全文获取类型
收费全文 | 33608篇 |
免费 | 7646篇 |
国内免费 | 10406篇 |
专业分类
测绘学 | 5023篇 |
大气科学 | 5415篇 |
地球物理 | 7433篇 |
地质学 | 20236篇 |
海洋学 | 5179篇 |
天文学 | 806篇 |
综合类 | 3111篇 |
自然地理 | 4457篇 |
出版年
2024年 | 263篇 |
2023年 | 785篇 |
2022年 | 2006篇 |
2021年 | 2426篇 |
2020年 | 1924篇 |
2019年 | 2266篇 |
2018年 | 2226篇 |
2017年 | 2101篇 |
2016年 | 2022篇 |
2015年 | 2133篇 |
2014年 | 2314篇 |
2013年 | 2556篇 |
2012年 | 2703篇 |
2011年 | 2622篇 |
2010年 | 2607篇 |
2009年 | 2407篇 |
2008年 | 2421篇 |
2007年 | 2127篇 |
2006年 | 1967篇 |
2005年 | 1719篇 |
2004年 | 1279篇 |
2003年 | 962篇 |
2002年 | 997篇 |
2001年 | 1009篇 |
2000年 | 919篇 |
1999年 | 827篇 |
1998年 | 585篇 |
1997年 | 529篇 |
1996年 | 509篇 |
1995年 | 387篇 |
1994年 | 380篇 |
1993年 | 323篇 |
1992年 | 304篇 |
1991年 | 193篇 |
1990年 | 174篇 |
1989年 | 130篇 |
1988年 | 107篇 |
1987年 | 88篇 |
1986年 | 67篇 |
1985年 | 50篇 |
1984年 | 42篇 |
1983年 | 34篇 |
1982年 | 35篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 30篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1958年 | 10篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
地球科学研究产生了大量的地球数据,其特点决定了地球数据共享的必要性。分析了网络化过程中地球数据共享存在的若干问题,介绍了XML Web Service及其相关技术.提出了基于XML Web Service的地球数据共享模型。在VS.NET中对XML Web Service在地球数据共享的应用进行了测试.指出XML Web Service是未来实现全球级的地球数据共享应用的理想选择。 相似文献
992.
采空区上方修建大型建筑物地基稳定性评价 总被引:6,自引:0,他引:6
地表移动变形随时间的稳定性及剩余变形问题一直是采动覆岩沉陷研究的重要方面。笔者分析了采动地表移动变形的时间过程,探讨了地表沉陷的延续时间及地表剩余沉陷的预计方法,给出了采空区上方修建大型建筑物地基稳定性评价的指标,对采空区上建设建筑物提出了相应的技术措施。 相似文献
993.
Benjamin J. Kadlec David A. Yuen Xili L. Yang Evan F. Bollig Yunsong Wang Gordon Erlebacher Maxwell Rudolph 《Visual Geosciences》2004,9(1):61
We report here our experiences from using easily acquired web-cam components for collaborative ventures in the Earth sciences. We have used a variety of hardware and different software. We demonstrate from various locations in the U.S.A. the feasibility of using web-cam in multitudinous activities, relevant for conducting research and knowledge dissemination. We summarize the quality of the connections from the various combinations of communicating parties. Today, web-cams can be utilized as an economical and viable means of point-to-point communication in the Earth science community. Greater bandwidth is sorely needed for activities such as multi-party conferencing on the present internet network. We propose that web-cam can be readily deployed as a web-service for facilitating collaborative research over the GRID infrastructure, using the middleware Narada-Brokering. Web-cam will play an important role in the emerging field of geoinformatics. 相似文献
994.
995.
T. N. Yang 《Journal of Metamorphic Geology》2004,22(7):653-669
The Qinglongshan eclogites in the Southern Sulu ultrahigh pressure metamorphic (UHPM) terrane show very different retrograded textures from their counterparts in the Northern Sulu terrane, implying a different thermal history. Scanning electron and optical microscope observations indicate that the peak assemblage of the Qinglongshan eclogite is anhydrous, composed of Grt + OmpI + Rt + (Ky + coesite). These primary minerals were replaced by second and third stage minerals, resulting in symplectite pseudomorphs or coronas. The following relationships are inferred: OmpI → OmpII + Ab + Fe‐oxide symplectite (type I) and Rt → Rt + Ilm intergrowth; and, Ky → Pg, OmpII (+Pl) → Amp (+Pl) symplectite (type II), and Grt → Prg (+Fe‐oxide). Mineral chemistry and mass‐balance demonstrate that the pseudomorphed textures were developed by metasomatism involving dissolution and precipitation intensified by fluids along grain boundaries. The formation of symplectite type I produced Fe, Mg and Na but consumed Ca and Si. The Mg and Fe diffused to garnet where exchange of (Mg, Fe) with Ca of the garnet resulted in compositional zonation with decreased Ca towards the edge of garnet grains where Ca was consumed during symplectite formation. The replacement of kyanite by paragonite consumed the extra Na. In the later stage, fluid infiltration partially transformed symplectite type I to type II, and narrow rims of pargasite resorbed garnet from their boundaries. Mass balance suggests that the transformation and resorption would have been coupled during fluid infiltration. In the latest stage, epidote and quartz were precipitated at very late stage as a result of fluid activity along microfractures. Tentative P–T conditions based on mineral reactions and thermocalc software suggest that the retrograded eclogite did not record the granulite facies retrograde evolution characteristic of eclogites from the Northern Sulu terrane. The difference in retrograde evolution between the Southern and Northern Sulu eclogites suggests a different exhumation history. 相似文献
996.
Genesis of Kanggur Gold Deposit in Eastern Tianshan Orogenic Belt, NW China: Fluid Inclusion and Oxygen and Hydrogen Isotope Constraints 总被引:3,自引:0,他引:3
Abstract. Primary fluid inclusions in quartz and carbonates from the Kanggur gold deposit are dominated by aqueous inclusions, with subsidiary CO2 -H2 O inclusions that have a constant range in CO2 content (10–20 vol %). Microthermometric results indicate that total homogenization temperatures have a wide but similar range for both aqueous inclusions (120 to 310C) and CO2 -H2 O inclusions (140 to 340C). Estimates of fluid salinity for CO2 -H2 O inclusions are quite restricted (5.9∼10.3 equiv. wt% NaCl), whereas aqueous inclusions show much wider salinity ranging from 2.2 to 15.6 equivalent wt %NaCl.
The 6D values of fluid inclusions in carbonates vary from -45 to -61 %, in well accord with the published δD values of fluid inclusions in quartz (-46 to -66 %). Most of the δ18 O and δD values of the ore-forming fluids can be achieved by exchanged meteoric water after isotopic equilibration with wall rock by fluid/rock interaction at a low water/rock ratio. However, the exchanged meteoric water alone cannot explain the full range of δ18 O and δD values, magmatic and/or meta-morphic water should also be involved. The wide salinity in aqueous inclusions may also result from mixing of meteoric water and magmatic and/or metamorphic water. 相似文献
The 6D values of fluid inclusions in carbonates vary from -45 to -61 %, in well accord with the published δD values of fluid inclusions in quartz (-46 to -66 %). Most of the δ
997.
998.
北京延庆北部地区后城组火山岩岩石化学特征与成因探讨 总被引:3,自引:0,他引:3
根据TAS图解 ,北京延庆北部地区后城组火山属于玄武粗安岩 流纹岩 (和粗面岩 )的双峰式组合。该套火山岩不属于典型的钾玄岩系列 ,在基性岩和中性岩中总体上以碱性系列和向碱性系列过渡的高钾钙碱性系列、钾玄岩系列为主 ,流纹岩类属于富钾质的拉斑系列。该套火山岩轻稀土元素明显富集。玄武粗安岩类岩石没有负铕异常或负铕异常不明显 ,而流纹岩存在明显的负铕异常。延庆北部地区后城组火山岩形成于燕山运动早期或中期阶段的造山变形事件趋于结束时的后碰撞构造环境中。 相似文献
999.
1000.
用GPS秒信号锁定高频振荡器的方法研究 总被引:1,自引:0,他引:1
对用远距离传输的GPS秒信号锁定本地高频晶体振荡器的方法进行了探讨。介绍了高精度的时间数字转换器TDC(Time to Digital Converter)和对滤波的方法进行了探讨。为了降低成本又能够满足设计要求的精度,还考虑了双D/A转换的方法。有关的硬件系统已经通过了调试和一系列的测试和实验,在测量和控制精度方面,能达到设计的要求。此外,提出了这个系统有待解决的问题,如双D/A转换的非线性问题,Kalman滤波抗野值及继续提高精度的问题。 相似文献