全文获取类型
收费全文 | 112283篇 |
免费 | 18497篇 |
国内免费 | 42675篇 |
专业分类
测绘学 | 4240篇 |
大气科学 | 25727篇 |
地球物理 | 27870篇 |
地质学 | 61812篇 |
海洋学 | 23133篇 |
天文学 | 20631篇 |
综合类 | 4140篇 |
自然地理 | 5902篇 |
出版年
2022年 | 963篇 |
2021年 | 1597篇 |
2020年 | 2998篇 |
2019年 | 6532篇 |
2018年 | 8034篇 |
2017年 | 7644篇 |
2016年 | 8011篇 |
2015年 | 5927篇 |
2014年 | 6645篇 |
2013年 | 8946篇 |
2012年 | 7207篇 |
2011年 | 7556篇 |
2010年 | 7403篇 |
2009年 | 7448篇 |
2008年 | 6299篇 |
2007年 | 6230篇 |
2006年 | 5617篇 |
2005年 | 4510篇 |
2004年 | 4788篇 |
2003年 | 4534篇 |
2002年 | 4103篇 |
2001年 | 3713篇 |
2000年 | 3187篇 |
1999年 | 2891篇 |
1998年 | 3034篇 |
1997年 | 3101篇 |
1996年 | 2483篇 |
1995年 | 2361篇 |
1994年 | 2202篇 |
1993年 | 2003篇 |
1992年 | 1785篇 |
1991年 | 1583篇 |
1990年 | 1617篇 |
1989年 | 1351篇 |
1988年 | 1227篇 |
1987年 | 1225篇 |
1986年 | 1037篇 |
1985年 | 1242篇 |
1984年 | 1283篇 |
1983年 | 1152篇 |
1982年 | 1149篇 |
1981年 | 982篇 |
1980年 | 942篇 |
1979年 | 853篇 |
1978年 | 806篇 |
1977年 | 738篇 |
1976年 | 669篇 |
1975年 | 663篇 |
1974年 | 630篇 |
1973年 | 686篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
The elm decline of 5000 14C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
12.
The growth of Glasgow from a small town into a heavily industrialised conurbation depended greatly on its local geological riches. Extensive mining and quarrying of a range of minerals took place from the 18th century onwards. The early underground stoop and room (pillar and stall) workings, and the backfilled quarries, together with variably consolidated natural superficial deposits, have bequeathed to the city a heritage of unwanted engineering problems which cannot easily be quantified. Recent work by the British Geological Survey (BGS) illustrates the scale of both geological and man-made problems. 相似文献
13.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
14.
15.
A numerical scheme is developed in order to simulate fluid flow in three dimensional (3‐D) microstructures. The governing equations for steady incompressible flow are solved using the semi‐implicit method for pressure‐linked equations (SIMPLE) finite difference scheme within a non‐staggered grid system that represents the 3‐D microstructure. This system allows solving the governing equations using only one computational cell. The numerical scheme is verified through simulating fluid flow in idealized 3‐D microstructures with known closed form solutions for permeability. The numerical factors affecting the solution in terms of convergence and accuracy are also discussed. These factors include the resolution of the analysed microstructure and the truncation criterion. Fluid flow in 2‐D X‐ray computed tomography (CT) images of real porous media microstructure is also simulated using this numerical model. These real microstructures include field cores of asphalt mixes, laboratory linear kneading compactor (LKC) specimens, and laboratory Superpave gyratory compactor (SGC) specimens. The numerical results for the permeability of the real microstructures are compared with the results from closed form solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
17.
V. G. Gorbatskii 《Astrophysics》1990,32(2):149-154
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990. 相似文献
18.
19.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
20.