全文获取类型
收费全文 | 8356篇 |
免费 | 764篇 |
国内免费 | 2篇 |
专业分类
9122篇 |
出版年
2023年 | 43篇 |
2022年 | 85篇 |
2021年 | 186篇 |
2020年 | 127篇 |
2019年 | 145篇 |
2018年 | 180篇 |
2017年 | 179篇 |
2016年 | 243篇 |
2015年 | 433篇 |
2014年 | 485篇 |
2013年 | 611篇 |
2012年 | 741篇 |
2011年 | 709篇 |
2010年 | 464篇 |
2009年 | 422篇 |
2008年 | 586篇 |
2007年 | 519篇 |
2006年 | 514篇 |
2005年 | 455篇 |
2004年 | 483篇 |
2003年 | 341篇 |
2002年 | 385篇 |
2001年 | 92篇 |
2000年 | 54篇 |
1999年 | 78篇 |
1998年 | 93篇 |
1997年 | 60篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 33篇 |
1992年 | 18篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1974年 | 6篇 |
1973年 | 14篇 |
1971年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有9122条查询结果,搜索用时 15 毫秒
121.
Sindre H. Eldøy Jan G. Davidsen Matthias Vignon Michael Power 《Journal of fish biology》2021,98(2):526-536
Subsequent to their introduction in the 1950s, Arctic charr Salvelinus alpinus have been able to establish a self-sustaining population that has adapted to the unique conditions of the sub-Antarctic Kerguelen Islands. Here, 48 individuals (198–415 mm) were caught with gillnets and their basic biology and feeding ecology were examined using stable isotope analysis. The Lac des Fougères population split use of littoral and pelagic resources evenly, although larger fish relied more heavily on littoral production and appear to follow the size-dependent life history habitat template seen in many Scandinavian lakes where smaller sized individuals occupy the pelagic zone and larger individuals dominate the littoral habitat. In Kerguelen, Arctic charr mature at the same ages (5.6 years) as Arctic charr in both sub-Arctic and Arctic lakes. Although mortality was average in comparison to comparator sub-Arctic lakes, it was high in comparison to Arctic lakes. Maximal age (>7+) was at the lower end of the range typically seen in sub-Arctic lakes. Although they inhabit a resource-poor environment, Kerguelen Arctic charr showed no evidence of cannibalism. Thus, while Arctic charr can survive and reproduce in the relatively unproductive Kerguelen lake environments, survival and growth nevertheless appear to be traded off against survival and longevity. The uniqueness of the population location and the recency of its introduction suggest that further monitoring of the population has the potential to yield valuable insights into both the adaptability of the species and its likely responses to ongoing large-scale environmental change as represented by climate change. 相似文献
122.
Gaowen Yang Yingjun Zhang Xin Yang Nan Liu Matthias C. Rillig Stavros D. Veresoglou Cameron Wagg 《Oikos》2021,130(3):354-365
Nutrient enrichment can reduce ecosystem stability, typically measured as temporal stability of a single function, e.g. plant productivity. Moreover, nutrient enrichment can alter plant–soil interactions (e.g. mycorrhizal symbiosis) that determine plant community composition and productivity. Thus, it is likely that nutrient enrichment and interactions between plants and their soil communities co-determine the stability in plant community composition and productivity. Yet our understanding as to how nutrient enrichment affects multiple facets of ecosystem stability, such as functional and compositional stability, and the role of above–belowground interactions are still lacking. We tested how mycorrhizal suppression and phosphorus (P) addition influenced multiple facets of ecosystem stability in a three-year field study in a temperate steppe. Here we focused on the functional and compositional stability of plant community; functional stability is the temporal community variance in primary productivity; compositional stability is represented by compositional resistance, turnover, species extinction and invasion. Community variance was partitioned into population variance defined as community productivity weighted average of the species temporal variance in performance, and species synchrony defined as the degree of temporal positive covariation among species. Compared to treatments with mycorrhizal suppression, the intact AM fungal communities reduced community variance in primary productivity by reducing species synchrony at high levels of P addition. Species synchrony and population variance were linearly associated with community variance with the intact AM fungal communities, while these relationships were decoupled or weakened by mycorrhizal suppression. The intact AM fungal communities promoted the compositional resistance of plant communities by reducing compositional turnover, but this effect was suppressed by P addition. P addition increased the number of species extinctions and thus promoted compositional turnover. Our study shows P addition and AM fungal communities can jointly and independently modify the various components of ecosystem stability in terms of plant community productivity and composition. 相似文献
123.
Carmen Benítez-Benítez Santiago Martín-Bravo Charlotte S. Bjorå Sebastian Gebauer rew L. Hipp Matthias H. Hoffmann Modesto Luceño Tyril M. Pedersen Anton Reznicek Eric Roalson Polina Volkova Okihito Yano Daniel Spalink Pedro Jiménez-Mejías 《植物分类学报:英文版》2021,59(4):642-667
Carex section Phacocystis (Cyperaceae) is one of the most diverse and taxonomically complex groups of sedges (between 116 and 147 species), with a worldwide distribution in a wide array of biomes. It has a very complicated taxonomic history, with numerous disagreements among different treatments. We studied the biogeography and niche evolution in a phylogenetic framework to unveil the relative contribution of geographical and ecological drivers to diversification of the group. We used a large species sampling of the section (82% of extant species) to build a phylogeny based on four DNA regions, constrained with a phylogenomic HybSeq tree and dated with six fossil calibrations. Our phylogenetic results recovered section Phacocystis s.s. (core Phacocystis) as sister to section Praelongae. Ancestral area reconstruction points toward the N Pacific as the cradle for the crown diversification of section Phacocystis during the Middle Miocene. Wide distributions were recurrently inferred across deep nodes. Large Northern Hemisphere lineages with geographical congruence were retrieved, pointing toward the importance of allopatric divergence at deep phylogenetic levels, whereas within-area speciation emerges as the predominant pattern at shallow phylogenetic level. The Southern Hemisphere (Neotropics, SW Pacific) was colonized several times from the Northern Hemisphere. The global expansion of Carex section Phacocystis did not entail major ecological changes along the inner branches of the phylogeny. Nevertheless, ecological differentiation seems to gain importance toward recent times. 相似文献
124.
Papenkort Stefan Böl Markus Siebert Tobias 《Biomechanics and modeling in mechanobiology》2021,20(5):2031-2044
Biomechanics and Modeling in Mechanobiology - Muscle architecture, which includes parameters like fascicle length, pennation angle, and physiological cross-sectional area, strongly influences... 相似文献
125.
Christophe J. Queval Antony Fearns Laure Botella Alicia Smyth Laura Schnettger Morgane Mitermite Esen Wooff Bernardo Villarreal-Ramos Waldo Garcia-Jimenez Tiaan Heunis Matthias Trost Dirk Werling Francisco J. Salguero Stephen V. Gordon Maximiliano G. Gutierrez 《PLoS pathogens》2021,17(3)
The Mycobacterium tuberculosis complex (MTBC) is a group of related pathogens that cause tuberculosis (TB) in mammals. MTBC species are distinguished by their ability to sustain in distinct host populations. While Mycobacterium bovis (Mbv) sustains transmission cycles in cattle and wild animals and causes zoonotic TB, M. tuberculosis (Mtb) affects human populations and seldom causes disease in cattle. The host and pathogen determinants underlying host tropism between MTBC species are still unknown. Macrophages are the main host cell that encounters mycobacteria upon initial infection, and we hypothesised that early interactions between the macrophage and mycobacteria influence species-specific disease outcome. To identify factors that contribute to host tropism, we analysed blood-derived primary human and bovine macrophages (hMϕ or bMϕ, respectively) infected with Mbv and Mtb. We show that Mbv and Mtb reside in different cellular compartments and differentially replicate in hMϕ whereas both Mbv and Mtb efficiently replicate in bMϕ. Specifically, we show that out of the four infection combinations, only the infection of bMϕ with Mbv promoted the formation of multinucleated giant cells (MNGCs), a hallmark of tuberculous granulomas. Mechanistically, we demonstrate that both MPB70 from Mbv and extracellular vesicles released by Mbv-infected bMϕ promote macrophage multinucleation. Importantly, we extended our in vitro studies to show that granulomas from Mbv-infected but not Mtb-infected cattle contained higher numbers of MNGCs. Our findings implicate MNGC formation in the contrasting pathology between Mtb and Mbv for the bovine host and identify MPB70 from Mbv and extracellular vesicles from bMϕ as mediators of this process. 相似文献
126.
Roman Jansen Holger Morschett Dennis Hasenklever Matthias Moch Wolfgang Wiechert Marco Oldiges 《Biotechnology progress》2021,37(4):e3144
In recent years, many fungal genomes have become publicly available. In combination with novel gene editing tools, this allows for accelerated strain construction, making filamentous fungi even more interesting for the production of valuable products. However, besides their extraordinary production and secretion capacities, fungi most often exhibit challenging morphologies, which need to be screened for the best operational window. Thereby, combining genetic diversity with various environmental parameters results in a large parameter space, creating a strong demand for time-efficient phenotyping technologies. Microbioreactor systems, which have been well established for bacterial organisms, enable an increased cultivation throughput via parallelization and miniaturization, as well as enhanced process insight via non-invasive online monitoring. Nevertheless, only few reports about microtiter plate cultivation for filamentous fungi in general and even less with online monitoring exist in literature. Moreover, screening under batch conditions in microscale, when a fed-batch process is performed in large-scale might even lead to the wrong identification of optimized parameters. Therefore, in this study a novel workflow for Aspergillus niger was developed, allowing for up to 48 parallel microbioreactor cultivations in batch as well as fed-batch mode. This workflow was validated against lab-scale bioreactor cultivations to proof scalability. With the optimized cultivation protocol, three different micro-scale fed-batch strategies were tested to identify the best protein production conditions for intracellular model product GFP. Subsequently, the best feeding strategy was again validated in a lab-scale bioreactor. 相似文献
127.
Lisa N. Meihls Vinzenz Handrick Gaetan Glauser Hugues Barbier Harleen Kaur Meena M. Haribal Alexander E. Lipka Jonathan Gershenzon Edward S. Buckler Matthias Erb Tobias G. K?llner Georg Jander 《The Plant cell》2013,25(6):2341-2355
Plants differ greatly in their susceptibility to insect herbivory, suggesting both local adaptation and resistance tradeoffs. We used maize (Zea mays) recombinant inbred lines to map a quantitative trait locus (QTL) for the maize leaf aphid (Rhopalosiphum maidis) susceptibility to maize Chromosome 1. Phytochemical analysis revealed that the same locus was also associated with high levels of 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) and low levels of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc). In vitro enzyme assays with candidate genes from the region of the QTL identified three O-methyltransferases (Bx10a-c) that convert DIMBOA-Glc to HDMBOA-Glc. Variation in HDMBOA-Glc production was attributed to a natural CACTA family transposon insertion that inactivates Bx10c in maize lines with low HDMBOA-Glc accumulation. When tested with a population of 26 diverse maize inbred lines, R. maidis produced more progeny on those with high HDMBOA-Glc and low DIMBOA-Glc. Although HDMBOA-Glc was more toxic to R. maidis than DIMBOA-Glc in vitro, BX10c activity and the resulting decline of DIMBOA-Glc upon methylation to HDMBOA-Glc were associated with reduced callose deposition as an aphid defense response in vivo. Thus, a natural transposon insertion appears to mediate an ecologically relevant trade-off between the direct toxicity and defense-inducing properties of maize benzoxazinoids. 相似文献
128.
Hae-Young Sohn Matthias Keller Torsten Gloe Peter Crause Ulrich Pohl 《Free radical research》2013,47(3):265-272
Since an increased endothelial superoxide formation plays an important role in the pathogenesis of endothelial dysfunction its specific detection is of particular interest. The widely used superoxide probe lucigenin, however, has been reported to induce superoxide under certain conditions, especially in the presence of NADH. This raises questions as to the conclusion of a NAD(P)H oxidase as the major source of endothelial superoxide. Using independent methods, we showed that lucigenin in the presence of NADH leads to the production of substantial amount of superoxide (~ 15-fold of control) in endothelial cell homogenates. On the other hand, these independent methods revealed that endothelial cells without lucigenin still produce superoxide in a NAD(P)H-dependent manner. This was blocked by inhibitors of the neutrophil NADPH oxidase diphenyleniodonium and phenylarsine oxide. Our results demonstrate that a NAD(P)H-dependent oxidase is an important source for endothelial superoxide but the latter, however, cannot be measured reliably by lucigenin. 相似文献
129.
Matthias Hoch Estelle Hirzel Peter Lindinger Philippe Linscheid Ivan Martin 《Journal of receptor and signal transduction research》2013,33(5):485-504
The melanocortin (MC) receptor type-1 (MC1-R) is the only one of the five MC receptor subtypes expressed in human adipose tissue explants, human mesenchymal stem cells (MSCs), and MSC-derived adipocytes. Following our recent expression studies (Obesity 2007, 15, 40–49), we now investigated the functional role of MC1-R in these tissues and cells to deduce the coupling state of MC1-R to intracellular output signals in human fat cells and tissue. Expression of MC1-R by undifferentiated and differentiated MSCs was quantified by real-time TaqMan PCR. Intracellular output signals (cAMP, lipolysis, secretion of IL-6, IL-10, and TNF-α), as well as effects on the metabolic rate and proliferation of human MSCs were analyzed by standard assays, exposing undifferentiated and differentiated MSCs and, in part, human adipose tissue explants to the potent MC1-R agonist, [Nle4, D-Phe7]-α -MSH (NDP-MSH). This agonist induced a weak cAMP signal in MSC-derived adipocytes. However, it did not affect lipolysis in these cells or in adipose tissue explants, nor did it modulate cytokine release and mRNA expression of IL-6, IL-8, and TNF-α upon LPS stimulation. In undifferentiated MSCs, NDP-MSH did not alter the metabolic rate, but it showed a significant antiproliferative effect. Therefore, it appears that MC1-R–effector coupling in (differentiated) human adipocytes is too weak to induce a regulatory effect on lipolysis or inflammation; by contrast, MC1-R stimulation in undifferentiated MSCs induces an inhibitory signal on cell proliferation. 相似文献
130.
Iris Kroeger Matthias Liess Frank Dziock Sabine Duquesne 《Journal of vector ecology》2013,38(1):82-89
Integrated management of mosquitoes is becoming increasingly important, particularly in relation to avoiding recolonization of ponds after larvicide treatment. We conducted for the first time field experiments that involved exposing natural populations of the mosquito species Culex pipiens to: a) application of the biological insecticide Bacillus thuringiensis israelensis (Bti), b) the introduction of natural competitors (a crustacean community composed mainly of Daphnia spp.), or c) a combined treatment that involved both introduction of a crustacean community and the application of Bti. The treatment that involved only the introduction of crustaceans had no significant effect on mosquito larval populations, while treatment with Bti alone caused only a significant reduction in the abundance of mosquito larvae in the short‐term (within 3–10 days after treatment). In contrast, the combined treatment rapidly reduced the abundance of mosquito larvae, which remained low throughout the entire observation period of 28 days. Growth of the introduced crustacean communities was favored by the immediate reduction in the abundance of mosquito larvae following Bti administration, thus preventing recolonization of ponds by mosquito larvae at the late period (days 14–28 after treatment). Both competition and the temporal order of establishment of different species are hence important mechanisms for efficient and sustainable mosquito control. 相似文献