全文获取类型
收费全文 | 820篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
化学 | 605篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 124篇 |
物理学 | 108篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 17篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 19篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 60篇 |
2011年 | 54篇 |
2010年 | 42篇 |
2009年 | 24篇 |
2008年 | 50篇 |
2007年 | 49篇 |
2006年 | 58篇 |
2005年 | 44篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有859条查询结果,搜索用时 31 毫秒
51.
Hunter CA Jones PS Tiger P Tomas S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(23):5435-5446
Chemical double-mutant cycles have been used to quantify intermolecular functional-group interactions in H-bonded zipper complexes in chloroform. If the same interaction is measured in zippers of different overall stability, the double-mutant cycles can be combined to produce a triple-mutant box. This construct quantifies cooperativity between the functional group interaction of interest and the other interactions that are used to change the overall stability of the complexes. The sum of two edge-to-face aromatic interactions (-2.9 +/- 0.5 kJ mol-1) is shown to be insensitive to changes of up to 13.7 +/- 0.2 kJ mol-1 in the overall stability of the complex. In principle, enthalpic cooperative effects caused by entropy-enthalpy compensation could perturb the measurement of intermolecular interactions when using the double-mutant cycle approach, but these experiments show that, for this system, the magnitude of the effect lies within the error of the measurements. 相似文献
52.
Evidence is presented for normal-spinel domain of homogeneity between the compositions InS1.50?ε and InS1.35. Structural study of a single crystal of composition InS1.44 indicates indium vacancies on the tetrahedral sites. The compound In2S3, regardless of conditions of formation, is a tetragonal superstructure of the spinel lattice (a0) with and c = 3a0. The spinel-type domain shows peritectic decomposition at 850°C for the composition InS1.40. 相似文献
53.
The existence of an ice Ih/XI proton-ordering transition to a low-temperature ferroelectric phase has sparked considerable debate in the literature. Electronic density functional theory calculations, extended using graph invariants, confirm that a transition to a low-temperature ferroelectric phase should occur. The predicted transition at 98 K is in qualitative agreement with the observed transition at 72 K, and the low-temperature phase is the ferroelectric phase determined in diffraction experiments. The theoretical methods used to predict the phase transition are validated by comparing their prediction to the well-characterized ice VII/VIII proton-ordering transition. 相似文献
54.
We report a detailed analytic and numerical study of electronic thermal conductivity in d-wave superconductors. We compare theory of the crossover at low temperatures from T dependence to T(3) dependence for increasing temperature with recent experiments on YBa(2)Cu(3)O(7) in zero magnetic field for T approximately [0.04 K,0.4 K] by Hill et al. [Phys. Rev. Lett. 92, 027001 (2004)]. Transport theory, including impurity scattering and inelastic scattering within strong-coupling superconductivity, can consistently fit the temperature dependence of the data in the lower half of the temperature regime. We discuss the conditions under which we expect power-law dependences over wide temperature intervals. 相似文献
55.
Tengel T Fex T Emtenas H Almqvist F Sethson I Kihlberg J 《Organic & biomolecular chemistry》2004,2(5):725-731
Identification of compounds from chemical libraries that bind to macromolecules by use of NMR spectroscopy has gained increasing importance during recent years. A simple methodology based on (19)F NMR spectroscopy for the screening of ligands that bind to proteins, which also provides qualitative information about relative binding strengths and the presence of multiple binding sites, is presented here. A library of fluorinated compounds was assembled and investigated for binding to the two bacterial chaperones PapD and FimC, and also to human serum albumin (HSA). It was found that library members which are bound to a target protein could be identified directly from line broadening and/or induced chemical shifts in a single, one-dimensional (19)F NMR spectrum. The results obtained for binding to PapD using (19)F NMR spectroscopy agreed well with independent studies based on surface plasmon resonance, providing support for the versatility and accuracy of the technique. When the library was titrated to a solution of PapD chemical shift and linewidth changes were observed with increasing ligand concentration, which indicated the presence of several binding sites on PapD and enabled the assessment of relative binding strengths for the different ligands. Screening by (19)F NMR spectroscopy should thus be a valuable addition to existing NMR techniques for evaluation of chemical libraries in bioorganic and medicinal chemistry. 相似文献
56.
We use Janelidze's Categorical Galois Theory to extend Brown and Ellis's higher Hopf formulae for homology of groups to arbitrary semi-abelian monadic categories. Given such a category A and a chosen Birkhoff subcategory B of A, thus we describe the Barr-Beck derived functors of the reflector of A onto B in terms of centralization of higher extensions. In case A is the category Gp of all groups and B is the category Ab of all abelian groups, this yields a new proof for Brown and Ellis's formulae. We also give explicit formulae in the cases of groups vs. k-nilpotent groups, groups vs. k-solvable groups and precrossed modules vs. crossed modules. 相似文献
57.
Neil S. Keddie Geert Bultynck Tomas Luyten Alexandra M.Z. Slawin Stuart J. Conway 《Tetrahedron: Asymmetry》2009,20(6-8):857-866
The synthesis of d-myo-inositol 1,4,5-trisphosphate (InsP3) from methyl α-d-glucopyranose, via a type 2 Ferrier rearrangement is reported. A key intermediate in this synthesis possesses orthogonal protecting groups at the 1-, 4- and 5-position, making it a versatile starting point for the synthesis of unnatural InsP3 derivatives. Biological evaluation of the synthetic InsP3 demonstrates that this compound evokes selective Ca2+ release via activation of InsP3 receptors. 相似文献
58.
This paper studies an iterative algorithm of the type of Gauss's algorithm mentioned by Stieltjes in his correspondence with Hermite (lettre 323) and later investigated by Myrberg. In particular, what appears to be a false statement by Stieltjes is corrected. The same algorithm, apparently being unaware of his predecessors, has also been considered by Lehmer. 相似文献
59.
60.
Tomas Lebl 《Tetrahedron》2010,66(51):9694-9702
Variable temperature NMR analysis and computational methods have been used to develop a detailed understanding of the 1H NMR spectra of a family of medium-sized ring containing compounds. The family consists of analogues containing 10-, 11- and 12-membered rings and in all cases the NMR spectra at room temperature showed a series of diastereotopic methylene signals despite the lack of a stereogenic centre in these systems. On repeating the NMR analysis at higher temperatures, all the signals coalesced for the 12-membered ring system consistent with full interconversion of ring conformers. This was not observed in the analogous 10- and 11-membered ring systems with the interchange of conformers remaining slow on the NMR timescale. However, 1D gs-NOESY/EXSY NMR experiments showed that in the smaller ring systems interconversion of diastereotopic protons did occur. Computational studies suggest that the dynamic process observed by NMR for the 10- and 11-membered rings systems is different from that observed in the 12-membered ring containing compound. 相似文献