全文获取类型
收费全文 | 6374篇 |
免费 | 1186篇 |
国内免费 | 1693篇 |
专业分类
测绘学 | 517篇 |
大气科学 | 1529篇 |
地球物理 | 1519篇 |
地质学 | 3243篇 |
海洋学 | 707篇 |
天文学 | 288篇 |
综合类 | 641篇 |
自然地理 | 809篇 |
出版年
2024年 | 43篇 |
2023年 | 96篇 |
2022年 | 257篇 |
2021年 | 311篇 |
2020年 | 248篇 |
2019年 | 270篇 |
2018年 | 281篇 |
2017年 | 271篇 |
2016年 | 352篇 |
2015年 | 285篇 |
2014年 | 342篇 |
2013年 | 342篇 |
2012年 | 313篇 |
2011年 | 355篇 |
2010年 | 364篇 |
2009年 | 341篇 |
2008年 | 300篇 |
2007年 | 284篇 |
2006年 | 239篇 |
2005年 | 228篇 |
2004年 | 181篇 |
2003年 | 201篇 |
2002年 | 217篇 |
2001年 | 213篇 |
2000年 | 234篇 |
1999年 | 353篇 |
1998年 | 342篇 |
1997年 | 337篇 |
1996年 | 252篇 |
1995年 | 237篇 |
1994年 | 217篇 |
1993年 | 187篇 |
1992年 | 142篇 |
1991年 | 130篇 |
1990年 | 84篇 |
1989年 | 77篇 |
1988年 | 79篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 33篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1958年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有9253条查询结果,搜索用时 15 毫秒
31.
32.
本文在分析导航型GPS输出数据格式的基础上,研究了智能手机与GPS之间的蓝牙数据链以及GPS坐标系到测量坐标系的转换方法,并在此基础上进行了基于Windows Mobile的应用程序开发。实践证明,采用这种方法定位精度可以达到6~7米,能应用于测量控制点的辅助定位及其他非高精度定位的专业领域。 相似文献
33.
34.
The spontaneous and evoked activity of electroreceptors were electrophysiologically studied. The results are:
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 380–386, 1991. 相似文献
1. | The spontaneous discharge rate ranged from 15 to 85 imp/s with a mode of 50 imp/s for 126 organs of 18 animals. |
2. | By analysis of periodic histograms and interspike interval histograms of responses to sinusoidal electric stimulations, the frequency response characteristic was determined. The frequency response curve shows a band pass type, the band width ranged from 5 Hz to 30 Hz and the best frequency is around 15 Hz. |
3. | The thresholds of responses for 47 organs were measured by injection of sinusoidal current into the organs. The threshold values were less than 0.1nA (61μV/cm) for 35 organs (74%), and less than 0.01nA (6.1 μV/cm) for the rest of 9 organs (19%). |
35.
Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern 总被引:2,自引:0,他引:2
Huai-zhong Yu Zheng-kang Shen Yong-ge Wan Qing-yong Zhu Xiang-chu Yin 《Tectonophysics》2006,428(1-4):87-94
The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events. 相似文献
36.
Comparison of methods to model the gravitational gradients from topographic data bases 总被引:7,自引:0,他引:7
A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1" elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical–vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods. 相似文献
37.
Aierken Sidike X.-M. Wang Alifu Sawuti H.-J. Zhu I. Kusachi N. Yamashita 《Physics and Chemistry of Minerals》2006,33(8-9):559-566
Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb2+, Ce3+ and Mn2+, respectively, as activators. The Pb2+ excitation band is observed at 243 nm, and the Ce3+ excitation band at 295 nm. The Pb2+ excitation band is also observed by monitoring the Ce3+ fluorescence, and the Pb2+ and Ce3+ excitation bands, in addition to six Mn2+ excitation bands, are also observed by monitoring the Mn2+ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb2+ → Ce3+, (2) Pb2+ → Mn2+, (3) Ce3+ → Mn2+ and (4) Pb2+ → Ce3+ → Mn2+. 相似文献
38.
1 Introduction Alunite [KAl3(SO4)2(OH)6] is a very important non-ferrous metal resource, so many countries throughout the world have made great investments in research on the mechanism of its formation, its geological characteristics and applications. O… 相似文献
39.
40.
CHENChujiang LIDeren ZHUQing 《地球空间信息科学学报》2005,8(1):33-38
This paper presents the studies of the refining of IKONOS-2 RPC, the transform of the datum, the mode of the control point distribution and the method of IKONOS stereo triangulation, so that IKONOS imagery can be used to collect the precise geospatial data and produce the large scale map. The transform between the IKONOS-2 image space and the national coordinate system based on the RPC have been developed, and the results of block adjustment with various control schemes in a practical project near Himalayas have been examined and analysed. The encouraging results of high positioning accuracy have been obtained. 相似文献