全文获取类型
收费全文 | 3765篇 |
免费 | 86篇 |
国内免费 | 31篇 |
专业分类
化学 | 2996篇 |
晶体学 | 50篇 |
力学 | 58篇 |
数学 | 178篇 |
物理学 | 600篇 |
出版年
2022年 | 25篇 |
2021年 | 32篇 |
2020年 | 34篇 |
2019年 | 37篇 |
2018年 | 22篇 |
2017年 | 31篇 |
2016年 | 48篇 |
2015年 | 68篇 |
2014年 | 78篇 |
2013年 | 265篇 |
2012年 | 171篇 |
2011年 | 230篇 |
2010年 | 128篇 |
2009年 | 106篇 |
2008年 | 192篇 |
2007年 | 198篇 |
2006年 | 218篇 |
2005年 | 203篇 |
2004年 | 181篇 |
2003年 | 196篇 |
2002年 | 195篇 |
2001年 | 45篇 |
2000年 | 52篇 |
1999年 | 54篇 |
1998年 | 40篇 |
1997年 | 39篇 |
1996年 | 52篇 |
1995年 | 52篇 |
1994年 | 47篇 |
1993年 | 32篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 51篇 |
1984年 | 46篇 |
1983年 | 31篇 |
1982年 | 58篇 |
1981年 | 42篇 |
1980年 | 54篇 |
1979年 | 60篇 |
1978年 | 44篇 |
1977年 | 33篇 |
1976年 | 32篇 |
1975年 | 26篇 |
1974年 | 29篇 |
1973年 | 20篇 |
排序方式: 共有3882条查询结果,搜索用时 429 毫秒
991.
The chemoselective and diastereoselective synthesis of syn-α-bromo-α-fluoro-β-lactams was achieved using the diethylzinc-mediated Reformatsky-type reaction of ethyl dibromofluoroacetate with imines. The reaction led to diastereomerically pure β-lactams in good to moderate yields (up to 78% yield) with only small amounts of aziridine derivatives. Noncyclized 3-amino-2-bromo-2-fluoro carboxylic esters, usual Reformatsky adducts, were not formed. In contrast, reactions carried out under typical Reformatsky conditions using zinc metal were poorly chemoselective, leading to mixtures of β-lactams and aziridine derivatives. 相似文献
992.
The unsymmetrically substituted disilyne, Dsi(2)(i)PrSi-Si≡Si-SiNpDsi(2) (Np = CH(2)(t)Bu) 2, was synthesized and characterized by X-ray crystallography to show a trans-bent structure with a silicon-silicon triple bond length of 2.0569(12) ?. The (29)Si chemical shifts of the triply bonded silicon atoms of 2 are quite different, being observed at 62.6 ppm for the Dsi(2)(i)PrSi side and 106.3 ppm for the Dsi(2)NpSi side, indicating different hybridizations on the triply bonded silicon atoms at each site. 相似文献
993.
Onoda A Ueya Y Sakamoto T Uematsu T Hayashi T 《Chemical communications (Cambridge, England)》2010,46(48):9107-9109
Interaction of apohemoprotein with a covalently immobilized heme moiety onto a gold nanoparticle surface resulted in supramolecular hemoprotein-gold nanoparticle conjugates. The addition of an apohemoprotein dimer further led to a densely-packed hemoprotein-gold nanoparticle assembly, which was visualized by TEM and AFM measurements. 相似文献
994.
Platinum dissolution and deposition in the polymer electrolyte membrane of a PEM fuel cell as studied by potential cycling 总被引:1,自引:0,他引:1
Yasuda K Taniguchi A Akita T Ioroi T Siroma Z 《Physical chemistry chemical physics : PCCP》2006,8(6):746-752
The behavior of platinum dissolution and deposition in the polymer electrolyte membrane of a membrane-electrode-assembly (MEA) for a proton-exchange membrane fuel cell (PEMFC) was studied using potential cycling experiment and high-resolution transmission electron microscopy (HRTEM). The electrochemically active surface area decreased depending on the cycle number and the upper potential limit. Platinum deposition was observed in the polymer electrolyte membrane near a cathode catalyst layer. Platinum deposition was accelerated by the presence of hydrogen transported through the membrane from an anode compartment. Platinum was transported across the membrane and deposited on the anode layer in the absence of hydrogen in the anode compartment. This deposition was also affected by the presence of oxygen in the cathode compartment. 相似文献
995.
996.
997.
998.
Elucidation of codoping effects on the solubility enhancement of Er3+ in SiO2 glass: striking difference between Al and P codoping 总被引:1,自引:0,他引:1
Saitoh A Matsuishi S Se-Weon C Nishii J Oto M Hirano M Hosono H 《The journal of physical chemistry. B》2006,110(15):7617-7620
The codoping effect mechanism of Al and P on the solubility enhancement of Er(3+) ion in SiO(2) glass was clarified by electron spin-echo envelope modulation spectroscopy. It turned out that doped P ions preferentially coordinate to the Er(3+) ion to form a "solvation shell structure", and the environment is similar to that in phosphate glass, while doped Al ions do not form such a selective solvation structure, taking octahedral coordination. This striking difference indicates that the primary roles of the P-doping and the Al-doping are attributed to "enthalpy of mixing" and to "entropy of mixing", respectively. 相似文献
999.
Biotin-capped gold nanoparticles assembled on flat gold with volume fraction f are studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM) in order to estimate the dielectric function of the gold nanoparticles based on the Maxwell-Garnett (MG) theory. The complex dielectric function (epsilon',epsilon') of the spherical nanoparticles at three representative wavelengths in the vis-near-IR region, i.e., lambda = 543, 632.8, and 1152 nm, is estimated for a surface homogeneously covered with nanoparticles in order to discuss the wavelength dependence of the dielectric function. The SPR response of a surface covered with particles in 2D aggregates is also analyzed. The experimental SPR curve of the particle aggregates deviates from the theoretical predictions, suggesting dipole interactions between particles. 相似文献
1000.
Yokota Y Miyazaki A Fukui K Enoki T Tamada K Hara M 《The journal of physical chemistry. B》2006,110(41):20401-20408
Electroactive tetrathiafulvalene (TTF)-containing alkanethiol self-assembled monolayers (SAMs) were designed and synthesized to elucidate the relationship between electrochemical responses and film structures. Two TTF derivative molecules having one alkanethiol chain (1) and two alkanethiol chains (2) were utilized to modulate the molecular packing arrangements in the SAMs, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR). SPR measurements in various contacting media demonstrated loose packing of SAM 1 and close packing of SAM 2 due to the different space fillings of the molecules. Two successive one-electron redox waves were observed for both SAMs by cyclic voltammetry. The peak widths of the redox waves were strongly dependent on the oxidation states of the TTF moieties, the packing arrangement of the SAMs, and the contacting medium. We found that TTF-based SAMs exhibited collective electrochemical responses induced by dynamic structural changes, depending on the degree of freedom for the component molecules in the SAMs. These results imply that the molecular design, taking into account the electrochemical responses, extends the available range of molecular-based functionalities in TTF-based SAMs. 相似文献