全文获取类型
收费全文 | 9865篇 |
免费 | 883篇 |
国内免费 | 828篇 |
出版年
2024年 | 26篇 |
2023年 | 155篇 |
2022年 | 330篇 |
2021年 | 571篇 |
2020年 | 400篇 |
2019年 | 435篇 |
2018年 | 423篇 |
2017年 | 307篇 |
2016年 | 433篇 |
2015年 | 608篇 |
2014年 | 781篇 |
2013年 | 757篇 |
2012年 | 923篇 |
2011年 | 777篇 |
2010年 | 542篇 |
2009年 | 423篇 |
2008年 | 461篇 |
2007年 | 493篇 |
2006年 | 407篇 |
2005年 | 340篇 |
2004年 | 301篇 |
2003年 | 234篇 |
2002年 | 206篇 |
2001年 | 176篇 |
2000年 | 156篇 |
1999年 | 153篇 |
1998年 | 72篇 |
1997年 | 69篇 |
1996年 | 75篇 |
1995年 | 53篇 |
1994年 | 64篇 |
1993年 | 52篇 |
1992年 | 75篇 |
1991年 | 59篇 |
1990年 | 39篇 |
1989年 | 51篇 |
1988年 | 30篇 |
1987年 | 34篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
Ruihua Cao Xing Ye Xingui Chen Long Zhang Xianwen Chen Yanghua Tian Panpan Hu Kai Wang 《PloS one》2015,10(9)
Biological motion (BM) perception is the compelling ability of the visual system to perceive complex animated movements effortlessly and promptly. A recent study has shown that BM can automatically lengthen perceived temporal duration independent of global configuration. The present study aimed mainly to investigate this temporal dilation effect of BM signals in Parkinson’s disease (PD) patients. We used the temporal dilation effect as an implicit measure of visual processing of BM. In all, 32 PD patients (under off-therapy conditions) and 32 healthy controls (HCs) participated in our study. In each trial, an upright BM sequence and an inverted BM sequence were presented within an interval in the center of the screen. We tested both canonical and scrambled BM sequences; the scrambled ones were generated by disturbing the global configuration of the canonical ones but preserving exactly the same local motion components. Observers were required to make a verbal two-alternative forced choice response to indicate which interval (the first or the second) appeared longer. Statistical analyses were conducted on the points of subjective equality (PSEs). We found that the temporal dilation effect was significantly reduced for PD patients compared with HCs in both canonical and scrambled BM conditions. Moreover, no temporal dilation effects of scrambled BM were shown in both early- and late-stage PD patients, while the temporal dilation effect of canonical BM was relatively preserved in the early stages. 相似文献
952.
Lung ultrasonography (LUS) is being increasingly utilized in emergency and critical settings. We performed a systematic review of the current literature to compare the accuracy of LUS and chest radiography (CR) for the diagnosis of adult community-acquired pneumonia (CAP). We searched in Pub Med, EMBASE dealing with both LUS and CR for diagnosis of adult CAP, and conducted a meta-analysis to evaluate the diagnostic accuracy of LUS in comparison with CR. The diagnostic standard that the index test compared was the hospital discharge diagnosis or the result of chest computed tomography scan as a “gold standard”. We calculated pooled sensitivity and specificity using the Mantel-Haenszel method and pooled diagnostic odds ratio using the DerSimonian-Laird method. Five articles met our inclusion criteria and were included in the final analysis. Using hospital discharge diagnosis as reference, LUS had a pooled sensitivity of 0.95 (0.93-0.97) and a specificity of 0.90 (0.86 to 0.94), CR had a pooled sensitivity of 0.77 (0.73 to 0.80) and a specificity of 0.91 (0.87 to 0.94). LUS and CR compared with computed tomography scan in 138 patients in total, the Z statistic of the two summary receiver operating characteristic was 3.093 (P = 0.002), the areas under the curve for LUS and CR were 0.901 and 0.590, respectively. Our study indicates that LUS can help to diagnosis adult CAP by clinicians and the accuracy was better compared with CR using chest computed tomography scan as the gold standard. 相似文献
953.
Aims
To investigate the association of demographic, clinical and psychosocial variables with levels of anxiety and depression in participants wearing an ocular prosthesis after eye enucleation.Methods
This cross-sectional study included 195 participants with an enucleated eye who were attending an ophthalmic clinic for prosthetic rehabilitation between July and November 2014. Demographic and clinical data, and self-reported feelings of shame, sadness and anger were collected. Participants also completed the National Eye Institute Visual Function Questionnaire, the Facial Appearance subscale of the Negative Physical Self Scale, and the Hospital Anxiety and Depression Scale. Regression models were used to identify the factors associated with anxiety and depression.Results
The proportion of participants with clinical anxiety was 11.8% and clinical depression 13.8%. More anxiety and depression were associated with poorer vision-related quality of life and greater levels of appearance concerns. Younger age was related to greater levels of anxiety. Less educated participants and those feeling more angry about losing an eye are more prone to experience depression. Clinical variables were unrelated to anxiety or depression.Conclusions
Anxiety and depression are more prevalent in eye-enucleated patients than the general population, which brings up the issues of psychiatric support in these patients. Psychosocial rather than clinical characteristics were associated with anxiety and depression. Longitudinal studies need to be conducted to further elucidate the direction of causality before interventions to improve mood states are developed. 相似文献954.
Xiaoming Zhu Yongfei Wang Xuelan Zhao Cuiping Jiang Qiongyue Zhang Wenjuan Jiang Yan Wang Haixia Chen Xuefei Shou Yao Zhao Yiming Li Shiqi Li Hongying Ye 《PloS one》2015,10(9)
Background
There are few studies of the incidence and clinical characteristics of pituitary apoplexy (PA) in pituitary adenoma patients, and the findings have been inconsistent.Objective
The aim of the study was to retrospectively assess the incidence, clinical presentation, surgical management and postoperative complications of PA in pituitary adenoma patients.Methods
A database was specifically designed to collect clinical, therapeutic, prognostic and histological information about pituitary adenoma patients. Using multivariate logistic regression, odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to identify associated factors.Results
A total of 2021 pituitary adenoma patients were recruited. 97 (4.8%) patients had PA. The incidence of PA was 10.11% in patients with pituitary macroadenoma, and 0.36% in patients with microadenoma. Variables for the logistic regression model independently associated with PA were sex (male vs. female, OR = 2.54, 95% CI: 1.59~4.07), tumor type (negative staining vs. positive staining, OR = 2.04, 95% CI: 1.29~3.23), and tumor size (macroadenoma vs. microadenoma, OR = 26.46, 95% CI = 9.66~72.46). Headache, visual deterioration, and vomiting were the most common symptoms in patients with pituitary adenoma. Patients with and without PA had similar frequency of visual deterioration, head trauma, acromegalic appearance, galactorrhoea, cold intolerance and Cushingoid appearance, but headache, vomiting, ptosis, diplopia, fever and blindness were significantly more common in patients with PA. Pearson Chi-Square tests revealed a significant difference in surgical approach between patients with and without PA (95.88% vs. 85.57%, P = 0.01).Conclusion
Our findings suggest that PA is not a rare event. Male sex, non-functioning tumor, and macroadenoma are associated with an increased risk of PA. Compared with pituitary adenoma patients without PA, patients with PA have more severe symptoms. 相似文献955.
Sun Wook Cho Jae Hyun Bae Gyeong Woon Noh Ye An Kim Min Kyong Moon Kyoung Un Park Junghan Song Ka Hee Yi Do Joon Park June-Key Chung Bo Youn Cho Young Joo Park 《PloS one》2015,10(12)
Osteoporosis-related fractures are one of the complications of Graves’ disease. This study hypothesized that the different actions of thyroid-stimulating hormone receptor (TSHR) antibodies, both stimulating and blocking activities in Graves’ disease patients might oppositely impact bone turnover. Newly diagnosed premenopausal Graves’ disease patients were enrolled (n = 93) and divided into two groups: patients with TSHR antibodies with thyroid-stimulating activity (stimulating activity group, n = 83) and patients with TSHR antibodies with thyroid-stimulating activity combined with blocking activity (blocking activity group, n = 10). From the stimulating activity group, patients who had matched values for free T4 and TSH binding inhibitor immunoglobulin (TBII) to the blocking activity group were further classified as stimulating activity-matched control (n = 11). Bone turnover markers BS-ALP, Osteocalcin, and C-telopeptide were significantly lower in the blocking activity group than in the stimulating activity or stimulating activity-matched control groups. The TBII level showed positive correlations with BS-ALP and osteocalcin levels in the stimulating activity group, while it had a negative correlation with the osteocalcin level in the blocking activity group. In conclusion, the activation of TSHR antibody-activated TSH signaling contributes to high bone turnover, independent of the actions of thyroid hormone, and thyroid-stimulation blocking antibody has protective effects against bone metabolism in Graves’ disease. 相似文献
956.
Ya-kai Huang Jian-chun Yu Wei-ming Kang Zhi-qiang Ma Xin Ye Shu-bo Tian Chao Yan 《PloS one》2015,10(11)
Background
Human pepsinogens are considered promising serological biomarkers for the screening of atrophic gastritis (AG) and gastric cancer (GC). However, there has been controversy in the literature with respect to the validity of serum pepsinogen (SPG) for the detection of GC and AG. Consequently, we conducted a systematic review and meta-analysis to assess the diagnostic accuracy of SPG in GC and AG detection.Methods
We searched PubMed, Embase, and the Chinese National Knowledge Infrastructure (CNKI) for correlative original studies published up to September 30, 2014. The summary sensitivity, specificity, positive diagnostic likelihood ratio (DLR+), negative diagnostic likelihood ratio (DLR-), area under the summary receiver operating characteristic curve (AUC) and diagnostic odds ratio (DOR) were used to evaluate SPG in GC and AG screening based on bivariate random effects models. The inter-study heterogeneity was evaluated by the I2 statistics and publication bias was assessed using Begg and Mazumdar’s test. Meta-regression and subgroup analyses were performed to explore study heterogeneity.Results
In total, 31 studies involving 1,520 GC patients and 2,265 AG patients were included in the meta-analysis. The summary sensitivity, specificity, DLR+, DLR-, AUC and DOR for GC screening using SPG were 0.69 (95% CI: 0.60–0.76), 0.73 (95% CI: 0.62–0.82), 2.57 (95% CI: 1.82–3.62), and 0.43 (95% CI: 0.34–0.54), 0.76 (95% CI: 0.72–0.80) and 6.01 (95% CI: 3.69–9.79), respectively. For AG screening, the summary sensitivity, specificity, DLR+, DLR-, AUC and DOR were 0.69 (95% CI: 0.55–0.80), 0.88 (95% CI: 0.77–0.94), 5.80 (95% CI: 3.06–10.99), and 0.35 (95% CI: 0.24–0.51), 0.85 (95% CI: 0.82–0.88) and 16.50 (95% CI: 8.18–33.28), respectively. In subgroup analysis, the use of combination of concentration of PGI and the ratio of PGI:PGII as measurement of SPG for GC screening yielded sensitivity of 0.70 (95% CI: 0.66–0.75), specificity of 0.79 (95% CI: 0.79–0.80), DOR of 6.92 (95% CI: 4.36–11.00), and AUC of 0.78 (95% CI: 0.72–0.81), while the use of concentration of PGI yielded sensitivity of 0.55 (95% CI: 0.51–0.60), specificity of 0.79 (95% CI: 0.76–0.82), DOR of 6.88 (95% CI: 2.30–20.60), and AUC of 0.77 (95% CI: 0.73–0.92). For AG screening, the use of ratio of PGI:PGII as measurement of SPG yielded sensitivity of 0.69 (95% CI: 0.52–0.83), specificity of 0.84 (95% CI: 0.68–0.93), DOR of 11.51 (95% CI: 6.14–21.56), and AUC of 0.83 (95% CI: 0.80–0.86), the use of combination of concentration of PGI and the ratio of PGI:PGII yield sensitivity of 0.79 (95% CI: 0.72–0.85), specificity of 0.89 (95% CI: 0.85–0.93), DOR of 24.64 (95% CI: 6.95–87.37), and AUC of 0.87 (95% CI: 0.81–0.92), concurrently, the use of concentration of PGI yield sensitivity of 0.46 (95% CI: 0.38–0.54), specificity of 0.93 (95% CI: 0.91–0.95), DOR of 19.86 (95% CI: 0.86–456.91), and AUC of 0.86 (95% CI: 0.52–1.00).Conclusion
SPG has great potential as a noninvasive, population-based screening tool in GC and AG screening. In addition, given the potential publication bias and high heterogeneity of the included studies, further high quality studies are required in the future. 相似文献957.
The clam Macridiscus multifarius with a planktonic larval stage of about 10 days is an ecologically and economically important species in the coastal regions of China. In this study, 3 mt-DNA markers (COI, 12S rRNA, and ND1) were used to investigate the population structure and demography of wild M. multifarius populations in 3 coastal localities of the East China Sea (ZS and ZP populations) and Beibu Gulf in the South China Sea (BH population). Sequences of 685 bp in COI, 350 bp in 12S rRNA, and 496 bp in ND1 were determined. High level and significant F
ST values were obtained among the different localities on the basis of either COI (F
ST = 0.100–0.444, p < 0.05) or 12S rRNA (F
ST = 0.199–0.742, p < 0.05) gene, indicating a high degree of genetic differentiation among the populations. F
ST values were significant but weak for the ND1 gene because it is highly conservative. The median-joining network suggested an obvious genetic differentiation between ZS and BH populations, and the finding is consistent with the results of our demographic analyses using the unweighted pair group method with arithmetic mean. Our study unraveled the extant population genetic structure of M. multifarius and explained the strong population structure of a species with a short planktonic larval stage species; this information could be useful for fishery management measures, including artificial breeding and conservation. 相似文献
958.
Yixin H. Ye Alison M. Carrasco Francesca D. Frentiu Stephen F. Chenoweth Nigel W. Beebe Andrew F. van den Hurk Cameron P. Simmons Scott L. O’Neill Elizabeth A. McGraw 《PLoS neglected tropical diseases》2015,9(6)
BackgroundDengue viruses (DENV) are the causative agents of dengue, the world’s most prevalent arthropod-borne disease with around 40% of the world’s population at risk of infection annually. Wolbachia pipientis, an obligate intracellular bacterium, is being developed as a biocontrol strategy against dengue because it limits replication of the virus in the mosquito. The Wolbachia strain wMel, which has been introduced into the mosquito vector, Aedes aegypti, has been shown to invade and spread to near fixation in field releases. Standard measures of Wolbachia’s efficacy for blocking virus replication focus on the detection and quantification of virus in mosquito tissues. Examining the saliva provides a more accurate measure of transmission potential and can reveal the extrinsic incubation period (EIP), that is, the time it takes virus to arrive in the saliva following the consumption of DENV viremic blood. EIP is a key determinant of a mosquito’s ability to transmit DENVs, as the earlier the virus appears in the saliva the more opportunities the mosquito will have to infect humans on subsequent bites.Conclusions/SignificanceThe saliva-based traits reported here offer more disease-relevant measures of Wolbachia’s effects on the vector and the virus. The lengthening of EIP highlights another means, in addition to the reduction of infection frequencies and DENV titers in mosquitoes, by which Wolbachia should operate to reduce DENV transmission in the field. 相似文献
959.
Xiu Xiu Jiang Xiang Wei Fei Li Zhao Xiao Lei Ye Liao Bin Xin Yang Qu Kai Hong Xu Rui Jin Wu Jun Lin 《PloS one》2015,10(12)
Aquaporin 5 (AQP5) participates in the migration of endometrial cells. Elucidation of the molecular mechanisms associated with AQP5-mediated, migration of endometrial cells may contribute to a better understanding of endometriosis. Our objectives included identifying the estrogen-response element (ERE) in the promoter region of the AQP5 gene, and, investigating the effects of AQP5 on ectopic implantation of endometrial cells. Luciferase reporter assays and electrophoretic mobility shift assay (EMSA) identified the ERE-like motif in the promoter region of the AQP5 gene. After blocking and up-regulating estradiol (E2) levels, we analysed the expression of AQP5 in endometrial stromal (ES) cells. After blocking E2 /or phosphatidylinositol 3 kinase(PI3K), we analysed the role of AQP5 in signaling pathways. We constructed an AQP5, shRNA, lentiviral vector to knock out the AQP5 gene in ES cells. After knock-out of the AQP5 gene, we studied the role of AQP5 in cell invasion, proliferation, and the formation of ectopic endometrial implants in female mice. We identified an estrogen-response element in the promoter region of the AQP5 gene. Estradiol (E2) increased AQP5 expression in a dose-dependent fashion, that was blocked by ICI182,780(an estrogen receptor inhibitor). E2 activated PI3K /protein kinase B(AKT) pathway (PI3K/AKT), that, in turn, increased AQP5 expression. (PI3K inhibitor) attenuated estrogen-enhanced, AQP5 expression. Knock-out of the AQP5 gene with AQP5 shRNA lentiviral vector significantly inhibited E2-enhanced invasion, proliferation of ES cells and formation of ectopic implants. Estrogen induces AQP5 expression by activating ERE in the promoter region of the AQP5gene, activates the PI3K/AKT pathway, and, promotes endometrial cell invasion and proliferation. These results provide new insights into some of the mechanisms that may underpin the development of deposits of ectopic endometrium. LY294002相似文献
960.