全文获取类型
收费全文 | 6749篇 |
免费 | 1478篇 |
国内免费 | 2256篇 |
专业分类
测绘学 | 962篇 |
大气科学 | 1031篇 |
地球物理 | 1330篇 |
地质学 | 4114篇 |
海洋学 | 1247篇 |
天文学 | 215篇 |
综合类 | 635篇 |
自然地理 | 949篇 |
出版年
2024年 | 61篇 |
2023年 | 171篇 |
2022年 | 324篇 |
2021年 | 433篇 |
2020年 | 353篇 |
2019年 | 402篇 |
2018年 | 435篇 |
2017年 | 399篇 |
2016年 | 399篇 |
2015年 | 374篇 |
2014年 | 488篇 |
2013年 | 514篇 |
2012年 | 526篇 |
2011年 | 511篇 |
2010年 | 507篇 |
2009年 | 506篇 |
2008年 | 509篇 |
2007年 | 490篇 |
2006年 | 487篇 |
2005年 | 398篇 |
2004年 | 278篇 |
2003年 | 246篇 |
2002年 | 206篇 |
2001年 | 203篇 |
2000年 | 213篇 |
1999年 | 191篇 |
1998年 | 118篇 |
1997年 | 108篇 |
1996年 | 96篇 |
1995年 | 83篇 |
1994年 | 95篇 |
1993年 | 72篇 |
1992年 | 58篇 |
1991年 | 43篇 |
1990年 | 30篇 |
1989年 | 16篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1976年 | 7篇 |
1974年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
2.
3.
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
4.
从ROSAT巡天和定点观测结果的对比出发,发现了几个低银纬的巡天源表中的X射线源在定点观测中没有出现.本文计算了在这些位置的定点观测中出现点源的流强上限,发现比巡天源表中这些源的流强值低很多,这表明它们的流强变化很大,可能是X射线双星系统中的一类———X射线暂现源. 相似文献
5.
6.
The UV spectra of mixture solutions consisting of tyrosine,tryptophane,phenylalanine,cystine,histidineand 3,4-dihydroxyl phenylalanine have been measured.The numbers,identities and concentrations of theamino acids in the mixtures have been determined successfully using target factor analysis.The effectsof the wavelength range and the selected sampling interval on the results are discussed.Twenty-fivesynthetic mixture samples have been analysed successfully.The average recoveries are 98·9 for Tyr,96·5for Trp,105·6 for Phe,98·1 for Cys,98·9 for His and 106·4 for Di-phe.The results obtained are ingood agreement with those obtained by the Kalman filter method. 相似文献
7.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
8.
9.
The new polyenzyme method for making gravy from Harengula 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℃ , alkaline and neutral protease concentration of 1.5% respectively, hydrolysis time of 120 min, andflavorase 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 respectively1.9 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 from Harengula zunasi offal. In addition, in inorganic elements, the phosphorus content is the highest. 相似文献
10.
HUANGGuoqiang DONGShuanglin WANGFang 《中国海洋大学学报(英文版)》2005,4(1):56-60
Attractabilities of different diets and dietary selectivity of Chinese shrimp, Fenneropenaeus chinensis were studied through behavior observation and feeding experiment, respectively. The five diets used in the experiment are: Fish Flesh (FF), Shrimp Flesh (SF), Clam Foot (CF), Polychaete Worm (PW), and Formulated Diet (FD). No significant differences of attractability exist between any two different diets when every two natural diets or all five diets are provided simultaneously. On the other hand, significant differences of attractability exist between FD and every single natural diet when they are provided simultaneously. Results of behavioral observation indicate that natural diets are more attractive than FD. In feeding experiment, Chinese shrimp has distinct selectivity on different diets. It positively selects CF and PW, negatively selects FF and SF, and excludes FD absolutely. The results of the present studies indicate that the dietary selectivity of shrimp was based not only on the attractabilities of the diets, but also on the responses such as growth and food conversion. 相似文献