全文获取类型
收费全文 | 254451篇 |
免费 | 5448篇 |
国内免费 | 3578篇 |
专业分类
测绘学 | 6992篇 |
大气科学 | 19331篇 |
地球物理 | 53155篇 |
地质学 | 88447篇 |
海洋学 | 21632篇 |
天文学 | 54862篇 |
综合类 | 1108篇 |
自然地理 | 17950篇 |
出版年
2021年 | 2231篇 |
2020年 | 2618篇 |
2019年 | 2853篇 |
2018年 | 3648篇 |
2017年 | 3290篇 |
2016年 | 5801篇 |
2015年 | 4269篇 |
2014年 | 6995篇 |
2013年 | 14299篇 |
2012年 | 6549篇 |
2011年 | 8013篇 |
2010年 | 7089篇 |
2009年 | 9766篇 |
2008年 | 8446篇 |
2007年 | 7905篇 |
2006年 | 9651篇 |
2005年 | 7753篇 |
2004年 | 7660篇 |
2003年 | 7022篇 |
2002年 | 6664篇 |
2001年 | 5980篇 |
2000年 | 5608篇 |
1999年 | 4863篇 |
1998年 | 4881篇 |
1997年 | 4653篇 |
1996年 | 4242篇 |
1995年 | 4342篇 |
1994年 | 4032篇 |
1993年 | 3759篇 |
1992年 | 3505篇 |
1991年 | 3536篇 |
1990年 | 3642篇 |
1989年 | 3343篇 |
1988年 | 3170篇 |
1987年 | 3725篇 |
1986年 | 3251篇 |
1985年 | 4124篇 |
1984年 | 4636篇 |
1983年 | 4305篇 |
1982年 | 4221篇 |
1981年 | 3845篇 |
1980年 | 3595篇 |
1979年 | 3432篇 |
1978年 | 3444篇 |
1977年 | 3222篇 |
1976年 | 2960篇 |
1975年 | 2907篇 |
1974年 | 2862篇 |
1973年 | 3063篇 |
1972年 | 1993篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Ali Moamen Abdelmaksoud Ahmed Essa M. A. Abdelhady A. Darwish M. 《Natural Resources Research》2020,29(4):2575-2597
Natural Resources Research - Two main reservoirs are producing in Komombo Basin: the first one belongs to the C Member of the Six Hills Formation, and the second belongs to the Albian/Cenomanian... 相似文献
42.
Natural Resources Research - Borehole-controlled one-dimensional geo-electric data were integrated with water samples obtained from boreholes drilled near the vertical electrical sounding at 12... 相似文献
43.
Soil salinization, caused by salt migration and accumulation underneath the soil surface, will corrode structures. To analyze the moisture-salt migration and salt precipitation in soil under evaporation conditions, a mathematical model consisting of a series of theoretical equations is briefly presented. The filling effect of precipitated salts on tortuosity factor and evaporation rate are taken into account in relevant equations. Besides, a transition equation to link the solute transport equation before and after salt precipitation is proposed. Meanwhile, a new relative humidity equation deduced from Pitzer ions model is used to modify the vapor transport flux equation. The results show that the calculated values are in good agreement with the published experimental data, especially for the simulation of volume water content and evaporation rate of Toyoura sand, which confirm the reliability and applicability of the proposed model. 相似文献
44.
Structure-specific selection of earthquake ground motions for the reliable design and assessment of structures 总被引:1,自引:1,他引:0
A decision support process is presented to accommodate selecting and scaling of earthquake motions as required for the time domain analysis of structures. Code-compatible suites of seismic motions are provided being, at the same time, prequalified through a multi-criterion approach to induce response parameters with reduced variability. The latter is imperative to increase the reliability of the average response values, normally required for the code-prescribed design verification of structures. Structural attributes like the dynamic characteristics as well as criteria related to variability of seismic motions and their compliance with a target spectrum are quantified through a newly introduced index, δ sv–sc , which aims to prioritize motions suites for response history analysis. To demonstrate the applicability of the procedure presented, the structural model of a multi-story building was subjected to numerous suites of motions that were highly ranked according to both the proposed approach (δ sv–sc ) and the conventional one (δ conv ), that is commonly used for earthquake records selection and scaling. The findings from numerous linear response history analyses reveal the superiority of the proposed multi-criterion approach, as it extensively reduces the intra-suite structural response variability and consequently, increases the reliability of the design values. The relation between the target reliability in assessing structural response and the size of the suite of motions selected was also investigated, further demonstrating the efficiency of the proposed selection procedure to achieve higher response reliability levels with smaller samples of ground motion. 相似文献
45.
Laurentiu Danciu Karin Şeşetyan Mine Demircioglu Levent Gülen Mehdi Zare Roberto Basili Ata Elias Shota Adamia Nino Tsereteli Hilal Yalçın Murat Utkucu Muhammad Asif Khan Mohammad Sayab Khaled Hessami Andrea N. Rovida Massimiliano Stucchi Jean-Pierre Burg Arkady Karakhanian Hektor Babayan Mher Avanesyan Tahir Mammadli Mahmood Al-Qaryouti Doğan Kalafat Otar Varazanashvili Mustafa Erdik Domenico Giardini 《Bulletin of Earthquake Engineering》2018,16(8):3465-3496
46.
S. Akkar T. Azak T. Çan U. Çeken M. B. Demircioğlu Tümsa T. Y. Duman M. Erdik S. Ergintav F. T. Kadirioğlu D. Kalafat Ö. Kale R. F. Kartal K. Kekovalı T. Kılıç S. Özalp S. Altuncu Poyraz K. Şeşetyan S. Tekin A. Yakut M. T. Yılmaz M. S. Yücemen Ö. Zülfikar 《Bulletin of Earthquake Engineering》2018,16(8):3197-3228
A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper. 相似文献
47.
正Dear Members of the Editorial Board,Contributors and Friends,2018 is the tenth anniversary of the Wenchuan earthquake disaster.To commemorate the Wenchuan earthquake disaster,the journal of Earthquake Engineering and Engineering Vibration(EEEV)will publish special sections with invited papers in the issues of 2018(January,April and July).We sincerely appreciate the contributions from the following experts:Professor Xilin Lu,Professor Michel Bruneau,Professor Baitao Sun,and Professor Gian Paolo Cimellaro. 相似文献
48.
正Dear Members of the Editorial Board,Contributors and Friends of EEEV,To commemorate the tenth anniversary of the Wenchuan earthquake disaster,the journal of Earthquake Erngineering and Engineering Vibratiorn will publish special sections with invited papers in 2018.We sincerely appreciate the contributions from the following experts:Professor Akira WADA,and Professor Kuo-Chun CHANG. 相似文献
49.
The Haicheng earthquake (Ms 7.3) occurred in Liaoning Province (39°N–43°N, 120°E–126°E ), China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate prediction, although the area affected by the earthquake was 9200 km2 and covered cities with a population density of 1000 p/km2. In this study, the doubledifference (DD) tomography method was used to obtain high-resolution three-dimensional (3D) P- and S-wave velocity (Vp and Vs) structures and Vp/Vs as well as the earthquake locations. Tomography results suggest that velocity structure at shallow depth coincides well with topography and sediment thickness. The earthquake locations form a northwest-striking zone associated with the Jinzhou(JZ) Fault and a northeast-striking zone associated with the Haichenghe-Dayanghe (HD) Fault, and suggest that the JZ Fault consists of three faults and the Ms 7.3 Haicheng earthquake originated at the intersection of the JZ and the Faults. Lowvelocity zones (LVZs) with low Vp/Vs are observed at 15–20 km depth beneath the Haicheng (HC) region. We interpret the LVZs in the middle crust as regions of fluids, suggesting rock dehydration at high temperatures. The LVZs and low Vp/Vs in the upper crust are attributed to groundwater-filled cracks and pores. We believe that large crustal earthquakes in this area are caused by the combination of faulting and fluid movement in the middle crust. 相似文献
50.
Jason?PatskoskiEmail authorView authors OrcID profile A.?Sankarasubramanian 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):1065-1083
Reservoir sizing is one of the most important aspects of water resources engineering as the storage in a reservoir must be sufficient to supply water during extended droughts. Typically, observed streamflow is used to stochastically generate multiple realizations of streamflow to estimate the required storage based on the Sequent Peak Algorithm (SQP). The main limitation in this approach is that the parameters of the stochastic model are purely derived from the observed record (limited to less than 80 years of data) which does not have information related to prehistoric droughts. Further, reservoir sizing is typically estimated to meet future increase in water demand, and there is no guarantee that future streamflow over the planning period will be representative of past streamflow records. In this context, reconstructed streamflow records, usually estimated based on tree ring chronologies, provide better estimates of prehistoric droughts, and future streamflow records over the planning period could be obtained from general circulation models (GCMs) which provide 30 year near-term climate change projections. In this study, we developed paleo streamflow records and future streamflow records for 30 years are obtained by forcing the projected precipitation and temperature from the GCMs over a lumped watershed model. We propose combining observed, reconstructed and projected streamflows to generate synthetic streamflow records using a Bayesian framework that provides the posterior distribution of reservoir storage estimates. The performance of the Bayesian framework is compared to a traditional stochastic streamflow generation approach. Findings based on the split-sample validation show that the Bayesian approach yielded generated streamflow traces more representative of future streamflow conditions than the traditional stochastic approach thereby, reducing uncertainty on storage estimates corresponding to higher reliabilities. Potential strategies for improving future streamflow projections and its utility in reservoir sizing and capacity expansion projects are also discussed. 相似文献