全文获取类型
收费全文 | 1543篇 |
免费 | 77篇 |
国内免费 | 12篇 |
专业分类
化学 | 1055篇 |
晶体学 | 12篇 |
力学 | 72篇 |
综合类 | 4篇 |
数学 | 227篇 |
物理学 | 262篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 58篇 |
2021年 | 69篇 |
2020年 | 38篇 |
2019年 | 49篇 |
2018年 | 60篇 |
2017年 | 45篇 |
2016年 | 86篇 |
2015年 | 73篇 |
2014年 | 67篇 |
2013年 | 159篇 |
2012年 | 99篇 |
2011年 | 113篇 |
2010年 | 97篇 |
2009年 | 79篇 |
2008年 | 81篇 |
2007年 | 77篇 |
2006年 | 48篇 |
2005年 | 48篇 |
2004年 | 44篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 11篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 3篇 |
排序方式: 共有1632条查询结果,搜索用时 13 毫秒
21.
M. Saeed Butt Zareen Akhter M. Zafar-uz-Zaman Humaira Masood Siddiqi 《Colloid and polymer science》2008,286(12):1455-1461
The diamine, 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline, was prepared via the nucleophilic substitution reaction and was polymerized with
different dianhydrides either by one-step solution polymerization reaction or two-step procedure. The latter includes ring-opening
polyaddition to give poly(amic acid), followed by cyclodehydration to polyimides. The inherent viscosity ranges from 0.61–0.79 dl/g.
Some of the polymers were soluble in most of the organic solvents such as DMSO, DMF, DMAc, NMP, and m-cresol even at room temperature. The degradation temperature of the resultant polymers falls in the ranges from 240–500 °C
in nitrogen with only 10% weight loss. Specific heat capacity at 200 °C ranges from 1.0929–2.6275 J g−1 k−1. The temperature at which the maximum degradation of the polymer occurs ranges from 600–630 °C. The glass transition temperature
(Tg) values of the polyimides ranged from 185 to 272 °C. The activation energy and enthalpy of the polyimides ranged from
47.5–55.0 kJ/mole and 45.7–53.0 kJ/mole and the moisture absorption in the range of 0.23–0.72%. 相似文献
22.
This review covers the main strategies for the synthesis of N‐pivot lariat ethers as well as their specific syntheses. 相似文献
23.
Mujahid Farid Muhammad Abubakar Zaki Ul Zaman Asam Wajiha Sarfraz Mohsin Abbas Muhammad Bilal Shakoor Shafaqat Ali Sajid Rashid Ahmad Asim Jilani Javed Iqbal Abdullah G. Al-Sehemi Omar A. Al-Hartomy 《Molecules (Basel, Switzerland)》2022,27(13)
We investigated how different doses of microwave irradiation (MR) affect seed germination in Sorghum, including the level of remediation against textile and surgical wastewater (WW) by modulating biochemical and morpho-physiological mechanisms under glutamic acid (GA) application. The experiment was conducted to determine the impact of foliar-applied GA on Sorghum under wastewater conditions. Plants were treated with or without microwave irradiation (30 s, 2.45 GHz), GA (5 and 10 mM), and wastewater (0, 25, 50, and 100). Growth and photosynthetic pigments were significantly decreased in plants only treated with various concentrations of WW. GA significantly improved the plant growth characteristics both in MR-treated and -untreated plants compared with respective controls. HMs stress increased electrolyte leakage (EL), hydrogen peroxide (H2O2), and malondialdehyde (MDA) content; however, the GA chelation significantly improved the antioxidant enzymes activities such as ascorbate oxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) both in MR-treated and -untreated plants under WW stress compared with respective controls. The results suggested that the MR-treated plants accumulate higher levels of HMs under GA addition in comparison to the WW-only-treated and MR-untreated plants. The maximum increase in Cd accumulation was observed in the range of 14–629% in the roots, 15–2964% in the stems, and 26–4020% in the leaves; the accumulation of Cu was 18–2757% in the roots, 15–4506% in the stems, and 23–4605% in the leaves; and the accumulation of Pb was 13–4122% in the roots, 21–3588% in the stems, and 21–4990% in the leaves under 10 mM GA and MR-treated plants. These findings confirmed that MR-treated sorghum plants had a higher capacity for HMs uptake under GA and could be used as a potential candidate for wastewater treatment. 相似文献
24.
Johnson AC Greenwood P Hagström M Abbas Z Wall S 《Langmuir : the ACS journal of surfaces and colloids》2008,24(22):12798-12806
The slow aggregation process of a concentrated silica dispersion (Bindzil 40/220) in the presence of alkali chlorides (LiCl, NaCl, KCl, RbCl, and CsCl) was investigated by means of mobility measurements. At intervals during the aggregation, particles and aggregates were transferred from the liquid phase to the gas phase via electrospray (ES) and subsequently size selected and counted using a scanning mobility particle sizer (SMPS). This method enables the acquisition of particle and aggregate size distributions with a time resolution of minutes. To our knowledge, this is the first time that the method has been applied to study the process of colloidal aggregation. The obtained results indicate that, independent of the type of counterion, a sufficient dilution of the formed gel will cause the particles to redisperse. Hence, the silica particles are, at least initially, reversibly aggregated. The reversibility of the aggregation indicates additional non-DLVO repulsive steric interactions that are likely due to the presence of a gel layer at the surface. The size of the disintegrating aggregates was monitored as a function of the time after dilution. It was found that the most stable aggregates were formed by the ions that adsorb most strongly on the particle surface. This attractive effect was ascribed to an ion-ion correlation interaction. 相似文献
25.
Abbas Tarassoli Tahereh Sedaghat Hamid-Reza Goudarzi 《Central European Journal of Chemistry》2009,7(1):130-133
Aminolysis of N3P3CI6 by an oxodiamine, bis-(2-ortho-aminophenoxyethyl) ether, has been carried out under various experimental conditions and new
products with different architectures have been obtained. The reaction in diethyl ether when using a Na2CO3-water interface process gives the mono-BINO as major product. Reaction on Al2O3/KOH leads to the spirocyclic compound, while, when the reaction is carried out in toluene in the presence of NEt3, a mixture of mono- and di-BINO products are obtained. These new products have been characterized by IR, 1H and 31P NMR spectroscopy.
相似文献
26.
Dementin S Burlat B Fourmond V Leroux F Liebgott PP Abou Hamdan A Léger C Rousset M Guigliarelli B Bertrand P 《Journal of the American Chemical Society》2011,133(26):10211-10221
Electrons are transferred over long distances along chains of FeS clusters in hydrogenases, mitochondrial complexes, and many other respiratory enzymes. It is usually presumed that electron transfer is fast in these systems, despite the fact that there has been no direct measurement of rates of FeS-to-FeS electron transfer in any respiratory enzyme. In this context, we propose and apply to NiFe hydrogenase an original strategy that consists of quantitatively interpreting the variations of steady-state activity that result from changing the nature of the FeS clusters which connect the active site to the redox partner, and/or the nature of the redox partner. Rates of intra- and intermolecular electron transfer are deduced from such large data sets. The mutation-induced variations of electron transfer rates cannot be explained by changes in intercenter distances and reduction potentials. This establishes that FeS-to-FeS rate constants are extremely sensitive to the nature and coordination of the centers. 相似文献
27.
28.
Komeili Samane Takht Ravanchi Maryam Taeb Abbas 《Research on Chemical Intermediates》2018,44(2):1335-1349
Research on Chemical Intermediates - 0.03 wt% Pd catalysts on nickel and zinc aluminate supports were prepared by impregnation. The samples were characterized by XRD, BET, ICP, SEM, EDS,... 相似文献
29.
M. A. Salem M. H. Helal M. A. Gouda Y. A. Ammar M. S. A. El-Gaby S. Y. Abbas 《合成通讯》2018,48(13):1534-1550
Coumarins units have recently emerged as a hot topic of research due to their diverse applications. Their synthesis is partly based on classical methodologies such as Pechmann reaction or Knoevenagel condensation, but it also sparked the discovery of completely new pathways. In very recent years so-called vertically expanded coumarins were synthesized, effectively expanding the portfolio of existing architectures. This review serves as a guide through synthesis strategies to coumarins. 相似文献
30.
Maha A. Hegazy Hassan A. M. Hendawy Soheir A. Weshahy Samah S. Abbas 《液相色谱法及相关技术杂志》2018,41(5):203-222
Fluorometholone (FLM) and Sodium Cromoglycate (CMG) are co-formulated in ophthalmic preparation and showed marked instability under different conditions. Two specific, sensitive and precise stability-indicating chromatographic methods have been developed and validated for their determination in the presence of their degradation products and FLM impurity. Ten components were efficiently separated by them. The first method was HPTLC-spectrodensitometry, where the separation was achieved using silica gel 60?F254 HPTLC plates and developing system of ethyl acetate: methanol (9:1, v/v). The second method was a reversed phase HPLC associated with kinetic study of the degradation process and was successfully applied for determination of the studied compounds in spiked rabbit aqueous humor. The mobile phase was acetonitrile: methanol: 0.05?M potassium dihydrogenphosphate (0.1% trimethylamine); pH 2.5, adjusted with orthophosphoric acid (20: 30: 50, by volume). In both methods, the separated components were detected at 240?nm and system suitability was checked. Good correlation was obtained in the range of 0.10–24.00 and 0.20–48.00?µg band?1, for FLM and CMG by HPTLC. While for HPLC, the linearity ranges from 0.01–50.00 and 0.05–50.00?µg?mL?1 for both drugs. The methods were applied in pharmaceutical formulation, where they were compared to the reported method with no significant difference. 相似文献