全文获取类型
收费全文 | 224篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 198篇 |
数学 | 13篇 |
物理学 | 17篇 |
出版年
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 10篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有228条查询结果,搜索用时 15 毫秒
141.
142.
Clement GT Nomura H Kamakura T 《The Journal of the Acoustical Society of America》2011,130(4):1810-1819
Chirp-encoded excitation has been utilized for increased signal-to-noise ratio (SNR) in both linear and harmonic imaging. In either case, it is necessary to isolate the relevant frequency band to avoid artifacts. In contrast, the present study isolates and then combines the fundamental and the higher harmonics, treating them as a single, extended bandwidth. Pulse-inverted sum and difference signals are first used to isolate even and odd harmonics. Matched filters specific to the source geometry and the transmit signal are then separately applied to each harmonic band. Verification experiments are performed using up to the third harmonic resulting from an underwater chirp excitation. Analysis of signal peaks after scattering from a series of steel and nylon wires indicates increased compression using the extended bandwidth, as compared to well-established methods for fundamental and second harmonic chirp compression. Using third harmonic bands, a mean pulse width of 56% relative to fundamental compression and 48% relative to second harmonic compression was observed. Further optimization of the compression by altering the transmission indicated 17% additional reduction in the pulse width and a 47% increase in peak-to-sidelobe ratio. Overall, results establish the feasibility of extended bandwidth signal compression for simultaneously increasing SNR and signal resolution. 相似文献
143.
Arata Yajima Kou TodaKazunori Okada Hisakazu YamaneMasamichi Yamamoto Morifumi HasegawaRyo Katsuta Tomoo Nukada 《Tetrahedron letters》2011,52(25):3212-3215
The total synthesis of (±)-3β-hydroxy-9β-pimara-7,15-diene (1), a putative biosynthetic intermediate of the momilactones, was accomplished stereoselectively. Our methodology for the synthesis of 1 featured the stereoselective construction of the C-13 quaternary carbon center via the aldol-Tishchenko reaction. 3β-Hydroxy-9β-pimara-7,15-diene (1) was identified by full-scan GC-MS analysis as an endogenous compound in elicited rice cells. 相似文献
144.
145.
Epicoccamides A and D were synthesized through a route that utilizes fragment coupling via olefin cross-metathesis as a key step. The right-hand segment of the epicoccamides was synthesized by a tandem O-acylation–migration reaction, and the left-hand segments were stereoselectively synthesized through a modified version of Crich’s β-selective mannosylation. The previously assigned absolute configuration of the epicoccamide D was confirmed, and that of epicoccamide A was assigned as (5S,2′S) based on the NMR and CD spectra. This Letter provides the first example of the total synthesis of epicoccamide A. 相似文献
146.
Kiyokazu Imai Tomoo Shiomi Yasuyuki Tezuka Keizo Takahashi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1347-1358
The homopolymerization of a series of alkyl vinyl sulfoxides (CH2[dbnd]CHSOR; R = CH3 (MVSO), C2H5 (EVSO), t-C4H9 (BVSO)) and their copolymerization with vinyl acetate (VAc) with 2,2′-azobisisobutyronitrile (AIBN) as initiator at 60°C was attempted. MVSO was found to homopolymerize radically, but EVSO and BVSO were not. Poly-MVSO is soluble in chloroform, methanol, DMSO, and water, but insoluble in acetone and benzene. MVSO and EVSO were found to copolymerize with VAc, but BVSO was not. The copolymerization parameters obtained for both systems were as follows; r1(MVSO) = 2.23, r2 (VAc) = 0.09, and r1(EVSO) = 3.40, r2 (VAc) = 0.11, respectively. MVSO/vinyl alcohol (VA) copolymers were obtained through the saponification of MVSO/VAc copolymers by sodium hydroxide in methanol. The solubility of MVSO/VAc and of MVSO/VA copolymers toward various solvents was examined, and it was observed that the sulfoxide comonomer has a tendency to give amphiphilicit to poly(vinyl acetate) and poly(vinyl alcohol). The 24 mol% MVSO containing VAc copolymer is soluble in both benzene and water. 相似文献
147.
Takayuki Yaegashi Hiroki Takeshita Katsuhiko Takenaka Tomoo Shiomi 《Journal of polymer science. Part A, Polymer chemistry》2003,41(10):1545-1552
The free‐radical homopolymerization and copolymerization behavior of N‐(2‐methylene‐3‐butenoyl)piperidine was investigated. When the monomer was heated in bulk at 60 °C for 25 h without an initiator, about 30% of the monomer was consumed by the thermal polymerization and the Diels–Alder reaction. No such side reaction was observed when the polymerization was carried out in a benzene solution with 1 mol % 2,2′‐azobisisobutylonitrile (AIBN) as an initiator. The polymerization rate equation was found to be Rp ∝ [AIBN]0.507[M]1.04, and the overall activation energy of polymerization was calculated to be 89.5 kJ/mol. The microstructure of the resulting polymer was exclusively a 1,4‐structure that included both 1,4‐E and 1,4‐Z configurations. The copolymerizations of this monomer with styrene and/or chloroprene as comonomers were carried out in benzene solutions at 60 °C with AIBN as an initiator. In the copolymerization with styrene, the monomer reactivity ratios were r1 = 6.10 and r2 = 0.03, and the Q and e values were calculated to be 10.8 and 0.45, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1545–1552, 2003 相似文献
148.
Hiroki Takeshita Naoto Ishii Chie Araki Masamitsu Miya Katsuhiko Takenaka Tomoo Shiomi 《Journal of Polymer Science.Polymer Physics》2004,42(22):4199-4206
Formation of higher‐order structure in crystallization from microphase‐separated melts was studied for polystyrene–polyethylene (PS–PE) diblock copolymers and PS–PE–PS triblock copolymers with time‐resolved synchrotron small‐angle X‐ray scattering (SR–SAXS) techniques. The PE block was crystallized at temperatures when the PS block was in the glassy state. In both crystallization and melting processes, only the peak intensity in the SR–SAXS curve changed, however, the peak positions including higher‐order peaks did not change. This means that the microphase‐structure in the crystalline state was completely the same as that in the molten state. These behaviors were observed regardless of any melt microphase structure. Also, once a stable microphase structure was formed in the molten state, the structure was not changed even if crystallization and melting were repeated. Behavior of crystallization from such microphase‐separated melts was also studied. Apparent activation energies of crystallization were high for all block copolymers, compared with that for the PE homopolymer. In particular, the triblock copolymers showed higher apparent activation energies than the diblock copolymers. Both degrees of crystallinity and Avrami indices were greatly suppressed in crystallization from the cylindrical domain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4199–4206, 2004 相似文献
149.
Dr. Shrikant Bhat Dr. Leonore Wiehl Shariq Haseen Prof. Dr. Peter Kroll Dr. Konstantin Glazyrin Philipp Gollé-Leidreiter Prof. Dr. Ute Kolb Dr. Robert Farla Dr. Jo-Chi Tseng Dr. Emanuel Ionescu Prof. Dr. Tomoo Katsura Prof. Dr. Ralf Riedel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(10):2187-2194
We report the first oxynitride of tin, Sn2N2O (SNO), exhibiting a Rh2S3-type crystal structure with space group Pbcn. All Sn atoms are in six-fold coordination, in contrast to Si in silicon oxynitride (Si2N2O) and Ge in the isostructural germanium oxynitride (Ge2N2O), which appear in four-fold coordination. SNO was synthesized at 20 GPa and 1200–1500 °C in a large volume press. The recovered samples were characterized by synchrotron powder X-ray diffraction and single-crystal electron diffraction in the TEM using the automated diffraction tomography (ADT) technique. The isothermal bulk modulus was determined as Bo=193(5) GPa by using in-situ synchrotron X-ray diffraction in a diamond anvil cell. The structure model is supported by DFT calculations. The enthalpy of formation, the bulk modulus, and the band structure have been calculated. 相似文献
150.
Hydrogenation of Sulfoxides to Sulfides under Mild Conditions Using Ruthenium Nanoparticle Catalysts
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Takato Mitsudome Yusuke Takahashi Dr. Tomoo Mizugaki Prof. Dr. Koichiro Jitsukawa Prof. Dr. Kiyotomi Kaneda 《Angewandte Chemie (International ed. in English)》2014,53(32):8348-8351
The first demonstration of the hydrogenation of sulfoxides under atmospheric H2 pressure is reported. The highly efficient reaction is facilitated by a heterogeneous Ru nanoparticle catalyst. The mild reaction conditions enable the selective hydrogenation of a wide range of functionalized sulfoxides to the corresponding sulfides. The high redox ability of RuOx nanoparticles plays a key role in the hydrogenation. 相似文献