全文获取类型
收费全文 | 8392篇 |
免费 | 303篇 |
国内免费 | 106篇 |
专业分类
测绘学 | 205篇 |
大气科学 | 575篇 |
地球物理 | 1973篇 |
地质学 | 3050篇 |
海洋学 | 758篇 |
天文学 | 1224篇 |
综合类 | 20篇 |
自然地理 | 996篇 |
出版年
2021年 | 90篇 |
2020年 | 116篇 |
2019年 | 115篇 |
2018年 | 169篇 |
2017年 | 163篇 |
2016年 | 229篇 |
2015年 | 194篇 |
2014年 | 198篇 |
2013年 | 480篇 |
2012年 | 253篇 |
2011年 | 318篇 |
2010年 | 294篇 |
2009年 | 342篇 |
2008年 | 325篇 |
2007年 | 283篇 |
2006年 | 324篇 |
2005年 | 242篇 |
2004年 | 301篇 |
2003年 | 274篇 |
2002年 | 278篇 |
2001年 | 180篇 |
2000年 | 177篇 |
1999年 | 147篇 |
1998年 | 143篇 |
1997年 | 107篇 |
1996年 | 115篇 |
1995年 | 116篇 |
1994年 | 132篇 |
1993年 | 115篇 |
1992年 | 115篇 |
1991年 | 110篇 |
1990年 | 102篇 |
1989年 | 86篇 |
1988年 | 88篇 |
1987年 | 124篇 |
1986年 | 100篇 |
1985年 | 163篇 |
1984年 | 187篇 |
1983年 | 145篇 |
1982年 | 127篇 |
1981年 | 132篇 |
1980年 | 111篇 |
1979年 | 125篇 |
1978年 | 118篇 |
1977年 | 105篇 |
1976年 | 97篇 |
1975年 | 93篇 |
1974年 | 68篇 |
1973年 | 83篇 |
1972年 | 50篇 |
排序方式: 共有8801条查询结果,搜索用时 0 毫秒
11.
In an attempt to discover planetary eclipses, we observed the open cluster NGC 7086. On one night we observed the cluster and standard stars through the B and V filters, enabling us to make a colour-magnitude diagram. Plots of the differential magnitudes were inspected for variability, but no planetary eclipses were found. New variable stars were discovered and their light curves show some of them to be eclipsing binary stars. The location on the colour-magnitude diagram of some of the variable stars is consistent with cluster membership. 相似文献
12.
Lance B. Morrissey Philippe Janvier Simon J. Braddy John P. Bennett Susan B. Marriott Peter R. Tarrant 《Geology Today》2006,22(2):66-67
Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle. 相似文献
13.
14.
15.
Klauea historical summit lavas have a wide range in matrix 18OVSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, 18O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine 18O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma 18O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine 18O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination 相似文献
16.
17.
18.
19.
Robust Range-Only Beacon Localization 总被引:2,自引:0,他引:2
In this paper, we present a system capable of simultaneously estimating the position of an autonomous underwater vehicle (AUV) and the positions of stationary range-only beacons. Notably, our system does not require beacon positions a priori, and our system performs well even when range measurements are severely degraded by noise and outliers. We present a powerful outlier rejection method that can identify groups of range measurements that are consistent with each other, and a method for initializing beacon positions in an extended Kalman filter (EKF). We have successfully applied our algorithms to real-world data and have demonstrated a simultaneous localization and mapping (SLAM) system whose navigation performance is comparable to that of systems that assume known beacon locations 相似文献
20.