全文获取类型
收费全文 | 699篇 |
免费 | 10篇 |
国内免费 | 11篇 |
专业分类
化学 | 287篇 |
晶体学 | 6篇 |
力学 | 78篇 |
综合类 | 2篇 |
数学 | 116篇 |
物理学 | 231篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 5篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 42篇 |
2013年 | 36篇 |
2012年 | 26篇 |
2011年 | 49篇 |
2010年 | 50篇 |
2009年 | 76篇 |
2008年 | 75篇 |
2007年 | 58篇 |
2006年 | 28篇 |
2005年 | 33篇 |
2004年 | 31篇 |
2003年 | 12篇 |
2002年 | 22篇 |
2001年 | 22篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有720条查询结果,搜索用时 9 毫秒
41.
We modeled and studied the separation of uracil, nicotinamide, resorcinol, theobromine, theophylline, and caffeine on four C-18 columns of different lengths packed with the same stationary phase using water/methanol mobile phase at one temperature. Predictions of retention times and peak widths were compared with experimental results and were found to be sufficiently accurate for performing optimization calculations. With limits set on the required resolution and on maximum values for pressure and flow rate, calculations were performed for numerous virtual column lengths seeking the smallest possible analysis time for each length while allowing methanol concentration and flow rate to vary as required to minimize run time. Predictions were experimentally verified for the column lengths actually available. These calculations revealed the dependence of best-possible analysis time on column length, modifier concentration, flow rate, and pressure for the real system that was modeled, and provided insight into parameter interactions with respect to analysis times meeting the needs and limits specified. We show that when these parameters are considered in concert, rather than individually, conventional guidelines regarding setting their values may not always lead to the optimum. 相似文献
42.
《Journal of Coordination Chemistry》2012,65(1):47-56
Abstract Theoretical studies were carried out on a series of bis(phosphine) palladium ketene complexes (PR3)2Pd(CH2=C=O), and on the related CH2=C=O and Pd(PR3)2 molecular fragments in order to investigate the electronic structure and the bonding of the ketene ligand to the metal fragment in these complexes. An analysis of the frontier MOs has been performed in order to understand the interactions between the ketene and the metal fragments. The calculated results have shown that the η2-(C,C) mode is preferred over the η2-(C,O) mode by 10–15 kcal/mol in bis(phosphine) palladium ketene complexes. The basicity and bulkiness of the phosphine ligands PR3 have little effect on the bonding mode in (PR3)2Pd(CH2=C=O) complexes. The most stable structure was calculated to be the η2-(C,C) square planar geometry with the CH2 group of ketene out of the molecular plane. Comparison and discussion between the two bonding modes were also presented in this paper. 相似文献
43.
Specific ion effects on the electrophoretic mobility of small,highly charged peptides: A modeling study 下载免费PDF全文
Stuart A. Allison Hengfu Wu Tuyen M. Bui Lac Dang Giang H. Huynh Tam Nguyen Linda Soegiarto Bi C. Truong 《Journal of separation science》2014,37(17):2403-2410
In this work, we use coarse‐grained modeling to study the free solution electrophoretic mobility of small highly charged peptides (lysine, arginine, and short oligos thereof (up to nonapeptides)) in NaCl and Na2SO4 aqueous solutions at neutral pH and room temperature. The experimental data are taken from the literature. A bead modeling methodology that treats the electrostatics at the level of the nonlinear Poisson Boltzmann equation developed previously in our laboratory is able to account for the mobility of all peptides in NaCl, but not Na2SO4. The peptide mobilities in Na2SO4 can be accounted for by including sulfate binding in the model and this is proposed as one possible explanation for the discrepancy. Oligo arginine peptides bind more sulfate than oligo lysines and sulfate binding increases with the oligo length. 相似文献
44.
The torsional vibrations of star molecules are studied with a reduced dimensionality model. In this model, the molecule is described by two equivalent sets of lumped inertial cylinders and vibrational frequencies are predicted by solution of the coupled equations of motion. Force constants are determined by including them as free parameters in the model and fitting the computed frequencies to their analogs as determined using full normal coordinate analysis at the HFSCF level of theory. Best agreement between the methods occurs when torsional force constants are included for the first two layers of the molecule. This reveals that non-bonded torsional interactions are important in the vibrational dynamics of these systems. Further insight is afforded by an analysis of why simple harmonic oscillator models are sufficient for modeling some related systems but fail to reproduce the trend in global mode frequencies for saturated aliphatic star molecules. The analysis reveals that the origin of this failure lies in backbone flexibility in these branched polymeric systems. 相似文献
45.
Elham Doroodchi Thomas Michael Evans Behdad Moghtaderi 《Journal of nanoparticle research》2009,11(6):1501-1507
This article provides critical examinations of two mathematical models that have been developed in recent years to describe
the impact of nano-layering on the enhancement of the effective thermal conductivity of nanofluids. Discrepancy between the
two models is found to be an artefact of an incorrect derivation used in one of the models. With correct formulation, both
models predict effective thermal conductivity enhancements that are not significantly greater than those predicted by classical
Maxwell theory. This study indicates that nano-layering by itself is unable to account for the effective thermal conductivity
enhancements observed in nanofluids. 相似文献
46.
47.
48.
Grzegorz Stepniak Lukasz Maksymiuk Jerzy Siuzdak 《Optical and Quantum Electronics》2007,39(15):1281-1288
Frequency response of passive optical network (PON) based on multimode fibers is investigated. The network comprises fibers,
connectors and splitters/couplers. It is shown that due to mode filtering at splitters, the frequency response is different
for different network nodes in otherwise symmetrical network. 相似文献
49.
Modeling the effects of cohesive energy for single particle on the material removal in chemical mechanical polishing at atomic scale 总被引:1,自引:0,他引:1
This paper proposes a novel mathematical model for chemical mechanical polishing (CMP) based on interface solid physical and chemical theory in addition to energy equilibrium knowledge. And the effects of oxidation concentration and particle size on the material removal in CMP are investigated. It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation. Furthermore, it also shows a nonlinear dependence of removal rate on removal cohesive energy. The model predictions are in good qualitative agreement with the published experimental data. The current study provides an important starting point for delineating the micro-removal mechanism in the CMP process at atomic scale. 相似文献
50.
Melt or cold crystallization kinetics has a strong bearing on morphology and the extent of crystallization, which significantly affects the physical properties of polymeric materials. Nonisothermal crystallization kinetics are often analyzed by the classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) model or one of its variants, even though they are based on an isothermal assumption. As a result, during the nonisothermal (e.g. constant heating or cooling rate) crystallization of polymeric material, different sets of model parameters are required to describe crystallization at different rates, thereby increasing the total number of model parameters. In addition, due to the uncorrelated nature of these model parameters with the cooling or heating rate, accurate modeling at any intermediate condition is not possible. In the present work, these two limitations of the conventional approach have been eliminated by exhibiting the existence of a functional relationship between cooling or heating rate and effective activation energy during nonisothermal melt or cold crystallization in three linear aromatic polyesters. Furthermore, it has been shown that when the JMAK model is used in conjunction with this functional relationship, it is possible to precisely predict the experimental nonisothermal melt or cold crystallization kinetics at any linear cooling or heating rate with a single set of model parameters. 相似文献