全文获取类型
收费全文 | 118083篇 |
免费 | 7025篇 |
国内免费 | 8422篇 |
专业分类
测绘学 | 4792篇 |
大气科学 | 12589篇 |
地球物理 | 24587篇 |
地质学 | 45727篇 |
海洋学 | 11409篇 |
天文学 | 22035篇 |
综合类 | 3861篇 |
自然地理 | 8530篇 |
出版年
2022年 | 1902篇 |
2021年 | 2480篇 |
2020年 | 2231篇 |
2019年 | 2556篇 |
2018年 | 3986篇 |
2017年 | 3704篇 |
2016年 | 4484篇 |
2015年 | 3052篇 |
2014年 | 4459篇 |
2013年 | 6360篇 |
2012年 | 4570篇 |
2011年 | 5478篇 |
2010年 | 5162篇 |
2009年 | 6057篇 |
2008年 | 5294篇 |
2007年 | 5253篇 |
2006年 | 4664篇 |
2005年 | 3764篇 |
2004年 | 3495篇 |
2003年 | 3326篇 |
2002年 | 3201篇 |
2001年 | 2977篇 |
2000年 | 3000篇 |
1999年 | 3093篇 |
1998年 | 2863篇 |
1997年 | 2683篇 |
1996年 | 2388篇 |
1995年 | 2228篇 |
1994年 | 1949篇 |
1993年 | 1742篇 |
1992年 | 1551篇 |
1991年 | 1457篇 |
1990年 | 1424篇 |
1989年 | 1210篇 |
1988年 | 1151篇 |
1987年 | 1164篇 |
1986年 | 1031篇 |
1985年 | 1216篇 |
1984年 | 1347篇 |
1983年 | 1215篇 |
1982年 | 1127篇 |
1981年 | 1080篇 |
1980年 | 945篇 |
1979年 | 909篇 |
1978年 | 871篇 |
1977年 | 748篇 |
1976年 | 708篇 |
1975年 | 711篇 |
1974年 | 665篇 |
1973年 | 716篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
861.
K. Vinod kumar R. C. Lakhera Tapas R. Martha R. S. Chatterjee A. Bhattacharya 《Environmental Geology》2008,55(4):789-799
Mass movements such as landslides in mountainous terrains are natural degradation processes and one of the most important
landscape-building factors. Varunawat Parbat overlooking Uttarkashi town witnessed a series of landslides on 23 September
2003 and the debris slides and rock falls continued for 2 weeks. This landslide complex was triggered due to the incessant
rainfall prior to the event, and its occurrence led to the blockage of the pilgrim route to Gangotri (source of the Ganges
river) and evacuation of thousands of people to safer places. Though there was no loss of lives due to timely evacuation,
heavy losses to the property were reported. High-resolution stereoscopic earth observation data were acquired after the incidence
to study the landslide in detail with emphasis on the cause of the landslide and mode of failure. Areas along the road and
below the Varunawat foothill region are mapped for landslide risk. It was found that the foothill region of the Varunawat
Parbat was highly disturbed by man-made activities and houses are dangerously located below steep slopes. The potential zones
for landslides along with the existing active and old landslides are mapped. These areas are critical and their treatment
with priority is required in order to minimise further landslide occurrences. 相似文献
862.
Alessandro Tarantino Andrew M. Ridley David G. Toll 《Geotechnical and Geological Engineering》2008,26(6):751-782
This paper presents a review of techniques for field measurement of suction, water content, and water hydraulic conductivity
(permeability). Main problems in the use of field tensiometers are addressed and hints on how to improve tensiometer performance
are given. Advantages and limitations of instruments for indirect measurement of suction including electrical conductivity
sensors, thermal conductivity sensors, dielectric permittivity sensors, filter paper, and psychrometer are discussed. Techniques
for water content measurement based on dielectric methods are then presented. These include time and amplitude domain reflectometry
and capacitance. Finally, a brief overview of methods for measurement of water permeability in the field is presented. 相似文献
863.
长春季节性冻土地区土体微观结构与水分迁移的关系 总被引:1,自引:0,他引:1
利用扫描电子显微镜(SEM)技术,从土体微观结构特征出发,对长春—吉林公路某路段季节冻土的粒度成分、结构单元体成分、孔隙特征及结构特征进行了定量分析,并对其与水分迁移的关系进行了讨论。从SEM图像定量分析中可以看出,研究路段的土体,其微观颗粒——结构单元体、孔隙的定向性均较差,粒内微小孔隙发育,土体尽管在粘粒含量较高的情况下,也表现出孔隙主要在1~2μm内分布,即毛细孔隙极发育,说明样品具有各向同性的特点,即在外界条件相同的情况下水分迁移的通道在水平和垂直方向上具有相同的性质。 相似文献
864.
865.
866.
P. N. S. O'BRIEN 《Geophysical Prospecting》1969,17(4):511-547
Recordings were made with three types of detector of the primary compressional (P) and shear (S) wave pulses generated by explosions in boreholes. Charge weights varied from 0.08 kg to 9.5 kg and detector distances varied from about 3 m to about 80 m. Scaling by the simple factor W1/3 where W is the charge weight, enabled observations from different sized charges to be fitted to a single expression. Experiments were carried out in the Bunter sandstone and the London clay and both fluid and solid tamping were used. This variation in tamping had no significant effect on the P-waves but it may have affected the generation of SV-waves. In both media the P-wave energy carried at 30 m from the shot by frequencies less than 100 Hz decreased rapidly with depth and was usually 1–2 % of the available chemical energy for a shot depth of 15 m. The S-wave energy was much less than this, but was highly directional. The P-wave pulse had the appearance of a damped sinusoid in very good agreement with the predictions of the ‘equivalent radiator’ hypothesis. However, the surface of this radiator should be identified not with the blown cavity but with the surface at which the tensile stresses associated with the stress wave become less than the tensile strength of the rock. The predominant frequency for a 1 kg charge at a depth of 15 m was 24 Hz in the clay and 52 Hz in the sandstone. In these and similar media, therefore, an effort should be made to keep individual charges less than 1 kg in reflection shooting and less than 10 kg in refraction shooting. The value of Q was about 50 in clay and about 25 in the sandstone. These estimates are rather uncertain because of the small distances over which the pulses were observed. The Z-transforms of the sampled pulses indicated that they were all of minimum phase, or very near to it. 相似文献
867.
868.
A high resolution Boomer system was used to investigate the bedrock configuration of part of Port Jackson, New South Wales. The continuous reflection profiling technique was successful in delineating a channel incised in bedrock under a thickness of up to 60 m. of unconsolidated sediment covered by up to 20 m. of water. 相似文献
869.
H. G. Dawe 《The Photogrammetric Record》1969,6(34):335-347
This paper describes the planning and implementation of a very extensive aerial survey contract undertaken by Hunting Surveys on behalf of the Hong Kong Government. From photography carried out during January and February 1963, photogrammetric plotting at 1 : 600 and 1 : 1200 proceeded steadily over a period of 5 years to the point where all but the highest land in the Colony had been surveyed at one or other of these two large scales. The problems arising from the rather unique terrain conditions and the urban and industrial development of Hong Kong are dealt with mainly from the photographic and photogrammetric aspect but reference is made to the contribution of the Crown Lands and Survey Office of the Public Works Department of Hong Kong, who provided all ground control and undertook field verification. 相似文献
870.