全文获取类型
收费全文 | 36130篇 |
免费 | 1683篇 |
国内免费 | 11篇 |
出版年
2023年 | 207篇 |
2021年 | 373篇 |
2020年 | 240篇 |
2019年 | 312篇 |
2018年 | 393篇 |
2017年 | 362篇 |
2016年 | 582篇 |
2015年 | 1005篇 |
2014年 | 1148篇 |
2013年 | 1946篇 |
2012年 | 1653篇 |
2011年 | 1563篇 |
2010年 | 1090篇 |
2009年 | 1167篇 |
2008年 | 1297篇 |
2007年 | 1232篇 |
2006年 | 1201篇 |
2005年 | 1188篇 |
2004年 | 1079篇 |
2003年 | 923篇 |
2002年 | 1014篇 |
2001年 | 346篇 |
2000年 | 305篇 |
1999年 | 348篇 |
1998年 | 365篇 |
1997年 | 285篇 |
1996年 | 361篇 |
1995年 | 344篇 |
1994年 | 329篇 |
1993年 | 432篇 |
1992年 | 390篇 |
1991年 | 360篇 |
1990年 | 355篇 |
1989年 | 528篇 |
1988年 | 488篇 |
1987年 | 556篇 |
1986年 | 492篇 |
1985年 | 509篇 |
1984年 | 460篇 |
1983年 | 361篇 |
1982年 | 436篇 |
1981年 | 435篇 |
1980年 | 410篇 |
1979年 | 395篇 |
1978年 | 437篇 |
1977年 | 479篇 |
1976年 | 475篇 |
1975年 | 494篇 |
1974年 | 355篇 |
1973年 | 229篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
41.
42.
Dr. Ferd. Schur 《Plant Systematics and Evolution》1857,7(46):367-368
Ohne Zusammenfassung 相似文献
43.
Dr. H. Schw 《Plant Systematics and Evolution》1851,1(44):359-359
Ohne Zusammenfassung 相似文献
44.
Dr. Hohenacker 《Plant Systematics and Evolution》1864,14(4):119-120
Ohne Zusammenfassung 相似文献
45.
Jan Batelka Jakub Prokop Hans Pohl Ming Bai Weiwei Zhang Rolf G. Beutel 《Systematic Entomology》2019,44(2):396-407
Extremely miniaturized longipedes insects (body length c. 0.3 mm) embedded in two pieces of Cretaceous amber from Myanmar are described and interpreted. Using inverted fluorescence and light microscopy for detailed analysis of microstructures, the inclusions were identified as primary larvae of the beetle family Ripiphoridae, subfamily Ripidiinae. While the structure of thoracic and abdominal segments including appendages corresponds well with the groundplan known in recent members of Ripidiinae, a curved prosternal ridge with prominent spines (each c. 5 μm), the reduced condition of stemmata and antennae and the lack of sharp mandibles are unique features within the entire family, apparently apomorphies of the longipedes larvae. A sinuate prosternal edge with a dense row of spines (prosternoctenidium) might be homologous with ‘head ctenidia’ in some previously described miniaturized conicocephalate larvae, but further investigation is needed. The morphological differences between the head of longipedes larvae and extant Ripidiinae are interpreted as adaptations to different groups of hosts and life strategies. Palaeoethology of the longipedes larvae is briefly discussed. In addition, the systematic placement of conicocephalate larvae from Canadian, Myanmar and Russian Cretaceous ambers, already interpreted by various authors as primary instars within Coleopterida (assigned to either Strepsiptera or to the coleopteran Tenebrionoidea: Ripiphoridae), is discussed. 相似文献
46.
47.
48.
By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling. 相似文献
49.
50.