全文获取类型
收费全文 | 53067篇 |
免费 | 560篇 |
国内免费 | 1234篇 |
专业分类
测绘学 | 1975篇 |
大气科学 | 3750篇 |
地球物理 | 9680篇 |
地质学 | 22485篇 |
海洋学 | 3948篇 |
天文学 | 8403篇 |
综合类 | 2220篇 |
自然地理 | 2400篇 |
出版年
2022年 | 297篇 |
2021年 | 455篇 |
2020年 | 510篇 |
2019年 | 556篇 |
2018年 | 5744篇 |
2017年 | 4972篇 |
2016年 | 3669篇 |
2015年 | 772篇 |
2014年 | 1118篇 |
2013年 | 1709篇 |
2012年 | 2112篇 |
2011年 | 4070篇 |
2010年 | 3245篇 |
2009年 | 3795篇 |
2008年 | 3176篇 |
2007年 | 3688篇 |
2006年 | 1352篇 |
2005年 | 946篇 |
2004年 | 1098篇 |
2003年 | 1058篇 |
2002年 | 934篇 |
2001年 | 665篇 |
2000年 | 618篇 |
1999年 | 474篇 |
1998年 | 500篇 |
1997年 | 453篇 |
1996年 | 391篇 |
1995年 | 350篇 |
1994年 | 378篇 |
1993年 | 294篇 |
1992年 | 297篇 |
1991年 | 286篇 |
1990年 | 322篇 |
1989年 | 220篇 |
1988年 | 225篇 |
1987年 | 268篇 |
1986年 | 209篇 |
1985年 | 314篇 |
1984年 | 276篇 |
1983年 | 258篇 |
1982年 | 275篇 |
1981年 | 223篇 |
1980年 | 261篇 |
1979年 | 195篇 |
1978年 | 211篇 |
1977年 | 165篇 |
1976年 | 169篇 |
1975年 | 172篇 |
1974年 | 167篇 |
1973年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Long-term observational data (1992?C2009) on heavy metal (Cu, Zn, Pb, Cr, Ni, V, Mo, Co, Fe, and Mn) content of different links in the Ivankovo Reservoir ecosystem are used to consider the regularities in the distribution and behavior of heavy metals in the system anthropogenic pollution sources-reservoir and its drainage area, thus enabling the assessment of the pollution level of the Volga Source of water supply to Moscow. 相似文献
122.
N. I. Bondar’ 《Astronomy Reports》2017,61(2):130-137
Photometric data covering 1994–2009, obtained at the Crimean Astrophysical Observatory or retrieved from the ASAS and SuperWASP catalogs, were used to analyze the brightness variations of the rapidly rotating star V833 Tau, whose activity level is close to saturation. Combined with previously published results, these data represent for the first time all stages in the development of the star’s 19- year activity cycle. The photometric period and rotational-modulation amplitude for different epochs are determined, and the qualitative pattern of the spots is considered. The photometric period is close to the orbital period, but always exceeds it, indicating that surface inhomogeneities are located far from the equatorial plane. With the high spottedness of the star, reaching 28% at the cycle maximum, the rotationalmodulation amplitude is 0.05?0.1 m , and increases during the growth and decline phases of the 19-year cycle. The rotational modulation is due to spots with higher latitudes than in the case of the Sun, and concentrating on active longitudes. 相似文献
123.
M.?A.?LevitanEmail author T.?N.?Gelvi K.?V.?Syromyatnikov K.?D.?Chekan 《Geochemistry International》2018,56(4):304-317
Lithofacies zoning is described for the first time for the Neo- and Eopleistocene of the Bering Sea. Four lithofacies sedimentation zones are distinguished: (I) terrigenous; (II) siliceous–terrigenous; (III) siliceous, and (IV) volcanoterrigenous ones. Corresponding maps were treated using Ronov volumetric method to quantify sedimentation parameters for distinguished lithofacies zones (subzones) and types of Pleistocene sediments. It was revealed that terrigenous sediments predominate over other sediments. Accumulation of the terrigenous sediments was more intense (by 1.4 times) in the Neopleistocene than in the Eopleistocene. The sedimentation rate of siliceous sediments of the Bowers Ridge in the Eopleistocene was two times higher than in the Neopleistocene. 相似文献
124.
125.
126.
Artificial light at night: implications for early life stages development in four temperate freshwater fish species 总被引:1,自引:0,他引:1
Anika Brüning Franz Hölker Christian Wolter 《Aquatic Sciences - Research Across Boundaries》2011,73(1):143-152
Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now
increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example
hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends
farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal
trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction.
To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination
(LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments.
In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub.
Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching.
The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach.
In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking
the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase
in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has
not been identified on early life stages. 相似文献
127.
128.
Soil sediment samples of 10 layers with a spacing of 10 cm each were collected in different floodplain zones adjacent to Huolin
River in the Xianghai Nature Reserve, and contents of total N, total P and organic matters were analyzed. The results showed
that contents of total N, total P and organic matters were generally decreasing with the increase of distance from sample
locations to the river channel, and contents of the three items were generally higher in the upper soil layer than that in
the lower soil layer. The content variations displayed how flooding functions influenced nutrient matter content variations
in floodplain soils since the flood inundation frequencies of the sample locations varied. The correlation analysis displayed
that there were remarkable relativities between total N, total P and organic matters within definite spatial distance from
the Huolin River channel. 相似文献
129.
Karaevskaya E. S. Demidov N. E. Kazantsev V. S. Elizarov I. M. Kaloshin A. G. Petrov A. L. Karlov D. S. Schirrmeister L. Belov A. A. Wetterich S. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(10):1254-1270
Izvestiya, Atmospheric and Oceanic Physics - The archaeal composition of permafrost samples taken during the drilling of frozen marine sediments in the area of the Barentsburg coal mine on the east... 相似文献
130.
A field experiment was conducted from 2 May 2010 to 1 May 2012 in the Gurbantunggut Desert, the second largest desert in China, to investigate saltation activity and its threshold velocity, and their relations with atmospheric and soil conditions. The results showed that saltation activity occurred more frequently during 08:00–20:00 Local Standard Time in spring and summer, with air temperatures between 20.0 and 29.0 °C, water vapor pressures between 0.6 and 0.9 kPa, soil temperatures between 25.0 and 30.0 °C, and a soil moisture lower than 0.04 m3/m3. At 2 m height, the saltation threshold velocity varied between 11.1 and 13.9 m/s, with a mean of 12.5 m/s. Threshold velocity showed clear seasonal variations in the following sequence: spring (11.7 m/s) < autumn (12.7 m/s) < summer (13.6 m/s). Affected by soil conditions, aeolian sand transport was weak, with an average annual aeolian sand that transported across a section (1.0 m × 2.0 m) of less than 6.0 kg. 相似文献