全文获取类型
收费全文 | 44779篇 |
免费 | 2826篇 |
国内免费 | 3142篇 |
专业分类
测绘学 | 1885篇 |
大气科学 | 5025篇 |
地球物理 | 9394篇 |
地质学 | 18081篇 |
海洋学 | 4419篇 |
天文学 | 7575篇 |
综合类 | 1006篇 |
自然地理 | 3362篇 |
出版年
2022年 | 686篇 |
2021年 | 970篇 |
2020年 | 904篇 |
2019年 | 961篇 |
2018年 | 1553篇 |
2017年 | 1533篇 |
2016年 | 1805篇 |
2015年 | 1297篇 |
2014年 | 1782篇 |
2013年 | 2761篇 |
2012年 | 2037篇 |
2011年 | 2312篇 |
2010年 | 2102篇 |
2009年 | 2376篇 |
2008年 | 2098篇 |
2007年 | 1988篇 |
2006年 | 1864篇 |
2005年 | 1451篇 |
2004年 | 1351篇 |
2003年 | 1208篇 |
2002年 | 1216篇 |
2001年 | 1124篇 |
2000年 | 1022篇 |
1999年 | 890篇 |
1998年 | 786篇 |
1997年 | 871篇 |
1996年 | 687篇 |
1995年 | 687篇 |
1994年 | 640篇 |
1993年 | 526篇 |
1992年 | 495篇 |
1991年 | 438篇 |
1990年 | 466篇 |
1989年 | 410篇 |
1988年 | 387篇 |
1987年 | 422篇 |
1986年 | 366篇 |
1985年 | 460篇 |
1984年 | 452篇 |
1983年 | 480篇 |
1982年 | 448篇 |
1981年 | 408篇 |
1980年 | 422篇 |
1979年 | 355篇 |
1978年 | 325篇 |
1977年 | 318篇 |
1976年 | 279篇 |
1975年 | 280篇 |
1974年 | 284篇 |
1973年 | 275篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
31.
32.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
33.
Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
34.
Xie Rui-xiang Wang Min Shi Shuo-biao Xu Chun Li Wei-hua Yan Yi-hua 《Chinese Astronomy and Astrophysics》2003,27(4):426-434
Using the decimetric (700–1500 MHz) radio spectrometer and the synchronous observational system with high temporal resolution at four frequencies (1420, 2130, 2840 and 4260 MHz) of Yunnan Observatory, two rare events were observed on 2001 June 24 and 1990 July 30. The former was a small radio burst exhibiting pulsations with short periods (about 29, 40 and 100 ms) in the impulsive phase. The latter was a large radio burst, which at 2840 MHz produced radio pulsations with period of about 30 ms. This paper focuses on pulsations with very short periods in the range of 29–40 ms. The mechanism of generation of such pulsations may be modulation of radio radiation by the periodic trains of whistler packets originating in unstable regions of the corona. Alternatively, these pulsations can be attributed to wave-wave non-linear interactions of electrostatic upper hybrid waves driven by beams of precipitating electrons in flaring loops. 相似文献
35.
36.
37.
Measurements of 18O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0·8 km2; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38·5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2·4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
38.
39.
V. J. Mclntyre A. C. Gilmore J. B. Hearnshaw 《Journal of Astrophysics and Astronomy》1990,11(1):81-123
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings
of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper
presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements
of selected lines in the spectra 相似文献
40.