全文获取类型
收费全文 | 323篇 |
免费 | 35篇 |
专业分类
358篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 24篇 |
2014年 | 15篇 |
2013年 | 23篇 |
2012年 | 36篇 |
2011年 | 26篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 34篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 8篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1972年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有358条查询结果,搜索用时 0 毫秒
121.
Hugh A. L. Henry Mehdi Abedi Concepción L. Alados Karen H. Beard Lauchlan H. Fraser Anke Jentsch Juergen Kreyling Andrew Kulmatiski Eric G. Lamb Wei Sun Mathew R. Vankoughnett Susanna Venn Christiane Werner Ilka Beil Irmgard Blindow Sven Dahlke Maren Dubbert Alexandra Effinger Heath W. Garris Maite Gartzia Tobias Gebauer Mohammed A. S. Arfin Khan Andrey V. Malyshev John Morgan Charles Nock Janelle P. Paulson Yolanda Pueyo Holly J. Stover Xuechen Yang 《Ecosystems》2018,21(7):1432-1444
Reduced precipitation treatments often are used in field experiments to explore the effects of drought on plant productivity and species composition. However, in seasonally snow-covered regions reduced precipitation also reduces snow cover, which can increase soil frost depth, decrease minimum soil temperatures and increase soil freeze–thaw cycles. Therefore, in addition to the effects of reduced precipitation on plants via drought, freezing damage to overwintering plant tissues at or below the soil surface could further affect plant productivity and relative species abundances during the growing season. We examined the effects of both reduced rainfall (via rain-out shelters) and reduced snow cover (via snow removal) at 13 sites globally (primarily grasslands) within the framework of the International Drought Experiment, a coordinated distributed experiment. Plant cover was estimated at the species level, and aboveground biomass was quantified at the functional group level. Among sites, we observed a negative correlation between the snow removal effect on minimum soil temperature and plant biomass production the next growing season. Three sites exhibited significant rain-out shelter effects on plant productivity, but there was no correlation among sites between the rain-out shelter effect on minimum soil moisture and plant biomass. There was no interaction between snow removal and rain-out shelters for plant biomass, although these two factors only exhibited significant effects simultaneously for a single site. Overall, our results reveal that reduced snowfall, when it decreases minimum soil temperatures, can be an important component of the total effect of reduced precipitation on plant productivity. 相似文献
122.
Yao-Wu Yuan Janelle M. Sagawa Verónica S. Di Stilio H. D. Bradshaw Jr. 《Genetics》2013,194(2):523-528
The genetic and developmental basis of many ecologically important floral traits (e.g., carotenoid pigmentation, corolla tube structure, nectar volume, pistil and stamen length) remains poorly understood. Here we analyze a chemically induced floral mutant of Mimulus lewisii through bulk segregant analysis and transgenic experiments and identify a MIXTA-like R2R3 MYB gene that controls nectar guide formation in M. lewisii flowers, which involves epidermal cell development and carotenoid pigmentation. 相似文献
123.
Appleyard CB Cruz ML Isidro AA Arthur JC Jobin C De Simone C 《American journal of physiology. Gastrointestinal and liver physiology》2011,301(6):G1004-G1013
Evidence supports involvement of microflora in the transition of chronic inflammation to neoplasia. We investigated the protective efficacy of the probiotic VSL#3 in a model of colitis-associated colorectal cancer. Chronic colitis was induced in Sprague-Dawley rats by administration of trinitrobenzene sulfonic acid (TNBS), followed 6 wk later by systemic reactivation. To induce colitis-associated dysplasia and cancer, the animals received TNBS (intravenously) twice a week for 10 wk. One group received VSL#3 in drinking water from 1 wk before colitis induction until death. The colons were examined for damage and presence of dysplasia or cancer. Samples were analyzed for cell proliferation and apoptosis, vitamin D receptor (VDR) expression, angiogenic factors, and presence of alkaline sphingomyelinase or phosphatase. Microbial community composition was evaluated by terminal restriction fragment-length polymorphism analysis of the bacterial 16S rRNA gene. None of the probiotic-treated animals developed carcinoma, and no high-grade dysplasia was found in either the proximal or mid colon. In contrast, 29% of the animals in the control group developed carcinoma in one or more regions of the colon. VSL#3-treated animals had significantly less damage than the vehicle treated-controls in all areas of the colon, and this correlated with decreased richness and diversity of the mucosally adherent microbiota. Treatment with the probiotic increased the antiangiogenic factor angiostatin, VDR expression, and alkaline sphingomyelinase. We concluded that pretreatment with the probiotic VSL#3 can attenuate various inflammatory-associated parameters, delaying transition to dysplasia and cancer, thus offering its potential therapeutic use in patients with long-standing colitis. 相似文献
124.
Luyten YA Thompson JR Morrill W Polz MF Distel DL 《Applied and environmental microbiology》2006,72(1):412-417
Shipworms (wood-boring bivalves of the family Teredinidae) harbor in their gills intracellular bacterial symbionts thought to produce enzymes that enable the host to consume cellulose as its primary carbon source. Recently, it was demonstrated that multiple genetically distinct symbiont populations coexist within one shipworm species, Lyrodus pedicellatus. Here we explore the extent to which symbiont communities vary among individuals of this species by quantitatively examining the diversity, abundance, and pattern of occurrence of symbiont ribotypes (unique 16S rRNA sequence types) among specimens drawn from a single laboratory-reared population. A total of 18 ribotypes were identified in two clone libraries generated from gill tissue of (i) a single specimen and (ii) four pooled specimens. Phylogenetic analysis assigned all of the ribotypes to a unique clade within the gamma subgroup of proteobacteria which contained at least five well-supported internal clades (phylotypes). By competitive quantitative PCR and constant denaturant capillary electrophoresis, we estimated the number and abundance of symbiont phylotypes in gill samples of 13 individual shipworm specimens. Phylotype composition varied greatly; however, in all specimens the numerically dominant symbiont belonged to one of two nearly mutually exclusive phylotypes, each of which was detected with similar frequencies among specimens. A third phylotype, containing the culturable symbiont Teredinibacter turnerae, was identified in nearly all specimens, and two additional phylotypes were observed more sporadically. Such extensive variation in ribotype and phylotype composition among host specimens adds to a growing body of evidence that microbial endosymbiont populations may be both complex and dynamic and suggests that such genetic variation should be evaluated with regard to physiological and ecological differentiation. 相似文献
125.
Lawrence JL Schrick FN Hopkins FM Welborn MG McCracken MD Sonstegard T Wilson TJ Edwards JL 《Reproductive biology》2005,5(2):171-184
The objective was to evaluate development of cloned embryos constructed with serum-starved versus fed ovarian granulosa cells. Fusion of somatic cells with cytoplasts (50.7 and 50.7%; SEM=5.5), development of cloned embryos to 8-16-cell (59.4 and 62.6%; SEM=6.4), and compact morula/blastocyst-stages (24.9 and 26.5%; SEM=8.5) was similar for serum-starved and fed groups. More heifers were confirmed pregnant with clones derived from serum-starved cells (9/13, 67.2% versus 11/25, 44%). However, embryonic loss between 29-50 days was greater for clones constructed with serum-starved (88.9%) versus fed (36.4%) cells. Development of clones derived from serum-fed cells through placentation and differentiation was not predictive of competency to term. Fetal deaths occurred in the majority of late term pregnancies as a result of complications from hydrallantois. Only one fetus derived from serum-fed ovarian granulosa cells developed to term (278 days). At birth and for approximately 9 consecutive months thereafter, routine veterinary examinations confirmed expected growth patterns. In summary, the use of serum fed granulosa cells for nuclear transfer was coincident with a high incidence of third trimester losses associated with hydrallantois and fetal oversize. 相似文献
126.
Bolin Geng Gregory Basarab Janelle Comita-Prevoir Madhusudhan Gowravaram Pamela Hill Andrew Kiely James Loch Lawrence MacPherson Marshall Morningstar George Mullen Ekundayo Osimboni Alexander Satz Charles Eyermann Tomas Lundqvist 《Bioorganic & medicinal chemistry letters》2009,19(3):930-936
An SAR study of an HTS screening hit generated a series of pyridodiazepine amines as potent inhibitors of Helicobacter pylori glutamate racemase (MurI) showing highly selective anti-H. pylori activity, marked improved solubility, and reduced plasma protein binding. X-ray co-crystal E–I structures were obtained. These uncompetitive inhibitors bind at the MurI dimer interface. 相似文献
127.
128.
Weaver J 《PLoS biology》2011,9(11):e1001204
129.
130.
Janelle R. Thompson Mark A. Randa Luisa A. Marcelino Aoy Tomita-Mitchell Eelin Lim Martin F. Polz 《Applied microbiology》2004,70(7):4103-4110
Vibrios are ubiquitous marine bacteria that have long served as models for heterotrophic processes and have received renewed attention because of the discovery of increasing numbers of facultatively pathogenic strains. Because the occurrence of specific vibrios has frequently been linked to the temperature, salinity, and nutrient status of water, we hypothesized that seasonal changes in coastal water bodies lead to distinct vibrio communities and sought to characterize their level of differentiation. A novel technique was used to quantify shifts in 16S rRNA gene abundance in samples from Barnegat Bay, N.J., collected over a 15-month period. Quantitative PCR (QPCR) with primers specific for the genus Vibrio was combined with separation and quantification of amplicons by constant denaturant capillary electrophoresis (CDCE). Vibrio populations identified by QPCR-CDCE varied between summer and winter samples, suggesting distinct warm-water and year-round populations. Identification of the CDCE populations by cloning and sequencing of 16S rRNA genes from two summer and two winter samples confirmed this distinction. It further showed that CDCE populations corresponded in most cases to ~98% rRNA similarity groups and suggested that the abundance of these follows temperature trends. Phylogenetic comparison yielded closely related cultured and often pathogenic representatives for most sequences, and the temperature ranges of these isolates confirmed the trends seen in the environmental samples. Overall, this suggests that temperature is a good predictor of the occurrence of closely related vibrios but that considerable microdiversity of unknown significance coexists within this trend. 相似文献