全文获取类型
收费全文 | 31324篇 |
免费 | 522篇 |
国内免费 | 964篇 |
专业分类
测绘学 | 1592篇 |
大气科学 | 2432篇 |
地球物理 | 6878篇 |
地质学 | 13875篇 |
海洋学 | 1544篇 |
天文学 | 2727篇 |
综合类 | 2179篇 |
自然地理 | 1583篇 |
出版年
2022年 | 51篇 |
2021年 | 140篇 |
2020年 | 147篇 |
2019年 | 125篇 |
2018年 | 4920篇 |
2017年 | 4230篇 |
2016年 | 2947篇 |
2015年 | 538篇 |
2014年 | 470篇 |
2013年 | 497篇 |
2012年 | 1336篇 |
2011年 | 3080篇 |
2010年 | 2294篇 |
2009年 | 2660篇 |
2008年 | 2197篇 |
2007年 | 2578篇 |
2006年 | 328篇 |
2005年 | 436篇 |
2004年 | 626篇 |
2003年 | 593篇 |
2002年 | 416篇 |
2001年 | 196篇 |
2000年 | 168篇 |
1999年 | 116篇 |
1998年 | 148篇 |
1997年 | 100篇 |
1996年 | 66篇 |
1995年 | 53篇 |
1994年 | 71篇 |
1993年 | 58篇 |
1992年 | 65篇 |
1991年 | 49篇 |
1990年 | 72篇 |
1989年 | 52篇 |
1988年 | 41篇 |
1987年 | 43篇 |
1986年 | 39篇 |
1985年 | 45篇 |
1984年 | 44篇 |
1983年 | 51篇 |
1982年 | 39篇 |
1981年 | 54篇 |
1980年 | 55篇 |
1979年 | 44篇 |
1978年 | 36篇 |
1976年 | 34篇 |
1975年 | 34篇 |
1974年 | 33篇 |
1973年 | 37篇 |
1971年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Ken Ebisawa Aya Kubota Tsunefumi Mizuno Piotr Życki 《Astrophysics and Space Science》2001,276(1):11-14
The Ultra-luminous Compact X-ray Sources (ULXs)in nearby spiral galaxies and the Galactic super-luminaljet sources sharethe common spectral characteristic that they haveextremely high disk temperatures which cannot be explainedin the framework of the standard accretion disk modelin the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed `too hot' accretion disk spectra.We found that the Kerr disk spectrum becomes significantly hardercompared to the Schwarzschild disk only when the disk is highlyinclined.For super-luminal jet sources, which are known to beinclined systems, the Kerr disk model may thuswork if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic,as is is highly unlikely that their accretion disks are preferentiallyinclined. 相似文献
32.
Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms 总被引:1,自引:0,他引:1
In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices.
This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts
their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature,
surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results
show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive
accuracy error up to 35%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
33.
Francesca Matteucci Antonio Pipino 《Monthly notices of the Royal Astronomical Society》2005,357(2):489-496
We have studied the effects of a hypothetical initial generation containing very massive stars [ M > 100 M⊙ , pair-creation supernovae] on the chemical and photometric evolution of elliptical galaxies. To this purpose, we have computed the evolution of a typical elliptical galaxy with luminous mass of the order of 1011 M⊙ and adopted chemical evolution models already tested to reproduce the main features of ellipticals. We have tested several sets of yields for very massive zero-metallicity stars: these stars should produce quite different amounts of heavy elements than lower-mass stars. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results are at variance with the main observational constraints of ellipticals such as the average [〈α/ Fe〉* ] ratio in stars and the integrated colours. Therefore, we conclude that if Population III stars ever existed they must have been present for a very short period of time and their effects on the following evolution of the parent galaxy must have been negligible. This effect is minimum if a more realistic model with initial infall of gas rather than the classic monolithic model is adopted. Ultimately, we conclude that there is no need to invoke a generation of very massive stars in ellipticals to explain their chemical and photometric properties. 相似文献
34.
35.
Simulation of double cold cores of the 35°N section in the Yellow Sea with a wave-tide-circulation coupled model 总被引:1,自引:0,他引:1
Based on the MASNUM wave-tide-circulation coupled numerical model, the temperature structure along 35°N in the Yellow Sea
was simulated and compared with the observations. One of the notable features of the temperature structure along 35°N section
is the double cold cores phenomena during spring and summer. The double cold cores refer to the two cold water centers located
near 122°E and 125°E from the depth of 30m to bottom. The formation, maintenance and disappearance of the double cold cores
are discussed. At least two reasons make the temperature in the center (near 123°E) of the section higher than that near the
west and east shores in winter. One reason is that the water there is deeper than the west and east sides so its heat content
is higher. The other is invasion of the warm water brought by the Yellow Sea Warm Current (YSWC) during winter. This temperature
pattern of the lower layer (from 30m to bottom) is maintained through spring and summer when the upper layer (0 to 30m) is
heated and strong thermocline is formed. Large zonal span of the 35°N section (about 600 km) makes the cold cores have more
opportunity to survive. The double cold cores phenomena disappears in early autumn when the west cold core vanishes first
with the dropping of the thermocline position.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
36.
Vladimír Skalský 《Astrophysics and Space Science》1993,201(1):3-14
(a) Hubble's discovery of the expansion of the Universe makes it possible to choose unambiguously from the models described by Friedmann's equations of universe dynamics. (b) From the present temperature of the cosmic microwave background radiation, the specific entropy in the matter era and the model properties of the expansive nondecelerative universe, we can determine the present parameters of our Universe with deviations smaller than 2.2%. 相似文献
37.
María Luisa García Vargas Angeles Díaz Roberto Terlevich Elena Terlevich 《Astrophysics and Space Science》1993,205(1):77-84
In the frame of the Starburst Model, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed emission-line spectrum and the UV-optical Spectral Energy Distribution of the Seyfert 2 galaxies and LINERs. We apply the results of our models to three objects: NGC 5506, NGC 5643 and Mk 348. 相似文献
38.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献
39.
The present paper reports 9 species of pontoniine shrimps collected from Hainan IS-land ,South China Sea ,by the Joint Chinese-German Marine Biology Expeditions,in which Peri-climenaeus arabicus (Calman,1939) and Periclimenaeus hecate (Nobili,1904) are recorded for the first time from Hainan Island. 相似文献
40.
We present a new model for the chemical evolution of elliptical galaxies taking into account SN feedback, detailed nucleosynthesis
and galactic winds. We discuss the effect of galactic winds on the chemical enrichment of the ICM and compute the energy per
particle injected by the galaxies into the ICM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献