全文获取类型
收费全文 | 32071篇 |
免费 | 5211篇 |
国内免费 | 7633篇 |
专业分类
测绘学 | 2105篇 |
大气科学 | 1489篇 |
地球物理 | 6677篇 |
地质学 | 22385篇 |
海洋学 | 2364篇 |
天文学 | 6468篇 |
综合类 | 1687篇 |
自然地理 | 1740篇 |
出版年
2024年 | 90篇 |
2023年 | 385篇 |
2022年 | 862篇 |
2021年 | 1127篇 |
2020年 | 1170篇 |
2019年 | 1283篇 |
2018年 | 1079篇 |
2017年 | 1147篇 |
2016年 | 1312篇 |
2015年 | 1444篇 |
2014年 | 2129篇 |
2013年 | 2196篇 |
2012年 | 2298篇 |
2011年 | 2138篇 |
2010年 | 1942篇 |
2009年 | 2390篇 |
2008年 | 2250篇 |
2007年 | 2422篇 |
2006年 | 2223篇 |
2005年 | 1936篇 |
2004年 | 1770篇 |
2003年 | 1592篇 |
2002年 | 1321篇 |
2001年 | 1156篇 |
2000年 | 1100篇 |
1999年 | 1074篇 |
1998年 | 936篇 |
1997年 | 731篇 |
1996年 | 663篇 |
1995年 | 523篇 |
1994年 | 412篇 |
1993年 | 414篇 |
1992年 | 291篇 |
1991年 | 216篇 |
1990年 | 187篇 |
1989年 | 175篇 |
1988年 | 146篇 |
1987年 | 82篇 |
1986年 | 70篇 |
1985年 | 57篇 |
1984年 | 45篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 5篇 |
1978年 | 16篇 |
1977年 | 15篇 |
1973年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 86 毫秒
101.
102.
In many areas of engineering practice, applied loads are not uniformly distributed but often concentrated towards the centre of a foundation. Thus, loads are more realistically depicted as distributed as linearly varying or as parabola of revolution. Solutions for stresses in a transversely isotropic half‐space caused by concave and convex parabolic loads that act on a rectangle have not been derived. This work proposes analytical solutions for stresses in a transversely isotropic half‐space, induced by three‐dimensional, buried, linearly varying/uniform/parabolic rectangular loads. Load types include an upwardly and a downwardly linearly varying load, a uniform load, a concave and a convex parabolic load, all distributed over a rectangular area. These solutions are obtained by integrating the point load solutions in a Cartesian co‐ordinate system for a transversely isotropic half‐space. The buried depth, the dimensions of the loaded area, the type and degree of material anisotropy and the loading type for transversely isotropic half‐spaces influence the proposed solutions. An illustrative example is presented to elucidate the effect of the dimensions of the loaded area, the type and degree of rock anisotropy, and the type of loading on the vertical stress in the isotropic/transversely isotropic rocks subjected to a linearly varying/uniform/parabolic rectangular load. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
103.
104.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
105.
The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, ROSAT Position Sensitive Proportional Counter (PSPC) archival data of the classical Nova Mus 1983 (GQ Mus) have been re-analysed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spectra are fitted with the hot white dwarf (WD) atmosphere emission models developed for the remnants of classical novae near the Eddington luminosity. The post-outburst X-ray spectra of the remnant white dwarf are examined in the context of evolution on the Hertzsprung–Russell diagram using C–O enhanced atmosphere models. The data obtained in 1991 August (during the ROSAT All Sky Survey) indicate that the effective temperature is . The 1992 February data show that the white dwarf had reached an effective temperature in the range with an unabsorbed X-ray flux (i.e. ∼ bolometric flux) between and . We show that the H burning at the surface of the WD had most likely ceased at the time of the X-ray observations. Only the 1991 August data show evidence for ongoing H burning. 相似文献
106.
本文利用紫金山天文台赣榆站太阳精细结构望远镜拍得的高分辨率色球H_α照片,分析了三个典型活动区。文中利用并检验了七十年代获得的磁图推导法则,应用自己的数值模拟知识和Zwaan对AFS系新浮流区概括的特征,参考七十和九十年代总结的有关耀斑和EllermanBomb的出现规律,逐日分析活动区发展,定出其内部的中性线位置,提出简单和复合中性线的区分,由AFS系和亮谱斑同时出现判断新浮流区,从近离带图找等离子体不稳定点,从远离带图找普遍的磁场流场分布,由H_α结构的综合迹象推测磁场变化。总结出有关活动区H_α结构、磁场及等离子体性质关系的几点启示。 相似文献
107.
基于拖带坐标法建立了岩层大变形的一维非线性微分方程,然后用解析与数值方法研究了变刚度、可伸缩岩层在侧向压力及自重作用下的分叉特性,初步揭示了褶皱岩层初始挠曲的形成机理。 相似文献
108.
本文以爱黎-海斯卡宁均衡补偿假设模式为基础,利用圆模板编制了滇西北及邻区均衡重力异常图。分析了异常的基本特征与壳内构造的关系,并初步探讨了均衡重力异常和强震活动的相关性。 相似文献
109.
Ellerman bombs and type Ⅱ white-light flares share many common features despite the large energy gap between them.Both are considered to result from local heation in the solar lower atmosphere.This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere,with the aim to account for the common features of the two phenomena.Our numerical results manifest the following two typical characteristics of the assumed reconnection process:(1)magnetic reconnection saturates in-600-900s,which is just the lifetime of the two phenomens;(2)ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection,making the heation effect most significant in the lower chromosphere.The applicationof the reconnection model to the two phenomena is discussed in detail. 相似文献
110.