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排序方式: 共有1195条查询结果,搜索用时 10 毫秒
181.
Thomas Lamb Michael Abouyannis Smella Silva de Oliveira Rachana Shenoy K. Tulasi Geevar Anand Zachariah Sanjib Kumar Sharma Navin Bhatt Mavuto Mukaka Eli Harriss David G. Lalloo Elizabeth A. Ashley Wuelton Marcelo Monteiro Frank Smithuis Michael Eddleston 《PLoS neglected tropical diseases》2021,15(8)
182.
Jackman TR Bauer AM Greenbaum E Glaw F Vences M 《Molecular phylogenetics and evolution》2008,46(1):74-81
We use approximately 3100bp of mitochondrial (ND2, ND4) and nuclear (RAG1, phosducin) DNA sequence data to recover phylogenetic relationships among 14 of the 16 recognized taxa of the lizard genus Paroedura as well as two undescribed forms. These geckos are endemic to Madagascar and the Comores and are popularly kept and bred by herpetoculturalists. The closest relative of Paroedura is another Indian Ocean leaf-toed gecko, Ebenavia. Both Bayesian inference and maximum parsimony strongly support the monophyly of two major clades within Paroedura that conflict with existing species group assignments based on scale characteristics. Our well-resolved tree elucidates a biogeographic pattern in which eastern Paroedura are most basal and western and south-western species form a monophyletic group. Our data demonstrate the phylogenetic utility of phosducin, a novel marker in squamate phylogenetics, at the intrageneric level. 相似文献
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185.
Klára Řeháková Eliška Zapomělová Ondřej Prášil Jana Veselá Hana Medová Aharon Oren 《Hydrobiologia》2009,636(1):77-88
There are several conflicting hypothesis that deal with the influence of flooding in the natural river–floodplain systems.
According to the Flood Pulse Concept, the flood pulses are not considered to be a disturbance, while some recent studies have
proven that floods can be a disturbance factor of phytoplankton development. In order to test whether flooding acts as a disturbance
factor in the shallow Danubian floodplain lake (Lake Sakadaš), phytoplankton dynamics was investigated during two different
hydrological years—extremely dry (2003) without flooding and usually flooded (2004). A total of 18 phytoplankton functional
groups were established. The sequence of phytoplankton seasonality can be summarized P/D → E (W1, W2) → C/P (only in potamophase) → S2/H1/SN/S1 → W1/W2 → P/D. The canonical correspondence analysis (CCA) demonstrated that the water level was a significant environmental
variable in 2004. Due to the higher total biomass of Bacillariophyceae established under potamophase conditions, floodings
in the early spring seem to be a stimulating factor for phytoplankton development. On the other hand, the flood pulses in
May and June had dilution effects on nutrients, so that a significantly lower phytoplankton biomass was established indicating
that flooding pulses can be regarded as a disturbance event. Such conditions supported diatom development (D, P, C species)
and prolonged its dominance in the total phytoplankton biomass. A long-lasting Cyanoprokaryota bloom (various filamentous
species—S1, S2, SN and H1 representatives) with very high biomass characterized the limnophase (dry conditions) in summer and autumn of both
years. In-lake variables (lake morphology, internal loadings of nutrients from sediments, light conditions) seem to be important
for the appearance of Cyanoprokaryota bloom. The equilibrium phase was found during the Cyanoprokaryota bloom only in the
extremely dry year. This study showed that depending on the time scale occurrence, flood pulses can be a stimulating or a
disturbance factor for phytoplankton development in Lake Sakadaš.
Handling editor: J. Padisak 相似文献
186.
Eliška Zapomělová Jitka Jezberová Pavel Hrouzek Daniel Hisem Klára Řeháková Jaroslava Komárková 《Journal of phycology》2009,45(6):1363-1373
Occurrences of rare cyanobacteria Anabaena reniformis Lemmerm. and Aphanizomenon aphanizomenoides (Forti) Horecká et Komárek were recently detected at several localities in the Czech Republic. Two monoclonal strains of An. reniformis and one strain of Aph. aphanizomenoides were isolated from distant localities and different sampling years. They were characterized by a combination of morphological, genetic, and biochemical approaches. For the first time, partial 16S rRNA gene sequences were obtained for these morphospecies. Based on this gene, all of these strains clustered separately from other planktonic Anabaena and Aphanizomenon strains. They appeared in a cluster with Cylindrospermopsis Seenaya et Subba Raju and Raphidiopsis F. E. Fritsch et M. F. Rich, clustered closely together with two An. kisseleviana Elenkin strains available from GenBank. A new generic entity was defined (Sphaerospermum gen. nov., with the type species S. reniforme, based on the traditional species An. reniformis). These results contribute significantly to the knowledge base about genetic heterogeneity among planktonic Anabaena–like and Aphanizomenon–like morphospecies. Accordingly, the subgenus Dolichospermum, previously proposed for the group of planktonic Anabaena, should be revaluated. Secondary metabolite profiles of the An. reniformis and Aph. aphanizomenoides strains differed considerably from 17 other planktonic Anabaena strains of eight morphospecies isolated from Czech water bodies. Production of puwainaphycin A was found in both of the An. reniformis strains. Despite the relatively short phylogenetic distance from Cylidrospermopsis, the production of cylindrospermopsin was not detected in any of our strains. 相似文献
187.
188.
Bridge ES Schoech SJ Bowman R Wingfield JC 《Journal of experimental zoology. Part A, Ecological genetics and physiology》2009,311(1):35-44
Florida Scrub-Jays (Aphelocoma coerulescens) in a suburban environment with year-round access to multiple sources of abundant, human-source foods consistently breed earlier each year and have lower baseline levels of circulating corticosterone (CORT) than jays in a nearby wildland setting. These findings suggest that food supplies influence CORT levels, which in turn may partially determine the timing of reproduction. However, wildland birds with access to high-quality supplemental foods did not advance breeding or lower CORT levels to the degree observed in the suburbs. Therefore, rather than quality or quantity of food consumed, the perception of a reliable and predictable food supply may be an important factor in determining laying dates. If a predictable food supply accelerates the reproductive process, it follows that food provided on an unpredictable schedule may slow reproduction. We subjected captive Western Scrub-Jays (A. californica) to a 30-day photoperiod transition from short- to long-days and tested whether birds with access to food on an unpredictable schedule exhibited delayed or reduced production of reproductive hormones compared with birds given food on a predictable schedule. Baseline CORT concentrations increased slightly during the experiment, but did not differ between treatment groups. Birds with unpredictable food had slightly lower testosterone levels relative to controls, but there was no effect on estradiol or luteinizing hormone. Our findings offer weak support for the hypothesis that an unpredictable food supply will delay the onset of reproduction; however, the artificial lab environment may limit the application of these findings to free-living populations. 相似文献
189.
The aortic heart valve undergoes geometric and mechanical changes over time. The cusps of a normal, healthy valve thicken and become less extensible over time. In the disease calcific aortic stenosis (CAS), calcified nodules progressively stiffen the cusps. The local mechanical changes in the cusps, due to either normal aging or pathological processes, affect overall function of the valve. In this paper, we propose a computational model for the aging aortic valve that connects local changes to overall valve function. We extend a previous model for the healthy valve to describe aging. To model normal/uncomplicated aging, leaflet thickness and extensibility are varied versus age according to experimental data. To model calcification, initial sites are defined and a simple growth law is assumed. The nodules then grow over time, so that the area of calcification increases from one model to the next model representing greater age. Overall valve function is recorded for each individual model to yield a single simulation of valve function over time. This simulation is the first theoretical tool to describe the temporal behavior of aortic valve calcification. The ability to better understand and predict disease progression will aid in design and timing of patient treatments for CAS. 相似文献
190.
Synek L Schlager N Eliás M Quentin M Hauser MT Zárský V 《The Plant journal : for cell and molecular biology》2006,48(1):54-72
The exocyst is a hetero-oligomeric protein complex involved in exocytosis and has been extensively studied in yeast and animal cells. Evidence is now accumulating that the exocyst is also present in plants. Bioinformatic analysis of genes encoding plant homologs of the exocyst subunit, Exo70, revealed that three Exo70 subgroups are evolutionarily conserved among angiosperms, lycophytes and mosses. Arabidopsis and rice contain 22 and approximately 39 EXO70 genes, respectively, which can be classified into nine clusters considered to be ancient in angiosperms (one has been lost in Arabidopsis). We characterized two independent T-DNA insertional mutants of the AtEXO70A1 gene (exo70A1-1 and exo70A1-2). Heterozygous EXO70A1/exo70A1 plants appear to be normal and segregate in a 1:2:1 ratio, suggesting that neither male nor female gametophytes are affected by the EXO70A1 disruption. However, both exo70A1-1 and exo70A1-2 homozygotes exhibit an array of phenotypic defects. The polar growth of root hairs and stigmatic papillae is disturbed. Organs are generally smaller, plants show a loss of apical dominance and indeterminate growth where instead of floral meristems new lateral inflorescences are initiated in a reiterative manner. Both exo70A1 mutants have dramatically reduced fertility. These results suggest that the putative exocyst subunit EXO70A1 is involved in cell and organ morphogenesis. 相似文献