全文获取类型
收费全文 | 14870篇 |
免费 | 1474篇 |
国内免费 | 5篇 |
专业分类
16349篇 |
出版年
2023年 | 53篇 |
2022年 | 196篇 |
2021年 | 353篇 |
2020年 | 193篇 |
2019年 | 246篇 |
2018年 | 309篇 |
2017年 | 254篇 |
2016年 | 445篇 |
2015年 | 772篇 |
2014年 | 791篇 |
2013年 | 903篇 |
2012年 | 1208篇 |
2011年 | 1164篇 |
2010年 | 717篇 |
2009年 | 620篇 |
2008年 | 883篇 |
2007年 | 863篇 |
2006年 | 835篇 |
2005年 | 744篇 |
2004年 | 707篇 |
2003年 | 685篇 |
2002年 | 599篇 |
2001年 | 124篇 |
2000年 | 74篇 |
1999年 | 142篇 |
1998年 | 209篇 |
1997年 | 120篇 |
1996年 | 120篇 |
1995年 | 111篇 |
1994年 | 100篇 |
1993年 | 117篇 |
1992年 | 104篇 |
1991年 | 80篇 |
1990年 | 82篇 |
1989年 | 67篇 |
1988年 | 74篇 |
1987年 | 55篇 |
1986年 | 56篇 |
1985年 | 58篇 |
1984年 | 68篇 |
1983年 | 78篇 |
1982年 | 70篇 |
1981年 | 65篇 |
1980年 | 67篇 |
1979年 | 44篇 |
1978年 | 46篇 |
1976年 | 44篇 |
1975年 | 43篇 |
1974年 | 56篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Historical comparison of oracles in west Africa, mainly during the nineteenth century, shows how divination practices may alter. In the cases explored here, reputation, range of users, economic growth, and political influence interacted as these oracles developed; some at sites with internal and overseas trade access became complex, large-scale operations. But by about 1900, colonialists felt threatened by their secular and their spiritual power and smashed them physically, though not spiritually. Contextualized comparison shows that the many people who were involved as oracle organizers and supplicants must have had different motivations and interests. Some methodological implications of the findings are considered. As in many powerful secular organizations, access to insider knowledge was blocked, but oracular reputation was important, and the oracles had competitors. Success derived partly from collecting intelligence, with simultaneous advertisement that emphasized the mysterious power of their operations. 相似文献
32.
33.
Expression of an ABA-induced gene of tomato in transgenic tobacco during periods of water deficit 总被引:9,自引:1,他引:8
The gene le25 is an abscisic acid (ABA)-induced gene of tomatowhich is expressed both in wilted vegetative organs and developingseeds. Spatial and temporal expression was analysed in tobaccoplants transformed with a chimeric gene in which 5'-upstreamDNA sequences of le25 were fused to the E. coli uidA gene, whichencodes ß-glucuronidase (GUS). Histochemical stainingrevealed that GUS was expressed in all tissues of vegetativeorgans in response to water deficit. Exogenous ABA induced expressionto a lesser extent, even though ABA content was the same asdroughtstressed leaves, indicating a difference in responseto endogenous ABA compared to exogenous ABA. Water-deficit-inducedGUS expression in floral tissues was examined in pre-anthesisfloral buds from four different stages (IIV; 11, 16,33, 49 mm bud length, respectively). While non-stressed floralorgans showed no GUS activity except in pollen at stages IIIand IV, GUS activity was water-deficit-induced in sepals ofall stages, petals of stage II, and stigmas of stage II andIII. In seeds, GUS activity was detected in both the embryoand endosperm at 15 d post-anthesis, which coincided with alarge increase in the concentration of ABA in the seed. In transgenicplants, the le25 5'-flanking DNA drove expression of GUS duringwater deficit in two modes: non-tissue-specific expression invegetative organs, and tissue-specific expression in reproductiveorgans. The location of GUS activity indicated that ABA concentrationis elevated throughout the tissues of the leaf during periodsof water deficit. Key words: Tomato, ABA, drought stress, lea gene, water deficit 相似文献
34.
35.
36.
Production of Viscous Dextran-Containing Whey-Sucrose Broths by Leuconostoc mesenteroides ATCC 14935 下载免费PDF全文
Viscous broths were produced by growing Leuconostoc mesenteroides on a medium containing whey supplemented with sucrose. When combined with similarly produced xanthan-containing broths, a synergistic increase in viscosity was observed. 相似文献
37.
38.
39.
40.