全文获取类型
收费全文 | 26790篇 |
免费 | 4917篇 |
国内免费 | 6425篇 |
专业分类
测绘学 | 1178篇 |
大气科学 | 5904篇 |
地球物理 | 7214篇 |
地质学 | 13383篇 |
海洋学 | 2920篇 |
天文学 | 1379篇 |
综合类 | 3048篇 |
自然地理 | 3106篇 |
出版年
2024年 | 125篇 |
2023年 | 503篇 |
2022年 | 1157篇 |
2021年 | 1340篇 |
2020年 | 1113篇 |
2019年 | 1204篇 |
2018年 | 1514篇 |
2017年 | 1340篇 |
2016年 | 1608篇 |
2015年 | 1259篇 |
2014年 | 1635篇 |
2013年 | 1489篇 |
2012年 | 1355篇 |
2011年 | 1399篇 |
2010年 | 1501篇 |
2009年 | 1465篇 |
2008年 | 1324篇 |
2007年 | 1274篇 |
2006年 | 1021篇 |
2005年 | 886篇 |
2004年 | 772篇 |
2003年 | 798篇 |
2002年 | 739篇 |
2001年 | 691篇 |
2000年 | 919篇 |
1999年 | 1389篇 |
1998年 | 1118篇 |
1997年 | 1114篇 |
1996年 | 1004篇 |
1995年 | 881篇 |
1994年 | 827篇 |
1993年 | 696篇 |
1992年 | 543篇 |
1991年 | 438篇 |
1990年 | 324篇 |
1989年 | 304篇 |
1988年 | 268篇 |
1987年 | 171篇 |
1986年 | 147篇 |
1985年 | 114篇 |
1984年 | 70篇 |
1983年 | 57篇 |
1982年 | 70篇 |
1981年 | 56篇 |
1980年 | 30篇 |
1979年 | 29篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
湘西自治州北部铅锌矿带,处于桑植复向斜西南段,长100km以上,宽50km左右,矿带内铅锌矿点广布,受地层、构造、岩性的控制。上寒武统耗子沱群至下奥陶统大湾组共有7个含矿层位,北东向背斜倾伏端及北东向断裂、层间裂隙以及次级北西向横跨背斜是矿床控矿构造,有矿体赋存的含矿层有明显的硅化作用,且硅化体中Pb,Zn,Cu明显富集,分别为地层的66、32、8倍,Sr/Ba比值为0.60,无矿存在的硅化体则Pb,Zn,Cu含量接近地层或稍高于地层,Sr/Ba比值高达1.15。在砂子坡背斜南翼、红岩溪背斜北东端和南西倾伏端、盐井背斜,下奥陶统红花园组顶部含矿层内为找矿远景区。 相似文献
124.
The climate–population relationship has long been conceived. Although the topic has been repeatedly investigated, most of
the related works are Eurocentric or qualitative. Consequently, the relationship between climate and population remains ambiguous.
In this study, fine-grained temperature reconstructions and historical population data sets have been employed to statistically
test a hypothesized relationship between temperature change and population growth (i.e., cooling associated with below average
population growth) in China over the past millennium. The important results were: (1) Long-term temperature change significantly
determined the population growth dynamics of China. However, spatial variation existed, whilst population growth in Central
China was shown to be responsive to both long- and short-term temperature changes; in marginal areas, population growth was
only sensitive to short-term temperature fluctuations. (2) Temporally, the temperature–population relationship was obscured
in some periods, which was attributable to the factors of drought and social buffers. In summary, a temperature–population
relationship was mediated by geographic factors, the aridity threshold, and social factors. Given the upcoming threat posed
by climate change to human societies, this study seeks to improve our knowledge and understanding of the climate–society relationship. 相似文献
125.
Twenty-year temperature and precipitation extremes and their projected future changes are evaluated in an ensemble of climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5), updating a similar study based on the CMIP3 ensemble. The projected changes are documented for three radiative forcing scenarios. The performance of the CMIP5 models in simulating 20-year temperature and precipitation extremes is comparable to that of the CMIP3 ensemble. The models simulate late 20th century warm extremes reasonably well, compared to estimates from reanalyses. The model discrepancies in simulating cold extremes are generally larger than those for warm extremes. Simulated late 20th century precipitation extremes are plausible in the extratropics but uncertainty in extreme precipitation in the tropics and subtropics remains very large, both in the models and the observationally-constrained datasets. Consistent with CMIP3 results, CMIP5 cold extremes generally warm faster than warm extremes, mainly in regions where snow and sea-ice retreat with global warming. There are tropical and subtropical regions where warming rates of warm extremes exceed those of cold extremes. Relative changes in the intensity of precipitation extremes generally exceed relative changes in annual mean precipitation. The corresponding waiting times for late 20th century extreme precipitation events are reduced almost everywhere, except for a few subtropical regions. The CMIP5 planetary sensitivity in extreme precipitation is about 6 %/°C, with generally lower values over extratropical land. 相似文献
126.
Parameterization of the thermal impacts of sub-grid orography on numerical modeling of the surface energy budget over East Asia 总被引:4,自引:0,他引:4
Summary A parameterization scheme for the thermal effects of subgrid scale orography is incorporated into a regional climate model
(developed at Nanjing University) and its impact on modeling of the surface energy budget over East Asia is evaluated. This
scheme includes the effect of terrain slope and orientation on the computation of solar and infrared radiation fluxes at the
surface, as well as the surface sensible and latent heat fluxes. Calculations show that subgrid terrain parameters alter the
diurnal cycle and horizontal distributions of surface energy budget components. This effect becomes more significant with
increased terrain slope, especially in winter. Due to the inclusion of the subgrid topography, the surface area of a model
grid box changes over complex terrain areas. Numerical experiments, with and without the subgrid scale topography scheme,
show that the parameterization scheme of subgrid scale topography modifies the distribution of the surface energy budget and
surface temperature around the Tibetan Plateau. Comparisons with observations indicate that the subgrid topography scheme,
implemented in the climate model, reproduces the observed detailed spatial temperature structures at the eastern edge of the
Tibetan Plateau and reduces the tendency to overestimate precipitation along the southern coastal areas of China in summer. 相似文献
127.
利用中国科学院大气物理研究所的完全弹性三维雹云数值模式(IAP—CSM3D),对2007年7月21日发生在湛江的一次强对流进行数值模拟,分析了强对流的气流结构、垂直涡度、雷达回波及含水量分布变化特征。结果表明,模拟的回波最大强度与雷达实测结果较吻合。模拟的强对流发展阶段气流结构的典型特征为下层水平辐合,上层水平辐散,气流在5km高度发生转向;处于成熟阶段的底层辐合比发展阶段的更强。随着时间的推移,近地层气流先辐合后辐散,下沉辐散气流一直持续到冰雹云消散。模拟的风暴云高含水量中心与强回波中心相对应,出现在上升气流最大区域附近,这说明该风暴云的动力场与物质场配合较好。 相似文献
129.
We examined both long-term climate variability and anthropogenic contributions to current climate change for Xinjiang province of northwest China. Xinjiang encompasses several mountain ranges and inter-mountain basins and is comprised of a northern semiarid region and a more arid southern region. Climate over the last three centuries was reconstructed from tree rings and temperature series were calculated for the past 50 years using weather station data. Three major conclusions from these analyses are: (1) Although temperature varied considerably in Xinjiang over the last 200 years, it was non-directional until the last 50 years when a substantial warming trend occurred; (2) The semiarid North Xinjiang was representative of the northern hemisphere climate, while the more arid South Xinjiang resembled the southern hemisphere climate, meanwhile, (3) The entire Xinjiang province captured the global-scale climate signal. We also compared human contributions to global change between North and South Xinjiang, including land cover/land use, population, and greenhouse gas production. For both regions, urban areas acted as heat islands; and large areas of grassland and forest were converted to barren land, especially in North Xinjiang. Additionally, North Xinjiang also showed larger increase in population and greenhouse gas emissions mainly associated with animal production than those in South Xinjiang. Although Xinjiang province is a geographically coupled mountain–basin system, the two regions have distinct climate patterns and anthropogenic activities related to land cover conversion and greenhouse gas production. 相似文献
130.
Yangtze Delta floods and droughts of the last millennium: Abrupt changes and long term memory 总被引:6,自引:1,他引:6
Summary Climate variability and flood events in the Yangtze Delta, which is a low-lying terrain prone to flood hazards, storm tides and typhoons, are studied in terms of a trend and detrended fluctuation analysis of historical records. The data used in this paper were extracted from historical records such as local annuals and chronologies from 1000–1950 and supplemented by instrumental observations since 1950. The historical data includes frequencies of floods, droughts and maritime events on a decadal basis. Flood magnitudes increase during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age, which are characterised by arid climate events, are followed by wet and cold climate conditions with frequent flood hazards. For trend analysis, the Mann-Kendall test is applied to determine the changing trends of flood and drought frequency. Flood frequency during 1000–1950 shows a negative trend before 1600 A.D. and a positive trend thereafter; drought frequency increases after 1300. The detrended fluctuation analysis of the flood and drought frequencies reveals power law scaling up to centuries; this is related to long-term memory and is similar to the river Nile floods. 相似文献