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   11161篇
  免费   862篇
  国内免费   15篇
耳鼻咽喉   56篇
儿科学   296篇
妇产科学   148篇
基础医学   1449篇
口腔科学   195篇
临床医学   1282篇
内科学   1820篇
皮肤病学   157篇
神经病学   1538篇
特种医学   713篇
外科学   1214篇
综合类   160篇
一般理论   11篇
预防医学   1198篇
眼科学   280篇
药学   808篇
中国医学   21篇
肿瘤学   692篇
  2022年   64篇
  2021年   151篇
  2020年   90篇
  2019年   136篇
  2018年   175篇
  2017年   130篇
  2016年   176篇
  2015年   207篇
  2014年   239篇
  2013年   340篇
  2012年   488篇
  2011年   511篇
  2010年   327篇
  2009年   272篇
  2008年   486篇
  2007年   520篇
  2006年   498篇
  2005年   513篇
  2004年   502篇
  2003年   469篇
  2002年   474篇
  2001年   254篇
  2000年   355篇
  1999年   317篇
  1998年   223篇
  1997年   167篇
  1996年   200篇
  1995年   153篇
  1994年   136篇
  1993年   149篇
  1992年   215篇
  1991年   215篇
  1990年   288篇
  1989年   212篇
  1988年   218篇
  1987年   191篇
  1986年   169篇
  1985年   184篇
  1984年   148篇
  1983年   128篇
  1982年   113篇
  1981年   122篇
  1980年   92篇
  1979年   94篇
  1978年   93篇
  1977年   67篇
  1976年   59篇
  1975年   70篇
  1974年   54篇
  1968年   55篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
OBJECTIVE: Our goal was to determine the etiology of headache in patients who were referred for sinus evaluation but were found to have no evidence of rhinosinusitis on computed tomography (CT) of the sinuses and on endoscopic examination. METHODS: Data were collected prospectively from 100 patients with headache but with normal sinus CT and endoscopic examination. Headache and 20-Item Sino-Nasal Outcomes Test (SNOT-20) scores of patients with the chief complaint of headache and who requested further neurologic evaluation (group I) were compared with the scores of patients who did not list headache as a significant symptom (group II) and with the scores of patients without headache (group III). RESULTS: The most common neurologic diagnosis for group I patients (n = 36) was migraine headaches (58%). These patients also had higher mean SNOT-20 scores (24 +/- 3.3) compared to group II patients with mild headache (14.6 +/- 2.3) or group III patients without headache (12.4 +/- 2.1). CONCLUSION: Migraine was the most common type of headache in patients with normal sinus CT treated for presumed rhinosinusitis as the cause of the headache. Patients with headache as their chief complaint that required further neurologic evaluation had overall higher SNOT-20 scores than nonheadache patients, indicating greater disability of their overall quality of life index.  相似文献   
32.
Ependymomas are glial neoplasms whose clinical behavior is difficult to predict based on histology alone. Recently, a comparative genomic hybridization study identified frequent chromosome 9p and 13q losses in anaplastic ependymomas, suggesting that p16 and RB alterations may be involved in tumor progression. In order to test this hypothesis further, 101 myxopapillary, conventional, and anaplastic ependymomas (51 spinal and 50 intracranial tumors) were tested for RB and p16 deletions using fluorescence in situ hybridization. Clinical follow-up, ranging from 2 to 198 months (median 46 months), was obtained in 90 cases (91%). RB and p16 deletions were seen in 22 of 92 (24%) and 22 of 89 (25%) informative cases, respectively. Polysomies were more frequent in the grade I and II spinal tumors, consistent with prior reports of increased aneuploidy in such cases. No significant genetic associations were seen with tumor grade, recurrence, or death, suggesting that 9p and 13q deletions do not play a prominent role in the malignant progression of ependymomas, as has been implicated in other glioma subtypes.  相似文献   
33.
34.
BACKGROUND: Prior treatment with local hyperthermia has been shown to prevent mast cell degranulation and leucocyte histamine release, and to reduce mortality and cellular infiltrates in a model of acute lung injury. Local hyperthermia is effective in reducing the symptoms of the common cold and perennial and seasonal allergic rhinitis, nasal patency also being improved in rhinitis. It is possible that these effects are mediated by common anti-inflammatory mechanisms, and that this treatment may be effective in the treatment of asthma. The effect of prior local hyperthermia on the response to exercise challenge and histamine bronchoprovocation was therefore examined. METHODS: In a randomised, double blind, placebo controlled, crossover study, 10 asthmatic subjects with exercise induced asthma used machines delivering 40 1/minute of fully humidified air at either 42 degrees C (active treatment) or 31 degrees C (placebo treatment) for 30 minutes' tidal breathing. For each pretreatment, at two week intervals they underwent exercise challenges starting one and 24 hours after starting the inhalations. After a further two weeks the protocol was repeated with histamine substituted for the exercise challenges. RESULTS: The mean (SE) maximum percentage fall in forced expiratory volume in one second (FEV1) was significantly lower one hour after treatment with air at 42 degrees C (30.8% (3.1%)) than after treatment with air at 31 degrees C (22.3% (2.9%)). There was no significant effect on exercise challenge at 24 hours, or on histamine challenge at either time point, though there were nonsignificant trends towards protection with exercise at 24 hours and with histamine at one hour. CONCLUSION: In asthmatic subjects the response to exercise challenge is significantly attenuated one hour after treatment with local hyperthermia. This treatment warrants further investigation in the treatment of clinical asthma and other inflammatory disorders.  相似文献   
35.
Several degenerative diseases of the nervous system are characterized by the presence of neuronal inclusions. Most of these inclusions are made of abnormal filaments and share epitopes with cytoskeletal proteins. One of these inclusions, the neurofibrillary tangle of Alzheimer disease, has recently been shown to contain ubiquitin, a regulatory protein thought to play a role in the degradation of abnormal proteins. We carried out light and electron microscopic immunocytochemistry with several polyclonal and monoclonal antibodies to investigate the presence of ubiquitin in neuronal inclusions of neurodegenerative diseases. Ubiquitin was present not only in paired helical filaments that form the neurofibrillary tangle of Alzheimer disease, but also in the filamentous components of the inclusion characteristic of Parkinson disease, Pick disease, and progressive supranuclear palsy. In contrast, ubiquitin was not detected in other neuronal inclusions often found in aging and in Alzheimer disease, such as Hirano bodies and granulovacuolar degeneration. Reactivity with monoclonal antibodies suggests differences in the ubiquitin-acceptor proteins present in the inclusions studied. It is concluded that ubiquitin is selectively present in neuronal inclusions of degenerative diseases.  相似文献   
36.
The use of gas-liquid chromatography to detect short-chain organic acids in the amniotic fluid of patients with amnionitis has been previously described. Most of the studies describe patients in the early third trimester with such infections. The purpose of the current study was to confirm the correlation of infection with increased production of organic acids and to assess the effect of gestational age on the presence of these short-chain fatty acids in the amniotic fluid. Six patients with confirmed chorioamnionitis were used as positive control subjects. Seventy-two patients at various gestational ages from 18 to 42 weeks with negative Gram's stain and culture results from the amniotic fluid were used as negative control subjects. The data revealed an increased production of organic acids, particularly pyruvic, oxalic and succinic, in patients with amnionitis regardless of gestational age. Interestingly, patients with noninfected amniotic fluid also revealed an increase in the concentrations of volatile organic acids between 27 and 32 weeks' gestation. It appears from this study that previous results correlating chorioamnionitis with an increased production of organic acids in the amniotic fluid may have been confounded by gestational age.  相似文献   
37.
The metabolic consequences of external hypercapnia (1% CO2) were assessed in rainbow trout (Salmo gairdneri) in the presence or absence of circulating levels of the beta adrenoceptor antagonist, propranolol. External hypercapnia caused a severe extracellular respiratory acidosis and a less pronounced reduction of hepatic intracellular pH (pHi). pHi was restored to prehypercapnic values after 48 hr of continuous hypercapnia due to elevation of bicarbonate levels. In the presence of propranolol, hypercapnia elicited a pronounced activation of pyruvate kinase (PyK) (measured at both low and high phosphoenolpyruvate (PEP) concentrations) and inactivation of both total glycogen phosphorylase (GPase) and glycogen phosphorylase a (GPase a). In the absence of propranolol, the changes in enzyme activities were significantly reduced (low PEP PyK activity) or totally absent (GPase inactivation). These results suggest that beta adrenoceptor-mediated phenomena offset disruptive effects of hypercapnia on PyK and GPase activities and may be important in the control of gluconeogenesis and glycogenolysis during this acid-base disturbance. The adrenergic effects were not related to modification of hepatic intracellular acid-base status. Hypercapnia induced a rapid depletion of liver glycogen and concomitant hyperglycemia. These effects were not prevented by pretreating fish with propranolol and appeared to be unrelated to changes in GPase a activity. These results suggest that factors other than adrenergic activation of GPase a are involved in the enhancement of liver glycogenolysis.  相似文献   
38.
Platelets from diabetic subjects and animals are hypersensitive to agonists in vitro. Membrane fluidity modulates cell function and previously we observed reduced membrane fluidity in platelets from diabetic patients associated with hypersensitivity to thrombin. We previously reported that decreased fluidity of isolated platelet membranes from diabetic patients is associated with increased glycation of platelet membrane proteins, but not with any change in the cholesterol to phospholipid molar ratio. We have now examined in vitro whether incubation of platelet membranes in a high glucose medium causes sufficient glycation to reduce membrane fluidity. Incubation of platelet membranes from control subjects in a high glucose (16.1 mM) medium for 10 days at 37 degrees C led to an increase in the extent of glycation of membrane proteins and a decrease in membrane fluidity (indicated by an increase in steady state fluorescence polarization); most of the changes occurred within the first 3 days of incubation. Incubation of platelet membranes with 5.4 mM glucose had less effect. In contrast, incubation of platelet membranes with the same concentrations of 1-0-methylglucose did not cause a change in either the extent of glycation of proteins or membrane fluidity. We also determined if acetylation by aspirin or acetyl chloride of the sites available for glycation on platelet membrane proteins leads to a similar reduction in membrane fluidity. Pretreatment of platelet membranes with aspirin or acetyl chloride diminished the extent of glycation that occurred when platelet membranes were subsequently incubated with glucose, but membrane fluidity was reduced even in the absence of glucose; subsequent incubation with glucose caused no further reduction in membrane fluidity.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
39.
Transmission computed tomography (TCT) data provides useful complementary information to single-photon emission computed tomography (SPECT) reconstructions, especially for cardiac studies. In particular, TCT data has been used to correct for nonuniform attenuation in the chest. Typically the transmission data are acquired in a separate acquisition, but simultaneous acquisition is preferable both to save time and to avoid difficulties involved with registration. In this work, we present a technique for simultaneously acquiring 201Tl SPECT and TCT data using a 99mTc sheet source that requires only minor equipment modifications. The use of these isotopes results in cross-contamination of the emission and transmission data. We present a practical technique to compensate for this contamination using post-acquisition image processing. This technique was evaluated by performing phantom and patient studies. The resulting images compare well with data obtained from separate emission and transmission studies.  相似文献   
40.
Hematologic disorders in pregnancy are relatively common and encompass a wide spectrum of clinical conditions. The treatment and obstetric management of the majority of these diseases are well established, although controversy exists in areas such as sickle cell disease and ITP. Once the diagnosis of a specific disorder is confirmed, therapy is directed toward improved perinatal outcome. Recent advances in prenatal diagnostic techniques make in utero diagnosis feasible for most of the inherited disorders and aid in genetic counseling.  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