全文获取类型
收费全文 | 4899篇 |
免费 | 507篇 |
国内免费 | 1156篇 |
专业分类
化学 | 2710篇 |
晶体学 | 31篇 |
力学 | 1028篇 |
综合类 | 73篇 |
数学 | 1651篇 |
物理学 | 1069篇 |
出版年
2024年 | 9篇 |
2023年 | 56篇 |
2022年 | 94篇 |
2021年 | 137篇 |
2020年 | 182篇 |
2019年 | 172篇 |
2018年 | 156篇 |
2017年 | 172篇 |
2016年 | 243篇 |
2015年 | 162篇 |
2014年 | 223篇 |
2013年 | 489篇 |
2012年 | 291篇 |
2011年 | 319篇 |
2010年 | 287篇 |
2009年 | 315篇 |
2008年 | 301篇 |
2007年 | 352篇 |
2006年 | 306篇 |
2005年 | 330篇 |
2004年 | 335篇 |
2003年 | 248篇 |
2002年 | 237篇 |
2001年 | 188篇 |
2000年 | 142篇 |
1999年 | 124篇 |
1998年 | 93篇 |
1997年 | 65篇 |
1996年 | 67篇 |
1995年 | 88篇 |
1994年 | 64篇 |
1993年 | 60篇 |
1992年 | 50篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有6562条查询结果,搜索用时 984 毫秒
991.
The nanoparticles in solution represent a model system, where the well-established colloidal theories such as the Debye–Hückel theory and/or Derjaguin–Landau–Verwey–Overbeek theory can be implemented to predict the nanoparticle phase behavior. Recently, reentrant phase transitions in a wide range of colloids (e.g., inorganic and organic nanoparticles, polymers, and biomolecules) have been observed, which are not consistent with these theories. The colloids in the reentrant phase behavior undergo a phase change and return back to the original phase with respect to a specific physiochemical parameter (e.g., ionic strength, concentration of different additives, temperature, and so on). The nanoparticle–polymer/multivalent ion systems, demonstrating such phase transition and the corresponding phase behavior in terms of interparticle interactions, have been probed by small-angle scattering. It has been shown how the tuning in interparticle interactions using external parameters can lead to reentrant phase behavior and use the nanoparticle aggregation for building nanohybrids. The deviations of the present observations from those of the standard colloidal theories and the anticipated challenges are also discussed. 相似文献
992.
Iodine release in potassium iodide solution has been investigated under the irradiations of ultrasound and visible light respectively and simultaneously. We have observed that the amount of iodine liberated under the combined irradiation of ultrasound and visible light is larger than the sum of that under the respective irradiations of ultrasound and visible light, indicating a synergistic effect of ultrasound and visible light irradiations. Based on the investigation of the reaction kinetics of iodine liberated, we have ascribed the synergistic effect to the perfect stirring of the photochemical reactor induced by the applying simultaneous ultrasound. The ideal stirring can result in the homogenization of the primary light effect in the whole reaction medium, which induces the acceleration of the photochemical reaction. On behavior of our knowledge, there are few reports on the investigations of utilizing the combination of ultrasonic energy and light energy to accelerate the reaction yield and rate as well as the kinetics of the reaction. 相似文献
993.
A closer look at the indications of q-generalized Central Limit Theorem behavior in quasi-stationary states of the HMF model 总被引:1,自引:0,他引:1
We give a closer look at the Central Limit Theorem (CLT) behavior in quasi-stationary states of the Hamiltonian Mean Field model, a paradigmatic one for long-range-interacting classical many-body systems. We present new calculations which show that, following their time evolution, we can observe and classify three kinds of long-standing quasi-stationary states (QSS) with different correlations. The frequency of occurrence of each class depends on the size of the system. The different microscopic nature of the QSS leads to different dynamical correlations and therefore to different results for the observed CLT behavior. 相似文献
994.
995.
996.
正、负离子表面活性剂混合体系溶致液晶生成的相行为 总被引:1,自引:0,他引:1
研究了烷基(C8,C12,C14)三甲基溴化铵、烷基(C12,C14)溴化吡啶与烷基(C8,C12)硫酸钠混合体系溶致液晶形成的条件与结构的变化.在高浓度的水溶液中,随着正、负离子表面活性剂摩尔比接近于1,液晶结构由六角相过渡为层状相.表面活性剂非极性链长改变,对相行为影响显著,短碳链的正、负离子表面活性剂混合体系,在等摩尔比时,体系为层状液晶或立方液晶为主,夹杂少许沉淀.随碳链增长,两类表面活性剂间的静电吸引效果表现为生成沉淀的摩尔比例范围变宽,沉淀量增多,共存的液晶相减少,甚至消失.若只改变正离子的极性头基,季胺盐比吡啶盐与烷基硫酸盐的作用要强,形成不溶物的混合摩尔比例范围更宽. 相似文献
997.
998.
ZHANG Wenhui LIU Qing REN Yinghui YANG Bin ZHANG Xianbo ZHANG Chao MA Haixia ZHAO Fengqi HU Rongzu 《高等学校化学研究》2018,34(2):254-259
Two novel energetic alkalic metal salts of 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz), Li2(BTATz)·6H2O(compound 1) and Na2(BTATz)·2H2O(compound 2), have been synthesized by the reaction of BTATz with lithium hydroxide or sodium hydroxide in dimethylsulfoxide(DMSO) solution, respectively, and their structures were characterized by means of elemental analysis and Fourier transform infrared spectrometry(FTIR). Moreover, the single-crystal structure of compound 1 was determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P1/c. Furthermore, their thermal decomposition behaviors were investigated by means of differential scanning calorimetry(DSC) and thermogravimetry-differential thermal gravimetry(TG-DTG). The results show that the exothermic decomposition peak temperatures for compounds 1 and 2 were 642.65 and 644.46 K, respectively, and the kinetic equations of the main exothermic decomposition were also derived from non-isothermal method. Additionally, the thermal safety of the two compounds was evaluated by calculating self-accelerating decomposition temperature(TSADT) and critical temperature of thermal explosion(Tb). The results(the TSADT and Tb values are 605.43 and 635.69 K for compound 1; 607.38 and 638.96 K for compound 2) reveal that the two compounds exhibit better thermal safety than BTATz. 相似文献
999.
Chi Liu Rui Ye Liping Lian Weiguo Song Jun Zhang Siuming Lo 《Physics letters. A》2018,382(20):1324-1334
In the context of global aging, how to design traffic facilities for a population with a different age composition is of high importance. For this purpose, we propose a model based on the least effort principle to simulate heterogeneous pedestrian flow. In the model, the pedestrian is represented by a three-disc shaped agent. We add a new parameter to realize pedestrians' preference to avoid changing their direction of movement too quickly. The model is validated with numerous experimental data on unidirectional pedestrian flow. In addition, we investigate the influence of corridor width and velocity distribution of crowds on unidirectional heterogeneous pedestrian flow. The simulation results reflect that widening corridors could increase the specific flow for the crowd composed of two kinds of pedestrians with significantly different free velocities. Moreover, compared with a unified crowd, the crowd composed of pedestrians with great mobility differences requires a wider corridor to attain the same traffic efficiency. This study could be beneficial in providing a better understanding of heterogeneous pedestrian flow, and quantified outcomes could be applied in traffic facility design. 相似文献
1000.
Phase behavior and extraction ability of aqueous two-phase systems(ATPs) consisting of ionic liquids(ILs), Cs2CO3 and water were investigated in this paper. Four kinds of ionic liquids, namely, 1-amyl-3-methylimidazolium bromide([C5mim]Br), 1-hexyl-3-methylimidazolium bromide([C6mim]Br), 1-heptyl-3-methylimidazolium bromide ([C7mim]Br) and 1-octyl-3-methylimidazolium bromide([C8mim]Br), were examined to discuss the influence of alkyl groups. Binodal curves and tie-lines at 288.15, 298.15 and 308.15 K were obtained. The partitioning behavior for L-tryptophan in such ATPs was further investigated. The effect of temperature, pH, Cs2CO3 concentration and the structure of ionic liquids on the partitioning were discussed in detail. 相似文献