全文获取类型
收费全文 | 50901篇 |
免费 | 9567篇 |
国内免费 | 13611篇 |
专业分类
测绘学 | 3914篇 |
大气科学 | 9975篇 |
地球物理 | 12764篇 |
地质学 | 27322篇 |
海洋学 | 6135篇 |
天文学 | 2073篇 |
综合类 | 5647篇 |
自然地理 | 6249篇 |
出版年
2024年 | 151篇 |
2023年 | 686篇 |
2022年 | 2106篇 |
2021年 | 2377篇 |
2020年 | 2037篇 |
2019年 | 2264篇 |
2018年 | 2662篇 |
2017年 | 2390篇 |
2016年 | 2706篇 |
2015年 | 2428篇 |
2014年 | 2850篇 |
2013年 | 2869篇 |
2012年 | 2787篇 |
2011年 | 3285篇 |
2010年 | 3179篇 |
2009年 | 3182篇 |
2008年 | 2699篇 |
2007年 | 2656篇 |
2006年 | 2405篇 |
2005年 | 2356篇 |
2004年 | 2423篇 |
2003年 | 1998篇 |
2002年 | 1695篇 |
2001年 | 1714篇 |
2000年 | 1764篇 |
1999年 | 2306篇 |
1998年 | 1957篇 |
1997年 | 1848篇 |
1996年 | 1679篇 |
1995年 | 1393篇 |
1994年 | 1279篇 |
1993年 | 1287篇 |
1992年 | 1080篇 |
1991年 | 735篇 |
1990年 | 537篇 |
1989年 | 495篇 |
1988年 | 399篇 |
1987年 | 285篇 |
1986年 | 229篇 |
1985年 | 142篇 |
1984年 | 134篇 |
1983年 | 104篇 |
1982年 | 104篇 |
1981年 | 71篇 |
1980年 | 45篇 |
1979年 | 51篇 |
1978年 | 28篇 |
1977年 | 28篇 |
1976年 | 19篇 |
1958年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This paper systematically analyzes and proves the favorable factors of utilizing the ports and the railways in Northeast China for the Asia-Europe land bridge transportation. It will be more beneficial to Dalian Port and HaDa (Harbin-Dalian) and Binzhou (Harbin-Manzhouli) railways in Northeast China to the Siberia railway in Russia than 1) to other ports and the corresponding railways in China, 2) to the Nakhodka Port in Russia and the corresponding railways and 3) to the Chongjin Port in North Korea and the corresponding railways. This paper also puts forward the reform measures to adopt the ports and the railways in the northeast region in China for the land bridge transportation and the problems in transportation policies and management systems. 相似文献
52.
Mercury (Hg) was investigated in bone tissues of skua ( Catharacta maccormick) and penguin (Pygoscelis adeliae) collected in the maritime Antarctic using atomic fluorescence spectrometry (AFS) and synchrotron radiation X-ray fluorescence (SR-XRF) method. The total levels of mercury in bone tissues of penguin and skua are much lower than those in other organs (e. g. , kidney, liver). The toxic effects of mercury in bone tissues of seabirds in polar region are not known. We have used SR- XRF method to map the distribution of trace levels of mercury in bones. The levels of mercury are found to be enriched somewhere near the periosteal surface and/or endosteal surface. The distribution of mercury shows strongly correlation with that of some essential elements and probably poses negative effect on the bone metabolism inferring from the relationship of mercury with the other elements. These studies represent a first step toward understanding the toxic effects of mercury on bone of polar animals by suggesting the possible microscopic investigation. 相似文献
53.
Xue-Fei Chen Zhan-Wen HanNational Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences. Kunming Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):65-76
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the 相似文献
54.
中国1∶100万景观生态制图设计 总被引:5,自引:0,他引:5
中国1∶100万景观生态图系借鉴国内外传统景观制图方法和制图规范,在遥感、地理信息系统先进技术的支持下,设计研制其制图方法、制图内容、样图和技术流程,同时提出初步的景观分类系统,为今后编制中国1∶100万景观生态图奠定基础。 相似文献
55.
本区至今还是综合科学考察的空白区。为查明基本情况,1989年夏以乘汽车路线考察方式穿行该区而作了预查,搜集了当地地质、地理、生物等基本资料。经考察发现,区内野生动物资源丰富,上新世以来火山活动普遍,湖泊众多,矿产资源可能有良好前景;所在区又为自然地域和地质构造的重要界线,对青藏高原研究具有重大科学价值。 相似文献
56.
57.
TANGYa XIEJiasui SUNHui 《山地科学学报》2004,1(1):38-45
Dry valleys are a striking geographic landscape in Hengduan Mountains Region and are characterized by low rainfall, desert type of vegetation and fragile environment. Past efforts and resources have been concentrated mainly on rehabilitation of degraded ecosystem and fragile environment, particularly reforestation, while socio-economic development has been largely overlooked. Despite successes in pocket areas, the overall trend of unsustainability and environmental deterioration are continuing. It is important to understand that uplift of the Tibetan Plateau is the root cause of development of dry valleys, and development and formation of dry valleys is a natural process. Human intervention has played a secondary role in development of dry valleys and degradation of dry valleys though human intervention in many cases has speeded up environmental degradation of the dry valleys. It is important to understand that dry valleys are climatic enclaves and an integrated approach that combines rehabilitation of degraded ecosystems and socio-economic development should be adopted if the overall goal of sustainable development of dry valleys is to be achieved. Promotion of niche-based cash crops, rural energy including hydropower, solar energy, biogas and fuelwood plantation is recommended as the priority activities. 相似文献
58.
为了便于大型软件系统的后续开发和用户软件系统的升级,介绍了软件系统在Internet/Intranet上更新功能或数据的原理和方法,并用C#.Net进行了编程实现。 相似文献
59.
Brine shrimp (Artemia parthenogenetica) which had ingested three water-insoluble antibacterial drugs i.e. sulfadiazine(SD), oxytetracycline (OTC) and erythromycin
estolate (ERY-Es) were fed toTilapia and Mysis IIIof Penaeus orientalis K. The drug contents in the predators were then determined. After administration of drugs toTilapia and Mysis III, through the bio-encapsulation of the brine shrimp, efficacious therapeutical concentration of OTC and ERY-Es
(but not SD) in the predators could be reached and maintained for more than 8 hours. 相似文献
60.