全文获取类型
收费全文 | 5804篇 |
免费 | 238篇 |
国内免费 | 28篇 |
专业分类
化学 | 3885篇 |
晶体学 | 71篇 |
力学 | 161篇 |
数学 | 437篇 |
物理学 | 1516篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 59篇 |
2021年 | 154篇 |
2020年 | 104篇 |
2019年 | 106篇 |
2018年 | 86篇 |
2017年 | 93篇 |
2016年 | 149篇 |
2015年 | 170篇 |
2014年 | 219篇 |
2013年 | 377篇 |
2012年 | 422篇 |
2011年 | 456篇 |
2010年 | 293篇 |
2009年 | 244篇 |
2008年 | 427篇 |
2007年 | 364篇 |
2006年 | 374篇 |
2005年 | 307篇 |
2004年 | 288篇 |
2003年 | 237篇 |
2002年 | 234篇 |
2001年 | 168篇 |
2000年 | 111篇 |
1999年 | 95篇 |
1998年 | 54篇 |
1997年 | 29篇 |
1996年 | 45篇 |
1995年 | 56篇 |
1994年 | 34篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有6070条查询结果,搜索用时 15 毫秒
991.
992.
993.
Eui‐Jun Choi Chang‐Hyeon Kim Jung‐Ki Park 《Journal of Polymer Science.Polymer Physics》1999,37(17):2430-2438
The polycaprolactone (PCL)/starch blends were prepared by using the starch‐g‐PCL (SGCL) graft copolymers as compatibilizers, and their mechanical properties were correlated with the compatibilizing effect of the SGCL copolymers having various molecular structures. The modulus and strength of the PCL/starch blend were decreased, whereas the percent elongation and the toughness were increased remarkably with the addition of SGCL having appropriate graft structure. These property changes were analyzed in terms of the PCL crystallinity and the interfacial adhesion between the PCL matrix and starch dispersion phases, which were dominated by the compatibilizing effects of the SGCL copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2430–2438, 1999 相似文献
994.
Ansa‐zirconocene diamide complex rac‐(EBI)Zr(NMe2)2 [rac‐1, EBI = ethylene‐1,2‐bis(1‐indenyl)] reacted with AlR3 (R = Me, Et, iBu) or Al(iBu2)H and then with [CPh3][B(C6F5)4] (2) in toluene in order to perform propylene polymerization by cationic alkylzirconium species, which are in situ generated during polymerization. Through the sequential NMR‐scale reactions of rac‐1 with AlR3 or Al(iBu2)H and then with 2, rac‐1 was demonstrated to be transformed to the active alkyzirconium cations via alkylated intermediates of rac‐1. The cationic species generated by using AlMe3, AlEt3, and Al(iBu2)H as alkylating reagents tend to become heterodinuclear complex; however, those by using bulky Al(iBu)3 become base‐free [rac‐(EBI)Zr(iBu)]+ cations. The activity of propylene polymerization by rac‐1/AlR3/2 catalyst was deeply influenced by various parameters such as the amount and the type of AlR3, metallocene concentration, [Al]/[2] ratio, and polymerization temperature. Generally the catalytic systems using bulky alkylaluminum like Al(iBu)3 and Al(iBu)2H show higher activity but lower stereoregularity than those using less bulky AlMe3 and AlEt3. The alkylating reagent Al(iBu)3 is not a transfer agent as good as AlMe3 or AlEt3. The polymerization activities show maximum around [Al]/[2] ratio of 1.0 and increase monotonously with polymerization temperature. The overall activation energy of both rac‐1/Al(iBu)3/2 and rac‐1/Al(iBu)2H catalysts is 6.0 kcal/mol. As the polymerization temperature increases, the stereoregularity of the resulting polymer decreases markedly, which is demonstrated by the decrease of [mmmm] pentad value and by the increase of the amount of polymer soluble in low boiling solvent. The physical properties of polymers produced in this study were investigated by using 13C‐NMR, differential scanning calorimetry (DSC), viscometry, and gel permeation chromatography (GPC). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1523–1539, 1999 相似文献
995.
K. C. Nicolaou Phil S. Baran Rolf Jautelat Yun He Kin Chiu Fong Ha‐Soon Choi Won Hyung Yoon Yong‐Li Zhong 《Angewandte Chemie (International ed. in English)》1999,38(4):549-552
A seven‐step cascade reaction —in which selective mesylation, epoxide formation, epoxide lysis, cyclization, reiterative oxidation, and nitrogen–oxygen exchange occur sequentially—facilitates the construction of the maleic anhydride moiety of CP molecules 1 and 2 (>93% yield per step). Unstable intermediates of this reaction sequence were detected, providing evidence for the proposed mechanism and resulting in the discovery of a new chemical entity. 相似文献
996.
Michael A. Beswick Nick Choi Alexander D. Hopkins Yvonne G. Lawson Mary McPartlin Alexander Rothenberger Dietmar Stalke Andrew E. H. Wheatley Dominic S. Wright 《Angewandte Chemie (International ed. in English)》1999,38(20):3053-3055
Thermally unstable crystals of the title compound—the first bismuth phosphide complex to be structurally characterized (see picture)—are obtained by the reaction of [Bi(NMe2)3] with [tBuPHLi] (1:3) in THF/hexane. Berry pseudorotation of the pseudo-trigonal-bipyramidal [{(tBuP)3}2Bi]− ion is prevented for steric reasons. 相似文献
997.
Seyeon Oh Chang Hu Choi Bae-Jin Lee Joung-Hyun Park Kuk-Hui Son Kyunghee Byun 《Molecules (Basel, Switzerland)》2021,26(23)
It is well known that oxidative stress induces muscle atrophy, which decreases with the activation of Nrf2/HO-1. Fermented oyster extracts (FO), rich in γ-aminobutyric acid (GABA) and lactate, have shown antioxidative effects. We evaluated whether FO decreased oxidative stress by upregulating Nrf2/HO-1 and whether it decreased NF-κB, leading to decreased IL-6 and TNF-α. Decreased oxidative stress led to the downregulation of Cbl-b ubiquitin ligase, which increased IGF-1 and decreased FoxO3, atrogin1, and Murf1, and eventually decreased muscle atrophy in dexamethasone (Dexa)-induced muscle atrophy animal model. For four weeks, mice were orally administered with FO, GABA, lactate, or GABA+Lactate, and then Dexa was subcutaneously injected for ten days. During Dexa injection period, FO, GABA, lactate, or GABA+Lactate were also administered, and grip strength test and muscle harvesting were performed on the day of the last Dexa injection. We compared the attenuation effect of FO with GABA, lactate, and GABA+lactate treatment. Nrf2 and HO-1 expressions were increased by Dexa but decreased by FO; SOD activity and glutathione levels were decreased by Dexa but increased by FO; NADPH oxidase activity was increased by Dexa but decreased by FO; NF-κB, IL-6, and TNF-α activities were increased by Dexa were decreased by FO; Cbl-b expression was increased by Dexa but restored by FO; IGF-1 expression was decreased by Dexa but increased by FO; FoxO3, Atrogin-1, and MuRF1 expressions were increased by Dexa but decreased by FO. The gastrocnemius thickness and weight were decreased by Dexa but increased by FO. The cross-sectional area of muscle fiber and grip strength were decreased by Dexa but increased by FO. In conclusion, FO decreased Dexa-induced oxidative stress through the upregulation of Nrf2/HO-1. Decreased oxidative stress led to decreased Cbl-b, FoxO3, atrogin1, and MuRF1, which attenuated muscle atrophy. 相似文献
998.
Hye Ri Kim Daae Lee Ga Hyeon Lee Seong Kyun Kim Seong Jin Choi Ee Taek Hwang Anoth Maharjan Beom Soo Kim Dongyoung Kim Jong Hoon Joo 《Particle & Particle Systems Characterization》2019,36(9)
To elucidate the origin of antibacterial activity of ZnO nanoparticles, a reactive oxygen species (ROS) mechanism is systematically investigated based on electronic and protonic conductions. While the enhancement of antibacterial activity by an increase in electronic conductivity is marginal, an apparent improvement is observed by in the increase of protonic conductivity in terms of the surface basicity. This study first demonstrates that antibacterial activity can be enhanced by controlling the surface basicity of solid particles. The basicity of ZnO can be modulated by doping alkaline‐earth oxides such as MgO and CaO, and it results in the increase of hydroxyl defects on the surface of solid particles. The basicity shows a strong dependency on mobile OH concentrations. The increase of ROS hydroxyl radicals is confirmed by Mg (ZMO) or Ca‐doping (ZCO), which shows high antibacterial activity, and Ca‐doped ZnO exhibits the highest performance. It is clearly observed that the antibacterial activity is proportional to the basicity, which is controlled by the mobile OH formation. While both electrons and hydroxyl species are required for ROS reactions, it is concluded that the formation of hydroxyl species is a key factor in improving the antibacterial activity in ZnO. 相似文献
999.
Jaeyoung Hwang Seung Heon Lee Myong Yong Choi Kang Yeol Lee 《Current Applied Physics》2019,19(6):762-767
A simple method for synthesizing the BixPdy bimetallic particles is described. The structure, composition distribution and size of synthesized BixPdy bimetallic particles were characterized using a number of analytical techniques. The Bi:Pd atomic ratio (x:y) of the nanoparticles was determined to be approximately 1:3 (Bi24Pd76), 1:1 (Bi54Pd46) and 3:1 (Bi74Pd26). The (111) diffraction peaks within the X-ray diffraction patterns of the bimetallic nanoparticles shifted from 39.9° to 38.5° as the Bi content increased from 0% to 75%. The d-spacings calculated from the 2θ data of (111) planes were 2.33, 2.34, 2.32 and 2.26 nm for nanoparticles with a Bi:Pd atomic ratio of 3:1, 1:1, 1:3 and 0:1 respectively. The crystalline properties of the surface of the BixPdy bimetallic nanoparticles were observed in high-resolution transmission electron microscopy analysis. The d-spacings between the adjacent lattice planes were measured on the surface of BixPdy bimetallic nanoparticles by averaging 10 lattice fringes distance. A regular face-centered cubic lattice was observed throughout the prepared BixPdy bimetallic nanoparticles. The lattice d-spacing of the Bi3Pd1, Bi1Pd1 and Bi1Pd3, bimetallic nanoparticles was approximately 2.34, 2.33 and 2.32 Å, respectively, which can be indexed to the (111) planes. These measurements correspond to the values calculated using the Bragg equation (d = nλ/2sinθ). The catalytic activity of BixPdy bimetallic nanoparticles was determined for the nitro compound reduction and Suzuki-Miyaura coupling reactions under green conditions (in an aqueous solution). Bi1Pd3 nanoparticles were shown to provide the best catalytic performance during both reactions, resulting in a yield of 98% in both cases. 相似文献
1000.