全文获取类型
收费全文 | 991篇 |
免费 | 113篇 |
国内免费 | 1篇 |
出版年
2021年 | 13篇 |
2020年 | 28篇 |
2019年 | 47篇 |
2018年 | 46篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 34篇 |
2014年 | 40篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 26篇 |
2010年 | 41篇 |
2009年 | 28篇 |
2008年 | 33篇 |
2007年 | 38篇 |
2006年 | 37篇 |
2005年 | 26篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 15篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 34篇 |
1998年 | 31篇 |
1997年 | 15篇 |
1996年 | 29篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 11篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1970年 | 10篇 |
1969年 | 5篇 |
排序方式: 共有1105条查询结果,搜索用时 15 毫秒
941.
Shao ZH Hsu CW Chang WT Waypa GB Li J Li D Li CQ Anderson T Qin Y Schumacker PT Becker LB Hoek TL 《Cell biology and toxicology》2006,22(3):149-158
Grape seed proanthocyanidin extract (GPSE) at high doses has been shown to exhibit cytotoxicity that is associated with increased
apoptotic cell death. Nitric oxide (NO), being a regulator of apoptosis, can be increased in production by the administration
of GSPE. In a chick cardiomyocyte study, we demonstrated that high-dose (500 μg/ml) GSPE produces a significantly high level
of NO that contributes to increased apoptotic cell death detected by propidium iodide and terminal deoxynucleotidyl transferase-mediated
dUTP nick-end labeling (TUNEL) staining. It is also associated with the depletion of intracellular glutathione (GSH), probably
due to increased consumption by NO with the formation of S-nitrosoglutathione. Co-treatment with L-NAME, a NO synthase inhibitor, results in reduction of NO and apoptotic cell death.
The decline in reduced GSH/oxidized GSH (GSSG) ratio is also reversed. N-Acetylcysteine, a thiol compound that reacts directly with NO, can reduce the increased NO generation and reverse the decreased
GSH/GSSG ratio, thereby attenuating the cytotoxicity induced by high-dose GSPE. Taken together, these results suggest that
endogenous NO synthase (NOS) activation and excessive NO production play a key role in the pathogenesis of high-dose GSPE-induced
cytotoxicity. 相似文献
942.
943.
944.
Daniel E Impoinvil Joseph Keating Charles M Mbogo Matthew D Potts Rinku Roy Chowdhury John C Beier 《Journal of vector ecology》2008,33(1):107-116
In this study we 1) describe the abundance of Anopheles and culicine immatures in different water body types in urban Malindi, Kenya, 2) compare Anopheles immature density in relation to culicine immature density, and 3) identify characteristics that influence the likelihood of water bodies being co-colonized by Anopheles and culicines. Entomological and environmental cross-sectional surveys conducted in 2001 and 2002 were used in the analysis. A total of 889 Anopheles and 7,217 culicine immatures were found in diverse water body types in 2001 and 2002. Car-track pools (n = 45) and unused swimming pools (n = 25) comprised 61% (70 of 115) of all water bodies found and served as the main habitats for Anopheles immatures. Of the 38 water bodies found containing Anopheles immature mosquitoes, 63% (24 of 38) were car-track pools and unused swimming pools. Culicine immatures utilized several water body types as habitats. We found that Anopheles and culicine immatures had higher density when occurring individually compared to when they occurred simultaneously. We determined that season, permanency, and water body area size influenced the likelihood of water bodies being simultaneously positive for Anopheles and culicines. Though Anopheles immatures were found in diverse water body types, their numbers were low compared to culicine immatures. The low density of Anopheles immatures suggests that Anopheles larval control is an achievable goal in Malindi. 相似文献
945.
Scent-marking displays provide honest signals of health and infection 总被引:10,自引:0,他引:10
Males of many species produce scent marks and other olfactorysignals that function to intimidate rivals and attract females.It has been suggested that scent marks provide an honest, cheat-proofdisplay of an individual's health and condition. Here we reportseveral findings that address this hypothesis in wild-derivedhouse mice (Mus musculus domesticus). (1) We exposed males tofemale odor, which induces an increase in testosterone, andfound that sexual stimulation significantly increased the males'scent-marking and the attractiveness of their scent marks tofemales. (2) We challenged sexually stimulated males with anonreplicating strain of bacteria (Salmonella enterica C5TS)to activate immunity and found that this significantly decreasedthe males' scent-marking and the attractiveness of their scentmarks to females. (3) We collected scent marks from infectedand sham-infected males when they were sexually stimulated ornot, and we found that females could significantly discriminatethe scent marks of infected versus control males, but only whenthe males were sexually stimulated. Taken together, our resultsindicate that male mice modulate their scent-marking displaydepending on their health and perceived mating opportunities.Increased scent marking enhances males' attractiveness to females,scent marks provide an honest indicator of bacterial infection(and perhaps immune activation), and females are able to assessthe health of males more easily when males mark at a high rate. 相似文献
946.
Eucalyptus globulus Labill. ssp. globulus is an important tree species for the pulp and paper industry, and several breeding programmes throughout the world are striving
to improve key traits such as growth and wood density. This study aimed to detect quantitative trait loci (QTL) for growth,
wood density, relative bark thickness and early flowering in a single full-sib E. globulus family grown across seven sites. Growth was measured a number of times over a 6-year period, enabling temporal stability
of growth QTL to be studied. Ten putative QTL (LOD > 2.0) were detected in the single family, which was of moderate size.
Based on permutations of the trait data, six of these QTL were significant at the experimentwise significance level of 0.1
for at least one of the four models implemented in analysis to remove site effects. For wood density, two putative QTL explained
20% of the variance for the trait, indicating that a small number of QTL might explain a reasonable proportion of the trait
variance. One of these QTL was found to be independent of QTL for growth whereas the second QTL co-segregated with a QTL for
relative incremental growth. The marker nearest to this QTL was associated with fast growth but low wood density. A putative
growth QTL at year 6 was found to be relatively stable across ages. In addition, it was found that residuals from models based
on measurements from across all families across all sites in the trial detected QTL with greater experimentwise significance. 相似文献
947.
Ocaña-de Jesús RL AT Gutiérrez-Ibáñez JR Sánchez-Pale MD Mariezcurrena-Berasain G Velázquez-Garduño A Laguna Cerda I Rojas Puebla 《Phyton》2015,84(1):45-50
The aim of the current research was to determine tomato (Solanum lycopersicum L.) microbiological quality produced under greenhouse conditions in 5 municipalities of the State of Mexico. Studies were conducted during the 2013 production cycle to know the risks and apply prevention strategies prior to its consumption. A microbiological analysis of samples of irrigation water, soil and 100 tomato fruits variety cid was performed to determine Aerobic Mesophiles, Total Coliforms and Fecal Coliforms. The methodology used were those according to the Official Mexican Standards NOM- 109-SSA1-1994, NOM-110-SSA1-1994, NOM-092-SSA1-1994, NOM-113-SSA1-1994, and the Regulations of the National French Organization for Standardization (AFNOR) NF V08-60, and NOM-093-SSA1-1994, which establish the allowable limits for the study microorganisms. The results showed a zero level of pollution in water and soil samples. For fruits, levels of Aerobic Mesophilic were within the maximum limits permitted by the standards. The municipality of Texcaltitlan showed the highest average for these microorganisms (10083.80 CFU/mL). Huixquilucan showed 2266.84 CFU/mL for Total Coliforms. For Fecal Coliforms, municipalities of Coatepec and Texcaltitlan exceeded the allowed limit. 相似文献
948.
SUKYUNG KIM HOONHEE SEO MD ABDUR RAHIM HANIEH TAJDOZIAN YUN-SOOK KIM HO-YEON SONG 《Polish journal of microbiology》2021,70(3):345
Human vaginal microorganisms play an important role in maintaining good health throughout the human life cycle. An imbalance in the vaginal microbiota is associated with an increased risk of pelvic inflammatory disease (PID). This study aimed to characterize and compare vaginal microbial profiles of premenopausal Korean women with and without PID. 74 Korean premenopausal female vaginal samples were obtained; 33 were from healthy women (a control group) and 41 from PID patients. Vaginal fluid samples were collected from the vaginal wall and posterior cervix and then analyzed by 16S ribosomal ribonucleic acid (rRNA) gene-based amplicon sequencing. Results showed a significant difference between the vaginal microbial communities of the two groups (Jensen-Shannon, p = 0.014; Bray-Curtis, p = 0.009; Generalized UniFrac, p = 0.007; UniFrac, p = 0.008). Lactobacillus accounted for the highest percentage (61.0%) of the control group but was significantly decreased (34.9%) in PID patients; this was the most significant difference among all bacterial communities (p = 0.028, LDA effect size = 5.129). In addition, in the PID patient group, species diversity significantly increased (Simpson, p = 0.07) as the proportion of various pathogens increased evenly, resulting in a polymicrobial infection. Similarly, lactate, which constituted the highest percentage of the organic acids in the control group, was significantly decreased in the PID patient group (p = 0.04). The present study’s findings will help understand PID from the microbiome perspective and are expected to contribute to the development of more efficient PID diagnosis and treatment modalities. 相似文献
949.
D A Steane G E McKinnon R E Vaillancourt B M Potts 《Molecular phylogenetics and evolution》1999,12(2):215-223
Sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA were obtained for 35 species of Eucalyptus s.s. and seven taxa representing five outgroup genera (Allosyncarpia, Angophora, Arillastrum, Corymbia, and Stockwellia). The sequences were analyzed cladistically. The data distinguished clearly between the two major subgenera of Eucalyptus s.s. (Symphyomyrtus and Monocalyptus) but indicated that subgenus Eudesmia may be paraphyletic. ITS sequence data demonstrated the potential to resolve relationships between sections within subgenus Symphyomyrtus. Within sections, however, taxa were poorly differentiated. At the generic level, Corymbia appeared to be paraphyletic due to the exclusion of Angophora. The positions of Allosyncarpia and Arillastrum relative to the ingroup remain unresolved. ITS sequence data may prove valuable for resolving other phylogenetic relationships at higher taxonomic levels within Eucalyptus. 相似文献
950.
Pollinator diversity and crop pollination services are at risk 总被引:1,自引:0,他引:1
Steffan-Dewenter I Potts SG Packer L 《Trends in ecology & evolution》2005,20(12):651-2; author reply 652-3