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   34397篇
  免费   2669篇
  国内免费   457篇
耳鼻咽喉   359篇
儿科学   1019篇
妇产科学   609篇
基础医学   4962篇
口腔科学   517篇
临床医学   3239篇
内科学   7387篇
皮肤病学   761篇
神经病学   2587篇
特种医学   1388篇
外国民族医学   16篇
外科学   4188篇
综合类   1292篇
现状与发展   1篇
一般理论   2篇
预防医学   2674篇
眼科学   680篇
药学   2588篇
  6篇
中国医学   622篇
肿瘤学   2626篇
  2023年   269篇
  2022年   647篇
  2021年   1082篇
  2020年   674篇
  2019年   839篇
  2018年   1037篇
  2017年   751篇
  2016年   745篇
  2015年   909篇
  2014年   1160篇
  2013年   1509篇
  2012年   2179篇
  2011年   2188篇
  2010年   1351篇
  2009年   1123篇
  2008年   1614篇
  2007年   1677篇
  2006年   1589篇
  2005年   1497篇
  2004年   1329篇
  2003年   1266篇
  2002年   1198篇
  2001年   1115篇
  2000年   1103篇
  1999年   978篇
  1998年   357篇
  1997年   307篇
  1996年   272篇
  1995年   226篇
  1994年   215篇
  1993年   185篇
  1992年   519篇
  1991年   502篇
  1990年   483篇
  1989年   450篇
  1988年   461篇
  1987年   391篇
  1986年   380篇
  1985年   371篇
  1984年   258篇
  1983年   192篇
  1982年   123篇
  1981年   111篇
  1979年   211篇
  1978年   113篇
  1977年   128篇
  1976年   116篇
  1974年   130篇
  1972年   128篇
  1969年   104篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This prospective study was designed to determine the frequency and natural history of hydroureteronephrosis (HUN) after placement of an aortobifemoral vascular graft. A total of 30 patients were evaluated by the study protocol, which included: pre and postoperative biological kidney function tests, preoperative and early postoperative (14th day) intravenous pyelograms and a late (mean 18th month) urologic examination by renal ultrasonic tomography. Four asymptomatic, early cases of HUN were observed in the 57 ureters examined (7%); all four complications regressed in less than 30 days. No cases of symptomatic early or late HUN were observed in this series. Asymptomatic early HUN was a frequent complication in our series (7%) but its benign course does not justify systematic screening. These asymptomatic complications contrast with the symptomatic cases of early or late HUN reported in the literature which necessitated urologic and vascular investigations.  相似文献   
62.
四种口服头孢菌素的体外抗菌活性的比较研究   总被引:2,自引:0,他引:2  
本文报道口服Cefixime对900株需氧菌和厌氧菌的体外抗菌作用,并与其它口服的头孢克罗、头孢羟氨苄和头孢氨苄进行了比较。Cefixime对链球菌具较强作用,但对葡萄球菌的作用较差;对肠球菌无效。对肠杆菌科细菌的抗菌活性四者之中以Cefixime最强。Cefixime对头孢氨苄耐药株仍具高度活性,其MIC均值可降低60~1200倍以上。绿脓杆菌、硝酸盐阴性杆菌、鲁氏不动杆菌和产碱杆菌对Cefixime和其它3种头孢菌素的敏感性均较差。四者对厌氧菌的作用除厌氧球菌外其抗菌活性都很弱。Cefixime对β-内酰胺酶稳定,口服吸收良好,抗菌作用强,是一个值得进行临床研究的口服头孢菌素。  相似文献   
63.
During 1989, 316 members of a cohort of homosexual men were tested for HIV-specific DNA by the polymerase chain reaction (PCR) using a pair of gag-region primers. Of 125 HIV-seronegative subjects, 123 (98.4%) were PCR-negative while 158 (82.7%) of 191 HIV-seropositive subjects were PCR-positive. Fewer of the 33 subjects who were seropositive and PCR-negative were at Centers for Disease Control (CDC) stage IV than the seropositive, PCR-positive subjects (6 versus 25%; P = 0.030). The seropositive, PCR-negative group had higher mean CD4 counts (640 versus 490 x 10(6) cells/l; P = 0.006), higher CD4: CD8 ratios (0.92 versus 0.64; P = 0.004), lower immunoglobulin (Ig) G levels (1290 versus 1645 mg/dl; P = 0.002), lower IgA levels (168 versus 251 mg/dl; P less than 0.001), and lower C1q binding activity (8 versus 14%; P = 0.010) than the seropositive, PCR-positive subjects. The median rate of CD4 cell decline in the 3 years preceding the PCR sample was less marked in the seropositive, PCR-negative group than the seropositive, PCR-positive group (-58 versus -77 x 10(6) cells/l per year; P = 0.028). To control for duration of infection, we restricted the analysis to the subgroups of 11 seropositive, PCR-negative subjects and 34 seropositive, PCR-positive subjects who had seroconverted earlier in the cohort study. Both subgroups had similar durations of infection, yet the same pattern of differences persisted.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
64.
65.
The relationship of alcohol use to diet was examined in 2272 male and 2337 female adults aged 45 y and older who provided a quantitative diet history during 1977-1979. Mean values for each dietary variable, adjusted for smoking, ethnicity, income, and education, were compared in each sex between abstainers and drinkers and by tertile of ethanol intake. Linear relationships with extent of drinking were also sought. Drinkers were found to be less obese than abstainers. Consumption of carbohydrate, vitamins, calcium, fruits, fruit juices, and raw vegetables was greater among abstainers whereas consumption of fat (particularly polyunsaturated fatty acids), cholesterol, zinc, meat, pickled vegetables, and dried fish was greater among drinkers. Because validations of dietary questionnaires have shown that alcohol consumption is more accurately recalled than food intake, the possibility of a residual confounding effect for these dietary variables should be considered in epidemiologic studies of alcohol and health.  相似文献   
66.
A 69-year-old woman presented with a single enlarged lymph node in the left axilla. Clinical examination and other investigations, including various imaging methods, failed to reveal the primary tumour. However, indium-111 pentetreotide scan revealed a site of uptake in the anterior region of the left thorax. Peroperative imaging with t111In-pentetreotide confirmed the tumour uptake and use of a nuclear surgical probe allowed precise localization of the tumour, which was completely resected.  相似文献   
67.
The polymerization of lactides with various D /L enantiomeric compositions using achiral Schiff's base/aluminium methoxide as initiator (SALENAlOCH3) in dichloromethane solution at 70°C is reported. The conversion was kept below 70% in order to limit transesterification reactions. The polymers obtained after precipitation show a narrow molecular weight distribution (ratio of weight- to number-average molecular weights M w/M n = 1,1–1,2) and an optical rotation higher than that expected from the optical purity of the starting monomers. The examination of the thermal properties reveals that whatever their enantiomeric composition all the prepared polymers are crystalline. This unusual behavior is explained by an end-chain propagation mechanism producing stereocopolymers with long enantiomeric sequences, i.e., increased isotacticity as substantiated by an examination of the microstructure of the polymers by means of 13C nuclear magnetic resonance. A stereocomplex formation was observed for stereocopolymers with optical purities below 40%.  相似文献   
68.
Acute or rapidly progressive visual loss in children needs urgent attention and treatment. It may be unilateral orbilateral. Etiology depends upon the involved areas: eye ball, optic nerve, retro-chiasmatic pathways. Psychogenic origin is quite common in school-age children, however, it has to be considered last. Unilateral visual loss may be overlooked. Acute total transitory visual loss may be due to epilepsy or to migraine. Rapidly progressive visual loss may be due to retinal disease, optic neuritis or cortical blindness. Management of visual loss depends on clinical features, associated symptoms, and aspect of the optic disc. It needs collaboration between ophthalmologist,pediatrician and neuropediatrician. Retinal hemorrhages first call to mind a traumatic origin. Swelling of the optic disc may be due to increased intracranial pressure or due to optic neuritis. When the optic disc is normal it is necessary to rule out organic diseases before establishing the diagnosis of a psychogenic vision disturbance. In emergency, brain neuroimaging is the best way to diagnose intracranial mass and visualize optic pathways.  相似文献   
69.
目的:探讨MRI对先天性胆脂瘤的诊断价值。方珐:回顾性分析7例经手术病理证实的先天性胆脂瘤的MRI表现,7例均为脑外型,其中6例胆脂瘤位于桥小脑角区,l例胆脂瘤位于脊髓内.结果:先天性胆脂瘤的绝大多数MRI表现为T1WI呈低信号,T2WI呈高信号,信号欠均匀,且病灶具有“见缝就钻”的特点。增强扫描,病灶无强化,但如合并感染可有轻度强化。结论:MRI的表现及特殊序列FLAIR、SPIR像的相互补充应用对先天性胆脂瘤的诊断及鉴别诊断具有重要意义。  相似文献   
70.
1991—2002年间采用可长期消耗T淋巴细胞的人单克隆抗体(Cam path-1H)治疗58例多发性硬化症(M S)患者,患者的临床症状和炎性替代标记物得到抑制。在M S的复发-缓解(R R)和继发进展(SP)期,Cam path-1H可降低患者的年复发率(分别由2.2降至0.19和由0.7降至0.001,P<0.001)。7年前使  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