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101.
Irreplaceable mortality of Helicoverpa armigera due to natural enemies was studied in cotton in western Kenya. Field populations of H. armigera were followed in three types of subplots: where crawling predators were suppressed, where both crawling and flying predators were suppressed and where predators were unaffected. Ants were the predominant crawling predators, whereas anthocorids were the predominant flying predators. H. armigera mortality from egg to late larval stage was very high (96.4-99.7%) and was greater in the second than in the first generation. Suppression of the different groups of predators did not increase the density of the pest. It is argued that the high level of background mortality obscured the role of predators. The possible role of host-plant condition on background mortality is discussed. 相似文献
102.
103.
Two-component systems (TCSs) are diverse and abundant signal transduction pathways found predominantly in prokaryotes. This
review focuses on insights into TCS evolution made possible by the sequencing of whole prokaryotic genomes. Typical TCSs comprise
an autophosphorylating protein (a histidine kinase), which transfers a phosphoryl group onto an effector protein (a response
regulator), thus modulating its activity. Histidine kinases and response regulators are usually found encoded as pairs of
adjacent genes within a genome, with multiple examples in most prokaryotes. Recent studies have shed light on major themes
of TCS evolution, including gene duplication, gene gain/loss, gene fusion/fission, domain gain/loss, domain shuffling and
the emergence of complexity. Coupled with an understanding of the structural and biophysical properties of many TCS proteins,
it has become increasingly possible to draw inferences regarding the functional consequences of such evolutionary changes.
In turn, this increase in understanding has the potential to enhance both our ability to rationally engineer TCSs, and also
allow us to more powerfully correlate TCS evolution with behavioural phenotypes and ecological niche occupancy. 相似文献
104.
Programmed cell death during development of cowpea (Vigna unguiculata (L.) Walp.) seed coat 下载免费PDF全文
NATHÁLIA BASTOS LIMA FERNANDA GOMES TRINDADE MAURA DA CUNHA ANTÔNIA ELENIR AMÂNCIO OLIVEIRA JENNIFER TOPPING KEITH LINDSEY KÁTIA VALEVSKI SALES FERNANDES 《Plant, cell & environment》2015,38(4):718-728
The seed coat develops primarily from maternal tissues and comprises multiple cell layers at maturity, providing a metabolically dynamic interface between the developing embryo and the environment during embryogenesis, dormancy and germination of seeds. Seed coat development involves dramatic cellular changes, and the aim of this research was to investigate the role of programmed cell death (PCD) events during the development of seed coats of cowpea [Vigna unguiculata (L.) Walp.]. We demonstrate that cells of the developing cowpea seed coats undergo a programme of autolytic cell death, detected as cellular morphological changes in nuclei, mitochondria, chloroplasts and vacuoles, DNA fragmentation and oligonucleosome accumulation in the cytoplasm, and loss of membrane viability. We show for the first time that classes 6 and 8 caspase‐like enzymes are active during seed coat development, and that these activities may be compartmentalized by translocation between vacuoles and cytoplasm during PCD events. 相似文献
105.
A metagenetic approach to determine the diversity and distribution of cyst nematodes at the level of the country,the field and the individual 下载免费PDF全文
106.
107.
Hendrik Adams Pier A Scotti Hans De Cock Joen Luirink Jan Tommassen 《European journal of biochemistry》2002,269(22):5564-5571
Signal sequences often contain alpha-helix-destabilizing amino acids within the hydrophobic core. In the precursor of the Escherichia coli outer-membrane protein PhoE, the glycine residue at position -10 (Gly-10) is thought to be responsible for the break in the alpha-helix. Previously, we showed that substitution of Gly-10 by alpha-helix-promoting residues (Ala, Cys or Leu) reduced the proton-motive force dependency of the translocation of the precursor, but the actual role of the helix breaker remained obscure. Here, we considered the possibility that extension of the alpha-helical structure in the signal sequence resulting from the Gly-10 substitutions affects the targeting pathway of the precursor. Indeed, the mutations resulted in reduced dependency on SecB for targeting in vivo. In vitro cross-linking experiments revealed that the G-10L and G-10C mutant PhoE precursors had a dramatically increased affinity for P48, one of the constituents of the signal-recognition particle (SRP). Furthermore, in vitro cross-linking experiments revealed that the G-10L mutant protein is routed to the SecYEG translocon via the SRP pathway, the targeting pathway that is exploited by integral inner-membrane proteins. Together, these data indicate that the helix breaker in cleavable signal sequences prevents recognition by SRP and is thereby, together with the hydrophobicity of the signal sequence, a determinant of the targeting pathway. 相似文献
108.
109.
Ecological effects of invasive alien insects 总被引:1,自引:0,他引:1
Marc Kenis Marie-Anne Auger-Rozenberg Alain Roques Laura Timms Christelle Péré Matthew J. W. Cock Josef Settele Sylvie Augustin Carlos Lopez-Vaamonde 《Biological invasions》2009,11(1):21-45
A literature survey identified 403 primary research publications that investigated the ecological effects of invasive alien
insects and/or the mechanisms underlying these effects. The majority of these studies were published in the last 8 years and
nearly two-thirds were carried out in North America. These publications concerned 72 invasive insect species, of which two
ant species, Solenopsis invicta and Linepithema humile, accounted for 18% and 14% of the studies, respectively. Most publications investigated effects on native biodiversity at
population or community level. Genetic effects and, to a lesser extent, effects on ecosystem services and processes were rarely
explored. We review the effects caused by different insect invaders according to: their ecosystem roles, i.e. herbivores,
predators, parasites, parasitoids and pollinators; the level of biological organisation at which they occur; and the direct
and indirect mechanisms underlying these effects. The best documented effects occur in invasive ants, Eurasian forest herbivores
invasive in North America, and honeybees. Impacts may occur through simple trophic interactions such as herbivory, predation
or parasitism. Alien species may also affect native species and communities through more complex mechanisms such as competition
for resources, disease transmission, apparent competition, or pollination disruption, among others. Finally, some invasive
insects, particularly forest herbivores and ants, are known to affect ecosystem processes through cascading effects. We identify
biases and gaps in our knowledge of ecological effects of invasive insects and suggest further opportunities for research.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
110.
Corry-Anke Brandsma Machteld N Hylkema Marie Geerlings Wouter H van Geffen Dirkje S Postma Wim Timens Huib AM Kerstjens 《Respiratory research》2009,10(1):108
There is increasing evidence that a specific immune response contributes to the pathogenesis of COPD. B-cell follicles are present in lung tissue and increased anti-elastin titers have been found in plasma of COPD patients. Additionally, regulatory T cells (Tregs) have been implicated in its pathogenesis as they control immunological reactions. We hypothesize that the specific immune response in COPD is smoke induced, either by a direct effect of smoking or as a result of smoke-induced lung tissue destruction (i.e. formation of neo-epitopes or auto antigens). Furthermore, we propose that Tregs are involved in the suppression of this smoke-induced specific immune response.The presence of B cells, memory B cells and Tregs was assessed by flow cytometry in peripheral blood of 20 COPD patients and 29 healthy individuals and related to their current smoking status.COPD patients had lower (memory) B-cell percentages and higher Treg percentages in peripheral blood than healthy individuals, with a significant negative correlation between these cells. Interestingly, current smokers had higher percentages of (class-switched) memory B cells than ex-smokers and never smokers, irrespective of COPD.This increase in (class-switched) memory B cells in current smokers is intriguing and suggests that smoke-induced neo-antigens may be constantly induced in the lung. The negative correlation between B cells and Tregs in blood is in line with previously published observations that Tregs can suppress B cells. Future studies focusing on the presence of these (class switched) memory B cells in the lung, their antigen specificity and their interaction with Tregs are necessary to further elucidate the specific B-cell response in COPD. 相似文献