全文获取类型
收费全文 | 33882篇 |
免费 | 690篇 |
国内免费 | 390篇 |
专业分类
测绘学 | 941篇 |
大气科学 | 3246篇 |
地球物理 | 7108篇 |
地质学 | 12048篇 |
海洋学 | 2494篇 |
天文学 | 7094篇 |
综合类 | 85篇 |
自然地理 | 1946篇 |
出版年
2020年 | 227篇 |
2019年 | 228篇 |
2018年 | 595篇 |
2017年 | 599篇 |
2016年 | 869篇 |
2015年 | 544篇 |
2014年 | 832篇 |
2013年 | 1599篇 |
2012年 | 806篇 |
2011年 | 1143篇 |
2010年 | 1000篇 |
2009年 | 1400篇 |
2008年 | 1165篇 |
2007年 | 1023篇 |
2006年 | 1125篇 |
2005年 | 935篇 |
2004年 | 886篇 |
2003年 | 917篇 |
2002年 | 928篇 |
2001年 | 800篇 |
2000年 | 837篇 |
1999年 | 701篇 |
1998年 | 677篇 |
1997年 | 705篇 |
1996年 | 608篇 |
1995年 | 590篇 |
1994年 | 538篇 |
1993年 | 449篇 |
1992年 | 444篇 |
1991年 | 441篇 |
1990年 | 450篇 |
1989年 | 423篇 |
1988年 | 402篇 |
1987年 | 490篇 |
1986年 | 446篇 |
1985年 | 500篇 |
1984年 | 592篇 |
1983年 | 593篇 |
1982年 | 532篇 |
1981年 | 518篇 |
1980年 | 476篇 |
1979年 | 458篇 |
1978年 | 484篇 |
1977年 | 415篇 |
1976年 | 377篇 |
1975年 | 385篇 |
1974年 | 442篇 |
1973年 | 421篇 |
1972年 | 263篇 |
1971年 | 236篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
National flood discharge mapping in Austria 总被引:5,自引:0,他引:5
This article presents the approach and the results of a study in which 30, 100 and 200 year return period flood discharges
were estimated for 26,000 km of Austrian streams. Three guiding principles were adopted: combination of automatic methods
and manual assessments by hydrologists to allow speedy processing and account for the local hydrological situation; combination
of various sources of information including flood peak samples, rainfall data, runoff coefficients and historical flood data;
and involvement of the Hydrographic Services to increase the accuracy and enhance the acceptance of results. The flood discharges
for ungauged catchments were estimated by the Top-kriging approach with manual adjustment to the local flood characteristics.
The adopted combination approach proved to be very efficient both in terms of the project time required and in terms of the
accuracy and acceptability of the estimated flood discharges of given return periods. 相似文献
182.
H. G. Dawe 《The Photogrammetric Record》1969,6(34):335-347
This paper describes the planning and implementation of a very extensive aerial survey contract undertaken by Hunting Surveys on behalf of the Hong Kong Government. From photography carried out during January and February 1963, photogrammetric plotting at 1 : 600 and 1 : 1200 proceeded steadily over a period of 5 years to the point where all but the highest land in the Colony had been surveyed at one or other of these two large scales. The problems arising from the rather unique terrain conditions and the urban and industrial development of Hong Kong are dealt with mainly from the photographic and photogrammetric aspect but reference is made to the contribution of the Crown Lands and Survey Office of the Public Works Department of Hong Kong, who provided all ground control and undertook field verification. 相似文献
183.
Frequency distributions of true interfacial angles in high-grade,regional metamorphic rocks from Broken Hill indicate that interfacialtension varies with relative crystallographic orientation incommon minerals. In some single-phase aggregates (e.g. quartz,feldspar, garnet, and calcite) the grains are equant and polygonal,anisotropy of interfacial tension having only a small effecton the appearance of such aggregates. This is also true of two-phaseaggregates of these phases, but their appearance is complicatedby the presence of inclusions, the relative proportions of ihephases, and the characteristic dihedral angle formed by a grainof one phase in contact with two grains of the other. In phases for which interfacial tension is more orientation-dependent,crystal forms exert some control on the appearance of the microstructure.For example, in hornblende and pyroxene aggregates, some interfacesare parallel to planes of the form {110}, although most areirrational. In still more anisotropic phases, low-energy forms(e.g. {001} of biotite and {110} of sillimanite) are very stable,giving rise to a predominance of planar, rational boundariesover curved, adjustment boundaries. Anisotropy of interfacial tension is expressed in the shapesof inclusions. However, even where strongly anisotropic mineralsare involved, inclusions with partly planar boundaries occuralongside inclusions with completely curved boundaries. 相似文献
184.
E. H. Thompson 《The Photogrammetric Record》1967,5(29):385-396
This paper discusses a simple method of computing independent strips under certain reasonable approximations. It is shown that, if the method is regarded as if it were computation by polynomials, the order of the polynomial is decided by the nature of the control provided and not by the number of controlled models. This conclusion should throw some light on the vexed (and perennial) problem of the choice of orders for polynomials. 相似文献
185.
186.
Ohne Zusammenfassung 相似文献
187.
F. Steinhauser O. Burkard W. Mörikofer M. Toperczer 《Meteorology and Atmospheric Physics》1962,13(2):290-304
Ohne Zusammenfassung 相似文献
188.
W. H. Evans 《Pure and Applied Geophysics》1962,52(1):162-168
Summary The application of the snow plow approximation to the magnetic pinch effect in the return stroke of lightning is described. Results are presented for a constant electric field and for a measured stroke current. In general, the solutions indicate that the magnetic pinch effect is important for cases of high currents, small channel diameters, and low degrees of ionization. 相似文献
189.
Ohne Zusammenfassung 相似文献
190.
H. Eghbali 《Contributions to Mineralogy and Petrology》1964,11(1):15-19
Ohne Zusammenfassung 相似文献