全文获取类型
收费全文 | 774篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 518篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 151篇 |
物理学 | 117篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 28篇 |
2019年 | 29篇 |
2018年 | 20篇 |
2017年 | 8篇 |
2016年 | 30篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 41篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 27篇 |
2009年 | 24篇 |
2008年 | 33篇 |
2007年 | 18篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 16篇 |
2003年 | 27篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1995年 | 9篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1969年 | 7篇 |
1944年 | 6篇 |
1943年 | 7篇 |
1928年 | 4篇 |
1914年 | 4篇 |
1910年 | 5篇 |
排序方式: 共有816条查询结果,搜索用时 18 毫秒
21.
Felix Nußbaumer Raphael Plangger Manuel Roeck Christoph Kreutz 《Angewandte Chemie (International ed. in English)》2020,59(39):17062-17069
We present the access to [5‐19F, 5‐13C]‐uridine and ‐cytidine phosphoramidites for the production of site‐specifically modified RNAs up to 65 nucleotides (nts). The amidites were used to introduce [5‐19F, 5‐13C]‐pyrimidine labels into five RNAs—the 30 nt human immunodeficiency virus trans activation response (HIV TAR) 2 RNA, the 61 nt human hepatitis B virus ? (hHBV ?) RNA, the 49 nt SAM VI riboswitch aptamer domain from B. angulatum, the 29 nt apical stem loop of the pre‐microRNA (miRNA) 21 and the 59 nt full length pre‐miRNA 21. The main stimulus to introduce the aromatic 19F–13C‐spin topology into RNA comes from a work of Boeszoermenyi et al., in which the dipole‐dipole interaction and the chemical shift anisotropy relaxation mechanisms cancel each other leading to advantageous TROSY properties shown for aromatic protein sidechains. This aromatic 13C–19F labeling scheme is now transferred to RNA. We provide a protocol for the resonance assignment by solid phase synthesis based on diluted [5‐19F, 5‐13C]/[5‐19F] pyrimidine labeling. For the 61 nt hHBV ? we find a beneficial 19F–13C TROSY enhancement, which should be even more pronounced in larger RNAs and will facilitate the NMR studies of larger RNAs. The [19F, 13C]‐labeling of the SAM VI aptamer domain and the pre‐miRNA 21 further opens the possibility to use the biorthogonal stable isotope reporter nuclei in in vivo NMR to observe ligand binding and microRNA processing in a biological relevant setting. 相似文献
22.
23.
24.
Donohue R Mazzaglia A Ravoo BJ Darcy R 《Chemical communications (Cambridge, England)》2002,(23):2864-2865
Cationic amphiphilic beta-cyclodextrins, substituted with hydrophobic n-alkylthio chains at the primary hydroxyl side and hydrophilic omega-amino-oligo(ethylene glycol) units at the secondary side, form bilayer vesicles with a diameter of 30-35 nm (when alkyl = hexadecyl) or nanoparticles with a diameter of ca. 120 nm (when alkyl = hexyl) in water. 相似文献
25.
Raphael Bousso Stephen W. Hawking 《International Journal of Theoretical Physics》1999,38(4):1227-1252
The wave function of the universe is usuallytaken to be a functional of the threemetric on aspacelike section, , which is measured. It issometimes better, however, to work in the conjugaterepresentation, where the wave function depends on a quantityrelated to the second fundamental form of . Thismakes it possible to ensure that is part of aLorentzian universe by requiring that the argument of the wave function be purely imaginary. Wedemonstrate the advantages of this formalism first inthe well-known examples of the nucleation of a de Sitteror a Nariai universe. We then use it to calculate the pair creation rate for submaximal blackholes in de Sitter space, which had been thought tovanish semiclassically. We also study the quantumevolution of asymptotically de Sitter black holes. Forblack holes whose size is comparable to that of thecosmological horizon, this process differs significantlyfrom the evaporation of asymptotically flat black holes.Our model includes the one-loop effective action in the s-wave and large-N approximation.Black holes of the maximal mass are in equilibrium.Unexpectedly, we find that nearly maximal quantumSchwarzschild–de Sitter black holes antievaporate.However, there is a different perturbative mode thatleads to evaporation. We show that this mode will alwaysbe excited when a pair of maximal cosmological blackholes nucleates. 相似文献
26.
We develop a controlled high-temperature expansion for nonequilibrium steady states of the driven lattice gas, the "Ising model" for nonequilibrium physics. We represent the steady state as P(eta) alpha e(-betaH(eta)-psi(eta)) and evaluate the lowest order contribution to the nonequilibrium effective interaction psi(eta). We see that, in dimensions d > or = 2, all models with nonsingular transition rates yield the same summable psi(eta), suggesting the possibility of describing the state as a Gibbs state similar to equilibrium. The models with the Metropolis rule show exceptional behavior. 相似文献
27.
We consider finite time blow up solutions to the critical nonlinear Schrödinger equation For a suitable class of initial data in the energy space H1, we prove that the solution splits in two parts: the first part corresponds to the singular part and accumulates a quantized amount of L2 mass at the blow up point, the second part corresponds to the regular part and has a strong L2 limit at blow up time.Part of this work has been supported by grant DMS-0111298. 相似文献
28.
29.
We consider finite time blow-up solutions to the critical nonlinear Schrödinger equation iut=-u-|u|4/Nu with initial condition u0H1. Existence of such solutions is known, but the complete blow-up dynamic is not understood so far. For a specific set of initial data, finite time blow-up with a universal sharp upper bound on the blow-up rate has been proved in [22], [23].We establish in this paper the existence of a universal blow-up profile which attracts blow-up solutions in the vicinity of blow-up time. Such a property relies on classification results of a new type for solutions to critical NLS. In particular, a new characterization of soliton solutions is given, and a refined study of dispersive effects of (NLS) in L2 will remove the possibility of self similar blow-up in energy space H1. 相似文献
30.
In theories of gravity with a positive cosmological constant, we consider product solutions with flux, of the form (A)dS
p
×S
q
. Most solutions are shown to be perturbatively unstable, including all uncharged dS
p
×S
q
spacetimes. For dimensions greater than four, the stable class includes universes whose entropy exceeds that of de Sitter space, in violation of the conjectured N-bound. Hence, if quantum gravity theories with finite-dimensional Hilbert space exist, the specification of a positive cosmological constant will not suffice to characterize the class of spacetimes they describe. 相似文献