全文获取类型
收费全文 | 1611篇 |
免费 | 80篇 |
专业分类
1691篇 |
出版年
2023年 | 11篇 |
2022年 | 31篇 |
2021年 | 41篇 |
2020年 | 26篇 |
2019年 | 39篇 |
2018年 | 57篇 |
2017年 | 47篇 |
2016年 | 62篇 |
2015年 | 96篇 |
2014年 | 95篇 |
2013年 | 152篇 |
2012年 | 155篇 |
2011年 | 141篇 |
2010年 | 77篇 |
2009年 | 73篇 |
2008年 | 90篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 46篇 |
2004年 | 46篇 |
2003年 | 65篇 |
2002年 | 46篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1691条查询结果,搜索用时 0 毫秒
991.
Maria Alice Garcia Bento Ivana Miranda Fernando Luis Mantelatto Fernando José Zara 《Arthropod Structure & Development》2018,47(6):627-642
We described the spermatozoal ultrastructure and conducted a molecular analysis of Dromiidae Hypoconcha parasitica, Hypoconcha arcuata, Moreiradromia antillensis and Dromia erythropus. To elucidate the relationship between the different species of this brachyuran group, we also compared the spermatozoal morphologies and phylogenetic positioning among species of Dromiidae, Dromioidea and Podotremata. Specimens were collected from the northern coast of São Paulo, Brazil and were fixed and processed followed by transmission electron microscopy and molecular analysis routines. The Dromiidae spermatozoa studied are characterized by a discoidal acrosome, with three or four concentric zones, which are centrally separated by a bilaterally capitate perforatorial chamber, with a “mushroom”-shaped apex in the Hypoconchinae and a “T-shape” in Dromiinae. Above the perforatorial chamber, there is an apical protuberance, continuous with the subopercular region and the operculum, which forms a low, centrally perforated dome. Under differential interference contrast microscopy, the spermatozoa show 3 to 4 radial arms. The spermatozoal characters in Hypoconchinae and Dromiinae do not separate these subfamilies from the Dromiidae and Dromioidea. Ultrastructural differentiation was only found between representative Dromioidea and other Podotremata. Thus, the spermiotaxonomy of these Hypoconcha, Moreiradromia and Dromia species corroborated previous morphological and molecular studies, supporting the monophyly of Dromiidae and Dynomenidae in relation to Homolidae and Latreilliidae. 相似文献
992.
993.
Cytokinins in Tobacco and Wheat Chloroplasts. Occurrence and Changes Due to Light/Dark Treatment 下载免费PDF全文
Eva Benkov Erwin Witters Walter Van Dongen Jan Kolar Vclav Motyka Bretislav Brzobohatý Harry A. Van Onckelen Ivana Machckov 《Plant physiology》1999,121(1):245-252
Although cytokinins (CKs) affect a number of processes connected with chloroplasts, it has never been rigorously proven that chloroplasts contain CKs. We isolated intact chloroplasts from tobacco (Nicotiana tabacum L. cv SR1) and wheat (Triticum aestivum L. cv Ritmo) leaves and determined their CKs by liquid chromatography/tandem mass spectroscopy. Chloroplasts from both species contained a whole spectrum of CKs, including free bases (zeatin and isopentenyladenine), ribosides (zeatin riboside, and isopentenyladenosine), ribotides (isopentenyladenosine-5'-monophosphate, zeatin riboside-5'-monophosphate, and dihydrozeatin riboside-5'-monophosphate), and N-glucosides (zeatin-N(9)-glucoside, dihydrozeatin-N(9)-glucoside, zeatin-N(7)-glucoside, and isopentenyladenine-N-glucosides). In chloroplasts there was a moderately higher relative amount of bases, ribosides, and ribotides than in leaves, and a significantly increased level of N(9)-glucosides of zeatin and dihydrozeatin. Tobacco and wheat chloroplasts were prepared from leaves at the end of either a dark or light period. After a dark period, chloroplasts accumulated more CKs than after a light period. The differences were moderate for free bases and ribosides, but highly significant for glucosides. Tobacco chloroplasts from dark-treated leaves contained zeatin riboside-O-glucoside and dihydrozeatin riboside-O-glucoside, as well as a relatively high CK oxidase activity. These data show that chloroplasts contain a whole spectrum of CKs and the enzymatic activity necessary for their metabolism. 相似文献
994.
995.
Ivana Živić Miroslav Živić Katarina Bjelanović Djuradj Milošević Sanja Stanojlović Radoslav Daljević Zoran Marković 《Hydrobiologia》2014,732(1):147-159
The aim of this study was to predict global warming effects on benthic macroinvertebrate community structure by using a small temperate geothermal stream as a model system. We collected benthic macroinvertebrates, measured physical and chemical water properties at eight localities up the Kudo?ki stream steep water temperature gradient, and used 11 metrics and indexes to characterize community structure. Species richness and evenness decreased, but total abundance increased with the increase of average annual water temperature (t av), with species richness being most and total abundance least sensitive to this parameter. The increase of Gastropoda relative abundance and the decrease of Ephemeroptera, Plecoptera and Trichoptera richness, respectively, were the earliest responses of taxonomic groups to t av increase. Relative abundance of Orthocladiinae decreased and that of Chironomini increased with the increase of t av. This indicates that Chironomidae are not reliable predictors of global warming effects in running waters, and that lower taxonomic levels, subfamily or tribe, are more suitable for that purpose. Changes in community structure did not linearly follow t av increase, since a great community shift was observed at t av ≈ 20°C indicating that present trends of community responses to changes in climatic conditions should not be linearly extrapolated to future warming. 相似文献
996.
The infection of chickens with avian Hepatitis E virus (avian HEV) can be asymptomatic or induces clinical signs characterized by increased mortality and decreased egg production in adult birds. Due to the lack of an efficient cell culture system for avian HEV, the interaction between virus and host cells is still barely understood. In this study, four truncated avian HEV capsid proteins (ORF2-1 – ORF2-4) with an identical 338aa deletion at the N-terminus and gradual deletions from 0, 42, 99 and 136aa at the C-terminus, respectively, were expressed and used to map the possible binding site within avian HEV capsid protein. Results from the binding assay showed that three truncated capsid proteins attached to avian LMH cells, but did not penetrate into cells. However, the shortest construct, ORF2-4, lost the capability of binding to cells suggesting that the presence of amino acids 471 to 507 of the capsid protein is crucial for the attachment. The construct ORF2-3 (aa339-507) was used to study the potential binding of avian HEV capsid protein to human and other avian species. It could be demonstrated that ORF2-3 was capable of binding to QT-35 cells from Japanese quail and human HepG2 cells but failed to bind to P815 cells. Additionally, chicken serum raised against ORF2-3 successfully blocked the binding to LMH cells. Treatment with heparin sodium salt or sodium chlorate significantly reduced binding of ORF2-3 to LMH cells. However, heparinase II treatment of LMH cells had no effect on binding of the ORF2-3 construct, suggesting a possible distinct attachment mechanism of avian as compared to human HEV. For the first time, interactions between avian HEV capsid protein and host cells were investigated demonstrating that aa471 to 507 of the capsid protein are needed to facilitate interaction with different kind of cells from different species. 相似文献
997.
998.
Isoperoxidase B 1 isolated from winter wheat (Triticum aestivum L., cv. Jubilar) seedlings was shown to catalyze ethylene formation from α-keto, γ-methylmercaptobutyric acid (KMBA). In
the presence of Mn2+, indole-3-acetic acid (IAA), andp-coumaric acid, the kinetics by isoperoxidase B 1 catalyzed conversion of KMBA into ethylene and other products was similar
to that of IAA oxidation. The reaction rate was therefore controlled by IAA through its electrondonating properties.
Exogenous IAA induced ethylene formation in the segments of etiolated wheat coleoptiles. IAA-induced ethylene production was
enhanced by L-methionine and mitomycin C. Aminoethoxy-analogue of rhizobitoxine, ferulic acid, sodium benzoate, cycloheximide
and actinomyoin D exhibited significant inhibitory effects. These data indicate that the overall reaction mechanism in coleoptile
segments involves RNA and protein synthesis.
The site of IAA action is not specific; 2,4-dichlorophenoxyacetic, α-naphthylacetic and indole-3-butyric acids, respectively,
possessed comparable inductive effect as IAA. Indole-3-propionic acid, indole, L-tryptophan and glucobrassicin had only low
inductive efficiency, and moreover indole and L-tryptophan slowed down IAA-induced ethylene formation. 相似文献
999.
Maddalena Donzelli Claudia Negri Angelo Mandarino Laura Rossi Ennio Prosperi Isabelle Frouin Rosa Bernardi Alexander Burkle A. Ivana Scovassi 《Journal of molecular histology》1997,29(11):831-837
Cell death by apoptosis was analysed in HeLa cells either treated with the antitumoral drug bleomycin or depleted of growth
factors by long-term culture without medium change. The interference of apoptosis with normal cell cycle progression was followed
by flow cytometry in cells stained with propidium iodide and with antibody to S-phase-related PCNA protein. Bleomycin-treated
cells showed a net accumulation in G2/M phase paralleled by the appearance of material with a subdiploid DNA content. Cells with a subdiploid DNA content were
also present in growth factor-depleted cultures and were shown to derive from all the cell cycle phases. To identify apoptotic
features in HeLa cell cultures, we applied a recently developed assay based on the simultaneous analysis in the single cell
of three parameters, namely chromatin condensation, DNA degradation and poly(ADP-ribose) synthesis. Apoptotic cells were visualized
by sequential reactions: Hoechst staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling assay
and immunoreaction with anti-poly(ADP-ribose) monoclonal antibody. Positive reactions were obtained for cells at different
stages of the apoptotic programme showing condensed nuclei, fragmented chromatin and apoptotic bodies
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
1000.
Ivana Bulatovic Cristian Ibarra Cecilia ?sterholm Heng Wang Antonio Beltrán-Rodríguez Manuel Varas-Godoy Agneta M?nsson-Broberg Per Uhlén András Simon Karl-Henrik Grinnemo 《PloS one》2015,10(3)
Generation of new cardiomyocytes is critical for cardiac repair following myocardial injury, but which kind of stimuli is most important for cardiomyocyte regeneration is still unclear. Here we explore if apoptotic stimuli, manifested through caspase activation, influences cardiac progenitor up-regulation and cardiomyocyte differentiation. Using mouse embryonic stem cells as a cellular model, we show that sublethal activation of caspases increases the yield of cardiomyocytes while concurrently promoting the proliferation and differentiation of c-Kit+/α-actininlow cardiac progenitor cells. A broad-spectrum caspase inhibitor blocked these effects. In addition, the caspase inhibitor reversed the mRNA expression of genes expressed in cardiomyocytes and their precursors. Our study demonstrates that sublethal caspase-activation has an important role in cardiomyocyte differentiation and may have significant implications for promoting cardiac regeneration after myocardial injury involving exogenous or endogenous cell sources. 相似文献