全文获取类型
收费全文 | 84718篇 |
免费 | 1140篇 |
国内免费 | 841篇 |
专业分类
测绘学 | 2390篇 |
大气科学 | 6084篇 |
地球物理 | 16619篇 |
地质学 | 29350篇 |
海洋学 | 7590篇 |
天文学 | 20047篇 |
综合类 | 280篇 |
自然地理 | 4339篇 |
出版年
2022年 | 479篇 |
2021年 | 836篇 |
2020年 | 910篇 |
2019年 | 1014篇 |
2018年 | 2212篇 |
2017年 | 2085篇 |
2016年 | 2653篇 |
2015年 | 1453篇 |
2014年 | 2502篇 |
2013年 | 4321篇 |
2012年 | 2671篇 |
2011年 | 3481篇 |
2010年 | 3100篇 |
2009年 | 4102篇 |
2008年 | 3530篇 |
2007年 | 3609篇 |
2006年 | 3374篇 |
2005年 | 2509篇 |
2004年 | 2562篇 |
2003年 | 2401篇 |
2002年 | 2360篇 |
2001年 | 2079篇 |
2000年 | 1976篇 |
1999年 | 1680篇 |
1998年 | 1716篇 |
1997年 | 1637篇 |
1996年 | 1369篇 |
1995年 | 1316篇 |
1994年 | 1164篇 |
1993年 | 1047篇 |
1992年 | 977篇 |
1991年 | 980篇 |
1990年 | 996篇 |
1989年 | 891篇 |
1988年 | 853篇 |
1987年 | 945篇 |
1986年 | 869篇 |
1985年 | 1046篇 |
1984年 | 1236篇 |
1983年 | 1061篇 |
1982年 | 1038篇 |
1981年 | 935篇 |
1980年 | 846篇 |
1979年 | 825篇 |
1978年 | 839篇 |
1977年 | 695篇 |
1976年 | 648篇 |
1975年 | 656篇 |
1974年 | 596篇 |
1973年 | 663篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
421.
The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
422.
A. I. Orgilyanov E. E. Malkov B. I. Pisarskii P. S. Badminov D. Ganchimeg 《Geography and Natural Resources》2011,32(2):132-139
We examine the various types of mineral waters occurring on the projected specially protected transboundary natural territory
“Istoki Amura”, on the Hentei-Dauria neotectonic high. We suggest the pattern of rational utilization of the mineral springs
according to the nature conservation status of the terrain (nature reserves, national parks, and public access areas). 相似文献
423.
Some evidence of climate change in twentieth-century India 总被引:1,自引:0,他引:1
The study of climate changes in India and search for robust evidences are issues of concern specially when it is known that
poor people are very vulnerable to climate changes. Due to the vast size of India and its complex geography, climate in this
part of the globe has large spatial and temporal variations. Important weather events affecting India are floods and droughts,
monsoon depressions and cyclones, heat waves, cold waves, prolonged fog and snowfall. Results of this comprehensive study
based on observed data and model reanalyzed fields indicate that in the last century, the atmospheric surface temperature
in India has enhanced by about 1 and 1.1°C during winter and post-monsoon months respectively. Also decrease in the minimum
temperature during summer monsoon and its increase during post-monsoon months have created a large difference of about 0.8°C
in the seasonal temperature anomalies which may bring about seasonal asymmetry and hence changes in atmospheric circulation.
Opposite phases of increase and decrease in the minimum temperatures in the southern and northern regions of India respectively
have been noticed in the interannual variability. In north India, the minimum temperature shows sharp decrease of its magnitude
between 1955 and 1972 and then sharp increase till date. But in south India, the minimum temperature has a steady increase.
The sea surface temperatures (SST) of Arabian Sea and Bay of Bengal also show increasing trend. Observations indicate occurrence
of more extreme temperature events in the east coast of India in the recent past. During summer monsoon months, there is a
decreasing (increasing) trend in the frequency of depressions (low pressure areas). In the last century the frequency of occurrence
of cyclonic storms shows increasing trend in the month of November. In addition there is increase in the number of severe
cyclonic storms crossing Indian Coast. Analysis of rainfall amount during different seasons indicate decreasing tendency in
the summer monsoon rainfall over Indian landmass and increasing trend in the rainfall during pre-monsoon and post-monsoon
months. 相似文献
424.
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
425.
426.
427.
S. Miyamoto 《Planetary and Space Science》1960,2(4):256-260
This interpretation of lunar surface features is based on the differentiation of siliceous and basaltic substances similar to those of the earth. Our hypothesis is that lunar maria are composed of basaltic matter similar to that of terrestrial ocean basins, and that the lunar continents (bright regions) are composed of siliceous blocks. 相似文献
428.
429.
Palaeomagnetism of Holocene lake sediments from north Poland 总被引:1,自引:0,他引:1
K. M. Creer E. Hogg Z. Malkowski J. E. Mojski E. Niedziolka-Krol P. W. Readman P. Tucholka 《Geophysical Journal International》1979,59(2):287-313
Summary. Detailed palaeomagnetic investigations of 17 cores of Holocene lake sediments from four lakes in Poland show a pattern of declination variations similar to those found in Lake Windermere, England and in addition a well defined pattern of inclination variations. A total of nine inclination swings are observed compared to five declination swings and their phase relationships are such that both sets of swings cannot be periodic. Exact dating of the palaeomagnetic record is not possible as radiocarbon ages are over 1000 yr older than those deduced from palynological studies. Thermomagnetic and X-ray studies on magnetic concentrates confirm the results of studies of remanence cooling, IRM acquisition and coercivity experiments which are consistent with fine grained magnetite as the main magnetic mineral in the sediments. 相似文献
430.
S. G. Dobrovolski 《Water Resources》2014,41(6):728-737
A number of uncertainties of forecasts of changes in the annual runoff depths at global scale, obtained using information on results of integration of 21 IPCC climate models is studied. Following possible errors of these forecasts are calculated: errors of models; differences between main (IPCC) scenarios of emission of greenhouse gases in the atmosphere and resultant changes of global temperatures; mistakes in estimates of average long-term observed values of the runoff depths for the “control” period. Global maps of a “significance index” of forecasted changes in the runoff depths (estimations of changes in the annual runoff depths divided by mean square root values of errors of these estimations) for 2025, 2050, 2075 and 2100 are presented. It is shown that the most significant global changes of the runoff depths (growth in the north of Eastern Siberia, of the Russian Far East, of North America, falling in the “Greater Mediterranean Region”) are predicted for the second quarter of 21st century. Further changes of the runoff amplify only in the Amazon basin (reduction, by 2075). Almost everywhere else (including almost all European territory of Russia, Western Siberia, south of Eastern Siberia and of the Far East) the significance of changes in the runoff depths during 21st century is negligible. 相似文献