全文获取类型
收费全文 | 75922篇 |
免费 | 1588篇 |
国内免费 | 739篇 |
专业分类
测绘学 | 1867篇 |
大气科学 | 5503篇 |
地球物理 | 15437篇 |
地质学 | 26930篇 |
海洋学 | 6646篇 |
天文学 | 16970篇 |
综合类 | 230篇 |
自然地理 | 4666篇 |
出版年
2022年 | 413篇 |
2021年 | 747篇 |
2020年 | 831篇 |
2019年 | 899篇 |
2018年 | 1997篇 |
2017年 | 1860篇 |
2016年 | 2363篇 |
2015年 | 1444篇 |
2014年 | 2347篇 |
2013年 | 4059篇 |
2012年 | 2463篇 |
2011年 | 3331篇 |
2010年 | 2771篇 |
2009年 | 3760篇 |
2008年 | 3490篇 |
2007年 | 3260篇 |
2006年 | 3060篇 |
2005年 | 2515篇 |
2004年 | 2424篇 |
2003年 | 2279篇 |
2002年 | 2076篇 |
2001年 | 1916篇 |
2000年 | 1836篇 |
1999年 | 1479篇 |
1998年 | 1569篇 |
1997年 | 1467篇 |
1996年 | 1172篇 |
1995年 | 1216篇 |
1994年 | 1031篇 |
1993年 | 932篇 |
1992年 | 910篇 |
1991年 | 821篇 |
1990年 | 912篇 |
1989年 | 767篇 |
1988年 | 701篇 |
1987年 | 871篇 |
1986年 | 703篇 |
1985年 | 917篇 |
1984年 | 996篇 |
1983年 | 927篇 |
1982年 | 889篇 |
1981年 | 775篇 |
1980年 | 714篇 |
1979年 | 658篇 |
1978年 | 640篇 |
1977年 | 603篇 |
1976年 | 597篇 |
1975年 | 540篇 |
1974年 | 554篇 |
1973年 | 511篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
Generally speaking, variable stars are monitored through observing campaigns which coordinate multi-site telescopes at various
longitudes. A new practice is in progress: devoted networks involving robotic telescopes. We will review these two technologies
and will emphasize the NORT (Network of Oriental Robotic Telescopes) project which we are promoting in North Africa, Middle-Eastern
countries and Asia.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
172.
An optoelectronic instrument has been developed to analyze the scales and scale patterns of chum salmon. This device, with specially developed software, has been used to study populations of salmon. Fish from two different rivers approximately 200 km apart from each other were grouped with an accuracy of 82% or more. Machine-measured ages coincided with those derived from visual estimation in approximately 80% of the fish sampled. These results suggest the proposed system could be of practical use for measuring and analyzing the scale patterns that allow one to accurately measure both natural and farmed populations of salmon 相似文献
173.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献
174.
J. M. Gregory J. A. Church G. J. Boer K. W. Dixon G. M. Flato D. R. Jackett J. A. Lowe S. P. O'Farrell E. Roeckner G. L. Russell R. J. Stouffer M. Winton 《Climate Dynamics》2001,18(3-4):225-240
Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present
an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes
simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario
IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal
expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might
not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout
the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts
to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the
ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as
much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack
of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need
for detailed analysis and intercomparison in order to understand and reduce the disagreements.
Received: 1 September 2000 / Accepted: 20 April 2001 相似文献
175.
We study the solar cycle evolution during the last 8 solar cycles using a vectorial sunspot area called the LA (longitudinal asymmetry) parameter. This is a useful measure of solar activity in which the stochastic, longitudinally evenly distributed sunspot activity is reduced and which therefore emphasizes the more systematic, longitudinally asymmetric sunspot activity. Interesting differences are found between the LA parameter and the more conventional sunspot activity indices like the (scalar) sunspot area and the sunspot number. E.g., cycle 19 is not the highest cycle according to LA. We have calculated the separate LA parameters for the northern and southern hemisphere and found a systematic dipolar-type oscillation in the dominating hemisphere during high solar activity times which is reproduced from cycle to cycle. We have analyzed this oscillation during cycles 16–22 by a superposed epoch method using the date of magnetic reversal in the southern hemisphere as the zero epoch time. According to our analysis, the oscillation starts by an excess of the northern LA value in the ascending phase of the solar cycle which lasts for about 2.3 years. Soon after the maximum northern dominance, the southern hemisphere starts dominating, reaching its minimum some 1.2–1.7 years later. The period of southern dominance lasts for about 1.6 years and ends, on an average, slightly before the end of magnetic reversal. 相似文献
176.
177.
178.
179.
Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995. 相似文献
180.
Abstract— Platinum group elements (PGE) enrichments are found in Fe-Ni blebs (<1 μm) in Al- and Cr-rich objects in the ordinary chondrites Ste. Marguerite, Forest Vale, Montferré. In Ste. Marguerite, high ZrO2 concentrations (baddeleyite) are also present in a chromite inclusion. Iridium enrichment in this material compared to its metal content is confirmed by INAA. The widespread occurrence of PGE in Al- and Cr-rich objects, mostly present in H-group chondrites of nearly equilibrated types, must be taken into account to understand their conditions of formation. 相似文献