全文获取类型
收费全文 | 1588篇 |
免费 | 52篇 |
国内免费 | 4篇 |
专业分类
化学 | 1358篇 |
晶体学 | 15篇 |
力学 | 15篇 |
数学 | 40篇 |
物理学 | 216篇 |
出版年
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 19篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 40篇 |
2014年 | 40篇 |
2013年 | 92篇 |
2012年 | 72篇 |
2011年 | 76篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 79篇 |
2007年 | 107篇 |
2006年 | 103篇 |
2005年 | 77篇 |
2004年 | 82篇 |
2003年 | 69篇 |
2002年 | 78篇 |
2001年 | 39篇 |
2000年 | 32篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1967年 | 8篇 |
排序方式: 共有1644条查询结果,搜索用时 62 毫秒
161.
Yoshimi Sueishi Atsushi Miyata Daisuke Yoshioka Masato Kamibayashi Yashige Kotake 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(3-4):357-364
The effect of CD-inclusion on spin-trapping rates and spin-adduct decay rates for sulfur trioxide radical anion (SO3 ??) was investigated. SO3 ?? radical was produced with UV photolysis of sodium sulfite in basic aqueous solution, and spin-trapped with various spin traps, i.e., PBN (α-phenyl-N-t-butylnitrone), DMPO (5,5-dimethyl pyrroline-1-oxide), and three other phosphoryl DMPO-type spin traps. A modified β-CD, 6-O-α-d-glucosyl-β-cyclodextrin (G-β-CD) having better inclusion properties than β-CD, was employed. Upon adding excess G-β-CD, decay rates of SO3 ?? radical adducts significantly decreased in most spin traps. Half-lives of SO3 ?? radical adducts of phosphoryl spin traps were one to two orders of magnitude longer than that of PBN or DMPO, and the G-β-CD addition further extended the half-life time. The spin traps containing phosphoryl-group all showed higher SO3 ?? trapping rates than those of PBN and DMPO, but two phosphoryl spin traps achieved slower trapping rates by G-β-CD addition. In addition, the structures of CD-inclusion complexes of spin traps were established by means of 1D and 2D NMR measurements. Based on the results, the influences of inclusion on the spin-trapping rate processes and spin-adduct stabilizations were discussed. We conclude that substituents in DMPO-type spin traps may be modified to provide best spin-trapping capabilities in the presence or absence of CD. 相似文献
162.
The matrix-isolation infrared spectrum of a thermally evaporated ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][OTf]), was measured by FTIR spectroscopy and analyzed with the aid of DFT calculations. The main chemical species in the observed IR spectrum was mainly identified as the 1:1 cation-anion pair, which corresponds to the second stable ion-pair structure bonded through five hydrogen bonds between three O atoms of the anion side and four H atoms of the cation. 相似文献
163.
Chang KS Yoshioka T Kanezashi M Tsuru T Tung KL 《Chemical communications (Cambridge, England)》2010,46(48):9140-9142
A new molecular dynamics simulation method was successfully applied to construct a homogeneous organic-inorganic hybrid silica membrane using the hybrid-pcff (h-pcff) potential function. Analysis suggested that the hybrid BTESE silica membrane provided a looser network and larger cavity size for the enhancement of gas permeability and selectivity. 相似文献
164.
T. Ino Y. ArimotoT. Yoshioka K. MishimaK. Taketani S. MutoH.M. Shimizu H. KiraY. Sakaguchi T. OkuK. Sakai T. ShinoharaJ. Suzuki H. OtonoH. Oide S. YamashitaS. Imajo H. FunahashiM. Yamada Y. IwashitaM. Kitaguchi M. HinoZ. Suzuki T. SanukiT. Seki K. HirotaK. Ikeda H. SatoY. Otake H. OhmoriT. Morishima T. Shima 《Physica B: Condensed Matter》2011,406(12):2424-2428
We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10−3 using polarized 3He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, which are planned in this beamline. 相似文献
165.
Shinohara J Kobayashi K Sato-Akaba H Itozaki H 《Solid state nuclear magnetic resonance》2011,40(3):121-125
Toward searching for illegal drugs, we investigated the pulsed nuclear quadrupole resonance (NQR) response of 14N in (1R,2S)-(-)-norephedrine, based on the predictions of quantum chemical calculations. Two pairs of spectral lines (ν+=3.089, 3.093 MHz and ν−=2.594, 2.608 MHz) were observed despite its molecule structure having only a single nitrogen atom. This indicates that the molecular crystal has two nonequivalent nitrogen atoms in the unit cell. The temperature dependence of the NQR frequencies and relaxation properties were investigated for the purpose of accurate remote sensing of the drugs. The NQR frequency shift was approximately 0.23 kHz/K around room temperature. The spin-lattice relaxation and spin-phase memory times were 5.2–10.2 ms and 0.6–1.5 ms, respectively. 相似文献
166.
Atsushi Mineshige Yoshiki OhnishiRyuta Sakamoto Yusuke DaikoMasafumi Kobune Tetsuo YazawaHideki Yoshioka Takayuki NakaoTomokazu Fukutsuka Yoshiharu Uchimoto 《Solid State Ionics》2011,192(1):195-199
Electronic as well as ionic conducting properties for oxyapatite-type solid electrolytes based on lanthanum silicate, La9.333 + xSi6O26 + 1.5x (LSO) were investigated in the oxygen-excess region (x > ca. 0.3). We have found that the oxygen excess-type LSO (OE-LSO), namely La10Si6O27 on weighted basis, exhibited high conductivity, and substitution of the Si-site of LSO with some dopants (Mn+) had a positive effect toward the conducting property. Furthermore, it was also found that addition of a very small amount of iron ions into the M-doped OE-LSO, La10(Si6-yMn+y)O27-(2-0.5n)y, improved its conductivity. On the other hand, replacement of the La-site with various ions for La10(Si6-yMn+y)O27-(2-0.5n)y did little to improve conductivity. The electronic transport numbers for Al-doped OE-LSO with Fe-addition, (1-α){La10(Si5.8Al0.2)O26.9}-α(FeOγ), evaluated with the Hebb-Wagner polarization method were very low: i.e., 1.1 × 10− 3 and 2.9 × 10− 3 under P(O2) = 1.1 × 104 Pa at 1073 K for α = 0.00 and 0.005, respectively. Conductivity for each sample was unchanged under humidified atmosphere at 1073 K sustained for over 50 h, revealing that both compositions were chemically stable. It was concluded that 0.995{La10(Si5.8Al0.2)O26.9}-0.005(FeOγ) is suitable for the fuel cell electrolytes because of its high and almost pure ionic conductivity, and its good chemical stability under humidified as well as reducing conditions. 相似文献
167.
Shunsuke Kanematsu Kazuhiko Matsumoto Rika Hagiwara 《Electrochemistry communications》2009,11(6):1312-1315
Fluorohydrogenate ionic liquids of quaternary phosphonium cations, tri-n-butylmethylphosphonium (P4441) fluorohydrogenate, tetra-n-butylphosphonium (P4444) fluorohydrogenate, and tri-n-butyl-n-octylphosphonium (P4448) fluorohydrogenate, have been synthesized by the metatheses of anhydrous hydrogen fluoride and the corresponding phosphonium chloride precursors. All the obtained salts have melting points below room-temperature with a vacuum-stable composition of P444m(FH)2.3F (m = 1, 4, and 8) and were characterized by density, conductivity, and viscosity measurements. Linear sweep voltammetry with a glassy carbon working electrode shows that the P444m(FH)2.3Fs have wide electrochemical windows exceeding 5.2 V. In particular, P4441(FH)2.3F has an electrochemical window of 6.0 V, which is the widest among fluorohydrogenate ionic liquids reported to date. The thermal stability of these ionic liquids is also improved compared to the salts of N-heterocyclic ammonium cations. 相似文献
168.
H. Yoshioka H. Kurosaki H. Yoshioka 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(1):217-220
The aqueous solutions of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) containing various amount of (-)-epigallocatechin gallate
(EGCg) were mixed with tritiated water, then frozen and β-ray irradiatedin situ for 90 days at −80°C. ESR spectra were measured as a function of time after melting the sample at room temperature. The intensity
of the hydroxyl (OH)_ radical adduct, DMPO-OH, was obtained by the extrapolation to zero time. The ratio of the reaction rate
constants of the OH radical with EGCg and DMPO,k
EGCg/k
DMPO, was obtained kinetically. The result was compared with the case of DNA and EGCg in tritiated water, in order to make clear
the mechanism of the protection of DNA from the radiation-induced scission with EGCg. 相似文献
169.
Shin-ichiro Hayashi Munenori Yoshioka Shuji Usui Kiyofumi Haneda Takahiro Kondo Kim B. McAuley Takahiro Tominaga 《Radiation Physics and Chemistry》2010,79(7):803-808
In radiotherapy treatment, polymer gel dosimetry can be used for verifying three-dimensional (3D) dose distributions. Gelatin is generally used as a gelling agent in the dosimeters. In this paper, another role of gelatin in a methacrylic-acid-based gel dosimeter (MAGAT) is investigated. Temperature increases due to exothermic polymerization in the irradiated gel are measured directly. Dose–R2 responses are also obtained using MRI. It is shown that no appreciable increases in either temperature or R2 are observed in MAGAT dosimeters made without gelatin, and that significant temperature and R2 increases are observed when very low gelatin concentrations are used. These results indicate that gelatin is an important enabler for radiation-induced free-radical polymerization in methacrylic-acid-based gels. When gelatin is replaced by amino acids, changes in temperature are observed, along with small changes in R2. The resulting dosimeter solutions remain transparent because the polymer does not precipitate as it does in regular MAGAT dosimeters containing gelatin. When the amino acids are replaced by acids without amino groups, no temperature or R2 changes are observed, indicating that no polymer forms. These results show that amino groups (and possibly other functional groups) on the gelatin catalyze the radiation-induced free-radical polymerization that occurs in MAGAT dosimeters. 相似文献