全文获取类型
收费全文 | 7525篇 |
免费 | 611篇 |
国内免费 | 216篇 |
专业分类
测绘学 | 300篇 |
大气科学 | 961篇 |
地球物理 | 2446篇 |
地质学 | 2684篇 |
海洋学 | 883篇 |
天文学 | 519篇 |
综合类 | 221篇 |
自然地理 | 338篇 |
出版年
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 50篇 |
2020年 | 45篇 |
2019年 | 57篇 |
2018年 | 541篇 |
2017年 | 481篇 |
2016年 | 406篇 |
2015年 | 225篇 |
2014年 | 263篇 |
2013年 | 324篇 |
2012年 | 750篇 |
2011年 | 561篇 |
2010年 | 258篇 |
2009年 | 274篇 |
2008年 | 252篇 |
2007年 | 244篇 |
2006年 | 230篇 |
2005年 | 929篇 |
2004年 | 965篇 |
2003年 | 714篇 |
2002年 | 226篇 |
2001年 | 117篇 |
2000年 | 76篇 |
1999年 | 46篇 |
1998年 | 28篇 |
1997年 | 35篇 |
1996年 | 23篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有8352条查询结果,搜索用时 187 毫秒
111.
红壤丘陵区农业开发中的生态环境效应及其调控 总被引:3,自引:0,他引:3
文章以江西余江县为例。通过实验研究,历史资料对比分析及邻近参照等方法。研究红壤区农业开发中的生态环境效应。农业开发引起的微观环境效应在于改变土壤水分及其运动状况,加速土壤物质迁移及降低土壤肥力质量;区域性效应是植被减少,农业面源污染,水土流失扩大及气候异常;全球性影响除区域集聚效应外,则是农业活动中产生的温室气体对全球气候的影响等,采取的调控对策主要是:保持合理开发,适当减轻土地压力,优化农业开发模式,更新农业耕作技术。强化环境整治与生态建设。 相似文献
112.
113.
本文对松辽盆地东南部后五家户气田划分出22种沉积微相,建立7种相层序,分析了扇三角洲及三角洲沉积环境对天然气成藏的控制作用。指出了扇三角洲前缘砂体和三角洲前缘砂体较为发育,沉积物源来自气田东北部和东南部两个方向。后五家户气田多为构造—岩性气藏和岩性气藏。 相似文献
114.
Introduction The Western Kunlun Mountain Pass M=8.1 earthquake occurred on November 14, 2001 is the other M=8 earthquake occurred 50 years after Dangxiong, Tibet M=8.0 earthquake in Chinese mainland. The earthquake has caused the attention of the seismologists in the following aspects: 1) The fracture length is more than 400 km, which is far away from the estimated length by the statistic empirical function between the magnitude and the fracture length (WANG, et al, 2002); 2) The aftersh… 相似文献
115.
Dinosaur tracks from the Cretaceous of South Korea: Distribution, occurrences and paleobiological significance 总被引:2,自引:0,他引:2
Abstract Abundant dinosaur fossils including dinosaur footprints, eggs and nests, teeth and bones have been found from the Cretaceous non-marine deposits of Korea. Among them, dinosaur tracks are the most distinctive, and some track sites are among the most famous in the world. Until now, 27 dinosaur track localities have been discovered from the Cretaceous strata in the Gyeongsang Basin and several small basins. Ornithopod tracks are most abundant at most Korean track sites, and most of them are identified as Caririchnium ; that is, large ornithopod footprints with wide hoof impressions. Most theropod tracks are found in Neungju Basin and they consist of various types of small or medium-sized bird-like footprints, and other large footprints. Sauropod tracks are also abundant in the Gyeongsang Basin. The sauropod tracks vary in size, shape, and pattern of trackway, and suggest that diverse sauropods existed in this area. These diverse tracks in South Korea suggest that various dinosaurs flourished at the margins of lakes distributed in the southern part of the Korean Peninsula during the Cretaceous. 相似文献
116.
117.
Han-Joon Kim Hyeong-Tae Jou Hyun-Moo Cho Harmen Bijwaard Takeshi Sato Jong-Kuk Hong Hai-Soo Yoo Chang-Eob Baag 《Tectonophysics》2003,364(1-2):25-42
Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into the adjacent Ulleung Basin from multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data. The Ulleung Basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal. The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the margin is characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under the slope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced during continental rifting in response to high upper mantle temperature. The acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Korean margin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin. 相似文献
118.
Andesitic pillow lavas containing biogenic, solid bitumen (SB) are a constituent of a Neoproterozoic volcanosedimentary sequence (Teplá-Barrandian unit, Bohemian Massif) in the Mítov area of the Czech Republic. A black shale formation that is crosscut by these andesitic basalts is 565 Ma old. Carbon disulfide extracts of two powdered samples of SB contain 0.2 and 0.3 ppm of C60, respectively, as determined by high-pressure liquid chromatography. The peak assignment based on retention time is fully supported by high-resolution electron ionization mass spectrometry (EI-MS). No C70 was detected, nor was C60 found in two other SB samples from this locality. Other investigated carbonaceous samples from Bohemia (coals and anthracites of Upper Paleozoic age and anthraxolite, graphitoids, and graphite of Upper Proterozoic age) did not contain fullerenes at concentrations above the detection limit of 0.01 ppm. The absence of C60 in these samples was confirmed by EI-MS. The proposed mechanism of fullerene formation involves a primary algal phase, generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series, and their high-temperature transformation related to the extrusion of basalt. An important feature for fullerene conservation was the enclosure of fullerenes in SB with a structure similar to glasslike carbon, where the fullerene was protected against oxidation. 相似文献
119.
M. C. Kim 《Journal of Geodesy》1997,71(12):749-767
The fundamental geometry of satellite ground tracks and their crossover problem are investigated. For idealized nominal ground
tracks, the geometry is governed by a few constant parameters whose variations lead to qualitative changes in the crossover
solutions. On the basis that the theory to locate crossovers has not been studied in sufficient detail, such changes are described
in regard to the number of crossover solutions in conjunction with their bifurcations. Employing the spinor algebra as a tool
for establishing the ground-track crossing condition, numerical methodologies to locate crossovers appearing in general dual-satellite
ground-track configurations are also presented. The methodologies are applied to precisely determined orbital ephemerides
of the GEOSAT, ERS-1, and TOPEX/POSEIDON altimeter satellites.
Received: 19 November 1996 / Accepted: 12 May 1997 相似文献
120.