全文获取类型
收费全文 | 316篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 215篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 21篇 |
物理学 | 85篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 24篇 |
2020年 | 9篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 12篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 27篇 |
2012年 | 34篇 |
2011年 | 26篇 |
2010年 | 14篇 |
2009年 | 16篇 |
2008年 | 21篇 |
2007年 | 22篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有329条查询结果,搜索用时 254 毫秒
91.
De Almeida MV De Assis JV Couri MR Anconi CP Guerreiro MC Dos Santos HF De Almeida WB 《Organic letters》2010,12(23):5458-5461
Two synthetic epoxide derivatives, important intermediates in organic synthesis, were obtained from L-quebrachitol, and their conformations were proposed based on spectroscopic analysis. Density functional theory (DFT) calculations of infrared and NMR spectra were shown to be reliable enough for organic chemistry applications. The observed structures were determined with the aid of the DFT spectroscopic data, stressing the relevance and utility of combined experimental/theoretical studies and also the usefulness of the (13)C NMR B3LYP/6-31G(d,p) calculations. 相似文献
92.
Analytical approach for monitoring endocrine-disrupting compounds in urban waste water treatment plants 总被引:1,自引:0,他引:1
Roda A Mirasoli M Michelini E Magliulo M Simoni P Guardigli M Curini R Sergi M Marino A 《Analytical and bioanalytical chemistry》2006,385(4):742-752
The presence of endocrine-disrupting compounds in influent and effluent water samples from four waste water treatment plants located in Italy was studied. The estrogen-like activity of the water samples was measured using a chemiluminescent recombinant yeast assay which is based on genetically engineered yeast cells that express the human estrogen receptor. This receptor, once activated, elicits the expression of the reporter gene lac-Z and, consequently, the production of β-galactosidase, which is then measured by chemiluminescence. To control and minimize sample matrix effects, an external control based on a modified yeast strain stably expressing β-galactosidase was developed and also used in the assay. Rapid and sensitive chemiluminescent enzyme immunoassays were also developed and validated for the quantification of 17β-estradiol, estrone, and estriol in waste water samples. Results from both methods were compared with a reference high-performance liquid chromatography and electrospray ionization tandem mass spectrometry (HPLC ESI-MS-MS) method developed for the quantification of natural estrogens. The recombinant yeast assay revealed a significant estrogenic activity in the influent samples, ranging from 80 to 400 pmol/L 17β-estradiol equivalents (EEQ), which was reduced by 70–95 % in the effluent samples. The yeast assay also showed a systematic 20–30 % overestimation of estrogenic activity relative to the HPLC ESI-MS-MS method, suggesting the presence of other compounds in the samples with estrogenic activity. The chemiluminescent enzyme immunoassays showed the presence of estrogens in the influent samples (mean concentrations: 350–450 pmol/L for estrone, 5–100 pmol/L for 17β-estradiol, 25–300 pmol/L for estriol), with significantly lower concentrations detected in the respective effluent samples. The waste water treatment was able to reduce natural estrogen concentrations by 40–95 %, although a high variability was observed. The enzyme immunoassay data correlated well with data obtained by the HPLC ESI-MS-MS method. Although the recombinant yeast assay represents a useful tool for a first-level screening of estrogenic activity due to its simplicity and high analytical throughput, sample matrix effects observed in waste water of industrial origin were found to strongly affect the yeast cells response, even when properly corrected for using the external control, thereby limiting its use to urban waste water. Its integration with chemiluminescent enzyme immunoassays would improve its performance by reducing false negative results, thereby enabling its use in extensive studies monitoring for the presence of endocrine-disrupting compounds in urban treatment plant effluents. 相似文献
93.
Freire MG Gomes L Santos LM Marrucho IM Coutinho JA 《The journal of physical chemistry. B》2006,110(45):22923-22929
The interactions between water and n-perfluoroalkanes or substituted alpha-(omega-)fluoroalkanes used in blood substitute formulations were investigated experimentally and using ab initio calculations. The solubility of water in C(6)-C(9) perfluoroalkanes and five C(8) analogues of substituted fluoroalkanes was measured in the temperature range between 288 and 318 K at atmospheric pressure, using a Karl Fischer coulometer. From these data, the thermodynamic functions and partial molar solvation quantities such as Gibbs energy, enthalpy, and entropy were determined and compared with the interaction energies in 1:1 water-fluoroalkane complexes in vacuum, obtained using B3LYP/6-311++G(d,p). The experimental solubility data indicates a significant specific interaction between the water and the alpha-(omega-)substitute atom (H, I, Br, or Cl) in the fluoroalkanes. 相似文献
94.
95.
Identification of microorganisms in biofluids of individuals with periodontitis and chronic kidney disease using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry 下载免费PDF全文
96.
Anaerobic waste stabilization ponds: a low-cost contribution to a sustainable wastewater reuse cycle
Waste stabilization ponds (WSP) have been used extensively all over Europe over the last 50 yr for the treatment of municipal
and industrial wastewaters. Models presented in manuals should be used only for guidance, and local experience from pilot
and full-scale plants of a particular pond type is extremely valuable. Anaerobic WSP are single-stage, continuous-flow, anaerobic
reactors operating at ambient temperatures and low volumetric organic loading as a pretreatment method. This article presents
a literature review on the different available operational parameters of anaerobic ponds and exmaples from full-scale plant
performance world-wide. On a wastewater management scheme, involving reuse for agriculture, the zero-energy demand of a waste
stabilization pond series for the effective removal of organic and microbiological loading under existing legislation and
guidelines will remain a valuable tool for sustainable development. 相似文献
97.
Mara E. F. Braibante Gunter Clar Marcos A. P. Martins 《Journal of heterocyclic chemistry》1993,30(4):1159-1160
1-Methyl-5-(trifluoromethyl)-1H-pyrazoles 2, 3 and 4,5-dihydro-1-phenyl-5-(trifluoromethyl)-1H-pyrazol-5-ol 4 were prepared by reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones 1 and hydrazine, methylhydrazine, and phenylhydrazine, respectively, in good yields. Compound 1 proved to be a versatile building block for the regiospecific construction of pyrazole rings having an 5-trifluoromethyl substituent. 相似文献
98.
Paolo Linda Cynthia Ebert Mara Lovrecich Fulvio Rubessa 《Journal of heterocyclic chemistry》1984,21(1):271-272
The hydroxide ion catalyzed hydrolysis of indole-1-carboxamide and indole-1-(N,N-dimethyl)carboxamide has been studied in water at 60.0° and [OH−] concentration between 0.3--2.4N. The rate constants of formation of the tetrahedral intermediate are strongly increased by N-substitution with a heteroaromatic ring in comparison with simple amides. Carbamazepine, (5H-dibenz[b,f]azepine)-5-carboxamide, a potent anticonvulsant drug, is particularly stable under these conditions. 相似文献
99.
Julio Marañón 《Physics letters. A》1984,104(9):459-464
By applying the saddle-point approximation to the N-body Feynman path integral formulation, the classical Hartree-Fock Molecular Orbital (M.O.) equations of quantum chemistry are obtained. 相似文献
100.