全文获取类型
收费全文 | 54132篇 |
免费 | 757篇 |
国内免费 | 519篇 |
专业分类
测绘学 | 1449篇 |
大气科学 | 3821篇 |
地球物理 | 10013篇 |
地质学 | 19341篇 |
海洋学 | 4983篇 |
天文学 | 13040篇 |
综合类 | 210篇 |
自然地理 | 2551篇 |
出版年
2022年 | 371篇 |
2021年 | 663篇 |
2020年 | 698篇 |
2019年 | 720篇 |
2018年 | 1585篇 |
2017年 | 1517篇 |
2016年 | 1878篇 |
2015年 | 996篇 |
2014年 | 1768篇 |
2013年 | 2879篇 |
2012年 | 1868篇 |
2011年 | 2389篇 |
2010年 | 2088篇 |
2009年 | 2696篇 |
2008年 | 2317篇 |
2007年 | 2364篇 |
2006年 | 2212篇 |
2005年 | 1635篇 |
2004年 | 1650篇 |
2003年 | 1556篇 |
2002年 | 1486篇 |
2001年 | 1307篇 |
2000年 | 1224篇 |
1999年 | 999篇 |
1998年 | 1046篇 |
1997年 | 954篇 |
1996年 | 820篇 |
1995年 | 787篇 |
1994年 | 690篇 |
1993年 | 613篇 |
1992年 | 596篇 |
1991年 | 595篇 |
1990年 | 628篇 |
1989年 | 495篇 |
1988年 | 507篇 |
1987年 | 537篇 |
1986年 | 491篇 |
1985年 | 613篇 |
1984年 | 678篇 |
1983年 | 594篇 |
1982年 | 565篇 |
1981年 | 503篇 |
1980年 | 469篇 |
1979年 | 477篇 |
1978年 | 459篇 |
1977年 | 374篇 |
1976年 | 346篇 |
1975年 | 359篇 |
1974年 | 312篇 |
1973年 | 346篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
J. I. S. Zonneveld Dr. 《GeoJournal》1983,7(2):121-129
Modern geography is based on ecological thinking. In this paper some geoecological notions are discussed: the scales and levels regarding spatial magnitude and complexity, the “hierarchy” of landscape units and espcially the scale of time and the concept of the supper-imposing “stamps”. This last mentioned concept is very important in relation to the problem regarding regionalization and its possibilities. Three “stamps” are recognized: 1. the substrate, 2. the climatic conditions, 3. the human (noötic) influence. Holistic regionalization in which all elements (including the human influences) are telling to full advantage, is unsatisfactory. 相似文献
142.
M.R. Kaplan A. Coronato N.R.J. Hulton J.O. Rabassa P.W. Kubik S.P.H.T. Freeman 《Geomorphology》2007,87(4):284-301
We measured in situ 10Be, 26Al and36Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained 40Ar/39Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter. 相似文献
143.
Mass spectra in the range 2 ≦ M/Q ≦ 3 provided by a high resolution mode of the ISEE-3 Plasma Composition Experiment were evaluated for three selected periods during early 1980. The observed Ne/O ratios are compatible with estimated solar abundance ratios. In two of the three periods, the He/Ne-ratios agree with the Apollo foil results. Freezing-in temperatures for oxygen are similar to those obtained by other groups. Possible reasons for an unexpectedly high flux at M/Q = 2.4 are discussed. 相似文献
144.
145.
Quasi-biennial oscillations of solar activity are investigated using several global indices. The Singular Spectrum Analysis is used to separate out and study quasi-biennial oscillations; this method is one of the modifications of the main components method. The principal components of the solar cycle are stable 11-year, secular, and quasi-biennial variations. The periods and shapes of individual variations in each quasi-biennial train depend on the length and power of the particular 11-year cycle. 相似文献
146.
147.
The analysis of drainage network composition 总被引:1,自引:0,他引:1
J. S. Smart 《地球表面变化过程与地形》1978,3(2):129-170
The Horton method of analyzing drainage network composition is reviewed, with the conclusion that it has not been very effective either in improving understanding or in developing useful methods of characterizing drainage basins. New methods which are based on the link rather than the Horton (or Strahler) stream are described. A number of detailed examples of the application of these new methods to the topologic and geometric properties of networks are provided. The results are compared with the predictions of the random model. Data used in the analysis were obtained from 1:24,000 U.S.G.S. topographic maps of eastern Kentucky. Thirty drainage basins were selected and their channel networks were outlined first by the contour-crenulation (CC) method and then by another, more objective, method (SC) in which stream sources were identified by a quantitative slope criterion. The CC and SC samples comprise about 8,700 and 1,700 links, respectively. The three most important results of the analysis are: (1) the channel networks are slightly but significantly more elongated than predicted by the random model, (2) there are fewer second magnitude links than predicted, and (3) the length distribution for interior links depends upon the kind of link (interior or exterior) joined downstream. These features are found in both CC and SC networks. 相似文献
148.
A. M. Nikanorov L. P. Sokolova O. S. Reshetnyak M. Yu. Kondakova A. O. Danilenko 《Russian Meteorology and Hydrology》2010,35(4):281-288
The results of calculation and analysis of the inflow of dissolved chemical substances to the estuarine area of the Northern
Dvina River are considered. Based on the long-term regime hydrochemical information of the State Service of Observation and
Monitoring of the Natural Environmental State, the anthropogenic load of dissolved chemical substances on the estuarine area
and on the estuarine coastal water is estimated per inflow volumes. The extent of the water environment pollution of the near-delta
part of the Northern Dvina River and its delta is estimated. The distribution of pollutant inflow among arms and channels
in delta is under consideration. 相似文献
149.
Results of three-colour VRI CCD photometry are presented obtained during 11 nights in 2001. Twelve new minima timings are derived. The eclipse depth
decreases with wavelength, being equal to 1.28, 1.13 and 1.02 for V, R and I, respectively. The instrumental magnitudes and colours are tabulated for the mid-eclipse, out-of-eclipse part and the eclipsed
component. The V−R colour of the eclipsed component of emission is by 0.22 mag bluer than that for mid-eclipse, indicating a much higher temperature
of the eclipsed region. 相似文献
150.
Zircon fission track dating and track length analysis in the high‐grade part of the Asemigawa region of the Sanbagawa belt demonstrates a simple cooling history passing through the partial annealing zone at 63.2 ± 5.8 (2 σ) Ma. Combining this age with previous results of phengite and amphibole K–Ar and 40Ar/39Ar dating gives a cooling rate of between 6 and 13 °C Myr?1, which can be converted to a maximum exhumation rate of 0.7 mm year?1 using the known shape of the P–T path. This is an order of magnitude lower than the early part of the exhumation history. In contrast, zircon fission track analyses in the low‐grade Oboke region show that this area has undergone a complex thermal history probably related to post‐orogenic secondary reheating younger than c. 30 Ma. This event may correlate with the widespread igneous activity in south‐west Japan around 15 Ma. The age of subduction‐related metamorphism in the Oboke area is probably considerably older than the generally accepted range of 77–70 Ma. 相似文献