全文获取类型
收费全文 | 21647篇 |
免费 | 3676篇 |
国内免费 | 3022篇 |
专业分类
化学 | 17070篇 |
晶体学 | 201篇 |
力学 | 1636篇 |
综合类 | 124篇 |
数学 | 805篇 |
物理学 | 8509篇 |
出版年
2024年 | 60篇 |
2023年 | 253篇 |
2022年 | 611篇 |
2021年 | 725篇 |
2020年 | 828篇 |
2019年 | 677篇 |
2018年 | 586篇 |
2017年 | 702篇 |
2016年 | 870篇 |
2015年 | 1000篇 |
2014年 | 1188篇 |
2013年 | 1776篇 |
2012年 | 1371篇 |
2011年 | 1641篇 |
2010年 | 1360篇 |
2009年 | 1466篇 |
2008年 | 1513篇 |
2007年 | 1515篇 |
2006年 | 1409篇 |
2005年 | 1236篇 |
2004年 | 1167篇 |
2003年 | 931篇 |
2002年 | 859篇 |
2001年 | 577篇 |
2000年 | 547篇 |
1999年 | 474篇 |
1998年 | 426篇 |
1997年 | 368篇 |
1996年 | 342篇 |
1995年 | 295篇 |
1994年 | 247篇 |
1993年 | 204篇 |
1992年 | 196篇 |
1991年 | 158篇 |
1990年 | 125篇 |
1989年 | 96篇 |
1988年 | 101篇 |
1987年 | 55篇 |
1986年 | 65篇 |
1985年 | 47篇 |
1984年 | 47篇 |
1983年 | 19篇 |
1982年 | 45篇 |
1981年 | 29篇 |
1980年 | 33篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The sub-millisecond protonation dynamics of the chromophore in S65T mutant form of the green fluorescent protein (GFP) was
tracked after a rapid pH jump following laser-induced proton release from the caged photolabile compoundo-nitrobenzaldehyde. Following a jump in pH from 8 to 5 (which is achieved within 2 μs), the fluorescence of S65T GFP decreased
as a single exponential with a time constant of ∼90 μs. This decay is interpreted as the conversion of the deprotonated fluorescent
GFP chromophore to a protonated non-fluorescent species. The protonation kinetics showed dependence on the bulk viscosity
of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation
is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal
structural rearrangements to stabilize a protonated chromophore. The possible implications of these observations to protein
dynamics in general is discussed 相似文献
102.
In this paper, we examine a variant of the uncapacitated lot-sizing model of Wagner–Whitin that includes fixed charges on the stocks. Such a model is natural in a production environment where stocking is a complex operation, and appears as a subproblem in more general network design problems.
Linear-programming formulations, a dynamic program, the convex hull of integer solutions and a separation algorithm are presented. All these turn out to be very natural extensions of the corresponding results of Barany et al. (Math. Programming Stud. 22 (1984) 32) for the uncapacitated lot-sizing problem. The convex hull proof is based on showing that an extended facility location formulation is tight and by projecting it onto the original space of variables. 相似文献
103.
104.
A rigorous and systematic intercomparison of codes used for the retrieval of trace gas profiles from high-resolution ground-based solar absorption FTIR measurements is presented for the first time. Spectra were analyzed with the two widely used independent, retrieval codes: SFIT2 and PROFFIT9. Vertical profiles of O3, HNO3, HDO, and N2O were derived from the same set of typical observed spectra. Analysis of O3 was improved by using updated line parameters. It is shown that profiles and total column amounts are in excellent agreement, when similar constraints are applied, and that the resolution kernel matrices are also consistent. Owing to the limited altitude resolution of ground-based observations, the impact of the constraints on the solution is not negligible. It is shown that the results are also compatible for independently chosen constraints. Perspectives for refined constraints are discussed. It can be concluded that the error budget introduced by the radiative transfer code and the retrieval algorithm on total columns deduced from high-resolution ground-based solar FTIR spectra is below 1%. 相似文献
105.
106.
Photoluminescence (PL), photostimulated luminescence (PSL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on LiYF4:U4+ and pure LiYF4 crystals. The PL and EPR investigations have identified the presence of Eu3+, Tb3+ and Gd3+ ions in both of these crystals possibly due to their existence in the starting materials. The luminescence observed during afterglow, PSL and TSL revealed that emission occurs at wavelength positions 382, 413, 437 and 544 nm, which are characteristic of Tb3+ ions. The present investigations using PSL and TSL in combination with PL studies before and after gamma irradiation have revealed that selective energy transfer to Tb3+ ions occurs during electron–hole recombination processes like PSL and TSL. Even though other luminescent ions (U4+ and Eu3+) are present in the system and U4+/U3+ ions are participating in electron capture/release processes, the selective energy transfer results in Tb3+ ions acting as luminescence centers. 相似文献
107.
Piotr Winiarek Juan Carlos Q. Colmenares Elbieta Fedoryska 《Reaction Kinetics and Catalysis Letters》2004,81(2):333-339
Transformations of diphenylmethane were investigated in a flow system in the presence of alumina and silica-alumina modified
with boron trifluoride at atmospheric pressure and elevated temperatures. Hydrogen transfer reaction was observed on addition
of tetralin to the substrate stream.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
108.
The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems. 相似文献
109.
110.
The vibronic spectra of charge transfer excitons (CTE) in a molecular one-component or alternatingly ordered two-component chain are treated in the framework of a dynamic approach (neglecting thermal excitations of the intramolecular vibrations). The model introduces two mechanisms of coupling between CTEs and vibrational quanta: (1) shift of the equilibrium positions of the nuclei in the ionized donor or acceptor; (2) change of the vibrational frequency in the ionized molecule. This model allows to generalize the simple CTE Hamiltonian and the vibronic Hamiltonian of Frenkel excitons. The linear optical susceptibility is calculated in the vibronic region (one CTE and one vibrational quantum). The double splitting of vibronics of CTEs was analyzed: (1) the splitting connected with the location of the intramolecular vibration on the donors or on the acceptors; (2) the splitting connected with the symmetry of the vibronic spectra (in the degenerate case). The general structure of the vibronic spectra of CTEs is established. It contains structureless absorption lines, which correspond to two-particle bands (the phonon is excited on a neutral molecule neighboring the donor or the acceptor) and Lorentz-type lines of one-particle states, which correspond to the bound propagation of the CTE and the phonon. 相似文献