全文获取类型
收费全文 | 7751篇 |
免费 | 1614篇 |
国内免费 | 2098篇 |
专业分类
测绘学 | 650篇 |
大气科学 | 1466篇 |
地球物理 | 2076篇 |
地质学 | 4095篇 |
海洋学 | 1184篇 |
天文学 | 315篇 |
综合类 | 757篇 |
自然地理 | 920篇 |
出版年
2024年 | 34篇 |
2023年 | 126篇 |
2022年 | 370篇 |
2021年 | 397篇 |
2020年 | 345篇 |
2019年 | 432篇 |
2018年 | 407篇 |
2017年 | 403篇 |
2016年 | 426篇 |
2015年 | 432篇 |
2014年 | 481篇 |
2013年 | 511篇 |
2012年 | 598篇 |
2011年 | 554篇 |
2010年 | 576篇 |
2009年 | 552篇 |
2008年 | 521篇 |
2007年 | 482篇 |
2006年 | 440篇 |
2005年 | 360篇 |
2004年 | 335篇 |
2003年 | 283篇 |
2002年 | 254篇 |
2001年 | 270篇 |
2000年 | 281篇 |
1999年 | 241篇 |
1998年 | 192篇 |
1997年 | 212篇 |
1996年 | 171篇 |
1995年 | 143篇 |
1994年 | 136篇 |
1993年 | 105篇 |
1992年 | 97篇 |
1991年 | 63篇 |
1990年 | 50篇 |
1989年 | 47篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1958年 | 10篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
781.
782.
对任丘油田开发过程中油田水水质特征及演化规律进行了初步分析,探讨了人工注水对油田水质的演化影响,其结果表明,注入水对油田水泊稀释混合作用明显,破坏了油层内部水-岩作用平衡,改变了井下原来的水文地球化学环境,根据诺模图求得的一些离子含量与其实际值之间存在明显差异,表明机械混合与水-岩相互作用并存,这与实际情况是吻合的。 相似文献
783.
黄县早第三纪断陷盆地充填特征及层序划分 总被引:1,自引:0,他引:1
黄县早第三纪断陷盆地充填沉积序列共划分出三个层序(三级层序),层序Ⅰ不完整,层序Ⅱ和层序Ⅲ皆由低位体系域、扩张体系域和萎缩体系域三个基本单位构成。层序界面主要有区域构造运动界面和盆地构造应力转换面体系域转换界面两种类型。聚煤作用、油气聚集主要发生在盆地低水位至扩张期,低水位和扩张体系域含有主要的煤层和油气母岩(生油岩)。 相似文献
784.
Han Zaisheng 《Hydrogeology Journal》1998,6(3):416-420
Groundwater plays an important role for urban and industrial water supply in northern China. More than 1000 groundwater wellfields
have been explored and installed. Groundwater provides about half the total quantity of the urban water supply. Complete regulations
and methods for the exploration of groundwater have been established in the P.R. China. Substantial over-exploitation of groundwater
has created environmental problems in some cities. Some safeguarding measures for groundwater-resource protection have been
undertaken.
Received, August 1997 · Revised, February 1998 · Accepted, April 1998 相似文献
785.
使用紫金山天文台青海观测站13.7米毫米波射电望远镜,于1996年12月10日至1997年1月2日和1997年3月25日至1997年4月4日对海尔-波普彗星的CO分子J=1—0转动跃迁谱线(频率为115.27120GHz)进行了观测.观测谱线表明,CO分子相对于地心的速度比彗星整体相对于地心的速度要小些,即有蓝移现象.这反映了CO分子是由该彗星迎着太阳的面以一定的速度产生出来的.从观测谱线中还初步估算了该彗星CO分子的产生速率. 相似文献
786.
INTRODUCTIONInhighlyextendedregions(β>1.5-2)suchastheBasinandRangeProvinceandpasivemargins,extensionaltectonicsystemischaract... 相似文献
787.
运用伏特拉核函数基本理论,建立了南桐矿区红岩煤矿矿井涌水量的线性、非线性核函数模型,介绍了计算核孙数模型所用的递归算法,同时对模拟结果的残差进行了分析,并用AR模型进行了改进。 相似文献
788.
长治水泥厂区域地震地质环境评价 总被引:1,自引:0,他引:1
长治水泥厂位于山西隆起区南部长治盆地, 长治盆地属中强潜在震原区。场地附近晋获断裂现代活动相对较弱, 晚更新后断裂基本停止活动, 对水泥厂场地无直接影响。 相似文献
789.
The recovery of nickel, copper and cobalt from ocean manganese nodules by a segregation roasting technique was investigated under a wide range of conditions with several nodule samples all of which gave similar results. The best conditions for the segregation of the metals were achieved with CaCl2 as the chloride source at a batch retention time of approximately two hours; the highest recoveries were obtained at approximately 850°C for copper and at 1,050°C for nickel and cobalt. At 850°C, copper recovery was 75%, but nickel and cobalt recoveries were only about 25%. At 1,050°C, the nickel and cobalt recoveries were increased to about 60%, but the copper recovery dropped to only 35%. Electron-probe microanalysis showed the segregated metal to be an alloy, indicating that gaseous reactions play an important role in the reduction of chlorides to metal during the process. 相似文献
790.
Prof. Dr. T. N. Krishnamurti H. S. Bedi Wei Han 《Meteorology and Atmospheric Physics》1998,67(1-4):117-134
Summary In this paper we address the issue of monsoon forecasts in relation to the organization of convection. Given a physical initialization procedure, within a data assimilation, it is possible to use the detailed distribution of rainfall from mesoconvective precipitating elements to define the initial state of a global model. If that is carried out using a very high resolution model then the initial state can carry within it an organization of convection within the resolvable scales. Then the impact of physical initialization on the maintenance and prediction of tropical weather such as the monsoon can be determined. Lacking such an initialization, one can expect the convectively driven energetics to be biased, and a slow degradation of the forecasts can follow. Several examples of forecasts at different resolutions are discussed here. The main findings of this study are that improved forecast results are obtained when physical initialization is invoked where the observed rain and the model resolution are comparable, i.e. the footprint of the highest resolutions rainfall estimates obtained from satellite based data sets (principally we use the SSM/I instrument over the oceans). At this resolution, we note that the model is able to carry an organization of convection in the initialization and in the forecasts through the medium-range time scale.We have compared our results of monsoon studies at a resolution T255 with those at resolution T62. The transform grid separation at the resolution T255 is approximately 50 km and at the resolution T62, it is approximately 200 km. We find that the model at the higher resolution (T255) performs better and has more realistic energy conversions for the convectively driven synoptic scale monsoon.An organization of convection, at the synoptic scales, is not seen in the forecasts at lower resolutions, T62, where the rainfall patterns are generally much broader and tend to be more zonal. Such organization appears more realistic at the resolution T255. Variances of the energy conversion, calculated in the two-dimensional spectral space, from physically initialized short range forecasts at the higher resolution are seen to be largest on the scales of the monsoon. Similar calculations for the reanalyzed fields at lower resolutions show the spectral distribution of variances to be biased towards local Hadley scale overturnings.With 12 Figures 相似文献