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   27287篇
  免费   2370篇
  国内免费   1377篇
耳鼻咽喉   447篇
儿科学   575篇
妇产科学   267篇
基础医学   2107篇
口腔科学   719篇
临床医学   2864篇
内科学   3471篇
皮肤病学   383篇
神经病学   974篇
特种医学   1203篇
外科学   2515篇
综合类   5809篇
现状与发展   8篇
一般理论   3篇
预防医学   2971篇
眼科学   321篇
药学   3029篇
  35篇
中国医学   2029篇
肿瘤学   1304篇
  2024年   135篇
  2023年   324篇
  2022年   810篇
  2021年   1059篇
  2020年   861篇
  2019年   597篇
  2018年   655篇
  2017年   665篇
  2016年   646篇
  2015年   960篇
  2014年   1198篇
  2013年   1598篇
  2012年   2423篇
  2011年   2459篇
  2010年   2149篇
  2009年   1834篇
  2008年   2031篇
  2007年   1943篇
  2006年   1748篇
  2005年   1362篇
  2004年   1027篇
  2003年   903篇
  2002年   657篇
  2001年   673篇
  2000年   547篇
  1999年   297篇
  1998年   117篇
  1997年   106篇
  1996年   67篇
  1995年   58篇
  1994年   51篇
  1993年   45篇
  1992年   88篇
  1991年   99篇
  1990年   85篇
  1989年   53篇
  1988年   46篇
  1987年   68篇
  1986年   54篇
  1985年   74篇
  1984年   48篇
  1983年   42篇
  1980年   23篇
  1979年   39篇
  1978年   22篇
  1977年   21篇
  1975年   28篇
  1974年   27篇
  1973年   26篇
  1969年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Recent advances in the study of evoked responses settled a definition of transient and steady-state visual evoked responses (VER) and discovered the existence of Temporal Frequency Regions in humans. This paper reports data from visual responses evoked by low and high frequency stimuli. White flashes were performed in albino Sprague Dawley rats from 7 to 90 days of age. Frequency analysis technique offered the possibility to evaluate the amplitude parameters and their variations dependent on intensity of luminance and on development. The responses suggested the existence of two temporal frequency regions in the rat: a first one at about 8 Hz, related to high frequencies of EEG, a second one at frequencies ranging from 12 to 24 Hz, related to luminance sensitivity. The development of the second region is correspondent to the complete development of transient VER parameters.  相似文献   
92.
Cell mediated lympholysis (CML) has been proposed as an in vitro model of the rejection process that results from transplantation of allogeneic tissue. To date, the absolute frequencies of cytotoxic T lymphocytes (CTL) and their precursors (CTL.P) have not been directly estimated in man because of technical difficulties. Through optimizing the conditions for radiometric detection of 51Cr release and the attendant improvement in CML sensitivity, direct CTL frequency estimates have been determined in peripheral blood (PBL), spleen (SPL), and lymph nodes (LNC) after in vitro allostimulation using unrelated human cells and limiting dilution assays. The mean frequency of CTL generated from PBL is 1 in 826 cells (0.121% +/- 0.101%) which, from preliminary experiments, is significantly greater than that generated from either LNC or SPL (p less than 0.05). With restimulation of primed cells on day 10, the frequency of CTL generated from PBL was increased 400%. The CTL.P frequency (0.0064% +/- 0.0050%) was approximately 5% of the corresponding CTL frequency. The CTL.P frequencies were found to be minimal estimates as both accessory "filler" cells and T cell growth factors increased the level of detection of CTL.P an average of threefold. The limiting cell dilution assay as detailed in this report should be a powerful tool for defining the cellular requirements and related factors necessary for optimal induction of a CTL response and should provide the means for determination of the immunogenetic requirements and the allospecificity of human cytotoxic lymphocytes.  相似文献   
93.
In our previous study, the combination of the concentrations of carcinoembryonic antigen (CEA) and CA125 and the findings from cytological examination in 189 benign and malignant pleural and peritoneal effusions was useful in the diagnosis/classification of malignant effusions. Sensitivity of CEA (level, greater than 5 ng/mL) was 68%; specificity was 99% for the diagnosis of malignant effusions secondary to carcinoma of the lung, breast, gastrointestinal tract, and mucinous carcinoma of the ovary. Sensitivity of CA125 (level, greater than 5000 U/mL) was 85%; specificity was 96% for the diagnosis of malignant effusions in carcinoma of the ovary, fallopian tube, and endometrium. We now expanded the study to include 840 pleural and peritoneal effusions (benign, n = 520; malignant, n = 320) and analyzed the data by the statistical method of Rudolph and colleagues. Based on new cutoff values, ie, CEA level at 6.3 ng/mL and CA125 level at 3652 U/mL, the sensitivities for detection of malignant effusions secondary to carcinomas of the lung, breast, and gastrointestinal tract and mucinous carcinoma of the ovary varied between 75% and 100%; specificity was 98%. Sensitivity of CA125 for detection of malignant effusions from müllerian epithelial carcinoma was 71%; specificity was 99%. The elevated CEA fluid level alone helped to diagnose malignant effusions of the gastrointestinal tract in 54%, breast in 19%, and lung in 16%. The high CA125 fluid level was predictive of müllerian epithelial carcinoma. Adjunctive use of CEA and CA125 levels in fluid enhances the sensitivity of cytological diagnosis and may be predictive of the primary site in patients who present with carcinoma of an unknown primary source.  相似文献   
94.
We tested the optokinetic nystagmus (OKN) reflex of various hypopigmented mutant mice and ultrastructurally examined the pigmentation of various ocular structures in these mutants. Using electron microscopy we examined the pigmentation of the choroid and retinal pigment epithelium (RPE) and measured the numerical density, volume density, and distribution of RPE melanosomes of mice with the following phenotypes: (1) wild type, (2) mutants that have abnormal or no OKN in response to horizontally moving, full-field stimulation, and (3) other mutants that have normal OKN but reduced choroidal pigmentation. We also measured the OKN of all these mice in response to horizontally moving stimuli that were restricted to the nasal or to the temporal retina. We found that in the mutants with normal OKN the numerical density of melanosomes in the RPE was within the range found for wild type, while the numerical density was reduced for the mutants with abnormal OKN. For one mutant with normal RPE pigmentation and normal OKN, the choroidal pigmentation was nearly absent. For the genotypes with abnormal OKN the volume density of the RPE melanosomes and percent apical melanosomes were sometimes greater and sometimes less than normal. The OKN patterns of these mice fell into the following categories: (1) wild type; (2) field-restriction dependent OKN with small following movements but no OKN in response to full-field stimulation, normal OKN in response to stimulation of the nasal retina, and OKN of reversed direction in response to stimulation of the temporal retina; (3) oblique with slow oblique following movements and reduced numbers of OKNs with oblique quick phases in response to horizontally moving, full-field stimulation, nearly normal OKN in response to stimulation of the nasal retina, and OKN of reversed direction in response to stimulation of the temporal retina. The horizontal component of the oblique response to full-field stimulation was in the same direction for the two eyes, but the vertical component was in the opposite direction. (4) Slow, small amplitude, with no or very small following movements in response to full-field stimulation, following movements in response to stimulation of the nasal retina and reversed "following" movements in response to stimulation of the temporal retina but few or no quick phases of the OKN for any stimulus condition. These results show that a variety of abnormalities of the OKN occur for hypopigmentation mutants of the mouse.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
95.
目的 探讨慢溃宁方对葡聚糖硫酸钠(DSS)诱导的溃疡性结肠炎(UC)小鼠肠道菌群的调控作用,和对NOD样受体(NLR)P3/胱天蛋白酶(Caspase)-1/Gasdermin D(GSDMD)细胞焦亡通路所介导炎症的影响。方法 SPF级C57BL/6小鼠60只,随机分为空白组、模型组、慢溃宁方组(20 g·kg-1)、美沙拉秦组(0.266 g·kg-1),各组15只。小鼠通过自由饮用3%DSS溶液,7 d构建UC模型。造模开始12 h后,治疗组每天灌胃给药,其余组灌胃等体积生理盐水。记录小鼠每日体质量等情况,并评估计算疾病活动指数(DAI)。第8天麻醉后,脱臼颈椎处死小鼠,收集结肠和粪便,记量结肠长度;观察结肠组织苏木素-伊红(HE)染色后的病理学改变;结肠中肿瘤坏死因子-α(TNF-α)、白细胞介素-1β(IL-1β)、白细胞介素-18(IL-18)水平用酶联免疫吸附测定法(ELISA)检测;基于16S rRNA测序技术检测各组小鼠粪便中肠道菌群的差异;NLRP3/Caspase-1/GSDMD蛋白结肠组织中含量用蛋白免疫印迹法(Western blot)检测。结果 相较于空白组,模型组小鼠的DAI升高(P<0.01),结肠长度显著缩短(P<0.01),结肠黏膜损伤严重,TNFα、IL-1β、IL-18水平均明显升高(P<0.01),且结肠组织中NLRP3/Caspase-1/GSDMD蛋白含量显著升高(P<0.01),肠道菌群结构改变,门水平上的放线菌门、拟杆菌门与变形菌门丰度减少,厚壁菌门丰度增加;属水平上的乳酸杆菌、普雷沃氏菌和鼠杆菌属丰度减少,拟杆菌属、芽孢杆菌、毛螺旋菌属NK4A136丰度增加。慢溃宁方组、美沙拉秦组相较于模型组,第3天后DAI显著降低(P<0.01),结肠长度均显著增加(P<0.01),结肠的炎症浸润及黏膜结构损伤减轻,且结肠TNF-α、IL-1β、IL-18水平均显著下降(P<0.01),NLRP3/Caspase-1/GSDMD蛋白在结肠组织中的含量明显降低(P<0.05,P<0.01),门水平上的变形菌门和拟杆菌门丰度增加,厚壁菌门丰度减少。结论 慢溃宁方可通过抑制细胞经典焦亡通路,缓解UC小鼠结肠炎症反应,减轻结肠损伤,并对肠道菌群紊乱有改善作用。  相似文献   
96.
We aimed to report the implementation of a phenylketonuria (PKU) transition program and study the effects of follow-up with an adult team on metabolic control, adherence, and loss of follow-up. Fifty-five PKU patients were analysed in the study periods (SP): 2 years before (SP1) and after the beginning of adult care (SP2). Retrospective data on metabolic control and number of clinic appointments were collected for each SP, and protein intakes were analysed. In SP2, three patients (6%) were lost to follow-up. There was a small but statistically significant increase in median number of annual blood spots from SP1 to SP2: 11 (7–15) vs. 14 (7–20); p = 0.002. Mean ± SD of median blood Phe remained stable (525 ± 248 µmol/L vs. 552 ± 225 µmol/L; p = 0.100); median % of blood Phe < 480 µmol/L decreased (51 (4–96)% vs. 37 (5–85)%; p = 0.041) and median number of clinic appointments increased from SP1 to SP2: (5 (4–6) vs. 11 (8–13); p < 0.001). No significant differences were found regarding any parameter of protein intake. Our results suggest that the implementation of an adult service was successful as impact on metabolic control was limited and attendance remained high. Continuous dietetic care likely contributed to these results by keeping patients in follow-up and committed to treatment.  相似文献   
97.
In patients with phenylketonuria (PKU), treated by diet therapy only, evidence suggests that areal bone mineral density (BMDa) is within the normal clinical reference range but is below the population norm. Aims: To study longitudinal bone density, mass, and geometry over 36 months in children with PKU taking either amino acid (L-AA) or casein glycomacropeptide substitutes (CGMP-AA) as their main protein source. Methodology: A total of 48 subjects completed the study, 19 subjects in the L-AA group (median age 11.1, range 5–16 years) and 29 subjects in the CGMP-AA group (median age 8.3, range 5–16 years). The CGMP-AA was further divided into two groups, CGMP100 (median age 9.2, range 5–16 years) (n = 13), children taking CGMP-AA only and CGMP50 (median age 7.3, range 5–15 years) (n = 16), children taking a combination of CGMP-AA and L-AA. Dual X-ray absorptiometry (DXA) was measured at enrolment and 36 months, peripheral quantitative computer tomography (pQCT) at 36 months only, and serum blood and urine bone turnover markers (BTM) and blood bone biochemistry at enrolment, 6, 12, and 36 months. Results: No statistically significant differences were found between the three groups for DXA outcome parameters, i.e., BMDa (L2–L4 BMDa g/cm2), bone mineral apparent density (L2–L4 BMAD g/cm3) and total body less head BMDa (TBLH g/cm2). All blood biochemistry markers were within the reference ranges, and BTM showed active bone turnover with a trend for BTM to decrease with increasing age. Conclusions: Bone density was clinically normal, although the median z scores were below the population mean. BTM showed active bone turnover and blood biochemistry was within the reference ranges. There appeared to be no advantage to bone density, mass, or geometry from taking a macropeptide-based protein substitute as compared with L-AAs.  相似文献   
98.
School meals present several cost benefits overtime at the short, medium, and long term for individuals and society. This cross-sectional study aims to analyse the nutritional composition and evaluate the adequacy of school lunches. One hundred and fifty-eight samples were collected and analysed from 10 primary schools in Sintra’s municipality, served during one week. On average, energy (27.7% daily energetic requirements) and carbohydrate (48.1%) contents did not reach the reference values, and the content of protein (19.5%) exceeded the reference value (p < 0.05). The mean total fat (28.8%) and saturated fatty acids (5.4%) content complied with the recommendations. The mean salt (1.7 g) and dietary fibre (8.3 g) content exceeded the reference value but did not differ significantly from the recommendations. Addressing school canteens is crucial, not only in a nutritional approach, but also as an opportunity to achieve healthier, sustainable, and accessible food systems, aligned with the Sustainable Development Goals 2030. We highlighted the importance of evaluating evidence-based practices and disseminated practice-based evidence regarding the adequacy of school lunches.  相似文献   
99.
The biomedical potential of the edible red seaweed Agarophyton chilense (formerly Gracilaria chilensis) has not been explored. Red seaweeds are enriched in polyunsaturated fatty acids and eicosanoids, which are known natural ligands of the PPARγ nuclear receptor. PPARγ is the molecular target of thiazolidinediones (TZDs), drugs used as insulin sensitizers to treat type 2 diabetes mellitus. Medical use of TZDs is limited due to undesired side effects, a problem that has triggered the search for selective PPARγ modulators (SPPARMs) without the TZD side effects. We produced Agarophyton chilense oleoresin (Gracilex®), which induces PPARγ activation without inducing adipocyte differentiation, similar to SPPARMs. In a diet-induced obesity model of male mice, we showed that treatment with Gracilex® improves insulin sensitivity by normalizing altered glucose and insulin parameters. Gracilex® is enriched in palmitic acid, arachidonic acid, oleic acid, and lipophilic antioxidants such as tocopherols and β-carotene. Accordingly, Gracilex® possesses antioxidant activity in vitro and increased antioxidant capacity in vivo in Caenorhabditis elegans. These findings support the idea that Gracilex® represents a good source of natural PPARγ ligands and antioxidants with the potential to mitigate metabolic disorders. Thus, its nutraceutical value in humans warrants further investigation.  相似文献   
100.
目的探讨失效模式与效应分析法(failure mode and effects analysis,FMEA)在神经内科ICU医院感染控制中的应用,发现高风险因素,为院感防控提供参考依据。方法根据神经内科ICU临床实际情况,通过FMEA风险评估法对34项医院感染风险事件进行风险评估,按照"二八法则"筛选出风险优先级事件。结果根据每一项风险因素的平均RPN值进行风险排序,按照"二八法则"筛选出风险优先级前6位的事件分别是:本科室医护人员手卫生依从性不到位(平均RPN值=5.6)、导尿管日常维护不到位(平均RPN值=4.17)、多耐患者未有效执行接触隔离措施(平均RPN值=3.80)、物表清洁消毒未有效执行(平均RPN值=3.73)、未严格掌握留置导尿指征(平均RPN值=3.70)、未保持尿液引流系统的密闭性(平均RPN值=3.53)。结论FMEA风险评估法可以发现神经内科ICU医院感染防控中的薄弱环节,为精准化感控措施的制订提供依据。  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