全文获取类型
收费全文 | 4574篇 |
免费 | 372篇 |
出版年
2023年 | 45篇 |
2022年 | 66篇 |
2021年 | 137篇 |
2020年 | 144篇 |
2019年 | 145篇 |
2018年 | 183篇 |
2017年 | 155篇 |
2016年 | 227篇 |
2015年 | 283篇 |
2014年 | 287篇 |
2013年 | 358篇 |
2012年 | 372篇 |
2011年 | 339篇 |
2010年 | 196篇 |
2009年 | 188篇 |
2008年 | 216篇 |
2007年 | 217篇 |
2006年 | 185篇 |
2005年 | 151篇 |
2004年 | 135篇 |
2003年 | 112篇 |
2002年 | 120篇 |
2001年 | 80篇 |
2000年 | 87篇 |
1999年 | 75篇 |
1998年 | 12篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 30篇 |
1991年 | 30篇 |
1990年 | 32篇 |
1989年 | 28篇 |
1988年 | 27篇 |
1987年 | 19篇 |
1986年 | 28篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1971年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有4946条查询结果,搜索用时 31 毫秒
1.
malvolio, the Drosophila homologue of mouse NRAMP-1 (Bcg), is expressed in macrophages and in the nervous system and is required for normal taste behaviour. 总被引:4,自引:0,他引:4 下载免费PDF全文
We report the sequence, expression pattern and mutant phenotype of malvolio (mvl), the Drosophila homologue of mammalian natural resistance-associated macrophage proteins (NRAMPs). In the mouse, this novel transporter is encoded by Bcg, a dominant gene that confers natural resistance to intracellular parasites. mvl was identified in a screen for mutants that affect taste behaviour. We show that loss-of-function as well as insertional mutants in mvl display defects in taste behaviour with no alterations in the physiology of the sensory neurons. Activity of the reporter enzyme beta-galactosidase, that reflects the expression pattern of mvl, is seen in mature sensory neurons and in macrophages. The conceptual translation of the mvl cDNA shows a striking similarity (65% identity) with human NRAMP with almost complete identity in a conserved consensus motif found in a number of ATP-coupled transporters. Based on its phenotype and expression pattern as well as its structural similarities to NRAMPs and a nitrate transporter in Aspergillus nidulans, we discuss a possible role for MVL in nitrite/nitrate transport and its implications. 相似文献
2.
3.
Ajeet Pratap Singh Rudra Nayan Das Gururaj Rao Aman Aggarwal Soeren Diegelmann Jan Felix Evers Hrishikesh Karandikar Matthias Landgraf Veronica Rodrigues K. VijayRaghavan 《PLoS genetics》2013,9(4)
Olfactory sensory neurons connect to the antennal lobe of the fly to create the primary units for processing odor cues, the glomeruli. Unique amongst antennal-lobe neurons is an identified wide-field serotonergic neuron, the contralaterally-projecting, serotonin-immunoreactive deutocerebral neuron (CSDn). The CSDn spreads its termini all over the contralateral antennal lobe, suggesting a diffuse neuromodulatory role. A closer examination, however, reveals a restricted pattern of the CSDn arborization in some glomeruli. We show that sensory neuron-derived Eph interacts with Ephrin in the CSDn, to regulate these arborizations. Behavioural analysis of animals with altered Eph-ephrin signaling and with consequent arborization defects suggests that neuromodulation requires local glomerular-specific patterning of the CSDn termini. Our results show the importance of developmental regulation of terminal arborization of even the diffuse modulatory neurons to allow them to route sensory-inputs according to the behavioural contexts. 相似文献
4.
Maria de Lourdes Lucio Ferrarese Osvaldo Ferrarese-Filho JoĂo Domingos Rodrigues 《Acta Physiologiae Plantarum》2000,22(2):121-124
Ferulic acid uptake by soybean root in nutrient culture was investigated by the depletion method at different concentrations,
temperatures and pH. Results showed that soybean roots absorbed this compound at greater rates in the concentrations between
0.05-mM and 1.0-mM and it was concentration dependent. Ferulic acid uptake was unaffected at pH 4.5 or 6.0 but reduced at
pH 7.0. At pH 6.0, uptake rates decreased significantly with increasing temperature of nutrient solution. 相似文献
5.
6.
Solans Mariana Vobis Gernot Cassán Fabricio Luna Virginia Wall Luis Gabriel 《World journal of microbiology & biotechnology》2011,27(9):2195-2202
The aim of the present study was to evaluate phytohormone production by symbiotic and saprophytic actinomycetes isolated from
the actinorhizal plant Ochetophila trinervis which had previously proved to stimulate nodulation by Frankia. Three saprophytic strains out of 122, isolated from the rhizosphere of this plant with multiple enzymatic activities were
selected for plant growth experiments in pots: Streptomyces sp. (BCRU-MM40), Actinoplanes sp. (BCRU-ME3) and Micromonospora sp. (BCRU-MM18). For experiments, the symbiotic N2-fixing strain Frankia (BCU110501), isolated from nodules of the same actinorhizal plant was used. Phytohormone production was evaluated in supernatant
of non-inoculated and inoculated culture media in exponential growth phase. Indole 3-acetic acid (IAA) and gibberellic acid
(GA3) were analyzed by gas chromatography-mass spectrometry (GC–MS), while zeatine (Z) production was determined by gas chromatography-flame
ionization detector and high performance liquid chromatography (HPLC fluorescent and UV). The levels of the three phytohormones
produced by the saprophytic rhizoactinomycetes were higher than that produced by the symbiotic Frankia strain. Zeatine biosynthesis was higher (μg ml−1) than IAA and GA3 (ng ml−1), and Micromonospora strain produced the highest levels of these phytohormones. Although O. trinervis has been shown to be intercellularly infected by Frankia without mediation of root hair deformation, when plants were co-inoculated with actinomycetes’ culture, some root hair deformation
was observed. This is the first report on identification of IAA, GA3 and Z in saprophytic actinomycetes and their potential role in plant–microbe interaction. 相似文献
7.
D Ocampos C D Rosa E Rodrigues R Rosa 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,88(2):625-630
Kinetic studies were carried out on the reaction catalyzed by pyruvate kinase (ATP:pyruvate phosphotransferase, E.C. 2.7.1.40) purified from white striated (epaxial) muscle of two marine fish Mugil lisa (Brazilian mullet) and Chaetoditerus faber (harvest fish). This included the establishment of kinetic parameters. Attention was given to the effect of fructose 1,6-bisphosphate (Fru-P2) on PK activity. Effects of ATP, alanine and the divalent ions, Mg2+, Mn2+, Cu2+, Be2+ and Co2+, on the fish muscle enzyme were also studied. 相似文献
8.
Pedro Gnaspini Gisele C. S. Rodrigues 《Journal of Zoological Systematics and Evolutionary Research》2011,49(4):273-284
Arachnids of the order Opiliones (harvestmen), which includes around 6000 specìes, have a pair of scent glands that open at the sides of the body, producing substances used as defence. Several types of behavioural, morphological and chemical defensive mechanisms have been identified in the order as a whole, although some of these tactics were restricted to particular groups. Only around 60 species have been studied from this perspective so far, more than half of which belong to the largest harvestman family within the order Laniatores, the Gonyleptidae, and have only recently been studied in an evolutionary perspective, showing the usefulness of defensive characters in taxonomy and evolutionary biology. Within Laniatores, the Grassatores clade includes the Gonyleptidae and 20 additional families, mostly poorly or not previously studied. We describe the morphology of the structures involved in fluid displacement during chemical defence in 15 of these families (data on two additional families are available from the literature) and discuss the evolution of such traits based on an available phylogenetic hypothesis of relationships within Grassatores, using the representatives of Triaenonychidae (a non‐Grassatores family of Laniatores) for comparison. We conclude that most non‐gonyleptoid Grassatores share (maybe plesiomorphically) a series of characteristics, mostly strongly different from what is observed within the gonyleptoids, and that smaller groups seem to share diagnostic features related to chemical defence, as is the case of stygnids, cosmetids and triaenonychines, and especially of manaosbiids and cranaids, whose defensive morphologies largely resemble those of derived gonyleptids. The following main synapomorphies were detected: (a) Grassatores: the presence of a deep and well‐defined descending channel; (b) Samooidea+Zalmoxoidea+Assamioidea+Gonyleptoidea: lateral pegs along the lateral channel; (c) Samooidea+Zalmoxoidea: deep channels forming an H on the dorsal scute; (d) Gonyleptoidea: ozopore cutting dorsally (reversing in Agoristenidae and Stygnidae to a laterally placed oval ozopore), a wide and smooth lateral channel, reversing to a lateral channel whose bottom is covered with either small plates (Agoristenidae) or high tubercles (Stygnidae), and apophyses of coxa II close to or covering the ozopore. 相似文献
9.
Centromere pattern in different mouse seminiferous tubule cells 总被引:1,自引:0,他引:1
Centromere arrangement in different mouse seminiferous tubule cells was analyzed using an anticentromere antiserum from a patient with the CREST syndrome of scleroderma. A peptide of 18 kd was recognized by this serum on immunoblotting of mouse nuclear proteins from seminiferous tubule cells. In the cells studied by immunofluorescence, different patterns of centromere arrangement were observed. A speckled arrangement of centromeres was found in spermatogonia, double spots corresponding to meiotic bivalents were found in pachytene cells, and clusters of a haploid numer of centromeres were found in early and acrosome phase spermatids. In Sertoli cells, only three centromeric spots were detected, corresponding to the nucleolar organizer chromosome pairs. A relationship between the functional stage of the cell and the arrangement of and conformational changes in the centromeres is considered. 相似文献
10.
Felipe V. Freitas Jos Eustquio Dos Santos Júnior Fabricio R. Santos Fernando A. Silveira 《Systematic Entomology》2019,44(4):728-744
The bee tribe Eucerini is a large monophyletic taxon occurring in all continents, except Oceania and Antarctica, but far more diverse in the Americas and, especially, in the Neotropics. The phylogenetic relationships within its subtribe Eucerina, which contains the bulk of Eucerini diversity, is poorly understood, this being especially true for the relationships among its Neotropical representatives, which have been poorly represented in all phylogenetic studies, including Eucerini, to date. This leads to a generalized lack of confidence on the monophyly of the groups currently accepted as genera and subgenera. Here, a phylogenetic study based on three molecular markers (COI, 18S, and 28S, totalling about 1700 bp) and 58 morphological characters is presented as a contribution to the understanding of the relationships of the so‐called Thygater‐Trichocerapis group, and especially of the genus Thygater Holmberg, which has not previously been extensively sampled. Representatives of Trichocerapis, including its monotypic subgenus T. (Dithygater), are included for the first time in a phylogenetic study. The main results were: (i) support for the monophyly of the Thygater‐Trichocerapis group; (ii) support for the monophyly of Thygater; (iii) recognition of two main clades in Thygater, each one containing the type species of one of the previously recognized subgenera; and (iv) additional support for the position of Alloscirtetica as sister to all remaining Eucerina. Based on these results a redefinition of the scope of the two subgenera of Thygater is proposed, with changes in the subordination of three of its species, T. (Nectarodiaeta) chaetaspis comb.n. , T. (Nectarodiaeta) paranaensis comb.n. and T. (Thygater) mexicana comb.n. 相似文献