全文获取类型
收费全文 | 8854篇 |
免费 | 1989篇 |
国内免费 | 2025篇 |
专业分类
测绘学 | 799篇 |
大气科学 | 1063篇 |
地球物理 | 3220篇 |
地质学 | 4289篇 |
海洋学 | 1516篇 |
天文学 | 479篇 |
综合类 | 809篇 |
自然地理 | 693篇 |
出版年
2024年 | 63篇 |
2023年 | 153篇 |
2022年 | 286篇 |
2021年 | 321篇 |
2020年 | 353篇 |
2019年 | 427篇 |
2018年 | 308篇 |
2017年 | 355篇 |
2016年 | 376篇 |
2015年 | 456篇 |
2014年 | 501篇 |
2013年 | 571篇 |
2012年 | 565篇 |
2011年 | 597篇 |
2010年 | 448篇 |
2009年 | 599篇 |
2008年 | 515篇 |
2007年 | 641篇 |
2006年 | 576篇 |
2005年 | 466篇 |
2004年 | 437篇 |
2003年 | 407篇 |
2002年 | 371篇 |
2001年 | 334篇 |
2000年 | 346篇 |
1999年 | 331篇 |
1998年 | 307篇 |
1997年 | 278篇 |
1996年 | 267篇 |
1995年 | 201篇 |
1994年 | 211篇 |
1993年 | 187篇 |
1992年 | 140篇 |
1991年 | 92篇 |
1990年 | 95篇 |
1989年 | 84篇 |
1988年 | 63篇 |
1987年 | 40篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
371.
Tomoharu Senjyu 《Journal of Oceanography》1999,55(2):111-122
In the southern Japan Sea there is a salinity minimum layer between the Tsushima Current Water and the Japan Sea Proper Water.
Since the salinity minimum corresponds to the North Pacific Intermediate Water, it is named the Japan Sea Intermediate Water
(JIW). To examine the source and circulation of JIW, the basin-wide salinity minimum distribution was investigated on the
basis of hydrographic data obtained in 1969. The young JIW, showing the highest oxygen concentration and the lowest salinity,
is seen in the southwestern Japan Sea west of 133°E, while another JIW with lower oxygen and higher salinity occupies the
southeastern Japan Sea south of the subpolar front. Since the young JIW shows high oxygen concentrations, high temperatures
and low densities, the source of the water is probably in the surface layer. It is inferred that the most probable region
of subduction is the subarctic front west of 132°E with the highest oxygen and the lowest salinity at shallow salinity minimum.
In addition, property distributions suggest that JIW takes two flow paths: a eastward flow along the subarctic front and an
southward flow toward the Ulleung Basin. On the other hand, a different salinity minimum from JIW occupies the northern Japan
Sea north of the subarctic front, which shows an apparently higher salinity and high oxygen concentration than JIW. However,
this salinity minimum is considered not to be a water mass but to be a boundary between overlying and underlying water masses.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
372.
通过γ射线穿透油、气、水混合物后的透射和散射计数,经理论模拟计算,实现对原油含水率在线计量分析,测量含水率范围为3%-100%,精度在2%以内。在实际应用过程中,运行稳定,易于操作,特别是修正了由于原油中含气地含水率测量带来的误差,技术和性能指标均已契过以往各种含水测量仪,通过应用,实现了海洋石油开发公司采油一、二分公司和油气集输大队的分队计量,使生产管理水平整体上了一个新台阶。 相似文献
373.
374.
淡化速度和幅度对凡纳对虾幼体存活和活力的影响 总被引:1,自引:0,他引:1
进行了淡化速度、幅度对凡纳对虾(Litopenaeus vannamei)的影响试验,结果表明:每36h和24h降低盐度2~3的两种淡化速度,对虾苗存活率较高,分别为86.7%和83.3%;淡化时间分别为396h和264h。每12h降低盐度2~3的淡化速度,从盐度29.7降至16.3,存活率为90.0%;从盐度16.3降至0,成活率为60.3%。每次降幅为1.3~1.4和2.6~2.7时,最终存活率较高,最终淡化到纯淡水中的存活率分别为83.3%和80.0%。每次降幅度为5.3~5.4时,在降到19.0以前,存活率都还较高,但此后的效果不佳,淡化至淡水时,成活率仅为53.3%。 相似文献
375.
Hydrodynamic modeling of flushing time in a small estuary of North Bay, Florida, USA 总被引:1,自引:0,他引:1
Freshwater fraction method is popular for cost-effective estimations of estuarine flushing time in response to freshwater inputs. However, due to the spatial variations of salinity, it is usually expensive to directly estimate the long-term freshwater fraction in the estuary from field observations. This paper presents the application of the 3D hydrodynamic model to estimate the distributions of salinity and thus the freshwater fractions for flushing time estimation. For a case study in a small estuary of the North Bay in Florida, USA, the hydrodynamic model was calibrated and verified using available field observations. Freshwater fractions in the estuary were determined by integrating freshwater fractions in model grids for the calculation of flushing time. The flushing time in the North Bay is calculated by the volume of freshwater fraction divided by the freshwater inflow, which is about 2.2 days under averaged flow conditions. Based on model simulations for a time series of freshwater inputs over a 2-year period, a power regression equation has been derived from model simulations to correlate estuarine flushing time to freshwater inputs. For freshwater input varying from 12 m3/s to 50 m3/s, flushing time in this small estuary of North Bay changes from 3.7 days to 1.8 days. In supporting estuarine management, the model can be used to examine the effects of upstream freshwater withdraw on estuarine salinity and flushing time. 相似文献
376.
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
377.
378.
选取具有显著产毒差异的利玛原甲藻(Prorocentrum lima) SHG株与2XS株为研究对象,以2-13C-甘氨酸为示踪原料结合高分辨质谱方法,为腹泻性贝类毒素及其酯化态毒素合成与代谢途径的研究提供新方法和思路。结果表明,两株藻共发现16种腹泻性贝毒及其酯化态毒素成分。对照培养条件下SHG株(大田软海绵酸毒素含量为7.88 pg/cell,鳍藻毒素1含量为4.35 pg/cell)的产毒能力高于2XS株(大田软海绵酸毒素5.70pg/cell),而甘氨酸作为氮源培养条件可显著提高两株藻的产毒总量(P<0.05)。13C-甘氨酸标记组与甘氨酸培养组单细胞产毒量无显著变化(P>0.05)。腹泻性贝毒被标记后其同位素异构体丰度发生变化,其中酯化态受13C标记的影响程度更高,二级质谱图清晰表示出其碎片离子及脱水峰的标记情况。该方法直观阐明了甘氨酸可作为P. lima标记原料的产毒供体,并使用稳定同位素标记方法首次实现了酯化态的同步标记,有助于腹泻性贝毒生成机制的进一步研究。 相似文献
379.
地热资源是一种新型无污染能源,具有极高的开采价值,已经受到世界各国的关注.盆地因其特殊的地质条件,内部往往蕴涵着丰富的地热资源,且具有易开采、利用的特点.但目前地热资源勘探的手段和研究方法单一,制约着地热资源的开采与开发.而盆地地热场模拟技术已经较为成熟,并在油气成藏模拟中广泛应用.我们可以在已有的技术手段下结合盆地地热模拟技术来提高勘探的精度.本文还探讨了以地温控制方程与地下热水水流方程相结合来建立模型,模拟盆地地热资源. 相似文献
380.
从数据管理及后期应用的角度提出了数据平台的要领,讨论了该数据平台的物理结构、逻辑结构,在分类与组织的基础上给出了相应的数据字典。同时,还基于该平台探讨了测井曲线库及图形库的建设方法,并实现了具体功能。 相似文献