全文获取类型
收费全文 | 534篇 |
免费 | 53篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 34篇 |
地球物理 | 277篇 |
地质学 | 95篇 |
海洋学 | 65篇 |
天文学 | 49篇 |
综合类 | 11篇 |
自然地理 | 67篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 23篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 35篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 51篇 |
2012年 | 17篇 |
2011年 | 34篇 |
2010年 | 22篇 |
2009年 | 25篇 |
2008年 | 36篇 |
2007年 | 29篇 |
2006年 | 31篇 |
2005年 | 31篇 |
2004年 | 15篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 14篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有617条查询结果,搜索用时 46 毫秒
41.
目的:应用高分辨CT(HRCT)扫描方法,增加对头颅腔隙梗塞诊断的可靠性,材料和方法:对临床疑有腔隙的病人,在基底节区及可疑部位加用HRC扫描,遇到腔隙病灶与像素颗粒难以区分时在相同层面或上下1-2mm处做HRCT扫描。结果,有489例常规CT正常的病例哪现了腔隙灶,在遇到的502例不易诊断的可疑病灶中,经HRCT确诊的真正腔隙灶300例,伪腔隙(像素)202例,同时发现HRCT对正常脑组织结构的显示要较常规CT越得多,结论HRCT不仅能提高腔隙性梗塞的检出率,还能辨伪腔隙,是弥补常规CT对腔隙诊断不足的较好手段。 相似文献
42.
黄土丘陵沟壑区小流域降雨入渗产流点面转化 总被引:7,自引:6,他引:7
在充分考虑小流域土壤入渗速率点面转化及地表结皮等影响因素在内的基础上 ,提出了小流域土壤入渗速率点面转化公式 :fm=fn×Sn/S×an×bn。以纸坊沟小流域为例 ,将实测的流域土壤入渗速率值 (点渗值 )利用上式进行转化 (面渗值 ) ,并与流域径流出口观测站由降雨径流观测值根据水量平衡原理推算出的面渗值进行对比 ,平均相对误差仅为 2 .42 %。初步得出流域土壤面渗率与不同治理度、年内 5~ 9月降雨总量间的单因子和复合因子高精度回归方程 ,为流域综合治理后的水资源量变化趋势提供一条量化途径 相似文献
43.
44.
作者报告了100例脑脓肿,其中一般性脑脓肿62例、脑内小脓肿38例(强化灶小于1.5cm),并对发病部位,临床表现及CT表现的主要特点进行了讨论。 相似文献
45.
46.
Bao Xueyang 《中国地震研究》2006,20(2):190-201
INTRODUCTIONThe modulus of rock is one of the basic elastic parameters of the earth’s medium. Under theassumption of linear elastic theory and Poisson medium,other parameters can be calculated fromit .But the real earth mediumis nonlinear elastic and has not a simple linear relationship between stressand strain.This causes relatively big differences betweenthe dynamic andthe static modulus of rock.In nonlinear elastic theory,the Young’s modulusEis replaced bythe nonlinear elastic modul… 相似文献
47.
Nutrient dynamics in Mediterranean temporary streams: A case study in Pardiela catchment (Degebe River, Portugal) 总被引:1,自引:0,他引:1
Ana Isabel Lilleb Manuela Morais Pedro Guilherme Rita Fonseca Antnio Serafim Ramiro Neves 《Limnologica》2007,37(4):337-348
Most of the streams in the Mediterranean region are temporary, following predictable seasonal of flooding and drying, with a transition from lotic conditions to shallow lentic conditions. The goal of our study was to assess the nitrogen and phosphorus dynamics in channel-bed processes of temporary streams between floods. Results show that, during winter, temperatures ranged between 9.5 and 11.2 °C and oxygen concentration ranged from 8.0 to 9.5 mg L−1, whereas, during summer, temperatures varied between 21.2 and 26.8 °C and oxygen between 1.2 and 5.3 mg L−1, with oxygen depletion in the pools during the night. The nitrate concentrations were far more abundant during winter (February), while ammonium concentration increased after stream fragmentation into pools (especially in July when oxygen depletion conditions favoured ammonification). Results on sediment profiles showed that the most active sediment layers for NH4-N are the top 2–3 cm, corresponding to the sediment depositional sites of the stream. Phosphate concentrations had larger variability, yet concentrations decreased from winter to spring and increased again in summer, when the shallow water pools were formed. Sediment profiles at the sediment depositional sites showed that PO4-P was more dynamic in the first 6 cm.
In Mediterranean temporary streams, nutrient dynamics vary seasonally, as the system transits from lotic conditions to shallow lentic conditions, evidencing the regeneration of nutrients from organic and inorganic matter during the flow cessation period. 相似文献
48.
An example of identifying karst groundwater flow 总被引:3,自引:2,他引:1
Hydrogeological investigations for the purpose of regulating the karst aquifer were carried out in the mountain massif of
Kucaj in the Carpatho-Balkan range of eastern Serbia. Different geophysical methods were applied in order to identify the
position of karstified zones with active circulation of karst underground streams. Especially good results were obtained by
using the spontaneous potential method for the exploration and construction of boreholes and wells. In the valleys of Crni
Timok and Radovanska reka the measurements have been carried out upstream along the whole width of the alluvium to the limestone
periphery. A number of positive and negative anomalies have been recorded. In the centres of positive anomalies several boreholes
were located: HG-19 (centre of anomaly +30 mV, total length of the biggest cavern is 9 m); HG-1 (+20 mV, cavern of 2 m); HG-15
(max. +114 mV, effective cavernousness is 17%).
Received: 20 February 1995 · Accepted: 12 September 1997 相似文献
49.
成组中强震前后动态小震的时空活动特征 总被引:1,自引:0,他引:1
分析了进入活跃时段以来,新疆及邻近地区自1995年3月19日和硕Ms5.0地震后,相继发生的12次Ms≥4.7地震前后调制小震和动态小震的时空活动特征,据此提出了孕系统失稳模式; 相似文献
50.
CAI Qiangguo 《国际泥沙研究》1998,(2)
PHYSICALPROCESSBASEDSOILEROSIONMODELINASMALLWATERSHEDINTHEHILLYLOESSREGION1CAIQiangguo2ABSTRACTAphysicalprocesbasedperstorm... 相似文献