全文获取类型
收费全文 | 1748篇 |
免费 | 82篇 |
国内免费 | 468篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 145篇 |
地球物理 | 773篇 |
地质学 | 639篇 |
海洋学 | 186篇 |
天文学 | 79篇 |
综合类 | 302篇 |
自然地理 | 119篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 24篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 37篇 |
2013年 | 20篇 |
2012年 | 66篇 |
2011年 | 94篇 |
2010年 | 32篇 |
2009年 | 55篇 |
2008年 | 77篇 |
2007年 | 105篇 |
2006年 | 106篇 |
2005年 | 106篇 |
2004年 | 105篇 |
2003年 | 101篇 |
2002年 | 104篇 |
2001年 | 121篇 |
2000年 | 130篇 |
1999年 | 51篇 |
1998年 | 46篇 |
1997年 | 79篇 |
1996年 | 30篇 |
1995年 | 44篇 |
1994年 | 51篇 |
1993年 | 60篇 |
1992年 | 48篇 |
1991年 | 70篇 |
1990年 | 44篇 |
1989年 | 60篇 |
1988年 | 47篇 |
1987年 | 28篇 |
1986年 | 23篇 |
1985年 | 44篇 |
1984年 | 30篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 28篇 |
1979年 | 5篇 |
1947年 | 7篇 |
1939年 | 7篇 |
1926年 | 5篇 |
1924年 | 4篇 |
排序方式: 共有2298条查询结果,搜索用时 15 毫秒
961.
模糊类别制图的空间统计学方法 总被引:4,自引:1,他引:3
类别地图是地理信息系统(GIS)应用中所利用的重要数据类别。这类数据可以从摄影测量和遥感技术得到。用摄影测量方法(影像判读)制作的类别地图常以点、线和多边形的离散目标形式描述,而遥感图像分类方法输出的类别地图以连通光栅块形式表达。不论哪一种情况,在每一个多边形或者光栅块(即制图单元)中仅允许单一类别,边界内部非均匀性和模糊形已经被“过滤”了。这样的类别地图沿用了古曲脆集合论,因为每个制图单元只允许 相似文献
962.
ONTHEPREDICTIONOFTRANSIENTBEDLEVELSDUETOAGGRADATIONANDDEGRADATIONINCLUDINGARMOURINGA.B.PALANIAPPAN1,R.J.GARDE2andP.N.GODBOLE3... 相似文献
963.
1INTRODUCTIONTheaceleratedreleaseofsedimentfromsoilandrocksurfacesanditsmovementto,through,andfromstreamsisthemostpervasivean... 相似文献
964.
在由某一台站观测到的地震波记录确定地震能量时,有必要知道震源机制在所选取的1985-1986年发生在西波希米亚的震群资料中,由于资料稀少,无法由P波初动求解震源机制. 相似文献
967.
Linkin V Harri AM Lipatov A Belostotskaja K Derbunovich B Ekonomov A Khloustova L Kremnev R Makarov V Martinov B Nenarokov D Prostov M Pustovalov A Shustko G Jarvinen I Kivilinna H Korpela S Kumpulainen K Lehto A Pellinen R Pirjola R Riihela P Salminen A Schmidt W McKay CP 《Planetary and Space Science》1998,46(6-7):717-737
A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars. 相似文献
968.
Observations of OCS and a search for OC3S are reported, with particular reference to cold dust clouds. OCS has been detected for the first time in dark clouds with a mean fractional abundance relative to hydrogen of approximately 3 x 10(-9); this is approximately 4 times greater than that observed for giant molecular clouds. This results is discussed in the context of molecule formation mechanisms. Observations of the J = 1 --> 0 transition of OCS indicate that this transition is amplifying the background continuum radiation in the direction of Sgr B2. 相似文献
969.
Thaddeus P Gottlieb CA Hjalmarson A Johansson LE Irvine WM Friberg P Linke RA 《The Astrophysical journal》1985,294(1):L49-L53
The C3H radical, a linear carbon chain with a 2 pi electronic ground state, has been identified in the millimeter-wave spectra of two astronomical sources, IRC +10216 and TMC-1, and conclusively confirmed (accompanying Letter) in a laboratory glow discharge. In IRC +10216 four rotational transitions have been observed, three in the lower fine-structure ladder (2 pi 1/2) and one in the upper (2 pi 3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2 --> 1/2 transition of the 2 pi 1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216 the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2 pi 1/2 ladder is low (8.5 K), owing to rapid radiative decay, while Trot across the ladders is high (approximately 52 K) because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84" is 2.8 x 10(13) cm-2, an order of magnitude less than that of C2H and C4H. A determination of the spectroscopic constraints of C3H that permitted the entire radio spectrum of this molecule to be calculated to high accuracy has been derived from analysis of the combined astronomical and laboratory data presented in the accompanying Letter. 相似文献
970.
Hodge J Longstaff B Steven A Thornton P Ellis P McKelvie I 《Marine pollution bulletin》2005,51(1-4):113-118
We present an overview of a portable underway water quality monitoring system (RUM-Rapid Underway Monitoring), developed by integrating several off-the-shelf water quality instruments to provide rapid, comprehensive, and spatially referenced 'snapshots' of water quality conditions. We demonstrate the utility of the system from studies in the Northern Great Barrier Reef (Daintree River) and the Moreton Bay region. The Brisbane dataset highlights RUM's utility in characterising plumes as well as its ability to identify the smaller scale structure of large areas. RUM is shown to be particularly useful when measuring indicators with large small-scale variability such as turbidity and chlorophyll-a. Additionally, the Daintree dataset shows the ability to integrate other technologies, resulting in a more comprehensive analysis, whilst sampling offshore highlights some of the analytical issues required for sampling low concentration data. RUM is a low cost, highly flexible solution that can be modified for use in any water type, on most vessels and is only limited by the available monitoring technologies. 相似文献