全文获取类型
收费全文 | 3153篇 |
免费 | 413篇 |
国内免费 | 464篇 |
专业分类
测绘学 | 250篇 |
大气科学 | 261篇 |
地球物理 | 435篇 |
地质学 | 1207篇 |
海洋学 | 392篇 |
天文学 | 22篇 |
综合类 | 217篇 |
自然地理 | 1246篇 |
出版年
2024年 | 10篇 |
2023年 | 40篇 |
2022年 | 112篇 |
2021年 | 139篇 |
2020年 | 128篇 |
2019年 | 171篇 |
2018年 | 104篇 |
2017年 | 132篇 |
2016年 | 137篇 |
2015年 | 143篇 |
2014年 | 157篇 |
2013年 | 198篇 |
2012年 | 203篇 |
2011年 | 206篇 |
2010年 | 164篇 |
2009年 | 159篇 |
2008年 | 153篇 |
2007年 | 180篇 |
2006年 | 206篇 |
2005年 | 209篇 |
2004年 | 169篇 |
2003年 | 146篇 |
2002年 | 121篇 |
2001年 | 89篇 |
2000年 | 97篇 |
1999年 | 96篇 |
1998年 | 64篇 |
1997年 | 64篇 |
1996年 | 47篇 |
1995年 | 38篇 |
1994年 | 42篇 |
1993年 | 33篇 |
1992年 | 24篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有4030条查询结果,搜索用时 625 毫秒
931.
选择岩溶科学作地学发展的有限目标,系基于我国岩溶的地域优势、相对的人才优势及岩溶在社会经济发展中的重要地位。为目标的实现,分别就岩溶基础理论的发展,应用岩溶学工作的开展提出了五大课题(任务)和有关建议、措施。 相似文献
932.
933.
对硅质角砾岩型的320矿床的典型剖面进行综合物化探研究结果表明,这类矿床的隐伏铀矿体具有高值大范围的极化率(η_(?))异常,激电测深可圈定矿体的埋深、产状、规模等特征,激电法是寻找这类隐伏铀矿的高灵敏度方法。在这类矿体的地表还有γ,Po,He,Cu,Mo等物化探异常,根据这些综合异常可推断激电异常是否反映了隐伏铀矿体,大大提高物化探综合找矿的能力。对320矿区外围同类异常点进行综合物化探研究的结果,在WBC地区发现了大范围高值激电异常及其它综合物化探异常,而且地质条件、区域航测、重力、水化学、分散流等异常特征也与320矿区相似,预测为隐伏铀矿远景区。 相似文献
934.
Summary Optimization algorithms are developed to improve the selection of truck and shovel fleets for suface mine operations. These are based on performance estimation models developed by Fluor Utah (1977) and graphical display algorithms and other software within the SEAMPLAN system developed at Montana State University. The advantages and disadvantages of the method are considered. 相似文献
935.
贵州西南部灰家堡金矿田位于国家级南盘江-右江成矿区带北部,探明金资源量370 t,近东西向灰家堡背斜为矿田控矿构造,矿体呈层状似层状产于背斜轴线300■1 000 m范围,埋深0■1 400 m,是理论找矿的典型范例。为燕山期成矿。构造地球化学弱信息指示了深部隐伏矿存在的可能,地球物理判别了深部构造形态,为深部工程验证提供间接依据;矿田内局部地段矿体未圈边、深部断裂发现厚大矿体;根据找矿预测模型,开展深部找矿预测,仍有较好找矿潜力。 相似文献
936.
某冶炼厂附近农田镉污染调查与对策 总被引:5,自引:2,他引:3
对遭受某铜矿冶炼厂镉污染的湖北省某镇约30km^2的农田土壤进行了调查,对土壤耕作层与亚耕层以及污染源(废气、废水和炉渣)中全量Cd和有效态Cd含量的系统测定结果表明:未受Cd污染、受轻度污染及受中度污染的土壤面积分别占3.6%,82.1%,14.3%;土壤中全量Cd及有效态Cd含量的分布规律均表现为西灌区>东灌区>灌间区;土壤耕作层与亚耕层中全量Cd含量的差异不大,而有效态Cd则主要富集于土壤耕作层中;受土壤pH值的影响,Cd在污染区土壤中的活化率低于远离冶炼厂未受污染的农田对照区。该镇农田的Cd污染主要来源于某铜矿冶炼厂的废气和废水,而炉渣的污染相对较小。运用生态方法治理该镇农田的Cd污染具有一定的可行性和适用性,值得研究利用。 相似文献
937.
938.
双核型空间结构与锡澄经济带发展研究 总被引:2,自引:0,他引:2
本文运用区域经济发展理论,在分析无锡与江阴城市形态空间扩展变化、锡澄地区经济发展现状基础上,提出加快发展锡澄经济带,逐步形成“工”字型(双核型)空间发展态势,港城协同发展,是无锡特大城市建设、经济社会可持续发展的重要战略选择。锡澄经济带发展应实行点轴式发展、梯度推进策略。 相似文献
939.
中国国际河流研究进展 总被引:8,自引:0,他引:8
1IntroductionThe increasing momentum of economic globalization and regional geopolitical cooperation no longer stand as the major drivers of a new world order. Resource and environmental diplomacy are now regarded as new elements establishing future international patterns. Transboundary resources and environmental issues in international river basins have attracted increasing global concern and professional attention. The impact of such issues penetrates into national security, international e… 相似文献
940.
Sonic anemometers in aeolian sediment transport research 总被引:3,自引:0,他引:3
Fast-response wind and turbulence instruments, including sonic anemometers, are used more and more in aeolian sediment transport research. These instruments give information on mean wind, but also on fluctuations and turbulent statistics, such as the uw covariance, which is a direct measure of Reynolds' stress (RS) and friction velocity. This paper discusses the interpretation of sonic anemometer data, the transformations needed to get proper results and turbulence spectra, and how they are influenced by instrument size, sampling frequency, and measurement height.Turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed, or to the covariance of horizontal and vertical wind speed. They are important in determining the measurement strategy when working with fast-response instruments, such as sonic anemometers, and are useful for interpreting the measurement results. Choices on the type of sonic anemometer, observation height, sampling period, sampling frequency, and filtering can be made on the basis of expected high and low-frequency losses in turbulent signals, which are affected by those variables, as well as wind speed and atmospheric stability.Friction velocity and RS, important variables in aeolian sediment transport research, are very sensitive to tilt or slope errors. During a field experiment, the slope sensitivity of the RS was established as 9% per degree of slope, which is 1.5 times the value reported in literature on the basis of theoretical considerations. An important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the RS. An error of 9% per degree of slope in the RS will translate into an error of approximately 4% per degree of slope in the calculated friction velocity.Space–time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous RS. This largely explains why, in previous studies, a poor correlation was found between instantaneous RS measured at 3 m height and saltation flux near the surface, whereas the correlation between wind speed at some height and saltation flux was much better. Therefore, the poor correlation between RS away from the surface and saltation flux does not contradict that saltation flux is caused by RS. 相似文献