全文获取类型
收费全文 | 48786篇 |
免费 | 11629篇 |
国内免费 | 3746篇 |
专业分类
化学 | 50941篇 |
晶体学 | 502篇 |
力学 | 1359篇 |
综合类 | 190篇 |
数学 | 3688篇 |
物理学 | 7481篇 |
出版年
2024年 | 25篇 |
2023年 | 250篇 |
2022年 | 314篇 |
2021年 | 635篇 |
2020年 | 1727篇 |
2019年 | 2995篇 |
2018年 | 1422篇 |
2017年 | 1082篇 |
2016年 | 3925篇 |
2015年 | 4033篇 |
2014年 | 4206篇 |
2013年 | 4966篇 |
2012年 | 4092篇 |
2011年 | 3463篇 |
2010年 | 3740篇 |
2009年 | 3647篇 |
2008年 | 3355篇 |
2007年 | 2582篇 |
2006年 | 2215篇 |
2005年 | 2382篇 |
2004年 | 2019篇 |
2003年 | 1854篇 |
2002年 | 2618篇 |
2001年 | 1895篇 |
2000年 | 1673篇 |
1999年 | 730篇 |
1998年 | 351篇 |
1997年 | 285篇 |
1996年 | 238篇 |
1995年 | 181篇 |
1994年 | 189篇 |
1993年 | 144篇 |
1992年 | 160篇 |
1991年 | 143篇 |
1990年 | 116篇 |
1989年 | 101篇 |
1988年 | 72篇 |
1987年 | 48篇 |
1986年 | 62篇 |
1985年 | 50篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The structures and electronic properties for C36 encapsulated in four single-wall armchair carbon nanotubes (C36@(n,n), n=6-9) were calculated using ab initio self-consistent field crystal orbital method based on density functional theory. The calculations show that the interwall spacing between the carbon nanotube and C36 plays an important role in the stabilities of resultant structures. The optimum interwall spacing is about 0.30 nm and the tubes can be considered as inert containers for the encapsulated C36. The Fermi levels and relative position of energy bands also have something to do with the interwall spacing. The shifts of Fermi level and C36-derived electron states modulate the electron properties of these structures. The extra electrons fill the bands of C36@(8,8) with the optimum interwall spacing almost in a rigid-band manner. 相似文献
992.
The electrocatalytic properties of the SiC particle‐modified glassy carbon electrode (MGC) for adrenaline oxidation were studied by cyclic voltammetry (CV), double‐potential step chronocoulometry (DPSCC), and electrochemical impedance spectroscopy (EIS) techniques in McIlvaine buffer solution. It was shown that the electrode modified with SiC particles markedly displayed an electrocatalytic effect on the process of the electrochemical reaction of adrenaline, i.e., the activity and the reversibility of the MGC electrode has been significantly improved. This was attributed to the adsorption effect of the electroactive adrenaline molecules on the MGC electrode surface. 相似文献
993.
Reaction of an alkyne‐bridged dicobalt complex, [Co2(CO)6(μ‐Me3SiC=Cpy)] 4 , with bis(diphenylphosphino)methylene (DPPM) or bis(diphenylphosphino)ethylene (DPPE) in THF at 55 °C yielded a DPPM or DPPE doubly bridged dicobalt compound, [{μ‐P,P‐PPh2CH2PPh2}Co2(CO)4(μ‐Me3SiC=Cpy)] 5 or [{μ‐P,P‐PPh2CH2CH2PPh2}Co2(CO)4(μ‐Me3SiC≡Cpy)] 6 . Compound 5 and 6 were characterized by spectroscopic means as well as X‐ray crystal structure determination. 相似文献
994.
Abdel‐Zaher Abdel‐Aziz Elassar 《中国化学会会志》2006,53(4):901-907
Methylquinoxaline derivative 1 undergoes bromination to give bromomethyl quinoxaline 2 , which could be transferred to cyanomethyl quinoxaline 3 . The latter compound 3 readily coupled with arene diazonium salts to give hydrazone derivatives 5a‐c . Compounds 5a,b reacted with active methylene reagents to give the target ring system, quinoxalinylpyridazine derivatives 8a‐c . Compound 1 reacted with DMFDMA to give the enamine derivative 9 , which coupled with arene diazonium salts to give the aldehydic hydrazone derivatives 10a‐c . Compound 10 reacted with active methylene compounds to give quinoxalinylpyridazine derivatives. UV characterization of some of the prepared compounds was reported. 相似文献
995.
Biochemistry is a branch subject of chemistry, which is the study of chemical structures and processes associated with living organisms. COVID-19 pandemic is a problem for human beings. From the perspective of biochemistry, this paper demonstrates the chemical structure and interactions of SARS-CoV-2's spike protein and its receptor (human angiotensin converting enzyme 2), and summarizes the related research progresses. The authors hope to provide insights for the development of COVID-19 vaccine. 相似文献
996.
Peng Lu Xueli Hu Yujie Li Yazhou Peng Meng Zhang Xue Jiang Youzhou He Min Fu Fan Dong Zhi Zhang 《Journal of Saudi Chemical Society》2019,23(8):1109-1118
A novel CaCO3/graphitic carbon nitride (g-C3N4) photocatalyst was synthesized for the first time via a facile calcination method using CaCO3 and melamine as precursors. The as-prepared samples were characterized using various techniques, such as scanning and transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, as well as Fourier-transform infrared, X-ray photoelectron, photoluminescence, and UV–vis diffuse reflectance spectroscopy. The results of the experiments confirm the successful coupling of CaCO3 to g-C3N4. The photocatalytic activity of the synthesized CaCO3/g-C3N4 composites was evaluated by assessing their performance in the photocatalytic degradation of crystal violet (CV) in water under visible light irradiation. The analysis shows that CaCO3/g-C3N4 exhibits higher photocatalytic activity towards CV degradation (76.0%) than pristine g-C3N4 (21.6%) and CaCO3 (23.2%). Radical trapping and electron spin resonance experiments show that hydroxyl radicals (OH) and holes (h+) are the key reactive species in the photocatalytic process. The enhanced photocatalytic activity of the composite is mainly attributed to the efficient separation rate of electron-hole pairs achieved through the incorporation of CaCO3. 相似文献
997.
水热条件下,合成了三个新的配合物[Ni(en)3] (ndt) ·H2O 1,
[Co(en)3] (ndt) ·H2O 2 和[Mn(en)3] (ndt) ·H2O
3。晶体结构通过X-射线单晶衍射进行了表征。三个配合物均属于单斜晶系,Cc空间群。[M(en)3]2+阳离子、ndt阴离子和结晶水分子通过氢键自组装出相同结构的三维网。通过紫外-可见-近红外漫反射光谱对这三个配合物的光吸收性能和能带进行了测定。 相似文献
998.
The assembly strategy to prepare a monolayer of bovine serum albumin on the surface of silica gel supported gold nanoparticles is described. The stereo‐specific recognition ability of this material was evaluated by enantioresolution of Dansyl‐norvaline. For enantiomeric separation, the influences of buffer concentration and the concentration of organic modifier on the separation performance were investigated. A better separation in terms of enantioresolution and peak shape was found with the phosphate concentration at 30 mM. Moreover, the peak shape and resolution can be improved by the addition of methanol solution. Enantioresolution of Dansyl‐norvaline was obtained from this material at optimized conditions. It appears that the immobilization of a monolayer of bovine serum albumin on gold nanoparticles as the chiral selector of Dansyl‐derivative amino acid is promising. 相似文献
999.
分形理论及其在高分子科学中的应用 总被引:6,自引:0,他引:6
介绍了分形的基本概念,分形维数的定义及计算方法,讨论了近年来分形理论在高分子科学研究方面的一些应用,内容主要包括高分子溶液、高分子材料的磨损,断裂及界面,高分子结晶过程、导电高分子等。 相似文献
1000.
标题配合物 [Cu(C8H4 F3O2 S) 2 (C12 H8N2 ) ]·C3H6 O属于三斜晶系 ,空间群为P1,并测得如下晶胞参数a =10 .5 77(3) ,b =15 .72 2 (4) ,c =10 .133(2 ) ,α =94 .5 3(2 ) ,β =10 0 .81(2 ) ,γ =96 .18(2 )° ,V =16 37.0 3 3,Z =2 ,Mr =74 4.18,Dx =1.5 1× 10 6 g·m- 3,F(0 0 0 ) =5 2 6 ,μ =8 2 4cm- 1,最终偏差因子为R =0 .0 83,Rw=0 .0 74。Cu(II)与 2个 4 ,4 ,4 三氟 1 (2 噻吩基 )丁二酮 1,3中的四个氧原子和菲咯啉中的两个氮原子 ,组成了一个畸变的八面体构型。 相似文献