全文获取类型
收费全文 | 44573篇 |
免费 | 839篇 |
国内免费 | 304篇 |
专业分类
测绘学 | 964篇 |
大气科学 | 3032篇 |
地球物理 | 8999篇 |
地质学 | 15974篇 |
海洋学 | 4011篇 |
天文学 | 9691篇 |
综合类 | 115篇 |
自然地理 | 2930篇 |
出版年
2022年 | 284篇 |
2021年 | 510篇 |
2020年 | 578篇 |
2019年 | 674篇 |
2018年 | 1174篇 |
2017年 | 1158篇 |
2016年 | 1294篇 |
2015年 | 741篇 |
2014年 | 1206篇 |
2013年 | 2211篇 |
2012年 | 1415篇 |
2011年 | 1929篇 |
2010年 | 1687篇 |
2009年 | 2131篇 |
2008年 | 1931篇 |
2007年 | 1959篇 |
2006年 | 1798篇 |
2005年 | 1286篇 |
2004年 | 1306篇 |
2003年 | 1293篇 |
2002年 | 1182篇 |
2001年 | 975篇 |
2000年 | 926篇 |
1999年 | 816篇 |
1998年 | 817篇 |
1997年 | 788篇 |
1996年 | 652篇 |
1995年 | 641篇 |
1994年 | 582篇 |
1993年 | 518篇 |
1992年 | 489篇 |
1991年 | 479篇 |
1990年 | 480篇 |
1989年 | 434篇 |
1988年 | 418篇 |
1987年 | 446篇 |
1986年 | 462篇 |
1985年 | 563篇 |
1984年 | 599篇 |
1983年 | 612篇 |
1982年 | 545篇 |
1981年 | 507篇 |
1980年 | 480篇 |
1979年 | 463篇 |
1978年 | 422篇 |
1977年 | 413篇 |
1976年 | 366篇 |
1975年 | 376篇 |
1974年 | 362篇 |
1973年 | 399篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
951.
952.
F. A. Lopes G. Michard M. Poulin A. Roué F. Prévot D. Jézéquel E. Viollier 《Aquatic Geochemistry》2010,16(4):587-610
A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing. 相似文献
953.
954.
G. L. Evans P. J. le B. Williams E. G. Mitchelson-Jacob 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1159-1168
The trend in Irish Sea nutrient concentrations over the last four decades has been considered to reflect changes in anthropogenic loading. Comparison of a long-term database for the Menai Strait, North Wales, with an established historic data set for the Cypris station, Isle of Man, indicates that climate also has a significant influence on observations of nutrient concentrations. Data are presented detailing long-term shifts in nitrate, phosphate and silicate measurements since the 1960s at these two fixed sampling sites in the Irish Sea. Broad systematic changes observed in all three nutrients over the decades show a rise from the 1960s through to the 1980s, followed generally by an overall decline in the 1990s. Decadal-scale salinity changes occur in the opposite sense to nutrient changes. Anthropogenic inputs from freshwater cannot fully account for observed nutrient trends, neither is there evidence for shifts in nutrient concentrations in oceanic waters over the past four decades. Climatically forced movement in the geographical position of the freshwater/seawater mixing zone over a decadal time scale could, however, give rise to the observed shifts in nutrient concentration and salinity. This cannot alter nutrient concentration and salinity per se, but causes the measurements taken at fixed sampling sites to fluctuate inversely over this time scale. It is concluded that there is complex interplay between anthropogenic loading and climate affecting the distribution of nutrients in the Irish Sea. 相似文献
955.
956.
The autonomous underwater glider "Spray" 总被引:4,自引:0,他引:4
A small (50-kg, 2-m long) underwater vehicle with operating speeds of 20-30 cm/s and ranges up to 6000 km has been developed and field tested. The vehicle is essentially an autonomous profiling float that uses a buoyancy engine to cycle vertically and wings to glide horizontally while moving up and down. Operational control and data relay is provided by GPS navigation and two-way communication through ORBCOMM low-Earth-orbit satellites. Missions are envisioned with profile measurements repeated at a station or spaced along a transect. The initial instrument complement of temperature, conductivity, and pressure sensors was used to observe internal waves and tides in the Monterey underwater canyon 相似文献
957.
958.
This work aims at contributing to improve knowledge on transient asymmetric flooding through theoretical and experimental research. First, a time domain theoretical model of ship motions and flooding is described. Results from experimental work are presented evidencing that transient asymmetric flooding may cause the capsizing of a Ro-Ro shaped barge. The theoretical model is used to predict the capsize of the Ro-Ro shaped barge. Reasonable agreement between experimental and theoretical results was found. Finally, a review of the European Gateway accident is given and the theoretical model is applied to the study of this type of accident. The conclusion is that this theoretical model, together with an accurate modelling of the flooding of machinery compartments, reproduces successfully the capsizing of the European Gateway due to transient asymmetric flooding. Therefore, the internal arrangement of Ro-Ro ships should be carefully studied at the design stage in order to avoid this phenomenon. 相似文献
959.
Boon JP van Zanden JJ Lewis WE Zegers BN Goksøyr A Arukwe A 《Marine environmental research》2002,54(3-5):719-724
The short-term effects of the commercial PBDE flame retardant mixtures Penta-BDE and cta-BDE on the expression of cytochrome P450 1A (CYP1A), vitellogenin (Vtg) and zona radiata proteins (Zrp) were investigated in juvenile salmon (Salmo salar). For this purpose, groups of fish were dosed twice (oral intake at days I and 4) with 10 and 50 mg/kg body weight of both commercial mixtures. The fishes were sacrificed at day 7 (n = 5 for each group) and 14 (n = 6 for each group), and blood, liver, fillet, and brain were collected. Blanks and positive controls were also part of the experiment. The expressions of Vtg, Zrp, and CYPIA were measured with several techniques (EROD, ELISA, Western, Northern and Slot Blot). The values in the groups of fish treated with Penta-BDE or Octa-BDE did not significantly differ from the reference group for any of the parameters tested. In contrast, the positive control groups treated with estradiol-17beta for Vtg and Zrp expression, and beta-naphthoflavone for CYP1A expression did show a significant response, indicating the potential sensitivity of the fishes for the parameters measured. Since the results of the chemical analyses showed concentrations of a number of PBDE congeners in liver, fillet, and brain that were about three orders of magnitude above those of fish from the North Sea, it is concluded that the short-term toxicity of both commercial PBDE mixtures for these endpoints was low. 相似文献
960.