全文获取类型
收费全文 | 3750篇 |
免费 | 304篇 |
国内免费 | 1篇 |
专业分类
4055篇 |
出版年
2024年 | 4篇 |
2023年 | 25篇 |
2022年 | 65篇 |
2021年 | 115篇 |
2020年 | 63篇 |
2019年 | 86篇 |
2018年 | 87篇 |
2017年 | 78篇 |
2016年 | 153篇 |
2015年 | 214篇 |
2014年 | 220篇 |
2013年 | 313篇 |
2012年 | 310篇 |
2011年 | 310篇 |
2010年 | 191篇 |
2009年 | 147篇 |
2008年 | 246篇 |
2007年 | 232篇 |
2006年 | 238篇 |
2005年 | 178篇 |
2004年 | 174篇 |
2003年 | 136篇 |
2002年 | 113篇 |
2001年 | 36篇 |
2000年 | 33篇 |
1999年 | 27篇 |
1998年 | 30篇 |
1997年 | 21篇 |
1996年 | 15篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 8篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1983年 | 5篇 |
1981年 | 4篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1949年 | 4篇 |
排序方式: 共有4055条查询结果,搜索用时 15 毫秒
231.
232.
Markéta Ondračková Kateřina Francová Martina Dávidová Matej Polačik Pavel Jurajda 《Ecological Research》2010,25(4):857-866
The success of introduced species is often facilitated by escape from the effects of natural predators and parasites. Introduced species can profit from this favourable situation, attaining higher population densities and greater individual sizes in novel areas. In this study, somatic condition and parasite infection were compared between native and non-native populations of Neogobius kessleri Günther; introduced only within the interconnected Danube and Rhine River system, and N. melanostomus (Pallas); widely introduced throughout several river systems in Europe and North America. Higher values of Fulton’s condition factor were observed in non-native populations of both goby species. Neogobius melanostomus attained higher gonadosomatic index values in non-native populations, indicating potential increased investment in reproduction in its new area. A lower splenosomatic index was observed in non-native populations, especially in N. melanostomus. Parasite infracommunity richness and mean abundance were higher in N. kessleri in both native and non-native populations, suggesting higher susceptibility of N. kessleri to these parasites. Non-native populations of both hosts showed higher infra-community richness as a result of acquiring parasites native to the new area, but lower parasite abundance. Differences in success of the introduction and establishment in new areas between the two fish species may be associated with a relatively low parasite infection rate and a higher gonadosomatic index in non-native populations of N. melanostomus in comparison to N. kessleri. 相似文献
233.
234.
Luciane A. Faine Danielle M.H. Cavalcanti Martina Rudnicki Simone Ferderbar Sandra M.D. Macedo Heraldo P. Souza Sandra H.P. Farsky Lisardo Boscá Dulcineia Saes Parra Abdalla 《The Journal of nutritional biochemistry》2010,21(2):125-132
The vascular effects of nitrolinoleate (LNO2), an endogenous product of linoleic acid (LA) nitration by nitric oxide-derived species and a potential nitrosating agent, were investigated on rat endothelial-leukocyte interactions. Confocal microscopy analysis demonstrated that LNO2 was capable to deliver free radical nitric oxide (·NO) into cells, 5 min after its administration to cultured cells, with a peak of liberation at 30 min. THP-1 monocytes incubated with LNO2 for 5 min presented nitrosation of CD40, leading to its inactivation. Other anti-inflammatory actions of LNO2 were observed in vivo by intravital microscopy assays. LNO2 decreased the number of adhered leukocytes in postcapillary venules of the mesentery network. In addition to this, LNO2 reduced mRNA and protein expression of β2-integrin in circulating leukocytes, as well as VCAM-1 in endothelial cells isolated from postcapillary venules, confirming its antiadhesive effects on both cell types. Moreover, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a nitric oxide scavenger, partially abolished the inhibitory action of LNO2 on leukocyte-endothelium interaction, suggesting that the antiadhesion effects of LNO2 involve a dual role in leukocyte adhesion, acting as a nitric oxide donor as well as through nitric oxide-independent mechanisms. In conclusion, LNO2 inhibited adhesion molecules expression and promoted ·NO inactivation of the CD40–CD40L system, both important processes of the inflammatory response. 相似文献
235.
Jens Müller Martina Beck Ursula Mettbach George Komis Gerd Hause Diedrik Menzel Jozef Šamaj 《The Plant journal : for cell and molecular biology》2010,61(2):234-248
The proper spatial and temporal expression and localization of mitogen‐activated protein kinases (MAPKs) is essential for developmental and cellular signalling in all eukaryotes. Here, we analysed expression, subcellular localization and function of MPK6 in roots of Arabidopsis thaliana using wild‐type plants and three mpk6 knock‐out mutant lines. The MPK6 promoter showed two expression maxima in the most apical part of the root meristem and in the root transition zone. This expression pattern was highly consistent with ‘no root’ and ‘short root’ phenotypes, as well as with ectopic cell divisions and aberrant cell division planes, resulting in disordered cell files in the roots of these mpk6 knock‐out mutants. In dividing root cells, MPK6 was localized on the subcellular level to distinct fine spots in the pre‐prophase band and phragmoplast, representing the two most important cytoskeletal structures controlling the cell division plane. By combining subcellular fractionation and microscopic in situ and in vivo co‐localization methods, MPK6 was localized to the plasma membrane (PM) and the trans‐Golgi network (TGN). In summary, these data suggest that MPK6 localizing to mitotic microtubules, secretory TGN vesicles and the PM is involved in cell division plane control and root development in Arabidopsis. 相似文献
236.
237.
José A. Donázar Ainara Cortés-Avizanda Martina Carrete 《European Journal of Wildlife Research》2010,56(4):613-621
Among vertebrates, specialization in scavenging has appeared only in “true” Gyps vultures, which usually base their diet almost exclusively on carcasses of medium and large-sized mammals, whereas all other
scavengers rely on broader ranges of prey. The availability of food for scavengers in Western Europe has not been limited
during recent decades permitting the existence and growth of huge vulture populations. From 2000 onwards, however, EU sanitary
legislation has progressively limited the abandonment of dead animals in the field resulting in a sudden reduction of food
availability with unknown ecological and conservation consequences. Here, we examine the dietary response of a tandem of carrion
eaters, the griffon vulture (Gyps fulvus) and the Egyptian vulture (Neophron percnopterus), showing different degrees of dietary specialization. Our results showed that after the reduction in numbers of supplementary
feeding stations (vulture restaurants) the niche breadth of the griffon vulture has broadened and now includes significant
amounts of wild rabbits (Oryctolagus cuniculus) and garbage. The diet of the Egyptian vulture, on the contrary, did not vary substantially. The diet overlap showed patterns
probably conditioned by interspecific competition and the progressive exploitation of unpredictable carcasses. On a short-term
scale, consequences for smaller scavengers could be negative due to the monopolization of resources by the dominant and much
more abundant griffon vulture, however in the long-term all guild species would benefit from the exploitation of unpredictable
carcasses, which could enhance the possibilities of coexistence. 相似文献
238.
Rhonda Christiane Meyer Barbara Kusterer Jan Lisec Matthias Steinfath Martina Becher Hanno Scharr Albrecht E. Melchinger Joachim Selbig Ulrich Schurr Lothar Willmitzer Thomas Altmann 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2010,120(2):227-237
The main objective of this study was to identify genomic regions involved in biomass heterosis using QTL, generation means, and mode-of-inheritance classification analyses. In a modified North Carolina Design III we backcrossed 429 recombinant inbred line and 140 introgression line populations to the two parental accessions, C24 and Col-0, whose F 1 hybrid exhibited 44% heterosis for biomass. Mid-parent heterosis in the RILs ranged from ?31 to 99% for dry weight and from ?58 to 143% for leaf area. We detected ten genomic positions involved in biomass heterosis at an early developmental stage, individually explaining between 2.4 and 15.7% of the phenotypic variation. While overdominant gene action was prevalent in heterotic QTL, our results suggest that a combination of dominance, overdominance and epistasis is involved in biomass heterosis in this Arabidopsis cross. 相似文献
239.
Martin Rudwaleit Filip Van den Bosch Martina Kron Sonja Kary Hartmut Kupper 《Arthritis research & therapy》2010,12(3):R117
Introduction
Tumor necrosis factor (TNF) antagonists reduce the signs and symptoms of spondyloarthritides, including ankylosing spondylitis (AS) and psoriatic arthritis (PsA). Our objective was to evaluate the effectiveness and safety of adalimumab, 40 mg every other week, for patients with AS or PsA and prior treatment with infliximab (IFX) and/or etanercept (ETN). 相似文献240.
The branch point (BP) is one of the three obligatory signals required for pre-mRNA splicing. In mammals, the degeneracy of the motif combined with the lack of a large set of experimentally verified BPs complicates the task of modeling it in silico, and therefore of predicting the location of natural BPs. Consequently, BPs have been disregarded in a considerable fraction of the genome-wide studies on the regulation of splicing in mammals. We present a new computational approach for mammalian BP prediction. Using sequence conservation and positional bias we obtained a set of motifs with good agreement with U2 snRNA binding stability. Using a Support Vector Machine algorithm, we created a model complemented with polypyrimidine tract features, which considerably improves the prediction accuracy over previously published methods. Applying our algorithm to human introns, we show that BP position is highly dependent on the presence of AG dinucleotides in the 3' end of introns, with distance to the 3' splice site and BP strength strongly correlating with alternative splicing. Furthermore, experimental BP mapping for five exons preceded by long AG-dinucleotide exclusion zones revealed that, for a given intron, more than one BP can be chosen throughout the course of splicing. Finally, the comparison between exons of different evolutionary ages and pseudo exons suggests a key role of the BP in the pathway of exon creation in human. Our computational and experimental analyses suggest that BP recognition is more flexible than previously assumed, and it appears highly dependent on the presence of downstream polypyrimidine tracts. The reported association between BP features and the splicing outcome suggests that this, so far disregarded but yet crucial, element buries information that can complement current acceptor site models. 相似文献