全文获取类型
收费全文 | 7408篇 |
免费 | 592篇 |
国内免费 | 182篇 |
专业分类
测绘学 | 281篇 |
大气科学 | 693篇 |
地球物理 | 2494篇 |
地质学 | 2858篇 |
海洋学 | 502篇 |
天文学 | 704篇 |
综合类 | 196篇 |
自然地理 | 454篇 |
出版年
2021年 | 36篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 474篇 |
2017年 | 404篇 |
2016年 | 307篇 |
2015年 | 192篇 |
2014年 | 165篇 |
2013年 | 232篇 |
2012年 | 710篇 |
2011年 | 533篇 |
2010年 | 191篇 |
2009年 | 224篇 |
2008年 | 198篇 |
2007年 | 201篇 |
2006年 | 208篇 |
2005年 | 910篇 |
2004年 | 944篇 |
2003年 | 703篇 |
2002年 | 243篇 |
2001年 | 109篇 |
2000年 | 81篇 |
1999年 | 57篇 |
1998年 | 33篇 |
1997年 | 47篇 |
1996年 | 42篇 |
1995年 | 42篇 |
1994年 | 34篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 41篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 35篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 36篇 |
1984年 | 38篇 |
1983年 | 42篇 |
1982年 | 32篇 |
1981年 | 31篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 25篇 |
1977年 | 34篇 |
1976年 | 34篇 |
1975年 | 29篇 |
1973年 | 21篇 |
1972年 | 22篇 |
1971年 | 18篇 |
排序方式: 共有8182条查询结果,搜索用时 15 毫秒
51.
52.
Kazufumi Takayanagi George T. F. Wong Margaret J. Filardo 《Journal of Oceanography》1989,45(2):129-133
Nitrate reductase activity and the concentrations of selenite and selenate were monitored for six months at the mouth of Chesapeake Bay (USA). A positive correlation was found between nitrate reductase activity and the concentration of selenite, suggesting that selenite may be formed in coastal waters and nitrate reductase may be involved in the process. 相似文献
53.
Brent L. Lewis Pamela D. Holt Steven W. Taylor Steven W. Wilhelm Charles G. Trick Alison Butler George W. Luther III 《Marine Chemistry》1995,50(1-4)
Thermodynamic stability constants have been estimated for the complexation of iron(III) with catecholate-type siderophores isolated from the marine bacterium Alteromonas luteoviolacea and from the marine cyanobacterium Synechococcus sp. PCC 7002. Stability constants were determined utilizing the “chelate scale” of Taylor et al. (1994). The scale is based upon a linear relationship between the reduction potentials and the pH-independent thermodynamic stability constants for known iron(III) complexes. Log K values for the alterobactin B ferric iron complex are 43.6 ± 1.5 at pH 8.2 and 37.6 ± 1.2 at pH 6, consistent with a shift from bis-catecholate to monosalicylate/monocatecholate iron coordination with decreasing pH. Synechococcus isolates PCC 7002 Nos. 1 and 3 formed iron(III) complexes with stability constants of approximately 38.1 ± 1.2 and 42.3 ± 1.5, respectively. The binding strengths of the iron(III) complexes examined in this study are quite high, suggesting that catecholate siderophores may play a role in the solubilization and biological uptake of iron in the marine environment. 相似文献
54.
Size-Fractionated Primary Production Estimated by a Two-Phytoplankton Community Model Applicable to Ocean Color Remote Sensing 总被引:3,自引:0,他引:3
In order to estimate primary production from ocean color satellite data using the Vertical Generalized Production Model (VGPM; Behrenfeld and Falkowski, 1997), we propose a two-phytoplankton community model. This model is based on the two assumptions that changes in chlorophyll concentration result from changes of large-sized phytoplankton abundance, and chlorophyll specific productivity of phytoplankton tends to be inversely proportional to phytoplankton size. Based on the analysis of primary production data, P
opt
B
, which was one parameter in the VGPM, was modeled as a function of sea surface temperature and sea surface chlorophyll concentration. The two-phytoplankton community model incorporated into the VGPM gave good estimates in a relatively high productive area. Size-fractionated primary production was estimated by the two-phytoplankton community model, and P
opt
B
of small-sized phytoplankton was 4.5 times that of large-sized phytoplankton. This result fell into the ranges observed during field studies. 相似文献
55.
The impact of wave loads and pore-water pressure generation on initiation of sediment transport 总被引:3,自引:0,他引:3
Edward C. Clukey Fred H. Kulhawy Philip L. -F. Liu George B. Tate 《Geo-Marine Letters》1985,5(3):177-183
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported. 相似文献
56.
57.
Long-term Sensor Drift Found in Recovered Argo Profiling Floats 总被引:5,自引:0,他引:5
We recovered three Argo profiling floats after 2 to 2.5 years of operation, and recalibrated their temperature, conductivity, and pressure sensors. The results demonstrate that these floats exhibited a significant drift in salinity of −0.0074 to −0.0125, primarily due to the conductivity sensor drift. Combined with the recalibration result for another previously recovered float, the indication is that the negative salinity drift increases nearly in proportion to the operating period of floats. The increasing rate is −0.0041 (±0.0015) year−1, which yields a salinity drift of −0.016 (±0.006) for the expected float lifetime of four years. The present result suggests that reducing the float surfacing time would improve the accuracy of the salinity measurements. 相似文献
58.
Takushi?NikiEmail author Taiki?Fujinaga Mariyo?F.?Watanabe Junji?Kinoshita 《Journal of Oceanography》2004,60(5):913-917
Solid-phase microextraction (SPME) is a simple, sensitive and less destructive method for the determination of dimethylsulfide
(DMS) in seawater. Combined with detection by gas chromatography-mass spectrometry (GC-MS), the method had sufficient sensitivity
(minimum detectable concentration of DMS was 0.05 nM), and practical levels of reproducibility (relative standard deviation
≤7%) and linearity (r
2 > 0.995) over a wide concentration range (0.5 to 910 nM). The protocol developed was applied to a Sagami Bay water sample
to determine concentrations of DMS and DMSP, and in situ DMSP-lyase activity. 相似文献
59.
Eddy Shedding from the Kuroshio Bend at Luzon Strait 总被引:16,自引:1,他引:16
TOPEX/POSEDIENT-ERS satellite altimeter data along with the mean state from the Parallel Ocean Climate Model result have been used to investigate the variation of Kuroshio intrusion and eddy shedding at Luzon Strait during 1992–2001. The Kuroshio penetrates into the South China Sea and forms a bend. The Kuroshio bend varies with time, periodically shedding anticyclonic eddies. Criteria of eddy shedding are identified: 1) When the shedding event occurs, there are usually two centers of high Sea Surface Height (SSH) together with negative geostrophic vorticity in the Kuroshio Bend (KB) area. 2) Between the two centers of high SSH there usually exists positive geostrophic vorticity. These criteria have been used to determine the eddy shedding times and locations. The most frequent eddy shedding intervals are 70, 80 and 90 days. In both the winter and summer monsoon period, the most frequent locations are 119.5°E and 120°E, which means that the seasonal variation of eddy shedding location is unclear. 相似文献
60.