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   272211篇
  免费   15679篇
  国内免费   7637篇
耳鼻咽喉   3486篇
儿科学   8707篇
妇产科学   3136篇
基础医学   18803篇
口腔科学   6598篇
临床医学   32631篇
内科学   45786篇
皮肤病学   3247篇
神经病学   13629篇
特种医学   27258篇
外国民族医学   43篇
外科学   37504篇
综合类   26331篇
现状与发展   29篇
预防医学   16340篇
眼科学   7437篇
药学   25691篇
  91篇
中国医学   4790篇
肿瘤学   13990篇
  2023年   2751篇
  2022年   6134篇
  2021年   12446篇
  2020年   6927篇
  2019年   12633篇
  2018年   7350篇
  2017年   6468篇
  2016年   8377篇
  2015年   11361篇
  2014年   20764篇
  2013年   17877篇
  2012年   21433篇
  2011年   18815篇
  2010年   17013篇
  2009年   16591篇
  2008年   15402篇
  2007年   15412篇
  2006年   13296篇
  2005年   9324篇
  2004年   5555篇
  2003年   4729篇
  2002年   3830篇
  2001年   3192篇
  2000年   2757篇
  1999年   1927篇
  1998年   2233篇
  1997年   2100篇
  1996年   1738篇
  1995年   1722篇
  1994年   1640篇
  1993年   1259篇
  1992年   1390篇
  1991年   1230篇
  1990年   1241篇
  1989年   1201篇
  1988年   1118篇
  1987年   999篇
  1986年   794篇
  1985年   1733篇
  1984年   1904篇
  1983年   1351篇
  1982年   1477篇
  1981年   1429篇
  1980年   1227篇
  1979年   1045篇
  1978年   795篇
  1977年   801篇
  1976年   682篇
  1974年   458篇
  1973年   433篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
The acute onset of peritoneal signs and shock in a 7year-old boy who had been hit in the epigastrium by a log-seesaw mandated surgical treatment. Enhanced computed tomography (CT) demonstrated complete laceration of the pancreas as well as duodenal injury, and a duodenoduodenostomy with distal pancreaticogastrostomy was subsequently performed. Temporary external drainage of the stomach and distal pancreas led to an uneventful recovery in the early postoperative period. Although the patient's postoperative development was appropriate for his age, the orifice of the distal pancreas spontaneously closed 2.5 years following surgery. We present this report to stress the fact that every effort should be made to preserve the pancreas following abdominal injury in children.  相似文献   
962.
The immunohistochemical occurrence of the high affinity neurotrophin (NT) receptors trkA, trkB, and trkC is shown in the pre-term newborn, infant, and adult human post-mortem cerebellum. Immunoreactive neuronal perikarya and processes were observed in all specimens examined, where they appeared unevenly distributed in the cerebellar cortical layers and deep nuclei, and showed regional differences among cerebellar lobules and folia. The trk receptor-antibodies, tested by Western blot on human cerebellum homogenates, revealed multiple immunoreactive bands for trkA and single bands for trkB and trkC. The results obtained show the tissue localization of the trk receptor-like immunoreactivity in the human cerebellum from prenatal to adult age. The analysis for codistribution of the receptors with the relevant ligand and among the receptors in discrete cortical and deep nuclei tissue fields shows a wide variety of conditions, from a good similarity in terms of type and density of labeled structures, to a lack of correspondence, and suggests the possibility of colocalization of trk receptors with the relevant neurotrophin and among them in the cerebellar cortex. These results sustain the concept that the neurotrophin trophic system participates in the development, differentiation, and maintenance of the human cerebellar connectivity and support the possibility of a multifactorial trophic support for the neurotrophins through target-derived and local mechanisms.  相似文献   
963.
For several different bone mineral measurements and various skeletal sites, we compared capability to discriminate between women in various age decades with and without spinal fracture, and attempted to identify the most effective cutoff level in discrimination of spinal fracture. The subjects were 88 women aged 50–59 years (including 32 with fracture), 95 women aged 60–69 years (including 54 with fracture), and 34 women aged 70–79 years (including 18 with fracture). Spinal trabecular and cortical bone mineral density (BMD) were measured using quantitative computed tomography (CT), and spinal, radial (ultra-distal, 10% distal and 33% distal), and calcaneal BMD were measured by dual X-ray absorptiometry. These BMD values were obtained in each subject on the same day. Three statistical techniques—Student's t-test, the logistic regression analysis, and the receiver operating characteristics (ROC) analysis— were applied and accuracy was calculated using the various cutoff values. The capability to discriminate between women with and those without fracture using these BMD values was different among the three age groups. In women aged 50–59 and 60–69 years, all measurements showed good capabilities for discriminating women with fracture. In women aged 70–79 years, these measurements showed lower capability than in those aged 50–59 and 60–69 years, but among them, the calcaneal and ultradistal radial BMD showed relatively good capability. The 10% and 33% distal radial BMD values were not useful in the detection of the high risk women with fracture. The cutoff BMD values for discrimination of women with fracture varied according to the sites and methods of measurement. For each specific age group, the most suitable measurement methods and the appropriate skeletal sites should be considered, and the effective cutoff values to discriminate those with fracture may differ according to the measurement methods, the skeletal sites examined, and age. Received: 5 February 1996 / Accepted: 18 June 1996  相似文献   
964.
目的:研究CT仿真结肠内窥镜(CT Virtual Colonoscopy,CTVC)的使用价值,应用方法及镜下表现。方法:使用Hispeed FX/i扫描机,扫描层厚3~5mm,螺距1~2,重叠重建率50%~67%。利用Navigator Smooth软件对容积扫描数据进行三维重建,获得仿真结肠内窥镜的影像,并与纤维肠镜和/或手术所见对照分析,全部病例经病理证实。结果:通过选择不同的观察方位,角度和阈值,CTVC能清楚显示靶器官内正常解剖结构的立体影像和病变的部位、大小、形态及其侵犯范围。CTVC对结肠病变形态的显示与FC或/和标本显示具有良好的对应性,另外,CTVC能从闭塞和狭窄的远端观察病变。但CTVC不能显示组织的颜色变化,不能活检。结论:CTVC作为一种新的非侵袭性结肠检查方法,可以作为纤维结肠镜的有效补充手段,有较好的临床应用价值。  相似文献   
965.
CT引导下胰腺穿刺早期诊断胰腺感染   总被引:13,自引:0,他引:13  
作者对1990年至1996年收治的122例重症急性胰腺炎中持续发热、白细胞增高、疑有感染的21例患者行CT引导下细针穿刺细菌学检查,确定有无胰腺感染。在CT引导下根据病变的部位选择适当的穿刺点及进针方向。穿刺点可经前腹壁、侧腹壁或脊柱旁,并对穿刺液行细菌学检查。结果:(1)21例共穿刺35例次,无穿刺所致并发症。(2)证实胰腺感染13例。细菌种类包括大肠杆菌、假单胞菌属及霉菌等;单一细菌感染7例,多种细菌感染6例。(3)胰腺感染者CT表现均为D或E级;除1例感染性假性囊肿发生于发病后3个月外,其他均发生于胰腺炎发病后4~15天,平均10.2天。(4)8例穿刺阴性者除1例因应激性溃疡大出血手术外,均经支持治疗治愈。提示CT引导下胰腺穿刺是早期诊断胰腺感染的可靠方法。  相似文献   
966.
Summary The effectiveness of extracranial-intracranial arterial bypass (EC-IC bypass) surgery on impaired haemodynamic status was studied in 12 patients with reduced regional cerebral perfusion pressure (rCPP) and elevated regional oxygen extraction fraction (rOEF) in the area distal to the symptomatic arterial lesion. Postoperative positron emission tomography (PET) study demonstrated a statistically significant decrease of rOEF in the operated hemispheres with disappearance of the pre-operative interhemispheric rOEF difference. Regional cerebral blood flow (rCBF) and regional cerebral oxygen metabolism (rCMRO2) were also increased in the operated hemispheres with disappearance of the pre-operative interhemispheric differences. Regional CBF/regional cerebral blood volume (rCBV) ratios of the symptomatic hemispheres were increased after surgery, but were still lower than in the contralateral hemispheres. We conclude that EC-IC bypass surgery improves impaired cerebral oxygen metabolic reserve.  相似文献   
967.
The effect of epidural infusions containing fentanyl on maternal gastric emptying in labour was examined using the rate of paracetamol absorption. Women were randomly allocated to receive one of two epidural infusions, bupivacaine 0.125% alone or bupivacaine 0.0625% with fentanyl 2.5 μgml−1 at a rate of 10–12 mlh−1. Paracetamol 1.5 g was given orally to women after either 30 ml of the infusion solution had been given (mean time 2.5 h, study A) or 40–50 ml (mean time 4.5 h, study B). Six venous blood samples were taken over the next 90 min for measurement of plasma paracetamol concentration. There were no significant differences in maximum plasma paracetamol concentration, time to maximum paracetamol concentration and area under the concentration–time curve between the two groups for study A. In study B the time to maximum plasma paracetamol concentration was significantly delayed in women receiving > 100 μg fentanyl compared with controls (p < 0.05). We conclude that the dose of fentanyl that may delay gastric emptying when given by epidural infusion is greater than 100 μg.  相似文献   
968.
Stress echocardiography has been considered an accurate method for the diagnosis of coronary artery disease in hypertensive patients and in patients with left ventricular hypertrophy. In contrast, the specificity of myocardial perfusion scintigraphy in these patients has been questioned. The aim of this study was to compare the accuracy of these two imaging modalities in conjunction with dobutamine stress test for the diagnosis of coronary artery disease in hypertensive patients with and without left ventricular hypertrophy. Dobutamine (up to 40 μg kg–1min–1) stress echocardiography in conjunction with sestamibi (MIBI) single-photon emission tomography (SPET) was performed in 84 patients with the diagnosis of systemic hypertension who had been referred for evaluation of myocardial ischaemia. Ischaemia was defined as new or worsened wall motion abnormalities at echocardiography and reversible perfusion defects at SPET. Significant coronary artery disease (≥50% luminal diameter stenosis) was detected in 66 patients (79%). The sensitivity, specificity and accuracy of the ischaemic pattern at echocardiography for the diagnosis of coronary artery disease were 73% (CI 63%–82%), 83% (CI 75%–91%) and 75% (CI 66%–84%), those for MIBI were 67% (CI 57%–77%), 83% (CI 75%–91%) and 70% (CI 60%–80%) respectively (P = NS vs echocardiography). Significant stenosis was detected in 123 (49%) of the 252 analysed coronary arteries. The sensitivity, specificity and accuracy of echocardiography for the regional diagnosis of coronary artery disease were 63% (CI 56%–69%), 90% (CI 86%–94%) and 77% (CI 72%–82%). Those for MIBI were 58% (CI 51%–64%), 91% (CI 87%–94%) and 75% (CI 69%–80) respectively (P = NS vs echocardiography). Left ventricular hypertrophy was detected in 59 patients (70%) by echocardiography and did not influence the overall or regional specificity of echocardiography or MIBI SPET. It is concluded that in hypertensive patients, dobutamine stress echocardiography and MIBI SPET have a comparable accuracy for the overall and regional diagnosis of coronary artery disease. Hypertensive patients with or without left ventricular hypertrophy should not be considered unsuitable candidates for stress myocardial perfusion scintigraphy. Received 10 July and in revised form 19 September 1997  相似文献   
969.
Pregnant mice were exposed to one of five regimens at 9.5 days of gestation: no treatment (group 1), intraperitoneal injection of normal saline (group 2), intraperitoneal injection of gadopentetate dimeglumine (group 3), intraperitoneal injection of gadopentetate dimeglumine and magnetic resonance (MR) exposure (group 4), and MR exposure alone (group 5). At 18 days of gestation, the mice were sacrifice and fetuses were removed and examined for the following end points: litter size, number alive or dead, fetal weight, extremity morphology, eye and ear development, and appearance of the head. A total of 739 fetuses were analyzed: group 1 (n = 161), group 2 (n = 149), group 3 (n = 142), group 4 (n = 136), and group 5 (n = 151). The only statistically significant difference was a lower mean fetal weight in the saline-injection group compared with the control group. The results show that MR exposure with and without gadopentetate dimeglumine had no adverse effect on the end points analyzed.  相似文献   
970.
Immunological data on the human fetal pancreas (HFP) are mainly confined to its constitutive expression of the MHC antigens. However, cytokines, such as gamma-interferon (g-IFN), released by lymphocytes during immune reactions, can induce or upregulate the expression of MHC products in allografts and alter their immunological behaviour. We investigated the effects of g-IFN on fresh and cultured HFPs aged 9–16 gestational weeks (gw). Following g-IFN stimulation of fresh HFPs, there was class I hyperexpression by the ductal cells, and some of the ductal, endothelial and islet cells also became class II+. Conventional tissue culture (5% CO2 in air at 37°C) reduced the number of interstitial class II+ cells within the HFP after 1 week but was associated with de novo class I expression by some of the ductal cells. Remarkably, the changes in major histocompatibility complex (MHC) antigen expression by the ductal cells occurred earlier and were markedly enhanced when the HFPs were cultured beforehand. The number of interstitial class II+ cells in fresh and cultured HFPs was not influenced by g-IFN. The significance of these observations with regard to clinical HFP transplantation is discussed.  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