全文获取类型
收费全文 | 169篇 |
免费 | 1篇 |
专业分类
化学 | 95篇 |
力学 | 2篇 |
数学 | 9篇 |
物理学 | 64篇 |
出版年
2023年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2015年 | 1篇 |
2013年 | 22篇 |
2012年 | 9篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 2篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 1篇 |
1995年 | 10篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 4篇 |
1962年 | 1篇 |
1948年 | 1篇 |
1939年 | 1篇 |
1938年 | 2篇 |
1935年 | 1篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1932年 | 1篇 |
1931年 | 4篇 |
1924年 | 2篇 |
排序方式: 共有170条查询结果,搜索用时 62 毫秒
81.
Abstract Conformational investigations using 1D TOCSY and ROESY 1H NMR experiments on 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hexopyranosyl)-2-deoxy-β-D-glucopyranose (8) and related disaccharides showed that for steric reasons the C-linked hexopyranosyl ring occurs in the usually unfavoured 1C4 conformation and reconfirmed the structure of 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)-2-deoxy-β-D-glucopyranose (5). Glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (13) with acetate 8 using trimethylsilyl triflate as a catalyst afforded the α-D-linked tetrasaccharide 14. A remarkable side product in this reaction was the unsaturated tetrasaccharide 2,3,6-tri-O-benzyl-4-O-[4,6-di-O-acetyl-2,3-dideoxy-2-C-(4,6-di-O-acetyl-2,3-dideoxy-β-D-erythro-hexopyranosyl)-α-D-erythro-hex-2-enopyranosyl]-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-(R)-O-benzylidene-α-D-glucopyranoside (16) where in the C-linked hexopyranosyl ring an isomerization to the β-anomer had taken place to allow for the favoured 4C1 conformation. The tetrasaccharide 14 was deacetylated and hydrogenolyzed to form the fully deprotected tetrasaccharide 18. The 1 C 4 conformation of the C-glycosidic pyranose of this tetrasaccharide was maintained as shown by an in depth NMR analysis of its peracetate 19. 相似文献
82.
Among numerous different AB2 structures with the hypothetical composition FeN2, the structures lying lowest in energy have been determined by a series of density‐functional electronic‐structure calculations. The most likely FeN2 phase crystallizing in the space group R$\bar 3Among numerous different AB(2) structures with the hypothetical composition FeN(2), the structures lying lowest in energy have been determined by a series of density-functional electronic-structure calculations. The most likely FeN(2) phase crystallizing in the space group R3m must be considered an iron pernitride incorporating binuclear N-N units (d=1.275??) with an anionic charge of 2-. This high-pressure magnetic phase with a bulk modulus of about 192?GPa and an iron saturation moment of approximately 1.68?μ(B) should already form at a pressure of 17?GPa at an assumed reaction temperature of 1000?K. Besides bonding Fe-N interactions, antibonding N-N and Fe-Fe interactions exist in the crystal structure. 相似文献
83.
Using large scale quantum Monte Carlo simulations and dual vortex theory, we analyze the ground state phase diagram of hard-core bosons on the kagome lattice with nearest-neighbor repulsion. In contrast with the case of a triangular lattice, no supersolid emerges for strong interactions. While a uniform superfluid prevails at half filling, two novel solid phases emerge at densities rho=1/3 and rho=2/3. These solids exhibit an only partial ordering of the bosonic density, allowing for local resonances on a subset of hexagons of the kagome lattice. We provide evidence for a weakly first-order phase transition at the quantum melting point between these solid phases and the superfluid. 相似文献
84.
85.
Absorptive corrections are calculated for the reactionsπ + p→K *+∑+(K *+ Y 1 *+ ) mediated byK-exchange andπ +p→K+ Y 1 *+ withK *-exchange. The effect of the finite width of the resonances is included. Numerical results are given for 5 and 8 GeV/c. 相似文献
86.
Walter Wessel Dipl.-Math. 《manuscripta mathematica》1970,2(4):309-334
A set of vertices of a graph G represents G if each edge of G is incident with at least one vertex of . A graph G is said to be edge-critical if the minimal number of vertices necessary to represent G decreases if any edge of G is omitted. Plummer [5] has given a method to construct an infinite family of edge-critical graphs with connectivity number 2. We use this method to construct a more extensive class of edge-critical graphs with connectivity number 2 and show that all edge-critical graphs with this connectivity number (K2) can be constructed from smaller edge-critical graphs. Finally we give examples of edge-critical graphs not constructable from smaller ones by this method. 相似文献
87.
Appropriate dithiane derivatives of D-threo configuration were prepared starting with D-arabinose and D-galactose, respectively. Their dianions served for nucleophilic additions to model aldehydes, thus comprising syntheses of the complex side chain of chromomycinone. In contrast to former reports a trianion formation of a dithiane-blocked α,β-dihydroxy aldehyde could not be confirmed. 相似文献
88.
The drawbacks of large, general tape sorting programs are pointed out, and a sorting subroutine is suggested as a remedy. The fundamental idea is the separation of the logic in tape sorting from the actual manipulation of external tape units by introduction of the concept of an elementary sorting loop. Examples show how common problems in sorting can be solved using the sorting loop concept. A few considerations in the design and implementation of a sorting subroutine are mentioned, and finally a measure of the efficiency of tape sorting methods is proposed. 相似文献
89.
Using the adaptive time-dependent density-matrix renormalization group method, we study the time evolution of strongly correlated spinless fermions on a one-dimensional lattice after a sudden change of the interaction strength. For certain parameter values, two different initial states (e.g., metallic and insulating) lead to observables which become indistinguishable after relaxation. We find that the resulting quasistationary state is nonthermal. This result holds for both integrable and nonintegrable variants of the system. 相似文献
90.
The intersection of a linearly ordered set of total subrelations of a total relation with range 2 need not be total, constructively. 相似文献