全文获取类型
收费全文 | 60028篇 |
免费 | 415篇 |
国内免费 | 1053篇 |
专业分类
测绘学 | 2057篇 |
大气科学 | 4031篇 |
地球物理 | 10929篇 |
地质学 | 26414篇 |
海洋学 | 4190篇 |
天文学 | 9387篇 |
综合类 | 2209篇 |
自然地理 | 2279篇 |
出版年
2022年 | 268篇 |
2021年 | 442篇 |
2020年 | 402篇 |
2019年 | 466篇 |
2018年 | 7147篇 |
2017年 | 6361篇 |
2016年 | 4291篇 |
2015年 | 653篇 |
2014年 | 863篇 |
2013年 | 1327篇 |
2012年 | 2493篇 |
2011年 | 5291篇 |
2010年 | 4563篇 |
2009年 | 4952篇 |
2008年 | 4055篇 |
2007年 | 5072篇 |
2006年 | 1162篇 |
2005年 | 1122篇 |
2004年 | 1188篇 |
2003年 | 1256篇 |
2002年 | 993篇 |
2001年 | 572篇 |
2000年 | 492篇 |
1999年 | 350篇 |
1998年 | 349篇 |
1997年 | 331篇 |
1996年 | 256篇 |
1995年 | 264篇 |
1994年 | 237篇 |
1993年 | 184篇 |
1992年 | 209篇 |
1991年 | 185篇 |
1990年 | 198篇 |
1989年 | 190篇 |
1988年 | 157篇 |
1987年 | 185篇 |
1986年 | 170篇 |
1985年 | 206篇 |
1984年 | 199篇 |
1983年 | 197篇 |
1982年 | 188篇 |
1981年 | 192篇 |
1980年 | 185篇 |
1979年 | 183篇 |
1978年 | 159篇 |
1977年 | 143篇 |
1976年 | 139篇 |
1975年 | 136篇 |
1974年 | 125篇 |
1973年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
2.
Costijn Zwart Niels C. Munksgaard Alain Protat Naoyuki Kurita Dionisia Lambrinidis Michael I. Bird 《水文研究》2018,32(15):2296-2303
This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ18O and δ2H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes. 相似文献
3.
4.
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
5.
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
6.
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
7.
8.
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
9.
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
10.