全文获取类型
收费全文 | 527篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 423篇 |
晶体学 | 8篇 |
力学 | 2篇 |
数学 | 13篇 |
物理学 | 95篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 19篇 |
2012年 | 37篇 |
2011年 | 32篇 |
2010年 | 19篇 |
2009年 | 19篇 |
2008年 | 31篇 |
2007年 | 35篇 |
2006年 | 47篇 |
2005年 | 36篇 |
2004年 | 33篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有541条查询结果,搜索用时 15 毫秒
121.
The H(2)C=CD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0(+) and 0(-). Tunneling-rotation transitions connecting the lower (0(+)) and upper (0(-)) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R- and two Q-branch transitions. Three and two pure rotational transitions in the K(a)=0 and 1 stacks, respectively, were also observed for each of the 0(+) and 0(-) states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be ΔE(0)=1187.234(17)?MHz, which is 1/14 that for H(2)C=CH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545?cm(-1), consistent with the value 1568?cm(-1) obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δa(F) ((β))=68.06(53)?MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H(2)C=CD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H(2)C=CD. 相似文献
122.
Chong Wu Wen-Juan Zhang Xi Zeng Lan Mu Sai-Feng Xue Zhu Tao Takehiko Yamato 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(1-2):125-131
A new fluorescent sensor 1 based on the rhodamine amide-armed homotrioxacalix[3]arene was synthesized, and its sensing behavior toward metal ions was investigated by UV–vis and fluorescence spectroscopies. Upon the addition of metal cations (Sb3+, Fe3+, Ni2+), a significant fluorescent enhancement in the range of 500–600 nm and colorimetric change was observed. 相似文献
123.
XiangYong Zheng WenJuan Zhang Lan Mu Xi Zeng SaiFeng Xue Zhu Tao Takehiko Yamatob 《Journal of inclusion phenomena and macrocyclic chemistry》2010,68(1-2):139-146
The novel fluorescent sensor 1, which is comprised of two rhodamine B lactams as fluorophores that are 1,3-alternately linked to a thiacalix[4]arene, behaves as a highly sensitive ion-induced fluorescent sensor for Fe3+ and Cr3+. This compound was synthesized, and its recognition of metal ions was evaluated by fluorescence and absorption spectroscopy. The possible mechanism of Fe3+- and Cr3+-induced spirocycle opening of 1 leads to fluorescent and colorimetric enhancement, and these properties were investigated by spectroscopy, 1H NMR and IR. The stoichiometric ratios and association constants of the complexes between 1 and these ions have been measured and calculated, and showed that the presence of Fe3+ or Cr3+ induced sensor 1 to form a stable 1:1 complex. 相似文献
124.
We investigate baryogenesis in the ν MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when θ13=0 and θ23=π/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. 相似文献
125.
Microchip technology has matured over the years into an important field in which novel technologies are being constantly invented,
and down-sizing and incorporation of already existing methodologies into the microscale is increasing assay performance and
bearing the promise of future total integration for simple, widespread use. One rapidly growing sub-discipline of the microchip
research field is focused around the integration of microchip technology and cell biology. In this review, we recapitulate
progress here at the Kitamori laboratory in direct relation to cell and microchip technologies, and show some examples of
successful integration of the two, going from controlled patterning of cells, on-chip cell culture stimulation, and cardiovascular
systems on a chip, to bio-microdevices integrating cardiovascular cells and microtechnology to create novel biodevices such
as biocompatible, miniature pumps. 相似文献
126.
Microchip-based liquid-liquid extraction for gas-chromatography analysis of amphetamine-type stimulants in urine 总被引:1,自引:0,他引:1
Miyaguchi H Tokeshi M Kikutani Y Hibara A Inoue H Kitamori T 《Journal of chromatography. A》2006,1129(1):105-110
A microchip-based liquid-liquid extraction for the gas chromatography analysis of urine for amphetamine-type stimulants has been developed. Partially modified microchannels with the capillarity restricted modification (CARM) method were employed for stabilizing the interface consisting of 1-chlorobutane and alkalized urine. Reliability of the microchip-based extraction was evaluated with respect to linearity, trueness and precision. As a practical demonstration, methoxyphenamine hydrochloride (50 mg) was administered to three healthy volunteers, and the concentration of methoxyphenamine in their urine was determined by both methods for comparison. This study showed the potential of pressure-driven microfluidics to contribute to the rapid automation analysis in forensic toxicology. 相似文献
127.
We developed a novel flow control system for a nanofluidic chemical process. Generally, flow control in nanochannels is difficult because of its high-pressure loss with very small volume flow rate. In our flow control method, liquid pressure in a microchannel connected to the nanochannels is regulated by utilizing a backpressure regulator. The flow control method was verified by using simple structured microchip, which included parallel nanochannels. We found that the observed flow rate was three times lower than the value expected from Hagen-Poiseuille's equation. That implied a size-dependent viscosity change in the nanochannels. Then, we demonstrated mixing of two different fluorescent solutions in a Y-shaped nanochannel and also a proton exchange reaction in the Y-shaped nanochannel. The flow control method will contribute to further integration of nanochemical systems. 相似文献
128.
Yamauchi M Tokeshi M Yamaguchi J Fukuzawa T Hattori A Hibara A Kitamori T 《Journal of chromatography. A》2006,1106(1-2):89-93
We have developed a miniaturized two-way detection system using thermal lens and fluorescence spectroscopies for microchip chemistry. The system was composed of laser diode (LD) modules, fiber-based optics combined with a gradient index lens, and miniaturized detection units for thermal lens and fluorescence signals. The detection limits in the thermal lens and fluorescence spectroscopies were 6.3 x 10(-9)M for Ni(II) phthalocyanine tetrasulfonic acid and 3.0 x 10(-9)M for cy5, respectively. The performance of the system with the miniaturized thermal lens was equivalent to that of a conventional thermal lens microscope. The fluorescence sensitivity was comparable to sensitivities offered by conventional miniaturized systems. 相似文献
129.
High-performance liquid chromatography (HPLC) with UV detection for the simultaneous determination of the free form of p-hydroxymethamphetamine (p-OHMA) and its metabolite, glucuronide (p-OHMAG) was accomplished for the first time. We achieved this by employing 1) an ion pair reagent for retention of sample to a solid-phase extraction (SPE) cartridge, Sep-Pak Light C18 and 2) a simple two-step stepwise elution technique for subsequent ion pair RP-HPLC. The proposed method was optimized for resolution of p-OHMAG, p-OHMA and MA. The method was successfully applied to urine samples collected from MA abusers. 相似文献
130.
Hirai H Komatsu K Honda M Kawamura T Yamamoto Y Yagi T 《The Journal of chemical physics》2010,133(12):124511
High pressure and low temperature experiments with CO(2) hydrate were performed using diamond anvil cells and a helium-refrigeration cryostat in the pressure and temperature range of 0.2-3.0 GPa and 280-80 K, respectively. In situ x-ray diffractometry revealed that the phase boundary between CO(2) hydrate and water+CO(2) extended below the 280 K reported previously, toward a higher pressure and low temperature region. The results also showed the existence of a new high pressure phase above approximately 0.6 GPa and below 1.0 GPa at which the hydrate decomposed to dry ice and ice VI. In addition, in the lower temperature region of structure I, a small and abrupt lattice expansion was observed at approximately 210 K with decreasing temperature under fixed pressures. The expansion was accompanied by a release of water content from the sI structure as ice Ih, which indicates an increased cage occupancy. A similar lattice expansion was also described in another clathrate, SiO(2) clathrate, under high pressure. Such expansion with increasing cage occupancy might be a common manner to stabilize the clathrate structures under high pressure and low temperature. 相似文献