全文获取类型
| 收费全文 | 8469篇 |
| 免费 | 1337篇 |
| 国内免费 | 1210篇 |
专业分类
| 测绘学 | 1059篇 |
| 大气科学 | 774篇 |
| 地球物理 | 1473篇 |
| 地质学 | 3582篇 |
| 海洋学 | 1560篇 |
| 天文学 | 14篇 |
| 综合类 | 636篇 |
| 自然地理 | 1918篇 |
出版年
| 2024年 | 32篇 |
| 2023年 | 122篇 |
| 2022年 | 300篇 |
| 2021年 | 362篇 |
| 2020年 | 357篇 |
| 2019年 | 387篇 |
| 2018年 | 313篇 |
| 2017年 | 371篇 |
| 2016年 | 390篇 |
| 2015年 | 349篇 |
| 2014年 | 546篇 |
| 2013年 | 567篇 |
| 2012年 | 498篇 |
| 2011年 | 507篇 |
| 2010年 | 438篇 |
| 2009年 | 490篇 |
| 2008年 | 532篇 |
| 2007年 | 570篇 |
| 2006年 | 561篇 |
| 2005年 | 448篇 |
| 2004年 | 406篇 |
| 2003年 | 340篇 |
| 2002年 | 363篇 |
| 2001年 | 337篇 |
| 2000年 | 255篇 |
| 1999年 | 211篇 |
| 1998年 | 205篇 |
| 1997年 | 149篇 |
| 1996年 | 130篇 |
| 1995年 | 100篇 |
| 1994年 | 91篇 |
| 1993年 | 76篇 |
| 1992年 | 60篇 |
| 1991年 | 33篇 |
| 1990年 | 23篇 |
| 1989年 | 26篇 |
| 1988年 | 14篇 |
| 1987年 | 12篇 |
| 1986年 | 10篇 |
| 1985年 | 10篇 |
| 1984年 | 13篇 |
| 1983年 | 7篇 |
| 1982年 | 4篇 |
| 1977年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
61.
本文介绍了海洋技术研究所质量管理处在维护质量体系运行方面的主要作法和经验体会，结合2000版ISO9201标准的新内容，提出适应新版标准的想法。 相似文献
62.
63.
64.
Seasonal patterns of use of coastal resources by otters have been studied, simultaneously performing diet analyses and spraint counts (expressed as marking intensity, MI). In spite of the small size of the study area, two different sectors could be clearly identified, a sandy and a rocky one. The origin (freshwater or coastal) of most prey types could also be determined. Surveys were performed bimonthly and classified as autumn–winter (A–W) or spring–summer (S–S).In the sandy sector, eels, flatfish and grey mullets were more frequently consumed in A–W, while crayfish was more frequently consumed in S–S. None of the identified prey types in the rocky sectors showed different frequency of occurrence values between the two periods. In this sector otter fed mainly on coastal prey throughout the year, while in the sandy one there was a clear shift from coastal prey to freshwater ones in S–S. The decrease of coastal prey consumption in S–S in the sandy sector coincided with the lowest MI values, showing that in this period otters use coastal areas less intensely. Though shifts in otter diet and use of space in the sandy sector are probably influenced by the population dynamics of estuarine fish species and crayfish, the increased tourist disturbance during spring and summer in the sandy sector could be an important determinant of the observed patterns. Finally, the results show that MI can be used as a reliable measure of habitat use by otters, at least in small areas. 相似文献
65.
66.
67.
68.
A preliminary optical classification of lakes in Estonia and south Finland which can also be used for small bays of the Baltic Sea is elaborated. The classification is based on the optical properties of water (diffuse attenuation coefficient, diffuse reflectance) and parameters that are routinely monitored in water bodies (Secchi depth, concentration of chlorophyll-a, total suspended matter and yellow substance). The data complex used for our classification covers different types of water ecosystems (ranging from oligotrophic to hypertrophic) and the variability of water constituent concentrations in the ice-free period in Estonia and south Finland. Using cluster analysis, we found 5 optical classes of waters: clear (C), moderate (M), turbid (T), very turbid (V) and brown (B). There is satisfactory correspondence between class of water, shape of diffuse attenuation coefficient and diffuse reflectance spectra and trophic state of the lakes. 相似文献
69.
简要阐述了环境经济学的基本理论,并以青岛为例,分析了海岸带环境管理现状和现行经济手段存在的问题,提出了运用经济手段加强海岸带环境管理的建议。 相似文献
70.
海口湾的溶解氧及海水水质指标限制值问题 总被引：4，自引：0，他引：4
海水溶解氧对海洋生物的生存、生长和发育相当重要,与生物活动有着密切的联系,它的含量变化是反映生物生长状况的一个重要标志,同时也是污染监测的重要指标.海口湾是海南省的重点海域,1989年以来,陈春华等对海口湾的环境问题进行了大量的研究[1~6],本论文就海口湾的溶解氧监测结果进行分析,并发现了溶解氧水质标准限制值存在的问题.每年在该湾布设10余个站点进行污染监测,有必要对海口湾近7年监测结果进行综合分析. 相似文献