全文获取类型
收费全文 | 7159篇 |
免费 | 953篇 |
国内免费 | 1495篇 |
专业分类
测绘学 | 1039篇 |
大气科学 | 1046篇 |
地球物理 | 1669篇 |
地质学 | 3025篇 |
海洋学 | 948篇 |
天文学 | 364篇 |
综合类 | 554篇 |
自然地理 | 962篇 |
出版年
2024年 | 21篇 |
2023年 | 70篇 |
2022年 | 135篇 |
2021年 | 184篇 |
2020年 | 182篇 |
2019年 | 252篇 |
2018年 | 198篇 |
2017年 | 270篇 |
2016年 | 293篇 |
2015年 | 343篇 |
2014年 | 385篇 |
2013年 | 475篇 |
2012年 | 384篇 |
2011年 | 424篇 |
2010年 | 358篇 |
2009年 | 459篇 |
2008年 | 551篇 |
2007年 | 544篇 |
2006年 | 528篇 |
2005年 | 455篇 |
2004年 | 432篇 |
2003年 | 386篇 |
2002年 | 339篇 |
2001年 | 275篇 |
2000年 | 290篇 |
1999年 | 228篇 |
1998年 | 203篇 |
1997年 | 193篇 |
1996年 | 119篇 |
1995年 | 124篇 |
1994年 | 115篇 |
1993年 | 100篇 |
1992年 | 66篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 25篇 |
1988年 | 29篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1954年 | 3篇 |
1905年 | 1篇 |
1900年 | 3篇 |
排序方式: 共有9607条查询结果,搜索用时 0 毫秒
81.
PowerBuilder 8.0中C/S模式应用过渡到B/S模式应用的实现技术 总被引:1,自引:0,他引:1
简要分析了PowerBuilder 8.0中各种B/S解决方案的优劣,探讨了适用于已有C/S模式应用过渡到B/S模式应用的实现方法,以及利用ASP技术实现对不同类型的客户测览器隐藏底层实现方法的技术,并给出了C/S模式应用过渡到B/S模式应用的一个实例。 相似文献
82.
83.
2-D crustal velocity structure and vp/vs are obtained by processing and interpretation of S-wave data from Maqen-Jingbian deep seismic sounding(DSS)profile.The result shows that there exist obvious differences in 2-D S-wave velocity structure and vp/vs ratio structure along the profile.The S-wave velocities are low and vp/vs ration is high for the westem section of the profile and Haiyuan region,while they are normal for the middle and eastern sections.The changes in lithologic characters of two major anomalous zones are discussed according to lateral variation of S-wave velocity structure and vp/vs ratio structure.It is concluded that the development and occurrence of the Haiyuan strong earthquake is not only related to tectonic activities,but also to lithologic characters of the region. 相似文献
84.
大庆徐家围子地区深部致密砂砾岩气层识别 总被引:3,自引:0,他引:3
大庆徐家圈子地区深部致密砂砾岩储层的骨架成分除了含有石英、长石外,还含有许多酸性喷发岩,而且各种骨架成分的含量随深度变化比较大;复杂的岩性使得气的影响被岩性的影响所淹没,从而造成常规气层识别方法失效。针对这一问题,应用神经网络方法准确求取地层颗粒密度和泥质含量,然后对中子和密度测井值进行岩性影响校正和泥质影响校正,使得求出的中子和密度孔隙度仅受地层气的影响,最后将得到的中子和密度孔隙度进行对比,应用中子和密度孔隙度的差异识别气层。 相似文献
85.
数字地籍测绘是目前土地管理部门的首选方案,需要制定街坊划分、界址线设定、工作底图与采集草图一体化作业、数据文件管理、街坊线、图斑的绘制等技术措施。 相似文献
86.
随着近年来计算机技术的发展,尤其是网络技术的发展,GIS在组成结构和应用技术等方面已与传统的GIS技术有了很大的不同,基于MapXtreme/MapX的WebGIS则是GIS技术发展的趋势。本文简单介绍WebGIS的发展趋势,结合一些例子介绍了利用MapXtreme的地理信息发布的技术和原理。 相似文献
87.
88.
Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water–air, water–LNAPL and LNAPL–air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water–air, water–LNAPL and LNAPL–air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water–air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting. 相似文献
89.
Stanley N. Davis Stephen Moysey DeWayne L. Cecil Marek Zreda 《Hydrogeology Journal》2003,11(2):217-227
Natural production of the radionuclide chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear
weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production
prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the
probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional
pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
Electronic Publication 相似文献
90.
Sediment Phosphorus Chemistry and Microbial Biomass along a Lowland New Zealand Stream 总被引:1,自引:0,他引:1
R. W. McDowell 《Aquatic Geochemistry》2003,9(1):19-40
An evaluation of the distribution of P concentrations in streamflow, P fractions andthe microbial biomass P pool was made of bed and bank sediments along a lowlandstream in New Zealand. Agricultural intensification increased downstream. However,most P fractions decreased downstream (total P decreased from c. 400 to 250 mg kg-1) in bed sediments, while P in streamflow remained relatively constant (generally < 0.005 mg l-1) and sediment microbial P increased from 2 to 8 mg kg-1. An investigation of P release from dried and rewetted sediments showed that solution P (CaCl2-P) increased, on average > 300%, and proportional to the size of the microbial biomass P pool before drying, except in sediments with much organic carbon (OC). When supplied with a P source (1 mg l-1) and then simultaneously with a C source (glucose, 100 mg l-1), all sediment behaved similarly and biotic sorption accounted for, on average, 27 and 34% of the total sediment uptake, respectively (maximum of 58%). The quantity of P taken up was related to the initial size of the microbial biomass P pool, and the availability of P as influenced by organic P complexes and OC. The sediment microbial biomass represents a transient, but small store of P could be useful to indicate bioavailable P inputs. 相似文献