全文获取类型
收费全文 | 62143篇 |
免费 | 781篇 |
国内免费 | 621篇 |
专业分类
测绘学 | 1637篇 |
大气科学 | 4334篇 |
地球物理 | 11630篇 |
地质学 | 22486篇 |
海洋学 | 5717篇 |
天文学 | 14601篇 |
综合类 | 224篇 |
自然地理 | 2916篇 |
出版年
2022年 | 440篇 |
2021年 | 747篇 |
2020年 | 776篇 |
2019年 | 845篇 |
2018年 | 1906篇 |
2017年 | 1778篇 |
2016年 | 2186篇 |
2015年 | 1111篇 |
2014年 | 2024篇 |
2013年 | 3294篇 |
2012年 | 2147篇 |
2011年 | 2769篇 |
2010年 | 2441篇 |
2009年 | 3136篇 |
2008年 | 2715篇 |
2007年 | 2754篇 |
2006年 | 2539篇 |
2005年 | 1850篇 |
2004年 | 1876篇 |
2003年 | 1763篇 |
2002年 | 1688篇 |
2001年 | 1481篇 |
2000年 | 1411篇 |
1999年 | 1123篇 |
1998年 | 1176篇 |
1997年 | 1071篇 |
1996年 | 906篇 |
1995年 | 885篇 |
1994年 | 775篇 |
1993年 | 686篇 |
1992年 | 651篇 |
1991年 | 669篇 |
1990年 | 706篇 |
1989年 | 553篇 |
1988年 | 571篇 |
1987年 | 608篇 |
1986年 | 553篇 |
1985年 | 698篇 |
1984年 | 756篇 |
1983年 | 679篇 |
1982年 | 638篇 |
1981年 | 575篇 |
1980年 | 553篇 |
1979年 | 556篇 |
1978年 | 538篇 |
1977年 | 437篇 |
1976年 | 401篇 |
1975年 | 410篇 |
1974年 | 371篇 |
1973年 | 398篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Claude R. Duguay Greg M. Flato Martin O. Jeffries Patrick Mnard Kim Morris Wayne R. Rouse 《水文研究》2003,17(17):3465-3483
A one‐dimensional thermodynamic model for simulating lake‐ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow‐ice) on a daily basis, as well as freeze‐up and break‐up dates. The lake‐ice model is used to simulate ice‐growth processes on shallow lakes in arctic, sub‐arctic, and high‐boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow‐ice formation, compares favourably with field measurements. Ice‐on and ice‐off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break‐up. It is also shown that lake morphometry, depth in particular, is a determinant of ice‐off dates for shallow lakes at high latitudes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
72.
73.
74.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2006,368(4):1764-1772
Pulsar radio emission is modelled as a sum of two completely polarized non-orthogonal modes with the randomly varying Stokes parameters and intensity ratio. The modes are the result of polarization evolution of the original natural waves in the hot, magnetized, weakly inhomogeneous plasma of the pulsar magnetosphere. In the course of the wavemode coupling, the linearly polarized natural waves acquire purely orthogonal elliptical polarizations. Further on, as the waves pass through the cyclotron resonance, they become non-orthogonal. The pulse-to-pulse fluctuations of the final polarization characteristics and the intensity ratio of the modes are attributed to the temporal fluctuations in the plasma flow.
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
75.
76.
77.
C. S. M. Turney K. Van Den Burg S. Wastegrd S. M. Davies N. J. Whitehouse J. R. Pilcher C. Callaghan 《第四纪科学杂志》2006,21(4):335-345
High‐precision correlation of palaeoclimatic and palaeoenvironmental records is crucial for testing hypotheses of synchronous change. Although radiocarbon is the traditional method for dating late Quaternary sedimentary sequences, particularly during the last glacial–interglacial transition (LGIT; 15–9 ka), there are inherent problems with the method, particularly during periods of climate change which are often accompanied by major perturbations in atmospheric radiocarbon content. An alternative method is the use of tephras that act as time‐parallel marker horizons. Within Europe, numerous volcanic centres are known to have erupted during the LGIT, providing considerable potential for high‐precision correlation independent of past radiocarbon fluctuations. Here we report the first identification of the Vedde Ash and Askja Tephra in Ireland, significantly extending the known provenance of these events. We have also identified two new horizons (the Roddans Port Tephras A and B) and tentatively recognise an additional horizon from Vallensgård Mose (Denmark) that provide crucial additional chronological control for the LGIT. Two phases of the Laacher See Tephra (LST) are reported, the lower Laacher See Tephra (LLST) and probably the C2 phase of the Middle Laacher See Tephra (MLST‐C2) indicating a more northeasterly distribution of this fan than reported previously. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
78.
79.
E. Tóth F. Deak C. S. Gyurkócza Z. S. Kasztovszky R. Kuczi G. Marx B. Nagy S. Oberstedt L. Sajó-Bohus C. S. Sükösd G. Toth N. Vajda 《Environmental Geology》1997,31(1-2):123-127
A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations
have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena.
Received: 20 November 1995 · Accepted: 18 June 1996 相似文献
80.