全文获取类型
收费全文 | 772篇 |
免费 | 24篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 71篇 |
地球物理 | 213篇 |
地质学 | 212篇 |
海洋学 | 65篇 |
天文学 | 174篇 |
综合类 | 2篇 |
自然地理 | 49篇 |
出版年
2021年 | 12篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 43篇 |
2012年 | 13篇 |
2011年 | 37篇 |
2010年 | 30篇 |
2009年 | 37篇 |
2008年 | 35篇 |
2007年 | 33篇 |
2006年 | 25篇 |
2005年 | 30篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 3篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 16篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有801条查询结果,搜索用时 31 毫秒
91.
Bas van Geel R. Dale Guthrie Jens G. Altmann Peter Broekens Ian D. Bull Fiona L. Gill Boris Jansen Aline M. Nieman Barbara Gravendeel 《Quaternary Science Reviews》2011,30(17-18):2289-2303
Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae, Artemisia and other light-demanding taxa, indicating an open, treeless landscape (‘mammoth steppe’). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid rbcL gene and trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies. 相似文献
92.
A. Smith R. W. Atkins S. Bradbury O. Celik Y. C. K. Chow P. Cogan C. Dowdall S. J. Fegan P. Fortin D. Gall G. H. Gillanders J. Grube K. J. Gutierrez T. A. Hall D. Hanna J. Holder D. Horan S. B. Hughes T. B. Humensky I. Jung P. Kaaret G. Kenny M. Kertzman D. B. Kieda A. Konopelko H. Krawczynski F. Krennrich M. J. Lang S. Le Bohec G. Maier J. Millis P. Moriarty R. A. Ong J. S. Perkins K. Ragan G. H. Sembroski J. A. Toner L. Valcarcel V. V. Vassiliev R. G. Wagner S. P. Wakely T. C. Weekes R. J. White D. A. Williams 《Astrophysics and Space Science》2007,309(1-4):299-303
In this paper we present the results of the past two years observations on the galactic microquasar LS I +61 303 with the
Whipple 10 m gamma-ray telescope. The recent MAGIC detection of the source between 200 GeV and 4 TeV suggests that the source
is periodic with very high energy (VHE) gamma-ray emission linked to its orbital cycle. The entire 50-hour data set obtained
with Whipple from 2004 to 2006 was analyzed with no reliable detection resulting. The upper limits obtained in the 2005–2006
season covered several of the same epochs as the MAGIC Telescope detections, albeit with lower sensitivity. Upper limits are
placed on emission during the orbital phases of 0→0.1 and 0.8→1, phases which are not included in the MAGIC data set.
相似文献
93.
David W. Hughes 《Monthly notices of the Royal Astronomical Society》2001,326(2):515-523
The mass distribution and perihelion distribution of long-period comets are re-assessed. The mass distribution index is found to be 1.598±0.016 , indicating that the distribution is somewhat steeper than was obtained by previous analyses of an amalgam of all the available historical data. The number of long-period comets that have orbital perihelion distances, q , that fall in a specific q to q +d q range is found to be independent of q . It is also noted that the flux of long-period comets to the inner Solar system has remained constant throughout recorded history.
The number of long-period comets, , per 1-au interval of perihelion distance, per year, brighter than H , entering the inner Solar system is found to be given by log10 =−2.607+0.359 H . It is therefore estimated that, for example, about 0.5, 30 and 2000 long-period comets with absolute magnitudes brighter than 0, 5 and 10 respectively pass the Sun on orbits with perihelion distances less than 2.0 au, every century. 相似文献
The number of long-period comets, , per 1-au interval of perihelion distance, per year, brighter than H , entering the inner Solar system is found to be given by log
94.
E. N. Archibald J. S. Dunlop D. H. Hughes S. Rawlings S. A. Eales R. J. Ivison 《Monthly notices of the Royal Astronomical Society》2001,323(2):417-444
We present the results of the first major systematic submillimetre survey of radio galaxies spanning the redshift range 1< z <5. The primary aim of this work is to elucidate the star formation history of this sub class of elliptical galaxies by tracing the cosmological evolution of dust mass. Using SCUBA on the JCMT, we have obtained 850-μm photometry of 47 radio galaxies to a consistent rms depth of 1 mJy, and have detected dust emission in 14 cases. The radio galaxy targets have been selected from a series of low-frequency radio surveys of increasing depth (3CRR, 6CE, etc.), in order to allow us to separate the effects of increasing redshift and increasing radio power on submillimetre luminosity. Although the dynamic range of our study is inevitably small, we find clear evidence that the typical submillimetre luminosity (and hence dust mass) of a powerful radio galaxy is a strongly increasing function of redshift; the detection rate rises from ≃15 per cent at z <2.5 to ≳75 per cent at z >2.5, and the average submillimetre luminosity rises at a rate ∝(1+ z )3 out to z ≃4. Moreover, our extensive sample allows us to argue that this behaviour is not driven by underlying correlations with other radio galaxy properties such as radio power, radio spectral index, or radio source size/age. Although radio selection may introduce other more subtle biases, the redshift distribution of our detected objects is in fact consistent with the most recent estimates of the redshift distribution of comparably bright submillimetre sources discovered in blank field surveys. The evolution of submillimetre luminosity found here for radio galaxies may thus be representative of massive ellipticals in general. 相似文献
95.
96.
Ben B. Balsley Dale A. Lawrence Ronald F. Woodman David C. Fritts 《Boundary-Layer Meteorology》2013,147(1):165-178
We report results of preliminary high-resolution in situ atmospheric measurements through the boundary layer and lower atmosphere over the southern coast of Perú. This region of the coast is of particular interest because it lies adjacent to the northern coastal edge of the sub-tropical south-eastern Pacific, a very large area of ocean having a persistent stratus deck located just below the marine boundary layer (MBL) inversion. Typically, the boundary layer in this region during winter is topped by a quasi-permanent, well-defined, and very large temperature gradient. The data presented herein examine fine-scale details of the coastal atmosphere at a point where the edge of this MBL extends over the coastline as a result of persistent onshore flow. Atmospheric data were gathered using a recently-developed in-house constructed, GPS-controlled, micro-autonomous-vehicle aircraft (the DataHawk). Measured quantities include high-resolution profiles of temperature, wind, and turbulence structure from the surface to 1,300 m. 相似文献
97.
P.D.Hughes P.L.Gibbard J.C.Woodward 《《幕》》2005,28(2):85-92
Glacial deposits in locally-glaciated mountain regions are often expressed through their surface form and the study of these deposits constitutes a major branch of geomorphology. Studies of glacial depositional records in mountain areas have often neglected formal stratigraphical procedure resulting in an ad hoc development of quasi-stratigraphical nomenclature. Here, a formal stratigraphical procedure is recommended, since this enables a systematic approach to the subdivision of glacial deposits in mountain regions. Moreover, such an approach facilitates, in some instances, the development of a formal chronostratigraphy that can be compared to regional and global geological time scales. This is important in locally-glaciated mountain regions where glacial deposits represent one of the most important records of cold stage environments. Given that glacial landforms represent a key component of the Quaternary record, maintaining a formal link between geomorphological and geological stratigraphical procedure is a fundamental requirement of a consistent and comparable stratigraphical framework. 相似文献
98.
We present near-IR spectra of solid CO2 in H2O and CH3OH, and find they are significantly different from that of pure solid CO2. Peaks not present in either pure H2O or pure CO2 spectra become evident when the two are mixed. First, the putative theoretically forbidden CO2 (2ν3) overtone near 2.134 μm (4685 cm−1), that is absent from our spectrum of pure solid CO2, is prominent in the spectra of H2O/CO2=5 and 25 mixtures. Second, a 2.74-μm (3650 cm−1) dangling OH feature of H2O (and a potentially related peak at 1.89 μm) appear in the spectra of CO2-H2O ice mixtures, but are probably not diagnostic of the presence of CO2. Other CO2 peaks display shifts in position and increased width because of intermolecular interactions with H2O. Warming causes some peak positions and profiles in the spectrum of a H2O/CO2=5 mixture to take on the appearance of pure CO2. Absolute strengths for absorptions of CO2 in solid H2O are estimated. Similar results are observed for CO2 in solid CH3OH. Since the CO2 (2ν3) overtone near 2.134 μm (4685 cm−1) is not present in pure CO2 but prominent in mixtures, it may be a good observational (spectral) indicator of whether solid CO2 is a pure material or intimately mixed with other molecules. These observations may be applicable to Mars polar caps as well as outer Solar System bodies. 相似文献
99.
Evapotranspiration was studied at a salt marsh site in the Hunter River estuary, NSW, Australia, during 1996–8. Estimates of actual evapotranspiration (Ea) were obtained for three sites using the eddy correlation method. These values were compared with results obtained with the Penman and Penman–Monteith equations, and with pan evaporation. The Penman–Monteith method was found to be most reliable in estimating daily and hourly evapotranspiration. Surface resistance values averaging 12 s m?1 were derived from the eddy correlation estimates. Recent tidal flooding and rainfall were found to decrease surface resistance and increase Ea/Ep ratios. Estimates of evapotranspiration obtained using the Penman–Monteith method were shown to be sensitive to changes in surface resistance, canopy height and the method used to estimate net radiation from incoming solar radiation. These results underline the importance of accurately estimating such parameters based on site‐specific data rather than relying on empirical equations, which are derived primarily for crops and forests. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献