全文获取类型
收费全文 | 2395篇 |
免费 | 444篇 |
国内免费 | 560篇 |
专业分类
测绘学 | 120篇 |
大气科学 | 437篇 |
地球物理 | 690篇 |
地质学 | 1313篇 |
海洋学 | 234篇 |
天文学 | 89篇 |
综合类 | 244篇 |
自然地理 | 272篇 |
出版年
2023年 | 34篇 |
2022年 | 116篇 |
2021年 | 111篇 |
2020年 | 111篇 |
2019年 | 118篇 |
2018年 | 161篇 |
2017年 | 154篇 |
2016年 | 125篇 |
2015年 | 118篇 |
2014年 | 152篇 |
2013年 | 173篇 |
2012年 | 142篇 |
2011年 | 149篇 |
2010年 | 156篇 |
2009年 | 155篇 |
2008年 | 117篇 |
2007年 | 132篇 |
2006年 | 83篇 |
2005年 | 71篇 |
2004年 | 83篇 |
2003年 | 69篇 |
2002年 | 59篇 |
2001年 | 69篇 |
2000年 | 92篇 |
1999年 | 85篇 |
1998年 | 68篇 |
1997年 | 74篇 |
1996年 | 90篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 47篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1936年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有3399条查询结果,搜索用时 15 毫秒
991.
Yan XU Lei NIE Huangping DING Yin WANG Jian LIU Wei LU Zhenying ZHANG Xue GONG Shiwei SHEN 《东北亚地学研究》2006,9(2):141-146
On the basis of the study on the engineering geological characteristics of No. 2 dump of Nanfen iron mine and the analysis of the failure mode of dump landslide, the stability of the present dump, the stability of the dump 20 years later and the stability of double-bench dump are analyzed. Then, the debris flow risk is evaluated by fuzzy mathematics method. Finally, the comprehensive treatment for the dump is suggested. It is concluded that ① In rainy and snowmelt period, the stability would be decreasing sharply when ground water is not drained out in time; ② Double-bench dumping mode will improve stability of the dump little;③ Debris flow risk is middle danger. The interim debris flow with medium scale may occur. ④ Monitoring, draining and baffling work ought to be well done. ⑤In order to prevent the damage of landslide and debris flow, three measures are adopted, including setting rockfall net, setting the debris flow barrier and removing the residents. 相似文献
992.
Through studying biological and ecological characteristics ofTamarix L., we found wide adaptability to different ecological environment and high endurance of adversity. When planted in the edge of desert and periphery of oasis,Tamarix will act as excellent sand-fixing shrubs, improve ecological environment and play a positive role. However, introducingTamarix unreasonably will deteriorate the ecological environment and reduce biodiversity and play a negative role. Grasping the biological and ecological characteristics ofTamarix will do much to benefit further developing and utilizing of the resources
相似文献993.
Information on the palaeoenvironment from Late Pleistocene to Holocene in northwestern Yannan Plateau has been deduced from a study of a 28.81m-long core taken from Napahai Lake.The results from Relative Brightness In-dex(RBI) as well as those from the lithological analyses of bulk sediments,total organic carbon and granulometric analy-ses have been used to reconstruct the environmental and climatic evolution of the area.The ages were provided by three ^14C datings.The record suggested a climate fluctuation between warm-dry and cool-wet from ca.57 to 32ka B.P.which led a shallowing and swamping of the lake.The water level again increased quickly at ca.32ka B.P.,reached itˊs peak during LGM(Last Glacial Maximum,ca.18-20kaB.P.)and remained relative high until ca.15kaB.P.The high wa-ter level at LGM is attributed to cold-wet conditions.The area experienced an abrupt and unstable climatic changes dur-ing the transition period form 15 to 10ka B.P.with a dominated littoral environment.Awarm-dry climate led to the contrac-tion of the lake during the Holocene and reed-swamps became dominant..After a minor wet-cool pulse during the Late Holocene,the modern climate became to be established. 相似文献
994.
995.
广西地矿建设发展中心在承担钦州至灵山陆屋镇一级公路施工中,根据不同性质的地段,采用不同的爆破方法,即节约了成本,又圆满完成路基施工任务,获得良好的社会效益和经济效益。 相似文献
996.
I. Adler J. I. Trombka P. Lowman R. Schmadebeck H. Blodget E. Eller L. Yin R. Lamothe G. Osswald J. Gerard P. Gorenstein P. Bjorkholm H. Gursky B. Harris J. Arnold A. Metzger R. Reedy 《Earth, Moon, and Planets》1973,7(3-4):487-504
A number of experiments carried in orbit on the Apollo 15 and 16 spacecraft were used in the compositional mapping of the lunar surface. The observations involved measurements of secondary (fluorescent) X-rays, gamma rays and alpha particle emissions. A large scale compositional map of over 20% of the lunar surface was obtained for the first time. It was possible to demonstrate significant chemical differences between the mare and the highlands, to find specific areas of high radioactivity and to learn something about the composition of the Moon's hidden side.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
997.
Guo-Xiong Mei Jian-Hua Yin Jin-Min Zai Zong-Ze Yin Xiao-Li Ding Guo-Fu Zhu Lok Man Chu 《国际地质力学数值与分析法杂志》2004,28(2):111-129
This paper presents a finite layer procedure for Biot's consolidation analysis of layered soils using a cross-anisotropic elastic constitutive model. The program is first verified using published results. Then, using this program, the influences of cross-anisotropy on the immediate settlement, the final settlement, and the consolidation behaviour are investigated by changing one model parameter at one time. The results obtained using the cross-anisotropic elastic model are compared with results using an isotropic elastic model. It is found that the cross-anisotropy has very large influences on the immediate settlement, the final settlement, and the consolidation behaviour. Curves or tables of the immediate settlement coefficients, the final settlement coefficients, and the average degree of consolidation are obtained and presented in the paper. These curves or tables can be easily used to estimate the immediate settlement, the final settlement, and the consolidation settlement of a cross-anisotropic soil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
998.
笔者以近 30年来的地质成果资料 ,从鄂北地层层序与成因 ,古生物类型与生态 ,岩石化学、微量元素、稀土元素、重矿物特征 ,岩浆岩分布 ,地球物理异常及类蛇绿岩、蓝片岩和榴辉岩带的存在等 ,将鄂北地区划分出三个古生物地层构造单元。以枣阳市鹿头镇—广水市郝店镇剪切带、连接新城—广济断裂为界 ,之北是桐柏古生物地层构造区 ,之南是扬子北部边缘古生物地层构造区。以襄樊—广济断裂为界 ,之北是扬子北部边缘古生物地层构造区 ,之南是扬子地台古生物地层构造区 相似文献
999.
A new convenient combinatorial method is developed here to derive the invariant points in multisystem closed nets – the absent phase substitution (APS) method. It substantially simplifies the derivation of the closed nets in multisystems with many components and phases. For the multisystems whose total phase number (NPS) ≤ twice the number of the absent phases (m) in an invariant assemblage, the method can yield regular closed nets with or without globally absent phases; for other multisystems, the method can yield the regular closed nets with globally absent phases. As examples, the APS method was used to predict: (1) the regular closed nets of unary to quinary n + 4‐phase multisystems, unary 6‐phase multisystem and ternary 8‐phase multisystem; (2) the basic properties of the regular closed nets of the quaternary and quinary multisystems with n + 4 and n + 5 phases. Two multisystems were chosen to demonstrate how to select a realistic closed net from the numerous possible closed nets of a complex multisystem, and how to derive a realistic partially closed‐net, closed‐net‐diagram and the related realistic straight‐line‐net‐diagram. Comparisons of our APS method for the derivation of complicated closed nets with other methods indicate that this method is much simpler and more efficient. 相似文献
1000.
Seasonal and spatial dynamics of nutrients and phytoplankton biomass in Victoria Harbour and its vicinity before and after sewage abatement 总被引:1,自引:0,他引:1
Ho AY Xu J Yin K Yuan X He L Jiang Y Lee JH Anderson DM Harrison PJ 《Marine pollution bulletin》2008,57(6-12):313-324
This study investigated the seasonal and spatial dynamics of nutrients and phytoplankton biomass at 12 stations in Hong Kong (HK) waters during a three year period from 2004 to 2006 after upgraded sewage treatment and compared these results to observations before sewage treatment. Pearl River estuary (PRE) discharge significantly increased NO(3) and SiO(4) concentrations, particularly in western and southern waters when rainfall and river discharge was maximal in summer. Continuous year round discharge of sewage effluent resulted in high NH(4) and PO(4) in Victoria Harbour (VH) and its vicinity. In winter, spring and fall, the water column at all stations was moderately mixed by winds and tidal currents, and phytoplankton biomass was relatively low compared to summer. In summer, the mean surface phytoplankton chl biomass was generally > 9 microL(-1) in most areas as a result of thermohaline stratification, and high nutrients, light, and water temperature. In summer, the potential limiting nutrient is PO(4) in the most productive southern waters and it seldom decreased to limiting levels ( approximately 0.1 microM), suggesting that phytoplankton growth may be only episodically limiting. The mean bottom dissolved oxygen (DO) remained > 3.5 mg L(-1) at most stations, indicating that the eutrophication impact in HK waters was not as severe as expected for such a eutrophic area. After the implementation of chemically enhanced primary sewage treatment in 2001, water quality in VH improved as indicated by a significant decrease in NH(4) and PO(4) and an increase in bottom DO. In contrast, there were an increase in chl a and NO(3), and a significant decrease in bottom DO in southern waters in summer, suggesting that hypoxic events are most likely to occur in this region if phytoplankton biomass and oxygen consumption keep increasing and exceed the buffering capacity of HK waters maintained by monsoon winds, tidal mixing and zooplankton grazing. Therefore, future studies on the long-term changes in nutrient loading from PRE and HK sewage discharge will be crucial for developing future strategies of sewage management in HK waters. 相似文献