全文获取类型
收费全文 | 2051篇 |
免费 | 166篇 |
专业分类
2217篇 |
出版年
2023年 | 12篇 |
2022年 | 20篇 |
2021年 | 53篇 |
2020年 | 25篇 |
2019年 | 25篇 |
2018年 | 36篇 |
2017年 | 26篇 |
2016年 | 57篇 |
2015年 | 110篇 |
2014年 | 103篇 |
2013年 | 130篇 |
2012年 | 148篇 |
2011年 | 177篇 |
2010年 | 95篇 |
2009年 | 76篇 |
2008年 | 125篇 |
2007年 | 121篇 |
2006年 | 115篇 |
2005年 | 132篇 |
2004年 | 136篇 |
2003年 | 110篇 |
2002年 | 94篇 |
2001年 | 15篇 |
2000年 | 7篇 |
1999年 | 20篇 |
1998年 | 27篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有2217条查询结果,搜索用时 15 毫秒
81.
Jeffrey?D.?HollandEmail author Lenore?Fahrig Naomi?Cappuccino 《Journal of Insect Conservation》2005,9(2):109-119
Reproductive rate has been suggested to have a positive effect on the amount of habitat loss a species can tolerate while emigration from habitat patches has been suggested to have both positive and negative effects. Forest fragmentation has been suggested to have negative effects on forest species. We determined the extinction threshold for 12 species of saproxylic (dead wood dependent) longhorned beetles (Coleoptera: Cerambycidae) using trap catch data from Ontario, Canada. We also determined the maximum egg production of each species and whether they were likely to move outside of forest patches. We found a strong negative relationship between reproductive rate and the minimum habitat amount required for species presence. This relationship is obscured if the scale of investigation is not appropriate for the study organism. As well, species caught moving outside forest habitat had lower extinction thresholds than species not caught moving outside forest but this was not significant after accounting for reproductive rate. Fragmentation did not have an effect on the minimum habitat requirements. These relationships can inform predictions of which species will be most affected by habitat loss. 相似文献
82.
Orfila C Sørensen SO Harholt J Geshi N Crombie H Truong HN Reid JS Knox JP Scheller HV 《Planta》2005,222(4):613-622
An insertion in the promoter of the Arabidopsis thaliana QUA1 gene (qua1-1 allele) leads to a dwarf plant phenotype and a reduction in cell adhesion, particularly between epidermal cells in seedlings
and young leaves. This coincides with a reduction in the level of homogalacturonan epitopes and the amount of GalA in isolated
cell walls (Bouton et al., Plant Cell 14: 2577 2002). The present study was undertaken in order to investigate further the link between QUA1 and cell wall biosynthesis. We have used rapidly elongating inflorescence stems to compare cell wall biosynthesis in wild
type and qua1-1 mutant tissue. Relative to the wild type, homogalacturonan α-1-4-D-galacturonosyltransferase activity was consistently reduced in qua1-1 stems (by about 23% in microsomal and 33% in detergent-solubilized membrane preparations). Activities of β-1-4-D-xylan synthase, β-1-4-D-galactan synthase and β-glucan synthase II activities were also measured in microsomal membranes. Of these, only β-1-4-D-xylan synthase was affected, and was reduced by about 40% in qua1-1 stems relative to wild type. The mutant phenotype was apparent in inflorescence stems, and was investigated in detail using
microscopy and cell wall composition analyses. Using in situ PCR techniques, QUA1 mRNA was localized to discrete cells of the vascular tissue and subepidermal layers. In mutant stems, the organization of
these tissues was disrupted and there was a modest reduction in homogalacturonan (JIM5) epitopes. This study demonstrates
a specific role for QUA1 in the development of vascular tissue in rapidly elongating inflorescence stems and supports a role
of QUA1 in pectin and hemicellulose cell wall synthesis through affects on α-1,4-D-galacturonosyltransferase and β-1,4-D-xylan synthase activities. 相似文献
83.
Mukherjee A Morosky SA Delorme-Axford E Dybdahl-Sissoko N Oberste MS Wang T Coyne CB 《PLoS pathogens》2011,7(3):e1001311
The host innate immune response to viral infections often involves the activation of parallel pattern recognition receptor (PRR) pathways that converge on the induction of type I interferons (IFNs). Several viruses have evolved sophisticated mechanisms to attenuate antiviral host signaling by directly interfering with the activation and/or downstream signaling events associated with PRR signal propagation. Here we show that the 3C(pro) cysteine protease of coxsackievirus B3 (CVB3) cleaves the innate immune adaptor molecules mitochondrial antiviral signaling protein (MAVS) and Toll/IL-1 receptor domain-containing adaptor inducing interferon-beta (TRIF) as a mechanism to escape host immunity. We found that MAVS and TRIF were cleaved in CVB3-infected cells in culture. CVB3-induced cleavage of MAVS and TRIF required the cysteine protease activity of 3C(pro), occurred at specific sites and within specialized domains of each molecule, and inhibited both the type I IFN and apoptotic signaling downstream of these adaptors. 3C(pro)-mediated MAVS cleavage occurred within its proline-rich region, led to its relocalization from the mitochondrial membrane, and ablated its downstream signaling. We further show that 3C(pro) cleaves both the N- and C-terminal domains of TRIF and localizes with TRIF to signalosome complexes within the cytoplasm. Taken together, these data show that CVB3 has evolved a mechanism to suppress host antiviral signal propagation by directly cleaving two key adaptor molecules associated with innate immune recognition. 相似文献
84.
Polygyny does not explain the superior competitive ability of dominant ant associates in the African ant‐plant,Acacia (Vachellia) drepanolobium 下载免费PDF全文
John H. Boyle Dino J. Martins Julianne Pelaez Paul M. Musili Staline Kibet S. Kimani Ndung'u David Kenfack Naomi E. Pierce 《Ecology and evolution》2018,8(3):1441-1450
The Acacia drepanolobium (also known as Vachellia drepanolobium) ant‐plant symbiosis is considered a classic case of species coexistence, in which four species of tree‐defending ants compete for nesting space in a single host tree species. Coexistence in this system has been explained by trade‐offs in the ability of the ant associates to compete with each other for occupied trees versus the ability to colonize unoccupied trees. We seek to understand the proximal reasons for how and why the ant species vary in competitive or colonizing abilities, which are largely unknown. In this study, we use RADseq‐derived SNPs to identify relatedness of workers in colonies to test the hypothesis that competitively dominant ants reach large colony sizes due to polygyny, that is, the presence of multiple egg‐laying queens in a single colony. We find that variation in polygyny is not associated with competitive ability; in fact, the most dominant species, unexpectedly, showed little evidence of polygyny. We also use these markers to investigate variation in mating behavior among the ant species and find that different species vary in the number of males fathering the offspring of each colony. Finally, we show that the nature of polygyny varies between the two commonly polygynous species, Crematogaster mimosae and Tetraponera penzigi: in C. mimosae, queens in the same colony are often related, while this is not the case for T. penzigi. These results shed light on factors influencing the evolution of species coexistence in an ant‐plant mutualism, as well as demonstrating the effectiveness of RADseq‐derived SNPs for parentage analysis. 相似文献
85.
The effects of glucagon, 3′,5′-AMP, 3′,5′-GMP and dexamethasone on ion fluxes and transmembrane-potential changes were compared in perfused livers from normal and adrenalectomized rats. Glucagon and cyclic nucleotide administration resulted in a similar redistribution of Na+ and K+ and membrane hyperpolarization in both groups. Dexamethasone at a dose which restores the gluconeogenic response after adrenalectomy, had no effect on either the ion movements or membrane potential and did not alter the responses to cyclic nucleotides or glucagon in either normal or adrenalectomized rat livers. These results suggest that the permissive effect of glucacorticoids on gluconeogenesis might be related to an event following ion movement. 相似文献
86.
Masaaki Yoshida Naoki Kiyota Kazuichi Maruyama Hiroshi Kunikata Masahiro Toyokawa Shigehiro Hagiwara Koichi Makimura Naomi Sato Shinji Taniuchi Toru Nakazawa 《Mycopathologia》2018,183(2):451-457
Endogenous fungal endophthalmitis (EFE) caused by disseminated fusariosis is a rare condition that generally has a poor outcome, even with intensive therapy. Here, we describe a case in which this type of EFE was diagnosed with vitreous sampling and was successfully treated with 25-gauge vitrectomy and antifungals, including liposomal amphotericin B and voriconazole. A 16-year-old male patient undergoing treatment for acute myeloid leukemia complained of eye pain and blurred vision in his right eye. Treatment was initiated for a vitreous opacity, possibly associated with herpetic retinitis, but the patient worsened and he was referred to us. Right-eye visual acuity was limited to light perception. We suspected endogenous endophthalmitis and performed 25-gauge vitrectomy with antibiotic perfusion of ceftazidime, vancomycin, and voriconazole. Vitreous culturing revealed the presence of Fusarium solani species complex, and enhanced computed tomography revealed disseminated fusariosis lesions in the lung, spleen, and the soft tissue of the left upper arm. The patient received antifungal treatment with liposomal amphotericin B and voriconazole, and these conditions were eliminated. Visual acuity recovered to 20/400 after additional vitrectomy for tractional retinal detachment and was maintained at this level during the 6-month follow-up period. The success of our treatment allowed the capture of optical coherence tomography images of the retina during fusarium-associated endogenous endophthalmitis and the follow-up period. Furthermore, this case showed that immediate vitrectomy for suspected EFE and intensive treatment can lead to a good clinical outcome. 相似文献
87.
Analysis of Vibrio seventh pandemic island II and novel genomic islands in relation to attachment sequences among a wide variety of Vibrio cholerae strains 下载免费PDF全文
Tuan Hai Nguyen Tho Duc Pham Naomi Higa Hanako Iwashita Taichiro Takemura Makoto Ohnishi Kouichi Morita Tetsu Yamashiro 《Microbiology and immunology》2018,62(3):150-157
88.
John W. Scott Jonathan S. Oakhill Naomi X.Y. Ling Christopher G. Langendorf Richard C. Foitzik Bruce E. Kemp Olaf-Georg Issinger 《Biochemical and biophysical research communications》2014
The AMP-activated protein kinase (AMPK) regulates cellular and whole-body energy balance in response to changes in adenylate charge and hormonal signals. Activation of AMPK in tissues such as skeletal muscle and liver reverses many of the metabolic defects associated with obesity and Type 2 diabetes. Here we report a bi-quinoline (JJO-1) that allosterically activates all AMPK αβγ isoforms in vitro except complexes containing the γ3 subunit. JJO-1 does not directly activate the autoinhibited α subunit kinase domain and differs among other known direct activators of AMPK in that allosteric activation occurs only at low ATP concentrations, and is not influenced by either mutation of the γ subunit adenylate-nucleotide binding sites or deletion of the β subunit carbohydrate-binding module. Our findings indicate that AMPK has multiple modes of allosteric activation that may be exploited to design isoform-specific activators as potential therapeutics for metabolic diseases. 相似文献
89.
Kasumi Takeuchi Wataru Tsuchiya Naomi Noda Rintaro Suzuki Toshimasa Yamazaki Dieter Haas 《Environmental microbiology》2014,16(8):2538-2549
In Pseudomonas protegens CHA0 and other fluorescent pseudomonads, the Gac/Rsm signal transduction pathway controls secondary metabolism and suppression of fungal root pathogens via the expression of regulatory small RNAs (sRNAs). Because of its high cost, this pathway needs to be protected from overexpression and to be turned off in response to environmental stress such as the lack of nutrients. However, little is known about its underlying molecular mechanisms. In this study, we demonstrated that Lon protease, a member of the ATP‐dependent protease family, negatively regulated the Gac/Rsm cascade. In a lon mutant, the steady‐state levels and the stability of the GacA protein were significantly elevated at the end of exponential growth. As a consequence, the expression of the sRNAs RsmY and RsmZ and that of dependent physiological functions such as antibiotic production were significantly enhanced. Biocontrol of Pythium ultimum on cucumber roots required fewer lon mutant cells than wild‐type cells. In starved cells, the loss of Lon function prolonged the half‐life of the GacA protein. Thus, Lon protease is an important negative regulator of the Gac/Rsm signal transduction pathway in P. protegens. 相似文献
90.
Yanyan Guo Hushan Yuan Natalie M. Claudio Sreekanth Kura Naomi Shakerdge Thorsten R. Mempel Brian J. Bacskai Lee Josephson 《PloS one》2014,9(4)
“PEG-like Nanoprobes” (PN’s) are pharmacokinetically and optically tunable nanomaterials whose disposition in biological systems can be determined by fluorescence or radioactivity. PN’s feature a unique design where a single PEG polymer surrounds a short fluorochrome and radiometal bearing peptide, and endows the resulting nanoprobe with pharmacokinetic control (based on molecular weight of the PEG selected) and optical tunability (based on the fluorochrome selected), while the chelate provides a radiolabeling option. PN’s were used to image brain capillary angiography (intravital 2-photon microscopy), tumor capillary permeability (intravital fluorescent microscopy), and the tumor enhanced permeability and retention (EPR) effect (111In-PN and SPECT). Clinical applications of PN’s include use as long blood half-life fluorochromes for intraoperative angiography, for measurements of capillary permeability in breast cancer lesions, and to image EPR by SPECT, for stratifying patient candidates for long-circulating nanomedicines that may utilize the EPR mechanism. 相似文献