全文获取类型
收费全文 | 502篇 |
免费 | 29篇 |
专业分类
化学 | 392篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 32篇 |
物理学 | 97篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 14篇 |
2012年 | 27篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 28篇 |
2007年 | 36篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 16篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1975年 | 2篇 |
1970年 | 3篇 |
1933年 | 2篇 |
1932年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有531条查询结果,搜索用时 9 毫秒
111.
112.
Masahide Takahashi Masaru Suzuki Yuya Miyagawa Rie Ihara Yomei Tokuda Toshinobu Yoko Takashi Nemoto Seiji Isoda 《Journal of Sol-Gel Science and Technology》2010,54(3):319-324
Photo-curable vinyl modified silicate-phosphate alternating copolymers were prepared by a direct condensation of organochlorosilane
and organophosphoric acid in a solvent-free condition. The obtained copolymers have complete alternating copolymer structure
of silicate and phosphate unit, where the main oxo chain consist of –(Si–O–P–O)
n
-network. They exhibited an excellent solubility of ionic species such as ionic organic dyes. It was also demonstrated the
photo-reduction of Au+ ions to form Au nano particles for plasmonics applications. Micro patterns were also fabricated by soft lithographic processes.
These results indicate that the photo-curable alternating copolymers are one of promising materials for advanced optical information
processing devices. 相似文献
113.
114.
Rei Fujiwara 《Journal of luminescence》2009,129(3):231-237
A quantitative spectral analysis of the ultraviolet (UV) broad excitation bands, which are located in the range 300-400 nm, for red emissions at around 610 nm in Pr-doped CaTiO3, SrTiO3:Al and BaTiO3:Mg phosphors has been carried out using a peak fitting technique. The obtained results demonstrate that the UV broad band of CaTiO3:Pr consists of four primary excitation bands centered around 330, 335, 365 and 380 nm and those of both SrTiO3:Al and BaTiO3:Mg consist of three primary bands centered around 310, 345 and 370 nm. Based on the behavior patterns and the values of the respective primary excitation bands’ parameters, i.e. center gravity (λtop), maximum height (Imax) and full-width at half-maximum (FWHM), the UV-to-red relaxation processes in these titanate phosphors can be explained to be essentially the same, except for the existence of an additional relaxation pathway via electron-trap states in CaTiO3:Pr, which gives a characteristic shape of its UV excitation spectrum in the wavelength range of >360 nm. 相似文献
115.
116.
Kazufumi KITAGAKI Rei ONO Harumi KONISHI Michio NAKANISHI Hiroyuki MIURA Tatsuo AOKI Teruo NOGUCHI 《Physical Therapy Research》2022,25(3):106
Objective: This study aimed to investigate whether longitudinal changes in exercise capacity in patients with acute myocardial infarction (AMI) differ by sex and clarified what contributed to these differences. Methods: We retrospectively examined the differences in each variable between men and women in 156 patients with AMI (mean age: 65 ± 12 years; 82.0% male) who participated in a 3-month cardiac rehabilitation (CR) program and could be followed-up for exercise capacity 12-months after AMI onset. Sex-related differences in the change in peak oxygen uptake (peak VO2) at baseline, 3-months, and 12-months after AMI were analyzed. Results: Male patients with AMI were younger and had higher body mass index and employment rate than women. The attendance of the CR program was higher in women (men vs. women; 10 [3–15] vs. 14 [11–24] sessions, p = 0.0002). Women showed a significant lower %change in peak VO2 after 12 months (men vs. women; 7.8% [–0.49% to 14.6%] vs. 1.3% [–5.7% to 7.5%], p = 0.013). In multiple linear regression analysis, age (β = –0.76, 95% confidence interval [CI] = –1.0 to –0.50, p <0.0001) and female sex (β = –6.3, 95% CI = –9.1 to –3.5, p <0.0001) were negative independent predictors of change in peak VO2 over 12 months, while CR attendance (β = 0.21, 95% CI = 0.0032–0.42, p = 0.047) and recommended exercise habit after the CR program (β = 2.1, 95% CI = 0.095–4.1, p = 0.040) were positive independent predictors of change in peak VO2 over 12 months. Conclusion: In female patients, exercise capacity improved during the CR program but decreased to AMI onset levels after 12 months. 相似文献
117.
Two water-soluble, silver(I) complexes showing a wide spectrum of effective antibacterial and antifungal activities, i.e., ([Ag(Hhis)].0.2EtOH)2 (1; H2his = L-histidine) and [Ag(Hpyrrld)]2 (3; H2pyrrld = (S)-(-)-2-pyrrolidone-5-carboxylic acid) were prepared. In aqueous solution 1 and 3 were present as dimers, whereas in the solid state they were polymers. Crystallization of 1 by slow evaporation and/or vapor diffusion gave water-insoluble crystals of [Ag(Hhis)]n (2) showing modest antimicrobial activities. The complex 1 in the solid state is a polymer formed by intermolecular hydrogen-bonding interactions between dimeric [Ag(Hhis)]2 cores, while 2 is a different polymer without a core complex. X-ray crystallography revealed that 2 was a left-handed helical polymer consisting of a bent, 2-coordinate silver(I) atom bonding to the Namino atom of one Hhis- ligand and the N pi atom of a different Hhis- ligand. Of particular note is the fact that Ocarboxyl atoms do not participate in the coordination. X-ray crystallography also revealed that 3 was a left-handed helical polymer formed by self-assembly of dimeric [Ag(Hpyrrld)]2 cores with an intramolecular metal(I)-metal(I) interaction (Ag-Ag distance, 2.9022(7) A). The FT-IR and the solid-state 13C and 15N NMR spectra showed that the dimeric core of 1 was formed through Ag-N bonds, while that of 3 was formed through Ag-O bonds. The molecular ions of 1 and 3 were detected by the positive-ion electrospray ionization (ESI) mass spectrometry. For 1-3, characterization by elemental analysis, TG/DTA, FT-IR, and variable-temperature solid-state 13C NMR and room-temperature 15N NMR measurements was performed, and for 1 and 3, that by solution molecular weight measurements and solution (109Ag, 1H, and 13C) NMR spectroscopies was also carried out. The antibacterial and antifungal activities of 1 and 3 were remarkable and comparable to those of the previous silver(I)-N-heterocycle complexes. 相似文献
118.
119.
[reaction: see text] A new total synthesis of macrosphelides A and B using ring-closing metathesis (RCM) as a macrocyclization step is described. The substrate of the RCM could be synthesized from readily available chiral materials, methyl (S)-(+)-3-hydroxybutyrate and methyl (S)-(-)-lactate, with a high efficiency. The RCM proceeded in the presence of Grubbs' Ru-complex, providing a new effective synthetic route to these natural products. 相似文献
120.
An efficient synthesis of 3β-hydroxy-5-cholanic acid (8) and 3β-hydroxy-Δ5-cholanic acid (16) was carried out starting from 5-dihydropregnenolene (1) and pregnenolone (9). The monoacetates (3 and 11), prepared by Grignard reaction of 1 and 9 with 3,3-ethylenedioxypropylmagnesium bromide followed by acetylation, were dehydrated selectively to give the Δ20(22)-compounds (4 and 12) which on hydrogenation followed by acid treatment and Jones oxidation yielded 8 and 16, respectively. 相似文献