全文获取类型
收费全文 | 49214篇 |
免费 | 9023篇 |
国内免费 | 12319篇 |
专业分类
测绘学 | 3996篇 |
大气科学 | 10163篇 |
地球物理 | 12023篇 |
地质学 | 24493篇 |
海洋学 | 5990篇 |
天文学 | 2062篇 |
综合类 | 5462篇 |
自然地理 | 6367篇 |
出版年
2024年 | 199篇 |
2023年 | 737篇 |
2022年 | 2213篇 |
2021年 | 2627篇 |
2020年 | 2160篇 |
2019年 | 2469篇 |
2018年 | 2841篇 |
2017年 | 2522篇 |
2016年 | 2842篇 |
2015年 | 2523篇 |
2014年 | 2975篇 |
2013年 | 2997篇 |
2012年 | 2878篇 |
2011年 | 2983篇 |
2010年 | 3101篇 |
2009年 | 2892篇 |
2008年 | 2688篇 |
2007年 | 2536篇 |
2006年 | 2026篇 |
2005年 | 1904篇 |
2004年 | 1456篇 |
2003年 | 1412篇 |
2002年 | 1323篇 |
2001年 | 1431篇 |
2000年 | 1602篇 |
1999年 | 2170篇 |
1998年 | 1830篇 |
1997年 | 1712篇 |
1996年 | 1610篇 |
1995年 | 1350篇 |
1994年 | 1234篇 |
1993年 | 1094篇 |
1992年 | 899篇 |
1991年 | 677篇 |
1990年 | 521篇 |
1989年 | 478篇 |
1988年 | 402篇 |
1987年 | 245篇 |
1986年 | 220篇 |
1985年 | 148篇 |
1984年 | 135篇 |
1983年 | 109篇 |
1982年 | 96篇 |
1981年 | 70篇 |
1980年 | 45篇 |
1979年 | 47篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1975年 | 10篇 |
1958年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
网络经济已成为新的社会生产力的代表。广西地质矿产勘查开发局应该利用其行业和地域方面的固有优势,积极参与网络经济,以期打开矿业市场。文章提出了建立矿业网站的设想和框架。 相似文献
142.
143.
利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响,其数值结果包括弹性解和粘弹性解。结果表明,震后位移场的分布特征不仅与粘弹性层的流变特性有关,还与弹性层介质的剪切模量以及断层的同震错动有关。 相似文献
144.
INTRODUCTIONTheSubeiShoalandtheChangjiangRiverestuarineareainthewestoftheHuanghaiandEastChinaSeasisoneofthemarginalseasintheworld ,wheresuspendedmatterisextremelyhigh .Here ,notonlyistheretheTaiwanWarmCurrentoneoftheKuroshio’sbranchesintheEastChinaSea,butalsotheHuanghaiCoastalCurrent,andChangjiangDilutedWater.Sothestrongmixingbetweenthecoastalandoffshorewaterscomplicatessuspendedmatterdistributioninthisarea.HowthesuspendedmatterdischargedfromtheChangjiangRiverandtheabandonedHuan… 相似文献
145.
Dong-Mei Qin Ping Guo Zhan-Yi Hu Yong-Heng ZhaoNational Laboratory of Pattern Recognition Laboratory Institute of Automation Chinese Academy of Sciences Beijing dmqin@nlpr.ia.ac.cnDepartment of Computer Sciences Beijing Normal University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(3)
For LAMOST, the largest sky survey program in China, the solution of the problem of automatic discrimination of stars from galaxies by spectra has shown that the results of the PSF test can be significantly refined. However, the problem is made worse when the redshifts of galaxies are not available. We present a new automatic method of star/(normal) galaxy separation, which is based on Statistical Mixture Modeling with Radial Basis Function Neural Networks (SMM-RBFNN). This work is a continuation of our previous one, where active and non-active celestial objects were successfully segregated. By combining the method in this paper and the previous one, stars can now be effectively separated from galaxies and AGNs by their spectra-a major goal of LAMOST, and an indispensable step in any automatic spectrum classification system. In our work, the training set includes standard stellar spectra from Jacoby's spectrum library and simulated galaxy spectra of EO, SO, Sa, Sb types with redshift ranging from 0 to 1 相似文献
146.
Qing-Yao Liu Yu-Lan Yang National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 《中国天文和天体物理学报》2006,6(3):331-337
The variation in the orbital period of the W UMa type contact binary V502 Oph is analyzed. The orbital period exhibits a wavelike variation with a periodicity of 23.0 years and an amplitude of △P = 1.24×10~(-6) days superimposed on secular decrease of dP/dt = 1.68×10-7 day per year. The long-term decrease may be accompanied by the contraction of the secondary at a rate of 83 m per year and a mass transfer rate from the primary to the secondary of 4.28×10~8 M per year. The short-term oscillation may be explained by the presence of a third component. Orbital elements of the third body and its possible mass are presented. 相似文献
147.
Biogenic silicate accumulation in sediments, Jiaozhou Bay 总被引:1,自引:0,他引:1
1 INTRODUCTION Silicate, or silicic acid (H4SiO4), is a very im- portant nutrient in the ocean. Unlike other major nu- trients such as phosphate and nitrate or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical req… 相似文献
148.
The new polyenzyme method for making gravy fromHarengula zunasi offal involves protein enzymolysis with flavorase after proper alkaline and neutral protease levels were established by orthogonal
trials to select the best hydrolytic conditions for processing offal with alkaline and neutral protease. The conditions for
the polyenzyme method were pH of 7.0, temperature of 50°C, alkaline and neutral protease concentration of 1.5% respectively,
hydrolysis time of 120 min, and flavorase concentration of 2.0%, for 60 min. The new gravy-making technology yields a nutritious
and delicious gravy containing 40.3% of total essential amino acids, with delicious amino acids Glu, Asp, Gly, Ala, Pro and
Ser comprising 49.5%, total and amino nitrogen being respectively 1.9 and 1.1 g/100 g (amino acid nitrogen being 61.0% of
total nitrogen), The polyenzyme method was used to make 14.8% protein gravy fromHarengula zunasi offal. In addition, inorganic elements, the phosphorus content is the highest.
This project was aided financially by the Guangdong Science and Technology Office (No. 2KM06002S). 相似文献
149.
广西中三叠统浊流流向及坡向 总被引:1,自引:0,他引:1
通过对广西中三叠统浊积岩系中溢堤流沉积的识别,结合同一鲍马层序Tc段斜层理倾向与其底部槽模走向不一致的分析,以及横向冲刷模、U形障碍冲刷痕等冲蚀构造、大型滑动模等压刻构造的认识,筛选出宽阔水道充填沉积、扇状体及分支水道沉积中底模构造的指向数据,来指示浊流主体流向,并区分出溢堤流流向。从而确定了本区中三叠世时的浊流主体流向为NW向,平均为300°。根据滑塌沉积中滑塌包卷层轴面、滑塌面的测定,确定凤山县金牙处的古坡向平均为322°,与浊流主体流向基本一致。还认为中三叠世时右江盆地沉积物源来自桂东和桂东南蚀源区,海水由其南的越南境内进入。 相似文献
150.
本文引用了一种新的系统分析方法(层次分析法)对地下水库人工回灌的复杂系统进行了择优排序研究,取得了满意的结果。实践证明,层次分析法对于地下水库人工回灌方案的择优是一种简捷实用的决策方法。 相似文献