全文获取类型
收费全文 | 59848篇 |
免费 | 978篇 |
国内免费 | 808篇 |
专业分类
测绘学 | 1565篇 |
大气科学 | 4852篇 |
地球物理 | 12403篇 |
地质学 | 20288篇 |
海洋学 | 5248篇 |
天文学 | 13092篇 |
综合类 | 154篇 |
自然地理 | 4032篇 |
出版年
2020年 | 412篇 |
2019年 | 389篇 |
2018年 | 912篇 |
2017年 | 828篇 |
2016年 | 1309篇 |
2015年 | 902篇 |
2014年 | 1242篇 |
2013年 | 2952篇 |
2012年 | 1515篇 |
2011年 | 2176篇 |
2010年 | 1802篇 |
2009年 | 2580篇 |
2008年 | 2321篇 |
2007年 | 2209篇 |
2006年 | 2144篇 |
2005年 | 1911篇 |
2004年 | 1877篇 |
2003年 | 1797篇 |
2002年 | 1719篇 |
2001年 | 1481篇 |
2000年 | 1504篇 |
1999年 | 1425篇 |
1998年 | 1330篇 |
1997年 | 1322篇 |
1996年 | 1130篇 |
1995年 | 1040篇 |
1994年 | 952篇 |
1993年 | 875篇 |
1992年 | 836篇 |
1991年 | 778篇 |
1990年 | 805篇 |
1989年 | 679篇 |
1988年 | 697篇 |
1987年 | 773篇 |
1986年 | 724篇 |
1985年 | 957篇 |
1984年 | 1062篇 |
1983年 | 1027篇 |
1982年 | 878篇 |
1981年 | 839篇 |
1980年 | 820篇 |
1979年 | 738篇 |
1978年 | 766篇 |
1977年 | 666篇 |
1976年 | 675篇 |
1975年 | 651篇 |
1974年 | 673篇 |
1973年 | 675篇 |
1972年 | 409篇 |
1971年 | 345篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Analyses of sea level and current-meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non-local coastal forcing and local tidal forcing in the northern reach of San Francisco Bay, a partially mixed estuary. Low-frequency variations in sea level are dominated by non-local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations. Low-frequency currents demonstrate a gravitational circulation which is modified by changes in tidal-current speed over the spring-neap tidal cycle. Transients in gravitational circulation induce internal oscillations with periods of two to four days. 相似文献
92.
Stable oxygen isotope analysis and measurement of several dissolved cations and anions of bulk meltwater samples have provided information about the hydrochemical environment of the glacial hydrological system at Imersuaq Glacier, an outlet tongue from the Greenland ice‐sheet, West Greenland. The samples were collected at frequent intervals during the period 20–28 July 2000 in a small (<20 L s?1) englacial meltwater outlet at the glacier margin. The results document the following findings: (i) a marked diurnal variation of δ18O is related to the composition of oxygen isotope provenances, mainly near‐marginal local superimposed ice and basal up‐sheared ice further up‐glacier; (ii) a relationship is seen between all base cations (Na+, K+, Ca2+, Mg2+), SO42? and δ18O, indicating that solute acquisition is provided by solid–solution contact with the up‐sheared ice—as the relationship with Cl? is weak the influence of seasalt‐derived solutes is small in the area; (iii) when the melt rate is high, two diurnal maxima of δ18O values and solute concentrations are measured, and it is suggested that a snow meltwater component is responsible for the second maximum of δ18O—a short residence time leads to a delayed decrease in ion concentrations. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
93.
J. van der Plicht B. van Geel S. J. P. Bohncke J. A. A. Bos M. Blaauw A. O. M. Speranza R. Muscheler S. Bjrck 《第四纪科学杂志》2004,19(3):263-269
Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric 14C; (ii) a temporary decline of atmospheric CO2; and (iii) an increase in the GRIP 10Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
94.
E. F. Arias C. Boucher M. Feissel J. -F. Lestrade 《Astrophysics and Space Science》1991,177(1-2):187-192
The relative orientations of various VLBI celestial reference frames are evaluated on the basis of coordinate differences of common sources. It is shown that an accuracy better than 0.001 can be achieved. Possible regional deformations in the different catalogues are investigated; they are found to reach a few 0.001 in some restricted zones. The application of these studies to the realisation of a combined celestial reference frame consistent with the BIH Terrestrial System is outlined. 相似文献
95.
96.
97.
D. W. Proctor 《The Photogrammetric Record》1968,6(31):49-58
An analytical relative orientation of a stereo-pair of photographs was computed in an unusual system of co-ordinates. The disparity in the widely mismatched photographs, their tilts and narrow angles subtended resulted in a rather weak solution from which sections of the lunar surface have been plotted. The results were not good but were better than expected. The main outcome of the work is a, probably unique, demonstration of the versatility of analytical photogrammetry. 相似文献
98.
The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence. 相似文献
99.
100.
The wadic project: A comprehensive field evaluation of directional wave instrumentation 总被引:1,自引:0,他引:1
J. Allender T. Audunson S. F. Barstow S. Bjerken H. E. Krogstad P. Steinbakke L. Vartdal L. E. Borgman C. Graham 《Ocean Engineering》1989,16(5-6)
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results. 相似文献