全文获取类型
收费全文 | 1148篇 |
免费 | 32篇 |
国内免费 | 12篇 |
专业分类
化学 | 663篇 |
晶体学 | 12篇 |
力学 | 29篇 |
数学 | 114篇 |
物理学 | 374篇 |
出版年
2024年 | 7篇 |
2023年 | 27篇 |
2022年 | 23篇 |
2021年 | 30篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 41篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 60篇 |
2012年 | 91篇 |
2011年 | 92篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 70篇 |
2007年 | 47篇 |
2006年 | 57篇 |
2005年 | 41篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有1192条查询结果,搜索用时 15 毫秒
131.
Kumari Rinki Pradip K. Dutta Andy J. Hunt James H. Clark Duncan J. Macquarrie 《Macromolecular Symposia》2009,277(1):36-42
A novel chitosan-formaldehyde porous derivative (scaffolds) was prepared by reaction of 85% deacetylated chitosan with 37% aq. formaldehyde using supercritical carbon dioxide (sc. CO2). Prior to reaction, the chitosan hydrogel was prepared in 1% aq. acetic acid (AcOH) and formaldehyde. The prepared hydrogel was subjected to solvent exchange. The identity of the Schiff base was confirmed by Fourier transform infrared spectroscopy (FTIR). The chitosan-derivative was evaluated by thermal analysis, scanning electron microscopy, and porosimetry analysis. Overall, the sc. CO2 assisted chitosan derivative opens new perspectives as biomedical material. 相似文献
132.
An experimental investigation of flow around a square cylinder placed at various angles with respect to the approach fluid velocity is reported. The focus of the study is toward examining the sensitivity of the wake properties to the cylinder orientation and Reynolds number. Angles of incidence in the range of 0-60° and Reynolds numbers of 1340, 4990, and 9980 have been considered. Velocity measurements have been carried out using an X-wire hotwire anemometer. The Strouhal number and the drag coefficient of the cylinder have been computed from the wake measurements. Utilizing the velocity traces at distinct probe locations in the near and the far wake, statistical properties such as the RMS velocities and the spectra have been obtained. Results obtained in the present work revealed that for a cylinder with zero inclination, flow separates from the corners on the face exposed to the incoming flow. For inclinations greater than zero, the points of separation on the cylinder move downstream and the wake size increases, but the separated shear layer rolls up over a shorter distance. These factors lead to a reduced drag coefficient and a higher Strouhal number. The center-line recovery of the time-averaged velocity and the decay rates of velocity fluctuations depend on the Reynolds number. A marginal effect of the cylinder orientation is also seen. 相似文献
133.
Ion dynamics of AgI-doped Ag2O–TeO2 glasses and Ag2S doped glass nanocomposites have been studied using impedance spectroscopy and correlated with their structures investigated using Fourier transform infrared spectroscopy. The composition dependences of the dc conductivity and the activation energy of these glasses and nanocomposites have been compared with those of AgI-doped silver phosphate and borate glasses. We have studied the ion dynamics in the framework of the power-law and the electric modulus formalisms. We have established a correlation between the crossover rate of the mobile silver ions and the rearrangement of the structural units of glassy networks. The scaling of the conductivity spectra has been used to interpret the temperature and composition dependence of the relaxation dynamics. Analysis of the dielectric relaxation in the framework of modulus formalism indicates an increase in ion–ion cooperation in the glass compositions with increasing AgI content. 相似文献
134.
This paper presents the results of an experimental study of buoyancy-driven convective heat transfer between three parallel
vertical plates, symmetrically spaced with water as the intervening medium. The centre plate was electrically heated, while
the other side plates were water-cooled forming two successive parallel vertical channels of dimensions 20 cm × 3.5 cm × 35 cm
(length W, gap L, height H) each. Top, bottom and sides of the channels were open to water in the chamber which is the novel aspect of this study. Plate
surface temperature and bath temperature at different levels of height from the bottom of channel were measured by K-type
thermocouples. Experimental data have been correlated as under:
相似文献
135.
The reactions of dimeric complex [Rh(CO)2Cl]2 with hemilabile ether‐phosphine ligands Ph2P(CH2) nOR [n = 1, R = CH3 (a); n = 2, R = C2H5 (b)] yield cis‐[Rh(CO)2Cl(P ~ O)] (1) [P ~ O = η 1‐(P) coordinated]. Halide abstraction reactions of 1 with AgClO4 produce cis‐[Rh(CO)2(P ∩ O)]ClO4 (2) [P ∩ O = η 2‐(P,O)chelated]. Oxidative addition reactions of 1 with CH3I and I2 give rhodium(III) complexes [Rh(CO)(COCH3)ClI(P ∩ O)] (3) and [Rh(CO)ClI2(P ∩ O)] (4) respectively. The complexes have been characterized by elemental analyses, IR, 1H, 13C and 31P NMR spectroscopy. The catalytic activity of 1 for carbonylation of methanol is higher than that of the well‐known [Rh(CO)2I2]? species. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
136.
It is well known that the generalized Nash equilibrium problem, a model for multi-leader–follower games, can be reformulated as a quasivariational inequality. We show that, in fact, a reformulation in terms of a variational inequality can be obtained in the general setting of quasiconvex nondifferentiable decision functions. An existence result is deduced. 相似文献
137.
Dibyendu S. Bag Dhiraj Dutta T. C. Shami K. U. Bhasker Rao 《Journal of polymer science. Part A, Polymer chemistry》2009,47(9):2228-2242
A chiral monomer containing L ‐leucine as a pendant group was synthesized from methacryloyl chloride and L ‐leucine in presence of sodium hydroxide at 4 °C. The monomer was polymerized by free radical polymerization in propan‐2‐ol at 60 °C using 2,2′‐azobis isobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. The polymer, poly(2‐(Methacryloyloxyamino)‐4‐methyl pentanoic acid) is thus obtained. The molecular weight of the polymer was determined to be: Mw is 6.9 × 103 and Mn is 5.6 × 103. The optical rotation of both chiral monomer and its polymer varies with the solvent polarity. The amplification of optical rotation due to transformation of monomer to polymer is associated with the ordered conformation of chiral monomer unit in the polymeric chain due to some secondary interactions like H‐bonding. The synthesized monomer and polymer exhibit intense Cotton effect at 220 nm. The conformation of the chain segments is sensitive to external stimuli, particularly the pH of the medium. In alkaline medium, the ordered chain conformation is destroyed resulting disordered random coils. The ordered coiling conformation is more firmly present on addition of HCl. The polymer exhibits swelling‐deswelling characteristics with the change of pH of the medium, which is reversible. The Cotton effect decreases linearly with the increase of temperature which is reversible on cooling. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2228–2242, 2009 相似文献
138.
We study the effect of a nearby phase-conjugate mirror (PCM) on the gap soliton of a Kerr non-linear periodic structure. We
show that phase conjugation of the gap soliton (in the sense of replication of the amplitude profile in the reverse direction)
is possible under the condition of PCM reflectivity approaching unity. This is in contrast with the results for linear structures,
where the wave profiles can be conjugated for arbitrary values of the PCM reflectivity. The sensitivity of the conjugation
of the gap solitons to PCM reflectivity is ascribed to the fine balance of non-linearity with dispersion, necessary for their
existence. 相似文献
139.
The hard photon production from bremsstrahlung and annihilation with scattering that arise at two-loop level are estimated for a chemically non-equilibrated quark–gluon plasma in the framework of Hard Thermal Loop (HTL) resummed effective field theory. The rate of photon production is found to be suppressed due to unsaturated phase space compared to equilibrated plasma. For an unsaturated plasma, unlike the effective one-loop case, the reduction in the effective two-loop processes is found to be independent of gluon fugacity, due to an additional collinear enhancement arising from the decrease in thermal quark mass but strongly depends on quark and antiquark fugacities. It is also found that the photon production is dominated by bremsstrahlung mechanism, since the phase space suppression is higher for annihilation with scattering, in contrast to the equilibrated plasma where annihilation with scattering dominates the photon production. 相似文献
140.
N. K. Dutta N. D. Tran N. R. Choudhury 《Journal of Polymer Science.Polymer Physics》2005,43(11):1392-1400
Scanning thermal microscopy (SThM) has been used for the visualization and characterization of an ultrathin plasma polymer film of perfluoro(methylcyclohexane) at a submicrometer level. The morphology, molecular dynamics, and lateral homogeneity of the ultrathin film have all been examined precisely with SThM. The growth of the plasma polymer film on a silicon wafer (Si‐wafer) has also been precisely determined using a new burning‐hole technique. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1392–1400, 2005 相似文献