全文获取类型
收费全文 | 3168篇 |
免费 | 478篇 |
国内免费 | 427篇 |
专业分类
化学 | 2303篇 |
晶体学 | 30篇 |
力学 | 229篇 |
综合类 | 45篇 |
数学 | 311篇 |
物理学 | 1155篇 |
出版年
2024年 | 8篇 |
2023年 | 55篇 |
2022年 | 109篇 |
2021年 | 114篇 |
2020年 | 136篇 |
2019年 | 103篇 |
2018年 | 116篇 |
2017年 | 116篇 |
2016年 | 145篇 |
2015年 | 129篇 |
2014年 | 177篇 |
2013年 | 219篇 |
2012年 | 212篇 |
2011年 | 288篇 |
2010年 | 200篇 |
2009年 | 196篇 |
2008年 | 208篇 |
2007年 | 191篇 |
2006年 | 160篇 |
2005年 | 122篇 |
2004年 | 95篇 |
2003年 | 75篇 |
2002年 | 75篇 |
2001年 | 69篇 |
2000年 | 60篇 |
1999年 | 72篇 |
1998年 | 61篇 |
1997年 | 50篇 |
1996年 | 49篇 |
1995年 | 51篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有4073条查询结果,搜索用时 0 毫秒
21.
22.
Broadband Sheet Parametric Oscillator for x~((2)) Optical Frequency Comb Generation via Cavity Phase Matching 下载免费PDF全文
Xin Ni Kunpeng Jia Xiaohan Wang Huaying Liu Jian Guo Shu-Wei Huang Baicheng Yao Nicolò Sernicola Zhenlin Wang Xinjie Lv Gang Zhao Zhenda Xie Shi-Ning Zhu 《中国物理快报》2021,(6):37-49
We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs~2/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for x~((2)) comb. 相似文献
23.
We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids. The key to success is the use of an alcohol solvent, which makes a rationally designed COOMe-bonded Cu-allenylidene electrophilic intermediate stable enough to couple with amine nucleophiles before its decomposition. The reaction features wide functional group tolerance with high enantioselectivity, typically >90% ee, and is amenable to the modification of commercially available bioactive molecules. The resultant protected α-amino acids could be readily converted into a number of precious enantioenriched amines featuring α-hindered tertiary carbon centers, which are otherwise synthetically quite challenging, including those of α-amino aldehyde, peptides or α-vinyl amino ester with >92% ee in excellent yields. This protocol could be utilized for the synthesis of the protected bioactive α-ethylnorvaline in 3 steps, a significant advancement in comparison to an 11-step sequence reported previously.We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids. 相似文献
24.
Luhua Xiao Xiaoying Lu Huilin Yang Cuiqing Lin Le Li Chen Ni Yuan Fang Suifen Mo Ruoting Zhan Ping Yan 《Molecules (Basel, Switzerland)》2022,27(11)
In this study, the antioxidant and hypolipidemic effects of Mesona Chinensis Benth (MCB) extracts were evaluated. Seven fractions (F0, F10, F20, F30, F40, F50 and MTF) were obtained from the MCB ethanol extracts. Compared to the commercial antioxidants (vitamin C), MTF and F30 exhibited higher antioxidant activities in the antiradical activity test and the FRAP assay. The half-inhibition concentration (IC50) for MTF and F30 were 5.323 µg/mL and 5.278 µg/mL, respectively. MTF at 200 µg/mL significantly decreased the accumulation of TG in oleic acid (OA)-induced HepG2 cells and reversed the inhibitory effect of Compound C on AMPK (MTF and F30 significantly increased the glucose utilization of insulin-induced HepG2 cells). In addition, the components of MTF were identified by HPLC-MS, which were caffeic acid, quercetin 3-O-galactoside, isoquercetin, astragalin, rosmarinic acid, aromadendrin-3-O-rutinoside, rosmarinic acid-3-O-glucoside and kaempferol-7-O-glucoside. Through statistical correlations by Simca P software, it was found that the main antioxidant and hypolipidemic components of MCB might be caffeic acid, kaempferol-7-O-glucoside, rosmarinic acid-3-O-glucoside and aromadendrin-3-O-rutinoside, which may play important roles in the AMPK pathway. MTF and F30 in MCB could be potential health products for the treatment of hyperlipidemia. 相似文献
25.
Tingjunhong Ni Zichao Ding Fei Xie Yumeng Hao Junhe Bao Jingxiang Zhang Shichong Yu Yuanying Jiang Dazhi Zhang 《Molecules (Basel, Switzerland)》2022,27(11)
A series of triazole derivatives containing phenylethynyl pyrazole moiety as side chain were designed, synthesized, and most of them exhibited good in vitro antifungal activities. Especially, compounds 5k and 6c showed excellent in vitro activities against C. albicans (MIC = 0.125, 0.0625 μg/mL), C. neoformans (MIC = 0.125, 0.0625 μg/mL), and A. fumigatus (MIC = 8.0, 4.0 μg/mL). Compound 6c also exerted superior activity to compound 5k and fluconazole in inhibiting hyphae growth of C. albicans and inhibiting drug-resistant strains of C. albicans, and it could reduce fungal burdens in mice kidney at a dosage of 1.0 mg/kg. An in vivo efficacy evaluation indicated that 6c could effectively protect mice models from C. albicans infection at doses of 0.5, 1.0, and 2.0 mg/kg. These results suggested that compound 6c deserves further investigation. 相似文献
26.
27.
28.
Guanglong Chen Cheng Wang Haiyang Lu Jiansheng Liu Ruxin Li Guoquan Ni Zhizhan Xu 《中国光学快报(英文版)》2008,6(6)
We use an electrostatic model to study the average kinetic energy of ions ejected from the pure Coulomb explosions of methane clusters (CA4)n (light atom A=H and D). It is found that the ratio of the average kinetic energy of the ions to their initial average electrostatic potential energy is irrelevant to the cluster size. This finding implies that as long as the ratio is given, the average kinetic energies of the ions can be simply estimated from their initial average electrostatic potential energies, rather than from the time- consuming simulations. The ratios for the different charge states of carbon ions are presented. 相似文献
29.
Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse 下载免费PDF全文
The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subelusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the ease of homonuelear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuelear clusters with larger sizes are required to achieve a greater neutron yield. 相似文献
30.