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   8292篇
  免费   674篇
  国内免费   20篇
耳鼻咽喉   145篇
儿科学   239篇
妇产科学   212篇
基础医学   1112篇
口腔科学   409篇
临床医学   653篇
内科学   1822篇
皮肤病学   145篇
神经病学   930篇
特种医学   202篇
外国民族医学   1篇
外科学   1245篇
综合类   57篇
预防医学   488篇
眼科学   164篇
药学   461篇
中国医学   13篇
肿瘤学   688篇
  2023年   55篇
  2022年   99篇
  2021年   247篇
  2020年   169篇
  2019年   216篇
  2018年   268篇
  2017年   184篇
  2016年   203篇
  2015年   247篇
  2014年   317篇
  2013年   379篇
  2012年   503篇
  2011年   514篇
  2010年   292篇
  2009年   294篇
  2008年   418篇
  2007年   432篇
  2006年   376篇
  2005年   376篇
  2004年   333篇
  2003年   328篇
  2002年   321篇
  2001年   170篇
  2000年   166篇
  1999年   167篇
  1998年   83篇
  1997年   64篇
  1996年   52篇
  1995年   63篇
  1994年   65篇
  1993年   50篇
  1992年   125篇
  1991年   109篇
  1990年   119篇
  1989年   102篇
  1988年   86篇
  1987年   108篇
  1986年   78篇
  1985年   83篇
  1984年   61篇
  1983年   53篇
  1982年   32篇
  1981年   38篇
  1979年   60篇
  1978年   47篇
  1976年   31篇
  1975年   35篇
  1974年   36篇
  1973年   45篇
  1970年   35篇
排序方式: 共有8986条查询结果,搜索用时 15 毫秒
61.
BackgroundSleeve gastrectomy (SG) has become the most prevalent bariatric-metabolic surgical approach in the United States. Its popularity among surgeons and patients is mainly due to a better safety profile and less overall morbidity, with broad benefits from a systemic and metabolic perspective.ObjectiveComprehensively describe the short-term multiorgan metabolic effects of rapid weight loss after SG.SettingAcademic hospital, United States.MethodsWe retrospectively reviewed the charts of patients that underwent SG at our institution between 2012 and 2016. We analyzed the required variables to calculate multiple risk scores, such as cardiovascular, hypertension, and diabetes risk scores. Furthermore, the renal and hepatic functions and the metabolic and hematologic profiles were assessed at 12 months of follow-up.ResultsA total of 1002 patients were included in the analysis. The percentage of excess body mass index loss was, on average, 65% at 12 months of follow-up. We observed a positive cardio-renal-hepatic improvement, demonstrated by a substantial reduction of the 10-year cardiovascular risk. We noticed an improvement of renal function, which was more significant in chronic kidney disease (stage ≥2), and a significant improvement on liver function tests (measured by decreased aspartate aminotransferase and alanine transaminase) at 12 months of follow-up. Our data also show a positive impact on decreasing the risk of developing hypertension and type 2 diabetes. There was a positive impact on the lipid profile, with the exception of low-density lipoprotein.ConclusionThere are significant short-term benefits on multiorgan metabolic parameters after rapid weight loss in severely obese patients undergoing sleeve gastrectomy.  相似文献   
62.
Samples of aqueous fluid were obtained from 35 controls who were people undergoing routine cataract surgery. Similar samples were taken from seven patients with clinically definite multiple sclerosis (MS) and a previous history of optic neuritis, either at cataract surgery or as an elective procedure. Oligoclonal bands were found in only one subject who suffered from the MS-uveitis syndrome.  相似文献   
63.
64.
3'-Azido-2',3'-dideoxythymidine (AZT), the thymidine analogue used against human immunodeficiency virus 1 (HIV-1), exhibits bone marrow and blood toxicity in humans, presumably as the result of genotoxic mechanisms induced by incorporation of AZT into eukaryotic DNA. Preferential incorporation of AZT into telomeric regions of DNA of Chinese hamster ovary (CHO) cells has been previously demonstrated by immunofluorescence using anti-AZT antibodies. We quantitatively compared the amount of [H-3]-AZT bound to telomeric and non-telomeric sequences of CHO cell DNA. DNA from cells exposed to [H-3]-AZT was digested by a mixture of restriction enzymes, frequent cutters in the overall genome, without restriction sites in the telomeric repeat. As a result, the telomeric fraction (TF): isolated by separation columns, comprised longer sequences (> 2 kb) than the non-telomeric fraction (NTF). Radioactivity associated with each fraction revealed a three fold increase in [H-3]-AZT incorporated in the TF compared with the NTF. No preferential telomeric binding was detected for [H-3]-thymidine (Tdr) or [H-3]-5'bromodeoxyuridine (BrdU) in similar experiments or in DNA of AZT-treated mouse primary fibroblasts, cells with large telomeric repeats that lack telomerase. When the chromosomal ends of high molecular weight [H-3]-AZT-DNA were digested with Pal 31, the radioactivity was double in the TF compared with the NTF. Therefore incorporation of AZT in CHO immortalized cells but not in primary fibroblasts (that lack telomerase) indirectly shows that AZT incorporation could be telomerase-mediated.  相似文献   
65.
The circadian timekeeping system exhibits many functional changes with aging, including a loss of sensitivity to time cues such as systemic injections of the serotonergic agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). In order to elucidate the neurochemical mechanisms responsible for this age-related loss of sensitivity of the circadian pacemaker to serotonin agonists, the present study used quantitative autoradiography to determine whether aging decreases serotonin receptor populations in male Syrian hamsters. Four neuroanatomical regions that regulate circadian timekeeping were studied (the suprachiasmatic nuclei [SCN], the lateral geniculate nuclei [LGN], and the median raphe nucleus [MRN] and dorsal raphe nucleus [DRN]). The specific binding of [3H]8-OH-DPAT to serotonin7 (5-HT7) and serotonin1A (5-HT1A) receptors was investigated by competitive inhibition with ritanserin and pindolol, respectively. The results showed that the SCN, IGL, MRN, and DRN of the male Syrian hamster exhibited specific binding of [3H]8-OH-DPAT to both the 5-HT7 and 5-HT1A receptors, and that the latter receptor subtype is more abundant in all of these regions. At 17-19 months of age, a 50% decrease in 5-HT7 receptors was found in the DRN but not in any other regions. No significant age-related changes in 5-HT1A receptors were observed in any regions examined. The finding that a marked decrease in 5-HT7 receptors occurs in the DRN at the age previously characterized by loss of sensitivity to 8-OH-DPAT suggests that this region and this receptor subtype play important roles in 8-OH-DPAT induction of circadian phase shifts in vivo and that they constitute an important locus of aging in the circadian timing system.  相似文献   
66.
Women in the United States, particularly African-Americans and Hispanics, are at increased risk for HIV. The female condom now offers women a potentially important option for HIV prevention, yet few efforts have been made to increase its use. To elucidate strategies to promote the use of the female condom, we conducted in-depth interviews with 62 women recruited from the four major racial/ethnic groups of the U.S. (African-American, Asian-American, Hispanic, and white). Subject recruitment took place at a family planning clinic in San Francisco during 1996-97. We identified four major types of facilitators and barriers to use of the female condom: mechanical, psychosexual, interpersonal, and situational. Specifically, the mechanical facilitators and barriers included positive and negative aspects of the device, and difficulty with insertion. The psychosexual factors were female empowerment, more options for contraception and disease prevention, discomfort with vaginal insertion, and condom use norms. The interpersonal factors included: enhanced communication, relationship status, partner preferences, and partner objections. Finally, the situations that made women disinclined to use the device were: no access to the female condom when having sex and using other forms of contraceptives. The implications of these findings for HIV prevention and future research are discussed.  相似文献   
67.
We have investigated the role of coagulation and fibrinolysis during the metastatic lung colonization of F3II mouse mammary carcinoma cells. The selective synthetic urokinase inhibitor B623 significantly enhanced lung colonization and blocked the antimetastatic effect of heparin when administered i.p. during the first stages of metastasis formation. In B623-treated mice the overall activity of the fibrinolytic system was reduced and circulating urokinase was specifically inhibited by this agent. In vitro studies demonstrated that B623 induces the aggregation of F3II cells in the presence of mouse plasma and facilitates the entrapment of tumor cells in a fibrin gel matrix. Our data suggest that imbalances of fibrin deposition and removal may dramatically influence metastatic lung colonization.  相似文献   
68.
Summary Taurine, a putative inhibitory neurotransmitter, was injected in various doses intracerebroventricularly to conscious rats via pre-implanted polythene cannulas. The formation of DOPA and 5-hydroxytryptophan (5-HTP) in various brain regions was investigated by measuring the accumulation of these monoamine precursors induced within 30 min by the intraperitoneal injection of 3-hydroxybenzyl hydrazine HCl (NSD 1015, 100 mg/kg), an inhibitor of the aromatic L-amino acid decarboxylase readily penetrating into the brain. DIPA formation, but not 5-HTP formation was significantly enhanced by taurine in dose-related manner in all brain regions studied, indicating an increased synthesis of both dopamine and noradrenaline. Dopamine depletion induced by -methyltyrosine was significantly retarded by taurine, whereas noradrenaline depletion tended to be enhanced. Endogenous levels of dopamine were increased, whereas the following brain constituents were unchanged: tyrosine, tryptophan, noradrenaline, 5-HT and 5-hydroxyindoleacetic acid. In the exoeriments with NSD 1015, a dose-related decrease in rectal temperature and in motility was observed after taurine treatment, as compared to treatment with the decarboxylase inhibotor alone. Systemic parenteral administration of taurine caused no significant changes in brain monoamines, body temperature or behaviour but decreased the heart noradrenaline levels. The data indicate that taurine, which apparently has to be given intracerebroventricularly in order to reach the brain in sufficient amounts, causes inhibition of firing in central dopamine neurons but has the opposite effect on noradrenaline neurons, perhaps also peripherally, whereas 5-HT neurons appear to be unaffected. In addition, taurine appears to interfere with motor behaviour and temperature regulation, possibly via effects on catecholaminergic systems.  相似文献   
69.
The purpose of these experiments was to study the incidence of stress ulcers in restrained rats and to correlate it with hypothalamic and adrenal cortical and medullary activity, with and without vagotomy. A total of 217 adult rats were used, grouped into 56 sets, and distributed at random in 5 experimental groups. Restraint was followed by a 79% incidence of ulceration in the glandular portion of the gastric mucosa. Vagotomy made these worse (p<0.01). Hypothalamic levels of catecholamines and serotonin showed no significant changes. Urinary measurements revealed decreased excretion of 17-ketosteroids (p<0.001), increased excretion of uropepsinogen (p<0.01), and no significant changes in vanillylmandelic acid among the rats submitted to immobilization. In the adrenal glands of stressed animals, there was a decreased level of catecholamines (p<0.01) and no significant changes in corticosteroid content (17-ketosteroids). These results suggest that hypothalamic stimulation and the participation of the adrenal glands are not essential factors in the pathogenesis of restraint-induced experimental stress ulcer.  相似文献   
70.
Percutaneous dilatational tracheostomy (PDT) is being increasingly used. Concerns have been raised as to its safety, especially when it is done at the bedside. A prospective evaluation was conducted of 100 consecutive, unselected critically ill patients with PDT. The mean intensive care unit (ICU) stay before PDT was 12 days. One surgeon performed PDT alone (5 cases) or assisted residents (95 cases) in all operations; 84 were performed at the ICU bedside. Only the first six patients were taken to the operating room solely for tracheostomy. A modified technique was used: (1) the endotracheal tube was left in place during sequential dilations; (2) dilators were inserted in a 60-degree cephalad orientation to the skin and directed caudally after penetration of the anterior tracheal wall; (3) a digit was inserted through the tracheal opening to guide withdrawal of the endotracheal tube to the level of the vocal cords; and (4) size 8 tracheostomy cannulas were inserted over 28F dilators. The average time from skin incision to insertion of the tracheostomy tube was 12 minutes (< 10 minutes, 41 patients; 10 to 15 minutes, 37 patients; > 15 minutes, 22 patients). Sixty-five percent had unfavorable anatomic conditions due to spinal precautions or diffuse neck edema. Postoperative complications occurred in four patients; surgical emphysema after tracheal lacerations in three, cannula dislodgment in one. All complications were successfully managed without an operation by tube exchange (n= 3) or observation (n= 1); there was no procedure-related mortality. Forty patients were available for long-term follow-up (6–18 months after tracheostomy) by telephone; one had persistent hoarseness without respiratory difficulty. We concluded that bedside PDT is safe and easy to teach when performed with a technique that ensures correct instrumentation.  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