全文获取类型
收费全文 | 1668篇 |
免费 | 83篇 |
国内免费 | 9篇 |
专业分类
化学 | 1144篇 |
晶体学 | 10篇 |
力学 | 35篇 |
数学 | 245篇 |
物理学 | 326篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 18篇 |
2021年 | 70篇 |
2020年 | 47篇 |
2019年 | 62篇 |
2018年 | 54篇 |
2017年 | 44篇 |
2016年 | 94篇 |
2015年 | 52篇 |
2014年 | 84篇 |
2013年 | 124篇 |
2012年 | 148篇 |
2011年 | 141篇 |
2010年 | 78篇 |
2009年 | 71篇 |
2008年 | 89篇 |
2007年 | 106篇 |
2006年 | 93篇 |
2005年 | 76篇 |
2004年 | 62篇 |
2003年 | 32篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1760条查询结果,搜索用时 15 毫秒
111.
Diego Gamallo-Lorenzo 《Analytica chimica acta》2005,542(2):287-295
Microwave energy has been novelty applied to speed up a tetramethylammonium hydroxide (TMAH) alkaline digestion of seaweed samples and to assist distillation of iodine from seaweed alkaline digests. Iodide in the alkaline digests from seaweed and distilled iodine, reduced back to iodine in a hydroxylamine hydrochloride solution, was determined by a catalytic spectrophotometric method based on the catalytic effect of iodide on the oxidation of As(III) by Ce(IV) in H2SO4/HCl medium (Sandell-Kolthoff reaction). The determination of iodide was directly performed in the alkaline digests, while total iodine was assessed by analyzing the hydroxylamine hydrochloride solution after the distillation process. Microwave-assisted alkaline digestion was performed using 7.5 mL of TMAH and irradiating samples at 670 W for two 5.5 min steps. Microwave-assisted distillation was carried out using 4.0 mL of the alkaline digest and 3 mL of a 2.2 M hydrochloric acid and 0.05% (m/v) sodium nitrite solution, with a microwave power at 670 W for two 90 s steps. The distillate (iodine vapor) was bubbled in 10 mL of a 500 μg mL−1 hydroxylamine hydrochloride solution (accepting solution). The linear calibration ranges were 0.30-20.0 and 0.40-20.0 μg L−1 for iodide determination and total iodine determination, respectively. The limit of detection was 9.2 μg g−1 for iodide and 28.5 μg g−1 for total iodine. Repeatability of the overall procedures, expressed as R.S.D. for 11 determinations, was 2.6% for 196.3 μg g−1 of iodide measured after microwave-assisted alkaline digestion, and 5.8% for 954.3 μg g−1 of total iodine by microwave-assisted alkaline digestion followed by microwave-assisted distillation. Finally, accuracy of the methods was assessed by analyzing the NIST-09 (Sargasso) certified reference material and the methods were applied to the determination of iodide and total iodine in different Atlantic edible seaweed samples with satisfactory results. 相似文献
112.
113.
Fabian H. Gaioli Edgardo T. Garcia Alvarez Diego G. Arbo 《International Journal of Theoretical Physics》1999,38(1):183-198
This paper generalizes some previous resultspresented in Gaioli et al. [Int. J. Theor. Phys. 36,2167 (1997)]. We evaluate the autocorrelation functionof the stochastic acceleration and study the asymptotic evolution of the mean occupation number of aharmonic oscillator playing the role of a Brownianparticle. We also analyze some deviations from the Bosepopulation at low temperatures and compare it with the deviations from the exponential decay lawof an unstable quantum system. 相似文献
114.
Diego Julio Cirilo-Lombardo 《International Journal of Theoretical Physics》2008,47(11):3015-3028
The geometrical origin of a special type of non-degenerate supermetric is elucidated and the connection with processes of
topological origin in high energy physics is explained. The new mechanism of the localization of the fields in a particular
sector of the supermanifold is explained and the similarity and differences with a 5-dimensional warped model are shown. The
relation with gauge theories of supergravity based in the super SL(2,C) group is explicitly given and the possible original action is presented. From the point of view of the vacuum solutions,
the simplest Riemannian superspaces are described. 相似文献
115.
Wolfgang Petz Diego M. Andrada Markus Hermann Gernot Frenking Bernhard Neumüller 《无机化学与普通化学杂志》2017,643(16):1096-1099
The formation and X‐ray structure analysis of the PtIV complex [(CH2C{PPh2C6H4}2)PtI2] is reported. The molecule possesses the orthometalated ligand (PPh3)2C→CH2, which serves via its C2 fragment as an unprecedented four‐electron σ donor. 相似文献
116.
Effectiveness of Photodynamic Therapy in Elimination of HPV‐16 and HPV‐18 Associated with CIN I in Mexican Women 下载免费PDF全文
Elizabeth Maldonado Alvarado Martha Olivia Osorio Peralta Alejandra Moreno Vázquez Lydia Alejandra Martínez Guzmán Maria Eugenia Melo Petrone Zulma Iveth Enriquez Mar Dora Estela Jovel Galdamez Bárbara Carrión Solana Guadalupe Balderas Martínez Eduarda Parra Rossana Inés Castellanos Oliveros Rosa Linda Bello Leiva Araceli Espinosa Montesinos Citlalli Barrera Mendoza Selma Eugenia Medina García Eva Ramón Gallegos 《Photochemistry and photobiology》2017,93(5):1269-1275
This study aimed to determine the effectiveness of photodynamic therapy (PDT), using δ‐aminolevulinic acid (5‐ALA), in the elimination of premalignant cervical lesions in Mexican patients with human papillomavirus (HPV) infection and/or cervical intraepithelial neoplasia (CIN). Thirty women diagnosed with CIN I and/or positive for HPV participated in the study. Topical 6% 5‐ALA in gel form was applied to the uterine cervix; after 4 h, the lesion area was irradiated with a light dose of 200 J cm?2 at 635 nm. This procedure was performed three times at 48‐h intervals. Clinical follow‐up was performed at 3, 6, and 12 months after the initial PDT administration, by colposcopy, cervical cytology, histopathological analysis, polymerase chain reaction, and hybrid capture. Of HPV‐infected patients without evidence of CIN I, 80% cleared the infection, while HPV associated with CIN I was eliminated in 83% of patients (P < 0.05). At 12 months, CIN I had regressed in 57% of patients, although this response was not statistically significant. PDT using 6% 5‐ALA is concluded to be effective in eliminating HPV infection associated or not with CIN I. 相似文献
117.
A one pot method for the synthesis of ethyl 2-acetoxy-6-aroylcyclohex-1-ene-1-carboxylates and ethyl 2-acetoxy-6-heterocarbonylcyclohex-1-ene-1-carboxylates through Michael addition of the anions of ethyl carbonates of cyanohydrins to cyclohex-2-en-1-one and subsequent reaction with acetic anhydride is described. These compounds are potential intermediates for the synthesis of 9,10-anthraquinone and heterofused 1,4-naphthoquinone derivatives. 相似文献
118.
Rayne S. S. Magalhães Karina C. De Lima Diego S. G. de Almeida Joelma F. De Mesquita Elis C. A. Eleutherio 《Applied biochemistry and biotechnology》2017,181(3):914-924
In some pathogens, trehalose biosynthesis is induced in response to stress as a protection mechanism. This pathway is an attractive target for antimicrobials as neither the enzymes, Tps1, and Tps2, nor is trehalose present in humans. Accumulation of T6P in Candida albicans, achieved by deletion of TPS2, resulted in strong reduction of fungal virulence. In this work, the effect of T6P on Tps1 activity was evaluated. Saccharomyces cerevisiae, C. albicans, and Candida tropicalis were used as experimental models. As expected, a heat stress induced both trehalose accumulation and increased Tps1 activity. However, the addition of 125 μM T6P to extracts obtained from stressed cells totally abolished or reduced in 50 and 60 % the induction of Tps1 activity in S. cerevisiae, C. tropicalis, and C. albicans, respectively. According to our results, T6P is an uncompetitive inhibitor of S. cerevisiae Tps1. This kind of inhibitor is able to decrease the rate of reaction to zero at increased concentrations. Based on the similarities found in sequence and function between Tps1 of S. cerevisiae and some pathogens and on the inhibitory effect of T6P on Tps1 activity observed in vitro, novel drugs can be developed for the treatment of infectious diseases caused by organisms whose infectivity and survival on the host depend on trehalose. 相似文献
119.
Diego Todescato Danielle Maass Diego Alex Mayer J. Vladimir Oliveira Débora de Oliveira Selene M. A. Guelli Ulson de Souza Antônio Augusto Ulson de Souza 《Applied biochemistry and biotechnology》2017,183(4):1375-1389
Rhodococcus sp. has a broad catabolic diversity and unique enzymatic capabilities, and it is able to adapt under extreme conditions. Thereby, the production of this remarkable bacterium has a great biotechnological and industrial importance. In this sense, we sought to improve the R. erythropolis ATCC 4277 growth through a central composite design, by varying the components of nutrient medium (glucose, malt extract, yeast extract, CaCO3), temperature, and agitation. It was found that the concentrations of glucose and malt extract are not statistically significant, being reduced of 4.0 and 10.0 g L-1 to 2.0 and 5.0 g L?1, respectively. The CaCO3 concentration and temperature were also diminished of 2.0 to 1.16 g L?1and 28 to 23.7 °C, respectively. Optimal growth conditions provided a 240% increase in final biomass concentration, an increment in specific growth rate, and a growth yield coefficient about five times greater. Application of the optimal conditions in biodesulfurization and biodenitrogenation processes showed that desulfurization capability is not associated with optimal growth conditions; however, it was achieved a 47% of nitrogen removal in the assay containing 10% (w/w) of heavy gas oil. 相似文献
120.
M. Judith Percino Víctor M. Chapela Ling-Fa Montiel Enrique Pérez-Gutiérrez José Luis Maldonado 《Chemical Papers》2010,64(3):360-367
An efficient Knoevenagel route using green chemistry conditions was applied for the synthesis of halogen- and cyano- substituted
pyridinevinylene compounds. Absorption and fluorescence emission spectra of these conjugated compounds were recorded and compared
in order to evaluate the effect of substituents on the electronic properties of pyridinevinylene compounds. The substituents
studied were terminal Cl and F, two or three aromatic rings, as well as a cyano group attached to a C=C double bond. The compounds
synthesized are: (E)-2-(4-fluorostyryl)pyridine, (E)-2-(4-chlorostyryl)pyridine, (E)-4-(4-chlorostyryl)pyridine, 2,3-diphenylacrylonitrile, 3-phenyl-2-(pyridin-2-yl)acrylonitrile, 3-phenyl-2-(pyridin-3-yl)acrylonitrile,
2-phenyl-3-(pyridin-2-yl)acrylonitrile, 3,3′-(1,4-phenylene)bis(2-phenylacrylonitrile), 3,3′-(1,4-phenylene)bis(2-(pyridin-2-yl)acrylonitrile),
and 3,3′-(1,4-phenylene)bis(2-(pyridin-3-yl)acrylonitrile). The solvent-free method used in this work allows obtaining each
compound by controlling the reaction temperature. The compounds were characterized by infrared spectroscopy and 1H-NMR spectroscopy. 相似文献