全文获取类型
收费全文 | 9198篇 |
免费 | 2032篇 |
国内免费 | 3283篇 |
专业分类
测绘学 | 1097篇 |
大气科学 | 4708篇 |
地球物理 | 1784篇 |
地质学 | 3113篇 |
海洋学 | 1697篇 |
天文学 | 82篇 |
综合类 | 745篇 |
自然地理 | 1287篇 |
出版年
2024年 | 55篇 |
2023年 | 166篇 |
2022年 | 368篇 |
2021年 | 448篇 |
2020年 | 501篇 |
2019年 | 560篇 |
2018年 | 438篇 |
2017年 | 510篇 |
2016年 | 501篇 |
2015年 | 598篇 |
2014年 | 706篇 |
2013年 | 808篇 |
2012年 | 764篇 |
2011年 | 750篇 |
2010年 | 561篇 |
2009年 | 705篇 |
2008年 | 605篇 |
2007年 | 799篇 |
2006年 | 630篇 |
2005年 | 604篇 |
2004年 | 472篇 |
2003年 | 393篇 |
2002年 | 320篇 |
2001年 | 286篇 |
2000年 | 284篇 |
1999年 | 269篇 |
1998年 | 262篇 |
1997年 | 183篇 |
1996年 | 158篇 |
1995年 | 169篇 |
1994年 | 155篇 |
1993年 | 131篇 |
1992年 | 79篇 |
1991年 | 61篇 |
1990年 | 43篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
黄河口水下底坡微地貌及其成因探讨 总被引:3,自引:2,他引:3
高分辨率的回声测深、旁侧声纳及浅地层剖面记录首次直观地揭示了黄河口水下底坡上发育有大量形态不同的微地貌类型。据其形态特征和规模的差异,将它们划分为平滑海底、凹坑与洼地、冲沟、残留岗丘及扰动复合海底等五种类型。这些微地貌分布在不同水深条件下的不同水下三角洲单元上,并存在着相互联系和相互转化。黄河口海域特殊的沉积环境和复杂的动力条件是导致水下底坡微地貌形成发育的主要机制。 相似文献
24.
本文以赤道东太平洋海温作为主导因子,分析其与东亚温带气旋的关系。得出:高海温多气旋,低海温少气旋的对应关系较为明显。并进一步对不符合这种主要关系的年份从环流型。下垫面海温等作了分类鉴别分析。 相似文献
25.
26.
本文提出一个以带有定时器的低功耗微处理机为主体的温度记录器。其定时器用于开动微处理机,可由一个开关定为0.5、1、3或30分钟。仪器通过处理一个电容器向热敏电阻放电的时间来测量温度。仪器在工作中能显示温度值,并把温度值保存在微处理机的RAM之中。总共资料容量为2816次测值,量程为0~35℃,精度±0.1℃,分辨±0.02℃。 温度记录器具有液晶显示器,可直接读出温度值,配有标准计算机接口RS-232,能把保存的资料方便地倒给个人计算机。 这项工作是伍兹霍尔海洋研究所A.Bradley博士指导的。他提出的原理对研制可靠而廉价的温度记录器是一条新的途径。 相似文献
27.
Abstract. The oxygen consumption of Eudendrium glomeratum was measured monthly, throughout the period of active presence of the species in the field, to obtain indications on its physiological condition in the different phases of the cycle. Sets of one hundred polyps were assayed in the laboratory under normothermic (according to field temperature: 14–19°C) and hyperthermic conditions (22–25°C). The different response to identical temperatures at the extremes of the cycle, together with a differential ability to face stressful conditions in the same periods, suggests that other factors, besides temperature, regulate the seasonal cycle of Eudendrium glomeratum. 相似文献
28.
29.
Jennifer L. Mercer Meixun Zhao Steven M. Colman 《Estuarine, Coastal and Shelf Science》2005,63(4):675-682
Alkenone unsaturation indices (UK37 and UK′37) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between UK37 (and UK′37) values and temperature, and a significant negative correlation between UK37 (and UK′37) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. UK37 relationships (UK37=0.018 (T)−0.162, R2=0.84, UK′37=0.013 (T)−0.04, R2=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index UK′37 based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the UK37 vs. temperature slope, or nutrient levels are the main controller of the UK37 index. In addition, particularly high abundances (>5% of total C37 alkenones) of the tetra-unsaturated ketone, C37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones. 相似文献
30.
Ocean current forecasting is still in explorative stage of study. In the study, we face some problems that have not been met before. The solving of these problems has become fundamental premise for realizing the ocean current forecasting. In the present paper are discussed in depth the physical essence for such basic problems as the predictability of ocean current, the predictable currents, the dynamical basis for studying respectively the tidal current and circulation, the necessity of boundary model, the models on regions with different scales and their link. The foundations and plans to solve the problems are demonstrated. Finally a set of operational numerical forecasting system for ocean current is proposed. 相似文献