全文获取类型
收费全文 | 822篇 |
免费 | 26篇 |
国内免费 | 10篇 |
专业分类
化学 | 550篇 |
晶体学 | 1篇 |
力学 | 70篇 |
数学 | 103篇 |
物理学 | 134篇 |
出版年
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 27篇 |
2020年 | 46篇 |
2019年 | 46篇 |
2018年 | 41篇 |
2017年 | 42篇 |
2016年 | 54篇 |
2015年 | 28篇 |
2014年 | 47篇 |
2013年 | 80篇 |
2012年 | 72篇 |
2011年 | 70篇 |
2010年 | 50篇 |
2009年 | 31篇 |
2008年 | 41篇 |
2007年 | 34篇 |
2006年 | 27篇 |
2005年 | 19篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有858条查询结果,搜索用时 15 毫秒
91.
Mostafa Hosseini Ali Asghar Karkhane Bagher Yakhchali Mehdi Shamsara Saeed Aminzadeh Dena Morshedi Kamahldin Haghbeen Ibrahim Torktaz Esmat Karimi Zahra Safari 《Applied biochemistry and biotechnology》2013,169(3):773-785
Lipases are one of the highest value commercial enzymes as they have broad applications in detergent, food, pharmaceutical, and dairy industries. To provide chimeric Bacillus thermocatenulatus lipase (BTL2), the completely conserved pentapeptide (112Ala-His-Ser-Gln-Gly116) was replaced with similar sequences (207Gly-Glu-Ser-Ala-Gly211) of Candida rugosa lipase (CLR) at the nucleophilic elbow region. For this purpose, three mutations including A112G, H113E, and Q115A were inserted in the conserved pentapeptide sequence of btl2 gene. Based on the crystal structures of 2W22, the best structure of opened form of the chimeric lipases were garnered using the MODELLER v9.10 software. The native and chimeric lipases were docked to a set of ligands, and a trial version of Molegro Virtual Docker (MVD) software was used to obtain the energy values. Docking results confirmed chimeric lipase to be better than the native lipase. Following the in silico study, cloning experiments were conducted and expression of native and chimeric btl2 gene in Pichia pastoris was performed. The native and chimeric lipases were purified, and the effect of these mutations on characteristics of chimeric lipase studied and then compared with those of native lipase. Chimeric lipase exhibited 1.6-fold higher activity than the native lipase at 55 °C. The highest percentage of both lipases activity was observed at 60 °C and pH of 8.0. The ion Ca2+ slightly inhibited the activity of both lipases, whereas the organic solvent enhanced the lipase stability of chimeric lipase as compared with the native lipase. According to the results, the presence of two glycine residues at the conserved pentapeptide region of this chimeric lipase (112 Gly-Glu-Ser-Ala-Gly 116) may increase the flexibility of the nucleophilic elbow region and affect the enzyme activity level. 相似文献
92.
Mohammad S. Hosseini Ali R. Rzaei Sarab 《International journal of environmental analytical chemistry》2013,93(5):375-385
Twenty-five uncultivated surface soil samples collected from the northern and southern regions of Dhaka Export Processing Zone (DEPZ), industrial area of Bangladesh, were analyzed for their contents of Y, lanthanides and natural radionuclides (Th and U) using an inductively coupled plasma mass spectrometer (ICP-MS). Analogous concentrations of the Y, lanthanides, Th and U were observed in the both regions of DEPZ around several kilometer distances. Further, the measured values showed no particular contamination. However, the concentrations of the light lanthanides (La, Ce and Nd) in the Bangladeshi soils were around twice the worldwide average value. But, the smooth curve of the chondrite normalized patterns of the lanthanides suggested that the lanthanide contents of the Bangladeshi soils in this area are the results of the natural dispersion process rather than anthropogenic activities. In addition, the relatively high Th and U concentrations and Th/U ratio were observed in Bangladeshi soils of this area, most likely due to the effect of their parent materials such as clay stones which have a high Th/U ratio. Since this is the first precise result for the Y, lanthanides, Th and U contents in Bangladeshi soils, it could be useful in understanding the background level and the characteristics of these elements in Bangladeshi soils. 相似文献
93.
A highly efficient synthesis of 2‐arylamino‐2‐imidazolines and 2‐aminobenzimidazoles from aminoimino‐methanesulfonic acid derivatives is described. The method is simple and practical, generating imidazoline and benzimidazoline derivatives in excellent isolated yields. 相似文献
94.
Mojtaba Shamsipur Tahereh Poursaberi Morteza Hosseini Naader Alizadeh Mohammad Reza Ganjali 《Analytica chimica acta》2004,501(1):55-60
A highly sensitive and selective fluorimetric optode membrane for the determination of ultra trace amounts of Ni2+ ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) (TTBB), as a highly fluorescent chromoionophore, displays a calibration response for Ni2+ ions over a wide concentration range of 1.0×10−3 to 1.0×10−8 M. It has a relatively fast response of <40 s. In addition to high stability and reproducibility, and relatively long working lifetime, the sensor possesses good selectivity for nickel ions over several common diverse ions. The fluorescence signal of the optode membrane can be easily recovered by immersion in EDTA solution. The optode was applied successfully to the determination of traces of Ni2+ ion in edible oil and a wastewater sample from nickel electroplating industries. 相似文献
95.
Headspace solvent microextraction (HSME) into a single drop is developed for the determination of six trihalomethanes, CH2Cl2, CHCl3, C4H9Cl, CCl4, C2HCl3, and C2Cl4, in aqueous solution. A drop of benzyl alcohol containing bromoform, as an internal standard, is used for extraction. The analytes are extracted by suspending a 3-microL drop directly from the needle of a microsyringe. The needle passes through the septum of a vessel, and the needle tip appears above the surface of the solution. After the prescribed extraction time, the drop is drawn back into the syringe. The syringe is then removed, and its content is injected directly into a gas chromatography column for analysis. The main parameters affecting the HSME process, such as stirring speed, microdrop volume, sample solution temperature, microsyringe needle temperature, sample volume, solution pH, extracting solvent, and ionic strength of the solution, are studied. Also, the linear range and precision of the method are examined. 相似文献
96.
M.R. Ganjali B. Veismohammadi M. Hosseini P. Norouzi 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(2):575-578
A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 × 10−7 to 1.0 × 10−5 M and the detection limit is 1.4 × 10−7 M. The association constant of the 1:1 complex formation for L–Tb+3 was calculated to be 6.01 × 106 M−1, and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations. 相似文献
97.
A. R. Moghadassi S. Masoud Hosseini D. Henneke A. Elkamel 《Journal of Thermal Analysis and Calorimetry》2009,96(1):81-84
Thermal conductivity is an important parameter in the field of nanofluid heat transfer. This article presents a novel model
for the prediction of the effective thermal conductivity of nanofluids based on dimensionless groups. The model expresses
the thermal conductivity of a nanofluid as a function of the thermal conductivity of the solid and liquid, their volume fractions,
particle size and interfacial shell properties. According to this model, thermal conductivity changes nonlinearly with nanoparticle
loading. The results are in good agreement with the experimental data of alumina-water and alumina-ethylene glycol based nanofluids. 相似文献
98.
Rahmat Sadeghi Rahim Hosseini 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,348(1-3):177-185
The volumetric, compressibility and electrical conductivity properties of sodium n-heptyl sulfonate (C7SO3Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the micellar composition range. At each temperature, the infinite dilution apparent molar volumes of the monomer and micellar state of C7SO3Na in aqueous PEG solutions respectively are smaller and larger than those in pure water. However, the values of the infinite dilution apparent molar isentropic compressibility of both monomer and micellar states of C7SO3Na in aqueous PEG solutions are larger than those in pure water. Thermodynamic parameters of micellization of investigated surfactant in water and in aqueous solutions of PEG at different temperatures were estimated and it was found that the micelle formation process is endothermic and therefore, this process must be driven by entropy increase. The calculated Gibbs free energies of micellization for aqueous PEG solutions are more negative than those for pure water and become more negative by increasing temperature. The variation of the critical micelle concentration (CMC) of C7SO3Na in water and in aqueous PEG solutions with temperature was obtained and a comparison between the CMC of C7SO3Na obtained from different thermodynamic properties was also made. 相似文献
99.
The design, synthesis, and characterization of the 10 linear and bent acentric ligands 1 – 10 (tectons) based on the differentiation of two divergently disposed coordinating poles is reported. The nature of the two poles and their distance are varied by the use of different linear spacers. For these molecules, a monodentate coordinating site, i.e., a pyridine ring, and a tridentate coordinating site, i.e., a pyridine moiety bearing at the 2 and 6 positions either two thioether groups or two dimethylamino units (PySMe and PyN(Me2)2 type, resp.), a terpyridine, or a pyridine ring bearing two optically pure dihydrooxazole units, are combined. 相似文献
100.
S. Masoud Hosseini A. R. Moghadassi Dale E. Henneke 《Journal of Thermal Analysis and Calorimetry》2010,99(3):873-877
Immobilization of lead contamination in soils by precipitation of non-assimilable for plants Pb-phosphate was considered. Glassy fertilizer of controlled release rate of the nutrients for plants as a source of phosphate anions was applied. Thermal analysis methods (TG/DTG/DTA) were used for the identification of components of Pb-precipitate, which being in statu nascendi have nonstoichiometric composition and disordered crystallographic structure difficult to identify by XRD method. Application of TA methods permits to demonstrate the negative role of Pb complexing citric acid solution simulating the natural soil conditions, which inhibits the Pb-phosphate of pyromorphite type formation. 相似文献