全文获取类型
收费全文 | 1375篇 |
免费 | 118篇 |
国内免费 | 31篇 |
专业分类
化学 | 172篇 |
力学 | 432篇 |
综合类 | 5篇 |
数学 | 712篇 |
物理学 | 203篇 |
出版年
2023年 | 17篇 |
2022年 | 19篇 |
2021年 | 33篇 |
2020年 | 44篇 |
2019年 | 45篇 |
2018年 | 35篇 |
2017年 | 50篇 |
2016年 | 46篇 |
2015年 | 39篇 |
2014年 | 80篇 |
2013年 | 125篇 |
2012年 | 65篇 |
2011年 | 89篇 |
2010年 | 61篇 |
2009年 | 75篇 |
2008年 | 72篇 |
2007年 | 72篇 |
2006年 | 65篇 |
2005年 | 73篇 |
2004年 | 50篇 |
2003年 | 55篇 |
2002年 | 43篇 |
2001年 | 42篇 |
2000年 | 21篇 |
1999年 | 39篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1524条查询结果,搜索用时 15 毫秒
31.
A sensitive and convenient high-performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) assay is described for the (5-HT(lB/lD)) receptor agonist sumatriptan in human plasma. Sumatriptan was recovered from plasma (81.8 +/- 6.8%) by liquid-liquid extraction. The mobile phase flow rate was 0.3 mL/min and consisted of methanol:water:formic acid (90:10:0.1, v/v/v). The analytical column (4.6 x 100 mm) was packed with Partisil C(8) (5 micro m). The standard curve was linear from 0.7 to 70.4 ng/mL (r(2) > 0.99). The lower limit of quantitation was 0.7 ng/mL. The assay was specific, accurate (percentage deviation from nominal concentrations were <15%), precise and reproducible (within- and between-day coefficients of variation <10.3%). Sumatriptan in plasma was stable over three freeze/thaw cycles and at room temperature for one day. The utility of the assay was demonstrated by following sumatriptan plasma concentrations in two healthy subjects for 8-12 h following a single 20 mg intranasal dose. 相似文献
32.
K. Terada T. Masuda Y. Yoshihashi E. Yonemochi 《Journal of Thermal Analysis and Calorimetry》2006,85(3):675-680
Isothermal
microcalorimetry was used to evaluate excipient compatibility of solid dosage
form. Oxybutynin hydrochloride and cefaclor were used as model drugs for compatibility
test with excipients. The calorimetric data for compatibility test were compared
with those of HPLC data. Evaluation of compatibility between drug and excipient
of solid dosage form might be possible to use isothermal microcalorimetry
instead of conventional method. By using microcalorimetric method, the evaluation
of the compatibility between drug and excipient could be successfully performed
with a simple operation in a short time. The application of the isothermal
microcalorimetry would be useful for the screening test of the drug compatibility
with excipients. 相似文献
33.
Summary A rapid and accurate LC method is described for simultaneous determination of pseudoephedrine hydrochloride (PSE), acetaminophen (AMP), dextromethorphen hydrobromide (DEX), and diphenhydramine hydrochloride (DPH) in a compound formulation. Chromatographic separation of the four drugs was achieved on a Hypersil CN column (150 mm × 4.6 mm, 5 m particle) by use of a mobile phase comprising a mixture of 3 mM ion-pairing solution, 2% aqueous triethylamine solution, and 2 M phosphoric acid, 68:48:88 (v/v), pH 3.0, delivered at 1.0 mL min–1. Compounds were detected at 215 nm and the run time was less than 10 min. The linearity, accuracy, and precision of the method were found to be acceptable over the concentration ranges 6.1–36.4 g mL–1 for PSE, 65.0–390.0 g mL–1 for AMP, 3.1–18.6 g mL–1 for DEX, and 5.0–30.0 g mL–1 for DPH. 相似文献
34.
35.
A finite volume cell‐centered Lagrangian hydrodynamics approach, formulated in Cartesian frame, is presented for solving elasto‐plastic response of solids in general unstructured grids. Because solid materials can sustain significant shear deformation, evolution equations for stress and strain fields are solved in addition to mass, momentum, and energy conservation laws. The total stress is split into deviatoric shear stress and dilatational components. The dilatational response of the material is modeled using the Mie‐Grüneisen equation of state. A predicted trial elastic deviatoric stress state is evolved assuming a pure elastic deformation in accordance with the hypo‐elastic stress‐strain relation. The evolution equations are advanced in time by constructing vertex velocity and corner traction force vectors using multi‐dimensional Riemann solutions erected at mesh vertices. Conservation of momentum and total energy along with the increase in entropy principle are invoked for computing these quantities at the vertices. Final state of deviatoric stress is effected via radial return algorithm based on the J‐2 von Mises yield condition. The scheme presented in this work is second‐order accurate both in space and time. The suitability of the scheme is evinced by solving one‐ and two‐dimensional benchmark problems both in structured grids and in unstructured grids with polygonal cells. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
36.
A. K. Awasthi F. R. Meng J. F. Künzler J. G. Linhardt P. Papagelis G. Oltean S. A. Myers 《先进技术聚合物》2013,24(6):557-567
A series of novel mono‐ethylenically unsaturated polycarbosiloxanes macromonomers as compatibilizer materials for soft silicon hydrogels were prepared from the anionic ring‐opening polymerization (AROP) of 2,2,5,5‐tetramethyl‐2,5‐disila‐1‐oxacyclopentane followed by methacrylation. The characterization was performed by end‐group analysis and included the determination of molecular weight, molecular weight distributions, end‐group functionality, and impurity profiles using gas chromatography‐mass spectrometry, gel permeation chromatography, nuclear magnetic resonance, and matrix‐assisted laser desorption/ionization time of flight mass spectrometry. The synthetic procedure was optimized to minimize the formation of any dimer that would have the potential to act as a low molecular weight cross linker. In addition, the novel di‐ethylenically unsaturated polycarbosiloxanes were synthesized by cationic polymerization. Use of these silicone derivatives was explored in the formulation of contact lenses, and the structure–property relationship was examined. When copoymerized with hydrophilic monomers, these were able to give transparent and wettable films with desired properties, particularly a low moduli for contact lenses. Contact lens with high modulus is often shown to impart a higher degree discomfort when worn upon the eye. It was clear from the structure–property relationship that the modulus and the tensile strength of the formulated material depend on the nature and length of the polycarbosiloxane used and may be tuned for the purpose as needed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
37.
Abstract A rapid and sensitive spectrophotometric method is developed for the quantitative determination of piperazine, piperazine salts and diethylcarbamazine citrate. The method is based on the formation of donor-acceptor complexes between the compound and chloranilic acid. The interaction product has a characteristic absorption maximum at about 345 nm. The system obeys Beer's law in the concentration range of 1–10 ugml?1 of piperazine hexahydrate, adipate, phosphate, citrate and diethylcarbamazine citrate. The effects of several experimantal variables have been studied and the stoichiometric composition of the complex has been determined. The developed procedure has been found to be simple, rapid and precise and its application to various dosage forms was demonstrated and yields results comparable with the standard method. 相似文献
38.
Versatile chromatographic method for catechin determination in development of topical formulations containing natural extracts 下载免费PDF全文
《Biomedical chromatography : BMC》2018,32(2)
Catechin is found in several natural sources, as Eugenia dysenterica and Syzygium cumini extracts. Its antioxidant and UV‐protective properties suggest a potential use in cosmetic and dermatological formulations. A simple analytical method capable of giving support to experiments performed along the development of topical formulations containing this natural substance (i.e. drug assay, skin permeation and stability studies), however, is still needed. Thus, this work aimed to develop and validate a selective HPLC method for catechin determination during the development of topical formulations. Separation was achieved using an RP‐C18 column (300 × 3.9 mm; 10 μm), with a mobile phase of methanol–phosphoric acid 0.01 m (15: 85, v/v), a flow rate of 0.8 mL/min, temperature set at 40°C and UV detection at 230 nm. The method was linear in a range from 0.5 to 10.0 μg/mL (r = 0.9998), precise with an overall variation coefficient of 5.5% and accurate with catechin recovery from the skin layers >85%. Additionally, the method was sensitive (limit of detection, 0.109 μg/mL; limit of quantification, 0.342 μg/mL) and selective against plant extracts, skin matrices and formulation interferents, as well as catechin degradation products. It was also robust regarding both methodology parameters and analytical stability. 相似文献
39.
In this article, an ALE finite element method to simulate the partial melting of a workpiece of metal is presented. The model includes the heat transport in both the solid and liquid part, fluid flow in the liquid phase by the Navier–Stokes equations, tracking of the melt interface solid/liquid by the Stefan condition, treatment of the capillary boundary accounting for surface tension effects and a radiative boundary condition. We show that an accurate treatment of the moving boundaries is crucial to resolve their respective influences on the flow field and thus on the overall energy transport correctly. This is achieved by a mesh‐moving method, which explicitly tracks the phase boundary and makes it possible to use a sharp interface model without singularities in the boundary conditions at the triple junction. A numerical example describing the welding of a thin‐steel wire end by a laser, where all aforementioned effects have to be taken into account, proves the effectiveness of the approach.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
40.
The MHD Falkner–Skan equation arises in the study of laminar boundary layers exhibiting similarity on the semi‐infinite domain. The proposed approach is equipped by the orthogonal Sinc functions that have perfect properties. This method solves the problem on the semi‐infinite domain without truncating it to a finite domain and transforming domain of the problem to a finite domain. In addition, the governing partial differential equations are transformed into a system of ordinary differential equations using similarity variables, and then they are solved numerically by the Sinc‐collocation method. It is shown that the Sinc‐collocation method converges to the solution at an exponential rate. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献