全文获取类型
收费全文 | 19890篇 |
免费 | 3026篇 |
国内免费 | 3971篇 |
专业分类
测绘学 | 1292篇 |
大气科学 | 3277篇 |
地球物理 | 4757篇 |
地质学 | 9752篇 |
海洋学 | 2289篇 |
天文学 | 1679篇 |
综合类 | 1618篇 |
自然地理 | 2223篇 |
出版年
2024年 | 91篇 |
2023年 | 322篇 |
2022年 | 882篇 |
2021年 | 998篇 |
2020年 | 856篇 |
2019年 | 955篇 |
2018年 | 1155篇 |
2017年 | 1005篇 |
2016年 | 1121篇 |
2015年 | 897篇 |
2014年 | 1190篇 |
2013年 | 1221篇 |
2012年 | 1136篇 |
2011年 | 1187篇 |
2010年 | 1179篇 |
2009年 | 1123篇 |
2008年 | 1009篇 |
2007年 | 893篇 |
2006年 | 812篇 |
2005年 | 702篇 |
2004年 | 571篇 |
2003年 | 516篇 |
2002年 | 449篇 |
2001年 | 495篇 |
2000年 | 534篇 |
1999年 | 706篇 |
1998年 | 606篇 |
1997年 | 568篇 |
1996年 | 553篇 |
1995年 | 413篇 |
1994年 | 400篇 |
1993年 | 361篇 |
1992年 | 312篇 |
1991年 | 222篇 |
1990年 | 185篇 |
1989年 | 163篇 |
1988年 | 137篇 |
1987年 | 118篇 |
1986年 | 105篇 |
1985年 | 90篇 |
1984年 | 82篇 |
1983年 | 80篇 |
1982年 | 73篇 |
1981年 | 49篇 |
1980年 | 41篇 |
1979年 | 51篇 |
1978年 | 26篇 |
1976年 | 25篇 |
1975年 | 29篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
IMPACTS OF FUTURE SEA LEVEL RISE ON SALT WATER INTRUSION IN THE CHANGJIANG RIVER ESTUARY 总被引:1,自引:0,他引:1
杨桂山 《中国地理科学(英文版)》1992,2(1):30-41
Sea level rise could increase the salinity of an estuary by altering the balance between fresh water and salt water. The implications of sea level rise for increasing salinity have been examined in the Changjiang (Yangtze) River estuary. By correlative analysis of chlorinity, discharge and tidal level and calculation of two-dimensional chlorinity, distribution of the Changjiang River estuary, the changes of the intensity and lasting hours of salt water intrusion at Wusong Station and the changes of chlorinity distribution in the South Branch of the Changjiang River estuary have been estimated when future sea level rises 50-100 cm. The intensity of salt water intrusion in the future will be far more serious than current trend. 相似文献
62.
A parametric study of the evolution within, and signatures at, 1 AU of high-speed streams is performed with the use of a MHD, 21/2-D, time-dependent model. This study is an extension of an earlier one by Smith and Dryer (1990) who examined the ecliptic plane consequences of relatively short-duration, energetic solar disturbances. The present study examines both the erupting and corotating parts of long-duration, high-speed streams characteristic of coronal hole flows. By examining the variation of the simulated plasma velocity, density, temperature, and magnetic field at 1 AU, as well as the location of the solar coronal hole sources relative to the observer at 1 AU, we are able to provide some insight into the identification of the solar sources of interplanetary disturbances. We present and discuss two definitions for angle locating the solar source of interplanetary disturbances at 1 AU.We apply our results to the suggestion by Hewish (1988) that low-latitude coronal holes are suitably positioned to be the sources of major geomagnetic storms when the holes are in the eastern half of the solar hemisphere at the time of the commencement of the storm. Our results indicate that, for these cases, the streams emanating from within the hole must be very fast, greater than 1000 km s–1, or very wide, greater than 60°, at the inner boundary of 18 solar radii in our simulation. 相似文献
63.
64.
We outline some main results from recent analytical modelling of axisymmetric jets from the coronae of young stars and compare them to disk-wind and X-wind models. We emphazise the roles of the magnetic rotator and the disk in the formation and the evolution of the jet. We conjecture that with time both the efficiency of the magnetic rotator and the role of the disk as a primary source for the wind decline. 相似文献
65.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate… 相似文献
66.
67.
The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented. 相似文献
68.
I.IN~crIOXLocatedinthecoddlepatofTallmBasin,withanareaof33.76X104klnZ,theTaldirnakan~isinthehinterlandofEurasia.Blockedbythehighmountainsaround,vapourofoceancanhardlyreachthedesert.APartfromthis,asthedeSertisinthesinkingcompensationareaoftheascensionalaircurrentaamstheQinghal-XIZangPlateau,itSprecipitationisrareandtheevaporationcapacityisintensealltheyearround.Allthesecontributetotheformationsofthetypifydrydesertclimate.Theacidityindexofthedesertandthearoundregionisashighasmorethan50,w… 相似文献
69.
Electrons accelerated during solar flares are revealed by their electromagnetic radiation in different spectral ranges, emitted at different heights in the solar atmosphere. The observational analysis points to a common and continuous injection of particles. Based on this result, a quantitative investigation of the hard X-ray and microwave emissions observed during the 29 June, 1980 flare at 11: 40 UT has been performed. This is the first modelisation that takes into account both the inhomogeneity of the microwave source region and the dynamical evolution of the electron population. First results of our model computations demonstrate that during the most energetic phase of the event both hard X-rays and microwaves are described by electron populations resulting from the same injection function, and that the total numbers of electrons required for both emissions are compatible. Account for the inhomogeneity of the microwave source is shown to be a necessary condition for the interpretation of observed spectra.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985. 相似文献
70.
含有多重极点的有理真分式展开为部分分式,不需要计算低阶导数。列出被求函数的各阶导数的关系式,画出各阶导数作为节点的信号流图。该图无环路,既直观表现出各高阶导数的相互关系及影响的单向性,也使求节点增益的梅森公式特别简便。该方法将求高阶导数问题简化为代数运算,特别适合于编制成计算机程序 相似文献