全文获取类型
收费全文 | 19225篇 |
免费 | 1441篇 |
国内免费 | 1367篇 |
出版年
2024年 | 30篇 |
2023年 | 236篇 |
2022年 | 489篇 |
2021年 | 931篇 |
2020年 | 572篇 |
2019年 | 818篇 |
2018年 | 809篇 |
2017年 | 575篇 |
2016年 | 849篇 |
2015年 | 1130篇 |
2014年 | 1379篇 |
2013年 | 1485篇 |
2012年 | 1722篇 |
2011年 | 1572篇 |
2010年 | 1010篇 |
2009年 | 970篇 |
2008年 | 1093篇 |
2007年 | 1016篇 |
2006年 | 821篇 |
2005年 | 698篇 |
2004年 | 545篇 |
2003年 | 531篇 |
2002年 | 447篇 |
2001年 | 350篇 |
2000年 | 301篇 |
1999年 | 292篇 |
1998年 | 166篇 |
1997年 | 159篇 |
1996年 | 156篇 |
1995年 | 119篇 |
1994年 | 84篇 |
1993年 | 70篇 |
1992年 | 110篇 |
1991年 | 82篇 |
1990年 | 68篇 |
1989年 | 52篇 |
1988年 | 43篇 |
1987年 | 44篇 |
1986年 | 38篇 |
1985年 | 51篇 |
1984年 | 8篇 |
1983年 | 21篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1969年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Jung Dong-Hyun Seo Dong-Ho Kim Ga-Young Nam Young-Do Song Eun-Ji Yoon Shawn Park Cheon-Seok 《Applied microbiology and biotechnology》2018,102(11):4927-4936
Applied Microbiology and Biotechnology - Resistant starch (RS) in the diet reaches the large intestine without degradation, where it is decomposed by the commensal microbiota. The fermentation of... 相似文献
192.
193.
194.
The planthopper superfamily Fulgoroidea (Insecta: Hemiptera) is one of the most dominant groups of phytophagous insects. It comprises about 20 families, containing a total of 9000 species worldwide. Despite several recent studies, the phylogeny of Fulgoroidea is not yet satisfactorily resolved and the phylogenetic positions of several key families, especially Cixiidae, Delphacidae, Tettigometridae, Nogodinidae, Acanaloniidae and Issidae, are contentious. Here, we expand upon recent phylogenetic work using additional nuclear (18S and 28S) and novel mitochondrial (16S and cytb) markers. Maximum likelihood and Bayesian analyses yielded robust phylogenetic trees. In these topologies, a group containing Cixiidae and Delphacidae is recovered as the sister group to the remaining taxa. Tettigometridae is placed in a more nested position and is grouped with Caliscelidae. Sister relationships are found between Flatidae and Ricaniidae, and between Dictyopharidae and Fulgoridae. Nogodinidae and Issidae are confirmed to be non-monophyletic families. For major nodes of interest, divergence date estimates are generally older than those from the fossil record. 相似文献
195.
Assassin bugs are one of the most successful clades of predatory animals based on their species numbers (∼6,800 spp.) and wide distribution in terrestrial ecosystems. Various novel prey capture strategies and remarkable prey specializations contribute to their appeal as a model to study evolutionary pathways involved in predation. Here, we reconstruct the most comprehensive reduviid phylogeny (178 taxa, 18 subfamilies) to date based on molecular data (5 markers). This phylogeny tests current hypotheses on reduviid relationships emphasizing the polyphyletic Reduviinae and the blood-feeding, disease-vectoring Triatominae, and allows us, for the first time in assassin bugs, to reconstruct ancestral states of prey associations and microhabitats. Using a fossil-calibrated molecular tree, we estimated divergence times for key events in the evolutionary history of Reduviidae. Our results indicate that the polyphyletic Reduviinae fall into 11–14 separate clades. Triatominae are paraphyletic with respect to the reduviine genus Opisthacidius in the maximum likelihood analyses; this result is in contrast to prior hypotheses that found Triatominae to be monophyletic or polyphyletic and may be due to the more comprehensive taxon and character sampling in this study. The evolution of blood-feeding may thus have occurred once or twice independently among predatory assassin bugs. All prey specialists evolved from generalist ancestors, with multiple evolutionary origins of termite and ant specializations. A bark-associated life style on tree trunks is ancestral for most of the lineages of Higher Reduviidae; living on foliage has evolved at least six times independently. Reduviidae originated in the Middle Jurassic (178 Ma), but significant lineage diversification only began in the Late Cretaceous (97 Ma). The integration of molecular phylogenetics with fossil and life history data as presented in this paper provides insights into the evolutionary history of reduviids and clears the way for in-depth evolutionary hypothesis testing in one of the most speciose clades of predators. 相似文献
196.
197.
198.
Shan Gao Michaela C. Strüder‐Kypke Khaled A. S. Al‐Rasheid Xiaofeng Lin Weibo Song 《Zoologica scripta》2010,39(3):305-313
Gao, S., Strüder‐Kypke, M.C., Al‐Rasheid, K.A.S., Lin, X. & Song, W. (2010). Molecular phylogeny of three ambiguous ciliate genera: Kentrophoros, Trachelolophos and Trachelotractus (Alveolata, Ciliophora).—Zoologica Scripta, 39, 305–313. Very few molecular studies on the phylogeny of the karyorelictean ciliates have been carried out because data of this highly ambiguous group are extremely scarce. In the present study, we sequenced the small subunit ribosomal RNA genes of three morphospecies representing two karyorelictean genera, Kentrophoros, Trachelolophos, and one haptorid, Trachelotractus, isolated from the South and East China Seas. The phylogenetic trees constructed using Bayesian inference, maximum likelihood, maximum parsimony and neighbor‐joining methods yielded essentially similar topologies. The class Karyorelictea is depicted as a monophyletic clade, closely related to the class Heterotrichea. The generic concept of the family Trachelocercidae is confirmed by the clustering of Trachelolophos and Tracheloraphis with high bootstrap support; nevertheless, the order Loxodida is paraphyletic. The transfer of the morphotype Trachelocerca entzi Kahl, 1927 to the class Litostomatea and into the new haptorid genus Trachelotractus, as suggested by previous researchers based on morphological studies, is consistently supported by our molecular analyses. In addition, the poorly known species Parduczia orbis occupies a well‐supported position basal to the Geleia clade, justifying the separation of these genera from one another. 相似文献
199.
Zhichao Xu Ranran Gao Xiangdong Pu Rong Xu Jiyong Wang Sihao Zheng Yan Zeng Jun Chen Chunnian He Jingyuan Song 《基因组蛋白质组与生物信息学报(英文版)》2020,18(3):230-240
Scutellaria baicalensis (S. baicalensis) and Scutellaria barbata (S. barbata) are common medicinal plants of the Lamiaceae family. Both produce specific flavonoid compounds, including baicalein, scutellarein, norwogonin, and wogonin, as well as their glycosides, which exhibit antioxidant and antitumor activities. Here, we report chromosome-level genome assemblies of S. baicalensis and S. barbata with quantitative chromosomal variation (2n = 18 and 2n = 26, respectively). The divergence of S. baicalensis and S. barbata occurred far earlier than previously reported, and a whole-genome duplication (WGD) event was identified. The insertion of long terminal repeat elements after speciation might be responsible for the observed chromosomal expansion and rearrangement. Comparative genome analysis of the congeneric species revealed the species-specific evolution of chrysin and apigenin biosynthetic genes, such as the S. baicalensis-specific tandem duplication of genes encoding phenylalanine ammonia lyase and chalcone synthase, and the S. barbata-specific duplication of genes encoding 4-CoA ligase. In addition, the paralogous duplication, colinearity, and expression diversity of CYP82D subfamily members revealed the functional divergence of genes encoding flavone hydroxylase between S. baicalensis and S. barbata. Analyzing these Scutellaria genomes reveals the common and species-specific evolution of flavone biosynthetic genes. Thus, these findings would facilitate the development of molecular breeding and studies of biosynthesis and regulation of bioactive compounds. 相似文献
200.