全文获取类型
收费全文 | 247篇 |
免费 | 18篇 |
出版年
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 5篇 |
2012年 | 33篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 11篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 22篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 62 毫秒
91.
Why did punishment and the use of reputation evolve in humans? According to one family of theories, they evolved to support the maintenance of cooperative group norms; according to another, they evolved to enhance personal gains from cooperation. Current behavioral data are consistent with both hypotheses (and both selection pressures could have shaped human cooperative psychology). However, these hypotheses lead to sharply divergent behavioral predictions in circumstances that have not yet been tested. Here we report results testing these rival predictions. In every test where social exchange theory and group norm maintenance theory made different predictions, subject behavior violated the predictions of group norm maintenance theory and matched those of social exchange theory. Subjects do not direct punishment toward those with reputations for norm violation per se; instead, they use reputation self-beneficially, as a cue to lower the risk that they personally will experience losses from defection. More tellingly, subjects direct their cooperative efforts preferentially towards defectors they have punished and away from those they haven’t punished; they avoid expending punitive effort on reforming defectors who only pose a risk to others. These results are not consistent with the hypothesis that the psychology of punishment evolved to uphold group norms. The circumstances in which punishment is deployed and withheld–its circuit logic–support the hypothesis that it is generated by psychological mechanisms that evolved to benefit the punisher, by allowing him to bargain for better treatment. 相似文献
92.
Bonatto AC Souza EM Oliveira MA Monteiro RA Chubatsu LS Huergo LF Pedrosa FO 《Archives of microbiology》2012,194(8):643-652
PII are signal-transducing proteins that integrate metabolic signals and transmit this information to a large number of proteins. In proteobacteria, PII are modified by GlnD (uridylyltransferase/uridylyl-removing enzyme) in response to the nitrogen status. The uridylylation/deuridylylation cycle of PII is also regulated by carbon and energy signals such as ATP, ADP and 2-oxoglutarate (2-OG). These molecules bind to PII proteins and alter their tridimensional structure/conformation and activity. In this work, we determined the effects of ATP, ADP and 2-OG levels on the in vitro uridylylation of Herbaspirillum seropedicae PII proteins, GlnB and GlnK. Both proteins were uridylylated by GlnD in the presence of ATP or ADP, although the uridylylation levels were higher in the presence of ATP and under high 2-OG levels. Under excess of 2-OG, the GlnB uridylylation level was higher in the presence of ATP than with ADP, while GlnK uridylylation was similar with ATP or ADP. Moreover, in the presence of ADP/ATP molar ratios varying from 10/1 to 1/10, GlnB uridylylation level decreased as ADP concentration increased, whereas GlnK uridylylation remained constant. The results suggest that uridylylation of both GlnB and GlnK responds to 2-OG levels, but only GlnB responds effectively to variation on ADP/ATP ratio. 相似文献
93.
Diversity of Bacillus thuringiensis Strains from Latin America with Insecticidal Activity against Different Mosquito Species 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jorge E. Ibarra M. Cristina del Rincn Sergio Ordúz David Noriega Graciela Benintende Rose Monnerat Leda Regis Cludia M. F. de Oliveira Humberto Lanz Mario H. Rodriguez Jorge Snchez Guadalupe Pea Alejandra Bravo 《Applied microbiology》2003,69(9):5269-5274
The characterization of selected Bacillus thuringiensis strains isolated from different Latin America countries is presented. Characterization was based on their insecticidal activity against Aedes aegypti, Culex quinquefasciatus, and Anopheles albimanus larvae, scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and plasmid profiles as well as PCR analysis using novel general and specific primers for cry and cyt genes encoding proteins active against mosquitoes (cyt1, cyt2, cry2, cry4A, cry4B, cry10, cry11, cry17, cry19, cry24, cry25, cry27, cry29, cry30, cry32, cry39, and cry40). Strains LBIT315, LBIT348, and IB604 showed threefold higher mosquitocidal activity against A. aegypti and C. quinquefasciatus larvae than B. thuringiensis subsp. israelensis and displayed high similarities with the B. thuringiensis subsp. israelensis used in this study with regard to protein and plasmid profiles and the presence of cry genes. Strain 147-8906 has activity against A. aegypti similar to that of B. thuringiensis subsp. israelensis but has different protein and plasmid profiles. This strain, harboring cry11, cry30, cyt1, and cyt2 genes, could be relevant for future resistance management interventions. Finally, the PCR screening strategy presented here led us to identify a putative novel cry11B gene. 相似文献
94.
Dynamics of Fungal Communities in Bulk and Maize Rhizosphere Soil in the Tropics 总被引:9,自引:1,他引:8
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Newton C. Marcial Gomes Olajire Fagbola Rodrigo Costa Norma Gouvea Rumjanek Arno Buchner Leda Mendona-Hagler Kornelia Smalla 《Applied microbiology》2003,69(7):3758-3766
The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants. 相似文献
95.
Nayanna de Oliveira Ramos Melo Helio De Sousa Peres Júnior Clara Araujo Diniz Matheus De Sousa Silva Telma Leda Gomes de Lemos Francisco Vagnaldo Fechine Jamacaru Conceio Aparecida Dornelas 《Biomédica : revista del Instituto Nacional de Salud》2022,42(2):253
Introduction. Cyclophosphamide (CP) is used to treat malignant neoplasias and control autoimmune diseases. Still, one of its metabolites, acrolein, is toxic to the urothelium and can lead to hemorrhagic cystitis and severe discomfort.Objective. To evaluate the ability of red propolis to prevent and treat CP-induced hemorrhagic cystitis in rats.Materials and methods. Red propolis was extracted in 1% gum arabic and administered subcutaneously (sc). In the first experiment, groups IA, IIA, and IIIA and groups IB, IIB, and IIIB received water, gum arabic (GA), or propolis, respectively, for 30 days. Then water (controls) or CP (treatment) was administered i.p. In the second experiment, groups IVA, VA, and VIA received water i.p. while groups IVB, VB, and VIB received CP i.p. This was followed by 5 injections at 2-hour intervals with either water, GA, or propolis. Bladder tissue was examined according to Gray’s criteria.Results. The total inflammatory histology score was significantly smaller in group VIB (11.33 ± 2.07). Mild inflammation predominated in group VIB while most of the animals in group IVB had severe inflammation (p=0.0375). Ulcers were predominantly multiple in Groups IVA and VB but rare or absent in Group VIB (p=0.0118). Urothelial cells were mostly absent in groups IVB and VB and present/normal in group VIB (p=0.0052). Fibrin was abundant in groups IVB and VA but mostly absent in group VIB (p=0.0273).Conclusions. Red propolis can reduce inflammation in CP-induced hemorrhagic cystitis in rats. 相似文献
96.
Immunological Cross-Reactivity Between Simian Virus 40 Large T Antigen and D2 Hybrid T Antigen 总被引:3,自引:3,他引:0
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ernst A. Baumann Deborah Stedman Leda Raptis Abraham Fuks Roger Hand 《Journal of virology》1981,38(3):1090-1094
A specific antiserum was raised in rabbits against D2 hybrid T antigen that had been purified from HeLa cells infected with the adenovirus/simian virus 40 hybrid, Ad2(+)D2. The specificity of this serum was compared with that of a conventional hamster antiserum against simian virus 40-induced tumors by immunoprecipitation and by a new radioimmune assay that can detect nanogram quantities of D2 hybrid T antigen. 相似文献
97.
Michailowsky V Celes MR Marino AP Silva AA Vieira LQ Rossi MA Gazzinelli RT Lannes-Vieira J Silva JS 《Journal of immunology (Baltimore, Md. : 1950)》2004,173(1):463-470
In this study, we investigated the involvement of Th1 cytokines in the expression of cell adhesion molecules (CAM) and recruitment of inflammatory cells to the heart of mice infected with Trypanosoma cruzi. Our results show that endogenously produced IFN-gamma is essential to induce optimal expression of VCAM-1 and ICAM-1 on the cardiac vascular endothelium of infected mice. Furthermore, the influx of inflammatory cells into the cardiac tissue was impaired in Th1 cytokine-deficient infected mice, paralleling the intensity of VCAM-1 and ICAM-1 expression on the vascular endothelium. Consistent with the importance of ICAM-1 in host resistance, ICAM-1 knockout (KO) mice were highly susceptible to T. cruzi infection, as assessed by mortality rate, parasitemia, and heart tissue parasitism. The enhanced parasitism was associated with a decrease in the numbers of CD4(+) and CD8(+) T lymphocytes in the heart tissue of ICAM-1 KO mice. Additionally, ICAM-1 KO mice mounted an unimpaired IFN-gamma response and IFN-gamma-dependent production of reactive nitrogen intermediates and parasite- specific IgG2a. Supporting the participation of ICAM-1 in cell migration during T. cruzi infection, the entrance of adoptively transferred PBL from T. cruzi-infected wild-type C57BL/6 mice into the cardiac tissue of ICAM-1 KO mice was significantly abrogated. Therefore, we favor the hypothesis that ICAM-1 plays a crucial role in T lymphocyte recruitment to the cardiac tissue and host susceptibility during T. cruzi infection. 相似文献
98.
Santiago HC Feng CG Bafica A Roffe E Arantes RM Cheever A Taylor G Vieira LQ Vierira LQ Aliberti J Gazzinelli RT Sher A 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(12):8165-8172
IFN-gamma is known to be required for host control of intracellular Trypanosoma cruzi infection in mice, although the basis of its protective function is poorly understood. LRG-47 is an IFN-inducible p47GTPase that has been shown to regulate host resistance to intracellular pathogens. To investigate the possible role of LRG-47 in IFN-gamma-dependent control of T. cruzi infection, LRG-47 knockout (KO) and wild-type (WT) mice were infected with the Y strain of this parasite, and host responses were analyzed. When assayed on day 12 after parasite inoculation, LRG-47 KO mice, in contrast to IFN-gamma KO mice, controlled early parasitemia almost as effectively as WT animals. However, the infected LRG-47 KO mice displayed a rebound in parasite growth on day 15, and all succumbed to the infection by day 19. Additional analysis indicated that LRG-47-deficient mice exhibit unimpaired proinflammatory responses throughout the infection. Instead, reactivated disease in the KO animals was associated with severe splenic and thymic atrophy, anemia, and thrombocytopenia not observed in their WT counterparts. In addition, in vitro studies revealed that IFN-gamma-stimulated LRG-47 KO macrophages display defective intracellular killing of amastigotes despite normal expression of TNF and NO synthetase type 2 and that both NO synthetase type 2 and LRG-47 are required for optimum IFN-gamma-dependent restriction of parasite growth. Together, these data establish that LRG-47 can influence pathogen control by simultaneously regulating macrophage-microbicidal activity and hemopoietic function. 相似文献
99.
Pedelini L Garcia-Gimeno MA Marina A Gomez-Zumaquero JM Rodriguez-Bada P López-Enriquez S Soriguer FC Cuesta-Muñoz AL Sanz P 《Protein science : a publication of the Protein Society》2005,14(8):2080-2086
It was recently described that the alpha5 and the alpha13 helices of human pancreatic glucokinase play a major role in the allosteric regulation of the enzyme. In order to understand the structural importance of these helices, we have performed site-directed mutagenesis to generate glucokinase derivatives with altered residues. We have analyzed the kinetic parameters of these mutated forms and compared them with wild-type and previously defined activating mutations in these helices (A456V and Y214C). We found two new activating mutations, A460R and Y215A, which increase the affinity of the enzyme for glucose. Our results suggest that substitutions in the alpha5 or the alpha13 helices that favor the closed, active conformation of the enzyme, either by improving the interaction with surrounding residues or by improving the flexibility of the region defined by these two helices, enhance the affinity of the enzyme for glucose, and therefore its performance as a glucose phosphorylating enzyme. 相似文献
100.