全文获取类型
收费全文 | 123203篇 |
免费 | 1996篇 |
国内免费 | 1803篇 |
专业分类
测绘学 | 3747篇 |
大气科学 | 8795篇 |
地球物理 | 24594篇 |
地质学 | 46108篇 |
海洋学 | 9749篇 |
天文学 | 24751篇 |
综合类 | 2391篇 |
自然地理 | 6867篇 |
出版年
2022年 | 549篇 |
2021年 | 963篇 |
2020年 | 1060篇 |
2019年 | 1115篇 |
2018年 | 6815篇 |
2017年 | 6006篇 |
2016年 | 5274篇 |
2015年 | 1960篇 |
2014年 | 2984篇 |
2013年 | 5310篇 |
2012年 | 3962篇 |
2011年 | 6602篇 |
2010年 | 5434篇 |
2009年 | 6958篇 |
2008年 | 6072篇 |
2007年 | 6304篇 |
2006年 | 4039篇 |
2005年 | 3326篇 |
2004年 | 3460篇 |
2003年 | 3239篇 |
2002年 | 2905篇 |
2001年 | 2511篇 |
2000年 | 2391篇 |
1999年 | 1948篇 |
1998年 | 2053篇 |
1997年 | 1941篇 |
1996年 | 1596篇 |
1995年 | 1632篇 |
1994年 | 1389篇 |
1993年 | 1278篇 |
1992年 | 1242篇 |
1991年 | 1154篇 |
1990年 | 1300篇 |
1989年 | 1104篇 |
1988年 | 1017篇 |
1987年 | 1270篇 |
1986年 | 1039篇 |
1985年 | 1333篇 |
1984年 | 1456篇 |
1983年 | 1406篇 |
1982年 | 1272篇 |
1981年 | 1216篇 |
1980年 | 1070篇 |
1979年 | 986篇 |
1978年 | 1005篇 |
1977年 | 904篇 |
1976年 | 891篇 |
1975年 | 835篇 |
1974年 | 822篇 |
1973年 | 835篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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
152.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献
153.
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
154.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献
155.
156.
157.
The restricted problem of 2 + 2 bodies when one of the infinitesimal masses is further acted upon by the light pressure of the two primaries, is considered. The stationary solutions of this problem are found out. A short discussion is devoted to the stability of these solutions. 相似文献
158.
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
159.
G. Cevolani G. Bortolotti L. Foschini C. Franceschi G. Grassi G. Trivellone A. Hajduk V. Porubčan 《Earth, Moon, and Planets》1995,68(1-3):247-255
Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones. 相似文献
160.
This paper compares lead-acid batteries, sodium-sulfur batteries, solid polymer fuel cells and closed-cycle diesel engines for autonomous underwater vehicle (AUV) applications. The service is described in terms of a parametric mission and life cycle. A generic AUV is used as a basis for comparison. Power systems are evaluated by two criteria: (1) submerged endurance capability and (2) life cycle cost. This study determines categories of service for which each power system is preferred. The solid polymer fuel cell can provide greater submerged endurance than other power systems examined. For extremely long duration AUV missions, the fuel cell is the required system, indicating a possible market niche for today's fuel cell technology. Considering cost projections for each power system, the results also show that the SPFC can become cost-competitive with conventional technologies, particularly for services characterized by high levels of utilization 相似文献