全文获取类型
收费全文 | 434篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 33篇 |
地球物理 | 130篇 |
地质学 | 161篇 |
海洋学 | 39篇 |
天文学 | 67篇 |
综合类 | 2篇 |
自然地理 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 38篇 |
2012年 | 20篇 |
2011年 | 25篇 |
2010年 | 23篇 |
2009年 | 30篇 |
2008年 | 20篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 6篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1974年 | 4篇 |
1946年 | 1篇 |
排序方式: 共有463条查询结果,搜索用时 31 毫秒
51.
Mariachiara Caschetto Maurizio Barbieri Diana M. P. Galassi Lucia Mastrorillo Sergio Rusi Fabio Stoch Alessia Di Cioccio Marco Petitta 《Environmental Earth Sciences》2014,71(4):1791-1807
Many rivers worldwide are undergoing severe man-induced alterations which are reflected also in changes of the degree of connectivity between surface waters and groundwater. Pollution, irrigation withdrawal, alteration of freshwater flows, road construction, surface water diversion, soil erosion in agriculture, deforestation and dam building have led to some irreversible species losses and severe changes in community composition of freshwater ecosystems. Taking into account the impact of damming and flow diversion on natural river discharge, the present study is aimed at (i) evaluating the effects of anthropogenic changes on groundwater/surface water interactions; (ii) analyzing the fate of nitrogenous pollutants at the floodplain scale; and (iii) describing the overall response of invertebrate assemblages to such changes. Hydrogeological, geochemical and isotopic data revealed short- and long-term changes in hydrology, allowing the assessment of the hydrogeological setting and the evaluation of potential contamination by nitrogen compounds. Water isotopes allowed distinguishing a shallow aquifer locally fed by zenithal recharge and river losses, and a deeper aquifer/aquitard system fed by surrounding carbonate aquifers. This system was found to retain ammonium and, through the shallow aquifer, release it in surface running waters via the hyporheic zone of the riverbed. All these factors influence river ecosystem health. As many environmental drivers entered in action offering a multiple-component artificial environment, a clear relationship between river flow alteration and benthic and hyporheic invertebrate diversity was not found, being species response driven by the combination of three main stressors: ammonium pollution, man-induced changes in river morphology and altered discharge regime. 相似文献
52.
We constrain the properties of the spotted regions on the photosphere of the active late-type star DX Leonis by comparing the observed amplitudes of light and color variations with synthetic amplitudes obtained by means of Dorren's spot model and computed for a grid of values of spot temperatures, areas and latitudes. 相似文献
53.
54.
Sergio Torres 《Astrophysics and Space Science》1994,214(1-2):115-126
55.
We present a study of the vertical structure of clouds and hazes in the upper atmosphere of Saturn's Southern Hemisphere during 1994-2003, about one third of a Saturn year, based on Hubble Space Telescope images. The photometrically calibrated WFPC2 images cover the spectral region between the near-UV (218-255 nm) and the near-IR (953-1042 nm), including the 890 nm methane band. Using a radiative transfer code, we have reproduced the observed center-to-limb variations in absolute reflectivity at selected latitudes which allowed us to characterize the vertical structure of the entire hemisphere during this period. A model atmosphere with two haze layers has been used to study the variation of hazes with latitude and to characterize their temporal changes. Both hazes are located above a thick cloud, putatively composed of ammonia ice. An upper thin haze in the stratosphere (between 1 and 10 mbar) is found to be persistent and formed by small particles (radii ∼0.2 μm). The lower thicker haze close to the tropopause level shows a strong latitudinal dependence in its optical thickness (typically τ∼20-40 at the equator but τ∼5 at the pole, at 814 nm). This tropospheric haze is blue-absorbent and extends from 50 to 100 mbar to about ∼400 mbar. Both hazes show temporal variability, but at different time-scales. First, there is a tendency for the optical thickness of the stratospheric haze to increase at all latitudes as insolation increases. Second, the tropospheric haze shows mid-term changes (over time scales from months to 1-2 years) in its optical thickness (typically by a factor of 2). Such changes always occur within a rather narrow latitude band (width ∼5-10°), affecting almost all latitudes but at different times. Third, we detected a long-term (∼10 year) decrease in the blue single-scattering albedo of the tropospheric haze particles, most intense in the equatorial and polar areas. Long-term changes follow seasonal insolation variations smoothly without any apparent delay, suggesting photochemical processes that affect the particles optical properties as well as their size. In contrast, mid-term changes are sudden and show various time-scales, pointing to a dynamical origin. 相似文献
56.
57.
58.
P.J. Arango A. Devia A.F. Rojas C.A. Peña J.A. Ortiz E. Restrepo 《Astrophysics and Space Science》1997,256(1-2):517-521
We have been studying direct current glow discharges aiming at the production of different paint of coatings on steel substrates. In a set of preliminary experiments, long lasting (hours) discharges performed in a Nitrogen atmosphere between a stell anode (holding the substrates) and a titanium cathode separated by a small gap (few mm) produced very thin coatings of the substrates whose colour depend on the parameter of (interelectrodes gap, gas pressure, discharge current and time duration). In some conditions, the coatings showed a golden colour, typical of the Nti compound. A discussion of the results is given. 相似文献
59.
Sergio Torres 《Astrophysics and Space Science》1995,228(1-2):309-312
60.
The paper describes the design and the realization of a multiple-function photoelectric photometer made by Trieste Observatory
for Torino Observatory. The system design shows a two-beam, sequential multiband photon counting and analog photoelectric
photometer configuration based on a PDP8/E computer for the control and data acquisition and elaboration. The actual realization
of the system and the use of it in the one-beam configuration operating now at torino Observatory shows the advantages of
such a solution and the easiness in modifying and determining the system functions by software programs rather than by hardware
specials.
Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. The
realization of the machine was fully supported by Torino Observatory. Trieste Observatory-Instruments and Data Processing
Group (5/76). 相似文献