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   2216篇
  免费   134篇
  国内免费   16篇
耳鼻咽喉   29篇
儿科学   30篇
妇产科学   27篇
基础医学   242篇
口腔科学   50篇
临床医学   110篇
内科学   471篇
皮肤病学   122篇
神经病学   189篇
特种医学   67篇
外科学   345篇
综合类   4篇
预防医学   173篇
眼科学   79篇
药学   165篇
中国医学   2篇
肿瘤学   261篇
  2023年   14篇
  2022年   26篇
  2021年   43篇
  2020年   28篇
  2019年   40篇
  2018年   51篇
  2017年   46篇
  2016年   55篇
  2015年   63篇
  2014年   74篇
  2013年   85篇
  2012年   140篇
  2011年   170篇
  2010年   75篇
  2009年   60篇
  2008年   105篇
  2007年   105篇
  2006年   95篇
  2005年   101篇
  2004年   91篇
  2003年   82篇
  2002年   87篇
  2001年   56篇
  2000年   68篇
  1999年   58篇
  1998年   17篇
  1997年   17篇
  1996年   12篇
  1995年   10篇
  1994年   21篇
  1993年   14篇
  1992年   60篇
  1991年   40篇
  1990年   26篇
  1989年   33篇
  1988年   32篇
  1987年   37篇
  1986年   29篇
  1985年   25篇
  1984年   18篇
  1983年   18篇
  1982年   8篇
  1979年   14篇
  1978年   9篇
  1975年   9篇
  1974年   10篇
  1973年   12篇
  1971年   11篇
  1969年   13篇
  1967年   10篇
排序方式: 共有2366条查询结果,搜索用时 0 毫秒
101.
Clinicopathologic features of ampullary carcinoma without jaundice   总被引:3,自引:0,他引:3  
GOALS: To evaluate clinicopathological features of ampullary carcinoma without jaundice. BACKGROUND:: Obstructive jaundice is the most common symptom of patients with ampullary carcinoma. However, some patients with ampullary carcinoma do not have jaundice at the time of diagnosis. STUDY: Clinicopathologic findings of 23 patients with ampullary carcinoma showing no visible jaundice (serum total bilirubin <3.0 mg/dL) and 38 patients with ampullary carcinoma showing jaundice at the time of diagnosis were retrospectively compared. RESULTS: Fifteen of 23 patients with nonjaundiced ampullary carcinoma complained of fever and/or abdominal pain. Five asymptomatic patients were found to have a dilated bile duct on screening ultrasound or to have a tumor-like swelling of the papilla of Vater during routine upper gastrointestinal endoscopy. There was no significant difference in age, sex, size, macroscopic type, histologic type, rates of duodenal invasion, pancreatic invasion, and lymph node metastasis, and prognosis between the two groups. The cumulative 5-year and 10-year survival rates of nonjaundiced patients were 70.2% and 49.0%, compared with 33.6% and 29.4% of jaundiced patients. Ten of the 23 nonjaundiced ampullary carcinomas (43%) were in Stage I, whereas 4 of the 38 jaundiced ampullary carcinomas (11%) were in Stage I (P < 0.01). Mechanisms of nonjaundice in ampullary carcinoma were suspected to be determinant by the infiltrating pattern of the carcinoma to the lower portion of the bile duct. CONCLUSIONS: Mechanisms of nonjaundice in ampullary carcinoma might be determined by the infiltrating pattern of the carcinoma to the lower portion of the bile. As a greater number of nonjaundiced ampullary carcinomas were in an early stage, detection of them may provide an improved clinical outcome.  相似文献   
102.
Pituitary tumors are highly vascular neoplasms, which suggest an important role of angiogenesis in pituitary tumor growth. We used the human pituitary cell line (HP75) to examine the effects of the growth factors TGFβ1, bFGF, and EGF on cell growth, and on the regulation of the pro-angiogenic growth factor VEGF-A and the VEGFR-I and the anti-angiogenic molecules thrombospondin (TSP) TSP-1 and TSP-2 along with TSP-3. Real-time RT-PCR was used to measure mRNA levels, and Western blot was used to analyze TSP-1 and TSP-2 protein levels. TGFβ1 treatment (1×10−9 M) increased VEGF-A mRNA levels significantly (p<0.05) after 4 and 24 h of treatment. TGF β1 treatment decreased VEGF-R mRNA levels after 96 h of treatment (p<0.05). After 96 h of treatment, TSP-1 and TSP-2 mRNA levels were significantly increased (p<0.05) by TGFβ1 treatment, which also inhibited HP75 cell growth. Basic FGF also increased TSP-1 mRNA levels after 96 h of treatment, but did not regulate growth of the pituitary tumor cells. Basic FGF and EGF did not modulate changes in VEGF-A mRNA levels after 4 and 24 h of treatment, but EGF increased VEGF-A significantly (p<0.05) after 96 h of treatment. These results indicate that TGFβ1 treatment may regulate angiogenesis in pituitary cells by initially increasing levels of pro-angiogenic VEGF-A and then stimulating the anti-angiogenic molecules TSP-1 and TSP-2 levels.  相似文献   
103.
To clarify the invasive process of Vibrio parahaemolyticus, an invasion assay was performed using cells expressing dominant negative small GTPases of the Rho family. This assay showed that the dominant negative host phenotype facilitates bacterial invasion, suggesting that the mechanism of V. parahaemolyticus invasion differs from that reported for other invasive bacteria.  相似文献   
104.
105.
In order to confirm the role of 14-3-3 sigma (sigma) as a tumor suppressor in breast carcinogenesis, we have studied the expression of 14-3-3sigma immunohistochemically in usual ductal hyperplasia (UDH), ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) breast lesions. Immunostaining for estrogen receptor alpha (ERalpha), p53 and estrogen-responsive RING finger protein (Efp) was also carried out. Immunohistochemically, expression of 14-3-3sigma was seen in 92% UDH lesions and gradually decreased from 65% in DCIS to 23% in IDC. The expression of ERalpha decreased gradually from UDH to DCIS to IDC, while p53 showed an inverse staining pattern to that of ERalpha. The expression of Efp showed no significant difference among the three breast lesions. Hence, the present immunohistochemical study confirmed 14-3-3sigma as a tumor suppressor in breast carcinogenesis. A similar immunohistochemical analysis was then carried out on columnar cell hyperplasia with atypia (CCHA), in which the expression pattern of tumor suppressor 14-3-3sigma, ERalpha and p53 suggested that it might be possible that CCHA is a precancerous lesion.  相似文献   
106.
One of major metabolic pathways of [(+/-)-4-(4-cyanoanilino)-5,6-dihydro-7-hydroxy-7H-cyclopenta[d]-pyrimidine] (RS-8359), a selective and reversible monoamine oxidase type A inhibitor, is the aldehyde oxidase-catalyzed 2-hydroxylation at the pyrimidine ring. Donryu rats showed a dimorphic pattern for the 2-oxidation activity with about 20- to 40-fold variations in the Vmax/Km values between a low and a high activity group. The rats were classified as extensive metabolizers (EM) and poor metabolizers (PM) of RS-8359, of which ratios were approximately 1:1. One rat among the EM rats of each sex showed extremely high activity, and they were referred to as ultrarapid metabolizers. There was no significant difference in the expression levels of mRNA of aldehyde oxidase between the EM and PM rats. Analysis of nucleotide sequences showed four substitutions, of which the substitutions at 377G>A and 2604C>T caused 110Gly-Ser and 852Ala-Val amino acid changes, respectively. Amino acid residue 110 is located very near the second Fe-S center of aldehyde oxidase. Its change from nonchiral Gly to chiral Ser may result in a conformational change of aldehyde oxidase protein with the shift of isoelectric point value from 5.0 in the EM rats to 6.2 in the PM rats. The 110Gly-Ser amino acid substitution (377G>A) may be primarily responsible for the variations of aldehyde oxidase activity observed in Donryu rats, in addition to the difference of expression levels of aldehyde oxidase protein. If a new drug candidate is primarily metabolized by aldehyde oxidase, attention should be given to using a rat strain with high aldehyde oxidase activity and small individual variation.  相似文献   
107.
Summary Parasternal two-dimensional and Doppler echocardiography were compared with angiographic, surgical, and postmortem data in 213 patients with various forms of congenital heart disease for its accuracy in determining patency and anatomy of the ductus arteriosus (DA). The age range of the examined patients was from 1 day to 4 years (mean, 7.4 months). Echocardiography was always performed before any invasive procedure. An adequate window for imaging the DA was obtained by parasternal, two-dimensional echocardiography in 209 patients (98%). A persistent ductus arteriosus (PDA) was detected by invasive methods in 79 of 209 patients (38%), and by two-dimensional and Doppler echocardiography in 76 (sensitivity, 96%; specificity, 100%). The echocardiographic and angiographic findings agreed closely as to the duct's morphology. Our technique permits an accurate visualization of the duct in neonates, infants, and small children with various forms of congenital heart disease.  相似文献   
108.
Effects of acetylsailcylic acid (ASA) (aspirin) on the pathogenesisof fatty liver, cirrhosis and hepatocarcinogenesis caused bya choline-deficient L-amino acid-defined (CDAA) diet were examinedin male Fischer 344 rats fed a CDAA diet supplemented with 0,0.1, 0.2, 0.4 or 0.8% ASA for 30 weeks. ASA at concentrationsof >0.2% prevented the development of both cirrhosis andpreneoplastic and neoplastic nodules, but without any directlyassociated prevention of fatty changes. ASA also prevented hepatocyteproliferation and the generation of thiobarbituric acid-reactivesubstances and 8-hydroxydeoxyguanosine caused by feeding theCDAA diet, analyzed, respectively, after 1, 12 and 12 weeks.The results clearly indicate that the anti-inflammatory drugASA, which is not a lipotropic factor, can prevent the pathogenesisof cirrhosis and hepatocarcinogenesis caused by a CDAA diet,which is possibly partly associated with the prevention of reactiveoxygen species production.  相似文献   
109.
The present study was performed to assess the roles of hepatocellular oxidative damage to DNA and constituents other than DNA in rat liver carcinogenesis caused by a choline-deficient, l -amino acid-defined (CDAA) diet by examining the effects of the antioxidant N, N' -diphenyl- p -phenylenediamine (DPPD). The parameters used for cellular oxidative damage were the level of 8-hydroxyguanine (8-OHGua) for DNA and that of 2-thiobarbituric acid-reacting substance (TBARS) for constituents other than DNA. A total of 40 male Fischer 344 rats, 6 weeks old, were fed the CDAA diet for 12 weeks with or without DPPD (0.05, 0.10 or 0.20%) or butylated hydroxytoluene (BHT, 0.25%). In the livers of the rats, the numbers and sizes of glutathione S -transferasc (EC 2.5.1.18) placental form (GSTP)- and/or γ-glutamyltransferase (GGT, EC 2.3.2.2)-positive lesions and levels of 8-OHGua and TBARS were determined. The GSTP-positive lesions of 0.08 mm2 or larger were all stained positively for GGT as well in cross-sectional area, whereas the smaller lesions were generally negative for GGT. DPPD and BHT reduced the size of the GSTP-positive lesions without affecting their total numbers. At the same time, they reduced TBARS generation without affecting 8-OHGua formation in DNA. The present results indicate that oxidative DNA damage (represented by 8-OHGua formation) and damage to constituents other than DNA (represented by TBARS generation) may play different roles in rat liver carcinogenesis caused by the CDAA diet; the former appears to be involved in the induction of phenotypically altered hepatocyte populations while the latter may be related to the growth of such populations.  相似文献   
110.
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