全文获取类型
收费全文 | 5672篇 |
免费 | 301篇 |
国内免费 | 36篇 |
专业分类
化学 | 4237篇 |
晶体学 | 65篇 |
力学 | 143篇 |
数学 | 444篇 |
物理学 | 1120篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 85篇 |
2021年 | 143篇 |
2020年 | 116篇 |
2019年 | 137篇 |
2018年 | 107篇 |
2017年 | 90篇 |
2016年 | 198篇 |
2015年 | 201篇 |
2014年 | 230篇 |
2013年 | 366篇 |
2012年 | 457篇 |
2011年 | 526篇 |
2010年 | 316篇 |
2009年 | 302篇 |
2008年 | 448篇 |
2007年 | 358篇 |
2006年 | 316篇 |
2005年 | 293篇 |
2004年 | 244篇 |
2003年 | 197篇 |
2002年 | 202篇 |
2001年 | 79篇 |
2000年 | 105篇 |
1999年 | 60篇 |
1998年 | 53篇 |
1997年 | 40篇 |
1996年 | 37篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有6009条查询结果,搜索用时 46 毫秒
231.
The radical addition reactions of α-substituted β,β-difluorovinyl sulfones 1 with α-oxy and acyl radical species, such as 1,3-dioxolane, tetrahydrofuran, 1,4-dioxane, butanal and hexanal, afforded radical addition products 2--16 in good yields. 相似文献
232.
Novel 1,2,4‐triazole isonucleosides (1 and 2) were efficiently synthesized starting from D‐ribose and D‐xylose, respectively. The key steps were condensation of cyclic sulfate 8 with methyl‐1,2,4‐triazole‐3‐carboxylate and nucleophilic displacement of the tosylate 15 with methyl‐1,2,4‐triazole‐3‐carboxylate, respectively. 相似文献
233.
Samarium(II) iodide promoted reductive deacetoxylation of 7-aminocephalosporanic acid derivatives to synthesize 3-alkylidenecepham-4-carboxylates, which could be valuable intermediates for the synthesis of new cephalosporin antibiotics, was investigated. 相似文献
234.
A series of self-healable polyurethane (SHPU)/modified graphene (MG) nanocomposites were synthesized from poly(tetramethylene glycol) (PTMG) and 4,4′-methylene diphenyl diisocyanate (MDI) with minute amounts (0–1 wt%) of MG which was chemically modified graphene oxide (GO) with phenyl isocyanate and reduced in the presence of phenylhydrazine. 相似文献
235.
Yeon‐Ju Lee Dong‐Geun Lee Hyun Soo Rho Vladimir B. Krasokhin Hee Jae Shin Jong Seok Lee Hyi‐Seung Lee 《Journal of heterocyclic chemistry》2013,50(6):1400-1404
Three new 5‐hydroxyindole alkaloids ( 1 , 2 , 3 ) along with seven known analogs ( 4 , 5 , 6 , 7 , 8 , 9 , 10 ) were isolated from a Dokdo marine sponge Scalarispongia sp. The elucidation of the structures of the new compounds by spectroscopic analyses indicated that these compounds were an indole glyoxylate ( 1 ), a mono‐indole analog of hyrtinadine A ( 2 ), and a symmetrical bis‐indole with pyridine linker ( 3 ). The comparison of IC50 values for obtained compounds against a human leukemia cell line revealed that the bis‐indole structure is a requirement for cytotoxicity. 相似文献
236.
Yu Li Bijaya Thapa Hua Zhang Xuefei Li Fanghua Yu Eun-Kee Jeong Zhigang Yang Zhong-Xing Jiang 《Tetrahedron》2013
A family of fluorinated gemini surfactants derived from perfluoropinacol has been synthesized as novel 19F magnetic resonance imaging (19F MRI) agents. These fluorinated surfactants with 12 symmetric fluorine atoms and one singlet 19F MR peak can be conveniently prepared from perfluoropinacol and oligo(ethylene glycols) on multi-gram scales. Solubility, hydrophilicity (log P), and critical micelle concentration (CMC) measurements of these fluorinated surfactants indicated that high aqueous solubility can be achieved by introducing oligo(ethylene glycols) with appropriate length into perfluoropinacol, i.e., manipulating the fluorine content (F%). One of these fluorinated surfactants with high aqueous solubility and excellent 19F MR properties has been identified by 19F MRI phantom experiments as a promising 19F MRI agent. 相似文献
237.
238.
Jin‐Chul Kim Hyeon Yong Lee Seung Lok Hwang In Ho Lee M.‐J. Moon‐Jeong M.‐J. Rang 《Journal of Dispersion Science and Technology》2013,34(5):697-701
Two kinds of topical dosage forms of hinokitiol (HKL), namely vesicles and oil‐in‐water (O/W) emulsions, were prepared. Behenyl trimethylammonium chloride (BTMAC) and fatty acids were used as bilayer‐forming materials of the vesicles, and oils were employed as oil phases of the emulsions. The substantivity of HKL in the preparations was evaluated in vitro using hairless mouse skins. After applying the preparations onto the skin and rinsing it, the amount of HKL left on the skin was determined using high performance liquid chromatography (HPLC). It was higher when HKL was encapsulated in cationic vesicles rather than in nonionic vehicles, emulsions. An ionic interaction between the cationic vehicle and negatively charged skin is likely to account for the high substantivity. Among the emulsion preparations, an emulsion having octyl salicylate as oil phase exhibited the highest substantivity of HKL. This is probably because that the oil is a good solvent for HKL and it is skin‐retentive. In vivo hair growth‐promotion effect of each dosage form was investigated, where the sample application onto the clipped backs of female mice (C57BL6) and the subsequent rinsing of the backs were done once a day for 30 days. Only HKL in the cationic vesicles had hair growth promotion effect, possibly due to the significant substantivity. 相似文献
239.
Gye-Nam Kim Seung-Su Kim Hye-Min Park Won-Suk Kim Uk-Ryang Park Jei-Kwon Moon 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(1):71-78
Biological method was studied for remediation of soil/concrete contaminated with uranium and radium. Optimum experiment conditions for mixing ratios of penatron and soil, and the pH of soil was obtained through several bioremediations with soil contaminated with uranium and radium. It was found that an optimum mixing ratio of penatron for bioremediation of uranium soil was 1 %. Also, the optimum pH condition for bioremediation of soil contaminated with uranium and radium was 7.5. The removal efficiencies of uranium and radium from higher concentration of soil were rather reduced in comparison with those from lower concentration of soil. Meanwhile, the removal of uranium and radium in concrete by bioremediation is possible but the removal rate from concrete was slower than that from soil. The removal efficiencies of uranium and radium from soil under injection of 1 % penatron at pH 7.5 for 120 days were 81.2 and 81.6 %, respectively, and the removal efficiencies of uranium and radium from concrete under the same condition were 63.0 and 45.2 %, respectively. Beyond 30 days, removal rates of uranium and radium from soil and concrete by bioremediation was very slow. 相似文献
240.
J. M. Lim J. H. Jeong J. H. Lee 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):201-208
A growing demand of electrical energy derived from coal combustion led to a significant increase of coal ash as residues. Approximately 70 % of the fly ashes are recycled, while most of the bottom ashes have been land-filled in the ash pond in Korea. In this work, to evaluate the potential impacts of the residues from a coal power plant on the environment, its inorganic elemental components were determined by INAA and PGAA. Coal ash samples were collected from the biggest power plant complex in Korea. These samples were analyzed by using the NAA facilities in the HANARO research reactor of the Korea Atomic Energy Research Institute. A total of 31 elements were analyzed in the samples, and certified reference materials were used for the analytical quality control. The enrichment status of a given metal in fuel coal and ashes was investigated by its concentration ratio. In order to assess the impact of the coal combustion residues on ecosystem, their concentrations determined for each respective type of the samples were compared to both reference data and nearby beach sand samples. 相似文献