全文获取类型
收费全文 | 4408篇 |
免费 | 698篇 |
国内免费 | 561篇 |
专业分类
测绘学 | 854篇 |
大气科学 | 402篇 |
地球物理 | 1467篇 |
地质学 | 1672篇 |
海洋学 | 548篇 |
天文学 | 37篇 |
综合类 | 241篇 |
自然地理 | 446篇 |
出版年
2024年 | 8篇 |
2023年 | 31篇 |
2022年 | 87篇 |
2021年 | 134篇 |
2020年 | 148篇 |
2019年 | 161篇 |
2018年 | 152篇 |
2017年 | 204篇 |
2016年 | 178篇 |
2015年 | 178篇 |
2014年 | 247篇 |
2013年 | 321篇 |
2012年 | 276篇 |
2011年 | 298篇 |
2010年 | 219篇 |
2009年 | 285篇 |
2008年 | 313篇 |
2007年 | 306篇 |
2006年 | 296篇 |
2005年 | 241篇 |
2004年 | 222篇 |
2003年 | 192篇 |
2002年 | 138篇 |
2001年 | 146篇 |
2000年 | 152篇 |
1999年 | 119篇 |
1998年 | 96篇 |
1997年 | 95篇 |
1996年 | 80篇 |
1995年 | 63篇 |
1994年 | 63篇 |
1993年 | 45篇 |
1992年 | 34篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 8篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有5667条查询结果,搜索用时 7 毫秒
1.
2.
3.
Qian Huaisui 《中国地理科学(英文版)》1997,8(3):204-211
The crop estimates by remote sensing, developing quickly in recent decades, is a up-to-date technique. Regionalization for
large area crop estimates by remote sensing, a special applied regionalization, is the foundation of crop estimates in a large
area by remote sensing. According to the actual demands of wheat yield estimation by remote sensing and wheat agroclimatic
demarcation of China, this paper first puts forward some principles upheld in this regionalization and analyses its main bases.
Secondly, it works out the classificatory schemes about the optimum temporal for estimating wheat yield by remote sensing,
information sources of space remote sensing and landuse structure in China. Finally, According to the regionalization indices,
this study divides the wheat plantable region of China into 14 regions of crop yield estimates and 31 subregions of crop yield
estimates. 相似文献
4.
应用给定换热器结构材料而使换热量最大的两侧换热表面的最佳匹配准则和使可用能损失率最小的最佳运行参数准则。利用两个准则间的关系 ,采用迭代的方式完成换热器的优化设计 ,使换热器的设计达到材料省、换热效果好及运行费用低的目的 ,且能在设计阶段实现。 相似文献
5.
The ordinary kriging method, a geostatistical interpolation technique, was applied for developing contour maps of design storm depth in northern Taiwan using intensity–duration–frequency (IDF) data. Results of variogram modelling on design storm depths indicate that the design storms can be categorized into two distinct storm types: (i) storms of short duration and high spatial variation and (ii) storms of long duration and less spatial variation. For storms of the first category, the influence range of rainfall depth decreases when the recurrence interval increases, owing to the increasing degree of their spatial independence. However, for storms of the second category, the influence range of rainfall depth does not change significantly and has an average of approximately 72 km. For very extreme events, such as events of short duration and long recurrence interval, we do not recommend usage of the established design storm contours, because most of the interstation distances exceed the influence ranges. Our study concludes that the influence range of the design storm depth is dependent on the design duration and recurrence interval and is a key factor in developing design storm contours. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
7.
In order to understand the process of surface erosion and acquire basic data of conditions on hillslope without vege tation, a sprinkling experiment is conducted on a bare slope in Mt. Tanakami in the central part of Japan. Based on the mea surements of runoff, mean soil erosion depth, and sediment yield, etc. , the results suggest the following characteristics in the process of surface erosion in the experimental area. (1) The occurrence of sediment discharge is interrupted; (2) Surface runoff is a saturated overland flow; (3) The mean soil erosion depth is thick compared with other areas in Mt. Tanakami;(4) Sediment discharge process is detachment- limited. 相似文献
8.
Hemant K. Badola Jitendra S. Butola 《山地科学学报》2005,2(2):173-180
This paper examines the effect of ploughing depths (A -- 60 cm, B -- 45 cm and C -- 30 cm) on the growth and yield of Heracleum candicans Wall (Apiaceae), a threatened medicinal herb of the Himalayan region. This less-explored plant is being suggested as a potential crop for the mountain agriculture. The study was carried out in an orchard in Himachal Pradesh, India at 2500 m altitude, for two successive growth years. During the first year, all plants remained in juvenile state; in the second year, nearly 65 % plants produced flowers only under 60cm ploughing depth. Among its morphological traits, plant height, collar diameter and aboveground flesh weight were found to be strongly correlated (P 〈 0.01) with the belowground biomass during the first year (r =0.968, 0.925 and 0.973, respectively) and during the second year (r=0.945, 0.928 and 0.775, respectively). Increase in the ploughing depth was significantly correlated (P〈0.01) with all growth parameters, including the belowground dry weight, marketable portion of the produce. The belowground biomass (commercial yield; 16.28 Qt/hec) at depth A was about 2.6 and 4.7 times higher than those recorded at depths B and C, respectively. The results clearly justify the importance of deep ploughing and this paper strongly recommends it for economically sustainable cropping. 相似文献
9.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
10.
Randall D. Campbell 《Experimental Astronomy》2002,14(1):57-60
Keck's Long Wavelength Spectrometer (LWS), is the facility instrument used for imaging and spectroscopy in the wavelength
range of 3–28 μm at the Keck Observatory. LWS uses an 128 × 128 Si:As blocked impurity band (BIB) array manufactured by the
Boeing Corporation. This paper discusses the method used for optimizing the detector's operating parameters at a temperature
of 8.5 K and bias voltage of 1.2 V. A process for characterizing detective quantum efficiency of BIB detectors is also presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献