that: (i) in water, the formation of complexes for parent and substituted α-cyclodextrins
(αCDs) is determined by enthalpy. For parent and substituted β-cyclodextrins (βCDs), instead, hydrophobic interactions are
the prevailing forces determining complexation, as indicated by the small and negative or positive enthalpies and by the high
and positive entropies. (ii) In urea, hydrophilic interactions are attenuated. The formation of complexes with alkylated CDs
does not occur. (iii) The analysis of the thermodynamic properties confirms that inclusion is a process dominated by hydration phenomena.
Modifications experienced by the solvent water in the hydration shells of the interacting substances upon association determine
the formation of the complexes. 相似文献
67.
68.
S. Baccaro B. Bianchilli C. Casadio G. Rinaldi 《Radiation Physics and Chemistry》1998,52(1-6):187-191
In this paper gamma-radiation damages and effects on an epoxide matrix and on its particulate composite with coal fly ash have been studied; the curing of both formulations was carried out at room temperature by means of tetraethylenepentamine and of a tailored polyalkylenepolyaminophenolic product. The change on mechanical properties following the irradiation in air at room temperature has been tested as a function of the total absorbed dose. The chemical modification induced by the ionizing radiation on the matrices have been investigated by means of infrared spectrophotometry and differential scanning calorimetry. The high radiation resistance of the matrix and above all of the particulate composite suggests its use for the confinment of low and medium activity radwastes (nuclear or medical). 相似文献
69.
L. Cartechini R. Rinaldi W. Kockelmann S. Bonamore D. Manconi I. Borgia P. Rocchi B. Brunetti A. Sgamellotti 《Applied Physics A: Materials Science & Processing》2006,83(4):631-636
A combination of conventional analytical techniques, such as X-ray fluorescence (XRF) and scanning electron microscopy-electron probe microanalysis (SEM-EPMA), with novel applications of neutron scattering were employed for a non-destructive study of 6th century BC Etruscan bronze plates discovered almost two centuries ago in a princely chamber tomb in Umbria, Italy. The pieces were used to richly decorate a ceremonial carriage, two war chariots and some furniture. Analytical investigations have been carried out to provide the essential information to correctly assign several fragments in order to recompose the original plates. Analytical responses from XRF and SEM-EPMA, although indicative, were strongly affected by surface alteration and contamination. Rietveld analysis of neutron diffraction profiles emerged for its powerful capability to provide extensive non-destructive, high sensitivity information on bulk alloy composition and phase quantification allowing meaningful comparison among the pieces for the reconstruction of the original plates. In addition, strain and texture analyses demonstrated the capability of the technique to achieve a non-invasive characterization of manufacturing procedures. PACS 61.12.Ld; 81.40.Ef; 81.05.Bx 相似文献
70.
Exact ground states of Ising spin glasses: New experimental results with a branch-and-cut algorithm 总被引:4,自引:0,他引:4
C. De Simone M. Diehl M. Jünger P. Mutzel G. Reinelt G. Rinaldi 《Journal of statistical physics》1995,80(1-2):487-496
In this paper we study two-dimensional Ising spin glasses on a grid with nearest neighbor and periodic boundary interactions, based on a Gaussian bond distribution, and an exterior magnetic field. We show how using a technique called branch and cut, the exact ground states of grids of sizes up to 100×100 can be determined in a moderate amount of computation time, and we report on extensive computational tests. With our method we produce results based on more than 20,000 experiments on the properties of spin glasses whose errors depend only on the assumptions on the model and not on the computational process. This feature is a clear advantage of the method over other, more popular ways to compute the ground state, like Monte Carlo simulation including simulated annealing, evolutionary, and genetic algorithms, that provide only approximate ground states with a degree of accuracy that cannot be determineda priori. Our ground-state energy estimation at zero field is –1.317. 相似文献