全文获取类型
收费全文 | 146658篇 |
免费 | 4966篇 |
国内免费 | 849篇 |
出版年
2023年 | 163篇 |
2022年 | 475篇 |
2021年 | 1002篇 |
2020年 | 556篇 |
2019年 | 742篇 |
2018年 | 12647篇 |
2017年 | 11267篇 |
2016年 | 8812篇 |
2015年 | 3144篇 |
2014年 | 3137篇 |
2013年 | 3641篇 |
2012年 | 8414篇 |
2011年 | 16588篇 |
2010年 | 14294篇 |
2009年 | 10294篇 |
2008年 | 12881篇 |
2007年 | 14177篇 |
2006年 | 3075篇 |
2005年 | 3051篇 |
2004年 | 3435篇 |
2003年 | 3212篇 |
2002年 | 2657篇 |
2001年 | 1898篇 |
2000年 | 1694篇 |
1999年 | 1241篇 |
1998年 | 535篇 |
1997年 | 489篇 |
1996年 | 410篇 |
1995年 | 393篇 |
1994年 | 311篇 |
1993年 | 326篇 |
1992年 | 658篇 |
1991年 | 552篇 |
1990年 | 481篇 |
1989年 | 486篇 |
1988年 | 421篇 |
1987年 | 403篇 |
1986年 | 318篇 |
1985年 | 329篇 |
1984年 | 277篇 |
1983年 | 241篇 |
1982年 | 191篇 |
1981年 | 162篇 |
1979年 | 220篇 |
1978年 | 197篇 |
1977年 | 179篇 |
1976年 | 170篇 |
1974年 | 196篇 |
1972年 | 401篇 |
1971年 | 397篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
291.
Supernatant fluids of mitogen-activated human tonsil lymphocytes contain large amounts of a factor toxic to mouse L cells. This substance, with a m.w. of 80,000 +/- 5,000 daltons, is called alpha-lymphotoxin (alpha-LT), to differentiate it from another toxin elaborated by mitogen activated human blood lymphocytes, called beta-lymphotoxin (beta-LT), which differs from alpha-LT in size (45,000 +/- 5,000 daltons), antigenicity, and stability. Further purification of alpha-LT by sequential phosphocellulose and DEAE-cellulose chromatography and polyacrylamide gel electrophoresis (PAGE) identifies a series of cytotoxins differing in ion exchange characteristics and electrophoretic mobilities. The three PAGE fractions (PAGE Ia, Ib and II), recovered in 2, 4.6, and 21% yield from the starting serum-free culture supernatant, represent purifications of 24-, 24- and 1851-fold, respectively. Each cytotoxic fraction has a ribonuclease activity. Comparison of RNase and mouse L cell cytotoxic activities of the three alpha-LT fractions shows that both activities for all three fractions have a similar temperature stability pattern and that both are similarly inhibited by DNA, single strand forms better than double strands, by glycerol in 5 to 20% concentration, and by protein denaturing reagents. These observations suggest, but do not prove, that mouse L cell toxicity and RNase activity are mediated by the same substance, which appears to occur in multiple or isozymic forms. 相似文献
292.
In this paper we propose that the internal bracketing of a word with more than two morphemes is reflected in the phonetic implementation. We hypothesize that embedded forms show more phonetic reduction than forms at higher structural levels (‘Embedded Reduction Hypothesis’). This paper tests the prediction of the Embedded Reduction Hypothesis with triconstituent compounds. The analysis of the durational properties of almost 500 compound tokens shows that there is a lengthening effect on the non-embedded constituent, and a shortening effect on the adjacent embedded constituent. Yet, this predicted effect of embedding interacts with other lexical factors, above all the bigram frequency of the embedded compound. At a theoretical level, these effects mean that the durational properties of the cross-boundary constituents are indicative of the hierarchical structure and of the strength of the internal boundary of triconstituent compounds. Hence, morphological structure is reflected in the speech signal. 相似文献
293.
294.
295.
296.
Abstract Morphological features of mature larvae of Petelia rivulosa (Butler), Exangerona prattiaria (Leech) and Culcula panterinaria (Bremer & Grey) of Ennominae are described and illustrated. All specimens examined are deposited in the Insect Collection of Department of Forest Resources Protection, Kangwon National University, Korea. 相似文献
297.
298.
299.
Eric Delson 《Journal of Mammalian Evolution》2007,14(3):198-199
300.