全文获取类型
收费全文 | 897篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
化学 | 593篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 48篇 |
物理学 | 264篇 |
出版年
2023年 | 9篇 |
2022年 | 48篇 |
2021年 | 47篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 35篇 |
2015年 | 18篇 |
2014年 | 37篇 |
2013年 | 63篇 |
2012年 | 58篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 47篇 |
2007年 | 41篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 27篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1968年 | 4篇 |
1967年 | 2篇 |
排序方式: 共有932条查询结果,搜索用时 15 毫秒
81.
The rate constants of the reactions of e aq ? and the OH· radical with the oxalate ion in a neutral aqueous solution were measured by means of the pulse radiolysis technique. They were found to be (3.5 ± 0.5) × 107 and (1.5 ± 0.2) × 107 l mol?1 s?1, respectively. The radical anion ?OOC-C·OO2? is characterized by an optical absorption band that has a maximum at 270 nm and a molar absorption coefficient of (2400 ± 200) l mol?1 cm?1. The radical anion ·OOC-COO?, the product of the reaction with the OH· radical, exhibits absorption that has no maximum and increases in intensity with a decrease in the wavelength extending to the UV region (?220 = 1800 l mol?1 cm?1). The mechanism of radiation-chemical transformations in aqueous oxalate solutions is discussed. 相似文献
82.
Mydul Alam M Kumar Shrestha L Aramaki K 《Journal of colloid and interface science》2009,329(2):366-371
We have investigated the effects of glycerol on the formation and rheological behavior of cubic phase (I(1)) and related O/I(1) gel emulsion in a water/C(12)EO(8)/dodecane system at 25 degrees C. The phase behavior of the water/C(12)EO(8)/dodecane system was studied by optical observation and structures of different liquid crystalline phases were identified by small-angle X-ray scattering (SAXS) techniques. Addition of dodecane (2 wt%) to aqueous solutions of C(12)EO(8) in a concentrated region (40 wt%) leads to the formation of the I(1) phase (which was absent without the addition of oil). The I(1) phase solubilized some amount of oil and at higher oil concentrations the I(1)+O phase was formed, allowing the preparation of O/I(1) gel emulsion. Rheological measurements have shown that the complex viscosity, |eta( *)|, of the I(1) phase is tremendously high ( approximately 10(7) Pas) and it increases with increasing oil concentration, attains a maximum value near the phase boundary, and then decreases drastically in the I(1)+O region. The increasing |eta( *)| or decreasing tandelta(G(')/G(')) can be ascribed with the interactions among the neighboring micelles. The decreasing trend of the |eta( *)| in the I(1)+O region is simply due to the low volume fraction of the I(1) phase. It has been shown that glycerol decreases the viscosity of the I(1) phase and related gel emulsion, which is due to the I(1)-hexagonal phase (H(1)) microstructural transition. Digital images show the physical appearance of the emulsion, which depends on the glycerol concentration changes from translucent to transparent. 相似文献
83.
Kabir-ud-Din Malik Abdul Rub Md. Sayem Alam 《Journal of Dispersion Science and Technology》2013,34(9):1182-1187
Herein we report the micellization and clouding behavior of promethazine hydrochloride (PMT) in absence and presence of NaCl/ureas. The critical micelle concentration (CMC) of PMT is measured by conductivity method and the values decrease with increasing the NaCl concentration. With increasing the temperature, the CMC first increases then decreases. At 25°C, the maximum CMC values were obtained (with or without NaCl). The thermodynamic parameters are evaluated which indicate more stability of the PMT solution in presence of NaCl. PMT shows phase separation also. The cloud point (CP) of PMT decreases with increase in pH due to deprotonation of the drug molecules. Ureas decreased the CP and the behavior is explained on the basis of removal of water from the head group region. 相似文献
84.
Shah Alam Khan 《中国化学会会志》2004,51(6):1273-1277
Friedel‐Crafts cycloalkylation of biphenyl with 2,3‐dichlorobutyltrichlorosilane(Cl3Si‐CH2CHClCHClCH3) at a temperature of 100°C in the presence of anhydrous aluminum chloride catalyst gave cyclized product, 9‐methyl‐9‐(2‐trichlorosilylethyl)fluorene 1a , in 33% yield. Methylation of 1a with nucleophilic reagent such as methyl magnesium chloride, gave 9‐methyl‐9‐(2‐trimethylsilylethyl)fluorene 2 while bromination of 2 with excess amount of bromine in DMF resulted in 2,7‐dibromo‐9‐methyl‐9‐(2‐trichlorosilyl)fluorene 3 in good yield. All the compounds were structurally identified by GC/MS, 1H and 13C‐NMR spectroscopy. 相似文献
85.
Cotton fabric was coated with chitosan (CS) and polyethylene glycol (PEG) followed by freeze‐drying. The influence of PEG on the physical characteristics and the surface morphology was investigated. The scanning electron microscopy of the coated fabric revealed a porous structure. The porosity of the material was 54–70% and the pore size was in the range of 75–120µm. The increase in the PEG content in the blend composition led to an enhanced destabilization of pores, leading to an increase in the pore size with elongated morphology. There seems to be phase separation between the two components which is an important factor for the observed behavior of the porous structure. The Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) showed that the CS and PEG have limited interaction. DSC suggested that addition of PEG to CS does not interfere with the crystallization behavior due to limited interaction with CS. The thermogravimetric analysis (TGA) showed that the membranes are thermally stable and PEG enhances the thermal stability of the CS coated membranes. The air and water permeability of the membranes tended to decrease with the increase in the PEG content. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
86.
87.
88.
Daniel Schäpper Muhd Nazrul Hisham Zainal Alam Nicolas Szita Anna Eliasson Lantz Krist V. Gernaey 《Analytical and bioanalytical chemistry》2009,395(3):679-695
Biotechnology process development involves strain testing and improvement steps aimed at increasing yields and productivity. This necessitates the high-throughput screening of many potential strain candidates, a task currently mainly performed in shake flasks or microtiter plates. However, these methods have some drawbacks, such as the low data density (usually only end-point measurements) and the lack of control over cultivation conditions in standard shake flasks. Microbioreactors can offer the flexibility and controllability of bench-scale reactors and thus deliver results that are more comparable to large-scale fermentations, but with the additional advantages of small size, availability of online cultivation data and the potential for automation. Current microbioreactor technology is analyzed in this review paper, focusing on its industrial applicability, and directions for future research are presented. 相似文献
89.
Alam Gustavo Trov Silene Alessandra Santos Melo Raquel Fernandes Pupo Nogueira 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):215-220
Photodegradation of the pharmaceuticals amoxicillin (AMX), bezafibrate (BZF) and paracetamol (PCT) in aqueous solutions via the photo-Fenton process was investigated under black-light and solar irradiation. The influences of iron source, initial H2O2 concentration and matrix (distilled water and sewage treatment plant effluent) on degradation efficiency were discussed in detail. The results showed that (i) the degradation of the drugs was favored in the presence of potassium ferrioxalate (FeOx) in comparison to Fe(NO3)3; (ii) the increase of the H2O2 concentration improved the efficiency of AMX and BZF oxidation; however, the same was not observed for PCT; (iii) the influence of the matrix was observed for the degradation of BZF and PCT; (iv) under solar irradiation, the oxidation of the BZF and PCT is faster than under black-light irradiation. All these pharmaceuticals can be efficiently degraded employing the process evaluated. 相似文献
90.
Ryu Sato Toshiyuki Fujio Shiduko Nakajo Satoshi Ogawa Ashraful Alam 《Tetrahedron letters》2007,48(17):3013-3016
The synthesis of benzopentathiepin having a hydroxyl group at the neighboring position of polysulfur ring was performed by demethylation of 6-ethyl-9-methoxybenzopentathiepin with hydrogenbromide. Benzotrithiole having hydroxyl group was not isolated at all. The hydroxyl group was also alkylated with alkyl iodide in the presence of weak base. 相似文献