全文获取类型
收费全文 | 5450篇 |
免费 | 893篇 |
国内免费 | 873篇 |
专业分类
测绘学 | 135篇 |
大气科学 | 515篇 |
地球物理 | 810篇 |
地质学 | 2443篇 |
海洋学 | 1245篇 |
天文学 | 37篇 |
综合类 | 319篇 |
自然地理 | 1712篇 |
出版年
2024年 | 25篇 |
2023年 | 86篇 |
2022年 | 218篇 |
2021年 | 216篇 |
2020年 | 215篇 |
2019年 | 312篇 |
2018年 | 227篇 |
2017年 | 224篇 |
2016年 | 215篇 |
2015年 | 198篇 |
2014年 | 347篇 |
2013年 | 366篇 |
2012年 | 313篇 |
2011年 | 274篇 |
2010年 | 275篇 |
2009年 | 326篇 |
2008年 | 322篇 |
2007年 | 328篇 |
2006年 | 372篇 |
2005年 | 315篇 |
2004年 | 305篇 |
2003年 | 244篇 |
2002年 | 268篇 |
2001年 | 239篇 |
2000年 | 185篇 |
1999年 | 146篇 |
1998年 | 148篇 |
1997年 | 106篇 |
1996年 | 102篇 |
1995年 | 59篇 |
1994年 | 53篇 |
1993年 | 41篇 |
1992年 | 40篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1980年 | 1篇 |
排序方式: 共有7216条查询结果,搜索用时 437 毫秒
21.
在分析综合辽宁省海岸带调查和沿海经济贝类污染监测资料基础上,根据辽宁海岸带水质,沉积物和生物污染现状及发展趋势。针对所存在的问题,讨论了辽宁省海洋污染特别是赤潮对海洋资源的破坏,并在组织机构,地方立法,海岸带环境保护规划,污染源控制与整体环境改进,监测方案等方面提出了建设海上辽宁、加强辽宁省海洋环境保护与海岸可持续开发利用的建议。 相似文献
22.
23.
24.
Lock-release gravity currents with a viscous self-similar regime are simulated by use of the renormalization group(RNG) k - ε model for Reynolds-stress closure. Besides the turbulent regime with initially a slumping phase of a conslant current front speed and later an inviseid self-similar phase of front speed decreasing as t^-1/3(where t is the time measured from release), the viseous self-similar regime is satisfactorily reproduced with front speed decreasing as t^-4/5,consistent with well known experimental observations. 相似文献
25.
From the experimental studies in recent years, it has become known that when a wave breaks directly on a vertical faced coastal structure, high magnitude impact pressures are produced. The theoretical and experimental studies show that the dynamic response of such structures under wave impact loading is closely dependent on the magnitude and duration of the load history. The dynamic analysis and design of a coastal structure can be succeeded provided the design load history for the wave impact is available. Since these types of data are very scarce, it is much more convenient to follow a method which is based on static analysis for the dynamic design procedure. Therefore, to facilitate the dynamic design of a vertical plate that is exposed to breaking wave impact, a multiplication factor called “dynamic magnification factor” is herein presented which is defined as the ratio of the maximum value of the dynamic response to that found by static analysis. The computational results of the present study show that the dynamic magnification factor is a useful ratio to transfer the results of static analysis to the dynamic design of a coastal plate for the maximum impact pressure conditions of pmax/γH0≤18. 相似文献
26.
根据冲量相似的要求进行船舶在冲击作用下的模型试验,并将模型试验结果与理论计算及实际试验进行了对比和分析。 相似文献
27.
Andr Luiz Machado Pessanha Francisco Gerson Araújo 《Estuarine, Coastal and Shelf Science》2003,57(5-6):817-828
Fish assemblages from two beaches, one in the inner and the other in the outer Sepetiba Bay (latitude: 22°54′–23°04′S; longitude: 43°34′–44°10′W), Southeast Brazil, were sampled by beach seine net, simultaneously, on both seasonal and diel scales, between August 1998 and June 1999. Sites were selected to encompass different environmental conditions which reflect the two bay zones, thus providing a comprehensive assessment of the factors influencing surf zone fish assemblages, and their spatial, seasonal and diel variations. A total of 55 fish species was recorded, mostly young-of-the-year. Anchoa tricolor, Micropogonias furnieri, Gerres aprion, Diapterus rhombeus, Harengula clupeola, Atherinella brasiliensis and Mugil liza were numerically dominant and contributed to 95.2% of the total fish catches. Strong differences in fish assemblages were observed between the two areas, with higher number of species in the outer bay. Increases in fish numbers occurred in winter, while the highest biomass occurred in winter and summer. Transparency, followed by salinity, was responsible for most of the spatial variability and played an important role in structuring fish assemblages. Overall, diel patterns did not reveal any significant trends; however, if we consider each season separately, an increase in fish numbers during the day with peak at sunset was observed in winter, and a higher biomass occurred at night in winter and summer. Species preferences for various combinations of environmental variables are responsible for shifts in the structure and overall abundance of assemblages and dictated some patterns. The sciaenid M. furnieri, the second most abundant species, occurred only in the inner zone, being more abundant in winter. The species of Engraulidae were more abundant in the outer zone in winter/spring during the day. The gerreids G. aprion and D. rhombeus occurred mainly in summer. Overall, temporal fluctuations act more at a specific level than at a structural one, and may be linked to some particular stages of the fish life cycle, but do not significantly influence the spatial organization. 相似文献
28.
安徽宣城地区中晚更新世风成堆积与环境变迁 总被引:25,自引:7,他引:25
通过对宣城向阳中晚更新世沉积剖面的综合研究,认为该剖面与中国北方同时代的黄土—古土壤剖面相比较,虽然长江下游以南地区中晚更新世多个冰期中风成堆积的单层厚度与累积厚度,亦即风成物质的沉积通量与沉积速率均比北方黄土区要小,但它们所反映的气候与环境的变化具有明显的可比性。 相似文献
29.
本文揭示了天津海岸带影响经济开发的四个方面的地质环境特点;着重探讨三个方面的环境工程地质问题;并防止其形成和减轻地灾害的对策进行了研究。 相似文献
30.