全文获取类型
收费全文 | 41857篇 |
免费 | 7126篇 |
国内免费 | 10288篇 |
专业分类
测绘学 | 3747篇 |
大气科学 | 8122篇 |
地球物理 | 7279篇 |
地质学 | 21668篇 |
海洋学 | 5790篇 |
天文学 | 3436篇 |
综合类 | 2795篇 |
自然地理 | 6434篇 |
出版年
2024年 | 300篇 |
2023年 | 810篇 |
2022年 | 1589篇 |
2021年 | 1834篇 |
2020年 | 1710篇 |
2019年 | 2078篇 |
2018年 | 1529篇 |
2017年 | 1733篇 |
2016年 | 1803篇 |
2015年 | 2003篇 |
2014年 | 2520篇 |
2013年 | 2537篇 |
2012年 | 2640篇 |
2011年 | 2741篇 |
2010年 | 2349篇 |
2009年 | 2913篇 |
2008年 | 2762篇 |
2007年 | 2939篇 |
2006年 | 2756篇 |
2005年 | 2621篇 |
2004年 | 2259篇 |
2003年 | 2095篇 |
2002年 | 1816篇 |
2001年 | 1632篇 |
2000年 | 1601篇 |
1999年 | 1425篇 |
1998年 | 1263篇 |
1997年 | 878篇 |
1996年 | 732篇 |
1995年 | 660篇 |
1994年 | 619篇 |
1993年 | 546篇 |
1992年 | 365篇 |
1991年 | 320篇 |
1990年 | 219篇 |
1989年 | 183篇 |
1988年 | 146篇 |
1987年 | 79篇 |
1986年 | 45篇 |
1985年 | 48篇 |
1984年 | 28篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 5篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
利用浸出试验方法,对火电厂粉煤灰进行浸出特性的测定,对其有害特性进行鉴别并分析其浸出规律,从而为地下水受粉煤灰排水影响后的水质预测、堆灰场选址、环境影响评价提供依据. 相似文献
53.
西藏地区旱涝等级划分及时空分布特征 总被引:7,自引:3,他引:7
利用西藏22个站点1969-1998年逐日降水资料,采用d指数旱涝等级方法。按夏季(5-9月),初夏(5-6月),盛夏(7-8月)时段进行了旱涝等级划分。采用EOF分析方法对全区22个站点旱涝等级展开分解,得出西藏地区的旱涝时空分布特征,主要类型和周期,而且对西藏地区夏季(5-9月)的旱涝做了预测。 相似文献
54.
舞阳、襄城盐湖盆地未熟-低熟油成藏模式 总被引:3,自引:0,他引:3
舞阳、襄城凹陷下第三生活费为膏、盐岩相盐湖沉积。半咸水-咸水湖相、盐湖相是形成未熟-低熟油的良好环境,沉积旋回中期断坳式沉积形成了主要油源层系,其高丰度未熟烃类推岩体是形成未熟-低熟油藏的物质基础,中-高孔、中-高渗碎屑岩层构成了未熟-低熟油藏的重要储集层,并发育了较好的生储盖组合,这些有利条件为舞阳、襄城凹陷形成未熟-低熟油藏提供了重要保证。指出凹陷陡坡带为背斜、断鼻型油藏分布区,还可能有混合型油藏;中部洼陷带为岩性油藏、裂隙型油藏发育区;斜坡带主要发育断鼻型油藏。 相似文献
55.
About 30 samples representing major lithologies of Sulu ultrahigh-pressure (UHP) metamorphic rocks were collected from surface exposures and exploration wells, and compressional (Vp) and shear wave (Vs) velocities and their directional dependence (anisotropy) were determined over a range of constant confining pressures up to 600 MPa and temperatures ranging from 20 to 600 °C. Samples range in composition from acidic to ultramafic. P- and S-wave velocities measured at 600 MPa vary from 5.08 to 8.64 km/s and 2.34 to 4.93 km/s, respectively. Densities are in the range from 2.60 to 3.68 g/cm3. To make a direct tie between seismic measurements (refraction and reflection) and subsurface lithologies, the experimental velocity data (corresponding to shallow depths) were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000-m Chinese Continental Scientific Drilling Program (CCSD) crustal segment. Comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks. The strongly reflective zone beneath the Donghai drill site can be explained by the impedance contrasts between the different lithologies. Contacts between eclogite/peridotite and felsic rocks (gt-gneiss, granitic gneiss), in particular, may give rise to strong seismic reflections. In addition, shear-induced (lattice preferred orientation (LPO)-related) seismic anisotropy can increase reflectivity. For the explanation of the high velocity bodies (>6.4 km/s) around 1000 m and below 3200-m depth, large proportions of eclogite/peridotite (about 40 and 30 vol.%, respectively) are needed. 相似文献
56.
57.
The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality. 相似文献
58.
Predicting average annual groundwater levels from climatic variables: an empirical model 总被引:8,自引:0,他引:8
On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment. 相似文献
59.
60.
资源环境与社会经济协调发展探析 总被引:15,自引:2,他引:15
文章首先回顾了资源环境与社会经济发展的理论,提出资源环境与社会经济协调发展内涵:一方面,要在资源环境承载力范围内发展社会经济,追求社会经济发展的最大化,另一方面,环境承载力是动态的,要依靠社会经济发展不断提高,这两个方面是相互作用、相互制约的。在此基础上,详细论述了资源环境与社会经济协调发展的内容,并从社会经济发展、资源环境管理等角度探讨了资源环境与社会经济协调发展的政策调控,通过建立节约型国民经济体系、深化资源环境管理,实现区域一体化,以保证资源环境与社会经济协调发展的实现。 相似文献