全文获取类型
收费全文 | 2708篇 |
免费 | 236篇 |
出版年
2023年 | 10篇 |
2022年 | 24篇 |
2021年 | 48篇 |
2020年 | 26篇 |
2019年 | 42篇 |
2018年 | 47篇 |
2017年 | 41篇 |
2016年 | 60篇 |
2015年 | 108篇 |
2014年 | 118篇 |
2013年 | 169篇 |
2012年 | 221篇 |
2011年 | 214篇 |
2010年 | 125篇 |
2009年 | 98篇 |
2008年 | 199篇 |
2007年 | 208篇 |
2006年 | 175篇 |
2005年 | 175篇 |
2004年 | 156篇 |
2003年 | 145篇 |
2002年 | 129篇 |
2001年 | 28篇 |
2000年 | 17篇 |
1999年 | 32篇 |
1998年 | 40篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1962年 | 3篇 |
排序方式: 共有2944条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
Rebecca L. Cain Nathan P. Snow Joanne C. Crawford David M. Williams William F. Porter 《The Journal of wildlife management》2019,83(8):1762-1772
For more than a century, the Boone and Crockett Club has kept records of harvest locations for 38 categories of North American big game, which includes measurement details and sizes of enduring characteristics (e.g., antlers, skulls, horns). All white-tailed deer (Odocoileus virginianus) entered in the Club records (i.e., record deer) have large antlers because the measurements must meet or exceed a minimum size to qualify for entry. We used the records from the Club to test the hypothesis that the spatial distribution in the harvest of record deer was related to the number of antlered deer harvested, variations in land productivity, soil mineral content, and attributes of land cover for 9 states in the midwestern United States. We used a Bayesian theoretical framework to develop a spatial model that examined the influence of explanatory variables on the number of record deer harvested in each county. In our study area, 3,658 record deer were harvested in 692 of the 856 counties (80.8%). More record deer were harvested in counties that had more high-contrast edges, less contiguous land cover, and greater variation in soil productivity. These results provide information for managers and hunters to better understand the spatial distribution of record deer and factors that are correlated with their distribution. © 2019 The Wildlife Society. 相似文献
105.
Marina Lpez‐Pozo Jaume Flexas Javier Gulías Marc Carriquí Miquel Nadal Alicia V. Perera‐Castro María Jos Clemente‐Moreno Jorge Gago Encarnacin Núez‐Olivera Javier Martínez‐Abaigar Antonio Hernndez Unai Artetxe Joanne Bentley Jill M. Farrant Amy Verhoeven Jos Ignacio García‐Plazaola Beatriz Fernndez‐Marín 《Physiologia plantarum》2019,167(4):540-555
Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (Fv/fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt‐solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50–200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial Fv/fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi‐quantitative expression of DHT that facilitates comparisons of species with different morpho‐physiological traits and/or ecological attributes. 相似文献
106.
107.
Michaeline B. N. Albright Stilianos Louca Daniel E. Winkler Kelli L. Feeser Sarah-Jane Haig Katrine L. Whiteson Joanne B. Emerson John Dunbar 《The ISME journal》2022,16(2):331
Microbiome engineering is increasingly being employed as a solution to challenges in health, agriculture, and climate. Often manipulation involves inoculation of new microbes designed to improve function into a preexisting microbial community. Despite, increased efforts in microbiome engineering inoculants frequently fail to establish and/or confer long-lasting modifications on ecosystem function. We posit that one underlying cause of these shortfalls is the failure to consider barriers to organism establishment. This is a key challenge and focus of macroecology research, specifically invasion biology and restoration ecology. We adopt a framework from invasion biology that summarizes establishment barriers in three categories: (1) propagule pressure, (2) environmental filtering, and (3) biotic interactions factors. We suggest that biotic interactions is the most neglected factor in microbiome engineering research, and we recommend a number of actions to accelerate engineering solutions.Subject terms: Community ecology, Microbial ecologyMicrobiome engineering is a rapidly evolving frontier for solutions to improve human health, agricultural productivity, and climate management. Microbiome engineering seeks to improve the function of an ecosystem by manipulating the composition of microbes. Two major challenges for successful microbiome engineering are (1) the design of a microbiome with improved function and (2) the establishment of an improved microbiome in a recipient system of interest. While multiple articles and reviews have addressed functional design [1–3], microbiome establishment has received less attention. Here, we propose a strategy to improve microbiome engineering by focusing on microbial establishment and leveraging insights from macrobial ecology.Two general engineering strategies are to manipulate indigenous microbes [4] or to introduce new members [5]. The latter involves the design and delivery of inoculants (a.k.a., probiotics in medical and agricultural arenas) and is a rapidly growing biotechnology sector. In their most general form, both strategies have been practiced crudely for thousands of years in human health [6] and agriculture [7]. However, despite current technical advances, inoculants frequently still fail to establish or confer long-lasting (months to years) modifications to ecosystem function [8]. We argue that this repeated failure is in part driven by lack of emphasis on establishment of inoculants.The problem of organism establishment in recipient ecosystems is not unique to microbiome engineering; it has roots in macrobiology, particularly invasion biology and restoration ecology. We propose that adopting a cross-disciplinary conceptual framework to identify barriers to organism establishment, and then prioritizing these barriers through targeted research will accelerate successful microbiome engineering. In addition, recognizing differences in terminology and experimental design within and across disciplines will facilitate research integration across diverse ecosystems and scales. The components of a more holistic strategy are discussed below. 相似文献
108.
Fiona McQuaid Rachel Mulholland Yuma Sangpang Rai Utkarsh Agrawal Helen Bedford J. Claire Cameron Cheryl Gibbons Partho Roy Aziz Sheikh Ting Shi Colin R. Simpson Judith Tait Elise Tessier Steve Turner Jaime Villacampa Ortega Joanne White Rachael Wood 《PLoS medicine》2022,19(2)
BackgroundIn 2020, the SARS-CoV-2 (COVID-19) pandemic and lockdown control measures threatened to disrupt routine childhood immunisation programmes with early reports suggesting uptake would fall. In response, public health bodies in Scotland and England collected national data for childhood immunisations on a weekly or monthly basis to allow for rapid analysis of trends. The aim of this study was to use these data to assess the impact of different phases of the pandemic on infant and preschool immunisation uptake rates.Methods and findingsWe conducted an observational study using routinely collected data for the year prior to the pandemic (2019) and immediately before (22 January to March 2020), during (23 March to 26 July), and after (27 July to 4 October) the first UK “lockdown”. Data were obtained for Scotland from the Public Health Scotland “COVID19 wider impacts on the health care system” dashboard and for England from ImmForm.Five vaccinations delivered at different ages were evaluated; 3 doses of “6-in-1” diphtheria, tetanus, pertussis, polio, Haemophilus influenzae type b, and hepatitis B vaccine (DTaP/IPV/Hib/HepB) and 2 doses of measles, mumps, and rubella (MMR) vaccine. This represented 439,754 invitations to be vaccinated in Scotland and 4.1 million for England. Uptake during the 2020 periods was compared to the previous year (2019) using binary logistic regression analysis. For Scotland, uptake within 4 weeks of a child becoming eligible by age was analysed along with geographical region and indices of deprivation. For Scotland and England, we assessed whether immunisations were up-to-date at approximately 6 months (all doses 6-in-1) and 16 to 18 months (first MMR) of age.We found that uptake within 4 weeks of eligibility in Scotland for all the 5 vaccines was higher during lockdown than in 2019. Differences ranged from 1.3% for first dose 6-in-1 vaccine (95.3 versus 94%, odds ratio [OR] compared to 2019 1.28, 95% confidence intervals [CIs] 1.18 to 1.39) to 14.3% for second MMR dose (66.1 versus 51.8%, OR compared to 2019 1.8, 95% CI 1.74 to 1.87). Significant increases in uptake were seen across all deprivation levels.In England, fewer children due to receive their immunisations during the lockdown period were up to date at 6 months (6-in-1) or 18 months (first dose MMR). The fall in percentage uptake ranged from 0.5% for first 6-in-1 (95.8 versus 96.3%, OR compared to 2019 0.89, 95% CI 0.86– to 0.91) to 2.1% for third 6-in-1 (86.6 versus 88.7%, OR compared to 2019 0.82, 95% CI 0.81 to 0.83).The use of routinely collected data used in this study was a limiting factor as detailed information on potential confounding factors were not available and we were unable to eliminate the possibility of seasonal trends in immunisation uptake.ConclusionsIn this study, we observed that the national lockdown in Scotland was associated with an increase in timely childhood immunisation uptake; however, in England, uptake fell slightly. Reasons for the improved uptake in Scotland may include active measures taken to promote immunisation at local and national levels during this period and should be explored further. Promoting immunisation uptake and addressing potential vaccine hesitancy is particularly important given the ongoing pandemic and COVID-19 vaccination campaigns.Fiona McQuaid and colleagues assess the uptake of infant and pre-school immunisations in Scotland and England during the COVID-19 pandemic. 相似文献
109.
Antagonism of CD95 signaling blocks butyrate induction of apoptosis in young adult mouse colonic cells 总被引:5,自引:0,他引:5
Fan Yang-Yi; Zhang Jianhu; Barhoumi Rola; Burghardt Robert C.; Turner Nancy D.; Lupton Joanne R.; Chapkin Robert S. 《American journal of physiology. Cell physiology》1999,277(2):C310
There is greatinterest in utilizing butyrate as a chemopreventive agent for colontumorigenesis because of its ability to promote apoptosis in colontumor cell lines. Because CD95 (APO-1/Fas) transduces signals resultingin apoptosis, we tested the hypothesis that butyrate-dependentcolonocyte apoptosis is mediated by this death receptor. Butyrate (1 mM) exposure for 24 h upregulated expression of Fas andits ligand in young adult mouse colon (YAMC) cells. To delineate theproapoptotic effect of butyrate and to avoid the confounding effects ofdetachment from the extracellular matrix, adherent cell apoptosis wasmonitored as loss of plasma membrane asymmetry and dissipation ofmitochondrial membrane potential (mt) by lasercytometry. Soluble Fas receptor protein (Fas:Fc chimera) and caspaseinhibitors (z-VAD-fmk and z-IETD-fmk) blocked butyrate induction ofapoptosis. Treatment with Fas agonistic antibody (clone Jo-2)significantly induced cell death, indicating that Fas in colonocytes isfunctional. In addition, butyrate promoted apoptosis by inducing lossof mt and phospholipidasymmetry of the plasma membrane after 12 and 24 h of exposure,respectively, before cell detachment. Therefore, Fas receptor-dependentsignal transduction is involved in butyrate induction of apoptosis in colonocytes. 相似文献
110.
Ding JH Xu X Yang D Chu PH Dalton ND Ye Z Yeakley JM Cheng H Xiao RP Ross J Chen J Fu XD 《The EMBO journal》2004,23(4):885-896
Many genetic diseases are caused by mutations in cis-acting splicing signals, but few are triggered by defective trans-acting splicing factors. Here we report that tissue-specific ablation of the splicing factor SC35 in the heart causes dilated cardiomyopathy (DCM). Although SC35 was deleted early in cardiogenesis by using the MLC-2v-Cre transgenic mouse, heart development appeared largely unaffected, with the DCM phenotype developing 3-5 weeks after birth and the mutant animals having a normal life span. This nonlethal phenotype allowed the identification of downregulated genes by microarray, one of which was the cardiac-specific ryanodine receptor 2. We showed that downregulation of this critical Ca2+ release channel preceded disease symptoms and that the mutant cardiomyocytes exhibited frequency-dependent excitation-contraction coupling defects. The implication of SC35 in heart disease agrees with a recently documented link of SC35 expression to heart failure and interference of splicing regulation during infection by myocarditis-causing viruses. These studies raise a new paradigm for the etiology of certain human heart diseases of genetic or environmental origin that may be triggered by dysfunction in RNA processing. 相似文献