全文获取类型
收费全文 | 51694篇 |
免费 | 8796篇 |
国内免费 | 12090篇 |
专业分类
测绘学 | 5853篇 |
大气科学 | 8067篇 |
地球物理 | 9851篇 |
地质学 | 25508篇 |
海洋学 | 7057篇 |
天文学 | 4570篇 |
综合类 | 3740篇 |
自然地理 | 7934篇 |
出版年
2024年 | 199篇 |
2023年 | 611篇 |
2022年 | 1697篇 |
2021年 | 1982篇 |
2020年 | 2117篇 |
2019年 | 2612篇 |
2018年 | 1873篇 |
2017年 | 2225篇 |
2016年 | 2257篇 |
2015年 | 2582篇 |
2014年 | 3026篇 |
2013年 | 3218篇 |
2012年 | 3226篇 |
2011年 | 3320篇 |
2010年 | 2830篇 |
2009年 | 3462篇 |
2008年 | 3467篇 |
2007年 | 3723篇 |
2006年 | 3644篇 |
2005年 | 3325篇 |
2004年 | 2895篇 |
2003年 | 2641篇 |
2002年 | 2282篇 |
2001年 | 1950篇 |
2000年 | 1965篇 |
1999年 | 1747篇 |
1998年 | 1492篇 |
1997年 | 1128篇 |
1996年 | 957篇 |
1995年 | 792篇 |
1994年 | 743篇 |
1993年 | 631篇 |
1992年 | 488篇 |
1991年 | 367篇 |
1990年 | 265篇 |
1989年 | 243篇 |
1988年 | 179篇 |
1987年 | 115篇 |
1986年 | 80篇 |
1985年 | 51篇 |
1984年 | 34篇 |
1983年 | 20篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1954年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In order to understand the process of surface erosion and acquire basic data of conditions on hillslope without vege tation, a sprinkling experiment is conducted on a bare slope in Mt. Tanakami in the central part of Japan. Based on the mea surements of runoff, mean soil erosion depth, and sediment yield, etc. , the results suggest the following characteristics in the process of surface erosion in the experimental area. (1) The occurrence of sediment discharge is interrupted; (2) Surface runoff is a saturated overland flow; (3) The mean soil erosion depth is thick compared with other areas in Mt. Tanakami;(4) Sediment discharge process is detachment- limited. 相似文献
82.
模糊划分矩阵在岩土参数概率分布中的应用 总被引:1,自引:0,他引:1
讨论如何在小样本条件下用已有的过程经验与试验资料确定岩土参数概率分布,用模糊划分矩阵与BAYES方法相结合,给出由小样本试验数据确定岩土参数的概率分布。 相似文献
83.
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
84.
85.
86.
87.
88.
应用显微光度术、显微傅立叶红外光谱(Micro-FT.IR)和飞行时间二次离子质谱(TOF-SIMS)等原位微分析技术并结合均一温度测量对胜利油气区下第三系沙河街组沙三段中有机包裹体进行了研究。区分出两类有机包裹体,即原生有机包裹体和次生有机包裹体。结果表明两类有机包裹体特征不同,二者物质组成、有机质成分及化学结构、热演化程度等差别也较大。结合地质分析表明原生有机包裹体是沙三段烃源岩生成烃类运移产物,具“自生自储”特点,而次生有机包裹体是沙四段烃源岩生成的烃类二次运移的产物。沙三段是沙河街组油气运移和聚集的主要层位,因而是寻找油气资源的主要目标层。研究表明,有机包裹体是研究油气生成、运移、聚集和演化等成藏系统最有效的手段之一,在油气勘探中有重要的应用意义。 相似文献
89.
We carried out a series of linear stability analyses of the radial and low-degree non-radial p modes for stellar models with initial masses of . The stellar models were computed by using convective overshoot distance , 0.25 and 0.40 H P . Our numerical results show that the β Cephei instability strip forms a horn-shaped region pointing upwards near the main sequence on the Hertzsprung–Russell diagram (HRD). The lower part of the instability strip for the radial modes join the zero-age main-sequence (ZAMS) at , while the top of the instability strip extends up to . The instability strip for the non-radial modes is even wider. The overall instability strip is dominated by the radial and non-radial fundamental modes. The first overtone (the radial-order index is also pulsationally unstable. We have shown that the β Cephei stability is almost independent of the overshoot parameter d over used for the stellar models, while it depends critically on the metal abundance. With decreasing metal abundance, the instability region shrinks and eventually disappears for . 相似文献
90.
卫星激光测距的新进展 总被引:6,自引:0,他引:6
扼要综述了近几年国际上卫星激光测距的进展,介绍了国内激光测距网的现状,展望了未来卫星激光测距的发展。 相似文献