全文获取类型
收费全文 | 9677篇 |
免费 | 2554篇 |
国内免费 | 3953篇 |
专业分类
测绘学 | 1645篇 |
大气科学 | 1150篇 |
地球物理 | 1919篇 |
地质学 | 6687篇 |
海洋学 | 2249篇 |
天文学 | 146篇 |
综合类 | 945篇 |
自然地理 | 1443篇 |
出版年
2024年 | 129篇 |
2023年 | 394篇 |
2022年 | 776篇 |
2021年 | 898篇 |
2020年 | 760篇 |
2019年 | 909篇 |
2018年 | 794篇 |
2017年 | 727篇 |
2016年 | 747篇 |
2015年 | 785篇 |
2014年 | 754篇 |
2013年 | 866篇 |
2012年 | 925篇 |
2011年 | 916篇 |
2010年 | 792篇 |
2009年 | 787篇 |
2008年 | 683篇 |
2007年 | 584篇 |
2006年 | 533篇 |
2005年 | 466篇 |
2004年 | 367篇 |
2003年 | 255篇 |
2002年 | 263篇 |
2001年 | 243篇 |
2000年 | 213篇 |
1999年 | 113篇 |
1998年 | 55篇 |
1997年 | 64篇 |
1996年 | 55篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 27篇 |
1992年 | 27篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 8篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
2.
3.
4.
大冶铁矿的开发利用在为我国的钢铁事业作出巨大贡献的同时,也给矿区的地表环境、森林资源带来了很大的破坏。矿山公园的规划实施可极大地改善矿山环境,为矿山的可持续发展提供较好的途径。 相似文献
5.
A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a0. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a0 is induced. The predictions of the model are in reasonable agreement with observations. 相似文献
6.
Debris flows have caused serious loss of human lives and a lot of damage to properties in Taiwan over the past decades. Moreover, debris flows have brought massive mud causing water pollution in reservoirs and resulted in water shortage for daily life locally and affected agricultural irrigation and industrial usages seriously. A number of methods for prediction of debris flows have been studied. However, the successful prediction ratio of debris flows cannot always maintain a stable and reliable level. The objective of this study is to present a stable and reliable analytical model for occurrence predictions of debris flows. This study proposes an Artificial Neural Networks (ANN) model that was constructed by seven significant factors using back-propagation (BP) algorithm. These seven factors include (1) length of creek, (2) average slope, (3) effective watershed area, (4) shape coefficient, (5) median size of soil grain, (6) effective cumulative rainfall, and (7) effective rainfall intensity. A total of 178 potential cases of debris flows collected in eastern Taiwan were fed into the ANN model for training and testing. The average ratio of successful prediction reaching 93.82% demonstrates that the presented ANN model with seven significant factors can provide a stable and reliable result for the prediction of debris flows in hazard mitigation and guarding systems. 相似文献
7.
Evolution from Oceanic Subduction to Continental Collision: a Case Study from the Northern Tibetan Plateau Based on Geochemical and Geochronological Data 总被引:41,自引:0,他引:41
SONG SHUGUANG; ZHANG LIFEI; NIU YAOLING; SU LI; SONG BIAO; LIU DUNYI 《Journal of Petrology》2006,47(3):435-455
Two apparently distinct, sub-parallel, paleo-subduction zonescan be recognized along the northern margin of the Tibetan Plateau:the North Qilian Suture Zone (oceanic-type) with ophioliticmélanges and high-pressure eclogites and blueschistsin the north, and the North Qaidam Belt (continental-type) inthe south, an ultrahigh-pressure (UHP) metamorphic terrane comprisingpelitic and granitic gneisses, eclogites and garnet peridotites.Eclogites from both belts have protoliths broadly similar tomid-ocean ridge basalts (MORB) or oceanic island basalts (OIB)in composition with overlapping metamorphic ages (480440Ma, with weighted mean ages of 464 ± 6 Ma for North Qilianand 457 ± 7 Ma for North Qaidam), determined by zirconUPb sensitive high-resolution ion microprobe dating.Coesite-bearing zircon grains in pelitic gneisses from the NorthQaidam UHP Belt yield a peak metamorphic age of 423 ±6 Ma, 40 Myr younger than the age of eclogite formation, anda retrograde age of 403 ± 9 Ma. These data, combinedwith regional relationships, allow us to infer that these twoparallel belts may represent an evolutionary sequence from oceanicsubduction to continental collision, and continental underthrusting,to final exhumation. The QilianQaidam Craton was probablya fragment of the Rodinia supercontinent with a passive marginand extended oceanic lithosphere in the north, which was subductedbeneath the North China Craton to depths >100 km at c. 423Ma and exhumed at c. 403 Ma (zircon rim ages in pelitic gneiss). KEY WORDS: HP and UHP rocks; subduction belts; zircon SHRIMP ages; Northern Tibetan Plateau 相似文献
8.
在无线遥测地震仪器中 ,发射机长期使用容易出现输出功率下降、无输出功率、发射频率不准等故障。分析了发射机典型电路——石英晶体主振电路、倍频电路、激励级电路、功率放大级电路的基本原理。排除发射机的故障时 ,先从不同单元电路逐一检查、测试 ,判断故障类型 ,最后进行发射机总调试 相似文献
9.
10.