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   29868篇
  免费   3616篇
  国内免费   1041篇
耳鼻咽喉   163篇
儿科学   1730篇
妇产科学   700篇
基础医学   2615篇
口腔科学   755篇
临床医学   3493篇
内科学   4082篇
皮肤病学   203篇
神经病学   1614篇
特种医学   1328篇
外国民族医学   9篇
外科学   5207篇
综合类   4120篇
现状与发展   4篇
一般理论   1篇
预防医学   3053篇
眼科学   924篇
药学   2161篇
  12篇
中国医学   963篇
肿瘤学   1388篇
  2024年   43篇
  2023年   455篇
  2022年   655篇
  2021年   1242篇
  2020年   1168篇
  2019年   1220篇
  2018年   1175篇
  2017年   1109篇
  2016年   1093篇
  2015年   1089篇
  2014年   1934篇
  2013年   2274篇
  2012年   1732篇
  2011年   1861篇
  2010年   1511篇
  2009年   1499篇
  2008年   1530篇
  2007年   1540篇
  2006年   1422篇
  2005年   1385篇
  2004年   1162篇
  2003年   1024篇
  2002年   852篇
  2001年   780篇
  2000年   682篇
  1999年   533篇
  1998年   432篇
  1997年   423篇
  1996年   357篇
  1995年   287篇
  1994年   262篇
  1993年   221篇
  1992年   204篇
  1991年   170篇
  1990年   134篇
  1989年   109篇
  1988年   101篇
  1987年   93篇
  1986年   66篇
  1985年   126篇
  1984年   102篇
  1983年   91篇
  1982年   84篇
  1981年   89篇
  1980年   67篇
  1979年   32篇
  1978年   30篇
  1977年   26篇
  1976年   18篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 135 毫秒
91.
腰椎全板减压术后顽固下腰痛的原因分析   总被引:6,自引:4,他引:2  
[目的]分析腰椎全板切除术后残留下腰痛的原因,指导选择合理的手术方法。[方法]回顾分析1996~2000年作者采用全椎板切除减压治疗的腰椎管狭窄症患者临床资料,69例获得5年以上随访的患者作为本组研究对象,使用日本骨科学会(JOA)标准对患者的神经功能和下腰痛程度进行评分,根据手术前后下腰痛程度的变化将病例分为无残存下腰痛(lowbackpain,LBP)组和残存LBP组,针对术前的临床和影像学参数,使用软件包SPSS13.0进行对数回归分析,确定术后残存下腰痛的临床预测因素,并对这些影响因素进行两组间比较和统计分析。[结果]术前腰椎前突角、腰椎活动度和手术减压范围与术后残存下腰痛密切相关。残存LBP组患者术前腰椎生理前突和活动度分别为(22.27°±3.12°)和(22.91°±2.31°),显著低于无残存LBP组患者的腰椎前突和活动度(37.23°±2.19°)和(31.66°±1.52°),P值分别为0.000和0.002;而残存LBP组的减压节段(2.77±0.19节)明显高于无残存LBP组(1.70±0.10节),P值为0.000。[结论]对于术前腰椎前突减小,腰椎活动度下降的椎管狭窄症患者单纯施行多节段的腰椎全板减压容易导致术后顽固性下腰痛的出现,应引起作者重视。  相似文献   
92.
Measurement of ultrasonographic parameters provides information concerning not only bone density but also bone architecture. We investigated the usefulness of ultrasonographic parameters and bone mineral density (BMD) to evaluate the probability of Colles' fracture. Two-hundred eighty-nine postmenopausal women (62.3 +/- 8.7 yr) with (n = 76) and without (n = 213) Colles' fracture were studied. BMD of lumbar spine and proximal femur was evaluated in all women by dual-energy X-ray absorptiometry (DXA) and speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness in the calcaneus were measured by a Sahara ultrasonometer (Hologic). Patients suffering from Colles' fracture had lower values of BMD adjusted by height at the lumbar spine, L2-L4 (0.797 g/cm2 vs 0.860 g/cm2), femoral neck (0.685 g/cm2 vs 0.712 g/cm2 ), SOS (1518 m/sg vs 1525 m/sg), and stiffness (74.6 vs 77.7) (p < 0.05). Nevertheless, BUA values were similar in both groups. After stepwise logistic regression analysis, the area found under receiver operating characteristic (ROC) curves was 0.60 for L2L4 and 0.63 for a formula combining L2L4 and height. Our data suggest that patients suffering from Colles' fracture have lower values of BMD by DXA, SOS, and stiffness. However, the ability of these techniques to discriminate is low because the values for the area under ROC curve are 0.60 for L2-L4 and 0.63 for a formula derived of the combination of L2-L4 and height.  相似文献   
93.
We tested the hypothesis that bone mineral density (BMD) and bone mineral content (BMC) in proximal human femur specimens in the upper neck region of interest (ROI) and femoral neck axis length (FNAL) provide a significantly better prediction of femoral bone strength than standard ROIs in vitro. BMD and BMC were measured in 110 proximal femur specimens using a standard dual-energy X-ray absorptiometry (DXA) scanner. The analysis included a new ROI in the upper neck as well as the standard ROIs. FNAL was obtained from the scan images. The specimens' failure-load was measured in a mechanical loading device, simulating a fall on the greater trochanter. For the standard ROIs, correlations between failure-load and BMD ranged from R2 = 0.64 (shaft ROI) to R2 = 0.70, p < 0.001 (femoral neck). Prediction of strength by BMD did not significantly differ from those of BMC (R2 ranging from 0.65 to 0.75, p < 0.001). In the upper neck ROI, for both BMD and BMC correlations with failure-load were higher (R2 = 0.76 and 0.81, respectively; p < 0.001). A lower, yet still significant, correlation was found between FNAL and bone strength (R2 = 0.23, p < 0.001). Normalization of failure-load with respect to FNAL did not significantly increase the correlations with densitometric measures. This study provides in vitro evidence indicating that among the ROIs of the proximal femur the newly defined upper neck ROI provides the best prediction of bone strength. Only a weak association was observed between failure load and FNAL.  相似文献   
94.
Objective: The aim of this study was to determine the prevalence of low back pain (LBP) in a primary care setting population and examine its association with the symptoms of depression and somatization. Methods: This is a cross‐sectional study, utilising a survey carried out in primary health care clinics (PHCs) in Al‐Ain, United Arab Emirates (UAE). A multistage stratified sampling design was used and a representative sample of 1304 UAE nationals aged 18–65 years who attended PHC clinics for any reason were included and 1103 (84.5%) subjects agreed to participate and responded to the questionnaire during a period from June 2001 to January 2002. A specially designed questionnaire with three parts was used for the data collection: socio‐demographic information of the studied subjects, modified version of the Roland‐Morris scale for evaluating back‐related functional disability and SCL‐90 R for depression and somatization subscales was used to assess depressive and somatic symptoms. Results: Of the total number of subjects surveyed (1103), 586 (53.1%) were men and 517 (46.9%) women. The mean age was 34.9 ± 13.4 years for men and 33.5 ± 11.8 years for women. The prevalence of LBP in the studied subjects was 64.7% (95% CI, 60.7–68.5] with 46.7% among men and 53.3% among women. There were a significant differences between the subjects with LBP and without LBP with respect to gender (P < 0.001), body mass index (BMI) (P < 0.001), occupational status (P < 0.001) and living environment (P = 0.016). Functional disability was higher in patients with LBP. Young patients in aged 15–34 years, patients with preparatory/secondary educational level and students showed higher depressive symptoms. A similar pattern was found in patients with somatic symptoms. Factor analysis revealed a strong association between depression and somatization in LBP patients. Conclusions: Functional disability was higher in with LBP. Furthermore, symptoms of depression and somatization are prevalent among LBP patients.  相似文献   
95.
Summary Intraoperative mapping techniques allow a reliable identification or exclusion of eloquent brain areas and are well tolerated by the patients. In dominant opercular tumours radical surgery can only be achieved without lasting deficits with intraoperative histological examination of the resection line and mapping. If an early post-operative MRI shows residual opercular tumour in non-eloquent areas re-operation is recommended.In large dominant insular or opercular-insular tumours only biopsy is recommended, because only an incomplete removal can be accomplished, because the trial of radical removal carries a high risk of postoperative deficits due to possible vascular damage of the lenticulo-striate arteries or internal capsule. Because subtotal removal of low grade gliomas does not increase the progression free interval, we would not recommend surgery in these cases, as they carry a significant risk of a further deficit.  相似文献   
96.
Purpose. To estimate disease activity in patients with systemic sclerosis using contrast-enhanced MRI of the skin. Material and Methods. In a pre-study, sequences of a low-field (0.2 T) scanner (Artoscan, Esaote, Genova, Italy) were optimized for detection of intravenous contrast (0.1 mmol/l Gd-DTPA) in six patients with the autoimmune disease systemic scleroderma. Based on the results of the pre-study, 17 patients with scleroderma (7 sclerotic/10 active inflammatory disease) were scanned using gradient-spoiled 3D GRE sequences (FA 90 °, TR 100 ms, TE 18 ms), which had been established as most sensitive for intravenous contrast. Contrast enhancement of the skin was determined quantitatively by contrast-to-noise ratios (CNR), comparing post- to pre-contrast and dynamic scans (for 6 min, 1 acquisition/min). Patients in the chronic state with sclerodactylia and active inflammation of the hands were considered separately and compared to a control group (n = 10) matched according to age. Results. CNR increase after intravenous contrast was significantly higher in patients with active disease (86 ± 16 % increase) than sclerosing disease (29 ± 3 %, p < 0.05) and the control group (4 ± 2 %, p < 0.05). The dynamic examination showed a significantly slower decrease after the peak rise in the first minute in patients with active disease (CNR 15.4 ± 0.7 to 14.2 ± 1.4) than in those with chronic disease (14.1 ± 0.5 to 11.3 ± 0.9, p < 0.05). Discussion. Capillary leakage is the most likely explanation for the increased enhancement in patients with active scleroderma. Using sequences optimized for contrast detection, disease activity in the course of scleroderma and response to therapy can be determined by MRI in the future.   相似文献   
97.
妊娠期妇女的人体测量及脂肪贮存   总被引:1,自引:0,他引:1  
唐仪  王叶凡 《营养学报》1990,12(3):267-271
本文对30名居住北京城近郊区的健康初产孕妇,于妊娠早期、中期及末期连续进行人体测量,包括身长,体重,皮下脂肪厚度和肢体围,以观察孕期体重增长,身体脂肪含量及肌肉情况。测量结果,受试者从妊娠6周至37周平均体重增长13.0kg。三头肌、二头肌部位皮脂厚度在孕期无明显变化。肩胛下皮脂厚度至孕末期时明显较早期增加。髂骨上皮脂厚度在孕中期及末期均有明显增长,与早期相比差別显著。据皮脂厚度计算身体密度及脂肪含量络果,至孕末期身体脂肪含量占体重的百分比共增加3.7%。肢体围测量结果,仅臀围在妊娠中期后至末期明显较早期增大。大腿上部围略有增加,但与早期差别无显著意义。大腿中部、小腿腓肠肌部及上臂围孕期均无明显变化。  相似文献   
98.
Osteoporosis and Coronary Atherosclerosis in Asymptomatic Postmenopausal Women   总被引:23,自引:9,他引:14  
Estrogen deficiency is a risk factor for osteoporosis and coronary artery disease. Osteoporosis can be evaluated by measuring bone mineral density (BMD). Coronary atherosclerotic burden can be evaluated by measuring coronary calcium using electron beam computed tomography (EBT) of the heart. We compared coronary calcium scores in 45 asymptomatic postmenopausal women with normal and low BMD. BMD of the lumbar spine and proximal femur was measured by dual X-ray absorptiometry (DXA), and coronary calcium was measured quantitatively by EBT. Women were divided into control, osteopenia, and osteoporosis groups based on the T score of the lumbar spine. Women were similar in age, years since menopause, height, weight, and body mass index (BMI). BMD ± SD (g/cm2) of L1–L4 was 0.96 ± 0.11, 0.83 ± 0.03, and 0.73 ± 0.05, in control, osteopenia, and osteoporosis group, respectively. The total coronary calcium score ± SD (relative units) was 41.9 ± 83.1, 115.1 ± 181.9, and 221.7 ± 355.4 for control, osteopenia, and osteoporosis group, respectively; the score was significantly higher in the osteoporosis than in the control group. This study provides initial data suggesting that women with osteoporosis may have a higher risk of developing coronary atherosclerosis.  相似文献   
99.
Fast and slow twitch muscle fibers have distinct contractile properties. Here we determined that membrane excitability also varies with fiber type. Na+ currents (INA) were studied with the loose-patch voltage clamp technique on 29 histochemically classified human intercostal skeletal muscle fibers at the endplate border and <200 μm from the endplate (extrajunctional). Fast and slow twitch fibers showed slow inactivation of endplate border and extrajunctional INA and had increased INA at the endplate border compared to extrajunctional membrane. The voltage dependencies of INA were similar on the endplate border and extrajunctional membrane, which suggests thatboth regions have physiclogically similar channels. Fast twitch fibers had larger INA on the endplate border and extrajunctional membrane and manifest fast and slow inactivation of INA at more negative potentials than slow twitch fibers. For normal muscle, the differences between INA on fast and slow twitch fibers might: (1) enable fast twitch fibers to operate at high firing frequencies for brief periods; and (2) enable slow twitch fibers to operate at low firing frequencies for prolonged times. Disorders of skeletal membrane excitability, such as the periodic paralyses and myotonias, may impact fast and slow twitch fibers differently due to the distinctive Na+ channel properties of each fiber type. © 1993 John Wiley & Sons, Inc.  相似文献   
100.
Summary Precision of dual-photon absorptiometry (DPA) measurements was determined in a lumbar spine phantom and in humans. Approximately half of the measurements were made before and half after a153gadolinium source change. The phantom was measured with different amounts of acrylic, which simulates human soft tissue, in order to evaluate the influence of body thickness on bone mineral density (BMD). Results of scans analyzed with two software versions from Lunar Radiation Corp., the widely used 08B and a prototype 08C, are compared. DPA with a cold source significantly overestimated BMD in the phantom in the presence of large amounts (more than 25 cm) of soft tissue equivalent with version 08B but not with the newer version 08C. Similiarly, in nine subjects, there was a significant decrease in spine BMD after a source change when scans were analyzed with version 08B (mean difference 0.026 g/cm2,P=0.002) but not with 08C (0.01 g/cm2,P=0.234). No systematic effect of source change on femoral BMD measurements was observed. The SD of the mean difference of two measurements of the nine subjects was 0.019 g/cm2 (1.6% of the mean value) for the spine with software version 08B and 0.024 g/cm2 (2.0%) with version 08C, 0.03 g/cm2 (3.3%) for the femur neck, 0.03 g/cm2 (4.0%) for the greater trochanter, and 0.04 g/cm2 (4.9%) for Ward's triangle region of the proximal femur. The spine phanton was scanned on two other commercial bone densitometers in order to assess inter-instrument variation. Phantom measurements of L2-4 BMD made on two Lunar Radiation Corp model DP3 scanners which differed by 2% were 10 and 12% higher than those with a Norland Corp. model 2600 scanner.  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