全文获取类型
收费全文 | 11436篇 |
免费 | 2866篇 |
国内免费 | 4768篇 |
专业分类
测绘学 | 686篇 |
大气科学 | 6619篇 |
地球物理 | 2794篇 |
地质学 | 4601篇 |
海洋学 | 1795篇 |
天文学 | 208篇 |
综合类 | 778篇 |
自然地理 | 1589篇 |
出版年
2024年 | 78篇 |
2023年 | 223篇 |
2022年 | 474篇 |
2021年 | 558篇 |
2020年 | 596篇 |
2019年 | 733篇 |
2018年 | 619篇 |
2017年 | 652篇 |
2016年 | 639篇 |
2015年 | 749篇 |
2014年 | 917篇 |
2013年 | 1146篇 |
2012年 | 994篇 |
2011年 | 935篇 |
2010年 | 734篇 |
2009年 | 910篇 |
2008年 | 798篇 |
2007年 | 1020篇 |
2006年 | 845篇 |
2005年 | 815篇 |
2004年 | 647篇 |
2003年 | 541篇 |
2002年 | 452篇 |
2001年 | 404篇 |
2000年 | 375篇 |
1999年 | 351篇 |
1998年 | 328篇 |
1997年 | 271篇 |
1996年 | 216篇 |
1995年 | 220篇 |
1994年 | 198篇 |
1993年 | 171篇 |
1992年 | 103篇 |
1991年 | 87篇 |
1990年 | 56篇 |
1989年 | 45篇 |
1988年 | 57篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
挖孔桩在长春市应用及承载力评定 总被引:1,自引:0,他引:1
挖孔桩承载力的评价是国内、吉林省内重大课题,直接关系到它应用前景。本文试图结合国内现行诸规范,结合长春市实例,提出建议性意见,供广大设计者参考。 相似文献
993.
994.
995.
G Nageswara Rao 《Journal of Earth System Science》2001,110(1):87-94
It is well known that heavy rainfall occurs in the southwestern sector of the monsoon depressions due to strong convergence
in that sector. By examining the rainfall distribution associated with the monsoon disturbances (lows and depressions) in
one of the central Indian river basins, ‘Godavari’, the author found that when the disturbance-centre is away from the basin,
heavy rainfall may also occur in the basin area close to the confluence line and cause severe floods in the river. The confluence
line is the zone of convergence between the northeasterlies to the west of the disturbance centre and the monsoon westerlies.
This study further reveals the importance of the position and movement of the confluence line with respect to the basin, on
which the intensity and the raising period of the resulting flood depend. 相似文献
996.
997.
The spinel solid solution was found to exist in the whole range between Fe3O4 and γ-Fe2SiO4 at over 10 GPa. The resistivity of Fe3−
x
Si
x
O4 (0.0<x<0.288) was measured in the temperature range of 80∼300 K by the AC impedance method. Electron hopping between Fe3+ and Fe2+ in the octahedral site of iron-rich phases gives a large electric conductivity at room temperature. The activation energy
of the electron hopping becomes larger with increasing γ-Fe2SiO4 component. A nonlinear change in electric conductivity is not simply caused by the statistical probability of Fe3+–Fe2+ electron hopping with increasing the total Si content. This is probably because a large number of Si4+ ions occupies the octahedral site and the adjacent Fe2+ keeping the local electric neutrality around Si4+ makes a cluster, which generates a local deformation by Si substitution.
The temperature dependence of the conductivity of solid solutions indicates the Verwey transition temperature, which decreases
from 124(±2) K at x=0 (Fe3O4) to 102(±5) K at x=0.288, and the electric conductivity gap at the transition temperature decreases with Si4+ substitution.
Received: 15 March 2000 / Accepted: 4 September 2000 相似文献
998.
Agricultural practices, hydrology, and water quality of the 267-km2 Big Spring groundwater drainage basin in Clayton County, Iowa, have been monitored since 1981. Land use is agricultural; nitrate-nitrogen
(-N) and herbicides are the resulting contaminants in groundwater and surface water. Ordovician Galena Group carbonate rocks
comprise the main aquifer in the basin. Recharge to this karstic aquifer is by infiltration, augmented by sinkhole-captured
runoff. Groundwater is discharged at Big Spring, where quantity and quality of the discharge are monitored.
Monitoring has shown a threefold increase in groundwater nitrate-N concentrations from the 1960s to the early 1980s. The nitrate-N
discharged from the basin typically is equivalent to over one-third of the nitrogen fertilizer applied, with larger losses
during wetter years. Atrazine is present in groundwater all year; however, contaminant concentrations in the groundwater respond
directly to recharge events, and unique chemical signatures of infiltration versus runoff recharge are detectable in the discharge
from Big Spring.
Education and demonstration efforts have reduced nitrogen fertilizer application rates by one-third since 1981. Relating declines
in nitrate and pesticide concentrations to inputs of nitrogen fertilizer and pesticides at Big Spring is problematic. Annual
recharge has varied five-fold during monitoring, overshadowing any water-quality improvements resulting from incrementally
decreased inputs.
Electronic Publication 相似文献
999.
东安牛头寨地区锑矿床控制因素及成因探讨 总被引:1,自引:0,他引:1
锑矿床严格受构造控制,表现出逐级控矿特征:区域性F1断裂、牛头寨复式背斜及北北东、北北西、北西向次级断裂,分别控制着锑矿带、锑矿床的空间展布及锑矿脉的形态、产状与规模。地层岩石建造对成矿的控制,主要表现在赋矿地层中的白云岩、硅质岩等易碎裂,为矿液的运移提供了有利的通道。部分含矿地层的Sb高丰度,还可能成为矿提供了矿源。已有的研究表明,锑矿床的硫同位素组成具有岩浆硫特征,并混入了部分围岩沉积硫。石英的氢氧同位素组成反映出岩浆流体与变质水混入溶液特征。矿物包裹体的爆裂温度平均为157℃。石英的包裹体成分测试结果,揭示了矿液为K-Na-Ca-Cl型富硅的弱碱性溶液。矿床成因厘定为岩浆期后中低温热液脉状充填矿床。 相似文献
1000.
赤道印度洋-太平洋地区海气系统的齿轮式耦合和ENSO事件 II.数值模拟 总被引:14,自引:2,他引:14
首先应用IAP/LASG GOALS气候模式的多年积分的结果,对赤道中西太平洋和印度洋 的SST和纬向风场进行分析,发现在模式中也同样存在与观测资料分析结果相似的“印太齿 轮式耦合”。基于此,设计了赤道太平洋和印度洋海域纬向风应力异常的4组敏感性试验, 去研究太平洋和印度洋海气相互作用的联系。结果表明,在太平洋或印度洋上的大气异常 信号通过印-太齿轮组合(GIP)作为桥梁(atmospheric bridge),影响到另一地的海气 相互作用,从而将太平洋上的ENSO类年际变率信号与印度洋环流和亚洲季风纬向分量的变 化联系起来。 相似文献