全文获取类型
收费全文 | 962篇 |
免费 | 252篇 |
国内免费 | 39篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 25篇 |
地球物理 | 40篇 |
地质学 | 25篇 |
海洋学 | 1076篇 |
综合类 | 18篇 |
自然地理 | 67篇 |
出版年
2024年 | 14篇 |
2023年 | 41篇 |
2022年 | 40篇 |
2021年 | 47篇 |
2020年 | 35篇 |
2019年 | 39篇 |
2018年 | 32篇 |
2017年 | 83篇 |
2016年 | 51篇 |
2015年 | 36篇 |
2014年 | 75篇 |
2013年 | 48篇 |
2012年 | 68篇 |
2011年 | 85篇 |
2010年 | 80篇 |
2009年 | 52篇 |
2008年 | 39篇 |
2007年 | 71篇 |
2006年 | 46篇 |
2005年 | 42篇 |
2004年 | 39篇 |
2003年 | 29篇 |
2002年 | 15篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 1篇 |
排序方式: 共有1253条查询结果,搜索用时 375 毫秒
41.
42.
43.
44.
45.
46.
Access to information about past states of the environment and social systems is fundamental to understand, and cope with, the challenges of climate change and over-exploitation of natural resources at the onset of the 21st century. The loss of (old) data is a major threat to understanding better and mitigating long-term effects of human activities and anthropogenic changes to the environment. Although this is intuitively evident for old and local literature of any kind, even present-day international publishing of papers without the underlying raw data makes access to basic information a crucial issue. Here, we summarise experience resulting from a EU-funded International Science & Technology Cooperation (INCO) project (CENSOR) addressing Coastal Ecosystem Research and Management in the El Niño Southern Oscillation (ENSO) context. We show that indeed “Grey Literature” is still one of the most important sources of knowledge about natural science research and management of natural resource systems in Latin American countries. We argue that public archiving of original data of present-day research and old (Grey) Literature and easy public access are important for appreciating today's global environmental challenges caused by human activities, both past and present. 相似文献
47.
48.
The columnar cactus Polaskia chende, endemic to Central Mexico, occurs in the wild and in silviculturally managed populations where artificial selection for better edible fruits operates by sparing and favouring desirable phenotypes during vegetation clearance. Wild and managed populations were compared in morphology and reproductive biology to analyse if human selection has influenced phenotypic divergence, if it has modified breeding systems and if reproductive isolation exists between them. Fruits from managed populations were larger (6·36±0·17 cm3), heavier (19·62±1·32), sweeter (9·07±0·25 °Brix), and with thinner peel (2·09±0·13 mm) than those from wild populations (5·77±0·18 cm3, 15·73±0·85 g, 8·23±0·31 °Brix, and 2·58±0·14 mm, respectively). Both population types bloom synchronically, show diurnal anthesis, with bees as the most likely pollinators, and have breeding system predominantly self-incompatible. Spatial and temporal barriers to pollen exchange between wild and managed populations are unlikely, and morphological differences would be related with an ongoing process of artificial selection. 相似文献
49.
贵州织金新华含稀土磷矿床稀土元素地球化学及生物成矿基本特征 总被引:15,自引:0,他引:15
对贵州织金新华含稀土磷矿床进行的稀土元素及微量元素分析结果表明,磷块岩中普遍富集稀土元素,稀土总量∑REE较高,并富集Y元素及La,Nd等轻稀土元素。LREE/HREE比值较高。含稀土磷块岩普遍具Ce负异常,显示其对源区的继承性。指示成磷环境处于氧化程度相对较高状态。稀土元素球粒陨石标准化模式曲线、北美页岩标准化模式曲线、Ce元素异常、LREE/HREE比值、微量元素特征及岩石矿物特征表明,织金新华含稀土磷矿床具以正常海相生物-化学沉积等为主伴有海相热水沉积混合成因的特征。在磷矿成矿过程中沉积物沉积时,活体生物及死亡残骸不同程度地摄取和富集了La,Nd,Ce等稀土元素、Y元素及其他微量元素,沉积在含磷层位,构成大量的含稀土、含生物碎屑白云质磷块岩。 相似文献
50.
Azma Hanim Ismail Mashhor Mansor Wan Maznah W O 《湿地科学》2005,3(4):258-268
A study has been conducted on the status of water quality in two disused man made lakes, which have potential for cage aquaculture project. This study highlights the quality of water analyzed with reference to various physical - chemical parameters in two selected lakes and their suitability for fish farming. A number of parameters were measured including the amount of NH3 - N, NO3 - N, NO2 - N and total phosphorus while in - situ measurement including DO, pH, temperature, conductivity, TDS and Secchi disk visibility. Beside the physical -chemical of water, the location, morphometry and climate conditions were also investigated. The chemical data analyzed for six months indicated that Lake A and Lake B are characterized by relatively high DO, slightly neutral pH and low TSS. The concentration of NH3 -N and NO2 -N was very low (0. 058 mg/L and 0. 04 mg/L, respectively) and total phosphorus was usually in low concentration and sometimes would seem negligible. Besides, NO3 - N occurred in slightly higher concentration (1.75 mg/L). Results obtained indicated that the study site has high potentiality for development of inland fisheries practices. 相似文献