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   3852篇
  免费   168篇
  国内免费   36篇
耳鼻咽喉   58篇
儿科学   105篇
妇产科学   169篇
基础医学   317篇
口腔科学   152篇
临床医学   306篇
内科学   872篇
皮肤病学   95篇
神经病学   186篇
特种医学   213篇
外科学   730篇
综合类   76篇
预防医学   137篇
眼科学   94篇
药学   221篇
中国医学   7篇
肿瘤学   318篇
  2024年   2篇
  2023年   25篇
  2022年   53篇
  2021年   79篇
  2020年   41篇
  2019年   62篇
  2018年   92篇
  2017年   62篇
  2016年   98篇
  2015年   114篇
  2014年   133篇
  2013年   202篇
  2012年   260篇
  2011年   265篇
  2010年   146篇
  2009年   133篇
  2008年   249篇
  2007年   296篇
  2006年   278篇
  2005年   274篇
  2004年   213篇
  2003年   183篇
  2002年   146篇
  2001年   94篇
  2000年   71篇
  1999年   77篇
  1998年   45篇
  1997年   36篇
  1996年   30篇
  1995年   26篇
  1994年   22篇
  1993年   29篇
  1992年   23篇
  1991年   24篇
  1990年   18篇
  1989年   22篇
  1988年   22篇
  1987年   11篇
  1986年   16篇
  1985年   7篇
  1984年   8篇
  1983年   7篇
  1982年   9篇
  1981年   12篇
  1980年   13篇
  1978年   6篇
  1977年   7篇
  1976年   9篇
  1975年   2篇
  1955年   1篇
排序方式: 共有4056条查询结果,搜索用时 0 毫秒
21.

Background  

Arsenic in groundwater and its accumulation in plants and animals have assumed a menacing proportion in a large part of West Bengal, India and adjoining areas of Bangladesh. Because of the tremendous magnitude of the problem, there seems to be no way to tackle the problem overnight. Efforts to provide arsenic free water to the millions of people living in these dreaded zones are being made, but are awfully inadequate. In our quest for finding out an easy, safe and affordable means to combat this problem, a homeopathic drug, Arsenicum Album-30, appears to yield promising results in mice. The relative efficacies of two micro doses of this drug, namely, Arsenicum Album-30 and Arsenicum Album-200, in combating arsenic toxicity have been determined in the present study on the basis of some accepted biochemical protocols.  相似文献   
22.

Background

The current status of radioiodine-131 (RaI) dosimetry for Graves' hyperthyroidism is not clear. Recurrent hyperthyroidism and iatrogenic hypothyroidism are two problems which interact such that trying to solve one leads to exacerbation of the other. Optimized RaI therapy has therefore begun to be defined just in terms of early hypothyroidism (ablative therapy) as physicians have given up on reducing hypothyroidism.

Methods

Optimized therapy is evaluated both in terms of the greatest separation of cure rate from hypothyroidism rate (non-ablative therapy) or in terms of early hypothyroidism (ablative therapy) by mathematical modeling of outcome after radioiodine and critically discussing the three common methods of RaI dosing for Graves' disease.

Results

Cure follows a logarithmic relationship to activity administered or absorbed dose, while hypothyroidism follows a linear relationship. The effect of including or omitting factors in the calculation of the administered I–131 activity such as the measured thyroid uptake and effective half-life of RaI or giving extra compensation for gland size is discussed.

Conclusions

Very little benefit can be gained by employing complicated methods of RaI dose selection for non-ablative therapy since the standard activity model shows the best potential for cure and prolonged euthyroidism. For ablative therapy, a standard MBq/g dosing provides the best outcome in terms of cure and early hypothyroidism.  相似文献   
23.
Interactions between the CXCR4 chemokine receptor in breast cancer cells and the ligand CXCL12/SDF-1α are thought to play an important role in breast cancer metastases. In this pilot study, CXCR4 expression along with other biomarkers including HER2-neu and EGFR, were measured in primary tumor samples of patients with operable breast cancer to test whether any of these biomarkers alone and in combination could indicate breast cancer with high likelihood of metastasizing to bone marrow. Cytokeratin (CK) positive cells in bone marrow were identified by flow-cytometry following enrichment with CK 7/8 antibody-coupled magnetic beads. Primary tumors (n = 18) were stained with specific antibodies for CXCR4, HER2-neu, EGFR, and PCNA using an indirect avidin–biotin horseradish peroxidase method. The majority of the patients had T2/T3 tumors (72%), or lymph node involvement (67%) as pathologic characteristics that were more indicative of high-risk breast cancer. High CXCR4 cytoplasmic expression was found in 7 of 18 patients (39%), whereas 6 of 18 patients (33%) were found to have CK positivity in bone marrow. The median number of CK+ cells was 236 (range, 20–847) per 5 × 104 enriched BM cells. The presence of CK+ cells in bone marrow was found to be associated with increased expression of CXCR4 alone or in addition to EGFR and/or HER2-neu expression (P = 0.013, P = 0.005, and P = 0.025, respectively) in primary tumors. Furthermore, three patients with high CK positivity (>236 CK+ per 5 × 104 enriched bone marrow cells) in bone marrow exclusively expressed high levels of CXCR4 with EGFR/HER2-neu (P = 0.001). Our data suggest that high CXCR4 expression in breast cancer may be a potential marker in predicting isolated tumor cells in bone marrow. CXCR4 coexpression with EGFR/HER2-neu might further predict a particular subset of patients with high CK positivity in bone marrow.  相似文献   
24.
Kaplan C  Diril N  Sahin S  Cehreli MC 《Biomaterials》2004,25(18):4019-4027
The potential mutagenicity of a zinc phosphate (Poscal), a polycarboxylate (Aqualox) and glass ionomer cements with (Argion) and without (Meron) silver reinforcement were characterized by employing the Ames Salmonella/microsome test. The materials were eluted in dimethyl sulphoxide or physiologic saline and the aliquots were used either immediately or after an incubation period of 24h at 37 degrees C. Mutagenic effects of the materials were tested on Salmonella typhimurium strains TA 98, TA 100, TA 102 and TA 1535 using the standard plate incorporation assay, and in the presence or absence of S9 fraction from rat liver. Poscal and Aqualox elicited mutagenic effects on S. typhimurium TA 98 and TA 1535, whereas Meron exhibited mutagenic effects on S. typhimurium TA 98. No mutagenic effects were detected for Argion. The type of solvent, dose of the material and incubation as well as the interactions between these factors exhibited varying degrees of influences on the mutagenic activities of the cements (P<0.05 and P<0.1). We conclude that zinc phosphate, polycarboxylate, and glass ionomer cements may have possible mutagenic activities.  相似文献   
25.
Recording the motor output of the central nervous system from the cervical spinal cord was investigated as a method of generating voluntary command signals, potentially to be used in quadriplegic individuals. Corticospinal volleys evoked by motor cortex stimulation were recorded from the spinal cord surface with multicontact electrodes in anesthetized cats. The multicontact recordings were analyzed for their information-carrying capacity as a neural interface. Neural signals resulting from the stimulation of various points in the motor cortex were considered as symbols of an alphabet that were sent through a discrete information channel. The information capacity of this channel at the thermal noise level of the electrode contacts was calculated. The maximum information rate was 1.57 bits in a trial for a 4-symbol alphabet. The background noise that reduces the information rate to 50% of its maximum theoretical value was defined as the half-bitrate-noise-tolerance (HBR-NoiseTol) and used as a measure of symbol distinguishability. The HBR-NoiseTol for all trials on average was 24 +/- 12%, 18 +/- 10%, and 15 +/- 9% for interfaces with 2-, 3-, and 4-symbol alphabets (n = 11 trials). The average peak-to-peak amplitude of the neural volleys was 13.5 +/- 6.7 microV (n = 11). These results suggest that the corticospinal signals can be recorded with spatial selectivity from the spinal cord surface and thus warrant further investigation of their potential use for a spinal cord-computer interface.  相似文献   
26.
Pain during sexual activity and ejaculation are the unspoken long-term complications of groin hernia repair. Laparoscopic surgical techniques are associated with decreased post-operative pain and earlier return to daily activities, but its effect on these complications is unclear. This study aims to investigate the effect of transabdominal preperitoneal repair (TAPP) on de-novo pain during sexual intercourse and ejaculation and to compare with open repair. For this reason, two groups were determined according to the surgical technique: the Lichtenstein repair and the TAPP groups and a questionnaire was sent to the patients a minimum of 6 months following the surgery. A total of 317 patients included, as 115 in TAPP and 202 in Lichtenstein repair group. No significant difference was observed concerning pre-operative pain during sexual activity and ejaculation in both groups (p = .75, p = .56). Following the surgery, the number of patients experiencing painful sexual activity was significantly higher in the Lichtenstein repair group compared to the TAPP group (19.3% vs. 11.3%, respectively, p = .03). The post-operative painful ejaculation rate was also significantly lower for the TAPP group (p = .04). The lower rates of post-operative dysejaculation and pain during sexual activity can be achieved with the advantage of laparoscopic surgery.  相似文献   
27.
Formate metabolism in young swine   总被引:1,自引:0,他引:1  
Formate generated from methanol metabolism in vivo is the chemical entity responsible for the development of the methanol toxicity syndrome in the monkey. Compared to rats, monkeys are in a state of folate deficiency. This leads to a decreased ability to dispose of formate generated leading to its accumulation and the subsequent development of the classic symptoms of methanol toxicity. Rats possess a more efficient folate system; therefore, they metabolize formate very readily and do not exhibit methanol toxicity symptoms. In this report, the hepatic folate content and the ability to handle a formate "load" were evaluated in another animal species, the pig. The results obtained indicate that the pig, compared to all other species studied, has extremely low levels of folates and very low levels of a key enzyme in the folate pathway, namely 10-formyl H4folate dehydrogenase. Also the pig's ability to dispose of formate was extremely limited and slower than that observed in rats or monkeys. These results suggest that the pig may be a suitable animal model for studying formate metabolism and possibly methanol toxicity.  相似文献   
28.
Correlation of p53 gene/protein alterations with incidence of oncogene amplification, a potential marker of prognosis, was evaluated in 26 fresh breast cancer samples. p53 gene was analyzed by SSCP and DNA sequencing while p53 protein status was investigated by immunohistochemistry (IH). Amplification of c-erbB2/neu, c-myc, N-ras, int-2, hst, PRAD-1 and EGFR genes was studied by slot blot and in situ hybridizations. p53 alterations were found in 31% cases by SSCP and 42% by IH; gene amplification was detected in 27% cases. p53 gene alterations correlated significantly with gene amplification (p=0.006) and also with higher S-phase index (p=0.026), aneuploidy (p=0.026) and negative progesterone receptor status (p=0.043).  相似文献   
29.
30.
PURPOSE: To define the relation of nonoliguric renal failure to transurethral resection of the prostate (TURP), its clinical importance, and predictive factors. PATIENTS AND METHODS: The files of 439 patients who had undergone TURP at Hacettepe University School of Medicine, Department of Urology, between January 1991 and 1994 were analyzed. The patients were divided into three groups according to postoperative serum creatinine concentration and the presence of clinical signs and symptoms of TUR syndrome (Group I: patients with preoperative and postoperative creatinine in the normal range; Group II: patients suffering nonoliguric renal failure; and Group III: patients with TUR syndrome). The data of the groups were compared in terms of factors influencing nonoliguric renal failure. RESULTS: The mean postoperative concentrations of sodium, blood urea nitrogen, creatinine, and albumin in Groups II and III were statistically different from those in Group I (P < 0.001). There was a moderate relation between hyponatremia and the occurrence of nonoliguric renal failure (r(s) = -0.56). Capsule perforation increased the risk of nonoliguric renal failure 10.6 fold. All of the patients were managed by a conservative approach, and none of the patients died or progressed to end-stage renal disease. They were all discharged with a mean hospitalization period of 7 days and normal renal function tests. CONCLUSION: Nonoliguric renal failure was thought to be an early step in the pathophysiology of TUR syndrome with acute renal failure. It is an asymptomatic clinical picture that is undiagnosed unless laboratory examinations are performed. A conservative therapeutic approach is enough.  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