全文获取类型
收费全文 | 9360篇 |
免费 | 2028篇 |
国内免费 | 2825篇 |
专业分类
测绘学 | 984篇 |
大气科学 | 1965篇 |
地球物理 | 2376篇 |
地质学 | 4909篇 |
海洋学 | 1436篇 |
天文学 | 318篇 |
综合类 | 991篇 |
自然地理 | 1234篇 |
出版年
2024年 | 32篇 |
2023年 | 149篇 |
2022年 | 476篇 |
2021年 | 539篇 |
2020年 | 427篇 |
2019年 | 507篇 |
2018年 | 542篇 |
2017年 | 572篇 |
2016年 | 585篇 |
2015年 | 540篇 |
2014年 | 639篇 |
2013年 | 651篇 |
2012年 | 691篇 |
2011年 | 747篇 |
2010年 | 732篇 |
2009年 | 652篇 |
2008年 | 610篇 |
2007年 | 555篇 |
2006年 | 493篇 |
2005年 | 386篇 |
2004年 | 322篇 |
2003年 | 297篇 |
2002年 | 293篇 |
2001年 | 301篇 |
2000年 | 274篇 |
1999年 | 324篇 |
1998年 | 268篇 |
1997年 | 261篇 |
1996年 | 207篇 |
1995年 | 190篇 |
1994年 | 184篇 |
1993年 | 182篇 |
1992年 | 113篇 |
1991年 | 89篇 |
1990年 | 63篇 |
1989年 | 63篇 |
1988年 | 66篇 |
1987年 | 41篇 |
1986年 | 29篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1958年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 999 毫秒
991.
The effects of four microalgae,Chlorella vulgaris,Platymonas helgolandicavar,Isochrysis galbana,and Nitzschia closterium on the grazing and filtering rates of the marine rotifer,Brachionus plicatilis,were evaluated under laboratory conditions.The grazing rates in separate cultures of the four microalga were as follows:C.vulgaris > P.helgolandicavar > I.galbana > N.closterium.However,the filtering rates occurred in the following order:P.helgolandicavar > N.closterium > C.vulgaris > I.galbana.A mixed diets ex... 相似文献
992.
993.
The pathological changes of hemocytes in the haemolymph and hepatopancreas were examined in experimentally and naturally WSSV
(white spot syndrome virus) infected Fenneropenaeus chinensis. The results showed that the pathological manifestations of hemocytes were similar among moribund shrimps infected via injection,
feeding and by nature. Firstly, the total hemocyte counts (THCs) in WSSV-infected shrimp were significantly lower than those
in healthy shrimp. Secondly, necrotic, broken and disintegrated cells were often observed, and a typical hematolysis was present
in the haemolymph smear of WSSV-infected shrimp. Thirdly, necrosis and typical apoptosis of hemocytes were detected with TEM
in the peripheral haemolymph of WSSV-infected shrimp. Hyalinocytes and semi-granulocytes with masses of WSSVs in their nuclei
often appeared, whereas no granular hemocytes with WSSV were found in the hepatopancreas of moribund infected shrimps. All
our results supported that hemocytes were the main target cells of WSSV, and hyalinocytes and semigranular hemocytes seemed
to be more favorable for WSSV infection in F. chinensis. 相似文献
994.
Mountain areas are often rich in ecological diversity and recreational opportunities. Mountain tourism is thought to be an effective and important means for maintaining and expanding rural economies and, thus, improving the living conditions of rural societies. As mountain tourism service research is a professional field with several disciplines involved, a multi-disciplinary management pIatform is needed and it facilitates participation in sustainable mountain development by diverse stakeholders. With the source regions of the Yangtze and the Yellow River as a case study, this paper presents a conceptual framework for an adaptation management of mountain tourism services according to technical, policy, social and economic dimensions. The framework is based on a vulnerability assessment of mountain ecosystems, and can serve as a reference for the development of tourism service in other mountain areas. 相似文献
995.
996.
A quantitative analysis of the spatial pattern of rural settlements in the upper reaches of the Minjiang River was made with
the major data sources being the relevant ETM image and the national geographical database of China (including contour line,
river and road) at the scale of 1:250 000, and using image interpretation and field investigation to obtain spatial information
on rural settlements. The results of the spatial analysis technique of GIS and correlation analysis showed that most settlements
(78.2 %) were located in the mountain area at 1500 ∼ 2700 m altitude, and almost half in the arid valley area. More than 80.0
% of settlements had their slopes above 15°. Most settlements had good access to water resources, roads and communications,
and tended to cluster close to the road network rather than the river. About half of the rural settlements in the study area
were relatively concentrated, while the others were decentralized. Those with higher altitude usually had land with steep
slope, inconvenient water and road accesses, and were located far apart from each other. In view of such a situation, further
research should be done to make reasonable countermeasures on these settlements for better living conditions and ecosystem
stability. 相似文献
997.
Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the meter wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7?–?0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentley et al. (Solar Phys. 193, 227, 2000). 相似文献
998.
健康视角下城市建成环境对老年人日常步行活动的影响研究 总被引:2,自引:0,他引:2
“健康老龄化”背景下,促进身体活动是提升老年人健康水平的重要方式,也是当前多学科交叉研究的热点。依托南京市居民身体活动调查数据,选择老年人日常生活中最普遍且有益健康的步行活动作为研究主题,探究建成环境的影响,以期为相关理论与实践提供有益探索。研究表明:① 老年人日常步行空间范围可作为步行所涉及建成环境边界,不同类型的主要活动场所则可识别建成环境要素需求差异。② 日常生活所涉及的公共开放空间、商业及公共服务设施的密集性,以及主观建成环境感知对老年人交通性/休闲性步行活动具有显著影响。③ 基于老年人日常步行活动习惯及建成环境对步行活动的影响,可从有效供给日常步行生活空间、积极引导健康生活方式方面提出相应规划策略。 相似文献
999.
Wu Shaohong Liu Lulu Liu Yanhua Gao Jiangbo Dai Erfu Feng Aiqing Wang Wentao 《地理学报(英文版)》2019,29(4):483-495
Journal of Geographical Sciences - Building the Belt and Road is initiatives of China to promote win-win international cooperation in the new era, aiming at green, health, intellect and peace and... 相似文献
1000.
利用RT-PCR方法从半滑舌鳎(Cynoglossus semilaevis)中克隆了雄激素受体(Androgen receptor,AR)基因cDNA的部分序列(434 bp),经BLAST比对与狼鲈(Dicentrarchus labrax)、花溪(Kryptolebias marmoratus)、三斑海猪鱼(Halichoeres trimaculatus)和三刺鱼(Gasterosteus aculeatus)的雄激素受体同源性分别为84%,82%,82%和81%.组织表达分析表明,AR基因在半滑舌鳎的性腺、肝、胃、脾、肾、头肾、肠、鳃、心、脑和肌肉这11种组织中均有表达,表达量有所差异.肾中表达量最丰富,鳃中最少.根据其他硬骨鱼类表达模式,推测半滑舌鳎可能只含有1种AR. 相似文献