全文获取类型
收费全文 | 9779篇 |
免费 | 212篇 |
国内免费 | 40篇 |
专业分类
化学 | 5943篇 |
晶体学 | 76篇 |
力学 | 226篇 |
数学 | 1930篇 |
物理学 | 1856篇 |
出版年
2020年 | 101篇 |
2019年 | 91篇 |
2018年 | 74篇 |
2016年 | 161篇 |
2015年 | 141篇 |
2014年 | 152篇 |
2013年 | 347篇 |
2012年 | 310篇 |
2011年 | 328篇 |
2010年 | 240篇 |
2009年 | 219篇 |
2008年 | 314篇 |
2007年 | 320篇 |
2006年 | 288篇 |
2005年 | 311篇 |
2004年 | 270篇 |
2003年 | 214篇 |
2002年 | 249篇 |
2001年 | 136篇 |
2000年 | 190篇 |
1999年 | 149篇 |
1998年 | 115篇 |
1997年 | 144篇 |
1996年 | 137篇 |
1995年 | 136篇 |
1994年 | 161篇 |
1993年 | 150篇 |
1992年 | 155篇 |
1991年 | 119篇 |
1990年 | 122篇 |
1989年 | 116篇 |
1988年 | 131篇 |
1987年 | 117篇 |
1986年 | 150篇 |
1985年 | 182篇 |
1984年 | 168篇 |
1983年 | 140篇 |
1982年 | 170篇 |
1981年 | 167篇 |
1980年 | 177篇 |
1979年 | 163篇 |
1978年 | 164篇 |
1977年 | 164篇 |
1976年 | 148篇 |
1975年 | 167篇 |
1974年 | 126篇 |
1973年 | 136篇 |
1972年 | 89篇 |
1971年 | 93篇 |
1970年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Time-resolved electron transport studies on InGaAs/GaAs-QWIPs 总被引:1,自引:0,他引:1
S. Steinkogler H. Schneider R. Rehm M. Walther P. Koidl P. Grant R. Dudek H. C. Liu 《Infrared Physics & Technology》2003,44(5-6):355-361
Due to the short internal response time, quantum-well infrared photodetectors (QWIPs) are interesting for high-speed applications such as heterodyne spectroscopy or laser pulse monitoring. We studied the photocurrent transients of InGaAs/GaAs-QWIPs after irradiation with infrared laser pulses of 250 fs duration. The excitation wavelength of about 9 μm matches the peak wavelength of the QWIP structure. The photocurrent transient consists of two different dynamical components, representing the fast photoionization in the quantum-wells and the slow injection current that compensates the remaining space charge. The investigations of the different components as a function of temperature and bias voltage were performed on a nanosecond time-scale. The experimental separation of the two photocurrent contributions allows us to determine the photoconductive gain. The Fourier transform of the photocurrent transient was compared with other experimental methods including heterodyne detection and microwave rectification. The quantitative agreement between these different measurement techniques is excellent. 相似文献
22.
23.
Douglas R. White Jason Owen-Smith James Moody Walter W. Powell 《Computational & Mathematical Organization Theory》2004,10(1):95-117
Social action is situated in fields that are simultaneously composed of interpersonal ties and relations among organizations, which are both usefully characterized as social networks. We introduce a novel approach to distinguishing different network macro-structures in terms of cohesive subsets and their overlaps. We develop a vocabulary that relates different forms of network cohesion to field properties as opposed to organizational constraints on ties and structures. We illustrate differences in probabilistic attachment processes in network evolution that link on the one hand to organizational constraints versus field properties and to cohesive network topologies on the other. This allows us to identify a set of important new micro-macro linkages between local behavior in networks and global network properties. The analytic strategy thus puts in place a methodology for Predictive Social Cohesion theory to be developed and tested in the context of informal and formal organizations and organizational fields. We also show how organizations and fields combine at different scales of cohesive depth and cohesive breadth. Operational measures and results are illustrated for three organizational examples, and analysis of these cases suggests that different structures of cohesive subsets and overlaps may be predictive in organizational contexts and similarly for the larger fields in which they are embedded. Useful predictions may also be based on feedback from level of cohesion in the larger field back to organizations, conditioned on the level of multiconnectivity to the field. 相似文献
24.
Synthesis and Properties of the Layered Perovskite Phase Sr3Mo1.5Zn0.5O7‐δ The new layered perovskite phase Sr3Mo1.5Zn0.5O7‐δ was synthesized by solid state reaction using a Zn/ZnO oxygen buffer. The crystal structure was refined from X‐ray powder pattern by the Rietveld method. The compound crystallizes tetragonal in the space group I4/mmm (no. 139) with the lattice parameters a = 3.9631(3) Å, c = 20.583(1) Å. An oxygen deficiency corresponding to δ ≈ 0.25 was determinated, indicating the presence of molybdenum in mixed valence (Mo4+ and Mo6+). 相似文献
25.
Walter Benz Hamburg 《Results in Mathematics》2003,44(1-2):41-43
It will be proved that the functional equation of periodic lines has no solution for hyperbolic distances. 相似文献
26.
Reaction diffusion systems on cylindrical domains with terms that vary rapidly and periodically in the unbounded direction can be analyzed by averaging techniques. Here, using iterated normal form transformations and Gevrey regularity of bounded solutions, we prove a result on exponential averaging for such systems, i.e., we show that traveling wave solutions can be described by a spatially homogenous equation and exponentially small remainders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
27.
H. Glatzel R. Schneider T. Fauster V. Dose 《Zeitschrift für Physik B Condensed Matter》1992,88(1):53-61
Inverse photoemission spectra were taken for thin epitaxial iron films on Cu(100). For a film thickness of eight monolayers the observed electronic states are characteristic for a fcc(100) surface. Thed-bands of iron show a ferromagnetic exchange splitting of 1.1 eV, considerably smaller than the bulk value of 1.8 eV, which we observe for film thicknesses above 18 monolayers. 相似文献
28.
B. Pümpin H. Keller W. Kündig I. M. Savić J. W. Schneider H. Simmler P. Zimmermann E. Kaldis S. Rusiecki C. Rossel 《Hyperfine Interactions》1991,63(1-4):25-31
A systematic μSR study of the local magnetic field distribution in a series of oxygen deficient YBa2Cu3O
x
samples with 6.5⩽x⩽7.0 is reported. Special attention was given to perform the experiments under the same conditions, so that the oxygen content
of the measured samples was the only parameter varied. The behavior of the depolarization rate σ as a function of the oxygen
contentx was found to have strong similarities with the behavior of the critical temperatureT
c
as a function ofx. In particular, two step-like increases of σ were observed abovex=6.7 and 6.9. The temperature dependence of the normalized depolarization rate σ(T)/σ(0) is well described by the two-fluid model forx⩾6.781(1) and clearly deviates from this behavior forx⩽6.704(1). Our results are compared to those obtained by other groups. 相似文献
29.
30.
We investigate superconducting pair correlations in the attractive Hubbard model on a finite square lattice. Our aim is to understand the pronounced size dependence which they display in the weak and intermediate coupling regimes. These size effects originate from the electronic shell structure of finite systems and severely complicate a reliable extrapolation of numerical simulation data from small systems to the thermodynamic limit. To analyze the size effects in detail, we use the BCS approximation, as well as a particle number conserving modification of it and compare the results with those of quantum Monte Carlo simulations. As an application, we explore the possibility of reducing the shell effects in simulation data by changing the shape of the system and the imposed boundary conditions and by making use of the size dependence of corresponding BCS data. 相似文献