全文获取类型
收费全文 | 2404篇 |
免费 | 118篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 100篇 |
大气科学 | 169篇 |
地球物理 | 878篇 |
地质学 | 775篇 |
海洋学 | 155篇 |
天文学 | 305篇 |
综合类 | 10篇 |
自然地理 | 153篇 |
出版年
2021年 | 24篇 |
2020年 | 57篇 |
2019年 | 39篇 |
2018年 | 65篇 |
2017年 | 58篇 |
2016年 | 109篇 |
2015年 | 86篇 |
2014年 | 97篇 |
2013年 | 142篇 |
2012年 | 93篇 |
2011年 | 126篇 |
2010年 | 111篇 |
2009年 | 127篇 |
2008年 | 108篇 |
2007年 | 75篇 |
2006年 | 79篇 |
2005年 | 54篇 |
2004年 | 44篇 |
2003年 | 56篇 |
2002年 | 37篇 |
2001年 | 54篇 |
2000年 | 37篇 |
1999年 | 43篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 27篇 |
1986年 | 35篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 35篇 |
1982年 | 33篇 |
1981年 | 30篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1973年 | 24篇 |
1972年 | 16篇 |
1971年 | 18篇 |
排序方式: 共有2545条查询结果,搜索用时 906 毫秒
211.
ABSTRACT In many places, magnitudes and frequencies of floods are expected to increase due to climate change. To understand these changes better, trend analyses of historical data are helpful. However, traditional trend analyses do not address issues related to shifts in the relative contributions of rainfall versus snowmelt floods, or in the frequency of a particular flood type. We present a novel approach for quantifying such trends in time series of floods using a fuzzy decision tree for event classification and applied it to maximal annual and seasonal floods in 27 alpine catchments for the period 1980–2014. Trends in flood types were studied with Sen’s slope and double mass curves. Our results reveal a decreasing number of rain-on-snow and an increasing number of short rainfall events in all catchments, with flash floods increasing in smaller catchments. Overall, the results demonstrate the value of incorporating a fuzzy flood-type classification into flood trend analyses. 相似文献
212.
213.
This paper describes an algorithm which brings a regularizable polynomial perturbation of a three degree of freedom Kepler problem into a normal form which Poisson commutes with the Kepler Hamiltonian. We illustrate the alogrithm with an example: the quadratic Zeeman effect. For other applications of this algorithm see [1],[4], and [5]. The authors have written a program in MAPLE which implements the constrained normal form. 相似文献
214.
A comparison of soft X-ray pictures of the Sun (S-054 experiment of Skylab) with K-line spectroheliograms (Mount Wilson) shows that the X-ray bright points tend to emerge randomly throughout the Ca network pattern. However, all those bright points that developed into active regions emerged at the boundaries of network cells. This suggests that the magnetic flux of active regions comes from greater depths in the convection zone than the shallow flux that gives rise to the random emergence of bright points.Also Physics Department, C-011, University of California at San Diego, La Jolla, Calif., U.S.A. 相似文献
215.
Z. Švestka 《Solar physics》1976,47(1):375-384
Three problems are emphasized in particular: the preflare magnetic field configuration, velocity fields, and the nature of acceleration processes in flares. It is concluded that what we need most urgently are high-resolution hard X-ray, soft X-ray, and EUV-pictures, coronal spectra, and magnetograms with high resolution both in space and time. A space-shuttle equipped with instrumentation of this kind would contribute significantly to our knowledge of the flare process. 相似文献
216.
Zdislav Šíma 《Astrophysics and Space Science》1973,24(2):421-448
In this paper, the model of the ring envelope round the primary component and the stream of the gaseous mass flowing from
the secondary component to the primary is constructed on the basis of theoretical computations concerning the exchange of
the mass between the components of the binary. The paper studies the influence of the gaseous mass on the profiles of spectral
lines before and after occultation; the influence of the stream on the profile in case the secondary is near elongation, is
also investigated. The line profiles obtained by numerical computations show that their changes caused by outflowing mass
should be well detectable from spectrograms taken at particular phase of the binary. Changes in the lines may influence the
measurement of radial velocities. The method for distinguishing the influence of the stream from the influence of the ring
is described. 相似文献
217.
218.
The asymptotic distribution of the coefficient of cross-association between two sequences of nominal data is investigated under the assumption of independent random sampling from a multinomial distribution slightly modified to suit geological applications. This modification is due to merging consecutive strata of the same rock type into one lithological unit, and can be described by a simple Markov chain. A distinction is made between the case in which the theoretical frequencies are known, and the situation where these have to be estimated from the observed data. 相似文献
219.
Studia Geophysica et Geodaetica - 相似文献
220.
Huth Radan Mládek Richard Metelka Ladislav Sedlák Pavel Huthová Zuzana Kliegrová Stanislava Kyselý Jan Pokorná Lucie Halenka Tomáš Janoušek Martin 《Studia Geophysica et Geodaetica》2003,47(4):863-873
This note summarizes results of the first integration of regional numerical weather prediction model ALADIN in a climate mode. The ALADIN model, developed in an international cooperation led by Météo France, is operationally used for weather prediction. The grid step of the model is 12 km; the integration domain covers a major part of Europe. A one-month-long run has been performed with this model on observed boundary conditions (represented by assimilations by the global model ARPEGE). It is demonstrated that no excessive error is generated and accumulated in the model during the integration; hence the model is integrable for extended time periods and may serve a basis for a development towards a regional climate model. 相似文献