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   7329篇
  免费   600篇
  国内免费   134篇
耳鼻咽喉   90篇
儿科学   250篇
妇产科学   197篇
基础医学   867篇
口腔科学   90篇
临床医学   782篇
内科学   1600篇
皮肤病学   136篇
神经病学   662篇
特种医学   452篇
外科学   989篇
综合类   188篇
一般理论   5篇
预防医学   727篇
眼科学   282篇
药学   508篇
中国医学   5篇
肿瘤学   233篇
  2023年   30篇
  2021年   97篇
  2020年   53篇
  2019年   103篇
  2018年   116篇
  2017年   97篇
  2016年   98篇
  2015年   107篇
  2014年   163篇
  2013年   322篇
  2012年   338篇
  2011年   417篇
  2010年   257篇
  2009年   281篇
  2008年   400篇
  2007年   457篇
  2006年   406篇
  2005年   455篇
  2004年   440篇
  2003年   380篇
  2002年   373篇
  2001年   78篇
  2000年   48篇
  1999年   77篇
  1998年   165篇
  1997年   162篇
  1996年   182篇
  1995年   112篇
  1994年   131篇
  1993年   105篇
  1992年   49篇
  1991年   56篇
  1990年   56篇
  1989年   69篇
  1988年   66篇
  1987年   57篇
  1986年   80篇
  1985年   84篇
  1984年   57篇
  1983年   62篇
  1982年   76篇
  1981年   60篇
  1980年   74篇
  1979年   42篇
  1978年   55篇
  1977年   36篇
  1976年   51篇
  1975年   31篇
  1974年   37篇
  1973年   26篇
排序方式: 共有8063条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Background: General anesthetics inhibit evoked release of classic neurotransmitters. However, their actions on neuropeptide release in the central nervous system have not been well characterized.

Methods: The effects of representative intravenous and volatile anesthetics were studied on the release of sulfated cholecystokinin 8 (CCK8s), a representative excitatory neuropeptide, from isolated rat cerebrocortical nerve terminals (synaptosomes). Basal, elevated KCl depolarization-evoked and veratridine-evoked release of CCK8s from synaptosomes purified from rat cerebral cortex was evaluated at 35[degrees]C in the absence or presence of extracellular Ca2+. CCK8s released into the incubation medium was determined by enzyme-linked immunoassay after filtration.

Results: Elevation of extracellular KCl concentration (to 15-30 mm) or veratridine (10-20 [mu]m) stimulated Ca2+-dependent CCK8s release. Basal, elevated KCl- or veratridine-evoked CCK8s release was not affected significantly by propofol (12.5-50 [mu]m), pentobarbital (50 and 100 [mu]m), thiopental (20 [mu]m), etomidate (20 [mu]m), ketamine (20 [mu]m), isoflurane (0.6-0.8 mm), or halothane (0.6-0.8 mm).  相似文献   

5.
Performance characteristics of pooled rabbit IgG polyclonal anti-C3d are compared with one mouse IgM and three mouse IgG monoclonal anti-C3d antibodies (MAs). IgG MA,s employed singly or in combination, failed to precipitate C3d; by contrast, IgM MA and polyclonal anti-C3d precipitated C3d. Measurements of polyclonal anti-C3d concentration by chemical means and by 125I-C3d radioimmunoassay (RIA) agreed closely. RIA values were 50% of chemical measurement values for three of the four MAs. Use of sucrose density gradient ultracentrifugation to assess MA C3d/anti-C3d molar combining ratios for soluble anti-C3d/C3d was not possible because fast-sedimenting multimeric C3d/anti-C3d complexes did not form. Dissociation and competitive binding studies indicate that (1) two MAs had substantially lower affinities than the other anti-C3d antibodies, and (2) polyclonal anti-C3d recognizes more C3d epitopes than are recognized by individual MAs. The results demonstrate antigenic complexity of C3d fragment and illustrate the difficulties of predicting individual MA performance based on prior experience with polyclonal antibodies.  相似文献   
6.
A method of uretero-intestinal implantation of the intact ureters in two stages, combined with total cystectomy at the second stage, has been described. When properly done it usually is followed by no permanent obstruction to the upper urinary tract. In my series of 29 cases in which both stages of the ureteral transplantation have been completed, there were only 3 patients who died as the specific result of the uretero-intestinal anastomosis. The causes in 2 of these cases have been determined and subsequently eliminated by improvement in the surgical technique. In 4 other elderly patients with advanced carcinoma there were 2 deaths from coronary occlusion, 1 from pulmonary embolus, and 1 from volvulus. Radical surgery no.w is limited to patients who are good surgical risks, and in whom there is a reasonable chance of cure. To be suitable for radical cure by total cystectomy, metastases must be absent, and the tumor must be completely confined to the bladder wall and freely movable. This latter condition is best determined pre-operatively by recto-abdominal palpation under anaesthesia. The opposition to total cystectomy for cancer of the bladder which is otherwise incurable has been based on two principal considerations: (1) The results of the rerouting of the urinary stream have been too uncertain, and (2) a surgical procedure which contemplates two laparotomies has seemed too formidable. These objections should be largely eliminated by the results obtained in this series of 29 cases. Certain authors have also objected to cystectomy because the incidence of radical cures of the cancer has not been impressive. I believe the principal reason for this is that ureteral transplantation previously has been so hazardous that this operation and cystectomy usually have been postponed until the cancer has become advanced and the patient's condition desperate. When this stage is reached the opportunity for obtaining a radical cure has been missed. The restriction of total cystectomy to cases without metastases in which the primary tumor is completely confined to the bladder wall and freely movable should increase the incidence of radical cures.  相似文献   
7.
OBJECTIVE: To assess the impact of activity restriction (AR) on the incidence of preterm birth in women treated for preterm labor testing negative for fetal fibronectin (fFN). STUDY DESIGN: Women who were diagnosed with preterm labor and tocolyzed with magnesium sulfate were concurrently screened with fFN for the purpose of subsequent management. Included were consenting patients with negative fFN, gestational age 23 0/7-33 6/7 weeks, cervical dilation < or =3 cm, and minimal vaginal bleeding. Patients were randomized to AR or no AR. Primary study outcome was incidence of preterm delivery and interval from randomization to delivery. RESULTS: A total of 73 women with negative fFN were randomized (36 with AR, 37 without AR). The overall preterm birth rate was 40%, with 44.4% of patients with AR and 35.1% of patients without AR delivering preterm, p=0.478. CONCLUSION: Maternal AR did not impact pregnancy outcome. The incidence of preterm birth in symptomatic women testing fFN negative was higher than previously reported.  相似文献   
8.
BACKGROUND: The reconstruction of small defects of the alar groove can be a unique challenge owing to the importance of maintaining its concave structure. OBJECTIVE: To present a report of a patient with a small alar groove defect that was repaired using a combination of partial primary closure and second-intention healing. METHODS: A 73-year-old female was referred for the treatment of a basal cell carcinoma of the right nasal ala and underwent Mohs micrographic surgery with clearance of the lesion. The final defect, less than 1 cm, extended to the subcutaneous fat. Two absorbable subcutaneous sutures were placed in the defect, and the wound was then allowed to heal by second intention. RESULTS. This closure yielded a good cosmetic result, with preservation of the alar groove. CONCLUSION: A combination of primary closure and second-intention healing is a time-efficient, low-risk option for nonperforating, small alar groove defects.  相似文献   
9.
Metabolism is one of the major determinants for age-related changes in susceptibility to chemicals. Aldehydes are highly reactive molecules present in the environment that also can be produced during biotransformation of xenobiotics and endogenous metabolism. Although the lung is a major target for aldehyde toxicity, early development of aldehyde dehydrogenases (ALDHs) in lung has been poorly studied. The expression of ALDH in liver and lung across ages (postnatal day 1, 8, 22, and 60) was investigated in Wistar-Han rats. In adult, the majority of hepatic ALDH activity was found in mitochondria, while cytosolic ALDH activity was the highest contributor in lung. Total aldehyde oxidation capability in liver increases with age, but stays constant in lung. These overall developmental profiles of ALDH expression in a tissue appear to be determined by the different composition of ALDH isoforms within the tissue and their independent temporal and tissue-specific development. ALDH2 showed the most notable tissue-specific development. Hepatic ALDH2 was increased with age, while the pulmonary form did not. ALDH1 was at its maximum value at postnatal day 1 (PND1) and decreased thereafter both in liver and lung. ALDH3 increased with age in liver and lung, although ALDH3A1 was only detectible in lung. Collectively, the present study indicates that, in the case of aldehyde exposure, the in vivo responses would be tissue and age dependent.  相似文献   
10.
As a part of our ongoing study on Alzheimer's disease (AD) in elderly African Americans, we obtained clinical assessment and apolipoprotein E (ApoE) genotype data on 288 individuals (including 60 with AD). The ApoE σ4 allele frequency was significantly increased in AD patients compared with controls. The age-adjusted odds ratio (OR) for AD in σ4 homozygotes was 4.83 (95% confidence interval [CI], 1.71–13.64) compared with the σ3/σ3 genotype, but the OR for AD with the σ3/σ4 genotype did not reach significance (1.20; 95% CI, 0.58–2.45). These findings suggest that the association between ApoE σ4 and AD is weaker in African Americans than in whites.  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