全文获取类型
收费全文 | 434篇 |
免费 | 31篇 |
专业分类
化学 | 314篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 42篇 |
物理学 | 97篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 19篇 |
2011年 | 30篇 |
2010年 | 19篇 |
2009年 | 14篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 26篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 8篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有465条查询结果,搜索用时 15 毫秒
41.
42.
43.
Montserrat Cortina‐Puig Anastasia C. H. Scangas Zachary S. Marchese Silvana Andreescu Jean‐Louis Marty Carole Calas‐Blanchard 《Electroanalysis》2010,22(20):2429-2433
This paper describes the development of a xanthine oxidase/poly‐m‐phenylenediamine (XOD‐PPD)‐modified electrode. The biosensor was constructed by encapsulating XOD in a sol‐gel matrix deposited onto a platinum based screen‐printed electrode functionalized with a permselective PPD membrane. The hydrogen peroxide generated as a final product of the enzymatic reaction between the hypoxanthine and the XOD or by the spontaneous dismutation of superoxide radicals was selectively monitored at +700 mV. The use of a highly selective PPD layer blocked the nonspecific oxidation of other oxidizable molecules. Finally the biosensor was applied to the determination of the antioxidant capacity of acetylsalicylic acid. 相似文献
44.
We report on the rotational diffusion dynamics of the anionic chromophore resorufin in water and N-octyl-2-pyrrolidone (NOP) solutions as a function of solution electrolyte concentration. Our data show that resorufin exhibits a single exponential anisotropy decay in aqueous solutions containing up to 0.1 M lithium perchlorate (LiClO(4)). In contrast to the observed behavior of resorufin in pure NOP, where biexponential decay occurs, we also observe a single exponential anisotropy decay for resorufin in NOP with the addition of up to 0.1 M tetrabutylammonium bromide (TBAB) or tetraoctylammonium bromide (TOAB). For resorufin in NOP, the reorientation time constant increases with increasing electrolyte concentration, consistent with complexation between the resorufin anion and the electrolyte ammonium cation. We observe a qualitatively different trend in the aqueous resorufin solutions and understand these data for both solvent systems in the context of interactions between the chromophore and cationic species present. 相似文献
45.
Peter E.R. Blanchard Brianna R. Slater Ronald G. Cavell Arthur Mar Andrew P. Grosvenor 《Solid State Sciences》2010,12(1):50-58
The electronic structures of the quaternary oxyarsenides LaMAsO (M = Fe, Co, Ni) were examined with X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Interpretation of the metal 2p3/2 and arsenic 3d5/2 binding energies, as well as a satellite feature in the Co 2p XPS spectrum, suggests charges that are much less extreme than expected (i.e., not M2+ and As3?) because of the strong covalent character within the M–As bonds. As M is varied, the differing degrees of charge transfer from M to As atoms within these bonds are manifested by shifts in the As 3d5/2 binding energies and changes in the As K-edge intensities. This charge transfer is isolated within the [MAs] layer and does not influence the O 1s and La 3d XPS spectra. Fitting the experimental valence band spectra of these oxyarsenides LaMAsO yielded electron populations of states that support the formal charge assignment [La3+O2?][M2+As3?]. The mixed-metal series LaFe1?xM′xAsO (M′ = Co, Ni) was examined by XANES; analysis of the metal K- and L-edges, as well as of the Co 2p XPS satellite feature, revealed that no metal–metal charge transfer takes place. 相似文献
46.
Blanchard F Golde D Su FH Razzari L Sharma G Morandotti R Ozaki T Reid M Kira M Koch SW Hegmann FA 《Physical review letters》2011,107(10):107401
The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response. 相似文献
47.
This paper presents a new computational approach for solving optimal control problems governed by impulsive switched systems. Such systems consist of multiple subsystems operating in succession, with possible instantaneous state jumps occurring when the system switches from one subsystem to another. The control variables are the subsystem durations and a set of system parameters influencing the state jumps. In contrast with most other papers on the control of impulsive switched systems, we do not require every potential subsystem to be active during the time horizon (it may be optimal to delete certain subsystems, especially when the optimal number of switches is unknown). However, any active subsystem must be active for a minimum non-negligible duration of time. This restriction leads to a disjoint feasible region for the subsystem durations. The problem of choosing the subsystem durations and the system parameters to minimize a given cost function is a non-standard optimal control problem that cannot be solved using conventional techniques. By combining a time-scaling transformation and an exact penalty method, we develop a computational algorithm for solving this problem. We then demonstrate the effectiveness of this algorithm by considering a numerical example on the optimization of shrimp harvesting operations. 相似文献
48.
The loss of stability of a flow resulting from the interaction of a transverse jet and a crossflow has been studied experimentally
by means of several nonintrusive optical methods (Laser-Induced Fluorescence, Particle Streak Velocimetry). In particular,
flow visualizations have allowed measurement of the characteristic velocity of rotation of a counter-rotating vortex pair,
which is the prevailing system of this complex flow. It is shown that the elliptical geometry of the cross sections of these
vortex structures can cause the loss of stability of the jet according to the theory of Landman and Saffman (1987). The unstable
jet state is characterized by the generation of transverse unsteady rotating structures on the jet boundaries. These transverse
eddies are clearly identifiable and their regularity of occurrence is satisfactorily explained by the theory of Landman and
Saffman. Therefore, this study shows for the first time that the longitudinal structures must be taken into account in the
mechanism of stability arising from the meeting of a jet and a cross stream.
Received: 7 May 1997/Accepted: 20 March 1998 相似文献
49.
Paul Blanchard 《Semigroup Forum》1991,43(1):218-246
We study some syntactic properties of languages obtained from rational languages through counting operations. These counting operations use the congruences-threshold p, modulo n—on the set of integers. We show that in some cases they preserve the properties of syntactic monoids: the structure of idempotent and commutative monoids is not modified, aperiodic monoids with central idempotents keep their central idempotents and their regular D-classes still are groups although not trivial, aperiodic left (right) nilsimple semigroups still have regular R (L)-classes which are (non trivial) groups. If possible results are expressed in terms of varieties of semigroups or monoids. 相似文献
50.
A non linear system modelling phase changes in metallic alloys is studied. Two existence, uniqueness and regularity results are established in the reversible or irreversible setting. The technique uses non linear semi-groups theory and a fixed point method. 相似文献