全文获取类型
收费全文 | 8722篇 |
免费 | 1455篇 |
国内免费 | 2077篇 |
专业分类
测绘学 | 137篇 |
大气科学 | 328篇 |
地球物理 | 1872篇 |
地质学 | 5384篇 |
海洋学 | 788篇 |
天文学 | 2126篇 |
综合类 | 356篇 |
自然地理 | 1263篇 |
出版年
2024年 | 28篇 |
2023年 | 139篇 |
2022年 | 372篇 |
2021年 | 373篇 |
2020年 | 369篇 |
2019年 | 394篇 |
2018年 | 382篇 |
2017年 | 332篇 |
2016年 | 349篇 |
2015年 | 399篇 |
2014年 | 434篇 |
2013年 | 489篇 |
2012年 | 428篇 |
2011年 | 451篇 |
2010年 | 394篇 |
2009年 | 675篇 |
2008年 | 558篇 |
2007年 | 617篇 |
2006年 | 650篇 |
2005年 | 507篇 |
2004年 | 488篇 |
2003年 | 553篇 |
2002年 | 430篇 |
2001年 | 360篇 |
2000年 | 357篇 |
1999年 | 300篇 |
1998年 | 320篇 |
1997年 | 229篇 |
1996年 | 168篇 |
1995年 | 154篇 |
1994年 | 151篇 |
1993年 | 96篇 |
1992年 | 93篇 |
1991年 | 54篇 |
1990年 | 51篇 |
1989年 | 31篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 11篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
11.
12.
Nikos Prantzos 《Astrophysics and Space Science》2003,284(2):675-684
We develop a detailed model of the Milky Way (a `prototypical' disk galaxy) and extend it to other disks with the help of
some simple scaling relations, obtained in the framework of Cold Dark Matter models. This phenomenological (`hybrid') approach
to the study of disk galaxy evolution allows us to reproduce successfully a large number of observed properties of disk galaxies
in the local Universe and up to redshift z ∼ 1. The important conclusion is that, on average, massive disks have formed the bulk of their stars earlier than their lower
mass counterparts: the `star formation hierarchy' has been apparently opposite to the `dark matter assembly' hierarchy. It
is not yet clear whether `feedback' (as used in semi-analytical models of galaxy evolution) can explain that discrepancy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
14.
This paper briefly reviews the formulations used over the last 40 years for the solution of problems involving tensile cracking, with both the discrete and the smeared crack approaches. The paper focuses on the smeared approach, identifying as its main drawbacks the observed mesh‐size and mesh‐bias spurious dependence when the method is applied ‘straightly’. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and the strong discontinuity (discrete cracks) approaches are analysed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure stability of the solution, attaining the necessary convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious mesh‐size or mesh‐bias dependence, comparing very favourably with those obtained with other fracture and continuum mechanics approaches. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
15.
R. Surendiranath N. Kameswara Rao Ram Sagar J. S. Nathan K. K. Ghosh 《Journal of Astrophysics and Astronomy》1990,11(2):151-166
bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M)
0 = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1)
× 108 years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor
mass of the planetary nebula on the main sequence is ≥2.5M⊙
Based on observations obtained with the Vainu Bappu Telescope. 相似文献
16.
17.
A new technique designed to help quantify the degree of damage to the landscape from one area to another shows a close relationship between population density and the degree of landscape damage. The technique establishes a scale of damage from 0 to 5 (zero = no damage; 5 = severe damage) using data from aerial photographs, land-use maps, and field data. The related formula allows one to compare the relative degree of damage across regions using a combination of an absolute index, a theoretical index, a relative index, and population density. Xing'an County is used to demonstrate the technique. 相似文献
18.
Zhang Chuanling 《地球科学与环境学报》1997,(1)
文中详细地论述了新疆阿尔泰哈巴河一带古生代火山岩的地质、岩石化学、稀土元素地球化学特征。将其分为三个类型,认为火山岩是在陆缘裂陷槽的区域构造背景下发生和演化的。对各类型火山岩岩浆来源,上升模式也做了初步讨论。 相似文献
19.
20.