全文获取类型
收费全文 | 967篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 764篇 |
晶体学 | 10篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 59篇 |
物理学 | 151篇 |
出版年
2023年 | 10篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 23篇 |
2015年 | 28篇 |
2014年 | 28篇 |
2013年 | 46篇 |
2012年 | 57篇 |
2011年 | 63篇 |
2010年 | 35篇 |
2009年 | 38篇 |
2008年 | 69篇 |
2007年 | 71篇 |
2006年 | 85篇 |
2005年 | 64篇 |
2004年 | 50篇 |
2003年 | 44篇 |
2002年 | 37篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1967年 | 3篇 |
排序方式: 共有1009条查询结果,搜索用时 31 毫秒
991.
Min Ren Dr. Song‐Song Bao Dr. Norihisa Hoshino Prof. Dr. Tomoyuki Akutagawa Prof. Dr. Bingwu Wang Yu‐Chen Ding Prof. Dr. Shiqiang Wei Prof. Dr. Li‐Min Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9619-9628
A new dysprosium(III) phosphonate dimer {Dy(notpH4)(NO3)(H2O)}2 ? 8 H2O ( 1 ) [notpH6=1,4,7‐triazacyclononane‐1,4,7‐triyl‐tris(methylenephosphonic acid)] that contains two equivalent DyIII ions with a three‐capped trigonal prism environment is reported. Complex 1 can be transformed into {Dy(notpH4)(NO3)(H2O)}2 ( 2 ) in a reversible manner by desorption and absorption of solvent water at ambient temperature. This process is accompanied by a large dielectric response. Magnetic studies reveal that both 1 and 2 show thermally activated magnetization relaxation as expected for single‐molecule magnets. Moreover, the magnetic dynamics of the two compounds can be manipulated by controlling the number of solvent molecules at room temperature. 相似文献
992.
Tomoyuki Nakagaki Tomoko Sakai Tsutomu Mizuta Yoshihisa Fujiwara Prof. Manabu Abe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10395-10404
Kinetic stabilization and reactivity of π single‐bonded species have been investigated in detail by generating a series of singlet 2,2‐dialkoxy‐1,3‐diphenyloctahydropentalene‐1,3‐diyls ( DR s). The lifetime at 293 K in benzene was found to increase when the carbon chain length of the alkoxy groups was increased; 292 ns ( DRb ; OR=OR′=OCH3) <880 ns ( DRc ; OR=OR′=OC2H5) <1899 ns ( DRd ; OR=OR′=OC3H7) ≈2292 ns ( DRe ; OR=OR′=OC6H13) ≈2146 ns ( DRf ; OR=OR′=OC10H21). DRh (OR=OC3H7, OR′=OCH3; 935 ns) with the mixed‐acetal moiety is a longer‐lived species than another diastereomer DRg (OR=OCH3, OR′=OC3H7; 516 ns). Activation parameters determined for the first‐order decay process reveal that the enthalpy factor plays a crucial role in determining the energy barrier of the ring‐closing reaction, that is, from the π‐bonding to the σ‐bonding compounds. Computational studies using density functional theory provided more insight into the structures of the singlet species with π single‐bonded character and the transition states for the ring‐closing reaction, thereby clarifying the role of the alkoxy group on the lifetime and the stereoselectivity of the ring‐closing reaction. 相似文献
993.
Tomoyuki Kitano Dr. Tetsuya Shishido Dr. Kentaro Teramura Prof. Dr. Tsunehiro Tanaka 《Chemphyschem》2013,14(11):2560-2569
Thermally stable Brønsted acid sites were generated on alumina‐supported niobium oxide (Nb2O5/Al2O3) by calcination at high temperatures, such as 1123 K. The results of structural characterization by using Fourier‐transform infrared (FTIR) spectroscopy, TEM, scanning transmission electron microscopy (STEM), and energy‐dispersive X‐ray (EDX) analysis indicated that the Nb2O5 monolayer domains were highly dispersed over alumina at low Nb2O5 loadings, such as 5 wt %, and no Brønsted acid sites were presents. The coverage of Nb2O5 monolayer domains over Al2O3 increased with increasing Nb2O5 loading and almost‐full coverage was obtained at a loading of 16 wt %. A sharp increase in the number of hydroxy groups, which acted as Brønsted acid sites, was observed at this loading level. The relationship between the acidic properties and the structure of the material suggested that the bridging hydroxy groups (Nb? O(H)? Nb), which were formed at the boundaries between the domains of the Nb2O5 monolayer, acted as thermally stable Brønsted acid sites. 相似文献
994.
995.
A new type of hexane-soluble polymeric surfactant based on poly(4-tert-butoxystyrene) (P
t
BSt) was prepared by the nitroxide-mediated living radical polymerization, and their self-assemblies in hexane were explored.
Polystyrene-block-P
t
BSt diblock copolymers with six different P
t
BSt block lengths were obtained by the sequential living radical polymerization of styrene followed by 4-tert-butoxystyrene using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator; Mn(P
t
BSt block) = 13,500, 21,700, 26,600, 47,500, 91,300, and 108,000 at the constant length of the PSt block (Mn = 12,900). Dynamic
light-scattering studies demonstrated that the copolymers self-assembled into monodispersed spherical micelles in hexane.
The hydrodynamic diameter of the micelles increased with an increase in the P
t
BSt block length. The micellar size also increased as the copolymer concentration increased. However, the size decreased as
a result of the increasing temperature due to a decrease in the aggregation number. The 1H NMR analysis confirmed that the copolymers formed micelles with PSt cores. 相似文献
996.
Arikuma Y Nakayama H Morita T Kimura S 《Langmuir : the ACS journal of surfaces and colloids》2011,27(4):1530-1535
Electron transfer through α-helices has attracted much attention from the viewpoints of their contributions to efficient long-range electron transfer occurring in biological systems and their utility as molecular-electronics elements. In this study, we synthesized a long 80mer helical peptide carrying a redox-active ferrocene unit at the terminal and immobilized the helical peptide on a gold surface. The molecular length is calculated to be 134 ?, in which the helix accounts for 120 ?. The preparation conditions of the self-assembled monolayers were intentionally changed to obtain monolayers with different physical states to study the correlation between molecular motions and electron transfer. Ellipsometry and infrared spectroscopy showed that the helical peptide forms a self-assembled monolayer with vertical orientation. Electrochemical measurements revealed that an electron is transferred from the ferrocene unit to gold through the monolayer composed of this long helical peptide, and the experimental data are well explained by theoretical results calculated under the assumption that electron transfer occurs by a unique hopping mechanism with the amide groups as hopping sites. Furthermore, we have observed a unique dependence of electron transfer on the monolayer packing, suggesting the importance of structural fluctuations of peptides on the electron transfer controlled by the hopping mechanism. 相似文献
997.
Yoshimasa Makita Kenta FuruyoshiKeisuke Ikeda Tomoyuki FujitaShin-ichi Fujiwara Masahiro EharaAkiya Ogawa 《Tetrahedron letters》2011,52(32):4129-4131
A cyclotriveratrylene (CTV)-capped azaphosphatrane 4, which contains an endohedral proton within the cavity of the azaphosphatrane, was synthesized in high yield and then characterized. The endohedral proton of 4 was highly sheltered from strongly basic conditions by the CTV-capped structure. 相似文献
998.
Dimethyl and bis[(trimethylsilyl)methyl] zirconium complexes ([OSSO]ZrR2) [4, R = Me; 5, R = CH2SiMe3] having [OSSO]-type bis(phenolato) ligand 1 based on the trans-1,2-cyclooctanediylbis(thio) core have been synthesized by the reactions of the corresponding dichloro zirconium complex 3 with 2 equiv. of MeMgBr and Me3SiCH2MgCl, respectively, in Et2O/toluene at −78 °C. The molecular structures of these complexes 3-5 were characterized by NMR spectroscopy, elemental analyses, and X-ray crystallography. 1H and 13C NMR data of complexes 3-5 exhibited that they took the C2-symmetry in solution in the NMR time scale. In the crystal structures of 3-5, each zirconium center lies at the center of a distorted octahedral coordination sphere with cis sulfur atoms and trans oxygen atoms, which adopts a cis-α [(Λ∗,S∗,S∗)] configuration. 相似文献
999.
Yuji Masubuchi Tomoyuki Hata Teruki Motohashi Shinichi Kikkawa 《Journal of solid state chemistry》2011,184(9):2533-2537
Eu-doped lanthanum aluminum oxynitride (LaAl12(O,N)19) with magnetoplumbite structure was prepared by nitridation of the oxide precursor obtained from aluminum glycine gel and subsequent post-annealing. Eu-doped lanthanum aluminum oxynitride exhibited blue light emission at 440 nm with a shoulder at 464 nm under excitation at 254 nm. Isostructural Eu-doped calcium aluminum oxide (CaAl12O19) exhibited a single emission peak at 415 nm. Structural refinement using neutron powder diffraction indicated that the lanthanum site occupied partially by Eu2+ splits into 2d and 6h sites in the aluminum oxynitride. The longer emission and the shoulder peak in the former aluminum oxynitride were observed in relation to the increasing covalency as well as crystal field splitting around doped Eu2+ induced by site splitting involved with the two kinds of anions. 相似文献
1000.
Wuttikul C Taoka T Akashi T Nakagawa H Miyasaka T Sakamoto M Takayama K Wada T Kitano S Takahama J Marugami N Kichikawa K 《Magnetic resonance imaging》2008,26(10):1374-1380