全文获取类型
收费全文 | 3564篇 |
免费 | 98篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 54篇 |
大气科学 | 316篇 |
地球物理 | 820篇 |
地质学 | 1256篇 |
海洋学 | 338篇 |
天文学 | 494篇 |
综合类 | 10篇 |
自然地理 | 412篇 |
出版年
2021年 | 43篇 |
2020年 | 42篇 |
2019年 | 51篇 |
2018年 | 59篇 |
2017年 | 65篇 |
2016年 | 71篇 |
2015年 | 75篇 |
2014年 | 73篇 |
2013年 | 193篇 |
2012年 | 97篇 |
2011年 | 145篇 |
2010年 | 148篇 |
2009年 | 168篇 |
2008年 | 136篇 |
2007年 | 121篇 |
2006年 | 123篇 |
2005年 | 111篇 |
2004年 | 98篇 |
2003年 | 88篇 |
2002年 | 86篇 |
2001年 | 75篇 |
2000年 | 47篇 |
1999年 | 56篇 |
1998年 | 57篇 |
1997年 | 45篇 |
1996年 | 68篇 |
1995年 | 46篇 |
1994年 | 50篇 |
1993年 | 45篇 |
1992年 | 54篇 |
1991年 | 54篇 |
1990年 | 49篇 |
1989年 | 47篇 |
1988年 | 50篇 |
1987年 | 51篇 |
1986年 | 39篇 |
1985年 | 70篇 |
1984年 | 85篇 |
1983年 | 83篇 |
1982年 | 68篇 |
1981年 | 48篇 |
1980年 | 53篇 |
1979年 | 52篇 |
1978年 | 51篇 |
1977年 | 48篇 |
1976年 | 40篇 |
1975年 | 32篇 |
1974年 | 33篇 |
1973年 | 34篇 |
1972年 | 25篇 |
排序方式: 共有3700条查询结果,搜索用时 486 毫秒
411.
412.
William S. Burgett Michael M. Vick David S. Davis Matthew Colless Roberto De Propris Ivan Baldry Carlton Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Nicholas Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654
413.
414.
William W. Hsieh 《地球,A辑:动力气象学与海洋学》2001,53(5):599-615
Nonlinear principal component analysis (NLPCA) can be performed by a neural network model which nonlinearly generalizes the classical principal component analysis (PCA) method. The presence of local minima in the cost function renders the NLPCA somewhat unstable, as optimizations started from different initial parameters often converge to different minima. Regularization by adding weight penalty terms to the cost function is shown to improve the stability of the NLPCA. With the linear approach, there is a dichotomy between PCA and rotated PCA methods, as it is generally impossible to have a solution simultaneously (a) explaining maximum global variance of the data, and (b) approaching local data clusters. With the NLPCA, both objectives (a) and (b) can be attained together, thus the nonlinearity in NLPCA unifies the PCA and rotated PCA approaches. With a circular node at the network bottleneck, the NLPCA is able to extract periodic or wave modes. The Lorenz (1963) 3‐component chaotic system and the monthly tropical Pacific sea surface temperatures (1950–1999) are used to illustrated the NLPCA approach. 相似文献
415.
Albert M. Fowler K. Michael Merrill William Ball Arne Henden Fred Vrba Craig McCreight 《Experimental Astronomy》2002,14(1):61-68
The Orion program is a project to develop a 2K × 2K infrared focal plane using InSb p-on-n diodes for detectors. It is the
natural follow-up to the successful Aladdin 1K × 1K program started in the early 90's. The work is being done at the Raytheon
Infrared Operations Division (RIO, previously known as the Santa Barbara Research Center) by many of the same people who created
the Aladdin focal plane. The design is very similar to the successful Aladdin design with the addition of reference pixels,
whole array readout (no quadrants), two-adjacent-side buttability, and a packaging design that includes going directly to
the ultimate focal plane size of 4K × 4K. So far we have successfully made a limited number of hybrid modules with InSb detectors.
In this paper we will describe the design features and test data taken from some of these devices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
416.
William Liller 《Planetary and Space Science》1997,45(12):1505-1513
Systematic CCD photometry of Comet 1995 O1 (Hale-Bopp) began in early August 1995 shortly after its discovery (IAU Circular 6187) and continued until mid-November 1996. The light curve derived from a 34″ square centered on the nucleus shows clearly and objectively how the inner regions of the comet brightened during this 15 month period. Possible connections between sudden brightenings and reported outbursts are investigated. During the interval August–December 1995, the magnitude of the comet showed strong evidence of a periodicity of 20±5 days with a full amplitude of approximately 0.20 mag. It is noteworthy that this result spans both the period of 18 days suggested by Sekanina (1995, 1996) and the “superperiod” of 22±2 days reported by Jorda et al. (1997). However, in 1996 neither this periodicity nor any other could be detected with certainty in the photometric data. 相似文献
417.
Gary L Mills Alfred K Hanson James G Quinn William R Lammela N.Dennis Chasteen 《Marine Chemistry》1982,11(4):355-377
Dissolved organic matter (DOM) and dissolved copper-organic complexes were isolated from the estuarine waters of Narragansett Bay, RI, using reverse-phase liquid chromatography employing C18 Sep-Pak cartridges (Waters Associates). The cartridges were found to have a constant retention efficiency for processing ? 1-l volumes of seawater. Fractionation of the isolated material, by sequential elution of the Sep-Pak with water: methanol mixtures of increasing organic solvent concentration, yielded a fraction of the organic matter with a specific copper activity six times greater than the overall activity for the isolated DOM. Analysis of this fraction by high performance liquid chromatography suggested that the organic components are of intermediate polarity and have appreciable aromatic character.An investigation of the protonation characteristics of the isolated complexes indicated that most of the copper is associated with a broad range of acidic sites on the DOM. Analysis by electron paramagnetic resonance spectroscopy confirmed the organic association of the isolated copper and also suggested the presence of several types of binding sites which probably involve oxygen donor ligands.Studies of the exchange of 64Cu with these binding sites on the isolated DOM indicated that 70% of the sites undergo rapid exchange with copper in seawater while 20% of these sites did not exchange in a 24-h time period. 相似文献
418.
The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust.
Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern
Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial
in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents,
such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build
up the high levees.
Margin setting represents fan and/or source area 相似文献
419.
420.
Palynological analyses were completed for the A and B horizons of a forested Mollic Hapludalf to determine type, amount, and distribution of pollen and spores within the soil solum. Hypotheses regarding the origin of pollen and the mechanisms of its movement within soil bodies are also advanced. Pollen downwash within the mineral soil seems to be very slow and confined to the uppermost porous and most homogenized part of the solum. The predominance of non-arboreal pollen at depth was believed to be a result of deposition with the loess parent material. High arboreal pollen frequencies in the upper horizons coupled with increases in non-arboreal types at depth indicate gradual ongoing mixing from the present vegetation into the soil. 相似文献