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   4768篇
  免费   306篇
  国内免费   23篇
耳鼻咽喉   45篇
儿科学   218篇
妇产科学   180篇
基础医学   584篇
口腔科学   94篇
临床医学   558篇
内科学   948篇
皮肤病学   161篇
神经病学   333篇
特种医学   115篇
外国民族医学   2篇
外科学   464篇
综合类   62篇
一般理论   4篇
预防医学   532篇
眼科学   148篇
药学   340篇
中国医学   5篇
肿瘤学   304篇
  2024年   5篇
  2023年   59篇
  2022年   85篇
  2021年   207篇
  2020年   135篇
  2019年   160篇
  2018年   217篇
  2017年   167篇
  2016年   163篇
  2015年   142篇
  2014年   228篇
  2013年   316篇
  2012年   423篇
  2011年   428篇
  2010年   203篇
  2009年   143篇
  2008年   299篇
  2007年   341篇
  2006年   266篇
  2005年   301篇
  2004年   214篇
  2003年   187篇
  2002年   149篇
  2001年   24篇
  2000年   10篇
  1999年   15篇
  1998年   18篇
  1997年   25篇
  1996年   16篇
  1995年   13篇
  1994年   11篇
  1993年   15篇
  1992年   6篇
  1991年   5篇
  1990年   6篇
  1989年   11篇
  1988年   7篇
  1987年   4篇
  1986年   4篇
  1985年   9篇
  1984年   3篇
  1983年   4篇
  1982年   6篇
  1981年   4篇
  1980年   7篇
  1978年   3篇
  1976年   4篇
  1962年   2篇
  1960年   2篇
  1928年   2篇
排序方式: 共有5097条查询结果,搜索用时 46 毫秒
991.
Herein, a series of vanillin-crosslinked chitosan (Vn-CS) nanocomposites (NCs) containing various contents of ZnO nanoparticles (NPs) was prepared and characterized via FTIR spectroscopy, XRD, TGA, SEM and TEM. Changing the weight% of ZnO NPs in the prepared NCs resulted in an improvement in their antibacterial activity against Gram-negative and Gram-positive bacteria strains compared with the unmodified CS, and the encapsulation efficiency of 5-fluorouracil (5-FU) was found to be in the range of 61.4–69.2%. Subsequently, the release of 5-FU was monitored utilizing the mesoporous ZrO2–Co3O4 NPs modified carbon paste sensor via the square-wave adsorptive anodic stripping voltammetry (SW-AdASV) technique. Also, the release mechanism of 5-FU from each NC was studied by applying the zero-order, first-order, Hixson–Crowell and Higuchi models to the experimental results. The cytotoxicity of prepared NCs and 5-FU-encapsulated NCs was evaluated against the HePG-2, MCF-7 and HCT-116 cancer cell lines, in addition to the WI-38 and WISH normal cell lines using the MTT assay. Notably, 5-FU/CV10 NC exhibited the highest antitumor activity towards all tested cancer cell lines and a moderate activity against WI-38 and WISH normal cell lines with IC50 values of 28.02 ± 2.5 and 31.65 ± 2.7 μg mL−1, respectively. The obtained nanocomposites exhibited suitable selectivity with minimum toxicity against normal cells.

Herein, a series of vanillin-crosslinked chitosan (Vn-CS) nanocomposites (NCs) containing various contents of ZnO nanoparticles (NPs) was prepared and characterized via FTIR spectroscopy, XRD, TGA, SEM and TEM.  相似文献   
992.
In this article we examine how teens in Norway navigate the many options for mediated communication when interacting with parents and grandparents. Drawing on workshop discussions with mid-adolescents, we suggest that there is a digital gap in this cross-generation communication despite high Information and Communication Technology (ICT) penetration in the market. The gap appears to be a manifestation of the social dynamic at play when reshaping the relationship between adolescents and their caregivers. This dynamic includes both centrifugal and centripetal forces. Applying the perspective of relational dialectics, we elaborate on how these forces unfold in the domestication of an increasingly complex set of communication tools referred to as polymedia. The empirical analysis suggests that teens assess the tools differently depending on if it is for interaction with parents or grandparents. This is also related to whether the mediated communication sessions are instrumentally or expressively skewed.  相似文献   
993.
Self-enhancement, the tendency to view oneself positively, is a pervasive social motive widely investigated in the psychological sciences. Relatively little is known about the neurocognitive mechanisms underlying this motive, specifically in social-evaluative situations. To investigate whether positive emotion regulation circuitry, circuitry involved in modulating positive affect, relates to the self-enhancement motive in social contexts, we conducted an functional magnetic resonance imaging (fMRI) study in a healthy young adult sample. We hypothesized that self-enhancement indices (state and trait self-esteem) would relate to greater functional connectivity between right ventrolateral prefrontal cortex (RVLPFC), a region implicated in emotion regulation, and the ventral striatum (VS), a region associated with reward-related affect, during a social feedback task. Following social evaluation, participants experienced stable or decreased state self-esteem. Results showed that stable state self-esteem from pre- to post-scan and higher trait self-esteem related to greater RVLPFC–VS connectivity during positive evaluation. Stable-state self-esteem also related to greater RVLPFC–VS connectivity during negative evaluation. Moreover, RVLPFC activation during all types of feedback processing and left VS activation during negative feedback processing was greater for participants with stable-state self-esteem. These findings implicate neurocognitive mechanisms underlying emotion regulation in the self-enhancement motive and highlight a pathway through which self-enhancement may restore feelings of self-worth during threatening situations.  相似文献   
994.
995.
AIM: To assess the frequency and associated risk factors of diabetic retinopathy among Sudanese individuals with diabetes attending Makka Eye complex in Khartoum, Sudan. METHODS: The cross sectional hospital based study recruited 316 individuals with diabetes from Makkah Eye Complex Retina Clinic. Standard questionnaire was used to collect demographic data, medical history and life style characteristics. Blood samples were taken to measure HbA1c and lipid profile. Fundus and slit lamp examination were performed for screening of diabetic retinopathy. RESULTS: Among 316 participants, 187 (59.2%) were males and 129 (40.8%) were females. The mean age of participants was 58.7±10.5y. The overall frequency of retinopathy was 261 (82.6%). The percentages of the total participants with proliferative diabetic retinopathy (PDR) were 126 (39.9%) and non-proliferative diabetic retinopathy (NPDR) were 135 (42.7%). Importantly, duration of diabetes mellitus (DM) (72.2% of more than 10y), being on oral hypoglycaemic drugs (versus insulin), and hypertension were all significant risk factors for diabetic retinopathy (P=0.00, 0.01 and 0.00 respectively). Complications of diabetes like diabetic foot (17.7%), history of amputation (6.7%) and clinically significant macular edema (CSME) (47.4%) of the eyes were all significant risk factors (P<0.05). Logistic regression analysis showed that duration of diabetes, hypertension and CSME were found to be absolute risk factors (P=0.007, 0.003 and 0.000 respectively). Duration of DM of more than 10y have more than double risk (OR=2.8), while having hypertension triples the risk of retinopathy (OR=3.1). CONCLUSION: High rates of diabetic retinopathy are noted among individuals with diabetes attending Makkah Eye hospital in capital Khartoum. Urgent strategies are needed to monitor and treat hypertension and optimize diabetes control in individuals with diabetes. More investment in diabetes services is urgently needed.  相似文献   
996.
ContextTraditionally, Oleaceae plants are used to treat many diseases, such as rheumatism, hypercholesterolaemia, or ulcers.ObjectivesTo investigate the cytotoxic potential of Jasminum humile L., Jasminum grandiflorum L., and Olea europaea L. (Oleaceae) extracts against selected human cancer cells lines, followed by a phytochemical investigation of the most potent one.Materials and methodsThe 95% ethanol extracts of aerial parts of three oleaceous plants were examined for their cytotoxicity against HepG-2, MCF-7, and THP-1 cell lines using MTT assay and doxorubicin (positive control). J. humile was bio-selected and submitted to bio-guided fractionation. Chromatographic workup of ethyl acetate and n-butanol fractions afforded two new compounds; 1-methoxyjasmigenin (1) and 1-methyl-9-aldojasmigenin (2), along with five known ones (3–7). Structures were unambiguously elucidated using 1D/2D NMR and ESI-HRMS. Isolated compounds were assessed for their anti-proliferative potential, and both selectivity index and statistical significance were determined. Molecular docking was conducted against the Mcl-1 receptor using (AZD5991) as a standard.ResultsJasmoside (5) was the most potent anticancer compound showing IC50 values of 66.47, 41.32, and 27.59 µg/mL against HepG-2, MCF-7, and THP-1 cell lines, respectively. Moreover, isojasminin (4) exhibited IC50 values of 33.49, 43.12, and 51.07 µg/mL against the same cell lines, respectively. Interestingly, 5 exhibited the highest selectivity index towards MCF-7 and THP-1, even greater than doxorubicin. Molecular docking results were in full agreement with the MTT assay and the proposed SAR.ConclusionIn this study, two new compounds were purified. The biological activity highlighted jasmoside (5) as a lead anticancer drug for further future investigation.  相似文献   
997.
Each year the American Cancer Society (ACS) publishes a summary of its recommendations for early cancer detection, a report on data and trends in cancer screening rates, and select issues related to cancer screening. This article summarizes the current ACS guidelines, describes the anticipated impact of new health care reform legislation on cancer screening, and discusses recent public debates over the comparative effectiveness of different colorectal cancer screening tests. The latest data on the utilization of cancer screening from the National Health Interview Survey is described, as well as several recent reports on the role of health care professionals in adult utilization of cancer screening.  相似文献   
998.
Introduction: There is alarming evidence about the involvement of general anaesthesia in the development of postoperative cognitive dysfunction.

Aim: To clarify the impact of general anaesthesia on cognitive function and to study the possible effect of general anaesthesia on serum S100B, the marker of neuronal degeneration.

Methods: This is a prospective randomised controlled study carried out on 50 patients undergoing elective laparoscopic cholecystectomy under conventional general anaesthesia. Cognitive assessment for selected patients was done preoperative and 1?week postoperative using Paired Associate Learning test (PALT) for assessment of verbal memory and Benton Visual Retention test (BVRT) for assessment of visual memory. Quantitative determination of serum S100B was done for all patients in the basal sample and postoperative sample by applying an enzyme- linked immunoabsorbent assay technique on am automated ELISA platform.

Results: Regarding cognitive tests, there was a statistically significant difference between the mean value of preoperative PALT and postoperative PALT (p-value?=?.012). There was also a statistically significant difference between the mean value of preoperative BVRT and postoperative BVRT (p-value?=?.011). Regarding S100B, there was a statistically significant difference between preoperative and postoperative serum level (p-value?=?.002). There was also a statistically significant negative correlation between postoperative S100B serum level and the postoperative scores of both PALT and BVRT.

Conclusion: General anaesthesia is incriminated in the development of postoperative verbal and visual memory impairment and in the postoperative increase in serum S100B, the markers of neuronal degeneration.  相似文献   

999.
1000.

Background

Nutrition labels are important tools for consumers and for supporting public health strategies. Recent, published comparison of label and laboratory sodium values for US foods, and differences by brand type (national or private-label) or source (store or restaurant [fast-food and sit-down]) is unavailable.

Objective

The objective was to compare label and laboratory values for sodium and related nutrients (ie, total sugars, total fat, and saturated fat) in popular, sodium-contributing foods, and examine whether there are differences by brand type, and source.

Design

During 2010 to 2014, the Nutrient Data Laboratory of the US Department of Agriculture collected 3,432 samples nationwide of 125 foods, combined one or more samples of the same food (henceforth referred to as composites), and chemically analyzed them. For this comparative post hoc analysis, the Nutrient Data Laboratory linked laboratory values for 1,390 composites (consisting of one or more samples of the same food) of 114 foods to corresponding label or website (restaurant) nutrient values.

Main outcome measures

Label and laboratory values and their ratio for each composite, for each of the four nutrients (sodium, total fat, total sugars, and saturated fat).

Statistical analyses performed

Nutrient Data Laboratory analysis determined the ratio of laboratory to label value for each composite, and categorized them into six groups: ≥141%, 121% to 140%, 101% to 120%, 81% to 100%, 61% to 80%, and ≤60%. For sodium, the Nutrient Data Laboratory analysis determined the distribution of the ratios by food, food category, brand type, and source.

Results

For sodium, 5% of the composites had ratios of laboratory to label values >120% and 14% had ratios ≤80%. Twenty-two percent of private-label brand composites had ratios ≤80%, compared with 12% of national brands. Only 3% of store composites had ratios >120% compared with 11% of restaurant composites. Ratios ≤80% were more prevalent among sit-down restaurants (37%) compared with fast-food restaurants (9%).

Conclusions

This study shows that a majority of label and laboratory values sampled agree and underdeclaration of label values is limited. However, there is some disagreement. Periodic monitoring of the nutrient content of foods through laboratory analyses establishes validity of the food labels and helps identify foods and food categories where the label and laboratory values do not compare well, and hence may need laboratory analyses to support accuracy of food composition data.  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