全文获取类型
收费全文 | 1710350篇 |
免费 | 158660篇 |
国内免费 | 8475篇 |
专业分类
1877485篇 |
出版年
2021年 | 22896篇 |
2020年 | 15798篇 |
2019年 | 20037篇 |
2018年 | 22757篇 |
2017年 | 20664篇 |
2016年 | 32845篇 |
2015年 | 48327篇 |
2014年 | 57450篇 |
2013年 | 83871篇 |
2012年 | 55380篇 |
2011年 | 45619篇 |
2010年 | 51174篇 |
2009年 | 50777篇 |
2008年 | 39491篇 |
2007年 | 37554篇 |
2006年 | 40239篇 |
2005年 | 40284篇 |
2004年 | 39031篇 |
2003年 | 36051篇 |
2002年 | 33640篇 |
2001年 | 52963篇 |
2000年 | 50745篇 |
1999年 | 46053篇 |
1998年 | 28229篇 |
1997年 | 28209篇 |
1996年 | 27292篇 |
1995年 | 25382篇 |
1994年 | 25037篇 |
1993年 | 24044篇 |
1992年 | 38494篇 |
1991年 | 36447篇 |
1990年 | 34940篇 |
1989年 | 35340篇 |
1988年 | 32494篇 |
1987年 | 30510篇 |
1986年 | 28864篇 |
1985年 | 30278篇 |
1984年 | 28280篇 |
1983年 | 24492篇 |
1982年 | 23195篇 |
1981年 | 22043篇 |
1980年 | 20532篇 |
1979年 | 23829篇 |
1978年 | 21287篇 |
1977年 | 20137篇 |
1976年 | 18862篇 |
1975年 | 18938篇 |
1974年 | 19720篇 |
1973年 | 19977篇 |
1972年 | 17149篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
Volatiles from the epicuticular wax of watercress were collected by ether washing and examined using gas chromatographic and mass spectrometric analysi 相似文献
922.
923.
R. Balabsubramanian G. Raghunathan 《International journal of biological macromolecules》1982,4(6):377-378
The distribution of regular secondary structures, viz. α-helices and β-strands, along the length of over 70 properties whose secondary structural details have been reported, has been analysed. The occurrence of these regular structures tends to be a maximum at the N- and C-termini. Our analysis suggests that both these free ends could possibly serve as nucleating centers for secondary structures and could play an important role in the folding of proteins. 相似文献
924.
Nabiel A.M. Saleh Zeinab A.R. El-karemy Ragaa M.A. Mansour Abdel-Aziz A. Fayed 《Phytochemistry》1983,22(11):2501-2505
The flavonoids of five Geranium, fourteen Erodium and four Monsonia species were studied. Quercetin was the most common aglycone with lesse 相似文献
925.
The 5'-terminal 597 base-pairs (bp) of the Sprague-Dawley rat 18S ribosomal RNA gee and 10 bp of the adjoining transcribed spacer have been sequenced. Previously sequenced 10 large oligonucleotides of rat 18S RNA were located in this region. This mammalian sequence has been compared with the known sequences of yeast and frog 18S rDNA's. The analysis indicates that 534 bp of the 597 bp (89%) are conserved between rat and frog sequences but only 75% of the nucleotides are conserved between rat and yeast in this region. Two large and two small sections have been identified where insertions have been introduced during evolution. Of these 58 bp long inserted sections of the rat rDNA sequence, 50 bp (86%) were G-C base-pairs. 相似文献
926.
927.
928.
929.
930.