全文获取类型
收费全文 | 61467篇 |
免费 | 11030篇 |
国内免费 | 15133篇 |
专业分类
测绘学 | 4325篇 |
大气科学 | 13460篇 |
地球物理 | 15171篇 |
地质学 | 30090篇 |
海洋学 | 7320篇 |
天文学 | 2906篇 |
综合类 | 6851篇 |
自然地理 | 7507篇 |
出版年
2024年 | 223篇 |
2023年 | 869篇 |
2022年 | 2493篇 |
2021年 | 2920篇 |
2020年 | 2478篇 |
2019年 | 2826篇 |
2018年 | 3263篇 |
2017年 | 2979篇 |
2016年 | 3422篇 |
2015年 | 2924篇 |
2014年 | 3547篇 |
2013年 | 3474篇 |
2012年 | 3371篇 |
2011年 | 3524篇 |
2010年 | 3689篇 |
2009年 | 3592篇 |
2008年 | 3274篇 |
2007年 | 3122篇 |
2006年 | 2539篇 |
2005年 | 2384篇 |
2004年 | 1854篇 |
2003年 | 1808篇 |
2002年 | 1781篇 |
2001年 | 1812篇 |
2000年 | 2122篇 |
1999年 | 2974篇 |
1998年 | 2487篇 |
1997年 | 2455篇 |
1996年 | 2222篇 |
1995年 | 1937篇 |
1994年 | 1731篇 |
1993年 | 1557篇 |
1992年 | 1267篇 |
1991年 | 953篇 |
1990年 | 679篇 |
1989年 | 680篇 |
1988年 | 594篇 |
1987年 | 370篇 |
1986年 | 317篇 |
1985年 | 213篇 |
1984年 | 198篇 |
1983年 | 155篇 |
1982年 | 139篇 |
1981年 | 110篇 |
1980年 | 80篇 |
1979年 | 61篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1975年 | 11篇 |
1958年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
JIANGDong WANGNai-bin YANGXIao-huan WANGJi-hua 《中国地理科学(英文版)》2003,13(1):62-65
Daily and ten-day Normalized Difference Vegetation Index(NDVI) of crops were retrieved from meteorological statellite NOAA AVHRR images ,The temporal variations of the NDVI were analyzed during the whole growing season,and thus the principle of the interaction between NDIV profile and the growing status of crops was discussed,As a case in point,the relationship between integral NDVI and winter wheat yield of Henan Province in 1999 had been analyzed.By putting integral NDVI values of 60 sample counties into the winter wheat yield-integral NDVI coordination,scattering map was plotted. It demonstrated that integral NDVI had a close relation with winter wheat yield.These relation could be described with linear,cubic polynomial ,and exponential regression,and the cubic polynomial regression was the best way,In general ,NDVI reflects growing status of green vegetation ,so crop monitoring and crop yield estimation could be realized by using remote sensing technique on the basis of time serial NDVI data together with agriculture calendars. 相似文献
82.
83.
YANGYong-liang SHITong-guang JLANGLU-guang LIYue 《中国地理科学(英文版)》2003,13(2):130-133
In recent years, many coal-producing countries have paid great attention to the land subsidence causedby coal cutting. In China, because of the dense population in coalfield areas, the land subsidence hazard is more seri-ous. After a brief analysis on the mechanism of land subsidence, this paper gives a comprehensive and systematical ac-count on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endan-gered land, buildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and socialenvironment. In order to lessen the hazard of land subsidence, preventive measures should be taken to reduce the col-lapse amount, such as extraction with stowing, banded mining system, succession and coordination mining system, orhigh-pressure mudflow between rock strata. Measures of reinforcing or moving certain buildings should also be taken toreduce the destructive degree. In order to harness the subsidence land and bring them under control for fanning, mea-sures should be taken such as filling with spoil or fine breeze, excavating the deeper and covering the shallower land. 相似文献
84.
茅排金矿床属中-低温硫化物金矿床,矿体的分布严格受断裂构造控制.通过应用不同的物探方法来寻找控矿断裂,从而达到间接地寻找矿体分布的目的,取得了较好的效果。 相似文献
85.
The actual penetration depth of the Shoemaker-Levy 9 fragments into the Jovian atmosphere is still an open question. From fundamental equations of meteoric physics with variable cross-section, a new analytic model of energy release of the fragments is presented. In use of reasonable parameters, a series of results are calculated for different initial mass of the fragments. The results show that the largest fragment explodes above pressure levels of 3 bars and does not penetrate into the H2O cloud layer of the Jovian atmosphere, and that airburst of smaller fragments occur even above the upper cloud layer. 相似文献
86.
为建立社会主义市场经济的地矿工作新秩序,本文对国有地矿企业的经营者(厂长、经理)这一特殊群体进行了分析。着重研究了新形势下企业经营者实行年薪制的问题。指出年薪制就是以企业一个生产经营周期为单位确定经营者的报酬,这一周期通常为一年。进而阐述了为什么要实行企业经营者年薪制;企业经营者的收入应与职工工资完全脱钩;采用基础报酬加效益报酬的方法确定收入等等。并构想了实行经营者年薪制所需要的外部环境:建立经营者人才市场、经营者要能进能出、实行任职资格制度、建立风险机制、按劳动力市场经济规律办事。 相似文献
87.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献
88.
A new species,Clathrocorys gracilis nov. spec. of Tripocyrtidae (Radiolarians: Nassellaria) from surface water in northern South China Sea, is described in this
paper. The new species has four radial beams arising from the cephalic base centre, each foot with cup-shaped structure and
ramified bar in the proximal section (near cephalic base), and each wing with a large mesh in the middle, a medium mesh and
a small mesh on each side respectively.
Project supported by the NSFC (No. 40276044) and the Chinese Academy of Sciences (No. KSCX2-SW-101B). 相似文献
89.
Hui-Rong Ji Qi-Jun Pu Yi-Hua Yan Yu-Ying Liu Zhi-Jun Chen Cheng-Ming Tan Cong-Ling Cheng De-Bang Lao Shu-Ke Li Zhi-Qiang Wang Min-Hong Yu Jian-Nong Liu Li-Kang Zhang Ji-Yong Gao National Astronomical Observatories Chinese Academy of Sciences Beijing Hebei Semiconductor Research Institute Shijiazhuang 《中国天文和天体物理学报》2005,5(4):433-441
An improved Solar Radio Spectrometer working at 1.10-2.06 GHz with much improved spectral and temporal resolution, has been accomplished by the National Astronomical Observatories and Hebei Semiconductor Research Institute, based on an old spectrometer at 1-2 GHz. The new spectrometer has a spectral resolution of 4 MHz and a temporal resolution of 5ms, with an instantaneous detectable range from 0.02 to 10 times of the quiet Sun flux. It can measure both left and right circular polarization with an accuracy of 10% in degree of polarization. Some results of preliminary observations that could not be recorded by the old spectrometer at 1-2 GHz are presented. 相似文献
90.
本文用完全动力学程式计算了Ⅰ型超新星爆发。这些模型是依据氦或碳和氧构成星核,部分地或全部地产生瞬时完成的核燃烧。计算中将动力学方程、核统计平衡、Rayleigh-Taylor不稳定性等物理过程联合起来求解。重点比较了Rayleigh-Taylor不稳定性的影响,现不能作出完全肯定的结论。计算结果列在表1、表2和图2—6中。 相似文献