全文获取类型
收费全文 | 99148篇 |
免费 | 19145篇 |
国内免费 | 43395篇 |
专业分类
测绘学 | 4348篇 |
大气科学 | 26580篇 |
地球物理 | 25914篇 |
地质学 | 55544篇 |
海洋学 | 21755篇 |
天文学 | 15972篇 |
综合类 | 4479篇 |
自然地理 | 7096篇 |
出版年
2022年 | 696篇 |
2021年 | 1143篇 |
2020年 | 2491篇 |
2019年 | 5904篇 |
2018年 | 6583篇 |
2017年 | 6272篇 |
2016年 | 6797篇 |
2015年 | 5805篇 |
2014年 | 5680篇 |
2013年 | 8015篇 |
2012年 | 6010篇 |
2011年 | 6564篇 |
2010年 | 6191篇 |
2009年 | 6542篇 |
2008年 | 5556篇 |
2007年 | 5275篇 |
2006年 | 4963篇 |
2005年 | 4537篇 |
2004年 | 4974篇 |
2003年 | 4529篇 |
2002年 | 4186篇 |
2001年 | 3747篇 |
2000年 | 3356篇 |
1999年 | 3150篇 |
1998年 | 3224篇 |
1997年 | 3253篇 |
1996年 | 2660篇 |
1995年 | 2524篇 |
1994年 | 2280篇 |
1993年 | 2138篇 |
1992年 | 1909篇 |
1991年 | 1525篇 |
1990年 | 1678篇 |
1989年 | 1426篇 |
1988年 | 1224篇 |
1987年 | 1321篇 |
1986年 | 1135篇 |
1985年 | 1256篇 |
1984年 | 1448篇 |
1983年 | 1290篇 |
1982年 | 1212篇 |
1981年 | 1114篇 |
1980年 | 940篇 |
1979年 | 916篇 |
1978年 | 909篇 |
1977年 | 824篇 |
1976年 | 781篇 |
1975年 | 704篇 |
1974年 | 720篇 |
1973年 | 725篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
基于2008年6月14日~6月22日期间淀山湖水域实测水文资料探讨了夏季淀山湖水域水文特征。结果表明:(1)淀山湖水域感潮特征显著,潮波主要沿黄浦江上溯经拦路港、淀浦河、石塘港、西旺港传播入湖区,该水域潮汐以M2分潮为主,为非正规半日潮类型,湖区平均涨潮历时4.0~5.3h,平均落潮历时7.0~8.4h,最大潮差基本呈以拦路港为轴心渐次递减的分布格局;(2)湖区水流极弱,垂线平均最大流速介于0.02~0.05m/s区间;(3)商榻至拦路港航道以南水域,潮流往复流特征显著,主流向基本与各入流口门和主要出流口门——拦路港构成的轴线相一致;而商榻至拦路港航道以北水域则往复流性质较弱,涨潮流向相对较为分散;(4)夏季时,风生流和相应底部补偿流是控制湖区水流垂向分布格局的首要因素之一;(5)夏季时,珠砂港、商榻、白石矶和千灯浦等4个口门为淀山湖的主要入流通道,分别占总入流量的40.7%、39.2%、18.2%和1.9%;(6)夏季时,拦路港、淀浦河、西旺港和石塘港等4个口门为淀山湖的主要出流通道,分别占总出流量的84.0%、12.0%、2.5%和1.7%;(7)夏季时,本次测验中未加考虑的部分流量较小的口门流量以及湖面接收的降雨量对于严格的湖区水量收支平衡而言仍是不可忽略的。 相似文献
992.
Using a simple damped slab model,it was possible to show that a local wind induced 88%(15 of 17)of the near-inertial oscillations(NIO)observed in the mixed layer near the east coast of Korea from 1999 to 2004.The model,however,overestimated the energy level in about two-thirds of the simulated cases,because the slab model was forced with winds whose characteristic period was shorter than the damping time scale of the model at 1.5 d.At the observation site,due to typhoons and orographic effects,high-frequency wind forcing is quite common,as is the overestimation of the energy level in the slab model results.In short,a simple slab model with a damping time-scale of about 1.5 d would be enough to show that the local wind was the main energy source of the near-inertial energy in this area,but the model could not be used to accurately estimate the amount of the work done by the wind to the mixed layer. 相似文献
993.
分别采用扫描和透射电镜, 观察了正常和饥饿5d银鲳(Pampus argenteus)幼鱼的食道侧囊及肝脏超微结构的变化。结果表明, 正常银鲳幼鱼侧囊内壁具有许多平均高度为800?m的乳突, 上有次级突起。乳突黏膜由复层扁平上皮构成, 上皮细胞表面有指纹状的微嵴, 有缓解上皮细胞的机械损伤作用; 银鲳肝脏具肝血窦、胆小管、狄氏窦等结构, 肝细胞排列较紧密, 内含丰富的细胞器和脂滴, 核仁大而明显, 线粒体数目多, 多分布在细胞核、内质网和狄氏窦周围。饥饿后, 侧囊乳突变低矮, 平均高度700?m, 乳突上黏膜变薄, 逐渐退缩, 次级突起顶端露出了尖刺状的角质刺; 肝细胞体积缩小, 核变小, 细胞器数目减少, 线粒体水肿, 粗面内质网数量显著降低, 脂滴数量降低, 这是银鲳幼鱼对饥饿的生理性防御。 相似文献
994.
The vertical structure of the atmospheric boundary layer over the central Arctic Ocean 总被引:1,自引:1,他引:1
The tropopause height and the atmospheric boundarylayer (PBL) height as well as the variation of inversion layer above the floating ice surface are presented using GPS (global position system ) radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean (86°-88°N, 144°-170°W) during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind (over 12 m/s) are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone (800-85° N). The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station. 相似文献
995.
稳定同位素技术是研究生态系统中物质循环与能量流动的有效技术。利用稳定同位素技术研究了黑石礁海域浮游植物和6种海洋生物的δ13 C和δ15组成、营养位置、空间分布和月份变化。结果显示:浮游植物的δ15 C远低于其他物种,不同物种的δ13 C和δ15 N存在明显的差异,且有交叉现象,表明他们同化了不同的碳源;物种的δ15 N值空间差异较大而δ13 C值空间差异不明显,且δ15 N值与距离排污口的远近有关系,越靠近排污口δ15 N越大,与人类活动营养物质的输入有关系,可以用δ15 N监测人类活动对海洋生物的影响;孔石莼的δ15 N月平均变化很大,浮游植物δ15 N值基本没有变化,其他物种没有发生很大的变化;孔石莼是适合短期监测人类活动对海洋影响的物种。 相似文献
996.
太湖风浪场的计算与比较 总被引:1,自引:0,他引:1
首先探讨了浅水风浪数值模型—SWAN模型应用于模拟内陆湖泊风浪生成和传播变形时的特点。该模型存在不能有效地模拟近固壁边界处风浪场的缺点,以能正确地模拟湖区的风浪场和节约计算时间为原则,确定了计算范围。对太湖进行了风场和风浪场的现场观测。分别利用规范公式和SWAN模型两种方法、根据观测和预报的风场计算了湖区的有效波高,并将计算结果和现场观测值进行了详细比较。结果表明基于观测的风场,利用两种方法所计算的太湖风浪场的精度基本相当;在根据观测的风场、利用SWAN模型计算内陆湖泊的风浪场时,需要精心选择恰当的风场;在根据预报的风场预报湖区风浪场时,SWAN模型的精度要高于规范公式的精度。 相似文献
997.
A challenge of managing data poor fisheries lies in overcoming uncertainties associated with a lack of information on biological and socio-economic conditions. This paper focuses on site prioritisation for marine protected areas, a process that usually imposes moderate to heavy demands on data, time, local expertise, and funds. A fuzzy logic decision support tool for zoning marine areas that is suitable for use in data poor conditions is developed. This tool, the Protected Area Suitability Index (PASI), assesses the suitability of sites for protection based on fishers’ preferences for that site and the site’s conservation value. Only eight input attributes are required to run the PASI, which operates on a series of heuristic rules to estimate a site suitability score that ranges from 0 to 10, where 10 indicates that a site is highly suitable for being protected from fishing. Sensitivity analysis reveals that the PASI is relatively robust, and produces reliable results even as the system is degraded by the loss of data. Eighteen actively fished sites and 11 sites that are closed to fishing are assessed to evaluate how well the PASI is able to distinguish differences between sites. The estimated scores are significantly different (p<0.05), whereby non-fished sites are scored as being more suitable for protection than fished sites. The PASI can be used as a decision support tool to facilitate systematic marine spatial management under data poor conditions, especially in the task of identifying suitable sites for protection. 相似文献
998.
The second and third recorded births of southern elephant seals Mirounga leonina on the mainland of New Zealand occurred at Kaikoura in mid‐October 1976. One female pup died within 14 d of birth and the other (sex unknown) disappeared from the region with its mother on 19 November 1976. 相似文献
999.
The preferred depth of settlement and settlement period of two species of mussel spat were monitored at Yncyca Bay (NZMS1 S15 220460) and Wet Inlet (NZMS1 S16 265432) in the Marlborough Sounds on collectors suspended in 0–4 m of water between 20 October 1975 and 4 April 1976. Peak settlement of Mytilus edulis aoteanus was between 20 October 1975 and 4 January 1976, and decreased with increasing depth. Peak settlement of Perna canaliculus was between 16 February 1976 and 12 April 1976, and showed no preferred depth of settlement. Capture of wild stocks of Mytilus edulis aoteanus and Perna canaliculus spat for use in aquaculture has become more reliable through accurate forecasting of peak settlement periods, and knowledge of preferred depth of settlement of the two species. Preferred depth of settlement of spat may affect the shore zonation of mussels. 相似文献
1000.
Graham J. Wilson 《新西兰海洋与淡水研究杂志》2013,47(3):373-375
The discovery at Stewart Island of a hauling‐out ground regularly used by Hooker's sea lions (Phocarctos hooked) is described, and recent sightings of sea lions in southern New Zealand are reported. An attempted copulation between a male Hooker's sea lion and a dead female fur seal (Arctocephalus forsteri) is also described. 相似文献