全文获取类型
收费全文 | 67440篇 |
免费 | 25086篇 |
国内免费 | 50485篇 |
专业分类
测绘学 | 9832篇 |
大气科学 | 23836篇 |
地球物理 | 17768篇 |
地质学 | 54429篇 |
海洋学 | 21101篇 |
天文学 | 1099篇 |
综合类 | 6926篇 |
自然地理 | 8020篇 |
出版年
2024年 | 485篇 |
2023年 | 1134篇 |
2022年 | 2834篇 |
2021年 | 3733篇 |
2020年 | 3845篇 |
2019年 | 7212篇 |
2018年 | 6884篇 |
2017年 | 6448篇 |
2016年 | 6462篇 |
2015年 | 6689篇 |
2014年 | 6124篇 |
2013年 | 7229篇 |
2012年 | 7452篇 |
2011年 | 7361篇 |
2010年 | 7275篇 |
2009年 | 6489篇 |
2008年 | 6032篇 |
2007年 | 5822篇 |
2006年 | 5377篇 |
2005年 | 4735篇 |
2004年 | 4390篇 |
2003年 | 3548篇 |
2002年 | 3406篇 |
2001年 | 2992篇 |
2000年 | 2468篇 |
1999年 | 1867篇 |
1998年 | 1760篇 |
1997年 | 1804篇 |
1996年 | 1398篇 |
1995年 | 1323篇 |
1994年 | 1182篇 |
1993年 | 1142篇 |
1992年 | 1000篇 |
1991年 | 726篇 |
1990年 | 714篇 |
1989年 | 586篇 |
1988年 | 489篇 |
1987年 | 384篇 |
1986年 | 315篇 |
1985年 | 246篇 |
1984年 | 284篇 |
1983年 | 168篇 |
1982年 | 205篇 |
1981年 | 148篇 |
1980年 | 107篇 |
1979年 | 125篇 |
1978年 | 51篇 |
1977年 | 47篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
BIAN Jian-min LIN Nian-feng TANG Jie College of Environment Resources Jilin University Changchun Jilin China 《东北亚地学研究》2005,(Z1)
Desertification is an environmental issue in the world. The salt-alkalization desertification land area formed by both primary and secondary salt-alkalization has extended in a large scale, which has become a significant eco-environmental problem. Based on the characteristics of eco-environment and the situation of desertification in western Songnen plain, this paper reports the analyzes of its formation in background and cause. An early warning system on the salt-alkalization desertification is established and the GIS technology is used to abstract the information of desertification evaluation index. Supported by the integrated technology of the GIS and ANN, the orientation and quantitative result of desertification are gained, which is helpful to the eco-environment protection and resource development in western Songnen Plain. 相似文献
72.
秦岭凤太矿田层控铅锌(铜)矿床的金属物质、硫和成矿溶液主要来自深部基底的岩石,属海底喷流—沉积成因矿床。从这一理论认识出发可进一步分析控矿地质条件及今后在该区有效地寻找同类矿床。 相似文献
73.
The energy flow ofBranchiura sowerbyi was studied for the first time in China in a shallow macrophytic lake, Biandantang Lake, Hubei Province. The energy flow
was calculated from the measurement of flesh production (12.5241kJ/m2a), egestion (517.7302kJ/m2a), metabolism (38.3273 kJ/m2a), and excretion (4.3798kJ/m2a). The net growth efficiency of the species is about 22.7%, which accords well with the generally reported value for oligochaetes.
In addition, the relationship between starvation respiration (R, mgO2/ind·d), wet weight (Ww, mg) and temperature (T, °C) were also measured, with the regression function beingR=0.008Ww0.736 e0.050T.
Project supported by NSFC (30270278, 3960019), the foundation of the government of Hubei Province (No. 2000J109), and the
foundation of Ecological Station, CAS in the Institute of Hydrobiology. 相似文献
74.
DunaIiella salina, a halotolerent unicellular green alga, can accurmulate a Iarge amount of β-caroteneunder environmental conditions. The isorners of β-carotene extIacted from D. salina culturedin medium with different nitrate and phosphate concentrations were analysed by HPLC with Alox-Talumins column. At least six isomers were found in different proportions depending on the culture me-dia's nitrate and/or phosphate concentrations. Nitrate and/or phosphae defidency was conducive tothe accumulation of totaI cis isomers but not of al1 trans isomer. lt is sUggeSted that 1 mmol/L KNO_3and 0.1 mmol/L KH_2, PO_4 are favourable for accumulation of total cis β-carotene. 相似文献
75.
76.
青藏块体东北缘地壳水平运动状态 总被引:10,自引:6,他引:4
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。 相似文献
77.
WEIHai-quan JINBo-lu LIUYong-shun 《东北亚地学研究》2004,7(1):28-35
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption. 相似文献
78.
刘崇蓉 《地球信息科学学报》1996,(2):54-54
以往的南水北调工程局限在长江流域内,没有谈到从藏东调水。西线调水的方案很多,原有的规划是在本流域内.现在是跨流域调水。到底如何选取调水目标?那些地区是真缺水?调水顺序如何?应做全面和系统的规划,规划中要有西部需水的总体规划。 对于雅鲁藏布江的调水工程也要有全面的综合规划。供水和调水区可调多少水.要从总的经济效益来评价。这应是多学科、多方面专家共同讨论的问题。 相似文献
79.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
80.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献