全文获取类型
收费全文 | 1139篇 |
免费 | 20篇 |
国内免费 | 2篇 |
专业分类
化学 | 917篇 |
晶体学 | 29篇 |
力学 | 13篇 |
数学 | 43篇 |
物理学 | 159篇 |
出版年
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 53篇 |
2012年 | 50篇 |
2011年 | 50篇 |
2010年 | 42篇 |
2009年 | 19篇 |
2008年 | 52篇 |
2007年 | 80篇 |
2006年 | 67篇 |
2005年 | 68篇 |
2004年 | 55篇 |
2003年 | 53篇 |
2002年 | 59篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 27篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1968年 | 10篇 |
1967年 | 4篇 |
排序方式: 共有1161条查询结果,搜索用时 15 毫秒
41.
42.
43.
Tozuka Z Kaneko H Shiraga T Mitani Y Beppu M Terashita S Kawamura A Kagayama A 《Journal of mass spectrometry : JMS》2003,38(8):793-808
Triple-stage quadrupole (TSQ) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) and ion trap ESI-MS/MS can be used to cleave protonated molecules to produce carbocations and neutral molecules in the positive ion mode. Dissociation products which correspond to protonated forms of neutral fragment molecules can also be trapped and detected. These protonated molecules in turn can cleave via carbocation cleavage, ipso cleavage, onium cleavage or McLafferty or related rearrangements. One can elucidate the structures of metabolites from the differences in m/z ratios of the fragments arising from the original drug compound and its metabolite. This strategy for structural elucidation is further facilitated by estimates of the reactivity of drugs with oxygen diradicals involved in cytochrome P-450 cycles. 相似文献
44.
45.
Kengo Sugita Prof. Dr. Makoto Yamashita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4520-4523
The reaction between a dialkyl-substituted alumanyl anion and [Y(CH2SiMe3)2(thf)3][BPh4] resulted in the formation of (dialkylalumanyl)yttrium complex 2 , which exhibits the first 2-center–2-electron (2 c-2 e) Al−Y bond. The 1H and 13C NMR spectra of 2 together with an X-ray crystallographic analysis indicated a C2v symmetrical structure. DFT calculations on 2 revealed that its LUMO consists of overlapping 3 p- and 4 d-orbitals of the Al and Y atoms, respectively, and that the HOMO–LUMO gap is narrow. The UV/Vis spectrum of 2 exhibited a visible absorption at 432 nm, which suggests that the strong σ-donating and π-accepting character of the three-coordinate dialkylalumanyl ligand generates a colored d0-complex that does not contain any π-electrons. 相似文献
46.
S. Arai K. Sugita P. Ma Y. Ishikawa H. Kaetsu S. Isomura 《Applied physics. B, Lasers and optics》1989,48(5):427-435
We have been studying the practical CO2-laser-induced13C separation by a two-stage IRMPD process. The IRMPD of natural CHClF2 in the presence of Br2 mainly produced CBr2F2, which was found to be highly enriched with13C. The yield and13C-atom fraction of CBr2F2 were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br2 pressure using a CO2 TEA laser with an output less than 1 J pulse–1 in order to optimize experimental conditions for13C separation. For example, we obtained CBr2F2 at a13C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF2 and 10-Torr Br2 with the laser radiation at a wavenumber of 1045.02 cm–1 and at a fluence of 3.4 J cm–2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10–4 g of13C-enriched CBr2F2 (13C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher13C by the second-stage IRMPD of the CBr2F2 in the presence of oxygen. 相似文献
47.
K Yoshino M Fujiwara A Tanaka S Takahashi Y Nambu A Tomita S Miki T Yamashita Z Wang M Sasaki A Tajima 《Optics letters》2012,37(2):223-225
A high-speed quantum key distribution system was developed with the wavelength-division multiplexing (WDM) technique and dedicated key distillation hardware engines. Two interferometers for encoding and decoding are shared over eight wavelengths to reduce the system's size, cost, and control complexity. The key distillation engines can process a huge amount of data from the WDM channels by using a 1 Mbit block in real time. We demonstrated a three-channel WDM system that simultaneously uses avalanche photodiodes and superconducting single-photon detectors. We achieved 12 h continuous key generation with a secure key rate of 208 kilobits per second through a 45 km field fiber with 14.5 dB loss. 相似文献
48.
Analytical separation of tea catechins and food-related polyphenols by high-speed counter-current chromatography 总被引:2,自引:0,他引:2
Yanagida A Shoji A Shibusawa Y Shindo H Tagashira M Ikeda M Ito Y 《Journal of chromatography. A》2006,1112(1-2):195-201
High-speed counter-current chromatography (HSCCC) using the type-J coil planet centrifuge was applied to compositional analysis of tea catechins and separation of other food-related polyphenols. The HSCCC separation of nine different standard compounds and those from extracts of commercial tea leaves was performed with a two-phase solvent system composed of tert-butyl methyl ether-acetonitrile-0.1% aqueous trifluoroacetic acid (TFA) (2:2:3, v/v/v) by eluting the upper organic phase at a flow rate of 2 ml/min. The main compounds in the extract of non-fermented green tea were found to be monomeric catechins, their galloylated esters and caffeine. In addition to these compounds, oxidized pigments, such as hydrophobic theaflavins (TFs) and polar thearubigins (TRs) were also separated and detected from the extracts of semi-fermented oolong tea and fermented black tea. Furthermore, several food-related polyphenols, such as condensed catechin oligomers (procyanidins), phenolic acids and flavonol glycosides were clearly separated under the same HSCCC condition. These separation profiles of HSCCC provide useful information about the hydrophobic diversity of these bioactive polyphenols present in various types of teas and food products. 相似文献
49.
Eri Yoshida Atsutoshi Sugita 《Journal of polymer science. Part A, Polymer chemistry》1998,36(12):2059-2068
Synthesis of poly(styrene-b-tetrahydrofuran (THF)-b-styrene) triblock copolymers was performed by transformation from living cationic into living radical polymerization, using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO) as a transforming agent. Sodium 4-oxy-TEMPO, derived from 4-hydroxy-TEMPO, reacted with the living poly(THF), which was prepared by cationic polymerization of THF using trifluoromethanesulfonic acid anhydride as an initiator, resulting in quantitative formation of the poly(THF) with TEMPO at both the chain ends. The resulting polymers were able to serve as a polymeric counter radical for the radical polymerization of styrene by benzoyl peroxide, to give the corresponding triblock copolymer in quantitative efficiency. The polymerization was found to proceed in accordance with a living mechanism, because the conversion of styrene linearly increased over time, and the molar ratio of styrene to THF units in the copolymer also increased as a result of increasing the conversion. The TEM pictures demonstrated that the resulting copolymers promoted microphase segregation. It was found that the films of these copolymers showed contact angles intermediate between those of poly(THF) and of polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2059–2068, 1998 相似文献
50.
Ford WE Yasuda A Wessels JM 《Langmuir : the ACS journal of surfaces and colloids》2008,24(7):3479-3485
Coprecipitation of urea-melt modified carbon nanotubes and calcium carbonate from an aqueous solution by two methods yielded microcrystalline composite particles. Powders obtained by colloidal crystallization from a supersaturated solution that were isolated and dried soon after precipitation were a mixture of raspberry-shaped and rhombohedral particles. These were shown by infrared and X-ray diffraction analyses to be mainly calcite. Particles that were kept wet for 1 day or longer before being isolated were typically entirely rhombohedral with edge lengths in the range of 5-30 microm. Scanning electron microscopy investigations revealed that the nanotubes were adsorbed on the particle surface and also incorporated into the interior matrix. Removal of the calcium carbonate component by treating the particles with acid yielded nanotube shells whose size and shape reflected those of the original particles. 相似文献