全文获取类型
收费全文 | 4109篇 |
免费 | 893篇 |
国内免费 | 1274篇 |
专业分类
测绘学 | 137篇 |
大气科学 | 855篇 |
地球物理 | 1329篇 |
地质学 | 1906篇 |
海洋学 | 1039篇 |
天文学 | 119篇 |
综合类 | 208篇 |
自然地理 | 683篇 |
出版年
2024年 | 19篇 |
2023年 | 59篇 |
2022年 | 154篇 |
2021年 | 192篇 |
2020年 | 201篇 |
2019年 | 199篇 |
2018年 | 197篇 |
2017年 | 219篇 |
2016年 | 241篇 |
2015年 | 263篇 |
2014年 | 268篇 |
2013年 | 297篇 |
2012年 | 240篇 |
2011年 | 229篇 |
2010年 | 232篇 |
2009年 | 287篇 |
2008年 | 313篇 |
2007年 | 290篇 |
2006年 | 291篇 |
2005年 | 267篇 |
2004年 | 227篇 |
2003年 | 221篇 |
2002年 | 186篇 |
2001年 | 184篇 |
2000年 | 165篇 |
1999年 | 146篇 |
1998年 | 157篇 |
1997年 | 107篇 |
1996年 | 92篇 |
1995年 | 64篇 |
1994年 | 54篇 |
1993年 | 40篇 |
1992年 | 47篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有6276条查询结果,搜索用时 828 毫秒
111.
1 Introduction The annual mean world temperature increased by about 0.6℃ from the late 1800s to the 1980s (Wang, 1994). The global environmental change is marked with “global warming” and its possible effects on the ecosystem as well as the production … 相似文献
112.
Mongolian gerbils (Meriones unguiculatus) and Daurian pikas (Ochotona dauurica) are two key small mammal species in the Inner Mongolian grasslands, China. Mongolian gerbils displayed density-dependent population growth, but the time lag of density dependence was short and within season. The spring–autumn population growth rate was inversely related to population density in Mongolian gerbils of the Erdos desert grasslands. The autumn–spring population growth rate of Mongolian gerbils was inversely related to winter precipitation. Precipitation had stronger effects on the population growth of gerbils during the non-breeding season. The monthly population growth rate of Daurian pikas was positively related to the monthly precipitation and was inversely related to population density in central Inner Mongolia. Daurian pikas select habitats with tall plants. Increased precipitation enhances plant production and increases the height of plants in arid and semi-arid regions. This enhancement of plant height might increase the population growth of Daurian pikas. Mongolian gerbils live in short grasslands. Increased winter precipitation might result in higher winter mortality of Mongolia gerbils, or taller plants might supress gerbil population growth in wet years. Therefore, responses of small mammal species to changes in precipitation depend on the life history of small mammals and changes in vegetation induced by climatic changes. 相似文献
113.
In this study, hydrogeologic and hydrochemical information from the Mersin-Erdemli groundwater system were integrated and
used to determine the main factors and mechanisms controlling the chemistry of groundwaters in the area and anthropogenic
factors presently affecting them. The PHREEQC geochemical modeling demonstrated that relatively few phases are required to
derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area
fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) precipitation of calcite, amorphous
silica and kaolinite; (4) ion exchange. As determined by multivariate statistical analysis, anthropogenic factors show seasonality
in the area where most contaminated waters related to fertilizer and fungicide applications that occur during early summer
season. 相似文献
114.
《中国地球化学学报》2006,25(B08):127-128
115.
116.
通过对向斜洼地含水层水文地质特征的勘探及研究,对研究区的水文地质边界条件进行了概化,并用水均衡法估算了地下水资源量,对拟建一级电站引水渠沿线提取地下水进行融冰的可行性进行了研究,并提出了取水方案. 相似文献
117.
118.
Sandro Fuzzi Maria Cristina Facchini Stefano Decesari Emanuela Matta Mihaiela Mircea 《Atmospheric Research》2002,64(1-4)
We have recently set up a new procedure for characterising the water soluble organic compounds (WSOC) in fog water, for which information is still rather limited. Fog samples collected during the 1998–1999 fall–winter season in the Po Valley (Italy) were analysed following this procedure, which allows a quantitative determination of three main classes of organic compounds (neutral species, mono- and di-carboxylic acids, polycarboxylic acids), together accounting for ca. 85% of the total WSOC. This procedure also provides information on the main chemical characteristics of these three classes of compounds (functional groups, aliphatic vs. aromatic character, etc.). The enhanced chemical knowledge on fog/cloud chemical composition opens new scenarios as far as chemical and microphysical processes in clouds and fogs are concerned. 相似文献
119.
120.
东南极Lambert冰川-Amery冰架系统平衡通量分布的计算 总被引:2,自引:1,他引:2
通过对Lambert冰川盆地(LGB)考察路线上约1 700 km长的LGB剖面和距冰架末端约50 km、长150 km的A剖面, 分别利用GPS冰流速值及雷达测厚值进行冰通量的计算得出:每年流过LGB剖面的冰通量为43.95 Gta-1, 而通过A剖面的冰通量仅为26. 42 Gt*a-1, Amery冰架底部净融化量为7.8 Gt*a-1. 整个Lambert冰川-Amery冰架系统(LAS)地区的表面净物质平衡总量约为90 Gt*a-1; LGB地区的表面净物质平衡总量为46 Gt*a-1. 通过分析得出, 整个LAS地区及LGB地区均处于物质正平衡状态, 而LAS流域的上游区域S'则处于物质负平衡状态. 相似文献