全文获取类型
收费全文 | 1495篇 |
免费 | 76篇 |
国内免费 | 15篇 |
专业分类
化学 | 1006篇 |
晶体学 | 3篇 |
力学 | 52篇 |
数学 | 243篇 |
物理学 | 282篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 51篇 |
2021年 | 82篇 |
2020年 | 48篇 |
2019年 | 47篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 84篇 |
2015年 | 56篇 |
2014年 | 64篇 |
2013年 | 75篇 |
2012年 | 93篇 |
2011年 | 106篇 |
2010年 | 64篇 |
2009年 | 65篇 |
2008年 | 78篇 |
2007年 | 67篇 |
2006年 | 92篇 |
2005年 | 86篇 |
2004年 | 68篇 |
2003年 | 48篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1908年 | 2篇 |
1900年 | 1篇 |
1870年 | 1篇 |
排序方式: 共有1586条查询结果,搜索用时 484 毫秒
991.
The aim of the study was to evaluate the effects of Salvia hispanica and Nigella sativa seed addition on the volatile compounds and sensory characteristics (with particular emphasis on odor and flavor) of traditionally produced dry fermented sausages with reduced nitrites. Five different sausage formulations were prepared: control sample; samples with 1% and 2% addition of chia seed; samples with 1% and 2% addition of black cumin seed. The sausages were subjected to analysis including proximate chemical composition, volatile compound determination, and sensory analysis. The sausages with chia seed in the amounts of 1% and 2% as well as the sample with 1% addition of black cumin seed were characterized by positive sensory features, and their overall quality was rated above 7 c.u. on a 10-point scale, similar to the control sausage. Sausage samples with the addition of cumin seed were characterized by the highest herbal odor and flavor. The addition of Salvia hispanica and Nigella sativa seed significantly affected the amount of volatile compounds in fermented sausages. Sausages with black cumin presented the greatest amount of total volatile compounds, mainly contributed by terpenes. 相似文献
992.
On the long time behavior of the stochastic heat equation 总被引:2,自引:0,他引:2
We consider the stochastic heat equation in one space dimension and compute – for a particular choice of the initial datum
– the exact long time asymptotic. In the Carmona-Molchanov approach to intermittence in non stationary random media this corresponds
to the identification of the sample Lyapunov exponent. Equivalently, by interpreting the solution as the partition function of a directed polymer in a random environment, we obtain
a weak law of large numbers for the quenched free energy. The result agrees with the one obtained in the physical literature
via the replica method. The proof is based on a representation of the solution in terms of the weakly asymmetric exclusion
process.
Received: 11 November 1997 / Revised version: 31 July 1998 相似文献
993.
Radia Arab Susana Casal Teresa Pinho Rebeca Cruz Mohamed Lamine Freidja Jos Manuel Lorenzo Christophe Hano Khodir Madani Lila Boulekbache-Makhlouf 《Molecules (Basel, Switzerland)》2022,27(14)
Roasting is a key step for preparing sesame oil that leads to important changes in its organoleptic properties and quality. In this study, white sesame seeds were roasted for 20 min in an electric oven at different temperatures (120, 150, 180, 210, 250 and 300 °C). The oils extracted from unroasted and roasted seeds were compared for their chemical composition: fatty acids (including trans isomers), phytosterols, lignans (sesamin and sesamolin), tocopherols and total phenolic compounds, as well as their oxidative stability and antiradical capacity. There were no obvious differences in the oil densities, refractive indexes or iodine values, but the saponification values were affected by temperature. Relevant primary and secondary lipid oxidation were observed at T > 250 °C, resulting in a higher p-anisidine value and K232 as well as K268 values. Roasting improved oil yield (from 33.5 to 62.6%), increased its induction period (from 5.5 to 10.5 h) and enhanced the total phenolic content (from 152 to 194 mg/100 g) and antiradical activity of the extracted oil. Depending on roasting temperature, a gradual decline was recorded in total amounts of phytosterols (up to 17.4%), γ-tocopherol (up to 10.6%), sesamolin (maximum of 27.5%) and sesamin (maximum of 12.5%). All the investigated oils presented a low quantity in triglyceride polymers, clearly below the maximum tolerated quantity according to the European regulation. The optimal roasting temperature for obtaining high nutritional grade oil within the permissible values was 210 °C. The unsaponifiable components (including lignans and sterols) extracted from roasted seeds have been shown to be natural additives to fresh meatball products to extend shelf life. The results of this study may help to boost the nutritional content of plant-based diets by allowing for the use of roasted sesame seed oil and its components. 相似文献
994.
Francesco Galeotti Lorenzo Scatena Franco Trespidi Mariacecilia Pasini 《Molecules (Basel, Switzerland)》2022,27(23)
The continuous growth in energy demand requires researchers to find new solutions to enlarge and diversify the possible ways of exploiting renewable energy sources. Our idea is the development of a solar concentrator based on trapping the luminous radiation with a smart window. This system is able to direct light towards the photovoltaic cells placed on window borders and produce electricity, without any movable part and without changing its transparency. Herein, we report a detailed study of cellulose ethers, a class of materials of natural origin capable of changing their state, from transparent aqueous solution to scattering hydrogel, in response to a temperature change. Cellulose thermotropism can be used to produce a scattering spot in a window filled with the thermotropic fluid to create a new kind of self-tracking solar concentrator. We demonstrate that the properties of the thermotropic fluid can be finely tuned by selecting the cellulose functionalization, the co-dissolved salt, and by regulating their dosage. Lastly, the results of our investigation are tested in a proof-of-concept demonstration of solar concentration achieved by thermotropism-based light trapping. 相似文献
995.
Giovanni Luongo Antonietta Siciliano Giovanni Libralato Sara Serafini Lorenzo Saviano Lucio Previtera Giovanni Di Fabio Armando Zarrelli 《Molecules (Basel, Switzerland)》2021,26(6)
The discovery of various sartans, which are among the most used antihypertensive drugs in the world, is increasingly frequent not only in wastewater but also in surface water and, in some cases, even in drinking or groundwater. In this paper, the degradation pathway of olmesartan acid, one of the most used sartans, was investigated by simulating the chlorination process normally used in a wastewater treatment plant to reduce similar emerging pollutants. The structures of nine isolated degradation byproducts (DPs), eight of which were isolated for the first time, were separated via chromatography column and HPLC methods, identified by combining nuclear magnetic resonance and mass spectrometry, and justified by a proposed mechanism of formation beginning from the parent drug. Ecotoxicity tests on olmesartan acid and its nine DPs showed that 50% of the investigated byproducts inhibited the target species Aliivibrio fischeri and Raphidocelis subcapitata, causing functional decreases of 18% and 53%, respectively. 相似文献
996.
Ferreiro López-Riobóo Juana Isabel Crespo González Natalia López Mahía Purificación Muniategui Lorenzo Soledad Prada Rodríguez Dario 《Accreditation and quality assurance》2019,24(1):73-78
Accreditation and Quality Assurance - One of the fundamental stages in planning and developing any interlaboratory comparison is the selection and preparation of the test items to be distributed to... 相似文献
997.
998.
Helicene Monomers and Dimers: Chiral Chromophores Featuring Strong Circularly Polarized Luminescence
Cédric Schaack Lorenzo Arrico Eric Sidler Marcin Górecki Lorenzo Di Bari Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8003-8007
The synthesis and chiroptical properties of a series of enantiomerically pure, C2-symmetrical carbo[6]helicene dimers are reported. Two helicene cores are connected through a buta-1,3-diyne-1,4-diyl linker or a heteroaromatic bridge and bear arylethynyl substituents at their 15-positions. This ensures the possibility of extended electronic communication throughout the whole molecule. The new chromophores exhibit intense ECD spectra with strong bands in the UV/Vis region well above 400 nm. The anisotropy factor gabs (defined as Δϵ/ϵ) reaches values up to 0.047, which are unusually large for single organic molecules. They also display blue fluorescence, with good quantum yields (Φf∼0.25). The emitted light is circularly polarized to an outstanding extent: in some cases, the luminescence dissymmetry factor glum=2(IL−IR)/(IL+IR) attains values of |0.025|. To the best of our knowledge, such values are among the highest ever reported for non-aggregated organic fluorophores. 相似文献
999.
Luca Capaldo Lorenzo L. Quadri Davide Ravelli 《Angewandte Chemie (International ed. in English)》2019,58(49):17508-17510
The merging of a homogeneous photocatalytic system with an electrochemical cell, having exchanged electrons as the only common point, has been recently demonstrated. This combination opens unexplored pathways in synthesis and allowed net‐oxidative photocatalytic processes to be realized in the absence of a chemical oxidant, including: 1) the C?H alkylation of heteroarenes and 2) the coupling of azoles with arenes in the presence of an electrogenerated photocatalyst. 相似文献
1000.