全文获取类型
收费全文 | 1044篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
化学 | 854篇 |
晶体学 | 7篇 |
力学 | 18篇 |
数学 | 64篇 |
物理学 | 144篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 30篇 |
2015年 | 24篇 |
2014年 | 27篇 |
2013年 | 58篇 |
2012年 | 65篇 |
2011年 | 81篇 |
2010年 | 36篇 |
2009年 | 34篇 |
2008年 | 72篇 |
2007年 | 88篇 |
2006年 | 80篇 |
2005年 | 66篇 |
2004年 | 59篇 |
2003年 | 52篇 |
2002年 | 39篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 5篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1969年 | 5篇 |
1968年 | 5篇 |
排序方式: 共有1087条查询结果,搜索用时 15 毫秒
71.
Kazuo Takeuchi Junsuke Yabumoto Yoshiki Okada Terunao Kawai Rahman M. Montajir Yuichi Goto 《Journal of nanoparticle research》2005,7(2):287-293
A new dual-type differential mobility analyzer (dual-type DMA) was developed in order to detect transient number concentrations of airborne nanoparticles with diameters centralized at around 10 nm (for nuclei mode particles) and 100 nm (for accumulation mode particles) in automobile exhaust gas. The apparatus divides the gas sample into two parts, and each part is sent through one of two coaxially nested sections for analysis. For the scanning mode measurement, the nanoparticles are charged by 241Am and their size distributions are determined by varying the applied voltage over 2 min. The transient mode measurement, on the other hand, fixes the voltages for the two sections at peaks near 10 and 100 nm in order to monitor the transient behavior of the exhaust nanoparticles. The measurement principles and design of the dual-type DMA are detailed and the results for time response experiments are presented using model nanoparticles charged by a corona charger. The transient concentrations of the nuclei mode and the accumulation mode particles from a diesel engine were shown to be detected by this method, when 241Am was used for charging the particles. 相似文献
72.
73.
A regularly preemptive model D,MAP/D
1,D
2/1 is studied. Priority customers have constant inter-arrival times and constant service times. On the other hand, ordinary customers' arrivals follow a Markovian Arrival Process (MAP) with constant service times. Although this model can be formulated by using the piecewise Markov process, there remain some difficult problems on numerical calculations. In order to solve these problems, a novel approximation model MAP/MR/1 with Markov renewal services is proposed. These two queueing processes become different due to the existence of idle periods. Thus, a MAP/MR/1 queue with a general boundary condition is introduced. It is a model with the exceptional first service in each busy period. In particular, two special models are studied: one is a warm-up queue and the other is a cool-down queue. It can be proved that the waiting time of ordinary customers for the regular preemption model is stochastically smaller than the waiting time of the former model. On the other hand, it is stochastically larger than the waiting time of the latter model. 相似文献
74.
We successfully demonstrated low power penalty operation of a cross-phase modulated (XPM) wavelength converter using a semiconductor optical amplifier (SOA) power equalizer. We also clarified the SOA equalizing level for more adaptive wavelength conversion and achieved a power penalty of less than 1 dB over the wide input dynamic range of 15 dB. 相似文献
75.
Yuichi Kamiya 《Acta Mathematica Hungarica》2004,105(1-2):103-114
A. Beurling introduced harmonic functions attached to measurable functions satisfying suitable conditions and defined their spectral sets. The concept of spectral sets is closely related to approximations by trigonometric polynomials. In this paper we consider spectral sets of the harmonic functions attached to the Riemann zeta-function and its modification. 相似文献
76.
77.
Crosslinked poly(N-isopropylacrylamide) gel was tested on the feasibility for a preparative electrophoretic matrix. Horse heart myoglobin and bovine hemoglobin were well separated on the gel matrix electrophoretically by molecular sieving effect of the gel network. Relative mobilities of those proteins in the gel were larger than those in a crosslinked polyacrylamide gel of the same polymer concentration. After the separation, the protein-containing portion of the gel underwent swelling at 4°C and deswelling at 37°C, alternatively. As a result of the deswelling, each protein was recovered in a discharged solution out of the gel at almost 100% yield. 相似文献
78.
Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica 总被引:1,自引:0,他引:1
From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO2-Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants (KF and 1/n) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar-OH]/[COOH] and molecular weight, had the highest adsorbability (KF=17.5 (mg/g)(L/mg)(1/n), 1/n=0.67) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar-OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability (KF=7.1 (mg/g)(L/mg)(1/n), 1/n=0.39) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO2-Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO2 features the Ti modifiers of SiO2-Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO2-Ti will be used as a photodegradation catalyst in water purification plants. 相似文献
79.
We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO4·3/4H2O. The structure consists of MoO4 tetrahedra and CoO6 octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO6 and MoOn polyhedra similar to those of the hp-phase. 相似文献
80.
Shimazaki Y Tashiro M Motoyama T Iwatsuki S Yajima T Nakabayashi Y Naruta Y Yamauchi O 《Inorganic chemistry》2005,44(17):6044-6051
Synthetic, structural, spectroscopic, and kinetic studies have been carried out on the Pd(II) complexes of new 2N1O-donor ligands containing a pendent indole, 3-(N-2-pyridylmethyl-N-2-hydroxy-5-methoxybenzylamino)ethylindole (HMeO-iepp), 3-(N-2-pyridylmethyl-N-2-hydroxy-5-nitrobenzylamino)ethylindole (HNO2-iepp), and (N-2-pyridylmethyl-3-indolylethylamino)acetic acid (Hiepc) (H denotes a dissociable proton). [Pd(MeO-iepp)Cl] (2), [Pd(NO2-iepp)Cl] (3), and [Pd(iepc)Cl] (4) were prepared and revealed by X-ray analysis to have a pyridine nitrogen, an amine nitrogen, a phenolate or carboxylate oxygen, and a chloride ion in the coordination plane. UV absorption and 1H NMR spectral changes indicated that all the complexes could be converted to the indole-binding complexes where the O donor was replaced by the indole C2 atom by cyclopalladation in DMSO or DMF in the temperature range of 40-60 degrees C. Formation of the indole-binding complex species obeyed the first-order kinetics, from which the activation parameters were estimated. The formation rate was dependent on the properties of the O-donor group, a lower pKa value of its conjugate acid causing faster conversion to the indole-binding species in the order 2 (methoxyphenolate) < 3 (nitrophenolate) < 4 (carboxylate). On the other hand, the ratio of the indole-binding complex to the O-donor complex as a result of the conversion was greater for the complexes with a higher pKa value of the ligand OH group, the order being 2 > 3 > 4. 相似文献