全文获取类型
收费全文 | 18286篇 |
免费 | 3948篇 |
国内免费 | 3610篇 |
专业分类
测绘学 | 1548篇 |
大气科学 | 4911篇 |
地球物理 | 3525篇 |
地质学 | 5321篇 |
海洋学 | 4712篇 |
天文学 | 147篇 |
综合类 | 1263篇 |
自然地理 | 4417篇 |
出版年
2025年 | 2篇 |
2024年 | 348篇 |
2023年 | 386篇 |
2022年 | 674篇 |
2021年 | 884篇 |
2020年 | 909篇 |
2019年 | 1024篇 |
2018年 | 845篇 |
2017年 | 973篇 |
2016年 | 937篇 |
2015年 | 1043篇 |
2014年 | 1182篇 |
2013年 | 1644篇 |
2012年 | 1202篇 |
2011年 | 1187篇 |
2010年 | 962篇 |
2009年 | 1188篇 |
2008年 | 1148篇 |
2007年 | 1177篇 |
2006年 | 1077篇 |
2005年 | 986篇 |
2004年 | 787篇 |
2003年 | 724篇 |
2002年 | 646篇 |
2001年 | 542篇 |
2000年 | 511篇 |
1999年 | 443篇 |
1998年 | 415篇 |
1997年 | 395篇 |
1996年 | 266篇 |
1995年 | 272篇 |
1994年 | 256篇 |
1993年 | 202篇 |
1992年 | 154篇 |
1991年 | 100篇 |
1990年 | 76篇 |
1989年 | 50篇 |
1988年 | 63篇 |
1987年 | 25篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
本文提出了一种新的研究全球气候温度变化的思路。为发现全球气候变化的宏观规律,把生物圈系统作为一个整体的物质进行研究,从而把纷繁复杂的全球气候温度变化问题归纳成经典物理学的热量与温度变化问题。给出了广义生物圈的热平衡测量Q值和温度变化的热力学公式,并在实际数据的基础上通过计算发现人类使用矿物燃料和核能所排放的热量理论上可使全球海平面每年升高35 mm或者可使大气对流层温度每年升高011 ℃。该发现表明:能源热量因素已成为影响全球温度变化的重要因素。 相似文献
52.
53.
贵阳木本植物始花期对温度变化的敏感度 总被引:1,自引:0,他引:1
植物物候期的温度敏感度反映了植物是怎样及在何种程度上响应气候变化,研究不同物种物候期的温度敏感度有利于鉴别易受气候变化影响的物种。现有关于始花期的温度敏感度研究主要集中在温带地区,在亚热带地区研究仍较少。本文以位于亚热带的贵阳为研究区,利用1980-2014年60种典型木本植物的始花期观测资料,分析了该地区植物始花期变化趋势及对气温变化的敏感度,评估了样本量大小对敏感度估计稳定性的影响。结果表明:①研究时段内贵阳发生了明显的气候变化,年平均气温显著升高,其中春、秋季的增温比夏、冬季显著。②绝大多数植物(88.3%)的始花期在研究时段内呈提前趋势,其中显著提前的占物种总数的21.7%(P<0.05);60种植物始花期总体的提前趋势为2.89 d/10 a。③绝大多数(88.3%)植物始花期的年际变化与最优时段内平均气温呈显著负相关(P<0.05),所有植物始花期的总体敏感度为-5.75 d/℃。④样本量大小对温度敏感度估计的稳定性有显著影响,15年长序列能将敏感度估计结果的波动范围以99%的概率控制在2 d/℃之内。 相似文献
54.
Holocene climate and cultural evolution in late prehistoric-early historic West Asia 总被引:2,自引:0,他引:2
The precipitation climatology and the underlying climate mechanisms of the eastern Mediterranean, West Asia, and the Indian subcontinent are reviewed, with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation. Holocene climate change of the region is summarized from proxy records. The Indian monsoon weakened during the Holocene over its northernmost region, the Ganges and Indus catchments and the western Arabian Sea. Southern regions, the Indian Peninsula, do not show a reduction, but an increase of summer monsoon rain across the Holocene. The long-term trend towards drier conditions in the eastern Mediterranean can be linked to a regionally complex monsoon evolution. Abrupt climate change events, such as the widespread droughts around 8200, 5200 and 4200 cal yr BP, are suggested to be the result of altered subtropical upper-level flow over the eastern Mediterranean and Asia.The abrupt climate change events of the Holocene radically altered precipitation, fundamental for cereal agriculture, across the expanse of late prehistoric-early historic cultures known from the archaeological record in these regions. Social adaptations to reduced agro-production, in both dry-farming and irrigation agriculture regions, are visible in the archaeological record during each abrupt climate change event in West Asia. Chronological refinement, in both the paleoclimate and archaeological records, and transfer functions for both precipitation and agro-production are needed to understand precisely the evident causal linkages. 相似文献
55.
Diets of Steller sea lions off the coast of Hokkaido,Japan: An inter‐decadal and geographic comparison 下载免费PDF全文
Yoko Goto Akihiko Wada Noboru Hoshino Takahiro Takashima Masaki Mitsuhashi Kaoru Hattori Orio Yamamura 《Marine Ecology》2017,38(6)
Inter‐decadal and geographic variations in the diets of Steller sea lion, Eumetopias jubatus, were examined based on the contents of 408 stomachs collected from coastal areas around Hokkaido Island during the periods 1994–1998 and 2005–2012. The most important prey species in the 1990s were gadid fishes (walleye pollock [Gadus chalcogrammus], Pacific cod [Gadus microcephalus] and saffron cod [Eleginus gracilis]). The frequency of occurrence and gravimetric contribution of gadids decreased in the 2000s latter period at three study sites (Rausu, Shakotan and Rebun) and were replaced by Okhotsk Atka mackerel (Pleurogrammus azonus) and smooth lumpsucker (Aptocyclus ventricosus). However, analysis based on gravimetric composition indicated that the dietary diversity of prey showed only a slight inter‐decadal difference, reflecting the wide diversity of prey ingested during both study periods. These results indicate that Steller sea lions along the Hokkaido coast are opportunistic feeders that utilize a wide variety of prey, and appear to feed mainly upon prey that is easily obtained. 相似文献
56.
The potential impact of climate change on fluvial flooding is receiving considerable scientific and political interest thanks to evidence from climate model projections and a widely held belief that flood risk may be increasing at European levels. This review compares published work on historical trends in UK rainfall and river flow records with high‐resolution regional climate change projections, and attempts to reconcile apparent differences between the two. Attention is focused on the techniques used for climate change detection and attribution, as well as the potential confounding effects of land‐use change. International and domestic efforts to build adaptive capacity rest on improved quantification of uncertainty in flood risk at very local, catchment and regional scales. This will involve further research to better integrate climate and land‐management interactions, to understand changes in the dependence between different flood generating mechanisms, and to improve the characterization and communication of uncertainty at all stages of analysis. Resources are also needed to ensure that latest, but still uncertain, science is presented in an appropriate form to underpin policy development and is translated into sensible guidance for practitioners. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
57.
The Tibetan Plateau has one of the most complex climates in the world. Analysis of the climate in this region is important for understanding the climate change worldwide. In this study, climate patterns and trends in the Tibetan Plateau were analysed for the period from 1961 to 2001. Air temperature and precipitation were analysed on monthly and annual time scales using data collected from the National Meteorological Centre, China Meteorological Administration. Nonlinear slopes were estimated and analysed to investigate the spatial and temporal trends of air temperature and precipitation in the Tibetan Plateau using a Mann–Kendall method. Spatial analysis of air temperature and precipitation variability across the Tibetan Plateau was undertaken. While most trends are local in nature, there are general basinwide patterns. Temperature during the last several decades showed a long‐term warmer trend, especially the areas around Dingri and Zogong stations, which formed two increasing centres. Only one of the stations investigated exhibited decreasing trend, and this was not significant. Precipitation in the Tibetan Plateau has increased in most regions of the study area over the past several decades, especially in the eastern and central part, while the western Tibetan Region exhibited a decreased trend over the same period. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
58.
本文分析了重庆市气候特点及其对重庆农业的影响;并在全球气候变暖的大气候背景下,分析了重庆气候的变化趋势,并就气候变化对重庆农业可能造成的影响进行了初步的探讨;提出了重庆农业应对气候变化的适应性战略和技术措施。 相似文献
59.
运用数值模拟建立青藏高原兹格塘错流域土壤、植被、气候等的空间和属性数据库;接着,借助分布式流域尺度水文模型(SWAT模型),对兹格塘错1956—2006年间的流量进行模拟实验;最后,反演50年来兹格塘错流域水文过程,测试流域温度、降水和蒸发组合的敏感因子对湖泊水量变化的效应,探讨50年来湖泊水量对气候变化的响应。模拟实验的边界条件设置为自然地形、土壤、植被覆盖,其中土壤资料包括有机质含量、粒径等理化参数。模拟结果表明:兹格塘错的年平均流量为6.3m3/s,流量高峰集中在8月至10月,并且由于融雪补给的关系,3月出现另一个流量高峰;模拟结果与遥感解译所得到的结果吻合较好。敏感实验表明:兹格塘错流域内温度、降水和蒸发组合的敏感因子实验具有高原特征,即高原湖泊的水文过程和湖泊流量变化有着较为敏感的响应关系;兹格塘错流量受降水的影响最大,随着降水的增加,流量有所增加;在温度升高的情况下,流域蒸发量增加速度大,兹格塘错流量增加的效应不明显,而在冷湿模式下,流域蒸发量降低,兹格塘错流量增加显著。 相似文献
60.
根据1951-2010年珠江流域23个典型断面流量资料,用P-III型分布曲线拟合洪水系列进行频率计算,分析了珠江流域极端洪水事件的变化趋势。结果表明:1980年以来,珠江流域极端洪水事件发生的频次明显增加,尤其是自1990年以来增加趋势显著;1981-2010年较1951-1980年珠江流域约70%典型断面极端洪水事件呈增加趋势,主要分布在西江、北江、粤西;而近30%的典型断面呈减少趋势,主要分布在东江和桂南。 相似文献