全文获取类型
收费全文 | 461篇 |
免费 | 28篇 |
国内免费 | 1篇 |
专业分类
化学 | 386篇 |
晶体学 | 3篇 |
力学 | 2篇 |
数学 | 5篇 |
物理学 | 94篇 |
出版年
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 18篇 |
2012年 | 36篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 20篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 16篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1995年 | 3篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1974年 | 8篇 |
1973年 | 5篇 |
1972年 | 8篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有490条查询结果,搜索用时 34 毫秒
51.
The characteristics and applicability of the absorption spectroscopy system using the coherent transition radiation light source have been investigated. The configurations of the system are relatively simple. The operational conditions of an electron linear accelerator have been evaluated. The stability of the light intensity has been within ±2–3% in a wavenumber range of 4–13 cm−1. The light intensity has been found to be more than six orders of magnitude higher than that for the lowest limit for detection. 相似文献
52.
53.
54.
55.
Summary When a d.c. and a h.f. field are perpendicularly superposed in a electrical discharge (p 10–10–4 mm Hg), three types of discharge can exist, classified from the standpoint of d.c. conduction: (1) d.c. glow type, d.c.-dominant discharge with additional ionization by h.f. field; (2) space chargelimited type, the same as the conduction in the floating double probe in a plasma produced by h.f. field; (3) an intermediate stage between the first and second types, herein referred to as transition type. According to our analysis of the transition type at low pressure, the value of in high electric fields can be deduced from the measurement. 相似文献
56.
Tagaya M Ikoma T Takemura T Hanagata N Okuda M Yoshioka T Tanaka J 《Langmuir : the ACS journal of surfaces and colloids》2011,27(12):7635-7644
The adhesion process of osteoblast-like cells on hydroxyapatite (HAp) and oxidized polystyrene (PSox) was investigated using a quartz crystal microbalance with dissipation (QCM-D), confocal laser scanning microscope (CLSM), and atomic force microscope (AFM) techniques in order to clarify the interfacial phenomena between the surfaces and cells. The interfacial viscoelastic properties (shear viscosity (η(ad)), elastic shear modulus (μ(ad)), and tan δ) of the preadsorbed protein layer and the interface layer between the surfaces and cells were estimated using a Voigt-based viscoelastic model from the measured frequency (Δf) and dissipation shift (ΔD) curves. In the ΔD-Δf plots, the cell adhesion process on HAp was classified as (1) a mass increase only, (2) increases in both mass and ΔD, and (3) slight decreases in mass and ΔD. On PSox, only ΔD increases were observed, indicating that the adhesion behavior depended on the surface properties. The interfacial μ(ad) value between the material surfaces and cells increased with the number of adherent cells, whereas η(ad) and tanδ decreased slightly, irrespective of the surface. Thus, the interfacial layer changed the elasticity to viscosity with an increase in the number. The tan δ values on HAp were higher than those on PSox and exceeded 1.0. Furthermore, the pseudopod-like structures of the cells on HAp had periodic stripe patterns stained with a type I collagen antibody, whereas those on PSox had cell-membrane-like structures unstained with type I collagen. These results indicate that the interfacial layers on PSox and HAp exhibit elasticity and viscosity, respectively, indicating that the rearrangements of the extracellular matrix and cytoskeleton changes cause different cell-surface interactions. Therefore, the different cell adhesion process, interfacial viscoelasticity, and morphology depending on the surfaces were successfully monitored in situ and evaluated by the QCM-D technique combined with other techniques. 相似文献
57.
Jochmann P Leich V Spaniol TP Okuda J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(43):12115-12122
A facile and general synthetic pathway for the production of dearomatized, allylated, and C? H bond activated pyridine derivatives is presented. Reaction of the corresponding derivative with the previously reported reagent bis(allyl)calcium, [Ca(C3H5)2] ( 1 ), cleanly affords the product in high yield. The range of N‐heterocyclic compounds studied comprised 2‐picoline ( 2 ), 4‐picoline ( 3 ), 2,6‐lutidine ( 4 ), 4‐tert‐butylpyridine ( 5 ), 2,2′‐bipyridine ( 6 ), acridine ( 7 ), quinoline ( 8 ), and isoquinoline ( 9 ). Depending on the substitution pattern of the pyridine derivative, either carbometalation or C? H bond activation products are obtained. In the absence of methyl groups ortho or para to the nitrogen atom, carbometalation leads to dearomatized products. C(sp3)? H bond activation occurs at ortho and para situated methyl groups. Steric shielding of the 4‐position in pyridine yields the ring‐metalated product through C(sp2)? H bond activation instead. The isolated compounds [Ca(2‐CH2‐C5H4N)2(THF)] ( 2 b ?(THF)), [Ca(4‐CH2‐C5H4N)2(THF)2] ( 3 b ?(THF)2), [Ca(2‐CH2‐C5H3N‐6‐CH3)2(THF)n] ( 4 b ?(THF)n; n=0, 0.75), [Ca{2‐C5H3N‐4‐C(CH3)3}2(THF)2] ( 5 c ?(THF)2), [Ca{4,4′‐(C3H5)2‐(C10H8N2)}(THF)] ( 6 a ?(THF)), [Ca(NC13H9‐9‐C3H5)2(THF)] ( 7 a ?(THF)), [Ca(4‐C3H5‐C9H7N)2(THF)] ( 8 b ?(THF)), and [Ca(1‐C3H5‐C9H7N)2(THF)3] ( 9 a ?(THF)3) have been characterized by NMR spectroscopy and metal analysis. 9 a ?(THF)4 and 4 b ?(THF)3 were additionally characterized in the solid state by X‐ray diffraction experiments. 4 b ?(THF)3 shows an aza‐allyl coordination mode in the solid state. Based on the results, mechanistic aspects are discussed in the context of previous findings. 相似文献
58.
Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me(3)[12]aneN(4)), reacted with [K{N(SiHMe(2))(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe(2)N(SiHMe(2))}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H(2) (= Me(2)[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe(2))(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD)SiMe(2)N(SiHMe(2))}Sc{N(SiHMe(2))(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe(2))(2)}(2)SiMe(2)] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH(2)SiMe(3))(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH(2)SiMe(3))(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides. 相似文献
59.
Kensuke Okuda Hideki Muroyama Takashi Hirota 《Journal of heterocyclic chemistry》2011,48(6):1407-1413
Reactions of N‐(quinazolin‐4‐yl)amidines and their amide oximes with hydroxylamine hydrochloride gave cyclization products that were formed by an initial ring cleavage of the pyrimidine component followed by a ring closure formation of 1,2,4‐oxadiazole to give N‐[2‐([1,2,4]oxadiazol‐5‐yl)phenyl]formamide oximes. All isolated products were evaluated for in vitro inhibitory activity on the formation of pentosidine, which is one of representative advanced glycation end products. Some products exhibited significant inhibitory activity against pentosidine formation. J. Heterocyclic Chem., (2011). 相似文献
60.
Peckermann I Raabe G Spaniol TP Okuda J 《Chemical communications (Cambridge, England)》2011,47(17):5061-5063
Allyl and 2-methylallyl indium compounds were prepared by salt metathesis starting from indium trichloride and a Grignard reagent. They are highly fluxional in solution and reveal coordination numbers of the indium atoms of four and five in the solid state. 相似文献