全文获取类型
收费全文 | 474篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
化学 | 265篇 |
晶体学 | 4篇 |
力学 | 12篇 |
数学 | 32篇 |
物理学 | 168篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 23篇 |
2012年 | 29篇 |
2011年 | 28篇 |
2010年 | 21篇 |
2009年 | 13篇 |
2008年 | 30篇 |
2007年 | 37篇 |
2006年 | 28篇 |
2005年 | 24篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1970年 | 2篇 |
1961年 | 1篇 |
排序方式: 共有481条查询结果,搜索用时 15 毫秒
61.
Debnath S Dasgupta A Mitra RN Das PK 《Langmuir : the ACS journal of surfaces and colloids》2006,22(21):8732-8740
This paper delineates how the different counterions affect the physicochemical properties of the aqueous aggregates and thereby the lipase activities at the interface of cationic water-in-oil microemulsions. To this end, we have synthesized a series of cetyltrimethylammonium-based surfactants, 1-14, having aliphatic, aliphatic with aromatic substitution at the alpha position, and aromatic carboxylate anion as the counterion. The physicochemical characterizations of these aqueous aggregates were done by conductometric, tensiometric, fluorometric techniques to determine counterion binding (beta), critical micelle concentration (cmc), and micropolarity at the microenvironment. It has been found that the activity of lipase mainly increases with hydrophobicity (which is directly proportional to the counterion binding (beta) of the surfactant) of the counterion and reaches a maximum when the beta value is around 0.5. Increase in hydrophobicity as well as beta leads to the attachment of more counterions at interface resulting in enhancement of interfacial area. Consequently, the enzyme may attain flexible secondary conformation at the augmented surface area and also allow larger population of substrates and enzyme molecules at the interface leading to the enhancement in lipase activity. After an optimum value of beta, further increase probably produces a steric crowding at the interface, hindering the smooth occupancy of enzyme and the substrate in this region leading to decrease of enzyme activity, while molecular surface area of the counterion did not show any virtual influence on the lipase activity. Thus, the variation in the counterion structure and hydrophobicity plays a crucial role in modulating the lipase activity. 相似文献
62.
D.J. Hinde A.C. Berriman R.D. Butt M. Dasgupta C.R. Morton A. Mukherjee J.O. Newton 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):149-154
In the fusion of heavy nuclei, there is a distribution of fusion barrier energies resulting from coupling between intrinsic
motion and internal degrees of freedom. Precise experimental measurements of excitation functions have allowed the extraction
of the distributions by taking the second derivative using a point-difference method. In the case of statically deformed nuclei,
experimental data shows that the different fusion barrier energies correspond to different physical configurations of the
colliding nuclei, the latter affecting the subsequent dynamical trajectories over the potential energy surface, influencing
the ultimate reaction products, as for example in quasi-fission. The fusion barrier distribution is also valuable in understanding
the fusion of weakly bound nuclei, enabling a reliable prediction of the expected fusion cross-sections, and thus the determination
of fusion suppression factors at above-barrier energies.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
63.
Eikonalization of dual pole amplitudes, such as the Veneziano amplitude, is shown to lead to singularities in the impact parameter
plane, which, in the eikonal approximation, may be interpreted as branch points in the direct channel angular momentum plane.
This result is discussed in the light of dual absorption models. 相似文献
64.
Ozone has become the oxidant of choice for water disinfection, especially in large water treatment facilities. This paper describes a fast and sensitive method for the determination of ozone content by reaction with photoactivated chromotropic acid (CA, 4,5-dihydroxynaphthalene-2,7-disulfonic acid), which results in intense chemiluminescence (CL). Freshly ozonated water from a recirculating ozonizer/reservoir is injected into a carrier stream of deionized water in the flow-injection mode. This flow mixes with a stream of photoactivated CA solution in a spiral cell placed directly on top of an inexpensive miniature (8 mm diameter active area) photomultiplier tube (PMT). Alkaline CA is photoactivated by passing it through a FEP-Teflon® coil (residence time ∼ 50 s) wrapped around a 1 W UV lamp emitting at 254 nm; without photoactivation, the signal is ∼70-fold lower. The S/N = 3 limit of detection for aqueous ozone is 3 μg l−1 and good response slope is obtained up to an ozone concentration of 1.4 mg l−1, the highest that could be made in this study. The response obeyed a quadratic equation with r2 = 0.9984. No interference from permanganate ion is observed. The proposed system was applied to the monitoring of ozonation status of a playa lake water that exhibited significant ozone demand. 相似文献
65.
66.
Study of transport in the boundary layer of tokamak plasma in presence of magnetic divertors is extended to the second order
in ion collision frequency. Numerical results for ion and energy losses to the collector plates are presented for toroidal
and poloidal divertors. For the toroidal case, the Wiener-Hopf solution for the second order distribution function is obtained.
An error occurring in an earlier first order calculation is pointed out and corrected first order fluxes are also given. For
the poloidal divertor, asymmetry observed in ion and energy transport is found to persist in the second order result. 相似文献
67.
Comprehensive fission measurements, including mass-angle distributions, for the reaction of 32S with the prolate deformed nucleus 232Th at near-barrier energies show two distinct components in both mass and angle; surprisingly, both have characteristics of quasifission. Their relative probabilities vary rapidly with the ratio of the beam energy to the capture barrier, suggesting a relationship with deformation aligned (sub-barrier), or antialigned (above-barrier), configurations at contact. 相似文献
68.
In this paper, the extended Lagrangian formulation for a one-dimensional continuous system with gyroscopic coupling and non-conservative fields has been developed. Using this formulation, the dynamics of an internally and externally damped rotor driven through a dissipative coupling has been studied. The invariance of the extended or so-called umbra-Lagrangian density is obtained through an extension of Noether’s theorem. The rotor shaft is modeled as a Rayleigh beam. The dynamic behavior of the rotor shaft is obtained and validated through simulation studies. Results show an interesting phenomenon of limiting behavior of the rotor shaft with internal damping beyond certain threshold speeds which are obtained theoretically and affirmed by simulations. It is further observed that there is entrainment of whirling speeds at natural frequencies of the rotor shaft primarily depending on the damping ratio. 相似文献
69.
Dasgupta PK 《Journal of chromatography. A》2008,1213(1):50-55
Resolution of overlapped chromatographic peaks is generally accomplished by modeling the peaks as Gaussian or modified Gaussian functions. It is possible, even preferable, to use actual single analyte input responses for this purpose and a nonlinear least squares minimization routine such as that provided by Microsoft Excel Solver can then provide the resolution. In practice, the quality of the results obtained varies greatly due to small shifts in retention time. I show here that such deconvolution can be considerably improved if one or more of the response arrays are iteratively shifted in time. 相似文献
70.