全文获取类型
收费全文 | 448051篇 |
免费 | 4972篇 |
国内免费 | 1525篇 |
专业分类
化学 | 240433篇 |
晶体学 | 6835篇 |
力学 | 18902篇 |
综合类 | 10篇 |
数学 | 53498篇 |
物理学 | 134870篇 |
出版年
2020年 | 3180篇 |
2019年 | 3331篇 |
2018年 | 3708篇 |
2017年 | 3717篇 |
2016年 | 6628篇 |
2015年 | 4810篇 |
2014年 | 7040篇 |
2013年 | 20218篇 |
2012年 | 15143篇 |
2011年 | 18621篇 |
2010年 | 12277篇 |
2009年 | 12207篇 |
2008年 | 17310篇 |
2007年 | 17379篇 |
2006年 | 16750篇 |
2005年 | 15198篇 |
2004年 | 13843篇 |
2003年 | 12339篇 |
2002年 | 12120篇 |
2001年 | 13711篇 |
2000年 | 10527篇 |
1999年 | 8282篇 |
1998年 | 6782篇 |
1997年 | 6519篇 |
1996年 | 6469篇 |
1995年 | 5946篇 |
1994年 | 5705篇 |
1993年 | 5496篇 |
1992年 | 6178篇 |
1991年 | 5977篇 |
1990年 | 5707篇 |
1989年 | 5509篇 |
1988年 | 5728篇 |
1987年 | 5445篇 |
1986年 | 5215篇 |
1985年 | 7367篇 |
1984年 | 7513篇 |
1983年 | 6266篇 |
1982年 | 6681篇 |
1981年 | 6549篇 |
1980年 | 6325篇 |
1979年 | 6544篇 |
1978年 | 6639篇 |
1977年 | 6531篇 |
1976年 | 6490篇 |
1975年 | 6343篇 |
1974年 | 6188篇 |
1973年 | 6496篇 |
1972年 | 3969篇 |
1971年 | 3030篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of simpler linear differentialoperators and a nonlinear term. 相似文献
122.
123.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found. 相似文献
124.
For fairly high concentrations, the effective arsenic diffusioncoefficient is known to grow linearly with the concentration.In this paper, we consider the strongly enhanced diffusion ofarsenic by asymptotic methods, and extend the results of a previouspaper (King & Please, 1987) in three ways: we characterizean additional (low-concentration) region; we consider the influenceof the initial data; and we consider the case of constant surfaceconcentration. 相似文献
125.
126.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献
127.
128.
Aji P. Mathew Gabriel Groeninckx G. H. Michler H. J. Radusch Sabu Thomas 《Journal of Polymer Science.Polymer Physics》2003,41(14):1680-1696
The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the Tg values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003 相似文献
129.
R.J Hand 《Journal of Non》2003,315(3):276-287
Glass may be strengthened by epoxy coatings although the strengthening mechanisms remain unclear. Possible strengthening mechanisms are reviewed and are used to analyse strength data for both a solvent based and a water based coating system. The coatings either fill (solvent based coatings), or partially fill (water based coatings) surface cracks and it is shown that closure stresses arising from the thermal expansion mismatch of the coating within these cracks can account for the observed degrees of strengthening. It is also demonstrated that other suggested mechanisms such as flaw healing cannot fully account for the observed degree of strengthening. 相似文献
130.