全文获取类型
收费全文 | 2914篇 |
免费 | 360篇 |
国内免费 | 463篇 |
学科分类
地球科学 | 3737篇 |
出版年
2024年 | 13篇 |
2023年 | 40篇 |
2022年 | 75篇 |
2021年 | 97篇 |
2020年 | 119篇 |
2019年 | 134篇 |
2018年 | 73篇 |
2017年 | 131篇 |
2016年 | 128篇 |
2015年 | 143篇 |
2014年 | 202篇 |
2013年 | 189篇 |
2012年 | 228篇 |
2011年 | 205篇 |
2010年 | 141篇 |
2009年 | 144篇 |
2008年 | 143篇 |
2007年 | 175篇 |
2006年 | 156篇 |
2005年 | 164篇 |
2004年 | 119篇 |
2003年 | 113篇 |
2002年 | 99篇 |
2001年 | 95篇 |
2000年 | 76篇 |
1999年 | 67篇 |
1998年 | 64篇 |
1997年 | 71篇 |
1996年 | 56篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1993年 | 40篇 |
1992年 | 27篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1979年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有3737条查询结果,搜索用时 15 毫秒
1.
Geoff Kite 《水文研究》1993,7(2):227-233
Using current meters to estimate flows in fast mountain streams is difficult and inaccurate. The salt dilution method offers an easier and more accurate alternative. The method has been used for many years but is time consuming and messy because of the need to mix chemical solutions and measure chemical concentrations in the field. A computer program has been developed which uses a laptop computer to calculate the mixing length and the mass of salt needed. The program controls the conductivity measurements and calculates the streamflow directly in the field. The development of this program is described and examples are presented of the application of the method in the Rocky Mountains of Alberta and British Columbia. 相似文献
2.
In situ strength measurements on natural upper-mantle minerals 总被引:1,自引:0,他引:1
Junji Yamamoto Jun-ichi Ando Hiroyuki Kagi Toru Inoue Akihiro Yamada Daisuke Yamazaki Tetsuo Irifune 《Physics and Chemistry of Minerals》2008,35(5):249-257
Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700°C, we examined rheological
properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated
using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals
increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression
and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential
stress of 4–6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600°C. Neither orthopyroxene
nor spinel shows complete stress relaxation, but both retain some stress even at 700°C. The strength of the minerals decreases
in the order of chromian-spinel ≈ orthopyroxene > olivine for these conditions. This order of strength is consistent with
the residual pressure of fluid inclusions in mantle xenoliths. 相似文献
3.
4.
5.
A comparative error analysis of manual versus automated methods of data acquisition for algebraic strain estimation 总被引:1,自引:0,他引:1
This paper presents a statistical analysis of the algebraic strain estimation algorithm of Shimamoto and Ikeda [Shimamoto, T., Ikeda, Y., 1976. A simple algebraic method for strain estimation from deformed eillipsoidal objects: 1. Basic theory. Tectonophysics 36, 315–337]. It is argued that the error in their strain estimation procedure can be quantified using an expected discrepancy measure. An analysis of this measure demonstrates that the error is inversely proportional to the number of clasts used. The paper also examines the role of measurement error, in particular that incurred under (i) a moment based and (ii) manual data acquisition methods. Detailed analysis of these two acquisition methods shows that in both cases, the effect of measurement error on the expected discrepancy is small relative to the effect of the sample size (number of objects). Given their relative speed advantage, this result favours the use of automated measurement methods even if they incur more measurement error on individual objects. Validation of these results is carried out by means of a simulation study, as well as by reference to studies appearing in previous literature. The results are also applied to obtain an upper bound on the error of strain estimation for various studies published in the literature on strain analysis. 相似文献
6.
7.
A generic network design in close range photogrammetry is one where optimal multi-ray intersection geometry is obtained with as few camera stations as practicable. Hyper redundancy is a concept whereby, once the generic network is in place, many additional images are recorded, with the beneficial impact upon object point precision being equivalent to the presence of multiple exposures at each camera position within the generic network. The effective number of images per station within a hyper redundant network might well be in the range of 10 to 20 or more. As is apparent when it is considered that a hyper redundant network may comprise hundreds of images, the concept is only applicable in practice to fully automatic vision metrology systems, where it proves to be a very effective means of enhancing measurement accuracy at the cost of minimal additional work in the image recording phase. This paper briefly reviews the network design and accuracy aspects of hyper redundancy and illustrates the technique by way of the photogrammetric measurement of surface deformation of a radio telescope of 26 m diameter. This project required an object point measurement accuracy of σ = 0·065 mm, or 1/400 000 of the diameter of the reflector. 相似文献
8.
9.
2001年云南澜沧5.0、施甸5.2,5.9,5.3、宁蒗5.8、楚雄5.3和江川5.1级地震前,云南49项水氡前兆中的一些台站出现突出的异常。研究发现,根据这些异常项的异常特征和空间分布特征及历史震例,可对这几次地震预报的三要素,尤其是地点和时间做出较好的判断。 相似文献
10.