全文获取类型
收费全文 | 7060篇 |
免费 | 587篇 |
国内免费 | 750篇 |
专业分类
测绘学 | 300篇 |
大气科学 | 905篇 |
地球物理 | 1550篇 |
地质学 | 3101篇 |
海洋学 | 643篇 |
天文学 | 1048篇 |
综合类 | 361篇 |
自然地理 | 489篇 |
出版年
2023年 | 52篇 |
2022年 | 114篇 |
2021年 | 165篇 |
2020年 | 117篇 |
2019年 | 145篇 |
2018年 | 244篇 |
2017年 | 239篇 |
2016年 | 304篇 |
2015年 | 179篇 |
2014年 | 314篇 |
2013年 | 344篇 |
2012年 | 310篇 |
2011年 | 359篇 |
2010年 | 370篇 |
2009年 | 404篇 |
2008年 | 362篇 |
2007年 | 335篇 |
2006年 | 360篇 |
2005年 | 248篇 |
2004年 | 215篇 |
2003年 | 205篇 |
2002年 | 172篇 |
2001年 | 160篇 |
2000年 | 186篇 |
1999年 | 209篇 |
1998年 | 214篇 |
1997年 | 230篇 |
1996年 | 200篇 |
1995年 | 148篇 |
1994年 | 153篇 |
1993年 | 162篇 |
1992年 | 106篇 |
1991年 | 94篇 |
1990年 | 81篇 |
1989年 | 79篇 |
1988年 | 79篇 |
1987年 | 66篇 |
1986年 | 75篇 |
1985年 | 58篇 |
1984年 | 58篇 |
1983年 | 56篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 33篇 |
1979年 | 38篇 |
1977年 | 22篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 21篇 |
1973年 | 25篇 |
排序方式: 共有8397条查询结果,搜索用时 46 毫秒
1.
2.
利用“地震预报计算机专家系统”的思想对大同 -阳高 Ms6 .1地震前每一前兆异常事件进行综合评估 ,以每一异常的最可能发震时间来计算发震概率 ,利用地震前兆综合加权信息熵研究了系统熵值与地震的关系。对华北地区的地震前兆综合加权信息熵研究表明 ,在大同 -阳高 Ms6 .1地震前 ,信息熵出现了明显的减熵有序变化 相似文献
3.
A spectacular change in the lower corona on the south-west limb has been found in solar images taken by the Yohkoh soft X-ray telescope. The event is characterized by a large topological change in magnetic field and a large intensity decrease observed after the X1. 1/1B flare on 9 November, 1991. A coronal mass ejection (CME) was observed by the Mark III K-coronameter (MK3) at the HAO/Mauna Loa Observatory. Both the MK3 (white-light) and soft X-ray observations showed that one leg of this CME was located above the flare site. An interplanetary shock associated with this event was observed by Pioneer Venus Orbiter, and, possibly, by IMP-8.Also Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, U.S.A. 相似文献
4.
5.
本文论述了珠穆朗玛峯地区土壤中稀土元素的含量,以及它们在土壤中的分布模式,并发现土壤中稀土元素的含量水平在很大程度上受土壤母质的制约。 相似文献
6.
The auriferous veins at Jinniushan occurs within the Jinniushan faulted zone in the Kunyushan Granite. Optical observation reveals that gold ore body formed during the main stage of hydrothermal activity. Detailed geothermometric studies of fluid inclusions from the veins show that the forming temperature ranges between 130℃ and 370℃ and the salinity is from 4.01 to 15.21 wvt percent NaCl. The ore-forming fluid is featured by low to moderate salinity, and low to moderate temperature. According to investigations of the values of vapor/liquid and temperatures of the ore-forming fluids, we propose that the boiling fluid inclusions exist in the main mineralization stages. Fluid boiling is suggested as a mechanism for the precipitation of gold from the hydrothermal fluid in the Jinniushan gold deposit. 相似文献
7.
8.
A. Habib J. Vernin Z. Benkhaldoun H. Lanteri 《Monthly notices of the Royal Astronomical Society》2006,368(3):1456-1462
In this paper, we present a new method to estimate, for each turbulent layer labelled i , the horizontal wind speed v ( h i ) , the standard deviation of the horizontal wind speed fluctuations σ v ( hi ) and the integrated value of C 2 n over the thickness Δ hi of the turbulent layer C 2 n ( hi )Δ hi , where hi is the altitude of the turbulent layer. These parameters are extracted from single star scintillation spatiotemporal cross-correlation functions of atmospheric speckles obtained within the generalized mode. This method is based on the simulated annealing algorithm to find the optimal solution required to solve the problem. Astrophysics parameters for adaptive optics are also calculated using C 2 n ( hi ) and v ( hi ) values. The results of other techniques support this new method. 相似文献
9.
A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards 相似文献
10.
An empirical kinematic method developed by Hakamada and Akasofu (1982) is calibrated on the basis of a one-dimensional MHD solution. The calibrated results are used to simulate the stream-stream interaction and the background corotating structure in a simple situation and also during 22 November–6 December 1977. The solar wind disturbances caused by solar activities during this period are then introduced into the above background stream in simulating the heliospheric disturbance event which was observed by an aligned set of spacecraft at distances between 0.6 and 1.6 a.u. The observations and the simulated results are satisfactory, and a little more refinement in the simulation could reconstruct reasonably well the data by filling the data gaps in the solar wind speed, the density and the IMF magnitude. 相似文献