全文获取类型
收费全文 | 5119篇 |
免费 | 587篇 |
国内免费 | 582篇 |
出版年
2024年 | 15篇 |
2023年 | 102篇 |
2022年 | 122篇 |
2021年 | 166篇 |
2020年 | 188篇 |
2019年 | 197篇 |
2018年 | 194篇 |
2017年 | 217篇 |
2016年 | 197篇 |
2015年 | 210篇 |
2014年 | 229篇 |
2013年 | 359篇 |
2012年 | 179篇 |
2011年 | 223篇 |
2010年 | 198篇 |
2009年 | 263篇 |
2008年 | 266篇 |
2007年 | 292篇 |
2006年 | 285篇 |
2005年 | 239篇 |
2004年 | 226篇 |
2003年 | 225篇 |
2002年 | 193篇 |
2001年 | 159篇 |
2000年 | 144篇 |
1999年 | 134篇 |
1998年 | 130篇 |
1997年 | 108篇 |
1996年 | 104篇 |
1995年 | 84篇 |
1994年 | 82篇 |
1993年 | 60篇 |
1992年 | 59篇 |
1991年 | 58篇 |
1990年 | 53篇 |
1989年 | 39篇 |
1988年 | 29篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 37篇 |
1984年 | 45篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 2篇 |
排序方式: 共有6288条查询结果,搜索用时 156 毫秒
161.
162.
163.
Steven P. Harvey Jonah Messinger Kai Zhu Joseph M. Luther Joseph J. Berry 《Liver Transplantation》2020,10(26)
Time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS), a powerful analytical technique sensitive to all components of perovskite solar cell (PSC) materials, can differentiate between the various organic species within a PSC absorber or a complete device stack. The ability to probe chemical gradients through the depth of a device (both organic and inorganic), with down to 100 nm lateral resolution, can lead to unique insights into the relationships between chemistry in the absorber bulk, at grain boundaries, and at interfaces as well as how they relate to changes in performance and/or stability. In this review, the technique is described; then, from the literature, several examples of how TOF‐SIMS have been used to provide unique insight into PSC absorbers and devices are covered. Finally, the common artifacts that can be introduced if the data are improperly collected, as well as methods to mitigate these artifacts are discussed. 相似文献
164.
Dean Frawley Claudio Greco Berl Oakley Mohamed M. Alhussain Alastair B. Fleming Nancy P. Keller
zgür Bayram 《Cellular microbiology》2020,22(6)
For eukaryotes like fungi to regulate biological responses to environmental stimuli, various signalling cascades are utilized, like the highly conserved mitogen‐activated protein kinase (MAPK) pathways. In the model fungus Aspergillus nidulans, a MAPK pathway known as the pheromone module regulates development and the production of secondary metabolites (SMs). This pathway consists five proteins, the three kinases SteC, MkkB and MpkB, the adaptor SteD and the scaffold HamE. In this study, homologs of these five pheromone module proteins have been identified in the plant and human pathogenic fungus Aspergillus flavus. We have shown that a tetrameric complex consisting of the three kinases and the SteD adaptor is assembled in this species. It was observed that this complex assembles in the cytoplasm and that MpkB translocates into the nucleus. Deletion of steC, mkkB, mpkB or steD results in abolishment of both asexual sporulation and sclerotia production. This complex is required for the positive regulation of aflatoxin production and negative regulation of various SMs, including leporin B and cyclopiazonic acid (CPA), likely via MpkB interactions in the nucleus. These data highlight the conservation of the pheromone module in Aspergillus species, signifying the importance of this pathway in regulating fungal development and secondary metabolism. 相似文献
165.
166.
167.
Alexandre Fadel Kevin Lepot Nicolas Nuns Sylvie Regnier Armelle Riboulleau 《Geobiology》2020,18(4):445-461
Organic microfossils preserved in three dimensions in transparent mineral matrices such as cherts/quartzites, phosphates, or carbonates are best studied in petrographic thin sections. Moreover, microscale mass spectrometry techniques commonly require flat, polished surfaces to minimize analytical bias. However, contamination by epoxy resin in traditional petrographic sections is problematic for the geochemical study of the kerogen in these microfossils and more generally for the in situ analysis of fossil organic matter. Here, we show that epoxy contamination has a molecular signature that is difficult to distinguish from kerogen with time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). This contamination appears pervasive in organic microstructures embedded in micro‐ to nano‐crystalline carbonate. To solve this problem, a new semi‐thin section preparation protocol without resin medium was developed for micro‐ to nanoscale in situ investigation of insoluble organic matter. We show that these sections are suited for microscopic observation of Proterozoic microfossils in cherts. ToF‐SIMS reveals that these sections are free of pollution after final removal of a <10 nm layer of contamination using low‐dose ion sputtering. ToF‐SIMS maps of fragments from aliphatic and aromatic molecules and organic sulfur are correlated with the spatial distribution of organic microlaminae in a Jurassic stromatolite. Hydrocarbon‐derived ions also appeared correlated with kerogenous microstructures in Archean cherts. These developments in analytical procedures should help future investigations of organic matter and in particular, microfossils, by allowing the spatial correlation of microscopy, spectroscopy, precise isotopic microanalyses, and novel molecular microanalyses such as ToF‐SIMS. 相似文献
168.
169.
Julian Baur Jeannine Roy Martin A. Schfer Nalini Puniamoorthy Wolf U. Blanckenhorn Patrick T. Rohner 《Journal of evolutionary biology》2020,33(3):297-308
Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread dung flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male–male competition. We predicted that populations subject to increased male–male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male‐biased SSD in both species, which was not evident in conspecific populations with female‐biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling. 相似文献
170.
Dagmara Sirov Veronika Kreidlov Lubomír Adamec Jaroslav Vrba 《The Journal of eukaryotic microbiology》2020,67(5):608-611
The host specificity of the recently described ciliate species Tetrahymena utriculariae was tested in a greenhouse growth experiment, which included 14 different species of aquatic Utricularia as potential host plants. We confirmed the high specificity of the interaction between U. reflexa and T. utriculariae, the former being the only tested host species able to maintain colonization for prolonged time periods. We conclude that this plant–microbe relationship is a unique and specialized form of digestive mutualism and the plant–microbe unit a suitable experimental system for future ecophysiological studies. 相似文献