全文获取类型
收费全文 | 8915篇 |
免费 | 1463篇 |
国内免费 | 2220篇 |
专业分类
测绘学 | 535篇 |
大气科学 | 2222篇 |
地球物理 | 2174篇 |
地质学 | 4165篇 |
海洋学 | 1248篇 |
天文学 | 446篇 |
综合类 | 846篇 |
自然地理 | 962篇 |
出版年
2024年 | 19篇 |
2023年 | 101篇 |
2022年 | 334篇 |
2021年 | 396篇 |
2020年 | 325篇 |
2019年 | 409篇 |
2018年 | 435篇 |
2017年 | 373篇 |
2016年 | 502篇 |
2015年 | 427篇 |
2014年 | 492篇 |
2013年 | 538篇 |
2012年 | 433篇 |
2011年 | 493篇 |
2010年 | 430篇 |
2009年 | 511篇 |
2008年 | 448篇 |
2007年 | 420篇 |
2006年 | 362篇 |
2005年 | 346篇 |
2004年 | 283篇 |
2003年 | 287篇 |
2002年 | 255篇 |
2001年 | 295篇 |
2000年 | 336篇 |
1999年 | 492篇 |
1998年 | 356篇 |
1997年 | 369篇 |
1996年 | 355篇 |
1995年 | 285篇 |
1994年 | 252篇 |
1993年 | 227篇 |
1992年 | 172篇 |
1991年 | 139篇 |
1990年 | 122篇 |
1989年 | 124篇 |
1988年 | 108篇 |
1987年 | 63篇 |
1986年 | 61篇 |
1985年 | 43篇 |
1984年 | 41篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1958年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
121.
Benthic nutrient fluxes in the intertidal flat within the Changjiang (Yangtze River) Estuary 总被引:1,自引:0,他引:1
GAO Lei LI Daoji WANG Yanming YU Lihua KONG Dingjiang LI Mei LI Yun and FANG Tao State Key Laboratory of Marine Geology Tongji University Shanghai China State Key Laboratory of Estuarine Coastal Research East China Normal University Shanghai China 《中国地球化学学报》2008,27(1):58-71
In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang (Yangtze River) Estuary. Except for NH4^+, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrification rates, that utilizing NO3- transported from overlying water (Dw) in Dongtan sediments, were estimated to be from -16 to 193 μmol·h^-1·m^-2 with an average value of 63 μmol·h^-1·m^-2 (n=18). These estimated values are still underestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3^- production via nitrification. 相似文献
122.
The Baimazhai nickel deposit, Yunnan Province, China, is located in the southern part of the Sanjiang (Tri-river) alkali-rich intrusive rock belt (Sanjiang ARIR). In this paper was conducted ^40Ar-^39Ar dating of two phlogopites in lamprophyres which are, as dikes, widely distributed in the orefield, and two plateau ages were acquired, i.e., 32.46±0.62 Ma and 32.01±0.60 Ma, respectively (averaging 32.23±0.60 Ma). The ages are obviously younger than those of the ore-hosted complex and mineralization of the Baimazhai nickel deposit. In combination with the characteristics, it is indicated that lamprophyres in the orefield and those in the Sanjiang ARIR are similar in tectonic setting, mineral assemblage and geochemistry. It is considered that lamprophyres in the orefield are the important component of the Sanjiang ARIR, and the lamprophyres and ore-hosted complex in the orefield represent the products of two times of different magmatic activity from different mantle sources. On the other hand, the age of lamprophyres in the orefield is older than that of the strike-slip shearing of the Ailaoshan-Honghe fault belt, suggesting that the strike-slip shearing of the Ailaoshan-Honghe fault belt is not the factor leading to magmatic activity of lamprophyres in the orefield, while it is more possible that magmatic activity of the Sanjiang ARIR promoted strike-slip shearing of the fault belt. 相似文献
123.
CBERS-02B星HR与多光谱影像融合及评价 总被引:4,自引:0,他引:4
CBERS-02B星搭载了高分辨率全色相机HR和多光谱传感器CCD,HR影像可以与CCD影像融合,优势互补形成新的影像,既保持HR的高空间分辨率又保持CCD的光谱分辨率,HR影像同样可以与其它传感器影像融合形成新的影像。本文使用6种不同的融合方法融合HR与多光谱CCD以及SPOT5多光谱影像,并对融合结果进行了定性和定量评价,得到了HR与SPOT5多光谱影像融合较好的方法,表明了HR与其它传感器影像融合的潜力,同时也对HR和SPOT5多光谱融合影像及与CCD融合影像进行了初步的对比分析。 相似文献
124.
125.
126.
Response of riparian vegetation to water-table changes in the lower reaches of Tarim River, Xinjiang Uygur, China 总被引:1,自引:0,他引:1
Yaning Chen Zhonghe Pang Yapeng Chen Weihong Li Changchun Xu Xinming Hao Xiang Huang Tianming Huang Zhaoxia Ye 《Hydrogeology Journal》2008,16(7):1371-1379
The lower reaches of Tarim River in the Xinjiang Uygur region of western China had been dried out for more than 30 years before water began to be diverted from Konqi (Peacock) River via a 927-km-long channel in year 2000, aimed at improving the riparian ecological systems. Since then, eight intermittent water deliveries have been carried out. To evaluate the response of riparian vegetation to these operations, the groundwater regime and vegetation changes have been monitored along the 350-km-long stem of the river using a network of 40 dug wells at nine transects across the river and 30 vegetation plots at key sites. Results show that the water table rose remarkably, i.e. from a depth of 9.87 m before the water delivery to 3.16 m after the third water delivery. The lateral distance of affected water table extended to 1,050 m from the riverbank after the fourth water delivery. The riparian vegetation has changed in composition, type, distribution, and growing behavior. This shows that the water deliveries have had significant effects on restoration of riparian ecosystems. 相似文献
127.
Wenguang Yang Hongbo Zheng Ke Wang Xin Xie Guocheng Chen Xi Mei 《Frontiers of Earth Science》2008,2(2):170-176
Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials
for a high-resolution study on the paleoenvironment. Based on precise dating of AMS 14C, grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter, biological carbonate and
biogenic opal were removed. The results show that 15.5–63.5 μm coarse grain size ingredients may indicate East Asian winter
monsoon changes and that 2–9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon.
The results of grain size analysis, which suggest East Asian monsoon intensity, reveal that a winter monsoon dominated the
glacial regime and a summer monsoon dominated the Holocene regime. It was also shown that the summer monsoon increased gradually,
experienced several abrupt changes and reached a culmination in the early Holocene (11200–8500 a B.P.) since 36 ka. Controlled
by precession periodicity, it may be related with the amount of solar radiation at the highest stage, which needs further
study.
__________
Translated from Advances in Earth Science, 2007, 22(10): 1012–1018 [译自: 地球科学进展] 相似文献
128.
In northern Jiangsu coastal zone area, Guanhe River is the biggest river and has the best navigation conditions among rivers
which flow into the Yellow Sea. The grain sizes show gradual increase from the high intertidal zone to lower intertidal zone.
The heavy metal values have slight changes along both sides of the river mouth, but show an evident change perpendicular to
the tidal flat. In the latter case, they show a good correlation with grain size fluctuation, that is, the heavy metal values
gradually decline when the grain size increases from the high intertidal zone to the lower intra-tidal zone. Analyses of the
heavy metal elements show that on the Guanhe estuary surface sediment, the content of the elements Hg, As and Cu is above
background values; Pb and Zn contents are rather close to the background values; and Cd content is less than the background
values. The element Hg comes out to be harmful in a medium level to ecological environment, while the elements of Cr, As,
Cu, Pb, Zn and Cd fall in a safe range of MPL. On the whole, Guanhe estuary tidal flat is not very harmful to the ecology
in terms of the heavy metals.
__________
Translated from Marine Geology & Quaternary Geology, 2007, 27(5): 23–32 [译自: 海洋地质与第四纪地质] 相似文献
129.
洞穴完井工艺在寿阳地区煤层气钻井中的应用 总被引:4,自引:0,他引:4
洞穴完井工艺包括钻井、完井、排水采气等工序,为提高煤层渗透率,最大限度的保证煤层气解析与运移,洞穴完井一般要求有效井径3-4m,及一定范围的破碎带。远东能源公司为开采寿阳地区15#煤层中的煤层气,部署了4口生产井.其井身设计为三开结构。钻井主要设备为T685WS顶驱车载钻机及多台不同型号的空压机,采用潜孔锤冲击钻进.以空气、空气泡沫为冲洗介质,钻进至15#目标煤层底板以下46m处完钻,然后利用可伸缩式扩孔器进行扩孔。在扩孔至距三开井底8~10m时.开始采用空气和清水憋压,通过瞬间释放压力,使煤层坍塌,如此反复,至造穴直径达到要求。由于严格按照技术标准及操作流程作业,采取的技术措施合理,4口井均已顺利投入生产,增产效果显著。可见该种洞穴完井技术的应用,不仅可以保护煤层原生结构及环境,并且还能减少煤层气射孔、压裂等环节的费用.对于煤层气井施工具有重要的经济意义。 相似文献
130.