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   28920篇
  免费   1747篇
  国内免费   151篇
耳鼻咽喉   326篇
儿科学   747篇
妇产科学   526篇
基础医学   3804篇
口腔科学   772篇
临床医学   2181篇
内科学   7713篇
皮肤病学   659篇
神经病学   2470篇
特种医学   573篇
外科学   4320篇
综合类   182篇
一般理论   11篇
预防医学   2289篇
眼科学   604篇
药学   1706篇
  1篇
中国医学   104篇
肿瘤学   1830篇
  2023年   185篇
  2022年   384篇
  2021年   986篇
  2020年   488篇
  2019年   863篇
  2018年   998篇
  2017年   613篇
  2016年   632篇
  2015年   789篇
  2014年   1019篇
  2013年   1321篇
  2012年   2195篇
  2011年   2327篇
  2010年   1235篇
  2009年   1172篇
  2008年   1984篇
  2007年   1961篇
  2006年   1887篇
  2005年   1799篇
  2004年   1562篇
  2003年   1381篇
  2002年   1238篇
  2001年   371篇
  2000年   339篇
  1999年   334篇
  1998年   225篇
  1997年   220篇
  1996年   158篇
  1995年   135篇
  1994年   137篇
  1993年   115篇
  1992年   196篇
  1991年   166篇
  1990年   158篇
  1989年   120篇
  1988年   100篇
  1987年   100篇
  1986年   105篇
  1985年   101篇
  1984年   71篇
  1983年   62篇
  1982年   58篇
  1981年   48篇
  1980年   35篇
  1979年   29篇
  1976年   31篇
  1975年   33篇
  1974年   50篇
  1973年   30篇
  1970年   34篇
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
991.
992.
993.
A 71-years-old man presented with an incidentally finding of a tumor in the left pulmonary apex that measured approximately 4.5 cm of diameter. The patient, had de preceding of chronic smoking. Bronchoscopy with biopsy by transthoracic punction suggested the presence of epidermoid carcinoma. In the radiologic control, an increase in tumor size from 4.5 cm to 5 cm of the lesion was observed in a period of three months. The patient was submited to surgery and a tumorectomy by posterolateral thoracotomy was performed. The postoperatory evolution was satisfactory. The final diagnosis was hamartoma of the lung.  相似文献   
994.
OBJECTIVE: To estimate the prevalence of osteopenia and osteporosis using distal forearm dual-energy X-ray absorptiometry among a random sample of women of 50 years or older living in the city of Durango, Mexico. MATERIAL AND METHODS: 258 women participated in a cross-sectional study fielded at the Osteoporosis Clinic of Durango. Bone mineral density was determined by dual-energy X-ray absorptiometry. Scanning was performed on the distal third of the dominant forearm. Diagnosis of osteopenia and osteoporosis was based on the WHO criteria. RESULTS: Osteoporosis was diagnosed in 13.65% (95%CI: 9.6-18.5) and osteopenia in 30.12% (95% CI: 24.5-36.2) of participants. Mean age, weight, height and body mass index were 65 years, 60.5 kg, 147.8 cm and 28.3 kg/m2 respectively. CONCLUSIONS: Osteoporosis and osteopenia were a common diagnosis given the mean age of our sample. These results can be extrapolated to the general population thereby suggesting the need for preventive measures to decrease disease prevalence, especially considering the increase in life expectancy.  相似文献   
995.
The hypothetical protein encoded by Chlamydia pneumoniae open reading frame cpn0308 was detected in inclusion membranes of C. pneumoniae-infected cells using antibodies raised with Cpn0308 fusion proteins. The anti-Cpn0308 antibodies did not cross-react with IncA, a known C. pneumoniae inclusion membrane protein, although the anti-Cpn0308 antibody staining overlapped with the anti-IncA antibody labeling. The labeling of the inclusion membrane by the anti-Cpn0308 antibody was specifically blocked by the Cpn0308 but not IncA fusion proteins. The Cpn0308 antigen was detectable 24 h after infection and remained in the inclusion membrane throughout the infection course.  相似文献   
996.
997.
Melatonin reduces pyramidal neuronal death in the hippocampus and prevents the impairment of place learning and memory in the Morris water maze, otherwise occurring following global cerebral ischemia. The cytoarchitectonic characteristics of the hippocampal CA1 remaining pyramidal neurons in brains of rats submitted 120 days earlier to acute global cerebral ischemia (15-min four vessel occlusion, and melatonin 10mg/(kg h 6h), i.v. or vehicle administration) were compared to those of intact control rats in order to gain information concerning the neural substrate underlying preservation of hippocampal functioning. Hippocampi were processed according to a modification of the Golgi method. Dendritic bifurcations from pyramidal neurons in both the oriens-alveus and the striatum radiatum; as well as spine density and proportions of thin, stubby, mushroom-shaped, wide, ramified, and double spines in a 50 microm length segment of an oblique dendrite branching from the apical dendrite of the hippocampal CA1 remaining pyramidal neurons were evaluated. No impregnated CA1 pyramidal neurons were found in the ischemic-vehicle-treated rats. CA1 pyramidal neurons from ischemic-melatonin-treated rats showed stick-like and less ramified dendrites than those seen in intact control neurons. In addition, lesser density of spines, lower proportional density of thin spines, and higher proportional density of mushroom spines were counted in ischemic-melatonin-treated animals than those in the sinuously branched dendrites of the intact control group. These cytoarchitectural arrangements seem to be compatible with place learning and memory functions long after ischemia and melatonin neuroprotection.  相似文献   
998.
Summary In vitro experiments have previously identified in potato spindle tuber viroid (PSTVd), the type member of the nuclear viroids, an element of local tertiary structure termed loop E. Here, by direct UV irradiation of PSTVd-infected tomato tissue and subsequent RNA analysis by denaturing polyacrylamide gel electrophoresis, northern blot hybridization and primer extension, we report that PSTVd (+) RNA also forms the loop E in vivo. These results provide strong support for the physiological relevance of this structural motif, which is involved in a wide range of functions including replication, host specificity and pathogenesis.  相似文献   
999.
N-methyl-d-aspartate (NMDA) receptors play a crucial role in the regulation of neuronal development during embryogenesis and they also regulate the rate of neurogenesis and proliferation in the adult dentate gyrus. However, the mechanism by which they influence these processes is not fully understood. NMDA receptors seem to be functional in hippocampal precursor cells and recently generated granule neurons, although there is no anatomical correlate of these physiological observations. We have analyzed the expression of the NMDA receptor subunits NR1 and NR2B in precursor cells and recently generated granule neurons of the adult rat dentate gyrus, using 5'bromodeoxyuridine, green fluorescent protein-retrovirus and immunohistochemistry. Our results indicate that NR1 and NR2B are expressed in some proliferating cells of the adult subgranular zone. These receptors are absent from transiently amplifying progenitors (type 2-3 cells) but they are found in glial fibrillar acidic protein expressing cells in the subgranular zone, suggesting its presence in bipotential (type-1) precursor cells. NR1 and NR2B are rarely found in granule cells younger than 60 h. By contrast, many granule cells generated 14 days before killing express both NMDA receptor subunits. These results demonstrate that adult hippocampal neurogenesis may be regulated by NMDA receptors present in precursor cells and in differentiating granule neurons, although these receptors are probably not located on synapses. However, an indirect effect through NMDA receptors located in other cell types should not be excluded.  相似文献   
1000.
Twelve beta-lactam and non-beta-lactam antibiotics were evaluated against 115 clinical isolates of extended-spectrum beta-lactamase-producing (ESBLs) Escherichia coli using a broth microdilution test in accordance with the CLSI guidelines. Susceptibility was 100% with imipenem, ertapenem and amikacin, 95.7% with piperacillin-tazobactam, 91.3% with cefoxitin, 87% with tobramycin, 81.7% with amoxicillin-clavulanate, 80% with cefepime, 67.8% with ceftazidime, 27.8% with ciprofloxacin, 27% with levofloxacin and 13% with ceftriaxone. Ertapenem was the antibiotic with the lowest minimum inhibitory concentrations (MICs) for all isolates. There were no clinically relevant differences in the activity of the antibiotics in the presence of CTX-M-9 or SHV enzymes.  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