全文获取类型
收费全文 | 60094篇 |
免费 | 431篇 |
国内免费 | 1051篇 |
专业分类
测绘学 | 2063篇 |
大气科学 | 4018篇 |
地球物理 | 10977篇 |
地质学 | 26444篇 |
海洋学 | 4189篇 |
天文学 | 9409篇 |
综合类 | 2211篇 |
自然地理 | 2265篇 |
出版年
2022年 | 265篇 |
2021年 | 436篇 |
2020年 | 406篇 |
2019年 | 474篇 |
2018年 | 7150篇 |
2017年 | 6366篇 |
2016年 | 4297篇 |
2015年 | 671篇 |
2014年 | 881篇 |
2013年 | 1335篇 |
2012年 | 2498篇 |
2011年 | 5297篇 |
2010年 | 4567篇 |
2009年 | 4957篇 |
2008年 | 4061篇 |
2007年 | 5084篇 |
2006年 | 1178篇 |
2005年 | 1123篇 |
2004年 | 1191篇 |
2003年 | 1256篇 |
2002年 | 991篇 |
2001年 | 578篇 |
2000年 | 497篇 |
1999年 | 352篇 |
1998年 | 352篇 |
1997年 | 331篇 |
1996年 | 254篇 |
1995年 | 265篇 |
1994年 | 239篇 |
1993年 | 183篇 |
1992年 | 202篇 |
1991年 | 182篇 |
1990年 | 191篇 |
1989年 | 189篇 |
1988年 | 151篇 |
1987年 | 183篇 |
1986年 | 170篇 |
1985年 | 204篇 |
1984年 | 194篇 |
1983年 | 196篇 |
1982年 | 191篇 |
1981年 | 192篇 |
1980年 | 185篇 |
1979年 | 179篇 |
1978年 | 158篇 |
1977年 | 141篇 |
1976年 | 137篇 |
1975年 | 136篇 |
1974年 | 124篇 |
1973年 | 164篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Fully nonlinear features of heavy ion-acoustic solitary waves (HIASWs) have been investigated in an astrophysical degenerate relativistic quantum plasma (ADRQP) containing relativistically degenerate electrons and non-relativistically degenerate light ion species, and non-degenerate heavy ion species. The pseudo-energy balance equation is derived from the fluid dynamical equations by adopting the well-known Sagdeev-potential approach, and the properties of arbitrary amplitude HIASWs are examined. The small amplitude limit for the propagation of HIASWs is also recovered. The basic features (width, amplitude, polarity, critical Mach number, speed, etc.) of HIASWs are found to be significantly modified by the relativistic effect of the electron species, and also by the variation of the number density of electron, light ion, and heavy ion species. The basic properties of HIASWs, that may propagated in some realistic astrophysical plasma systems (e.g., in white dwarfs), are briefly discussed. 相似文献
62.
63.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
64.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
65.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin. 相似文献
66.
67.
Subglacial and subaqueous sediments deposited near the margin of a Late-glacial ice-dammed lake near Achnasheen, northern Scotland, are described and interpreted. The subglacial sediments consist of deformation tills and glacitectonites derived from pre-existing glaciolacustrine deposits, and the subaqueous sediments consist of ice-proximal outwash and sediment flow deposits, and distal turbidites. Sediment was delivered from the glacier to the lake by two main processes: (1) subglacial till deformation, which fed debris flows at the grounding line; and (2) meltwater transport, which fed sediment-gravity flows on prograding outwash fans. Beyond the ice-marginal environment, deposition was from turbidity currents, ice-rafting and settling of suspended sediments. The exposures support the conclusion that the presence of a subglacial deforming layer can exert an important influence on sedimentation at the grounding lines of calving glaciers. 相似文献
68.
AN ILLUSTRATIVE STUDY ON LOCAL LANDSCAPEAND ITS LONG-TERM CHANGES BASED ON IKONOS AND HISTORICAL AERIAL PHOTO 总被引:2,自引:0,他引:2
RUANRen-zong ErieCELLISt 《中国地理科学(英文版)》2004,14(2):162-169
Nowadays, the research works on landscape at fine scales using high-resolution images are uncommon.This research is based on the analysis of the combination of remote sensing data (1KONOS imagery acquired in 2002 and historical aerial photo taken in 1942). In the paper, the ecotopes in Qiujiadou and Xishao villages in Yixing City of Jiangsu Province in 1942 and 2002 were compared and landscape changes as well as the causes of the considerable changes were analyzed. It was found that the ecotope changes were at greater level in some aspects such as water surface and perennial vegetation coverage etc. This study at fine scale is globally significant for the rural areas, especially for the subsistence agricultural land, which occupies larger percentage in the earth. And it analyzes the structure of landscape based on a new landscape classification system--stratifications method. 相似文献
69.
70.
We examine a siphon-like mechanism for moving mass from the chromosphere to a gravitational well at the top of a magnetic loop to form a prominence. The calculations assume no apriori flow velocity at the loop base. Instead heating in the loop legs drives the flow. The prominence formation process requires two steps. First, the background heating rate must be reduced to on the order of 1 % of the initial heating rate required to maintain the coronal loop. This forms an initial condensation at the top of the loop. Second, the heating must take place only in the loop legs in order to produce a pressure differential which drives mass up into the well at the top of the loop. The heating rate in the loop must be increased once the prominence has begun to form or full prominence densities can not be achieved in a reasonable time. We conclude that this heating driven siphon-like mechanism is feasible for producing and maintaining prominences. 相似文献