全文获取类型
收费全文 | 636篇 |
免费 | 38篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 31篇 |
地球物理 | 177篇 |
地质学 | 232篇 |
海洋学 | 55篇 |
天文学 | 138篇 |
综合类 | 4篇 |
自然地理 | 20篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 39篇 |
2015年 | 31篇 |
2014年 | 34篇 |
2013年 | 37篇 |
2012年 | 22篇 |
2011年 | 31篇 |
2010年 | 30篇 |
2009年 | 41篇 |
2008年 | 29篇 |
2007年 | 48篇 |
2006年 | 34篇 |
2005年 | 26篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 22篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1970年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有675条查询结果,搜索用时 518 毫秒
81.
82.
83.
Sergio Torres 《Astrophysics and Space Science》1995,228(1-2):309-312
84.
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
85.
Philipp Matzneller Francesca Ventura Nicola Gaspari Paola Rossi Pisa 《Climatic change》2010,100(3-4):717-731
Agriculture is highly exposed to climate change, as farming activities directly depend on climatic conditions. Knowledge of the extent of such change and of related phenomena will help to answer the questions posed by society about adaptation strategies. The global situation is well described by the Fourth IPCC assessment report (IPCC 2007), but local studies are important to understand the impact and the priorities to adopt in adaptation strategies. In this study a historical set of meteorological data, collected during the period 1952–2007 at the University of Bologna (Italy) agrometeorological station, was analysed. Several indexes, such as Frost Severity Index, number of hot days, number of rainy days, etc., were calculated, and their trends in time were analysed. The results show a scenario of increasing temperatures and evapotranspiration, a decrease in rainy days and a deepening of the watertable. The effect of these changes on agriculture will be a decrease in water availability, an increase in heat stress in plants and an increase in drought risk. 相似文献
86.
The overall change of NEO spin rate due to planetary encounters and YORP is evaluated by using a Monte Carlo model. A large sample of test objects mimicking a source population is evolved over a timescale comparable with the Solar System age until they reach a steady state spin distribution that should reproduce the current NEO distribution. The spin change due to YORP is computed for each body according to a simplified model based on Scheeres [Scheeres, D.J., 2007a. Icarus 188, 430-450].The steady state cumulative distribution of NEO spin rates obtained from our simulation nicely reproduces the observed one, once our results are biased to match the diameter distribution of the sample of objects included in the observational database. The excellent agreement strongly suggests that YORP is responsible for the concentration of spin at low rotation rates. In fact, in the absence of YORP the steady state population significantly deviates from the observed one. The spin evolution due to YORP is also so rapid for NEOs that the initial rotation rate distribution of any source population is quickly relaxed to that of the observed population. This has profound consequences for the study of NEO origin since we cannot trace the sources of NEOs from their rotation rate only. 相似文献
87.
Elena M. Rossi † Mitchell C. Begelman 《Monthly notices of the Royal Astronomical Society》2009,392(4):1451-1455
When double neutron star or neutron star–black hole binaries merge, the final remnant may comprise a central solar-mass black hole surrounded by a ∼0.01–0.1 M⊙ torus. The subsequent evolution of this disc may be responsible for short γ-ray bursts (SGRBs). A comparable amount of mass is ejected into eccentric orbits and will eventually fallback to the merger site after ∼0.01 s. In this paper, we investigate analytically the fate of the fallback matter, which may provide a luminous signal long after the disc is exhausted. We find that matter in the eccentric tail returns at a super-Eddington rate and eventually (≳0.1 s) is unable to cool via neutrino emission and accrete all the way to the black hole. Therefore, contrary to previous claims, our analysis suggests that fallback matter is not an efficient source of late-time accretion power and unlikely to cause the late-flaring activity observed in SGRB afterglows. The fallback matter rather forms a radiation-driven wind or a bound atmosphere. In both the cases, the emitting plasma is very opaque and photons are released with a degraded energy in the X-ray band. We therefore suggest that compact binary mergers could be followed by an 'X-ray renaissance', as late as several days to weeks after the merger. This might be observed by the next generation of X-ray detectors. 相似文献
88.
Graziano Rossi Ravi K. Sheth Changbom Park Carlos Hernández-Monteagudo 《Monthly notices of the Royal Astronomical Society》2009,399(1):304-316
We present measurements of the clustering of hot and cold patches in the microwave background sky as measured from the Wilkinson Microwave Anisotropy Probe 5-year data. These measurements are compared with theoretical predictions which assume that the cosmological signal obeys Gaussian statistics. We find significant differences from the simplest Gaussian-based prediction. However, the measurements are sensitive to the fact that the noise is spatially inhomogeneous (e.g. because different parts of the sky were observed for different lengths of time). We show how to account for this spatial inhomogeneity when making predictions. Differences from the Gaussian-based expectation remain even after this more careful accounting of the noise. In particular, we note that hot and cold pixels cluster differently within the same temperature thresholds at few-degree scales. While these findings may indicate primordial non-Gaussianity, we discuss other plausible explanations for these discrepancies. In addition, we find some deviations from Gaussianity at sub-degree scales, especially in the W band, whose origin may be associated with extragalactic dust emission. 相似文献
89.
We present moderate resolution CCD spectra and R photometry for seven KP2001 stars. We revised the spectral classification of the stars in the range λλ4000−8700? . Our photometric
data confirmed the behavior of the light curves downloaded from the NSVS (Northern Sky Variability Survey) database. For KP2001-32,
presented as a Mira-type variable in NSVS, we estimated absolute bolometric M
b and K-band M
K
magnitudes as well as the distance using the period-luminosity relations. We also estimated the mass loss rate using the
calibration relations between mass loss rate and K - [12] index. From the position in infrared color-color diagrams, we confirmed the photometric classification of KP2001-221
as a semiregular variable, based on the light curve of the NSVS database. For the N-type carbon star KP2001-77 we estimated
distance and absolute magnitude M
K
using different calibration methods. For the remaining four objects we derived the absolute magnitudes and distances using
our CCD spectra and published JHK
S
magnitudes. We discuss the nature of these objects on the basis of the obtained results. 相似文献
90.