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   21995篇
  免费   1900篇
  国内免费   1617篇
耳鼻咽喉   182篇
儿科学   216篇
妇产科学   197篇
基础医学   2560篇
口腔科学   340篇
临床医学   2865篇
内科学   2996篇
皮肤病学   136篇
神经病学   1102篇
特种医学   775篇
外国民族医学   14篇
外科学   2525篇
综合类   3754篇
现状与发展   4篇
一般理论   1篇
预防医学   1519篇
眼科学   554篇
药学   2384篇
  25篇
中国医学   1255篇
肿瘤学   2108篇
  2025年   1篇
  2024年   339篇
  2023年   485篇
  2022年   958篇
  2021年   1081篇
  2020年   907篇
  2019年   749篇
  2018年   749篇
  2017年   657篇
  2016年   668篇
  2015年   955篇
  2014年   1186篇
  2013年   1025篇
  2012年   1456篇
  2011年   1632篇
  2010年   1060篇
  2009年   857篇
  2008年   1112篇
  2007年   1145篇
  2006年   1083篇
  2005年   1096篇
  2004年   662篇
  2003年   755篇
  2002年   583篇
  2001年   496篇
  2000年   543篇
  1999年   622篇
  1998年   378篇
  1997年   391篇
  1996年   286篇
  1995年   255篇
  1994年   255篇
  1993年   133篇
  1992年   172篇
  1991年   147篇
  1990年   120篇
  1989年   125篇
  1988年   106篇
  1987年   78篇
  1986年   58篇
  1985年   66篇
  1984年   19篇
  1983年   16篇
  1982年   11篇
  1981年   10篇
  1980年   6篇
  1979年   17篇
  1929年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
BackgroundTo evaluate the effect of diabetes comorbidities by baseline healthcare utilization on receipt of recommended eye examinations.MethodsRetrospective analysis of 310 691 nonelderly adults with type 2 diabetes in the IBM MarketScan Commercial Database from 2016 to 2019. Patients were grouped based on diabetes‐concordant (related) or ‐discordant (unrelated) comorbidities. Logistic regression was used to estimate the prevalence ratio (PR) for eye examinations by comorbidity status, healthcare utilization, and an interaction between comorbidities and utilization, controlling for age, sex, region, and major eye disease.ResultsPrevalence of biennial eye examinations varied by the four comorbidity groups: 43.5% (diabetes only), 52.7% (concordant + discordant comorbidities), 48.0% (concordant comorbidities only), and 45.3% (discordant comorbidities only). In the lowest healthcare utilization tertile, the concordant‐only and concordant + discordant groups had lower prevalence of examinations compared to diabetes only (PR 0.95 [95% CI 0.92–0.98] and PR 0.91 [95% CI 0.88–0.95], respectively). In the medium utilization tertile, the discordant‐only and concordant + discordant groups had lower prevalence of examinations (PR 0.89 [0.83–0.95] and PR 0.94 [0.90–0.98], respectively). In the highest utilization tertile, the concordant‐only and concordant + discordant groups had higher prevalence of examinations.ConclusionsAmong patients with low healthcare utilization, having comorbid conditions is associated with lower prevalence of eye examinations. Among those with medium healthcare utilization, patients with diabetes‐discordant comorbidities are particularly vulnerable. This study highlights populations of diabetes patients who would benefit from increased assistance in receiving vision‐preserving eye examinations.  相似文献   
102.
The low plasticity burnished surface roughness is significantly affected by the low plasticity burnishing (LPB) parameters. This research proposed the analytical prediction model to predict the LPBed surface roughness and optimal LPB pressure based on Hertz contact mechanics and the slip-line field theory. In this study, the surface formatted process was divided into the smoothing stage (SS) and the indentation stage (IS). The smoothing mechanism of SS and the deterioration mechanism of IS were analyzed theoretically. The analytical prediction model for the LPBed surface roughness was proposed based on Hertz contact mechanics and slip-line field theory. The proposed analytical prediction model was validated by the LPBed surface roughness of AISI 1042, and the error of the analytically predicted results was less than 13.3%. After validation, the proposed model was applied to predict the LPBed surface roughness of Inconel 718. The single-factor experiments were conducted. The error between the proposed model prediction results and experimental results was less than 7% for the LPBed surface roughness of Inconel 718. The optimal LPB pressure interval was calculated to be [12.2 MPa, 17.5 MPa], corresponding to the experimental one as [12 MPa, 18 MPa]. It indicated that the proposed model could accurately predict the LPBed surface roughness and conduct the LPB processing.  相似文献   
103.
Struvite is a chemically bonded ceramic product in the pipeline of a sewage treatment plant. In order to explore the fire extinguishing potential of struvite, a new type of struvite ultrafine dry powder with excellent performance was prepared by a simple process, and its fire extinguishing performance and mechanism were analyzed in depth. Under the same process conditions, the refinement degree (D50 = 5.132 μm) and the specific surface area (BET = 25.72 m2/g) of ultrafine struvite were larger than those of NH4H2PO4 (D50 = 8.961 μm, BET = 13.64 m2/g), making struvite more suitable for fire extinguishing. Besides, the pyrolysis process of struvite was relatively concentrated and absorbed more heat in a short time. Its heat absorption (458.4 J/mg) was higher than that of NH4H2PO4 (156.4 J/mg). Water, ammonia, and PO· were released during the pyrolysis of struvite, which effectively reduced fire temperature, diluted oxygen concentrations and captured free radicals. At the same time, the final products were magnesium orthophosphate and magnesium pyrophosphate, which formed a dense flame-retardant ceramic layer with good thermal insulation and environmental protection functions. In these cases, the fire extinguishing mechanism of struvite was determined to have three stages: the cooling effect, the asphyxiation effect, and the chemical effect. Correspondingly, the fire extinguishing time of struvite was three seconds faster than that of ammonium phosphate under 0.2 MPa based on the local oil basin test.  相似文献   
104.
Ta2O5 was deposited on quartz glass and Si substrates as a protective coating. The inherent RF magnetron sputtering power of 140 W was maintained during the deposition process. During the deposition process, amounts of 5%, 10%, and 15% of N2 were injected, and the total sputtering gas (N2+Ar) flow was kept at 40 sccm. The microstructure and surface morphology of the coatings were characterized, and the friction and wear experiments of the coatings were carried out. The results show that the coatings’ surface is smooth and the main chemical compositions are Ta, O, and N. The maximum average roughness of the coatings was prepared by pure argon sputtering. It is proved that the introduction of N2 reduces the surface roughness of the coatings and increases the surface hardness and elastic modulus of the coatings. Adhesive wear and brittle fracture are the two main wear forms of coatings. The wear debris is mainly composed of columnar particles and a flake structure.  相似文献   
105.
Cherry leaf roll virus (CLRV) is an important plant pathogen that causes severe and detrimental effects on cherry and other fruit plants. Despite recent progress in plant pathology, molecular biology, and population genetics of CLRV, the spatiotemporal spread of this virus remains poorly studied. In this study, we employed a Bayesian phylodynamics framework to investigate the spatial diffusion patterns of CLRV by analyzing the coat protein gene sequences of 81 viral isolates collected from five different countries. Consistent with the trade of cherry, our Bayesian phylodynamic analyses pointed to viral origins in New Zealand and identified multiple migration pathways between Germany and other countries, suggesting that Germany has played an important role in CLRV transmission. The results of our study will be useful in developing sustainable management strategies to control this pathogen.  相似文献   
106.
Dyslipidemia has been associated with cancer risk, yet the relationship between lipid ratios and nonsmall-cell lung cancer (NSCLC) is still unclear. This study aimed to explore the value of lipid ratios, including total cholesterol/high-density lipoprotein cholesterol (TC/HDL-C) and triglyceride/HDL-C (TG/HDL-C) as predictors of NSCLC in a Chinese population. Adult patients with histologically confirmed NSCLC, without a previous history of cancer, concomitant disease associated with lipid metabolism disorders, or usage of lipid-lowering drugs, were enrolled from a single center. Controls without NSCLC, matched for age and sex, were enrolled from the same Center. Lipid profile including TC, TG, HDL-C were measured in all participants. TC/HDL-C and TG/HDL-C were calculated based on the levels of TC, TG, HDL-C. Seven hundred eighty-two NSCLC cases and 599 controls were enrolled. NSCLC patients had significantly higher TG/HDL-C and TC/HDL-C levels than those in the control. After controlling for confounding factors, TG/HDL-C (OR = 4.489, 95% CI: 2.463–6.035, P < .001) and TC/HDL-C (OR = 2.396, 95% CI: 2.086–2.752, P = .001) were independently associated with NSCLC risk. The incidence of NSCLC was increased with rising tertiles of TG/HDL-C and TC/HDL-C. Moreover, patients with TNM II-IV stage NSCLC had higher TG/HDL-C and TC/HDL-C than those in TNM I and Tis stage. TG/HDL-C and TC/HDL-C are positively correlated with NSCLC risk and TG/HDL-C is more predictive than TC/HDL-C in predicting the risk of NSCLC. The highest AUC was that of TG/HDL (0.898), at a cutoff point of 0.62, with 83.6% sensitivity and 83.5% specificity.  相似文献   
107.
108.
This study aimed to evaluate the potential associations of dietary BCAAs (isoleucine, leucine, and valine) with physical function in the elderly Chinese population. A validated semiquantitative food frequency questionnaire and anthropometric and physical function measurements were used to collect data. We modeled trends in physical function indicators for BCAA quartiles using multivariate linear regression models. Among 4336 (43.97% men) participants aged 72.73 ± 5.48 years, a higher dietary intake of BCAAs was positively associated with increased handgrip strength (all p trends < 0.001), shorter times for 4-m fast walking (all p trends < 0.001) and repeated chair rises (all p trends < 0.001). No linear association was found between subtypes of amino acids and any physical functions (all p trends > 0.05). Individuals in the highest quartiles of BCAA intake had a reduced risk of developing low muscle strength, and the multiadjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) for women and men were 0.50 (0.38–0.65) and 0.67 (0.50–0.91), respectively. Similarly, higher BCAA consumption was associated with a lower risk of developing low physical performance (4-m walking speed: OR = 0.68 [0.50–0.93]; repeated chair rises: OR = 0.66 [0.54–0.81]). Higher dietary BCAA intake might be beneficial for physical function in the elderly population.  相似文献   
109.
Fatty acids play important roles in maintaining ovarian steroidogenesis and endometrial receptivity. Porcine primary ovarian granulosa cells (PGCs) and endometrial epithelial cells (PEECs) were treated with or without medium- and short-chain fatty acids (MSFAs) for 24 h. The mRNA abundance of genes was detected by fluorescence quantitative PCR. The hormone levels in the PGCs supernatant and the rate of adhesion of porcine trophoblast cells (pTrs) to PEECs were measured. Sows were fed diets with or without MSFAs supplementation during early gestation. The fecal and vaginal microbiomes were identified using 16S sequencing. Reproductive performance was recorded at parturition. MSFAs increased the mRNA abundance of genes involved in steroidogenesis, luteinization in PGCs and endometrial receptivity in PEECs (p < 0.05). The estrogen level in the PGC supernatant and the rate of adhesion increased (p < 0.05). Dietary supplementation with MSFAs increased serum estrogen levels and the total number of live piglets per litter (p < 0.01). Moreover, MSFAs reduced the fecal Trueperella abundance and vaginal Escherichia-Shigella and Clostridium_sensu_stricto_1 abundance. These data revealed that MSFAs improved pregnancy outcomes in sows by enhancing ovarian steroidogenesis and endometrial receptivity while limiting the abundance of several intestinal and vaginal pathogens at early stages of pregnancy.  相似文献   
110.
Meat adulteration have become a global issue, which has increasingly raised concerns due to not only economic losses and religious issues, but also public safety and its negative effects on human health. Using optimal primers for seven target species, a multiplex PCR method was developed for the molecular authentication of camel, cattle, dog, pig, chicken, sheep and duck in one tube reaction. Species-specific amplification from the premixed total DNA of seven species was corroborated by DNA sequencing. The limit of detection (LOD) is as low as 0.025 ng DNA for the simultaneous identification of seven species in both raw and heat-processed meat or target meat: as little as 0.1% (w/w) of the total meat weight. This method is strongly reproducible even while exposed to intensively heat-processed meat and meat mixtures, which renders it able to trace meat origins in real-world foodstuffs based on the authenticity assessment of commercial meat samples. Therefore, this method is a powerful tool for the inspection of meat adulterants and has broad application prospects.  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