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   2249篇
  免费   88篇
  国内免费   18篇
耳鼻咽喉   54篇
儿科学   22篇
妇产科学   61篇
基础医学   206篇
口腔科学   108篇
临床医学   116篇
内科学   509篇
皮肤病学   48篇
神经病学   163篇
特种医学   80篇
外科学   360篇
综合类   16篇
预防医学   55篇
眼科学   22篇
药学   117篇
中国医学   4篇
肿瘤学   414篇
  2022年   19篇
  2021年   54篇
  2020年   27篇
  2019年   32篇
  2018年   39篇
  2017年   48篇
  2016年   38篇
  2015年   44篇
  2014年   80篇
  2013年   74篇
  2012年   98篇
  2011年   138篇
  2010年   98篇
  2009年   68篇
  2008年   108篇
  2007年   127篇
  2006年   100篇
  2005年   96篇
  2004年   110篇
  2003年   92篇
  2002年   103篇
  2001年   75篇
  2000年   71篇
  1999年   65篇
  1998年   16篇
  1997年   21篇
  1996年   14篇
  1995年   20篇
  1994年   21篇
  1993年   27篇
  1992年   37篇
  1991年   32篇
  1990年   37篇
  1989年   46篇
  1988年   21篇
  1987年   25篇
  1986年   36篇
  1985年   27篇
  1984年   15篇
  1983年   9篇
  1980年   10篇
  1979年   17篇
  1978年   8篇
  1977年   10篇
  1975年   13篇
  1972年   8篇
  1971年   8篇
  1970年   9篇
  1969年   10篇
  1965年   8篇
排序方式: 共有2355条查询结果,搜索用时 62 毫秒
21.
We studied p53 and p21 expression simultaneously in gastric carcinoma tissues to investigate the clinical significance of p53-p21 pathway in this disease. One hundred sixty-four primary gastric carcinoma specimens were immunohistochemically stained for p53 and p21 protein, and clinicopathological features of the cases were examined. P53 was stained negatively, while p21 was stained positively in each normal stomach epithelium. P53, and p21 positive staining was observed in 82 (50%) and 61 (37.2%) tumors, respectively. Unexpectingly, no correlation was found between p53 and p21 staining status. Tumors demonstrating preserved p53-p21 pathway [p53(-)/p21(+)], observed in 20.1% of the tumors, displayed less aggressive characteristics, and no recurrent disease after curative resection. While tumors demonstrating disrupted p53-p21 pathway [p53(+)/p21(-)], observed in 32.9% of the tumors, displayed significantly more aggressive characteristics, poorer survival and higher recurrence rate than the tumors demonstrating other staining patterns. P53-p21 pathway was widely altered in gastric carcinomas. The combined evaluation of p53 and p21 expression in gastric carcinoma tissues is suggested to have clinical importance by indicating not only the malignant potential of each tumor, but also the prognosis of this disease.  相似文献   
22.
Chediak‐Higashi syndrome (CHS) is a rare autosomal recessive disorder characterized by severe immunologic defects, reduced pigmentation, bleeding tendency, and progressive neurological dysfunction. Most patients present in early childhood and die unless treated by bone marrow transplantation. About 10–15% of patients exhibit a much milder clinical phenotype and survive to adulthood, but develop progressive and often fatal neurological dysfunction. Very rare patients exhibit an intermediate adolescent CHS phenotype, presenting with severe infections in early childhood, but a milder course by adolescence, with no accelerated phase. Here, we describe the organization and genomic DNA sequence of the CHS1 gene and mutation analysis of 21 unrelated patients with the childhood, adolescent, and adult forms of CHS. In patients with severe childhood CHS, we found only functionally null mutant CHS1 alleles, whereas in patients with the adolescent and adult forms of CHS we also found missense mutant alleles that likely encode CHS1 polypeptides with partial function. Together, these results suggest an allelic genotype–phenotype relationship among the various clinical forms of CHS. © 2002 Wiley‐Liss, Inc.  相似文献   
23.
The mechanisms of arterial hypotension following intravenous anesthetic induction agents are multifactorial. The purpose of this study was to evaluate and compare the effects of thiopental, propofol and etomidate on hemodynamics, sympathetic outflow and arterial baroreflex sensitivity using not only neuraxis-intact but also totally baro-denervated rabbits. A total of 60 rabbits was anesthetized with urethane, tracheotomized, and mechanically ventilated with oxygen in nitrogen (FiO2 0.5). The left renal sympathetic nerve was isolated and placed on a bipolar electrode to record renal sympathetic nerve activity (RSNA). Thirty animals underwent a surgical preparation of total baroreceptor denervation. Bolus injections of an anesthesia induction dose of thiopental 4 mg/kg and twice the induction dose of propofol 4 mg/kg significantly decreased RSNA to the same extent (19.4+/-6.7 and 19.7+/-5.2% reduction, mean +/- SEM) and mean arterial pressure (MAP) also to the same extent (19.5+/-4.6 and 22.1+/-3.1% reduction) in the neuraxis-intact animals. RSNA was increased (34.5+/-6%) without reduction of MAP by an induction dose of etomidate, 0.3 mg/kg. Sympathetic barosensitivity was attenuated even 10 min after thiopental at 4 mg/kg or propofol at 4 mg/kg (68% and 54% of control, respectively). Propofol at 2 mg/kg (induction dose) and etomidate at 0.6 mg/kg decreased RSNA and MAP only in the baro-denervated animals. It was found from the barosensitivity study that patients can be hemodynamically unstable even though blood pressure has returned to normal after thiopental and propofol administration. Data suggest that etomidate can even stimulate the sympathetic nervous system and increase sympathetic outflow. It was also clearly found from the baro-denervated animal study that thiopental was stronger than propofol in directly suppressing sympathetic outflow at the induction dose.  相似文献   
24.
BackgroundSagittal spino-pelvic malalignment in patients with chronic low back pain (CLBP) have been reported in the past, which may also affect cervical spine lesions. The purpose of this study is to investigate the cervical alignment in patients with CLBP.MethodOf the patients who visited an orthopedic specialist due to low back pain lasting more than three months, 121 cases (average 71.5-years-old, 46 male and 75 female) with whole standing spinal screening radiographs were reviewed (CLBP group). Cervical parameters included cervical lordosis (CL), C2–C7 sagittal vertical axis (C2-7 SVA), and the T1 slope minus CL (T1S-CL). Cervical spine deformity was defined as C2-7 SVA >4 cm, CL <0°, or T1S-CL ≧20°. We compared the cervical alignment of these patients with 121 age and gender matched volunteers (control group).ResultsThe prevalence of cervical spine deformity was significantly higher in the CLBP group than in the control group (20.7% vs. 10.7%, P = 0.034). The mean CL was smaller in the CLBP group than in the control group (16.1° vs. 21.4°, P = 0.002). The mean C2-7 SVA was 17.6 mm vs. 18.7 mm in the CLBP group and in the control group, respectively (P = 0.817). The mean T1S-CL was larger in the CLBP group than in the control group (9.1° vs. 3.5°, P < 0.001). Multivariate analysis showed that people with CLBP were more likely to have cervical deformities than people without CLBP (odds ratio 2.16, 95% confidence interval 1.006 to 4.637).ConclusionsThis study results suggest that people with CLBP present with worse cervical sagittal alignment and higher prevalence of cervical spine deformities than age and gender matched volunteers with no CLBP. This means CLBP impacts cervical spine lesions negatively.Level of evidenceⅣ  相似文献   
25.
PURPOSETo determine the value of the acetazolamide challenge test with stable xenon-enhanced CT (Xe CT) for making therapeutic decisions in patients with chronic cerebrovascular disease.METHODSWe compared the Xe CT-measured acetazolamide response with various measures obtained by positron emission tomography. We performed both a positron emission tomographic scan and a Xe CT study in 11 patients with chronic cerebral ischemic diseases within a 1-week interval. An increase of cerebral blood flow after injection of acetazolamide was expressed as delta AT. Regional cerebral blood flow, cerebral oxygen metabolism, oxygen extraction fraction, and cerebral blood volume were measured with oxygen-15-labeled gases by positron emission tomography.RESULTSIn low-cerebral blood flow regions, decreased delta AT was accompanied by a significant elevation of oxygen extraction fraction and cerebral blood volume, compared with oxygen extraction fraction and cerebral blood volume in regions of normal delta AT. Plotting of regional data indicated that delta was significantly dependent on oxygen extraction fraction and cerebral blood volume. The area of decreased vascular reserve determined by the Xe CT image corresponded to the area of "misery perfusion" determined by positron emission tomography.CONCLUSIONThe acetazolamide challenge test with Xe CT may offer an alternative to positron-emission tomography in detecting lesions with elevated oxygen extraction fraction and cerebral blood volume (misery perfusion) that result from chronic hemodynamic stress.  相似文献   
26.
We describe a case of pilocytic astrocytoma of the cerebellum mimicking an acoustic schwannoma. The tumour protruded into the porus acusticus and enlarged the internal auditory meatus, which is a quite unusual characteristic of glial tumours. Received: 2 February 1999 Accepted: 21 April 1999  相似文献   
27.
The binding of benzo(a)pyrene (BP) to DNA in the presence ofliver microsomal preparations from 3-methylcholanthrene-treatedrats was increased 28.5% (P < 0.001) by addition of UDP-glucuronicacid to the incubation mixture at a 100 µM concentrationof BP. However this increase was not observed at lower concentrationsof BP. Analysis of DNA-hydrolysates by column chromatographyon Sephadex LH-20 indicated that this increase was due to greaterbinding of benzo(a)pyrene-7, 8-dihydrodiol-9, 10-epoxide. Theamount of bound adducts derived from 9-hydroxybenzo(a)pyrene(9-OH BP) was not significantly affected by UDP-glucuronic acid.Addition of UDP-glucuronic acid to incubation mixtures containingmicrosomes from untreated rat liver caused only a slight increasein total binding. These findings suggest that UDP-glucuronyltransferase may be involved in the activation of BP.  相似文献   
28.
There has been yet no report, to our knowledge, which clarified the affinity ("sensitivity") of catecholamines to cardiac chronotropic beta-adrenergic receptor or to vasoconstrictive alpha-adrenergic receptor of skeletal muscle resistance vessels in human borderline hypertension (BHT), using an analysis of the kinetics of the drug-receptor interaction. In the first half of this study, isoproterenol (ISO) infusion test was performed on "normal" subjects (n = 12) and subjects with BHT (n = 10). Dose-response relation was obtained in terms of various doses of ISO and the increments of heart rate (deltaHR) produced by ISO. In the latter half of this study, phenylephrine (PHE) infusion test was carried out in the series of "normal" subjects (n = 5) and subjects with BHT (n = 6), a partly different series from the first series of subjects. Dose-response relation, again, was obtained in terms of various doses of PHE and the increments of total peripheral resistance (deltaTPR) produced by PHE. These relations were displayed on Lineweaver-Burk's plot and the "affinity" of ISO to cardiac chronotropic beta-receptor or that of PHE to vasoconstrictive alpha-receptor of skeletal muscle resistance vessels was estimated, graphically, assuming that 1) drugs were diluted by a volume of body fluid equal to the blood volume which was actually measured in each individual and 2) this concentration of drugs existed around the receptor site, i.e., there was no significant individual variations in terms of the metabolism and the distribution of the drugs. Estimated "affinity" of ISO to cardiac chronotropic beta-receptor was 0.168 +/- 0.014 x 10(4) ml X ug-1 (mean +/- SE, n = 10) in patients with BHT, while it was 0.170 +/- 0.015 x 10(4) (n = 12) in "normal" subjects. Estimated "affinity" of PHE to vasoconstrictive alpha-receptor of skeletal muscle resistance vessels was 0.171 +/- 0.011 x 10(2) ml X ug-1 (n = 6) in patients with BHT, while it was 0.183 +/- 0.012 x 10(2) (n = 5) in "normal" subjects. It is concluded from these data, almost fairly, that there is no difference in terms of the estimated "affinity" of ISO to cardiac chronotropic beta-receptor or that of PHE to vasoconstrictive alpha-receptor between "normal" subjects and patients with BHT. It was also found, in PHE infusion tests, that the plasma adrenaline concentration was significantly higher in patients with BHT than in "normal" subjects, at least at two points of time in the test: a) immediately before PHE infusion, when every individual appeared to be considerably restful and b) at the end of 1-2 min after the completion of the infusion of the largest dose of PHE used.  相似文献   
29.
In order to clarify the interaction of volatile anesthetics and extracellular calcium ion on the myocardial contraction, effects of both isoflurane (1.0%) and halothane (0.5%) on the extracellular calcium ion concentration ([Ca2+]O)-tension curve were studied. Increasing [Ca2+]O enhanced the myocardial contraction response, and the maximal response was obtained at [Ca2+]O of 3.0mM. Halothane depressed the maximal value of the tension development in response to increasing [Ca2+]O, while isoflurane did not (P 0.01). The probit response of the developed tension to the changes in [Ca2+]O indicated that isoflurane increased the median effective concentration (EC50) of [Ca2+]O significantly from 0.484 ± 0.051 (mean ± SEM) to 0.870 ± 0.056mM (P = 0.001), but halothane did not (P = 0.018). Therefore, 1.0% isoflurane was concluded to move the [Ca2+]O-tension curve to the right, while a downwards shift occurred with 0.5% halothane.(Saeki S, Hirakawa M, Shimosato S: Effects of Isoflurane and Halothane on the Calcium Ion-tension Curve in Rat Myocardium. J Anesth 6: 172–175, 1992)  相似文献   
30.
The pathophysiology of secondary brain damage following experimental traumatic brain injury was investigated by measuring local cerebral blood flow (lCBF), local cerebral glucose utilization (lCGU), and activity of succinate dehydrogenase (SDH), which is a mitochondrial enzyme of the tricarboxylic acid cycle, in the rat brain after moderate lateral fluid percussion injury. Measurements used autoradiography for lCBF and lCGU with [14C]iodoantipyrine and [14C]2-deoxyglucose, respectively. Regional SDH activity was determined using quantitative imaging of formazan produced from 2,3,5-triphenyl tetrazolium chloride by SDH. lCBF decreased at 1 hour after injury and was significantly lower than the preinjury level in almost all regions of both hemispheres at 6 and 24 hours, and remained low at 2 weeks. lCGU increased 1 hour after injury but was significantly decreased at 6 and 24 hours, and at 2 weeks in most regions of both hemispheres. The ipsilateral hemisphere showed a significant decrease in the activity of SDH in the cortices, hippocampus, thalamus, and caudate/putamen, most conspicuously 72 hours after injury, whereas no significant decrease was observed in the contralateral hemisphere at any time. Necrosis in the injured cortex and reduction of the number of neurons in the ipsilateral hippocampus were observed 2 weeks after injury. The present study showed that a decrease in lCBF and mitochondrial dysfunction occur with glucose hypermetabolism around 1 hour after lateral fluid percussion injury, and that lCBF, lCGU, and mitochondrial function all deteriorate after 6 hours. This suggests that lCBF and cellular metabolism may change dynamically during the several hours following traumatic brain injury, and afterwards neuronal damage may result in an irreversible change in the areas with depressed glucose hypermetabolism in the early period after injury in combination with mitochondrial dysfunction.  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