全文获取类型
收费全文 | 2649篇 |
免费 | 150篇 |
国内免费 | 71篇 |
专业分类
2870篇 |
出版年
2023年 | 7篇 |
2022年 | 36篇 |
2021年 | 59篇 |
2020年 | 13篇 |
2018年 | 34篇 |
2017年 | 26篇 |
2016年 | 92篇 |
2015年 | 213篇 |
2014年 | 223篇 |
2013年 | 254篇 |
2012年 | 262篇 |
2011年 | 245篇 |
2010年 | 163篇 |
2009年 | 98篇 |
2008年 | 106篇 |
2007年 | 79篇 |
2006年 | 49篇 |
2005年 | 110篇 |
2004年 | 121篇 |
2003年 | 96篇 |
2002年 | 68篇 |
2001年 | 70篇 |
2000年 | 36篇 |
1999年 | 24篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 28篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1979年 | 5篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1968年 | 5篇 |
1960年 | 4篇 |
1957年 | 6篇 |
1955年 | 4篇 |
1951年 | 5篇 |
1943年 | 4篇 |
1926年 | 5篇 |
排序方式: 共有2870条查询结果,搜索用时 0 毫秒
71.
农作物遗传多样性农家保护的现状及前景 总被引:31,自引:1,他引:31
农作物地方品种的有效保护是农业生物多样性的可持续利用的基础。由于现代农业的集约化生产方式使大量农作物地方品种被少数高产改良品种所取代,造成农作物基因库的严重“基因流失”(genetic erosion)。农家保护是在农业生态系统中进行的动态保护,被保护的生物多亲性可在其生境中继续进化而产生新的遗传变异,在而是农业生物多样性就地保护的重要途径。然而,尽管人们对作物品种资源农家保护的兴趣不断增长,也有大量有关农家的保护的研究和案例分析,但目前为止还没有比较成功的农家保护实例报道。因此,对农家保护的机制及科学问题进行深入的研究,并寻求一条新的途径来充分发挥农家保护应有的作用,显得格外重要。利用生物多样性布局的水稻混合间栽的生产模式,不仅解决了病害控制的问题,而且也保护了水稻地方品种的多样性。这种混合间栽的生物多样性布局和生产方式可能成为农保护的一条新途径。 相似文献
72.
73.
74.
75.
Objectively Assessed Physical Activity and Weight Loss Maintenance among Individuals Enrolled in a Lifestyle Intervention 下载免费PDF全文
76.
Scialli AR;Public Affairs Committee of the Teratology Society 《Birth defects research. Part A, Clinical and molecular teratology》2006,76(2):73-77
Compared to normal-weight women, obese women have an increased risk of infertility and pregnancy complications. The most consistently described pregnancy complications are hypertensive disorders, gestational diabetes mellitus, thromboembolic events, and cesarean section. Fetal and neonatal complications may include congenital malformations, macrosomia, and shoulder dystocia. The literature suggests that women with a body mass index (BMI) >or=30 have approximately double the risk of having a child with a neural tube defect (NTD) compared to normal-weight women, and the increased risk associated with higher maternal body weight does not appear to be modified by folic acid supplementation. The Public Affairs Committee of the Teratology Society supports the public health initiatives identified by the U.S. Food and Drug Administration in 2004 and the research initiatives identified by the National Institutes of Health in 2004. The Public Affairs Committee recommends that clinicians counsel women about appropriate caloric intake and exercise and that health-care providers educate parents about appropriate childhood nutrition. Breast-feeding should be encouraged based on evidence of a protective effect against childhood obesity, as well as other health advantages. 相似文献
77.
Liu T Qian WJ Gritsenko MA Xiao W Moldawer LL Kaushal A Monroe ME Varnum SM Moore RJ Purvine SO Maier RV Davis RW Tompkins RG Camp DG Smith RD;Inflammation the Host Response to Injury Large Scale Collaborative Research Programm 《Molecular & cellular proteomics : MCP》2006,5(10):1899-1913
Although human plasma represents an attractive sample for disease biomarker discovery, the extreme complexity and large dynamic range in protein concentrations present significant challenges for characterization, candidate biomarker discovery, and validation. Herein we describe a strategy that combines immunoaffinity subtraction and subsequent chemical fractionation based on cysteinyl peptide and N-glycopeptide captures with two-dimensional LC-MS/MS to increase the dynamic range of analysis for plasma. Application of this "divide-and-conquer" strategy to trauma patient plasma significantly improved the overall dynamic range of detection and resulted in confident identification of 22,267 unique peptides from four different peptide populations (cysteinyl peptides, non-cysteinyl peptides, N-glycopeptides, and non-glycopeptides) that covered 3,654 different proteins with 1,494 proteins identified by multiple peptides. Numerous low abundance proteins were identified, exemplified by 78 "classic" cytokines and cytokine receptors and by 136 human cell differentiation molecules. Additionally a total of 2,910 different N-glycopeptides that correspond to 662 N-glycoproteins and 1,553 N-glycosylation sites were identified. A panel of the proteins identified in this study is known to be involved in inflammation and immune responses. This study established an extensive reference protein database for trauma patients that provides a foundation for future high throughput quantitative plasma proteomic studies designed to elucidate the mechanisms that underlie systemic inflammatory responses. 相似文献
78.
Aarti Kumar Shambhavi Mishra Shambhavi Singh Sana Ashraf Peiyi Kan Amit Kumar Ghosh Alok Kumar Raghav Krishna David K. Stevenson Lu Tian Peter M. Elias Gary L. Darmstadt Vishwajeet Kumar for the Shivgarh Emollient Research Group 《PLoS medicine》2021,18(9)
BackgroundHospitalized preterm infants with compromised skin barrier function treated topically with sunflower seed oil (SSO) have shown reductions in sepsis and neonatal mortality rate (NMR). Mustard oil and products commonly used in high-mortality settings may possibly harm skin barrier integrity and enhance risk of infection and mortality in newborn infants. We hypothesized that SSO therapy may reduce NMR in such settings.Methods and findingsThis was a population-based, cluster randomized, controlled trial in 276 clusters in rural Uttar Pradesh, India. All newborn infants identified through population-based surveillance in the study clusters within 7 days of delivery were enrolled from November 2014 to October 2016. Exclusive, 3 times daily, gentle applications of 10 ml of SSO to newborn infants by families throughout the neonatal period were recommended in intervention clusters (n = 138 clusters); infants in comparison clusters (n = 138 clusters) received usual care, such as massage practice typically with mustard oil. Primary analysis was by intention-to-treat with NMR and post-24-hour NMR as the primary outcomes. Secondary analysis included per-protocol analysis and subgroup analyses for NMR. Regression analysis was adjusted for caste, first-visit weight, delivery attendant, gravidity, maternal age, maternal education, sex of the infant, and multiple births. We enrolled 13,478 (52.2% male, mean weight: 2,575.0 grams ± standard deviation [SD] 521.0) and 13,109 (52.0% male, mean weight: 2,607.0 grams ± SD 509.0) newborn infants in the intervention and comparison clusters, respectively. We found no overall difference in NMR in the intervention versus the comparison clusters [adjusted odds ratio (aOR) 0.96, 95% confidence interval (CI) 0.84 to 1.11, p = 0.61]. Acceptance of SSO in the intervention arm was high at 89.3%, but adherence to exclusive applications of SSO was 30.4%. Per-protocol analysis showed a significant 58% (95% CI 42% to 69%, p < 0.01) reduction in mortality among infants in the intervention group who were treated exclusively with SSO as intended versus infants in the comparison group who received exclusive applications of mustard oil. A significant 52% (95% CI 12% to 74%, p = 0.02) reduction in NMR was observed in the subgroup of infants weighing ≤1,500 g (n = 589); there were no statistically significant differences in other prespecified subgroup comparisons by low birth weight (LBW), birthplace, and wealth. No severe adverse events (SAEs) were attributable to the intervention. The study was limited by inability to mask allocation to study workers or participants and by measurement of emollient use based on caregiver responses and not actual observation.ConclusionsIn this trial, we observed that promotion of SSO therapy universally for all newborn infants was not effective in reducing NMR. However, this result may not necessarily establish equivalence between SSO and mustard oil massage in light of our secondary findings. Mortality reduction in the subgroup of infants ≤1,500 g was consistent with previous hospital-based efficacy studies, potentially extending the applicability of emollient therapy in very low-birth-weight (VLBW) infants along the facility–community continuum. Further research is recommended to develop and evaluate therapeutic regimens and continuum of care delivery strategies for emollient therapy for newborn infants at highest risk of compromised skin barrier function.Trial registrationISRCTN Registry ISRCTN38965585 and Clinical Trials Registry—India (CTRI/2014/12/005282) with WHO UTN # U1111-1158-4665.In a cluster randomized trial, Aarti Kumar and colleagues study the effectiveness of a topical sunflower seed oil therapy in reducing neonatal mortality in Uttar Pradesh, India. 相似文献
79.
Bich-Tram Huynh Elsa Kermorvant-Duchemin Rattanak Chheang Frederique Randrianirina Abdoulaye Seck Elisoa Hariniaina Ratsima Zafitsara Zo Andrianirina Jean-Baptiste Diouf Armya Youssouf Abdou Sophie Goyet Vronique Ngo Siyin Lach Long Pring Touch Sok Michael Padget Fatoumata Diene Sarr Laurence Borand Benoit Garin Jean-Marc Collard Perlinot Herindrainy Agathe de Lauzanne Muriel Vray Elisabeth Delarocque-Astagneau Didier Guillemot On behalf of the BIRDY study group 《PLoS medicine》2021,18(9)
BackgroundSevere bacterial infections (SBIs) are a leading cause of neonatal deaths in low- and middle-income countries (LMICs). However, most data came from hospitals, which do not include neonates who did not seek care or were treated outside the hospital. Studies from the community are scarce, and few among those available were conducted with high-quality microbiological techniques. The burden of SBI at the community level is therefore largely unknown. We aimed here to describe the incidence, etiology, risk factors, and antibiotic resistance profiles of community-acquired neonatal SBI in 3 LMICs.Methods and findingsThe BIRDY study is a prospective multicentric community-based mother and child cohort study and was conducted in both urban and rural areas in Madagascar (2012 to 2018), Cambodia (2014 to 2018), and Senegal (2014 to 2018). All pregnant women within a geographically defined population were identified and enrolled. Their neonates were actively followed from birth to 28 days to document all episodes of SBI. A total of 3,858 pregnant women (2,273 (58.9%) in Madagascar, 814 (21.1%) in Cambodia, and 771 (20.0%) in Senegal) were enrolled in the study, and, of these, 31.2% were primigravidae. Women enrolled in the urban sites represented 39.6% (900/2,273), 45.5% (370/814), and 61.9% (477/771), and those enrolled in the rural sites represented 60.4% (1,373/2,273), 54.5% (444/814), and 38.1% (294/771) of the total in Madagascar, Cambodia, and Senegal, respectively. Among the 3,688 recruited newborns, 49.6% were male and 8.7% were low birth weight (LBW). The incidence of possible severe bacterial infection (pSBI; clinical diagnosis based on WHO guidelines of the Integrated Management of Childhood Illness) was 196.3 [95% confidence interval (CI) 176.5 to 218.2], 110.1 [88.3 to 137.3], and 78.3 [59.5 to 103] per 1,000 live births in Madagascar, Cambodia, and Senegal, respectively. The incidence of pSBI differed between urban and rural sites in all study countries. In Madagascar, we estimated an incidence of 161.0 pSBI per 1,000 live births [133.5 to 194] in the urban site and 219.0 [192.6 to 249.1] pSBI per 1,000 live births in the rural site (p = 0.008). In Cambodia, estimated incidences were 141.1 [105.4 to 189.0] and 85.3 [61.0 to 119.4] pSBI per 1,000 live births in urban and rural sites, respectively (p = 0.025), while in Senegal, we estimated 103.6 [76.0 to 141.2] pSBI and 41.5 [23.0 to 75.0] pSBI per 1,000 live births in urban and rural sites, respectively (p = 0.006). The incidences of culture-confirmed SBI were 15.2 [10.6 to 21.8], 6.5 [2.7 to 15.6], and 10.2 [4.8 to 21.3] per 1,000 live births in Madagascar, Cambodia, and Senegal, respectively, with no difference between urban and rural sites in each country. The great majority of early-onset infections occurred during the first 3 days of life (72.7%). The 3 main pathogens isolated were Klebsiella spp. (11/45, 24.4%), Escherichia coli (10/45, 22.2%), and Staphylococcus spp. (11/45, 24.4%). Among the 13 gram-positive isolates, 5 were resistant to gentamicin, and, among the 29 gram-negative isolates, 13 were resistant to gentamicin, with only 1 E. coli out of 10 sensitive to ampicillin. Almost one-third of the isolates were resistant to both first-line drugs recommended for the management of neonatal sepsis (ampicillin and gentamicin). Overall, 38 deaths occurred among neonates with SBI (possible and culture-confirmed SBI together). LBW and foul-smelling amniotic fluid at delivery were common risk factors for early pSBI in all 3 countries. A main limitation of the study was the lack of samples from a significant proportion of infants with pBSI including 35 neonatal deaths. Without these samples, bacterial infection and resistance profiles could not be confirmed.ConclusionsIn this study, we observed a high incidence of neonatal SBI, particularly in the first 3 days of life, in the community of 3 LMICs. The current treatment for the management of neonatal infection is hindered by antimicrobial resistance. Our findings suggest that microbiological diagnosis of SBI remains a challenge in these settings and support more research on causes of neonatal death and the implementation of early interventions (e.g., follow-up of at-risk newborns during the first days of life) to decrease the burden of neonatal SBI and associated mortality and help achieve Sustainable Development Goal 3.In a community-based, prospective cohort study, Bich-Tram Huynh and colleagues investigate the incidence and factors associated with several bacterial infections among neonates in rural and urban areas of three low-middle income countries. 相似文献
80.
Ian W. Pray Francesco Pizzitutti Gabrielle Bonnet Eloy Gonzales-Gustavson Wayne Wakeland William K. Pan William E. Lambert Armando E. Gonzalez Hector H. Garcia Seth E. ONeal for the Cysticercosis Working Group in Peru. 《PLoS neglected tropical diseases》2021,15(10)
BackgroundThe pork tapeworm (Taenia solium) is a parasitic helminth that imposes a major health and economic burden on poor rural populations around the world. As recognized by the World Health Organization, a key barrier for achieving control of T. solium is the lack of an accurate and validated simulation model with which to study transmission and evaluate available control and elimination strategies. CystiAgent is a spatially-explicit agent based model for T. solium that is unique among T. solium models in its ability to represent key spatial and environmental features of transmission and simulate spatially targeted interventions, such as ring strategy.Methods/Principal findingsWe validated CystiAgent against results from the Ring Strategy Trial (RST)–a large cluster-randomized trial conducted in northern Peru that evaluated six unique interventions for T. solium control in 23 villages. For the validation, each intervention strategy was replicated in CystiAgent, and the simulated prevalences of human taeniasis, porcine cysticercosis, and porcine seroincidence were compared against prevalence estimates from the trial. Results showed that CystiAgent produced declines in transmission in response to each of the six intervention strategies, but overestimated the effect of interventions in the majority of villages; simulated prevalences for human taenasis and porcine cysticercosis at the end of the trial were a median of 0.53 and 5.0 percentages points less than prevalence observed at the end of the trial, respectively.Conclusions/SignificanceThe validation of CystiAgent represented an important step towards developing an accurate and reliable T. solium transmission model that can be deployed to fill critical gaps in our understanding of T. solium transmission and control. To improve model accuracy, future versions would benefit from improved data on pig immunity and resistance, field effectiveness of anti-helminthic treatment, and factors driving spatial clustering of T. solium infections including dispersion and contact with T. solium eggs in the environment. 相似文献