全文获取类型
收费全文 | 1195篇 |
免费 | 33篇 |
专业分类
化学 | 658篇 |
晶体学 | 10篇 |
力学 | 41篇 |
数学 | 86篇 |
物理学 | 433篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2016年 | 16篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 54篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 61篇 |
2006年 | 64篇 |
2005年 | 45篇 |
2004年 | 46篇 |
2003年 | 34篇 |
2002年 | 28篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 19篇 |
1996年 | 10篇 |
1995年 | 22篇 |
1994年 | 29篇 |
1993年 | 34篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 25篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有1228条查询结果,搜索用时 15 毫秒
71.
The triple phase boundary transfer of anions from the aqueous into an organic phase can be driven electrochemically here with the tetraphenylporphyrinato‐Mn(III/II) (or TPPMn) redox system in 4‐(3‐phenylpropyl)‐pyridine) (or PPP). Anions investigated are perchlorate, chloride, fluoride, and bicarbonate. The bicarbonate and fluoride transfer processes are shown to be chemically more complex compared to the perchlorate and chloride cases with UV‐vis‐spectroelectrochemical measurements indicating a combination of HCO3?/CO32? transfer processes and association of fluoride with TPPMn(III)+, respectively. In situ spectroelectrochemistry is developed for ion‐transfer voltammetry into sub‐microliter organic phase regions on mesoporous ITO conducting film electrodes. 相似文献
72.
73.
Priplata A Niemi J Salen M Harry J Lipsitz LA Collins JJ 《Physical review letters》2002,89(23):238101
Noise can enhance the detection and transmission of weak signals in certain nonlinear systems, via a mechanism known as stochastic resonance. Here we show that input noise can be used to improve motor control in humans. Specifically, we show that the postural sway of both young and elderly individuals during quiet standing can be significantly reduced by applying subsensory mechanical noise to the feet. We further demonstrate with input noise a trend towards the reduction of postural sway in elderly subjects to the level of young subjects. These results suggest that noise-based devices, such as randomly vibrating shoe inserts, may enable people to overcome functional difficulties due to age-related sensory loss. 相似文献
74.
We present a model for a synthetic gene oscillator and consider the coupling of the oscillator to a periodic process that is intrinsic to the cell. We investigate the synchronization properties of the coupled system, and show how the oscillator can be constructed to yield a significant amplification of cellular oscillations. We reduce the driven oscillator equations to a normal form, and analytically determine the amplification as a function of the strength of the cellular oscillations. The ability to couple naturally occurring genetic oscillations to a synthetically designed network could lead to possible strategies for entraining and/or amplifying oscillations in cellular protein levels. 相似文献
75.
We present the first large-scale simulations of an ultracold neutral plasma, produced by photoionization of laser-cooled xenon atoms, from creation to initial expansion, using classical molecular-dynamics methods with open boundary conditions. We reproduce many of the experimental findings such as the trapping efficiency of electrons with increased ion number, a minimum electron temperature achieved on approach to the photoionization threshold, and recombination into Rydberg states of an anomalously low principal quantum number. In addition, many of these effects establish themselves very early in the plasma evolution ( similar ns) before the present experimental observations begin. 相似文献
76.
The synthesis of a series of novel acetylenic cyclophanes is described. X-ray crystallographic analysis of the core structure revealed a twisted conformation with helical chirality. Preliminary results suggest that these cyclophanes, with appropriate functionality, have the potential to act as unique liquid crystalline materials. 相似文献
77.
Neiman A Schimansky-Geier L Moss F Shulgin B Collins JJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):284-292
We study, in terms of synchronization, the nonlinear response of noisy bistable systems to a stochastic external signal, represented by Markovian dichotomic noise. We propose a general kinetic model which allows us to conduct a full analytical study of the nonlinear response, including the calculation of cross-correlation measures, the mean switching frequency, and synchronization regions. Theoretical results are compared with numerical simulations of a noisy overdamped bistable oscillator. We show that dichotomic noise can instantaneously synchronize the switching process of the system. We also show that synchronization is most pronounced at an optimal noise level-this effect connects this phenomenon with aperiodic stochastic resonance. Similar synchronization effects are observed for a stochastic neuron model stimulated by a stochastic spike train. 相似文献
78.
Osipov GV Collins JJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):54-57
Here we propose mechanisms for suppressing non-steady-state motions--propagating pulses, spiral waves, spiral-wave chaos--in excitable media. Our approach is based on two points: (1) excitable media are multistable; and (2) traveling waves in excitable media can be separated into fast and slow motions, which can be considered independently. We show that weak impulses can be used to change the values of the slow variable at the front and back of a traveling wave, which leads to wave front and wave back velocities that are different from each other. This effect can destabilize the traveling wave, resulting in a transition to the rest state. 相似文献
79.
Davanloo F. Collins C.B. Agee F.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(5):1463-1475
The stacked Blumlein pulse generators developed at the University of Texas at Dallas consist of several triaxial Blumleins stacked in series at one end. The lines are charged in parallel and synchronously commutated with a single switching element at the other end, In this may, relatively low charging voltages are multiplied to give a higher desired voltage across an arbitrary load. Extensive characterization of the stacked Blumlein pulsers indicates that these devices are capable of producing high-power pulses with rise times and repetition rates in the range of 0.3-50 ns and 1-300 Hz, respectively, using a conventional thyratron, spark gap, or photoconductive switch. This paper presents the progress in the development and use of these novel pulsers. Recent adaptation of the design has enabled the stacked Blumlein to produce 50-70 MW nanosecond pulses with risetimes on the order of 200-300 ps into nominally matched loads. The device has a compact line geometry and is commutated by a single photoconductive switch triggered by a low power laser diode 相似文献
80.