全文获取类型
收费全文 | 12918篇 |
免费 | 2272篇 |
国内免费 | 3094篇 |
专业分类
测绘学 | 1167篇 |
大气科学 | 2532篇 |
地球物理 | 3250篇 |
地质学 | 6526篇 |
海洋学 | 1471篇 |
天文学 | 519篇 |
综合类 | 1321篇 |
自然地理 | 1498篇 |
出版年
2024年 | 65篇 |
2023年 | 239篇 |
2022年 | 553篇 |
2021年 | 695篇 |
2020年 | 531篇 |
2019年 | 593篇 |
2018年 | 668篇 |
2017年 | 627篇 |
2016年 | 739篇 |
2015年 | 649篇 |
2014年 | 785篇 |
2013年 | 765篇 |
2012年 | 783篇 |
2011年 | 807篇 |
2010年 | 785篇 |
2009年 | 837篇 |
2008年 | 744篇 |
2007年 | 754篇 |
2006年 | 564篇 |
2005年 | 575篇 |
2004年 | 437篇 |
2003年 | 388篇 |
2002年 | 432篇 |
2001年 | 429篇 |
2000年 | 413篇 |
1999年 | 489篇 |
1998年 | 452篇 |
1997年 | 399篇 |
1996年 | 365篇 |
1995年 | 271篇 |
1994年 | 286篇 |
1993年 | 268篇 |
1992年 | 222篇 |
1991年 | 149篇 |
1990年 | 106篇 |
1989年 | 97篇 |
1988年 | 95篇 |
1987年 | 47篇 |
1986年 | 46篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1958年 | 10篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
蒋维东 《成都信息工程学院学报》1988,(2)
对南极地区的多年月平均气温资料进行聚类分析,结果表明,可以分为极区内陆、海湾区域、东南极沿岸和南极半岛地区四大类型。南极半岛地区一些位于南极圈之外的考察站反映的仍是南极气候状况。 相似文献
103.
大青山地区出露地层主要是侏罗系中统兰旗组安山岩、安山质角砾熔岩、凝灰岩等;侵入岩为晚侏罗世二长花岗岩;断裂发育,岩石蚀变强烈。金地球化学特征表明,金主要富集在侏罗系中统兰旗组火山岩中。金的原生晕、次生晕异常特征和分布表明,破碎蚀变岩带就是金矿化蚀变带。通过野外地质调查已在三道盘—马家窝铺的安山岩和二长花岗岩中发现了5条金矿化带和29条金银矿脉。实践证明,在大青山地区进行金矿普查运用地球化学方法是有效的。 相似文献
104.
Monthly changes in sedimentation and sediment properties were studied for three different culture treatments: sea cucumber monoculture (Mc), sea cucumber and scallop polyculture (Ps-c) and scallop monoculture (Ms). Results indicated that the survival rate of sea cucumber was significantly higher in Ps-c cultures than in Mc cultures. Sea cucumber yield was 69.6% higher in Ps-c culture than in Mc culture. No significant differences in body weight and scallop shell length were found between Ps-c and Ms cultures. The mean sedimentation rate of total particulate matter (TPM) was 72.2 g/(m2 d) in Ps-c cultures, with a maximum of 119.7 g/(m2 d), which was markedly higher than that of Mc (mean value). Sedimentation rates of organic matter (OM), total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in Ps-c cultures were also significantly higher than those in Mc cultures. TOC and TN contents of sediment increased rapidly in the first 5 months in Ms cultures and remained at a high level. TOC and TN contents in Mc and Ps-c cultures decreased during sea cucumber feeding seasons and increased during sea cucumber dormancy periods (summer and winter). The study demonstrates that co-culture of sea cucumber and scallop in earthen ponds is an alternative way to alleviate nutrient loads and improve water quality in coastal aquaculture systems. Moreover, it provides the additional benefit of an increased sea cucumber yield. 相似文献
105.
The trophic ecology of the small yellow croaker (Larimichthys polyactis) was studied using stable isotope analyses. Samples were collected from July to September 2009 and 34 individuals from eight sites were examined for stable carbon and nitrogen isotopes. Stable carbon isotope ratios (δ13C) ranged from -20.67 to -15.43, while stable nitrogen isotope ratios (δ15N) ranged 9.18-12.23. The relationship between δ13C and δ15N suggested high resource partitioning in the sampling area. Significant differences in stable isotope values among the eight sampling sites may be linked to environmental diversities involving various physical processes (such as ocean current, wind and tide) and different carbon sources. Furthermore, the stable isotope ratios may also explain the ontogenetic variability in diet and feeding, because δ13C and δ15N varied significantly with increasing body size. The findings are consistent with other studies on diet analyses in small yellow croaker. It was also demonstrated that stable isotope analysis could be used to estimate the trophic characters of small yellow croaker in feeding patterns and migrating habits. 相似文献
106.
Large scale northward expansion of warm water species Skeletonema tropicum (Bacillariophyceae) in China seas 总被引:2,自引:0,他引:2
Skeletonema tropicum is regarded as a species with an affinity to warm waters and it has never been reported in seas where temperatures drop below 11°C in winter. Previous studies in China reported that S. tropicum was restricted to subtropical and warm temperate seas (East and South China Seas), but the species was recently found during August cruises of 2009 and 2010 in Jiaozhou Bay, Yellow Sea, located several hundred kilometers to the north. Here, winter water temperatures often drop below 5°C. Identification of S. tropicum was confirmed under light and scanning electronic microscopes and maximum cell abundance in Jiaozhou Bay was estimated as 1.73×10 4 cell/L. This record of S. tropicum in Jiaozhou Bay represents a significant northward expansion in the geographic range of the species. Ship ballast water was identified as a possible carrier of S. tropicum from southern places along Chinese coastline, and in addition, thermal pollution from local power stations and seawater desalination plants may provide suitable conditions for species over-wintering. 相似文献
107.
介绍通过差分式结构设计和脉冲延迟细分方法解决CCD水管倾斜仪的抗干扰能力较弱、分辨力不高等不足. 相似文献
108.
<正>In the original article, the name of the fourth author is incorrect. The correct one is Kyoung Ho Kang, in which "Kang" is the family name. The publishing companies apologize to the author. 相似文献
109.
RTK-GPS��̬��λ���Ȳ����о� 总被引:1,自引:0,他引:1
??????RTK??GPS?????λ?????????????????????????????????????????3??????????????????????3?????????RTK??GPS???λ?????Ч????????????????????RTK??GPS?????????????????????RTK??GPS???λ??????????? 相似文献
110.
This study on the environmental quality of the Qingdao Cove intertidal zone sewage discharge area is based on data obtained
from the December of 1989 and 1990 macrobenthos investigations there, and uses pollution indicator species and computer aided
cladistic analysis to divide the area into a polluted area and a semipolluted area. The study showed the environmental quality
in 1990 improved over that in 1989.
Project supported by the National Natural Science Fonndation of China 相似文献