全文获取类型
收费全文 | 5415篇 |
免费 | 298篇 |
国内免费 | 598篇 |
专业分类
化学 | 3249篇 |
晶体学 | 5篇 |
力学 | 402篇 |
综合类 | 114篇 |
数学 | 1818篇 |
物理学 | 723篇 |
出版年
2024年 | 6篇 |
2023年 | 51篇 |
2022年 | 214篇 |
2021年 | 271篇 |
2020年 | 202篇 |
2019年 | 205篇 |
2018年 | 186篇 |
2017年 | 183篇 |
2016年 | 288篇 |
2015年 | 239篇 |
2014年 | 256篇 |
2013年 | 396篇 |
2012年 | 264篇 |
2011年 | 261篇 |
2010年 | 211篇 |
2009年 | 263篇 |
2008年 | 275篇 |
2007年 | 287篇 |
2006年 | 290篇 |
2005年 | 252篇 |
2004年 | 226篇 |
2003年 | 216篇 |
2002年 | 185篇 |
2001年 | 155篇 |
2000年 | 121篇 |
1999年 | 110篇 |
1998年 | 84篇 |
1997年 | 94篇 |
1996年 | 83篇 |
1995年 | 59篇 |
1994年 | 65篇 |
1993年 | 39篇 |
1992年 | 53篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 29篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 16篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有6311条查询结果,搜索用时 62 毫秒
991.
本文对非线性泛函分析中著名的Amann三解定理作了本质性的改进,并将其结果应用到核函数不恒为正的Hammerstein型积分方程,得到了新的结论. 相似文献
992.
993.
基于线性规划核心矩阵的单纯形算法 总被引:3,自引:0,他引:3
本文讨论了线性规划中的核心矩阵及其特性,探讨了利用核心矩阵实现单纯形算法的可能性,并进一步提出了一个基于核心矩阵的两阶段原始一对偶单纯形方法,该方法通过原始和对偶两个阶段的迭代,可以在有限次迭代中收敛到原问题的最优解或证明问题无解或无界.在试验的22个问题中,该算法的计算效率总体优于基于传统单纯形方法的MINOS软件. 相似文献
994.
In this paper, five different structural urethane acrylates modified by linseed oil were synthesized and then properties of their electron beam cured (EBC) coatings, i.e., adhesion, gloss, flexibility, impact resistance, hardness, tensile strength and elongation were studied. It was shown that these synthesizing conditions of urethane acrylates modified by linseed oil were temperate. Effect of structure of urethane acrylates modified by linseed oil on these properties of their EBC coatings was obvious, except gloss. According to synthetical properties of EBC coatings, the optimum oligomer among these was No. A, whose main chains were formed by hexane diacid, average functionality was 2, and oil content was 25.5%. With increasing of absorbed doses, these properties of EBC coatings, except gloss, changed correspondingly. It was advisable that absorbed dose wasn’t greater than 180 kGy. At higher absorbed doses, cobaltous naphthenate had obvious effect on these properties of EBC coatings, whose oil content of linseed oil was rather high. 相似文献
995.
996.
997.
The dynamics of SO2 emission during thermooxidation of Estonian oil shale, its semicoke, different samples of coal and their mixtures, as well
as the influence of Estonian oil shale ash addition (for modelling the CFBC process) on the dynamics were studied. The experiments
were carried out with thermogravimetric equipment under dynamic heating conditions (5 K min-1) in the atmosphere of dried air, with simultaneous gastitrimetric EGA.
It was established that SO2 emission from the fuels started at 200-320°C. Depending on the form of sulphur (organic, pyritic, sulphate), the emission
took place in two or three steps, and continued up to 580-650°C, during which 35-75% of the total sulphur was emitted into
the gaseous phase. Regulating the mole ratio of free CaO/S in the mixtures of fuels with oil shale ash addition the emission
of SO2 ceased abruptly at 460-540°C and it was limited to the level of 7-30%.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
998.
Mineral oil type lubricating oils have an important role in reducing engine wear. But after some period, depending on the
oil quality, oil replacement is needed since the oil loses its properties. In this paper, an engine oil was tested in a 1300
cc engine car and the change of the thermal stability of the collected portions of oil at different usage periods were experimented
by TG/DTG and DSC techniques. Results show that, as usage period increases lubricating oil contains more of the light components
that distill at low temperatures. The increase in the peak maximum temperature, Tmax, of the DTG, as usage period increases, proposes that the molecular mass of the oil increase, which presumably changes the
viscosity characteristics. Moreover as the usage period increases some residue type components, which only can be destroyed
at very high temperatures, are produced in oil phase.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
999.
The rheological behavior of a waxy crude oil was investigated using a coaxial cylinder viscometer. Experimental flow curves
were fitted with the Casson equation. The Casson model was modified to interpret the hysteresis between upward and downward
curves obtained in a series of consecutive runs. At the same shear rate, the mean axial ratio of the flow unit related to
a down-curve (↓) is smaller than that related to an equilibrium up-curve (↑). This results in a decrease of the Casson yield
stress τc↓ with respect to τc↑. A certain ξ coefficient describing departure from the equilibrium mean axial ratio was introduced into the model. Values
of ξ calculated from the Casson yield stresses agreed satisfactorily with the theoretically predicted ones. Deviations from
the Casson model at low shear rates were also explained.
Received: 28 July 1998 Accepted: 18 February 1999 相似文献
1000.
IntroductionThenumericalsimulationoftheevolutionaryhistoryofthebasinisconductedacordingtothemechanismofpetroleumgeologyandmec... 相似文献