全文获取类型
收费全文 | 1180篇 |
免费 | 93篇 |
国内免费 | 27篇 |
专业分类
化学 | 1018篇 |
晶体学 | 9篇 |
力学 | 14篇 |
数学 | 92篇 |
物理学 | 167篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 40篇 |
2021年 | 49篇 |
2020年 | 82篇 |
2019年 | 81篇 |
2018年 | 111篇 |
2017年 | 82篇 |
2016年 | 84篇 |
2015年 | 64篇 |
2014年 | 94篇 |
2013年 | 126篇 |
2012年 | 102篇 |
2011年 | 78篇 |
2010年 | 56篇 |
2009年 | 46篇 |
2008年 | 57篇 |
2007年 | 43篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1300条查询结果,搜索用时 421 毫秒
131.
132.
Maryam Ghaderabad Mahdieh Mansouri Sima Beigoli Atena Sharifi Rad Jamshid Mehrzad Mohammad Reza Saberi Jamshidkhan Chamani 《Journal of the Iranian Chemical Society》2017,14(7):1347-1364
This article describes the interaction of fluoxymesterone (Flu) with HSA and HTF in the absence and presence of cyclodextrins (CDs) (α, β and γ). According to fluorescence data, the binding of Flu to the proteins caused strong static quenching in the binary and ternary systems. The fluorescence quenching results demonstrated that HSA and HTF had two and one class of apparent binding sites with a distinct binding constant in the presence of the CDs, respectively. The effects of Flu on the structure of HSA and HTF were analyzed using synchronous fluorescence spectroscopy, which showed that the interaction of Flu with both proteins in the binary and ternary systems altered the microenvironment around the Trp and Tyr residues. The distance, r, between Flu and the proteins was obtained according to FRET which pointed at a successful formation of a drug-protein complex. Far-UV CD spectra indicated that the binding of the drug to both proteins induced changes in the secondary structure of HSA and HTF in the binary and ternary systems. Finally, molecular modeling provided possible binding sites of Flu within the proteins for the binary and ternary systems and also confirmed the experimental results. The obtained data can be useful for determining usage drug doses in drug delivery. 相似文献
133.
This paper considers a novel formulation of the multi-period network interdiction problem. In this model, delivery of the maximum flow as well as the act of interdiction happens over several periods, while the budget of resource for interdiction is limit. It is assumed that when an edge is interdicted in a period, the evader considers a rate of risk of detection at consequent periods. Application of the generalized Benders decomposition algorithm considers solving the resulting mixed-integer nonlinear programming problem. Computational experiences denote reasonable consistency with expectations. 相似文献
134.
We study the convergence rate of the proximal-gradient homotopy algorithm applied to norm-regularized linear least squares problems, for a general class of norms. The homotopy algorithm reduces the regularization parameter in a series of steps, and uses a proximal-gradient algorithm to solve the problem at each step. Proximal-gradient algorithm has a linear rate of convergence given that the objective function is strongly convex, and the gradient of the smooth component of the objective function is Lipschitz continuous. In many applications, the objective function in this type of problem is not strongly convex, especially when the problem is high-dimensional and regularizers are chosen that induce sparsity or low-dimensionality. We show that if the linear sampling matrix satisfies certain assumptions and the regularizing norm is decomposable, proximal-gradient homotopy algorithm converges with a linear rate even though the objective function is not strongly convex. Our result generalizes results on the linear convergence of homotopy algorithm for \(\ell _1\)-regularized least squares problems. Numerical experiments are presented that support the theoretical convergence rate analysis. 相似文献
135.
The synthesis of coumarins by hydroxyalkylation of phenols with ethyl acetoacetate (via Pechmann reaction) is attempted using magnetically separable and reusable CuFe2O4 nanoparticles in water.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications ® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
136.
Stable and even microcrystals of Avermectin (AVM) were produced by recrystallization in presence of a stabilizer. Sequential layer growth was achieved by the layer-by-layer (LbL) self-assembly of biocompatible polyelectrolytes (PEs). The coated colloids were characterized using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The in vitro release of Avermectin from microcapsules was studied under the simulated insect midgut conditions. W-doped TiO(2) photocatalysts were synthesized by a simple hydrothermal method, and characterized by Brunauer-Emmett-Teller (BET) surface area measurements and SEM. The photocatalytic activities of photocatalysts, which were undoped with TiO(2) and W-doped TiO(2), were evaluated by the photocatalytic oxidation degradation of AVM microcapsules in aqueous solution under UV illumination. The toxicity of the photodegradable insecticide was evaluated by the adult stage Martianus dermestoides. The results showed that AVM microcrystals which were obtained by association had a mean length of 13.8μm and a zeta potential of -34.7mV. The drug loading and encapsulation efficiency were 65.57±0.96% and 46.15±0.96%, respectively. The in vitro release experiments revealed that the polyelectrolytes prolonged the release time of the encapsulated AVM microcrystals. The sample which was prepared at 120°C with 4.0mol% W-doped amount had the highest photocatalytic activity. Toxicity of the novel photodegradable insecticide was higher in the adult stage compared to the 95% AVM as indicated by the lower LC(50) value. 相似文献
137.
Razieh FAZAELI Hamid ALIYAN Shadpour MALLAKPOUR Zahra RAFIEE Maryam BORDBAR 《催化学报》2011,32(4):582-588
A novel compound constructed from polyoxometalate (H3PW12O40,PW12) and poly(amidoamine) (PA) was prepared at room temperature in an aqueous solution by an impregnation method.A series of novel 1,3,5-triaryl-2-pyrazoline derivatives was synthesized by the reaction between chalcone and phenylhydrazine in the presence of the title compound,PW12/PA,in high yields.The structures of the compounds obtained were determined by IR and 1H NMR spectra. 相似文献
138.
Fatemeh Vahedi Mojtaba Sankian Malihe Moghadam Maryam Mohaddesfar Sirous Ghobadi Abdol Reza Varasteh 《Applied biochemistry and biotechnology》2011,163(7):895-905
Chenopodium album is a weedy annual plant in the genus Chenopodium. C. album pollen represents a predominant allergen source in Iran. The main C. album pollen allergens have been described as Che a 1, Che a 2, and Che a 3. The aim of this work was to clone the Che a 1 in Escherichia coli to establish a system for overproduction of the recombinant Che a 1 (rChe a 1). In order to clone this allergen, the pollens
were subjected to RNA extraction. A full-length fragment encoding Che a 1 was prepared by polymerase chain reaction amplification
of the first-strand cDNA synthesized from extracted RNA. Cloning was carried out by inserting the cDNA into the pET21b (+)
vector, thereafter the construct was transformed into E. coli Top10 cells and expression of the protein was induced by IPTG. The rChe a 1 was purified using histidine tag in recombinant
protein by means of Ni–NTA affinity chromatography. IgE immunoblotting, ELISA, and inhibition ELISA were done to evaluate
IgE binding of the purified protein. In conclusion, the cDNA for the major allergen of the C. album pollen, Che a 1, was successfully cloned and rChe a 1 was purified. Inhibition assays demonstrated allergic subjects sera
reacted with rChe a 1 similar to natural Che a 1 in crude extract of C. album pollen. This study is the first report of using the E. coli as a prokaryotic system for Che a 1 cloning and production of rChe a 1. 相似文献
139.
NiO nanoparticles with an average size of 12 nm and a high specific surface area of 88.5 m2/g were easily prepared via the thermal decomposition of the complex Ni(dmgH)2 and were characterized by TGA, XRD, FT-IR, TEM and BET surface area measurement. This nanosized transition metal oxide was used as a new heterogeneous catalyst for the reduction of nitroarenes under microwave irradiation. The efficient and selective reduction of aromatic nitro compounds into their corresponding amines was observed by using ethanol as a hydrogen donor (reducing agent) and KOH as a promoter under microwave irradiation. This highly regio- and chemoselective method is fast, simple, inexpensive, high yielding, clean and compatible with several sensitive functionalities, such as halogens, -OH, -OCH3, -CHO, -COCH3, -COOH, -COOEt, -CONH2, -CN, -CHCH2 and -NHCOCH3. This method is suitable for the large scale preparation of different substituted anilines as well as other arylamines. In addition, the catalytic activity of nanosized NiO is higher than that of the bulk sample. 相似文献
140.
Maryam MohammadiReza Mokhtari 《Journal of Computational and Applied Mathematics》2011,235(14):4003-4014
On the basis of a reproducing kernel space, an iterative algorithm for solving the generalized regularized long wave equation is presented. The analytical solution in the reproducing kernel space is shown in a series form and the approximate solution un is constructed by truncating the series to n terms. The convergence of un to the analytical solution is also proved. Results obtained by the proposed method imply that it can be considered as a simple and accurate method for solving such evolution equations. 相似文献