全文获取类型
收费全文 | 109311篇 |
免费 | 1592篇 |
国内免费 | 718篇 |
专业分类
测绘学 | 2362篇 |
大气科学 | 7293篇 |
地球物理 | 21238篇 |
地质学 | 39148篇 |
海洋学 | 9869篇 |
天文学 | 24974篇 |
综合类 | 289篇 |
自然地理 | 6448篇 |
出版年
2022年 | 711篇 |
2021年 | 1209篇 |
2020年 | 1341篇 |
2019年 | 1487篇 |
2018年 | 2964篇 |
2017年 | 2793篇 |
2016年 | 3250篇 |
2015年 | 1714篇 |
2014年 | 3167篇 |
2013年 | 5591篇 |
2012年 | 3473篇 |
2011年 | 4576篇 |
2010年 | 4149篇 |
2009年 | 5244篇 |
2008年 | 4630篇 |
2007年 | 4769篇 |
2006年 | 4374篇 |
2005年 | 3174篇 |
2004年 | 3132篇 |
2003年 | 2990篇 |
2002年 | 2885篇 |
2001年 | 2502篇 |
2000年 | 2457篇 |
1999年 | 1978篇 |
1998年 | 2061篇 |
1997年 | 1932篇 |
1996年 | 1678篇 |
1995年 | 1629篇 |
1994年 | 1397篇 |
1993年 | 1343篇 |
1992年 | 1230篇 |
1991年 | 1277篇 |
1990年 | 1269篇 |
1989年 | 1100篇 |
1988年 | 1023篇 |
1987年 | 1173篇 |
1986年 | 1085篇 |
1985年 | 1330篇 |
1984年 | 1481篇 |
1983年 | 1437篇 |
1982年 | 1330篇 |
1981年 | 1247篇 |
1980年 | 1122篇 |
1979年 | 1064篇 |
1978年 | 1010篇 |
1977年 | 933篇 |
1976年 | 884篇 |
1975年 | 878篇 |
1974年 | 855篇 |
1973年 | 946篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
471.
472.
473.
474.
G. Cayrel de Strobel Y. Lebreton C. Soubiran E.D. Friel 《Astrophysics and Space Science》1999,265(1-4):345-352
The authors of this paper try to disentangle the many problems arisen from a new enlarged sample of nearby low-mass,metal-rich-stars.
These stars have reliable absolute magnitudes, deduced from Hipparcos parallaxes, precise bolometric corrections, effective
temperatures and metal abundances from high resolution detailed spectroscopic analyses. Their ages have been derived from
a grid of isochrones calculated with up to date physics. The main goal of this paper is to determine the ages of the slightly
evolved SMR stars. Among those with well determinated ages about 80% of them have intermediate ages of (2 to 5 Gyr), but only
20% have ages of 8 Gyr or more. Nevertheless, the existence of very old metal-rich stars is confirmed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
475.
Actual surface fields of meteorological variables 1–3 hours before the heavy showers are analyzed in detail for the purpose
of their specification with WRF-ARW model. The complex of hygrothermodynamic characteristics needed for this purpose is discovered.
The detailed satellite, radar, and synoptic data are also considered. 相似文献
476.
V. A. Dolgii-Trach 《Russian Meteorology and Hydrology》2012,37(1):64-70
An optimization scheme is considered of the method of instrumental determination of soil moisture used within the Roshydromet
system. The scheme enables to reduce the volume of instrumental operations by 2.5–3 times using the empirical statistical
dependences between the water content in different layers of the soil profile. Efficiency of the filtration of outliers in
the data sample is studied on the basis of the analysis of regression residuals when deriving the regression equations. 相似文献
477.
Mihail E. Popescu 《Engineering Geology》1979,14(1):43-53
Engineering problems associated with expansive clay formations, which have a large swelling and shrinking potential, exist in different regions of Romania.In the general framework of the study of the behaviour of expansive clays, the present paper describes some particular aspects connected with the swelling and shrinkage processes and their engineering effects in Romania.The differences between swelling potential relationships, obtained by two different methods are presented and discussed. Swelling pressure tests were accomplished using the available standard techniques, as well as a specially developed cell pressure equipment.Attention is drawn to the stages of the shrinkage process as related to soil structure. It was found that, in a general case, there are three distinct?tages: initial, normal and residual shrinkage.Laboratory investigations have shown that in soils with an anisotropic structure, the directional variation of shrinkage strains is elliptical in shape, with the maximum shrinkage normal to particle orientation.The engineering aspects of the results are discussed. 相似文献
478.
479.
480.
D. A. Burney R. V. DeCandido L. P. Burney F. N. Kostel-Hughes T. W. Stafford Jr. H. F. James 《Journal of Paleolimnology》1995,13(3):209-217
A sediment core from a high-elevation bog on Maui in the Hawaiian Islands contains evidence for drier conditions between 9.4–5.8 kyr BP, followed by a wetter interval between 5.8–2.2 kyr BP, and a variable late Holocene. These precipitation changes may be a reflection of vertical displacements of the upper boundary of the mid-Pacific Trade Wind Inversion (TWI) cloud layer. Fires, probably volcanically ignited, occurred in the forests prior to human arrival. Polynesian activity in this high-elevation, remote site was apparently limited, with no pollen, charcoal, or sedimentological evidence for local anthropogenic disturbance. After European contact, grass fires increased and introduced plant species invaded the site. Values for Cd, Cu, Pb, and Zn in sediments throughout the Holocene indicate low trace-metal deposition from atmospheric particulates at the site, even in the twentieth century.This paper is one of a series of papers guest edited by Dr. Mark Brenner on tropical paleolimnology 相似文献