全文获取类型
收费全文 | 4406篇 |
免费 | 177篇 |
国内免费 | 12篇 |
专业分类
化学 | 3526篇 |
晶体学 | 39篇 |
力学 | 53篇 |
数学 | 246篇 |
物理学 | 731篇 |
出版年
2023年 | 41篇 |
2022年 | 69篇 |
2021年 | 92篇 |
2020年 | 107篇 |
2019年 | 86篇 |
2018年 | 56篇 |
2017年 | 57篇 |
2016年 | 117篇 |
2015年 | 109篇 |
2014年 | 151篇 |
2013年 | 246篇 |
2012年 | 325篇 |
2011年 | 346篇 |
2010年 | 178篇 |
2009年 | 143篇 |
2008年 | 298篇 |
2007年 | 279篇 |
2006年 | 276篇 |
2005年 | 286篇 |
2004年 | 246篇 |
2003年 | 200篇 |
2002年 | 179篇 |
2001年 | 68篇 |
2000年 | 56篇 |
1999年 | 58篇 |
1998年 | 41篇 |
1997年 | 51篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 9篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 31篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 14篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有4595条查询结果,搜索用时 15 毫秒
71.
Seo K Kim C Choi YS Park KA Lee YH Kim B 《Journal of the American Chemical Society》2003,125(46):13946-13947
CO2 molecule chemisorbs selectively on the zigzag tube edge without an activation barrier, whereas it physisorbs on the armchair edge of nanotubes. In addition, carbon nanotubes can be etched by an adsorbed oxygen atom of CO2 molecule. From our results, we suggest a selective etching mechanism for tuning the chirality of the mass-produced carbon nanotubes. 相似文献
72.
Photoswitching of the intramolecular magnetic interaction was demonstrated using diarylethenes with 2,5-bis(arylethynyl)-4-methyl-3-thienyl side group. Two nitroxide radicals were placed at each end of the 2,5-bis(arylethynyl)-4-methyl-3-thienyl group. Three kinds of aryl groups, 2,5-thienylene, p-phenylene, and m-phenylene groups, were used in the arylethynyl moiety. The diarylethene photoswitching units have an extended pi-conjugated chain on one side of the diarylethene. The photochromic reactivity was dependent on the arylethynyl group. Diarylethenes with m-phenylene group showed an efficient photochromic reactivity. Along with the photochromic reaction the diarylethenes showed photoswitching of an ESR spectrum originating from the change in the magnetic interaction between two unpaired electrons. The open-ring isomer showed stronger exchange interaction than the photogenerated closed-ring isomer. The magnetic interaction between two radicals via the pi-conjugated chain was altered by photocyclization due to the change of the hybrid orbital at the 2-position of the thiophene ring from sp(2) to sp(3). 相似文献
73.
Masamitsu Shirai Masahiro Tsunooka Makoto Tanaka Kanji Nishijima Katsukiyo Ishikawa 《Journal of polymer science. Part A, Polymer chemistry》1989,27(1):325-332
Novel photosensitive polymers were synthesized by the copolymerization of methyl methacrylate and 1,2,3,4-tetrahydro-1-naphthylideneimino p-styrenesulfonate (NISS) and by the ternary polymerization of methyl methacrylate, methacrylic acid, and 9-fluorenylideneiminop-styrene-sulfonate (FISS). NISS and FISS units showed good sensitivity to light of wavelengths below 300 nm and below 366 nm, respectively. Although the polymers were insoluble in aqueous alkaline solutions, on irradiation with UV light they became soluble in aqueous alkaline solutions. A remarkable decrease in molecular weight of the polymers was observed during the photolysis of imino sulfonate groups incorporated into the polymers, which assisted the dissolution of the irradiated polymers. 相似文献
74.
75.
Yoshiyuki Tanaka Makoto Arakawa Yohei Yamaguchi Chieko Hori Masahiro Ueno Takeyuki Tanaka Tatsushi Imahori Yoshinori Kondo 《化学:亚洲杂志》2006,1(4):581-585
A metal‐free acetylide was observed by using NMR spectroscopy. Metal‐free acetylides are closely related to reactive intermediates (carbanions) in solution; therefore, they have been regarded as unobservable species. However, we generated this highly reactive and unstable species through the deprotonation of phenylacetylene by using the strong nonmetallic phosphazene base tBu‐P4. In the presence of tBu‐P4, the J coupling between the ethynyl carbon and hydrogen nuclei (1JC,H) of phenylacetylene disappeared; this indicates the deprotonation of the alkyne terminal. Furthermore, a large low‐field shift (approximately 90 ppm) of the alkyne carbon resonance was observed. We concluded that we have observed a metal‐free carbanion with a formal charge on an sp‐hybridized carbon atom for the first time. 相似文献
76.
Masahiro Irie Setsuko Tomimoto Koichiro Hayashi 《Journal of polymer science. Part A, Polymer chemistry》1972,10(11):3243-3252
The photoinduced ionic polymerization of cyclohexene oxide was studied in the presence of pyromellitic dianhydride. The polymerization is initiated by the excited chargetransfer complex between cyclohexene oxide and the electron-acceptor and proceeds by a cationic mechanism. Photoinduced cationic polymerization of α-methylstyrene was also observed in the presence of pyromellitic dianhydride. The initiation mechanism of the polymerization was elucidated by means of electron spin resonance measurements. The concentration of pyromellitic dianhydride anion-radicals measured in this way was found to be proportional to the rate of polymerization. This result shows clearly that the photopolymerization is initiated by cation-radicals formed from photoexcited donoracceptor complexes. The attempted photocopolymerization of cyclohexene oxide and α-methylstyrene gave a mixture of homopolymers. The composition of the product depends on the wavelength of the light used. 相似文献
77.
78.
79.
80.
The lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) solvent system for cellulose was adopted as a mobile phase of size-exclusion chromatographic (SEC) analysis of cellulose, and the applicability of this system was examined using multi-angle laser light scattering and 13C-NMR analysis. The results indicate that 8% (w/v) LiCl/DMI ID a true solvent for cellulose, and that cellulose molecules dissolving ID 1% (w/v) LiCl/DMI are separated orderly depending on their molecular mass (MM) or root-mean-square (RMS) radius by the SEC system. Practically, no aggregates were detected ID the dilute cellulose/LiCl/DMI solutions. Furthermore, high stability of cellulose/LiCl/DMI solutions has been demonstrated; only a few percent of decline ID average MM was observed even after storage for 6 months at room temperature. Relationships between RMS radius and MM for hardwood bleached kraft pulp ID 1% LiCl/DMI was estimated as the following equation: g0.59, corresponding to a Mark–Houwink–Sakurada exponent of 0.77. 相似文献