全文获取类型
收费全文 | 91564篇 |
免费 | 1267篇 |
国内免费 | 841篇 |
专业分类
测绘学 | 2436篇 |
大气科学 | 6637篇 |
地球物理 | 17412篇 |
地质学 | 35037篇 |
海洋学 | 7662篇 |
天文学 | 19663篇 |
综合类 | 331篇 |
自然地理 | 4494篇 |
出版年
2021年 | 715篇 |
2020年 | 774篇 |
2019年 | 818篇 |
2018年 | 4083篇 |
2017年 | 3792篇 |
2016年 | 3382篇 |
2015年 | 1296篇 |
2014年 | 2093篇 |
2013年 | 3857篇 |
2012年 | 3059篇 |
2011年 | 5087篇 |
2010年 | 4529篇 |
2009年 | 5353篇 |
2008年 | 4514篇 |
2007年 | 5076篇 |
2006年 | 2868篇 |
2005年 | 2548篇 |
2004年 | 2468篇 |
2003年 | 2419篇 |
2002年 | 2233篇 |
2001年 | 1765篇 |
2000年 | 1694篇 |
1999年 | 1432篇 |
1998年 | 1480篇 |
1997年 | 1398篇 |
1996年 | 1196篇 |
1995年 | 1149篇 |
1994年 | 1045篇 |
1993年 | 945篇 |
1992年 | 898篇 |
1991年 | 868篇 |
1990年 | 943篇 |
1989年 | 749篇 |
1988年 | 791篇 |
1987年 | 854篇 |
1986年 | 775篇 |
1985年 | 1039篇 |
1984年 | 1115篇 |
1983年 | 1062篇 |
1982年 | 932篇 |
1981年 | 878篇 |
1980年 | 875篇 |
1979年 | 808篇 |
1978年 | 813篇 |
1977年 | 685篇 |
1976年 | 690篇 |
1975年 | 667篇 |
1974年 | 652篇 |
1973年 | 674篇 |
1971年 | 434篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
111.
A constitutive relation is derived for describing the mechanical response of chalk. The approach is based on a phenomenological framework which employs chemo‐plasticity. The properties of the material are assumed to be affected by the physico‐chemical processes that occur through the interaction between the skeleton and the pore fluid. The underlying mechanism is discussed by invoking a micromechanical analysis. The performance of the framework is illustrated by examining the evolution of mechanical characteristics in the presence of different pore fluids. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
112.
A. S. Samodurov 《Physical Oceanography》2006,16(3):129-140
We study the dynamic features of propagation of subsurface gravitational lenses and the conditions of changes in the modes
of control over their motion by various internal and external forces. As these forces, we study the action of drag, molecular
and turbulent viscosity due to the presence of internal and external forces, and deceleration caused by the effects of double
diffusion. We also analyze the modes of propagation of small-scale gravitational lenses. The information about these lenses
taken from the literature is supplemented and generalized.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 3–14, May–June, 2006. 相似文献
113.
Miller B.S. Zosuls A.L. Ketten D.R. Mountain D.C. 《Oceanic Engineering, IEEE Journal of》2006,31(1):87-94
Previous research on the cetacean auditory system has consisted mostly of behavioral studies on a limited number of species. Little quantitative physiologic data exists on cetacean hearing. The frequency range of hearing varies greatly across different mammalian species. Differences among species correlate with differences in the middle-ear transfer function. Middle-ear transfer functions depend on the mechanical stiffness of the middle ear and the cochlear input impedance. The purpose of this study was to measure the middle-ear stiffness for the bottlenose dolphin (Tursiops truncatus), a species specialized for underwater high-frequency hearing and echolocation. Middle-ear stiffness was measured with a force probe that applied a known displacement to the stapes and measured the restoring force. The average middle-ear stiffness in ten dolphin ears was 1.37 N//spl mu/m, which is considerably higher than that reported for most terrestrial mammals. The relationship between middle-ear stiffness and low-frequency hearing cutoff in Tursiops was shown to be comparable to that of terrestrial mammals. 相似文献
114.
115.
Hector Socas-Navarro David Elmore Anna Pietarila Anthony Darnell Bruce W. Lites Steven Tomczyk Steven Hegwer 《Solar physics》2006,235(1-2):55-73
The Spectro-Polarimeter for Infrared and Optical Regions (SPINOR) is a new spectro-polarimeter that will serve as a facility
instrument for the Dunn Solar Telescope at the National Solar Observatory. This instrument is capable of achromatic polarimetry
over a very broad range of wavelengths, from 430 to 1600 nm, allowing for the simultaneous observation of several visible
and infrared spectral regions with full Stokes polarimetry. Another key feature of the design is its flexibility to observe
virtually any combination of spectral lines, limited only by practical considerations (e.g., the number of detectors available, space on the optical bench, etc.).
Visiting Astronomers, National Solar Observatory, operated by the Association of Universities for Research in Astronomy, Inc.
(AURA), under cooperative agreement with the National Science Foundation. 相似文献
116.
A new approach to constraining seawater δ34S and sulphate concentration using francolite‐bound sulphate reveals an abrupt increase in δ34S to +50‰ around the Early–Middle Cambrian boundary. Such high δ34S values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500–700 μgL?1. We argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the Kalkarindji Large Igneous Province of northern Australia and that it triggered the collapse of early metazoan reef ecosystems during the latest Early Cambrian. Mass extinctions of the last 260 Myr have all coincided with enhanced volcanic activity, while several are also associated with positive shifts in seawater δ34S. Extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution. Terra Nova, 18, 257–263, 2006 相似文献
117.
118.
The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 105 to 1.6 × 106 M. The expansion velocity of the Ring is estimated to be 30–40 km s−1, which gives an expansion time scale of 1.5 × 105 year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN− from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring. 相似文献
119.
120.