全文获取类型
收费全文 | 10797篇 |
免费 | 1720篇 |
国内免费 | 1854篇 |
专业分类
测绘学 | 810篇 |
大气科学 | 960篇 |
地球物理 | 1436篇 |
地质学 | 6119篇 |
海洋学 | 1712篇 |
天文学 | 208篇 |
综合类 | 844篇 |
自然地理 | 2282篇 |
出版年
2024年 | 35篇 |
2023年 | 165篇 |
2022年 | 357篇 |
2021年 | 463篇 |
2020年 | 415篇 |
2019年 | 513篇 |
2018年 | 373篇 |
2017年 | 457篇 |
2016年 | 479篇 |
2015年 | 469篇 |
2014年 | 649篇 |
2013年 | 636篇 |
2012年 | 621篇 |
2011年 | 709篇 |
2010年 | 634篇 |
2009年 | 658篇 |
2008年 | 670篇 |
2007年 | 701篇 |
2006年 | 732篇 |
2005年 | 616篇 |
2004年 | 589篇 |
2003年 | 482篇 |
2002年 | 476篇 |
2001年 | 394篇 |
2000年 | 341篇 |
1999年 | 304篇 |
1998年 | 281篇 |
1997年 | 194篇 |
1996年 | 204篇 |
1995年 | 160篇 |
1994年 | 134篇 |
1993年 | 125篇 |
1992年 | 87篇 |
1991年 | 70篇 |
1990年 | 47篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
101.
天津港南部海区水体富营养化水平评价 总被引:1,自引:0,他引:1
根据2006年3月和7月的调查数据,对天津港南部海区海水的营养水平及动态变化进行了评价。考虑到水质状况和水体营养水平是水体中多项指标分析评价的综合结果.本文先通过单项指标评价法和营养指数法进行评价。然后又通过集对分析方法,选择化学需氧量(COD)、无机磷(DIP)、无机氮(DIN)、叶绿素a(Ch1—a)等作为评价指标,对该区海水富营养化水平进行了综合评价。评价结果表明集对分析方法更能反映海水的实际富营养化状况,计算结果显示天津港南部海域两期调查中除21,26.27和29站位在7月呈富营养化状态其余站位海水均在中营养(Ⅳ)及以下水平状况,未达到富营养化水平,水质状况较好。 相似文献
102.
103.
Video assessment of environmental impacts of salmon farms 总被引:1,自引:0,他引:1
104.
黄河口及其邻近海域大型底栖动物的初步研究——(二)生物与沉积环境的关系 总被引:1,自引:3,他引:1
1985年5—6月对黄河口及其邻近海域的27个站进行了大型底栖动物的首航次定量调查。分别对18种环境因子和68个优势种和习见种所做的聚类分析显示了黄河口水下三角洲与邻近海域的某些差异,并联系沉积环境将所研究海域划分为四个区:黄河口水下三角洲、莱州湾、渤海中部和渤海湾东部。对大型底栖动物与沉积速率的关系也做了初步探讨。 相似文献
105.
106.
如何计算整个系统的运转效率,特别是受不确定因素影响的系统(如过驳系统),仍然是一个非常重要的研究课题。文章提出基于模糊综合评判方法的效率计算方法,是一种新的尝试,这种方法较好的避免了人的主观随意性,更符合实际情况,同时又可以弥补统计方法的不足。文章对某沿海地区的一过驳系统进行了效率计算,取得比较好的效果。 相似文献
107.
This study uses a comparative approach to examine responses of marine ecosystems to climatic regime shifts. The three seas surrounding the Korean peninsula, the Japan/East Sea, the East China Sea and the Yellow Sea represent three contiguous but distinct ecosystems. Sampling has been carried out by the National Fisheries Research and Development Institute of South Korea since 1965, using the same methods in all three seas. Sampling was generally synoptic. Amplitude time series of 1st EOF modes for temperature, salinity, zooplankton biomass and concentrations of four major zooplankton taxa were used to determine whether the three marine ecosystems respond in a similar manner to climate variations. Temporal patterns of the variables were strongly similar among the three seas at decadal time scales, but very weakly similar at interannual scales. All three seas responded to a climatic regime shift that occurred in 1989. Temperature, zooplankton biomass and copepod concentrations increased in the late 1980s or early 1990s in all three seas. Concentrations of amphipods, chaetognaths and euphausiids also increased in the Japan/East Sea and the East China Sea, but not the Yellow Sea. The Yellow Sea ecosystem differs strongly from the other two seas, and water exchange between the Yellow Sea and the East China Sea is much weaker than that between the East China Sea and Japan/East Sea. Spatial patterns of zooplankton determined by the EOF analysis were closely related to currents and fronts in each of the three seas. 相似文献
108.
In recent years, bulk carriers have been identified with high risks of catastrophic structural failure and foundering, and with heavy loss of human life. This study, based upon Lloyd's of London casualty records, identified four risk factors that had significant, independent effect upon the likelihood of a bulk carrier foundering. The risk of foundering increased with the age of the ship, and was related to the ship's flag of registration. Most importantly, however, increased risks were found for heavy cargoes of iron ore and scrap steel or iron, and for trading routes to the Far East and from Europe to North America. Additional safety measures, in particular regarding ship design and high-risk trades, may well be necessary to reduce the high casualty rates. 相似文献
109.
The working group Mathematical Geology of the Freie Universität Berlin was formed in 1971. We review quantitative methods used by the working group since 1983 to treat mineral exploration problems. The methods applied vary from elementary statistical analysis of multivariate exploration data to optimal strategies for selecting favorable targets, and from multiobjective decision-making for additional drill hole locations to expert systems in exploration.The methods applied are directly related to the level of information at each stage of the exploration process. Special emphasis was placed on the relationship between and evaluation of subjective and objective data. Case studies illustrating the various methods are presented for different kinds of mineral deposits and exploration environments. 相似文献
110.