全文获取类型
收费全文 | 22792篇 |
免费 | 3429篇 |
国内免费 | 2443篇 |
专业分类
化学 | 16077篇 |
晶体学 | 276篇 |
力学 | 1353篇 |
综合类 | 187篇 |
数学 | 2296篇 |
物理学 | 8475篇 |
出版年
2024年 | 67篇 |
2023年 | 423篇 |
2022年 | 739篇 |
2021年 | 820篇 |
2020年 | 849篇 |
2019年 | 833篇 |
2018年 | 711篇 |
2017年 | 736篇 |
2016年 | 1015篇 |
2015年 | 1035篇 |
2014年 | 1170篇 |
2013年 | 1606篇 |
2012年 | 1866篇 |
2011年 | 1989篇 |
2010年 | 1297篇 |
2009年 | 1266篇 |
2008年 | 1463篇 |
2007年 | 1349篇 |
2006年 | 1217篇 |
2005年 | 970篇 |
2004年 | 774篇 |
2003年 | 658篇 |
2002年 | 632篇 |
2001年 | 461篇 |
2000年 | 454篇 |
1999年 | 481篇 |
1998年 | 422篇 |
1997年 | 423篇 |
1996年 | 463篇 |
1995年 | 365篇 |
1994年 | 381篇 |
1993年 | 272篇 |
1992年 | 254篇 |
1991年 | 233篇 |
1990年 | 165篇 |
1989年 | 129篇 |
1988年 | 117篇 |
1987年 | 97篇 |
1986年 | 95篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Maria Catarina Coutinho Varela da Silva João Luís Maia Figueirinhas 《Liquid crystals》2016,43(1):124-130
A number of polymer dispersed liquid crystal (PDLC) films based on dimethacrylate monomers were synthesised by polymer-induced phase separation (PIPS) using polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (TX-100) as an additive up to total solution weight of 10% aiming to modify the initial anchorage force of the liquid crystal (LC) molecules to the polymeric matrix. The effects of the addition of this additive to the PDLC films were studied resorting to electro-optical studies. Using a fitting model, several parameters were correlated such as the permanent memory effect (PME), the voltage required to achieve 90% of maximum transmittance (E90), the average elastic constant (K) and the rotational viscosity of the director (γ). The use of TX-100 results on an increase on the PME and γ, and decrease on the E90 and K. 相似文献
982.
Christina C. Roggatz Mercedes González-Wangüemert Hugo Pereira Maria João Rodrigues Manuela Moreira da Silva Luísa Barreira 《Natural product research》2016,30(18):2034-2040
This work reports for the first time the nutritional profile and antioxidant potential of the edible sea cucumber Holothuria arguinensis from the North-eastern Atlantic. H. arguinensis has high levels of protein, with the amino acids profile dominated by alanine, glycine and proline and low lysine/arginine ratios. Its carbohydrate and energetic contents are also low as well as the total lipid levels, although its lipid profile is rich in polyunsaturated fatty acids (PUFA), especially arachidonic, eicosapentaenoic and docosahexaenoic acids. In addition, H. arguinensis has high levels of calcium. The water and ethanol extracts show ability to scavenge free radicals and to chelate copper and iron ions. Our results indicate that H. arguinensis has a balanced nutritional quality suitable for human consumption. In addition, it contains compounds with antioxidant potential; thus its intake can contribute for a healthy and well-balanced diet. 相似文献
983.
Liang-Deng Nie Fei-Feng Wang Wei Ding Xiao-Xin Shi Xia Lu 《Tetrahedron: Asymmetry》2013,24(11):638-642
A novel azide-free asymmetric synthesis of oseltamivir phosphate 1 (Tamiflu®) starting from Roche’s epoxide is described. Roche epoxide 2 was converted into N-acetyl aminoalcohol 3 in 95% yield via a BF3·OEt2-catalyzed epoxide-opening with acetonitrile as a nucleophile. Compound 3 was then transformed into a methanesulfonate 4 in 98% yield. Compound 4 was converted into aziridine 5 in 91% yield. Aziridine 5 was subsequently converted into oseltamivir phosphate 1 via two paths (a and b). In the path a, compound 5 underwent aziridine-opening with diallylamine as a nucleophile to afford compound 7 in 93% yield; compound 7 could then be converted into oseltamivir phosphate 1 in 88% yield. In path b, compound 5 underwent aziridine-opening with isopropyl 2,2,2-trichloroacetimidate as a nucleophile to afford compound 8 in 94% yield, which was then converted into oseltamivir phosphate 1 in 82% yield. 相似文献
984.
A series of (3-oxo-1,3-diaryl) propylpropanedinitriles were synthesized by Michael addition reaction of chalcones and malononitriles in the presence of potassium fluoride on alumina. 相似文献
985.
Ting Huang Renguo Lu Hongyan Wang Yuning Ma Jianshu Tian Tongsheng Li 《Journal of Macromolecular Science: Physics》2013,52(7):1235-1248
The tribological properties of polyoxymethylene (POM) modified by nano-polytetrafluorethylene (nano-PTFE) were investigated by a block-on-ring wear tester. For comparison, modified POM with micro-polytetrafluoroethylene (micro-PTFE) was also studied. The modified POM with a much lower concentration of nano-PTFE showed the similar tribological properties compared with POM modified by micro-PTFE. The friction coefficient decreased with the increase of nano-PTFE, while the wear rate showed the lowest value when the concentration of nano-PTFE was 2%. Scanning electron microscope (SEM) micrographs revealed that transfer films played an important role in the friction process. The transfer films decreased and stabilized the friction coefficient. Comparing to POM/2%nano-PTFE, when the concentration of nano-PTFE reached 4%, the mechanical properties decreased significantly, possibly due to poor dispersion of nano-PTFE. 相似文献
986.
Bing Niu Yuhuan Jin Lin Lu Kaiyan Fen Lei Gu Zhisong He Wencong Lu Yixue Li Yudong Cai 《Molecular diversity》2009,13(3):313-320
The knowledge of whether one enzyme can interact with a small molecule is essential for understanding the molecular and cellular
functions of organisms. In this paper, we introduce a classifier to predict the small molecule– enzyme interaction, i.e.,
whether they can interact with each other. Small molecules are represented by their chemical functional groups, and enzymes
are represented by their biochemical and physicochemical properties, resulting in a total of 160 features. These features
are input into the AdaBoost classifier, which is known to have good generalization ability to predict interaction. As a result,
the overall prediction accuracy, tested by tenfold cross-validation and independent sets, is 81.76% and 83.35%, respectively,
suggesting that this strategy is effective. In this research, we typically choose interactions between small molecules and
enzymes involved in metabolism to ultimately improve further understanding of metabolic pathways. An online predictor developed
by this research is available at .
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
987.
988.
QU He-zhi DU Shan-shan YANG Shuo HUANG Lu ZHANG Lei XIAO Song HAO Dong-yun WANG Xiao-ping 《高等学校化学研究》2010,26(2):240-244
Mammalian cells express two isoforms of Cu-and Zn-containing superoxide dismutases(SODs),CuZnSOD and extracellular SOD(EC-SOD),involved in the defense system against reactive oxygen species(ROS).The two SODs have structurally homologous centre domain with distinct N-and C-terminuses,resulting in the different characteristics of the structure and function of the two molecules.We generated a hybrid SOD molecule(namely hySOD) via replacing the N-and C-terminuses of hCuZnSOD with the counterparts of hEC-SOD.The... 相似文献
989.
990.