全文获取类型
收费全文 | 671篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
化学 | 497篇 |
晶体学 | 16篇 |
力学 | 14篇 |
数学 | 53篇 |
物理学 | 118篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2016年 | 9篇 |
2015年 | 16篇 |
2014年 | 12篇 |
2013年 | 41篇 |
2012年 | 33篇 |
2011年 | 31篇 |
2010年 | 18篇 |
2009年 | 20篇 |
2008年 | 58篇 |
2007年 | 42篇 |
2006年 | 61篇 |
2005年 | 61篇 |
2004年 | 38篇 |
2003年 | 21篇 |
2002年 | 33篇 |
2001年 | 9篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有698条查询结果,搜索用时 384 毫秒
61.
Fujita S Ninomiya M Efdi M Ohguchi K Nozawa Y Koketsu M 《Natural product research》2010,24(17):1630-1636
Six chemical constituents were isolated from Enicosanthum cupulare (King) Airy-Shaw. The structures of the isolated compounds were determined using 1D, 2D-NMR and were found to be identical to those previously reported for these compounds. Three aporphine alkaloids, O-methylmoschatoline, liriodenine and oxostephanine were isolated from this plant for the first time. In addition, we examined the effects of these compounds on melanogenesis in murine B16 melanoma cells; O-methylmoschatoline increased melanin content in these cells. 相似文献
62.
Choi J Tachikawa T Kim Y Fujitsuka M Ihee H Majima T 《Chemical communications (Cambridge, England)》2010,46(48):9155-9157
The study of the structural reorganization and photophysical properties of Zn-Cytc using the single-molecule and ensemble-averaged spectroscopy shows that the photoblinking behaviors of single-Zn-Cytc depend on the folded and unfolded structures, whereas the fluorescence dynamics of Zn-Cytc observed in the bulk phase are hardly affected by the conformational change of a protein. 相似文献
63.
Lusternik–Schnirelmann category of a manifold gives a lower bound of the number of critical points of a differentiable map
on it. The purpose of this paper is to show how to construct cone-decompositions of manifolds by using functions of class
C
1 and their gradient flows, where cone-decompositions are used to give an upper bound for the Lusternik–Schnirelmann category
which is a homotopy invariant of a topological space. In particular, the Morse–Bott functions on the Stiefel manifolds considered
by Frankel (1965) are effectively used to construct the conedecompositions of Stiefel manifolds and symmetric Riemannian spaces to determine
their Lusternik–Schnirelmann categories. 相似文献
64.
65.
The purpose of this article is to study an existence of p-bases and mainly to give some regularity criteria for semilocal rings essentially of finite type over fields. 相似文献
66.
o-Ethynylbenzyl phenyl selenides regioselectively reacted with trifluoromethanesulfonic acid to afford the (Z)-1-methylidene-2-phenyl-1,3-dihydro-1H-benzo[c]selenophenium salts as the major products during the 5-exo-dig mode cyclization in good yields together with minor E isomers. The structure of the major (Z)-selenophenium salt was established by the single crystal X-ray crystallographic analysis using a tert-butyl derivative. 相似文献
67.
68.
Under pathological conditions, morphological changes of the cells and tissues may differ from those of normal conditions, which can be reflected by changes in light scattering (LS). Consequently, LS has been recognized as a potential non-invasive tool for optical diagnosis of living tissue. This paper aimed to identify the basic properties of LS of isolated brain mitochondria in vitro under normoxic and anoxic conditions in the presence and absence of Mg2+. An increase in LS was observed during anoxia in both the presence and absence of Mg2+. In both cases, the changes in LS initiated by anoxia and reoxygenation started concomitantly with the reduction of heme aa3. The rates of LS changes were slower than those of heme aa3, particularly in the presence of Mg2+. Mg2+ inhibited the morphological responses of mitochondria caused by the addition of ADP and ATP, and significantly reduced the oxygen consumption rate in state 4. These results are due to modulation of the K+/H+ antiporter affected by Mg2+. In addition, the mitochondria were well coupled, although the basal level of LS fell after addition of Mg2+. Therefore, the observed responses of mitochondria at anoxia were physiological and independent of the presence or absence of Mg2+. The relationship between LS and redox state of cytochrome c oxidase, an anoxic indicator, provides a basis to assess the tissue conditions in vivo. 相似文献
69.
Takashi Ishida Mamoru Shoji Yoshiyuki Miyabata Yasumasa Shibata Eiji Ohno Shunji Ohaira 《Optical Review》1994,1(2):183-187
A high density mark edge recording method on a phase change rewritable disk is reported. A carrier-to-noise ratio of 55 dB for a mark length of 0.55,μm is obtained by using a 680 nm, NA 0.6 head and a phase change rewritable disk. In mark edge recording, it is necessary to record each mark in correct length. A new laser power modulation pattern is proposed. This pattern consists of a first-pulse, a multi-pulse chain and a last-pulse. Both positions of the first-ptilse and the last-pulse are movable. By adjusting these positions, a jitter, σ/Tw (Tw is window margin), is improved to 6.5% in high density EFM (Eight to Fourteen Modulation) recording of 0.4 μm/bit. 相似文献
70.
Jin Akiyama Hiroshi Era Severino V. Gervacio Mamoru Watanabe 《Journal of Graph Theory》1989,13(5):571-573
Let the finite, simple, undirected graph G = (V(G), E(G)) be vertex-colored. Denote the distinct colors by 1,2,…,c. Let Vi be the set of all vertices colored j and let <Vi be the subgraph of G induced by Vi. The k-path chromatic number of G, denoted by χ(G; Pk), is the least number c of distinct colors with which V(G) can be colored such that each connected component of Vi is a path of order at most k, 1 ? i ? c. We obtain upper bounds for χ(G; Pk) and χ(G; P∞) for regular, planar, and outerplanar graphs. 相似文献