全文获取类型
收费全文 | 2787篇 |
免费 | 571篇 |
国内免费 | 314篇 |
专业分类
测绘学 | 110篇 |
大气科学 | 110篇 |
地球物理 | 445篇 |
地质学 | 608篇 |
海洋学 | 1727篇 |
天文学 | 7篇 |
综合类 | 166篇 |
自然地理 | 499篇 |
出版年
2025年 | 2篇 |
2024年 | 61篇 |
2023年 | 81篇 |
2022年 | 107篇 |
2021年 | 108篇 |
2020年 | 128篇 |
2019年 | 125篇 |
2018年 | 112篇 |
2017年 | 121篇 |
2016年 | 137篇 |
2015年 | 112篇 |
2014年 | 147篇 |
2013年 | 207篇 |
2012年 | 132篇 |
2011年 | 201篇 |
2010年 | 141篇 |
2009年 | 167篇 |
2008年 | 188篇 |
2007年 | 138篇 |
2006年 | 166篇 |
2005年 | 130篇 |
2004年 | 116篇 |
2003年 | 103篇 |
2002年 | 92篇 |
2001年 | 76篇 |
2000年 | 77篇 |
1999年 | 91篇 |
1998年 | 74篇 |
1997年 | 52篇 |
1996年 | 56篇 |
1995年 | 47篇 |
1994年 | 42篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3672条查询结果,搜索用时 15 毫秒
1.
M. Paul Mosley 《新西兰海洋与淡水研究杂志》2013,47(3-4):351-357
Riffles and points of divergence of branch channels in braided rivers are critical controls upon passage of fish and recreational boats because they are points at which depths are at a minimum. Depths on randomly selected riffles were measured in braided reaches of the Ashley, Hurunui, and Rakaia Rivers and related to discharge; minimum depths encountered in extended reaches of these rivers at a range of flows have also been measured. The data can be used to predict minimum available passage depths at a specified flow, or conversely, to predict the discharge required to maintain a specified minimum passage depth. However, presently available estimates of critical minimum depths required for various instream uses (migration of salmonids, jetboating) appear excessively conservative, and minimum depth requirements must be more accurately determined before instream flow needs can be properly assessed. 相似文献
2.
经济较发达地区交通建设对土地利用的影响——以泉州沿海大通道为例 总被引:1,自引:0,他引:1
基于对泉州沿海大通道沿线土地利用的实际调研,对沿海大通道修建前后的资料和数据作分析、对比,研究结果发现,沿海大通道建设一方面使沿线土地增值,改善土地利用空间结构,带动区域旅游业发展和有效提高沿海抗风浪能力;另一方面却导致了城市用地规模无序蔓延,土地建设质量和土地空间利用效率低下,还对沿线海岸带生态环境造成一定的损害。为此提出了道路沿线土地合理利用建议。 相似文献
3.
Spatial patterns and replacement in ten cacti were studied on an island of the coastal desert of Sinaloa, México. Four platyopuntias had 74–92% of their individuals beneath shrub canopies, whereas three globose cacti, one columnar cactus and two cylindropuntias had similar or higher percentages of individuals in open spaces. This study advances the idea that open-space colonization is enhanced by less harsh physical and biotic conditions in coastal deserts, and by certain morphological and physiological adaptations of cacti. The absence of nurse-shrub replacement is understood as a result of induced co-existence by physical damage from cyclones in the coastal zone. 相似文献
4.
Shigehisa Nakamura 《Marine Geodesy》2013,36(4):305-312
A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front. 相似文献
5.
应用综合污染指数法对锦州市近岸海域8个监测点位以及全海域2004年和2005年水质特征进行了分析,其结果表明全海域污染比较严重,且中度污染范围较广,近90%.除4#监测点属轻度污染,其余均属中度污染,且5#和7#监测点污染程度有加重趋势,应予以重视,最后就锦州市海水污染特征提出了相关防治措施. 相似文献
6.
The larval fish assemblage was investigated in the shallow, nearshore region of a proposed marine protected area in eastern Algoa Bay, temperate South Africa, prior to proclamation. Sampling was conducted at six sites along two different depth contours at ∼5 m and ∼15 m to assess shore association. Larvae were collected by means of stepped oblique bongo net tows deployed off a ski-boat, twice per season for 2 years between 2005 and 2007. In total, 6045 larval fishes were collected representing 32 families and 78 species. The Gobiidae, Cynoglossidae, Clupeidae, Engraulidae and Sparidae were the dominant fish families. Catches varied significantly among seasons peaking in spring with a mean of ∼200 larvae/100 m3. Mean overall larval density was higher along the deeper contour, at ∼15 m (40 larvae/100 m3). The preflexion stage of development dominated catches at the ∼5 m (80%) and ∼15 m (73%) depth contours. Body lengths of Argyrosomus thorpei, Caffrogobius gilchristi, Diplodus capensis, Heteromycteris capensis and Solea turbynei, all estuary associated species, were larger at the shallow sites nearer to shore. Larvae of coastal species that produce benthic eggs dominated catches (75%) in the shallow sites (∼5 m) but were less abundant (32%) farther from shore at the deeper (∼15 m) sites. All developmental stages of D. capensis, Engraulis capensis, H. capensis, Sardinops sagax and two Pomadasys species were found in the study area. It appears that some species use the shallow nearshore as a nursery area. 相似文献
7.
南海主要珊瑚礁水域软骨鱼类的组成与分布 总被引:1,自引:0,他引:1
利用1998年3~5月和1999年5~6月在西沙和南沙的12座珊瑚礁水域渔业资源专业调查资料以及1998年2月~1999年12月在南沙群岛水域进行的渔业资源监测调查资料,分析讨论了南海珊瑚礁水域软骨鱼类的组成与分布。专业调查结果:捕获软骨鱼类14属16种,渔获量计64尾2 844.1kg,优势种为大眼角鲨、鼬鲨、日本燕、侧条真鲨、灰六鳃鲨;监测调查表明南沙珊瑚礁水域的软骨鱼类在全年均可捕获,产量的变动主要与捕捞努力量相关。综合2种调查知:软骨鱼类在南海珊瑚礁水域总体分布范围较广,单鱼种在各个岛礁表现出一定的地域分布性;南海珊瑚礁区捕获软骨鱼类的主要作业方式为延绳钓和大型流刺网。 相似文献
8.
为掌握江苏盐城滨海湿地獐(Hydripotes inermis)的最新种群数量与分布状况,于2007年3~5月,在江苏省盐城滨海湿地用样线法对獐的春季种群数量与分布进行了调查.调查结果表明,獐在盐城滨海湿地有2个分布区,一个在射阳县境内,以盐城国家级珍禽自然保护区核心区为中心,扩散至射阳芦苇公司及其周边区域;另一个位于大丰县境内,从大丰麋鹿保护区的第一核心区至第三核心区及周边荒地.獐在盐城滨海湿地的总数量在372只左右,其中盐城国家级自然保护区核心区分布獐的数量和密度最高,其数量约为327只,密度为1.9只/km2.与20世纪90年代调查数据相比,獐的分布范围和数量均显著下降. 相似文献
9.
本文以我国东部沿海三大经济区域——环渤海、长三角、珠三角为研究对象,依据空间统计学的空间自相关方法,采用以高速公路里程数为影响因子改进的空间权重矩阵,以及全局和局部Moran I指数模型,通过ArcToolbox空间分析工具分析三大区域经济空间格局。研究结果表明,长三角与珠三角区域发展呈显著的空间正相关,长三角地区较之其他两地区发展最为成熟,发展极辐射大。同时地理环境对于区域经济发展作用明显,发展核心城市集中于沿江地区或平原地区。 相似文献
10.
Zhang Changkuan Wang Zhen Zhang Dongsheng
Associate Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing
Lecturer Dept. of Navigation Ocean Engineering Hohai University Nanjing
Professor Dept. of Navigation Ocean Engineering Hohai University Nanjing 《中国海洋工程》1995,(2)
A numerical model of shoreline change of sand beaches based on long-term field wave data is proposed, the explicit and implicit finite difference forms of the model are described, and an application of the model is presented. Results of the application indicate that the model is sensitive to the order of the input wave data, and that the effects of long-term wave series and the effects of the mean annual wave conditions on the model are different. Instead of a single wave condition, the wave series will make the calibration and the verification of the model more practical and the results of the model more reasonable. 相似文献