全文获取类型
收费全文 | 890篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 425篇 |
晶体学 | 14篇 |
力学 | 54篇 |
数学 | 164篇 |
物理学 | 278篇 |
出版年
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 51篇 |
2012年 | 47篇 |
2011年 | 48篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 39篇 |
2007年 | 46篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 26篇 |
2003年 | 35篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 24篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有935条查询结果,搜索用时 125 毫秒
81.
T. S. Chow 《Journal of Polymer Science.Polymer Physics》1987,25(1):137-148
This paper reports the theoretical prediction and experimental verification of the connection between the yield stress of amorphous polymers and the physical aging phenomenon. The analysis reveals the existence of a fundamental relationship between the nonequilibrium glassy state and the thermally activated process controlling viscoelastic and plastic deformation. The results show that the volume relaxation and deformation kinetics share the same relaxation times, and that the activation energy for deformation below Tg is much smaller than previously mentioned in the literature. This indicates that the phenomenon of physical aging plays a very important role in the deformation and processing of polymers at low temperatures. The effect of quenching and annealing on the yield stress is described in terms of the mean energy of hole formation, the departure of volume from its equilibrium state, the distribution of hole energies, and lattice volume. The same set of molecular parameters obtained from the molecular kinetic theory of the glass transition and volume relaxation predicts the yield stress as a function of cooling rate, annealing time, temperature, and strain rate. 相似文献
82.
Under carefully controlled conditions, boron trichloride or alkoxydichloroborane/ethyldiisopropylamine in CH2Cl2 can be used to effect diastereoselective aldol additions of ethyl ketones to saturated, α, β-unsaturated, or aromatic aldehydes. The C? C bond formation takes place with relative topicity ul (‘syn,’ configuration of the aldols), in selectivities ranging from 90 to 99% ds (Tables 1–3). Mechanistic aspects of the reaction are discussed. 相似文献
83.
84.
Wei-Liang Chow 《Mathematische Annalen》1940,117(1):98-105
Ohne Zusammenfassung 相似文献
85.
Epoxidized palm oil (EPO) (0–12 wt%) was added into petrochemical-based epoxy blends (diglycidyl ether of bisphenol-A (DGEBA)/cycloaliphatic
epoxide resin/epoxy novolac resin) to develop a thermal curable bio-based epoxy system. The thermal behaviors of the EPO,
epoxy blends (EB), and bio-based epoxy blends (EB/EPO) were characterized using differential scanning calorimetry (DSC), dynamic
mechanical thermal analysis (DMT) and thermo-mechanical analysis (TM). The glass transition temperature (T
g) and storage modulus (E′) of the EB/EPO system was reduced with the increasing of the EPO loading. This is attributed to the plasticizing effect
of the EPO. It was found that epoxy blends with higher loading of EPO possessed higher coefficient of thermal expansion (CTE)
and tanδ value. This is due to the increase of the free volume and chain flexibility in the three-dimensional network of the epoxy
blends. The internal thermal stresses of the EB/EPO were decreased as the increasing loading of EPO, owing to the reduction
of crosslink density, modulus of elasticity, and T
g in the epoxy blends. 相似文献
86.
In this demonstration, a stable and wavelength-tunable erbium-doped fiber (EDF) ring laser using dual-saturable-absorber-based
(DSAB) filter inside loop cavity is proposed and experimentally investigated. The proposed DSAB filter not only can filter
the side-mode in single-frequency output, but also can obtain the flattened output power spectrum within 1 dB variation in
the effectively range of 1529 to 1563 nm. In addition, the output stabilities of wavelength and power are also measured experimentally
and discussed. 相似文献
87.
K. L. Chow N. K. Mak M. H. Wong X. F. Zhou Y. Liang 《Journal of nanoparticle research》2011,13(3):1007-1017
The objective of this study was to investigate antimicrobial mechanisms of a new catalytic material (charge transfer auto
oxidation–reduction type catalyst, CT catalyst) that may have great potential for application in water/wastewater treatment.
Generation of reactive oxygen species (ROS) in bacteria-free solution, induction of ROS and oxidative damage in bacteria (including
E. coli and S. aureus) were examined for the CT catalyst. The results showed that significantly higher (p < 0.05, via t-test) amount of hydroxyl radicals was generated by the CT catalyst compared with the control, particularly after 6 h of contact
time that more than twice of the amount of the control was produced. The generation of ROS in the bacteria was greater under
higher pH and temperature levels, which closely related with the oxidative damage in cells. The results indicated that CT
catalyst induced oxidative damage in the bacteria might serve as an important mechanism interpreting the anti-microbial function
of the CT catalyst. 相似文献
88.
Chow JM Córcoles AD Gambetta JM Rigetti C Johnson BR Smolin JA Rozen JR Keefe GA Rothwell MB Ketchen MB Steffen M 《Physical review letters》2011,107(8):080502
We demonstrate an all-microwave two-qubit gate on superconducting qubits which are fixed in frequency at optimal bias points. The gate requires no additional subcircuitry and is tunable via the amplitude of microwave irradiation on one qubit at the transition frequency of the other. We use the gate to generate entangled states with a maximal extracted concurrence of 0.88, and quantum process tomography reveals a gate fidelity of 81%. 相似文献
89.
Srinivasulu Aitipamula Pui Shan Chow Reginald B. H. Tan 《Journal of chemical crystallography》2011,41(11):1604-1611
Abstract
Cocrystals of two important active pharmaceutical ingredients, carbamazepine and piracetam, with hydroquinone are reported. Cocrystal formation between the selected APIs and hydroquinone is investigated with the aid of solid-state grinding methods. Both the crystal structures belong to the triclinic, P [`1]P \bar{1} space group, with the cocrystal involving carbamazepine and hydroquinone having the unit cell parameters a = 6.9725 (14) ?, b = 8.8175 (18) ?, c = 15.083 (3) ?, α = 106.96 (3)°, β = 92.16 (3)°, γ = 103.23 (3)°, V = 858.0 (4) ?3 and Z = 2; and the cocrystal involving piracetam and hydroquinone has the unit cell parameters a = 6.4909 (13) ?, b = 6.5410 (13) ?, c = 11.612 (2) ?, α = 103.92 (3)°, β = 104.53 (3)°, γ = 91.06 (3)°, V = 461.59 (18) ?3 and Z = 2. Analysis of the cocrystals revealed that they are sustained by an alcohol–carboxamide heterosynthon. In addition, the cocrystal of carbamazepine and hydroquinone features an amide–alcohol heterosynthon and an alcohol–alcohol homosynthon. The cocrystal of piracetam and hydroquinone features an amide–amide dimer synthon. Cocrystal formation was evidenced from the shifts in the vibrational frequencies corresponding to the functional groups present on the cocrystal components. 相似文献90.
C.R.A. Catlow M. Cherry K.H. Chow S.P. Cottrell S.F.J. Cox E.A. Davis K.V. Wright 《Hyperfine Interactions》1997,106(1-4):119-122
The expectation that the hydroxyl analogue state of positive muons implanted in quartz should be stabilized by a suitable
charge compensation centre is supported by preliminary data. The diamagnetic fraction correlates with aluminium content over
the narrow range investigated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献