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   7441篇
  免费   507篇
  国内免费   43篇
耳鼻咽喉   63篇
儿科学   174篇
妇产科学   123篇
基础医学   1114篇
口腔科学   125篇
临床医学   540篇
内科学   1625篇
皮肤病学   392篇
神经病学   533篇
特种医学   318篇
外科学   1190篇
综合类   165篇
一般理论   4篇
预防医学   376篇
眼科学   263篇
药学   334篇
中国医学   31篇
肿瘤学   621篇
  2024年   11篇
  2023年   63篇
  2022年   127篇
  2021年   217篇
  2020年   140篇
  2019年   179篇
  2018年   200篇
  2017年   170篇
  2016年   218篇
  2015年   238篇
  2014年   340篇
  2013年   321篇
  2012年   566篇
  2011年   531篇
  2010年   291篇
  2009年   273篇
  2008年   395篇
  2007年   380篇
  2006年   344篇
  2005年   396篇
  2004年   336篇
  2003年   275篇
  2002年   310篇
  2001年   236篇
  2000年   224篇
  1999年   180篇
  1998年   69篇
  1997年   51篇
  1996年   48篇
  1995年   48篇
  1994年   38篇
  1993年   25篇
  1992年   78篇
  1991年   76篇
  1990年   71篇
  1989年   80篇
  1988年   91篇
  1987年   64篇
  1986年   50篇
  1985年   44篇
  1984年   35篇
  1983年   39篇
  1982年   7篇
  1981年   10篇
  1980年   6篇
  1979年   24篇
  1978年   10篇
  1977年   16篇
  1974年   9篇
  1969年   6篇
排序方式: 共有7991条查询结果,搜索用时 15 毫秒
991.
992.
Background: Fructose-1,6-bisphosphate (FBP) sometimes provides substantial cerebral protection during hypoxia or ischemia.31 P/sup 1 H nuclear magnetic resonance spectroscopy of cerebrocortical slices was used to study the effects of FBP on hypoxia-induced metabolic changes. In addition,13 C-labeled glucose was administered and13 C nuclear magnetic resonance spectroscopy was used to search for FBP-induced modulations in glycolysis and the pentose-phosphate pathway.

Methods: In each experiment, 80 slices (350 micro m) obtained from ten 7-day-old Sprague-Dawley rat litter mates were placed together in a 20-mm nuclear magnetic resonance tube, perfused, and subjected to 30 min of hypoxia (PO2 < 3 mmHg). Nine experiments were performed, with n = 3 in each of three groups: (1) no treatment with FBP; (2) 60 min of prehypoxia treatment with FBP (2 mM); and (3) 60 min of posthypoxia treatment with FBP (2 mM).31 P/sup 1 H Interleaved nuclear magnetic resonance spectra at 4.7 T provided average adenosine triphosphate, intracellular pH, and lactate. Cresyl violet stains of random slices taken at predetermined time points were studied histologically. Some experiments had [2-sup 13 C]glucose in the perfusate. Slices from these studies were frozen for perchloric acid extraction of intracellular metabolites and studied with high-resolution13 C nuclear magnetic resonance spectroscopy at 11.75 T.

Results: With no pretreatment with FBP, hypoxia caused an [nearly =] 50% loss of adenosine triphosphate, an [nearly =] 700% increase in lactate, and a decrease in intracellular pH to [nearly =] 6.4. Pretreatment with FBP resulted in no detectable loss of adenosine triphosphate, no increase in lactate, and minimal morphologic changes but did not alter decreases in intracellular pH.13 C Nuclear magnetic resonance spectra of extracted metabolites showed that pretreatment caused accumulation of [1-sup 13 C]fructose-6-phosphate, an early pentose-phosphate pathway metabolite. Posthypoxic treatment with FBP had no effects compared with no treatment.  相似文献   

993.
Nerve growth factor (NGF) has recently been implicated as a trophic agent in the survival and maintenance of basal forebrain cholinergic neurons. To test the hypothesis that NGF may play a role in the age-related degeneration of basal forebrain neurons and decline of cerebral cholinergic function, we have used a monoclonal antibody to the NGF receptor, 192 IgG, to immunocytochemically visualize and compare rat basal forebrain neurons responsive to NGF in aged (30 months) and young adult (10 months) rats. In a subpopulation of aged rats, NGF receptor-immunoreactive cells in the basal forebrain appear vacoulated and shrunken, and the neuropil staining is markedly reduced. While no substantial decline in cell density is apparent in Nissl-stained sections, the number of NGF receptor-positive cell profiles within the vertical limb of diagonal band nuclei is reduced by an average of 32% in aged rats. Marked reduction in the expression of NGF receptors in aged rats may signify loss of capacity of the basal forebrain neurons to bind and transport NGF from their terminals in the hippocampus and cortex, subsequent decrease in NGF delivered to the cell bodies, and eventual cellular dysfunction and death of neurons in aging.  相似文献   
994.
In order to evaluate the ultrastructural changes in IgA nephropathy (IgAN) and their relationship with light microscopic and clinical features, renal biopsy material from 239 Korean patients with IgAN was studied by light, electron and immunofluorescence microscopy. Forty-one were children and 198 were adults. Modified classification of Meadow et al (1972) for Henoch-Sch?nlein nephritis was used for the histologic grading of glomerular lesions. Forty-three adults (18%) exhibited histologic grades IV and V lesions in association with more severe clinical findings, when compared to the remaining 196 patients with histologic grades I to III. A significant difference was noted between children and adults in the severity of the glomerular lesions (P less than 0.01). Mesangial deposits were observed in all (100%), subendothelial deposits in 37%, subepithelial deposits in 18%, abnormalities in glomerular basement membrane (GBM) in 20%, mesangiolysis in 44%, and mesangial interposition in 25%. The frequency of GBM abnormalities and subepithelial deposits in children was significantly higher than that seen in adults (P less than 0.01). The abnormalities of GBM were not related to more severe clinical manifestations when our analysis was restricted to grade III histologic lesions. All of the above ultrastructural changes except for mesangial deposits were associated with more severe histologic grading in adults (P less than 0.025 or P less than 0.01). Yet a correlation between these ultrastructural changes and histologic grading could not be studied in children due to confinement of their histology within a more benign group. These results suggest that the five ultrastructural parameters described here appear to bear important prognostic value in adults with IgAN.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
995.
The motor cortex can be excited in adults using electromagnetic stimulation, and the latency to the evoked muscle action potential allows an assessment of the integrity of corticospinal tracts. We applied this technique in children to describe the maturation of corticospinal tracts. The latency from cortical stimulation to the onset of the evoked muscle action potentials and the subject''s height were recorded. The subject''s height was divided by the latency to the onset of the evoked muscle action potential to provide an index of the conduction velocity within descending motor pathways (VI). It is possible to evoke muscle action potentials after electromagnetic stimulation of the motor cortex in children including preterm babies and there is a stepwise increase in the sensitivity to stimulation between 8 and 11 years of age. In addition there is a progressive increase in VI with age; adult values are attained at about 11 years. The successful application of this technique in children suggests that electromagnetic stimulation of the motor cortex has the potential to allow detection of abnormality in motor pathways in newborn babies and young children.  相似文献   
996.
A case of fibrous pseudotumor of the left spermatic cord is reported. The patient was a 4-year-old boy with the complaint of swelling and pain of the left scrotal contents. An intrascrotal tumor was suspected and surgical exploration was carried out. A small tumor was resected and histological examination revealed fibrous pseudotumor. This tumor was not a true neoplasm, but was due to an inflammatory disease. The clinical and histological findings of the tumor are discussed.  相似文献   
997.
998.
Partial Atrioventricular Canal Defect ( PAVC ) The operative results of this anomaly is generally acceptable. Between 1978 and 1982, 32 patients with PAVC underwent intracardiac repair. Two operative deaths occurred in 41 and 42 years old patients who were in NYHA class 4 preoperatively. Postoperative mitral insufficiency was either nil or mild except in one patient with mitral valve prolapse which was left unrepaired. Complete Atrioventricular Canal Defect ( CAVC ) Our operative procedures for the repair of CAVC are as follows, 1) all of accessory chordae are cut off and the bridging leaflet is incised into mitral and tricuspid components. 2) Ventricular septum, atrioventricular valve and atrial septum are constructed with our designed endocardial cushion prosthesis (Dacron prosthesis with pericardial brim of 3-4 mm width in each side). Between 1978 and 1982, 20 patients with CAVC containing 16 infants less than 2 years old underwent intracardiac repair using this prosthesis. Thirteen patients had no severe associated anomalies and only one death occurred in this group. Three patients were combined with tetralogy of Fallot (one died) and two patients with double outlet right ventricle (one died). The other two patients had either coarctation of the aorta (died) or interruption of the aortic arch (survived).  相似文献   
999.
The affective disorder in schizophrenia is an important manifestation of the schizophrenic illness. Such clinical features of joylessness, interpersonal aversion, and affective blunting have been considered by Rado and Meehl to represent a neurophysiological deficit in pleasure capacity which they termed anhedonia, but is more aptly characterized by the term hypohedonia. A free-recall task employing 24 affectively laden words presented in random order over nine trials was given to a carefully selected group of nonpsychotic hospitalized schizophrenics, hospitalized nonschizophrenics, and normals. The results of the study demonstrate that normals remember pleasant words to a significantly greater extent than upleasant words. This Pollyanna tendency or the tendency to utilize pleasant words over upleasant words has been described by Osgood as a stable cross-cultural phenomenon. By contrast, the schizophrenics show a significantly lower recall of pleasant words when compared with normals, although they remember unpleasant words to a comparable degree as normals. These findings provide experimental support for the hypohedonia hypothesis in schizophrenia. The nonshcizophrenic patients recall pleasant and unpleasant words to a significantly greater degree than neutral words. They are thus affectively governed in the free-recall task and seem equally sensitized to both pleasant and unpleasant affect in their mnemonic processing.  相似文献   
1000.
To know the parameter related to improvement of each semen characteristic (sperm density and percentage of progressive motile sperm) after high ligation of the left internal spermatic vein, 119 men from infertile couples were investigated. In each individual, the semen characteristic was considered to be different from the postoperative mean value if it was over or below 2 SD of the preoperative mean. Although no relationship was detected with the age of the patient, the duration of infertility or the preoperative semen characteristics, a definite relationship was found between the degree of varicocele and the improvement in each semen characteristic. For improvement of the sperm density, each of the volume and the score count by Johnsen's scale of the affected and unaffected testes and the serum hormone values (LH, FSH and testosterone) showed correlations. Meanwhile, for the improvement of the percentage of progressive motile sperm, correlations were found only with each of the testicular volume on the unaffected side and the serum testosterone level.  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