全文获取类型
收费全文 | 524篇 |
免费 | 3篇 |
专业分类
化学 | 367篇 |
晶体学 | 3篇 |
力学 | 14篇 |
数学 | 20篇 |
物理学 | 123篇 |
出版年
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 21篇 |
2009年 | 5篇 |
2008年 | 25篇 |
2007年 | 36篇 |
2006年 | 37篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 24篇 |
2002年 | 10篇 |
2001年 | 22篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1960年 | 2篇 |
1919年 | 2篇 |
1918年 | 2篇 |
1917年 | 2篇 |
排序方式: 共有527条查询结果,搜索用时 9 毫秒
11.
Stanley A. Bajue Choy Lewis Karen Clarke Fitzgerald B. Bramwell Brian O. Patrick Carolyn Pratt Brock 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):m207-m211
The title complexes [μ‐(E)‐4,4′‐(ethene‐1,2‐diyl)dipyridine‐κ2N:N′]bis[halotris(4‐methylphenyl)tin(IV)], [Sn2(C7H7)6X2(C12H10N2)], where halo is chloro (X = Cl) and bromo (X = Br) are isostructural. In both crystals, the molecules lie on inversion centers, and there are voids of ca 80 Å3 that could, but apparently do not, accommodate water molecules. The corresponding iodo structure (X = I) is almost, but not quite, isostructural with the other two compounds; when Br is changed to I, the length of the c axis decreases by more than 1 Å and the voids are no longer large enough to accomodate any solvent molecule. The related complex [μ‐(E)‐4,4′‐(ethene‐1,2‐diyl)dipyridine‐κ2N:N′]bis[chlorotriphenyltin(IV)], [Sn2(C6H5)6Cl2(C12H10N2)], crystallizes in a related structure, but the molecules lie on general rather than on special positions. The molecular structures of the four complexes are similar, but the conformation of the phenyl derivative is approximately eclipsed rather than staggered. 相似文献
12.
Carolyn Pratt Brock 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(7):835-836
A new method for identifying and visualizing approximate symmetry in molecular crystals is discussed. 相似文献
13.
14.
Peter Lindemann Silvia E. Braslavsky Marie-Michle Cordonnier Lee H. Pratt Kurt Schaffner 《Photochemistry and photobiology》1993,58(3):417-424
Abstract–Thc kinetics of the microsecond phototransformation intermediates of 124 kDa Avena phytochrome (17001,2) were studied in the prcsence of bound monoclonal antibodies at various temperatures. A global analysis was applied to the decays at all wavelengths at each temperature in order to derive the rate constants and the decay-associated spectra of the three decay components. Monoclonal antibodies bound to specific epitopes altered the Arrhenius parameters of both 17001,2 decay components. The strongest influence on these parameters was observed with OAT 8 (epitope between residues 624 and 686), which decreased by more than 50% the activation parameters of both components. This decrease is interpreted to result from an increased flexibility induced by this antibody in the ground state or in the transition state of bonds changing during the decay of both 1700 transients. Thus, the OAT 8 cpitope appears to be functionally important during the decay of the 17001,2 intermediates. For the case of 11001 bound OAT 23 and OAT 25 (epitopes between residues 1 and 66) reduced even further the relatively small flexibility of these bonds in the red light-absorbing form of phytochrome (P1) without antibodies, as reflected by the high preex-ponential factors for its decay. This resulted also in higher activation energies for this decay in the presence of the antibodies. Thus, the amino-terminus should act as a rigid spacer of the chromophore cavity without affecting it during the microsecond transformation, because the Arrhenius parameters for these decays are similar to those for small phytochrome. The possible implications of the influence of the various antibodies on the bleaching remaining after the decay of 17001,2 are discussed. 相似文献
15.
[structure: see text] Divergent syntheses of sulfated sialyl Lewis X oligosaccharides corresponding to the core 1 and core 6 branches of the L-selectin ligand are reported. These synthetic targets incorporate a selectively protected serine residue at the reducing terminus, providing a functional handle for further conjugation. 相似文献
16.
The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states have been investigated by velocity map ion imaging. The selected rotational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states are prepared by three-photon excitation from the ground state. The absorption of fourth photon results in photoionization to produce H(2)(+) X (2)Sigma(g)(+) or photodissociation to produce a ground-state H(1s) atom and an excited H atom with n >or= 2. The H(2) (+) ion can be photodissociated by absorption of a fifth photon. The resulting H(+) or D(+) ion images provide information on the vibrational state dependence of the photodissociation angular distribution of the molecular ion. The excited H(n >or= 2) atoms produced by the neutral dissociation process can also be ionized by the absorption of a fifth photon. The resulting ion images provide insight into the excited state branching ratios and angular distributions of the neutral photodissociation process. While the experimental ion images contain information on both the ionic and neutral processes, these can be separated based on constraints imposed on the fragment translational energies. The angular distribution of the rings in the ion images indicates that the neutral dissociation of molecular hydrogen and its isotopes is quite complex, and involves coupling to both doubly excited electronic states and the dissociation continua of singly excited Rydberg states. 相似文献
17.
Priya MH Pratt LR Paulaitis ME 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13713-13718
We compare protein-protein and protein-polymer osmotic virial coefficients measured by static light scattering for aqueous solutions of lysozyme with low-molecular-weight, hydroxy-terminated (hPEG) and methyl-terminated (mPEG) poly(ethylene glycol) at two solution conditions: pH 7.0 and 0.01 M ionic strength, and pH 6.2 and 0.8 M ionic strength. We find that adding PEG to aqueous lysozyme solutions makes a net repulsive contribution to lysozyme-lysozyme interactions, independent of ionic strength and PEG end-group hydrophobicity. PEG end-group hydrophobicity has a profound effect on the magnitude of this contribution, however, at low ionic strength where mPEG-lysozyme attractive interactions become significant. The enhanced attractions promote mPEG-lysozyme preferential interactions at the expense of lysozyme self-interactions, which leads to lysozyme-lysozyme interactions that are more repulsive in the presence of mPEG. These preferential interactions also lead to the preferential exclusion of diffusable ions locally around the protein, which results in a pronounced ionic strength dependence of mPEG-mediated lysozyme-lysozyme interactions. 相似文献
18.
19.
The reactivities of two copper(II)-phenoxyl analogues of the oxidized, active form of the metalloenzyme galactose oxidase, [1tBu2]+ and [2tBu2]+, have been studied using the substrates benzyl alcohol and 9,10-dihydroanthracene, for a total of four reactions. The reaction stoichiometries in all cases show a 2:1 ratio of oxidant to benzaldehyde or anthracene product, indicating that [1tBu2]+ and [2tBu2]+ behave ultimately as only one-electron oxidants, but the reaction kinetics each indicate that only a single copper(II)-phenoxyl complex is involved in the rate-determining step. For each substrate, rate laws indicate that [1tBu2]+ and [2tBu2]+ react by different mechanisms: one proceeds by a simple bimolecular reaction, while the other first enters into a substrate-binding equilibrium before subsequently reacting by an intramolecular reaction. The reactions proceeding by the latter mechanism have faster overall rates, which correlates to a lower entropic barrier for the substrate-binding mechanism. Correlation of the reaction rates with the C-H bond dissociation energies of substrates as well as significant deuterium kinetic isotope effects indicates that the rate-determining steps involve hydrogen atom abstraction from the activated C-H bonds. A variable-temperature study (268-308 K) of the nonclassical KIE of the [1tBu2]+/benzyl alcohol reaction (kH/kD = 15 at 298 K) failed to show evidence for quantum tunneling. The rapid sequence by which a second 1 equiv of copper(II)-phenoxyl oxidant completes the reaction after the rate- and product-determining hydrogen atom abstraction step cannot be probed kinetically. Comparisons are made to the reactivities of other copper(II)-phenoxyl complexes reported in the literature and to galactose oxidase itself. 相似文献
20.