全文获取类型
收费全文 | 4506篇 |
免费 | 786篇 |
国内免费 | 656篇 |
专业分类
测绘学 | 290篇 |
大气科学 | 489篇 |
地球物理 | 1607篇 |
地质学 | 1545篇 |
海洋学 | 856篇 |
天文学 | 179篇 |
综合类 | 225篇 |
自然地理 | 757篇 |
出版年
2024年 | 13篇 |
2023年 | 33篇 |
2022年 | 121篇 |
2021年 | 145篇 |
2020年 | 185篇 |
2019年 | 182篇 |
2018年 | 167篇 |
2017年 | 212篇 |
2016年 | 202篇 |
2015年 | 221篇 |
2014年 | 259篇 |
2013年 | 422篇 |
2012年 | 233篇 |
2011年 | 243篇 |
2010年 | 218篇 |
2009年 | 257篇 |
2008年 | 266篇 |
2007年 | 291篇 |
2006年 | 253篇 |
2005年 | 247篇 |
2004年 | 253篇 |
2003年 | 201篇 |
2002年 | 181篇 |
2001年 | 163篇 |
2000年 | 161篇 |
1999年 | 116篇 |
1998年 | 119篇 |
1997年 | 111篇 |
1996年 | 76篇 |
1995年 | 52篇 |
1994年 | 74篇 |
1993年 | 47篇 |
1992年 | 51篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5948条查询结果,搜索用时 31 毫秒
61.
62.
63.
二色桌片参酶解液对转化细胞的效应 总被引:3,自引:2,他引:3
用二色桌片参(Mensamariaintercedens)酶解液处理转化的人胚肺成纤维细胞(NLF)后,细胞生长受到显著抑制,抑制率达64.84%,光镜下细胞透光性加强,铺展较好,细胞核形更为规则,核畸形现象减少;线粒体结构趋于正常;软琼脂集落实验表明,细胞集落形成率由23x10-5下降至12.5x10-5,裸小鼠致瘤实验显示抑瘤率为82.39%,差异显著(p<5%)。结果提示,二色桌片参酶解液可能逆转转化的HLF细胞的恶性表型,对其有一定的诱导分化作用。 相似文献
64.
台湾南湾秋末冬初水螅水母类的组成与分布 总被引:4,自引:0,他引:4
本文分析了2001年11月2~3日和12月8~10日在台湾南湾12个测站采集的表层和底层92份浮游动物样品,共鉴定水螅水母18种,其中8种是台湾周围海域的新记录.半口壮丽水母(Aglaura hemistoma)和四叶小舌水母(Liriope tetraphylla)为优势种,它们在11月和12月分别占水螅水母类总量的77%和94%以上.南湾水螅水母类的种类数和个体丰度均以12月(17种,3102×10~(-3)个/m~3)明显多于11月(6种,72×10~(-3)个/m~3).在冬季,外海高盐水团是影响水螅水母类分布的主要因素,盐度与水螅水母类多样性指数的相关关系显著,文章还比较了南湾与邻近海区水螅水母类的季节变化. 相似文献
65.
66.
67.
68.
Annual Cycle of Zooplankton Biomass, Abundance and Species Composition in the Neritic Area of the Balearic Sea, Western Mediterranean 总被引:7,自引:0,他引:7
Abstract. Seasonal changes in zooplankton biomass, abundance and species composition were studied at a neritic station in the Balearic Sea between April 1993 and May 1994. Sampling was carried out every 10 days in a zone influenced by the main current circulating through the Mallorca channel. Three main peaks of zooplankton biomass and abundance were observed: (1) at the beginning of summer when the thermocline developed, (2) in autumn when the thermocline broke down, and (3) in early spring. The smaller zooplankton fraction (100–250 μm) comprised on average 32 % of the total biomass and 73 % of total abundance. Copepods were the predominant group (64 % of the total abundance) with Clausocalanus, Oithona and Paracalanus being the most abundant genera. Paracalanus parvus, Clausocalanus furcatus, Acartia clausi, Oithona plumifera, Temora stylifera, Centropages typicus and Oncaea mediterranea were found to be the most important species in the area. Other abundant groups were cladocerans (15 %) and meroplankton larvae (12 %), both of which were particularly numerous during the stratified period. The copepod community was characterized by the above‐cited perennial species, which were abundant during the cycle studied. However, the influence of the hydrological conditions of the Balearic Sea, such as the Atlantic water influx and the physical structure of the water column (stratification and mixing), promoted the observed variability in zooplankton as well as the appearance of characteristic species during the annual cycle. 相似文献
69.
Fisheries in boreal ecosystems 总被引:2,自引:1,他引:2
70.
Anna Badosa Dani Boix Sandra Brucet Rocío Lpez-Flores Xavier D. Quintana 《Estuarine, Coastal and Shelf Science》2006,66(3-4):513-522
The role of the hydrological regime in the nutrients and zooplankton composition and dynamics has been analysed in five lagoons of La Pletera salt marshes (NE Iberian Peninsula) during a complete hydrological cycle (2002–2003). Two of the lagoons have their origin in the old river mouths while the other three were recently created in the framework of a Life Restoration project. This fact has also allowed us to study the effect of the lagoon age on nutrient and zooplankton composition and dynamics. The salt marsh hydrology is determined by a prolonged period of confinement without water inputs, irregularly interrupted by sudden water inputs due to flooding events (sea storms or intense rainfalls). While the dynamics of oxidized nitrogen compounds in the lagoons depends on the water inputs variability within each hydrological cycle, the internal load of phosphorus, total nitrogen and organic matter is related more to the cumulative mechanisms during the confinement periods. Accumulation processes may be easily related to lagoon age, since old lagoons have higher content of nutrients and organic matter, suggesting that these lagoons progressively accumulate nutrients during the successive confinement events. This is the usual case for most Mediterranean salt marshes without an artificially manipulated water regime. The zooplankton community in La Pletera integrates the effects of both the hydrological regime and the lagoon age since the former determines the temporal pattern of the main zooplankton species and the latter explains differences in composition and structure between old and new lagoons. 相似文献