全文获取类型
收费全文 | 1116篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 890篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 165篇 |
物理学 | 86篇 |
出版年
2023年 | 10篇 |
2022年 | 55篇 |
2021年 | 61篇 |
2020年 | 53篇 |
2019年 | 32篇 |
2018年 | 34篇 |
2017年 | 26篇 |
2016年 | 53篇 |
2015年 | 53篇 |
2014年 | 47篇 |
2013年 | 81篇 |
2012年 | 70篇 |
2011年 | 81篇 |
2010年 | 60篇 |
2009年 | 49篇 |
2008年 | 65篇 |
2007年 | 55篇 |
2006年 | 44篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1992年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1936年 | 2篇 |
1927年 | 2篇 |
1924年 | 2篇 |
1923年 | 1篇 |
排序方式: 共有1150条查询结果,搜索用时 15 毫秒
951.
Abdullah G. Al‐Sehemi Ahmed A. Al‐Ghamdi Nikolay T. Dishovsky Lachezar N. Radev Irena K. Mihailova Petrunka A. Malinova Nikolay T. Atanasov Gabriela L. Atanasova 《先进技术聚合物》2020,31(3):574-588
Bioactive glass was first synthesized by L. Hench in 1971. There are many studies on the properties of several metals and metal ions dopants used in the SiO2‐CaO‐P2O5 system of bioglasses, such as Ag, Cu, Zn, and Fe. A number of authors have carried out research related to the influence of silver oxide on the properties of bioglasses . However, publications on the properties of elastomer‐based composites containing bioactive glasses are relatively scarce. We have not found in the literature studies discussing how silver oxide concentration in bioglasses of the CaO‐SiO2‐P2O5‐Ag2O system affects the significant properties of a natural rubber biocomposite. In this regard, the purpose of the present work is to investigate the aforementioned influence on the properties of this type of composites, namely, vulcanization, physicomechanical, thermal, dynamic, dielectric, electric, and thermoconductive characteristics. We have established those parameters of the composites to be impacted considerably by both degree of filling with bioglass and the silver oxide content in the latter. The improvement in the composites thermostability and some of their physicomechanical performance is the most significant. The volume resistance decreases, and the thermal conductivity coefficients increase. Results from scanning electron microscopy and energy‐dispersive X‐ray (EDX) analyses have confirmed the influence of silver oxide initially on the phase composition of the bioglass, hence on the properties of the biocomposites through changes in the bioglass used as filler. The dielectric characteristics of some of the biocomposites suggest that they can be used as substrates and insulating layers in flexible antennas for short‐range wireless communications. 相似文献
952.
953.
Tănase Ionuț-Mihai Sbârcea Laura Ledeți Adriana Vlase Gabriela Barvinschi Paul Văruţ Renata-Maria Dragomirescu Anca Axente Carmen Ledeți Ionuț 《Journal of Thermal Analysis and Calorimetry》2020,141(3):1027-1039
Journal of Thermal Analysis and Calorimetry - Aripiprazole (ARP), an innovative atypical antipsychotic drug, exhibits very low aqueous solubility, affecting its dissolution and absorption and high... 相似文献
954.
Constantin Bolcu Dorina Modra Gabriela Vlase Nicolae Doca Ciprian Mihali Titus Vlase 《Journal of Thermal Analysis and Calorimetry》2014,115(1):489-494
Some silica-organic compounds were prepared by an addition reaction between γ-amino-propyl-triethoxy silane and 4,4′-diphenylmethane diisocyanate. The obtained products were characterized by FTIR spectrometry. The essential synthesis parameter was the molar ratio between the two reactants. The thermal behavior of the products was rather good, until 150 °C no mass loss or thermal effects being observed. The thermal behavior was determined under non-isothermal conditions, using TG/DTG/HF diagrams. Due to the hydroxyl end-groups, these compounds are recommended for adhesives between organic and inorganic surfaces. 相似文献
955.
956.
957.
Gabriela Jajko Dr. Paweł Kozyra Dr. Juan José Gutiérrez-Sevillano Dr. Wacław Makowski Prof. Sofia Calero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14653-14659
The rapidly rising level of carbon dioxide in the atmosphere resulting from human activity is one of the greatest environmental problems facing our civilization today. Most technologies are not yet sufficiently developed to move existing infrastructure to cleaner alternatives. Therefore, techniques for capturing carbon dioxide from emission sources may play a key role at the moment. The structure of the UiO-66 material not only meets the requirement of high stability in contact with water vapor but through the water pre-adsorbed in the pores, the selectivity of carbon dioxide adsorption is increased. We successfully applied the recently developed methodology for water adsorption modelling. It allowed to elucidate the influence of water on CO2 adsorption and study the mechanism of this effect. We showed that water is adsorbed in octahedral cage and stands for promotor for CO2 adsorption in less favorable space than tetrahedral cages. Water plays a role of a mediator of adsorption, what is a general idea of improving affinity of adsorbate. On the basis of pre-adsorption of methanol as another polar solvent, we have shown that the adsorption sites play a key role here, and not, as previously thought, only the interaction between the solvent and quadrupole carbon dioxide. Overall, we explained the mechanism of increased CO2 adsorption in the presence of water and methanol, as polar solvents, in the UiO-66 pores for a potential post-combustion carbon dioxide capture application. 相似文献
958.
Maria Victoria Neacsu Gabriela Ionita Carmen Topala Eliza Oprea Victorita Tecuceanu Iulia Matei 《Chemical Papers》2017,71(3):607-616
Finding new, biocompatible matrices that allow us to model the generation of free radicals is of utmost importance for balancing the harmful and beneficial effects of the latter. In this respect, we report here the simultaneous encapsulation of the radical source and the antioxidant agent in a polyethylene glycol/β-cyclodextrin (PEG/β-CD) covalent gel network. We used electron paramagnetic resonance spectroscopy to evaluate the scavenging action of plant extracts (purple loosestrife, comfrey, milfoil, horsetail, thyme, carob, green coffee) embedded in PEG/β-CD gels. Free radicals were generated in situ by UV irradiation of riboflavin co-embedded in the gels. Prior to this, the extracts were characterized in what concerns their antioxidant activity, and their major polyphenolic constituents were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry. Purple loosestrife showed the highest antioxidant capacity, followed by comfrey and milfoil. Using the 5,5-dimethyl-1-pyrroline N-oxide spin trap, we have demonstrated that the gel-embedded extracts effectively scavenge the reactive carbon-centered free radicals generated in gel. The PEG/β-CD gels have been shown to be a valuable alternative matrix for the encapsulation of plant active principles having antioxidant activity. Moreover, co-encapsulation of the radical source transforms these gels into a controlled environment in which free radical processes can be tailored. 相似文献
959.
Gabriela Cristea Ioana Feher D. Alina Magdas Cezara Voica Romulus Puscas 《Analytical letters》2017,50(17):2677-2690
ABSTRACT109 Romanian parsley, celery and parsnip root, cucumber, vegetable marrow, onion, and pepper samples were characterized by their stable isotope ratios and elemental concentrations in comparison to imported varieties. Organic and conventional agriculture practices were also compared as well as a differentiation between eggplant and peppers grown in greenhouses and those in the field. δ2H values were between ?70.8 and 5.6‰, while the δ18O values were between ?9.0 and 4.1‰. The δ15N values for white onions were from 2.8 to 11.1‰. For Romanian organic onions, the carbon isotopic values were lower (?29.2 to ?28.2‰) compared to conventional onions from other countries (?27.8‰ to ?23.8%). Linear discriminant analysis was used to characterize agricultural practices and the geographic origin of the vegetables. 相似文献
960.