首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   12534篇
  免费   817篇
  国内免费   9篇
  13360篇
  2024年   22篇
  2023年   51篇
  2022年   161篇
  2021年   245篇
  2020年   135篇
  2019年   218篇
  2018年   314篇
  2017年   259篇
  2016年   442篇
  2015年   649篇
  2014年   777篇
  2013年   830篇
  2012年   1109篇
  2011年   1080篇
  2010年   668篇
  2009年   519篇
  2008年   814篇
  2007年   700篇
  2006年   621篇
  2005年   574篇
  2004年   589篇
  2003年   470篇
  2002年   374篇
  2001年   356篇
  2000年   330篇
  1999年   229篇
  1998年   91篇
  1997年   79篇
  1996年   50篇
  1995年   49篇
  1994年   40篇
  1993年   30篇
  1992年   83篇
  1991年   55篇
  1990年   44篇
  1989年   48篇
  1988年   27篇
  1987年   28篇
  1986年   21篇
  1985年   23篇
  1984年   13篇
  1983年   15篇
  1982年   12篇
  1981年   12篇
  1980年   11篇
  1979年   9篇
  1978年   15篇
  1975年   13篇
  1974年   11篇
  1970年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Helminth infections are prevalent in Lao People’s Democratic Republic (Lao PDR). This study aimed at determining the prevalence and risk factors of intestinal helminthiasis in remote mountainous villages of northern Lao PDR. During the dry season in January 2017, a cross-sectional survey was conducted in 3 remote mountainous villages in Oudomxay province, Lao PDR. Villagers older than 18 years of age who agreed to submit stool samples or undergo an interview, were recruited. Stool samples from 198 individuals were examined by the Kato-Katz method, and a questionnaire surveyed 161 individuals among them. Univariable and multivariable logistic regression analyses were used to identify risk factors associated with the intestinal helminthiasis. An overall prevalence of intestinal helminthiasis was 75.8%. Hookworm infection was the most common (63.1%), followed by Opisthorchis viverrini/minute intestinal flukes (17.7%), Taenia spp. (15.2%), Trichuris trichiura (2.0%), Ascaris lumbricoides (1.5%), and Enterobius vermicularis (1.0%). Questionnaire analysis revealed sex (male) and absence of latrine to be significant risk factors for hookworm infection and consumption of raw meat for taeniasis. These results suggest that the mountainous area in northern Lao PDR has a different composition of helminth infections from other studies conducted in Lao PDR; a high prevalence of hookworm infection and taeniasis and low prevalence of T. trichiura and A. lumbricoides infections were observed. Also, liver flukes or intestinal flukes were similarly prevalent in the mountainous area.  相似文献   
102.
IL-35 subunit EBI3 is up-regulated in pulmonary fibrosis tissues. In this study, we investigated the pathological role of EBI3 in pulmonary fibrosis and dissected the underlying molecular mechanism. Bleomycin-induced pulmonary fibrosis mouse model was established, and samples were performed gene expression analyses through RNAseq, qRT-PCR and Western blot. Wild type and EBI3 knockout mice were exposed to bleomycin to investigate the pathological role of IL-35, via lung function and gene expression analyses. Primary lung epithelial cells were used to dissect the regulatory mechanism of EBI3 on STAT1/STAT4 and STAT3. IL-35 was elevated in both human and mouse with pulmonary fibrosis. EBI3 knockdown aggravated the symptoms of pulmonary fibrosis in mice. EBI3 deficiency enhanced the expressions of fibrotic and extracellular matrix-associated genes. Mechanistically, IL-35 activated STAT1 and STAT4, which in turn suppressed DNA enrichment of STAT3 and inhibited the fibrosis process. IL-35 might be one of the potential therapeutic targets for bleomycin-induced pulmonary fibrosis.  相似文献   
103.
Oak (Quercus spp.) and hornbeam (Carpinus spp.) are one of dominant tree species in East Asian temperate broad leaf deciduous forests and many insect species, including more than 65% of Lepidoptera species, feed on these trees. We sampled lepidopteran caterpillars from two 0.1 ha plots in a temperate forest to investigate the role of dominant trees (oaks and hornbeams) in herbivore community. In total, we identified 738 caterpillars from 223 Lepidopteran species on 34 tree species. Most caterpillar species were from species-rich families such as Geometridae 25% (56 spp.), Noctuidae, and Tortricidae. After excluding dominant trees, plant-herbivore network analyses showed increased network specialization and nestedness and decreased generality and vulnerability. These results suggest that oaks and hornbeams support a large Lepidopteran herbivore community, and co-occurring plant species support diverse but specific herbivores. Geographical distribution and plant community are closely related to diversity of the herbivore community. Future work is needed to investigate the likelihood that specialist herbivores become relatively more abundant in the forest as oaks are succeeded by hornbeams.  相似文献   
104.
Determine if sex differences exist in clinical characteristics and outcomes of adults hospitalized for coronavirus disease 2019 (COVID-19) in a US healthcare system. Case series study. Sequentially hospitalized adults admitted for COVID-19 at two tertiary care academic hospitals in New Orleans, LA, between 27 February and 15 July 2020. Measures included demographics, comorbidities, presenting symptoms, and laboratory results. Outcomes included intensive care unit admission (ICU), invasive mechanical ventilation (IMV), and in-hospital death. We included 776 patients (median age 60.5 years; 61.4% women, 75% non-Hispanic Black). Rates of ICU, IMV, and death were similar in both sexes. In women versus men, obesity (63.8 vs 41.6%, P < 0.0001), hypertension (77.6 vs 70.1%, P = 0.02), diabetes (38.2 vs 31.8%, P = 0.06), chronic obstructive pulmonary disease (COPD, 22.1 vs 15.1%, P = 0.015), and asthma (14.3 vs 6.9%, P = 0.001) were more prevalent. More women exhibited dyspnea (61.2 vs 53.7%, P = 0.04), fatigue (35.7 vs 28.5%, P = 0.03), and digestive symptoms (39.3 vs 32.8%, P = 0.06) than men. Obesity was associated with IMV at a lower BMI (> 35) in women, but the magnitude of the effect of morbid obesity (BMI ≥ 40) was similar in both sexes. COPD was associated with ICU (adjusted OR (aOR), 2.6; 95%CI, 1.5–4.3) and IMV (aOR, 1.8; 95%CI, 1.2–3.1) in women only. Diabetes (aOR, 2.6; 95%CI, 1.2–2.9), chronic kidney disease (aOR, 2.2; 95%CI, 1.3–5.2), elevated neutrophil-to-lymphocyte ratio (aOR, 2.5; 95%CI, 1.4–4.3), and elevated ferritin (aOR, 3.6; 95%CI, 1.7–7.3) were independent predictors of death in women only. In contrast, elevated D-dimer was an independent predictor of ICU (aOR, 7.3; 95%CI, 2.7–19.5), IMV (aOR, 6.5; 95%CI, 2.1–20.4), and death (aOR, 4.5; 95%CI, 1.2–16.4) in men only. This study highlights sex disparities in clinical determinants of severe outcomes in COVID-19 patients that may inform management and prevention strategies to ensure gender equity.  相似文献   
105.
106.
To confirm the beneficial effects of alpha (1,2)-fucosyltransferase (FUT1) M307 A on piglet survival on commercial farms, we performed PCR-RFLP analysis of FUT1 M307 in successfully marketed (n = 245) and disease affected/deceased pigs during weaning (n = 252) at a commercial farm. We also evaluated the FUT1 genotypes of 190 healthy pigs from three different genetic backgrounds. The distribution of genotypes differed between the successfully marketed and disease affected/deceased pig groups. The frequency of the A allele, associated with resistance to edema and post-weaning diarrhea, was higher in the post-weaning survival group (0.21) than in the non-survival group (0.16, P < 0.05). The odds ratio for piglet survival between AA and GG genotypes was 1.98; thus, piglet survival for individuals with the AA genotype was almost two-fold greater than for GG individuals. The FUT1 gene polymorphism can be used as an effective marker for selection programs to improve post-weaning piglet survival.  相似文献   
107.
For marine fish and invertebrates, larval dispersal plays a critical role in determining connections among source and sink habitats, and the lack of a predictive understanding of larval dispersal is a fundamental obstacle to the development of spatially explicit restoration plans for marine populations. We investigated larval dispersal patterns of eastern oyster in an estuary along the Northern Gulf of Mexico under different simulation scenarios of tidal amplitude and phase, river discharge, wind direction, and larval vertical migration, using a coupled biophysical transport model. We focused on the dispersal of larvae released from the commercially exploited (Cedar Point, CP) and non‐exploited (Bon Secour Bay, BSB) oyster populations. We found that high flushing rates through the dominant inlet prevented larval exchange between the commercially exploited and non‐exploited populations, resulting in negligible connectivity between them. Variations in tidal amplitude, river discharge and wind direction played a more important role in the amount of larvae retained in Mobile Bay when they are released from CP than from BSB. Under most of the scenarios, larvae from BSB were retained around the spawning area, while larvae from CP showed a predominant westward flow. Net sinking behavior of late‐stage larvae increased larval retention in the bay, but physical transport showed a higher impact in the amount of larvae retained. These findings have enhanced our understanding of larval dispersal of eastern oyster in a wide, shallow estuarine system, and been used to establish spatially explicit strategies for oyster restoration in the Mobile Bay system, Alabama.  相似文献   
108.
109.
110.
Asthma is a potentially life-threatening inflammatory disease of the lung characterized by the presence of large numbers of CD4+ T cells. These cells produce the Th2 and Th17 cytokines that are thought to orchestrate the inflammation associated with asthma. Bee venom (BV) has traditionally been used to relieve pain and to treat chronic inflammatory diseases. Recent reports have suggested that BV might be an effective treatment for allergic diseases. However, there are still unanswered questions related to the efficacy of BV therapy in treating asthma and its therapeutic mechanism. In this study, we evaluated whether BV could inhibit asthma and whether BV inhibition of asthma could be correlated with regulatory T cells (Treg) activity. We found that BV treatment increased Treg populations and suppressed the production of Th1, Th2 and Th17-related cytokines in an in vitro culture system, including IL2, IL4, and IL17. Interestingly, production of IL10, an anti-inflammatory cytokine secreted by Tregs, was significantly augmented by BV treatment. We next evaluated the effects of BV treatment on allergic asthma in an ovalbumin (OVA)-induced mouse model of allergic asthma. Cellular profiling of the bronchoalveolar lavage (BAL) and histopathologic analysis demonstrated that peribronchial and perivascular inflammatory cell infiltrates were significantly lowered following BV treatment. BV also ameliorated airway hyperresponsiveness, a hallmark symptom of asthma. In addition, IL4 and IL13 levels in the BAL fluid were decreased in the BV treated group. Surprisingly, the beneficial effects of BV treatment on asthma were eradicated following Treg depletion by anti-CD25 antibody injection, suggesting that the major therapeutic targets of BV were Tregs. These results indicate that BV efficiently diminishes bronchial inflammation in an OVA-induced allergic asthma murine model, and that this effect might correlate with Tregs, which play an important role in maintaining immune homeostasis and suppressing the function of other T cells to limit the immune response. These results also suggest that BV has potential therapeutic value for controlling allergic asthma responses.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号