全文获取类型
收费全文 | 49748篇 |
免费 | 7067篇 |
国内免费 | 10598篇 |
专业分类
测绘学 | 6467篇 |
大气科学 | 7638篇 |
地球物理 | 10872篇 |
地质学 | 19156篇 |
海洋学 | 6621篇 |
天文学 | 3979篇 |
综合类 | 3781篇 |
自然地理 | 8899篇 |
出版年
2024年 | 180篇 |
2023年 | 526篇 |
2022年 | 1454篇 |
2021年 | 1714篇 |
2020年 | 2082篇 |
2019年 | 2509篇 |
2018年 | 1798篇 |
2017年 | 2273篇 |
2016年 | 2267篇 |
2015年 | 2499篇 |
2014年 | 2827篇 |
2013年 | 3441篇 |
2012年 | 2991篇 |
2011年 | 3171篇 |
2010年 | 2482篇 |
2009年 | 3180篇 |
2008年 | 3258篇 |
2007年 | 3596篇 |
2006年 | 3490篇 |
2005年 | 2918篇 |
2004年 | 2596篇 |
2003年 | 2241篇 |
2002年 | 1890篇 |
2001年 | 1554篇 |
2000年 | 1573篇 |
1999年 | 1523篇 |
1998年 | 1345篇 |
1997年 | 1036篇 |
1996年 | 840篇 |
1995年 | 742篇 |
1994年 | 655篇 |
1993年 | 606篇 |
1992年 | 459篇 |
1991年 | 333篇 |
1990年 | 266篇 |
1989年 | 267篇 |
1988年 | 193篇 |
1987年 | 137篇 |
1986年 | 109篇 |
1985年 | 81篇 |
1984年 | 46篇 |
1983年 | 20篇 |
1982年 | 30篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
71.
PatMoore 《成都信息工程学院学报》2002,17(4):289-299
尽管语法在交际教学法鼎盛时期一度遭到冷遇,但现在又重新被英语语言教学所接纳,作为一种新的语法教学方式,发现原则综合了传统归纳发和演绎法的长处,概述了发现原则的理论依据,指出发现原则旨在鼓励学习者积极参与而非被动接受,符合当前认知主义对二语学习的认识。 相似文献
72.
The results of a photometric monitoring of the quasar 4C 38.41, performed at the optical R and B bands in 2002 February–March, are presented. With a 60/90 cm Schmidt telescope at the Xinglong station of the National Astronomical Observatories of China, we observed the source exhibiting amplitude variations of up to 0.78 mag in both bands during the whole campaign. Intraday and even intranight variations are detected as well. A typical variability time-scale of about 36 d is derived from our 2-month observations at the optical bands, which is identical to that found at a radio wavelength of 92 cm, suggesting a common origin for the variations in 4C 38.41 from optical to radio bands. 相似文献
73.
74.
75.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
76.
Sediment proxy records from a continuous, 1.5 million year long deep‐sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid‐Pleistocene Revolution (MPR). Red‐green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid‐Pleistocene climate shift was accompanied by a general change in ice‐drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
77.
Due to the geological time scales required for observation of catchment evolution, surrogates or analogues of field data are necessary to understand long‐term processes. To investigate long‐term catchment behaviour, two experimental model catchments that developed without rigid boundaries under controlled conditions are examined and a qualitative and quantitative analysis of their evolution is presented. Qualitatively, the experimental catchments have the visual appearance of field scale data. Observation demonstrates that changes in catchment shape and network form are conservative. Quantitative analysis suggests that the catchments reach an equilibrium form while a reduction in the channel network occurs. While the catchments are laboratory scale models, the results provide insights into field scale behaviour. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
78.
Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and
for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities
coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In
addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets
and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric
device MIDI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
80.
李毅心 《成都信息工程学院学报》2006,21(2):206-209
积件技术是教学软件发展的方向,探讨了用Power Builder前台结合SQL Server关系数据库后台进行多媒体教学积件管理的应用模式,并结合具体教学示例,进行了分析说明。 相似文献