全文获取类型
收费全文 | 1069篇 |
免费 | 33篇 |
国内免费 | 4篇 |
专业分类
化学 | 877篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 105篇 |
物理学 | 115篇 |
出版年
2023年 | 18篇 |
2022年 | 38篇 |
2021年 | 43篇 |
2020年 | 24篇 |
2019年 | 22篇 |
2018年 | 12篇 |
2017年 | 26篇 |
2016年 | 38篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 67篇 |
2012年 | 87篇 |
2011年 | 84篇 |
2010年 | 49篇 |
2009年 | 55篇 |
2008年 | 55篇 |
2007年 | 43篇 |
2006年 | 45篇 |
2005年 | 54篇 |
2004年 | 39篇 |
2003年 | 31篇 |
2002年 | 34篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1974年 | 3篇 |
1962年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有1106条查询结果,搜索用时 0 毫秒
121.
High-throughput phenotype screening and target identification have been combined in an effort to isolate antimicrobial, small-molecule therapeutics. This approach, developed by Brown and colleagues and reported in this issue, is a major technological advance for antimicrobial drug discovery. 相似文献
122.
123.
Maria Helena Godinho Assis Farinha Martins Mohamed Naceur Belgacem Luís Gil Nereida Cordeiro 《Macromolecular Symposia》2001,169(1):223-228
This paper deals with the use of cork powder, a by‐product from cork industry, as a filler to reinforce hydroxypropyl cellulose (HPC) matrix. Several films were prepared using HPC, as a matrix, filled with different amounts of cork powder (average diameter < 50 μm) (0.0; 0.5; 1.0 and 10.0% w/w) and in the presence or not of 1,4‐diisocyanatobutane (BDI) (7.0% w/w). Before the elaboration of these films, the surface properties of cork powder as well as that of suberin (main component of cork) were determined by Inverse Gas Chromatography (IGC). The tensile properties of the solid films obtained were studied and, as expected, for the films with BDI but without cork powder, the Young's modulus and the tensile strength increased, while the elongation decreased. However with the filled films it seemed that the Young's modulus decreased and the elongation increased. The Scanning Electron Microscopy showed that the fractured plane of samples with cross‐linking agent and cork powder displayed some nucleation points (0.3 μm) which indicates a strongly bonded interface and which could be considered as a responsible for the high mechanical properties observed. 相似文献
124.
Jorddy Neves Cruz Mozaniel Santana de Oliveira Eloisa Helena de Aguiar Andrade Rafael Rodrigues Lima 《Molecules (Basel, Switzerland)》2022,27(13)
Molecular modeling approaches are used in a versatile way to investigate the properties of diverse organic and inorganic structures such as proteins, biomolecules, nanomaterials, functionalized nanoparticles, and membranes. However, more detailed studies are needed to understand the molecular nature of interactions established in gelatin biofilms impregnated with bioactive compounds. Because of this, we used computational methods to evaluate how the major compounds of Piper divaricatum essential oil can interact with the gelatin biofilm structure. For this, we used as inspiration the paper published, where various properties of the essential oil impregnated gelatin biofilm P. divaricatum are reported. After our computer simulations, we related our molecular observations to biofilm’s structural and mechanical properties. Our results suggest that the major compounds of the essential oil were able to interrupt intermolecular interactions between the chains of the biofilm matrix. However, the compounds also established interactions with the amino acid residues of these chains. Our molecular analyses also explain changes in the structural and mechanical properties of the essential oil-impregnated biofilm. These results can support the planning of functional packaging impregnated with bioactive compounds that can protect food against microorganisms harmful to human health. 相似文献
125.
Maria Teresa do Prado Gambardella Regina Helena Porto Francisco Ana Maria G. Dias Rodrigues Gerimrio Freitas de Sousa 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):e176-e177
In the title compound, [SnCl3(CH3)(C6H5SOCH2)2]n, the octahedral SnIV centres are bridged by meso‐1,2‐bis(phenylsulfinyl)ethane ligands forming infinite chains along the [100] direction. 相似文献
126.
127.
128.
Dmitar Zori? Du?an Lazar Ognjen Rudi? Miroslava Radeka Jonjaua Ranogajec Helena Hir?enberger 《Journal of Thermal Analysis and Calorimetry》2012,110(1):489-495
The article presents the results of physical and chemical properties of lightweight aggregates (LWA) obtained by the thermal treatments of raw composition based on fly ash, supplied by electric plants from Serbia. The production process of LWA consists of raw material preparation, plastic shaping?Cextrusion, granulation, and thermal treatment at three temperatures: 1100, 1150, and 1200?°C. The final firing temperature (T?=?1150?°C) is chosen based on the mechanical and physical properties of the designed aggregates. The particle-size distribution of the LWAs is unimodal (d????16?mm) while the density value varies from 0.98 to 1.99?g/cm3. The water absorption values are determined by use of two methods: 24?h of soaking in cold water and 5?h of boiling. The thermal conductivity of unbound, fired LWA particles is determined by measuring the amount of axially transferred heat in the stationary state. The obtained value of the LWA thermal conductivity (???=?0.0872?W/mK, T?=?1150?°C) is suitable for the production of structural concrete blocks with improved thermal insulating properties. Because of their high-porosity and -compressive strength values, the designed LWA could be used instead of the conventional aggregates in the production of concrete blocks. Consequently, a real valorization of the waste material such as fly ash in Serbia was established. 相似文献
129.
Pascal Salaün Kristopher B. Gibbon-Walsh Georgina M.S. Alves Helena M.V.M. Soares Constant M.G. van den Berg 《Analytica chimica acta》2012
The oxidation potentials of As0/AsIII and Sb0/SbIII on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20 nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤ 2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the AsIII and SbIII are below 0.1 nM using 2 min and 10 min deposition times respectively. AsIII and SbIII can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As0 to AsIII was found to proceed through a transient AsIII species. Adsorption of this species on the gold electrode at potentials where SbIII diffused away is used for selective deposition of AsIII. Addition of EDTA removes the interfering effect of manganese when analysing AsIII. Imposition of a desorption step for SbIII analysis is required. Total inorganic arsenic (iAs = AsV + AsIII) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6 < pH < 2 using Edep = −1 V. Total inorganic antimony (iSb = SbV + SbIII) is determined at pH 1 using Edep = −1.8 V without interference by As. 相似文献
130.
Baldacci A Theurillat R Caslavska J Pardubská H Brenneisen R Thormann W 《Journal of chromatography. A》2003,990(1-2):99-110
γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ. 相似文献