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   4023篇
  免费   231篇
  国内免费   43篇
耳鼻咽喉   74篇
儿科学   81篇
妇产科学   84篇
基础医学   501篇
口腔科学   51篇
临床医学   344篇
内科学   834篇
皮肤病学   40篇
神经病学   260篇
特种医学   330篇
外科学   608篇
综合类   74篇
一般理论   2篇
预防医学   230篇
眼科学   195篇
药学   335篇
中国医学   8篇
肿瘤学   246篇
  2023年   21篇
  2022年   34篇
  2021年   73篇
  2020年   34篇
  2019年   62篇
  2018年   81篇
  2017年   50篇
  2016年   59篇
  2015年   79篇
  2014年   102篇
  2013年   158篇
  2012年   194篇
  2011年   207篇
  2010年   166篇
  2009年   139篇
  2008年   175篇
  2007年   181篇
  2006年   164篇
  2005年   161篇
  2004年   142篇
  2003年   131篇
  2002年   153篇
  2001年   76篇
  2000年   95篇
  1999年   90篇
  1998年   88篇
  1997年   68篇
  1996年   69篇
  1995年   51篇
  1994年   59篇
  1993年   58篇
  1992年   71篇
  1991年   84篇
  1990年   67篇
  1989年   81篇
  1988年   83篇
  1987年   89篇
  1986年   46篇
  1985年   56篇
  1984年   46篇
  1983年   34篇
  1982年   46篇
  1981年   35篇
  1980年   41篇
  1979年   29篇
  1978年   28篇
  1977年   25篇
  1976年   26篇
  1974年   16篇
  1971年   14篇
排序方式: 共有4297条查询结果,搜索用时 15 毫秒
51.
To define the effects of acute hyperglycemia per se (i.e., without the confounding effect of hyperinsulinemia) in human tissues in vivo, we performed global gene expression analysis using microarrays in vastus lateralis muscle and subcutaneous abdominal adipose tissue of seven healthy men during a hyperglycemic-euinsulinemic clamp with infusion of somatostatin to inhibit endogenous insulin release. We found that doubling fasting blood glucose values while maintaining plasma insulin in the fasting range modifies the expression of 316 genes in skeletal muscle and 336 genes in adipose tissue. More than 80% of them were downregulated during the clamp, indicating a drastic effect of acute high glucose, in the absence of insulin, on mRNA levels in human fat and muscle tissues. Almost all the biological pathways were affected, suggesting a generalized effect of hyperglycemia. The induction of genes from the metallothionein family, related to detoxification and free radical scavenging, indicated that hyperglycemia-induced oxidative stress could be involved in the observed modifications. Because the duration and the concentration of the experimental hyperglycemia were close to what is observed during a postprandial glucose excursion in diabetic patients, these data suggest that modifications of gene expression could be an additional effect of glucose toxicity in vivo.  相似文献   
52.
BACKGROUND & AIMS: In patients with severe, necrotizing pancreatitis, it is common to administer early, broad-spectrum antibiotics, often a carbapenem, in the hope of reducing the incidence of pancreatic and peripancreatic infections, although the benefits of doing so have not been proved. METHODS: A multicenter, prospective, double-blind, placebo-controlled randomized study set in 32 centers within North America and Europe. Participants: One hundred patients with clinically severe, confirmed necrotizing pancreatitis: 50 received meropenem and 50 received placebo. Interventions: Meropenem (1 g intravenously every 8 hours) or placebo within 5 days of the onset of symptoms for 7 to 21 days. Main Outcome Measures: Primary endpoint: development of pancreatic or peripancreatic infection within 42 days following randomization. Other endpoints: time between onset of pancreatitis and the development of pancreatic or peripancreatic infection; all-cause mortality; requirement for surgical intervention; development of nonpancreatic infections within 42 days following randomization. RESULTS: Pancreatic or peripancreatic infections developed in 18% (9 of 50) of patients in the meropenem group compared with 12% (6 of 50) in the placebo group (P = 0.401). Overall mortality rate was 20% (10 of 50) in the meropenem group and 18% (9 of 50) in the placebo group (P = 0.799). Surgical intervention was required in 26% (13 of 50) and 20% (10 of 50) of the meropenem and placebo groups, respectively (P = 0.476). CONCLUSIONS: This study demonstrated no statistically significant difference between the treatment groups for pancreatic or peripancreatic infection, mortality, or requirement for surgical intervention, and did not support early prophylactic antimicrobial use in patients with severe acute necrotizing pancreatitis.  相似文献   
53.
Forty cases of mesodermal adenosarcoma of the ovary occurred in women 30-84 years of age (mean 54 years). Abdominal discomfort and distension were the usual complaints. All the patients were treated with an oophorectomy, which was accompanied by a hysterectomy in 85%, a contralateral oophorectomy in 65%, and nonsurgical therapy in 28%. Tumor rupture occurred at or before the operation in 67% of the cases. Twenty-six tumors were stage I, 11 stage II, and 3 stage III. The tumors were unilateral in 97.5% of the cases and 5.5-50 cm (mean 14 cm) in greatest dimension; most of the tumors were predominantly solid but contained numerous small cysts. Microscopic examination revealed sarcomatous overgrowth in 12 tumors. Sex cord-like elements were present in six tumors (including four with sarcomatous overgrowth) and heterologous elements in five (including two with sarcomatous overgrowth). The highest mitotic index of the sarcomatous component was 1-25 (mean 6) mitotic figures per 10 high power fields. Only 6 of 26 women (23%) who were followed postoperatively for > or=5 years were free of tumor. In the other 20 patients recurrent tumor appeared at 0.4-6.6 years (mean 2.6 years) after operation as pure sarcoma (low grade or high grade) or adenosarcoma (with or without sarcomatous overgrowth). Eight women had additional recurrences, and four women had blood-borne metastases. One patient was alive at 15.7 years after the excision of pulmonary metastases. The 5-, 10-, and 15-year survival rates were 64%, 46%, and 30%, respectively. Age <53 years, tumor rupture, a high grade, and the presence of high-grade sarcomatous overgrowth appeared to be associated with recurrence or extraovarian spread. Ovarian adenosarcomas have a worse prognosis than uterine adenosarcomas, presumably because of the greater ease of peritoneal spread. Many of the tumors caused problems in differential diagnosis.  相似文献   
54.

Introduction and hypothesis

The aim was to assess the efficacy of three-compartment pelvic organ prolapse (POP) vaginal repair using the InteXen® biocompatible porcine dermal graft as compared to traditional colporrhaphy with sacrospinous ligament suspension.

Methods

Preoperative, operative, postoperative and follow-up data were collected retrospectively. Objective recurrence was defined as POP quantification ≥ stage II and subjective recurrence as a symptomatic bulge.

Results

Each group consisted of 63 patients. Surgery time was longer using InteXen® (72?±?24.5 vs 55?±?23.5 min, p?=?0.0002). Length of hospital stay (4.6?±?1.6 vs 4.9?±?2.1 days, p?=?0.34) as well as duration of follow-up (37.1 vs 35.7 months, p?=?0.45) were equivalent between the two groups. No case of mesh erosion or infection was noted. The objective (17% vs 8%, p?=?0.12) and subjective recurrence rates (13% vs 5%, p?=?0.12) between the two groups were not statistically different.

Conclusions

InteXen® was well tolerated but had similar efficacy to traditional colporrhaphy and sacrospinous ligament suspension.  相似文献   
55.
56.
Castle  V; Coates  G; Kelton  JG; Andrew  M 《Blood》1987,70(3):652-656
Thrombocytopenia is a common occurrence (20%) in sick neonates, but the causes have not been well studied. In this report we demonstrate that thrombocytopenia in the neonate is characterized by increased platelet destruction as shown by shortened homologous 111In-oxine-labeled platelet life spans. Thirty-one prospectively studied thrombocytopenic neonates were investigated by measuring the 111In-labeled platelet life span, platelet-associated IgG (PAIgG), and coagulation screening tests. In every infant, the thrombocytopenia was shown to have a destructive component since the mean platelet life span was significantly shortened to 65 +/- 6 (mean +/- SEM) hours with a range of one to 128 hours compared with adult values (212 +/- 8; range, 140 to 260; gamma function analysis). The platelet survival was directly related to the lowest platelet count and inversely related to both the highest mean platelet volume and duration of the thrombocytopenia. In 22 infants the percent recovery of the radiolabeled platelets was less than 50%, which suggested that increased sequestration also contributed to the thrombocytopenia. Infants with laboratory evidence of disseminated intravascular coagulation (n = 8) or immune platelet destruction evidenced by elevated levels of PAIgG (n = 13) had even shorter platelet survivals and a more severe thrombocytopenia compared with the ten infants in whom an underlying cause for the thrombocytopenia was not apparent. Full-body scintigraphic images obtained in 11 infants showed an increased uptake in the spleen and liver, with a spleen-to- liver ratio of 3:1. This study indicates that thrombocytopenia in sick neonates is primarily destructive, with a subgroup having evidence of increased platelet sequestration.  相似文献   
57.
Heparin-induced thrombocytopenia is characterized by moderate thrombocytopenia and thrombotic complications, whereas quinine/quinidine-induced thrombocytopenia usually presents with severe thrombocytopenia and bleeding. Using flow cytometry and assays of procoagulant activity, we investigated whether sera from patients with these immune drug reactions could stimulate normal platelets to generate platelet-derived microparticles with procoagulant activity. Sera or purified IgG from patients with heparin-induced thrombocytopenia stimulated the formation of platelet-derived microparticles in a heparin-dependent fashion. Further studies showed that heparin-induced thrombocytopenia sera also produced a marked increase in procoagulant activity. In contrast, sera from patients with quinine- or quinidine-induced thrombocytopenia did not generate platelet-derived microparticles nor generate increased procoagulant activity. However, quinine/quinidine-induced thrombocytopenia sera produced a significant increase in the binding of IgG to platelets in a drug-dependent fashion, whereas sera from patients with heparin-induced thrombocytopenia demonstrated no drug-dependent binding of IgG to platelets. We also observed increased levels of circulating microparticles in patients with acute heparin-induced thrombocytopenia compared with control patients. Our observations indicate that the generation of procoagulant platelet-derived microparticles in vivo is a plausible explanation for the thrombotic complications observed in some patients with heparin-induced thrombocytopenia.  相似文献   
58.
蝙蝠葛中的新生物碱——蝙蝠葛新林碱   总被引:3,自引:0,他引:3  
防已科植物蝙蝠葛(Menispermum daurioum DC.)的根茎,即北豆根,是一种重要的中药,具有清热解毒、消肿止痛等功效。已知含有近二十种生物碱,其中五种属双苄基四氢异喹啉类,即蝙蝠葛碱(dauricine,Ⅰ)、蝙蝠葛诺林碱(daurinoline,Ⅱ)、蝙蝠葛新诺林碱  相似文献   
59.
Microtubule reassembly in surface-activated platelets   总被引:2,自引:0,他引:2  
White  JG; Krumwiede  M; Sauk  JJ 《Blood》1985,65(6):1494-1503
It is generally accepted that a circumferential microtubule supports the discoid shape of resting platelets. The fate of the many-coiled polymer following platelet activation, however, has been a subject of considerable debate. Morphological investigations have suggested that the circumferential coils are constricted into tight rings around centrally concentrated organelles during platelet shape change. Biochemical studies employing colchicine-binding assays, on the other hand, have indicated that the bundle of microtubules dissolves almost completely within seconds after activation and reassembles in a new location one to four minutes later. The present study has accepted the latter hypothesis in order to examine the second part of the disassembly-reassembly theory proposed in biochemical studies. Platelets exposed to low temperatures sufficient to remove all microtubules were placed on glass slides and microscope grids to cause surface activation during rewarming. The combined stimuli of rewarming and surface activation might have been expected to cause more rapid assembly than warming alone or activation alone. This was not the case. Reassembly of microtubules during rewarming and simultaneous surface activation was not accelerated. In contrast to the constriction of microtubule rings observed during activation in control platelets, the diameters of coils that developed in chilled platelets one to two hours after rewarming and surface activation were twice those of control cells.  相似文献   
60.
Activation of an intracellular calcium-calmodulin complex may play an important role in myocardial injury induced by ischemia and reperfusion. Trifluoperazine, a calmodulin antagonist, was used before ischemia to enhance myocardial preservation by preventing intracellular calcium accumulation. The experimental model used an isolated in situ pig heart (19 control animals and 15 trifluoperazine-treated animals) subjected to occlusion of the left anterior descending coronary artery for 60 minutes followed by 60 minutes of hypothermic potassium crystalloid cardioplegic arrest and 60 minutes of reperfusion. Myocardial segmental function measured by ultrasonic crystals showed that active systolic segment shortening was abolished in the distribution of the left anterior descending artery after 60 minutes of occlusion irrespective of the treatment, whereas that not in the distribution of the left anterior descending artery increased by about 15% in both groups of animals. Restoration of systolic segment shortening in the distribution of the left anterior descending artery 60 minutes after reperfusion was 12% and 42% of baseline levels in untreated and trifluoperazine-treated animals, respectively (p less than 0.01). This improvement in segmental function by trifluoperazine was reflected in significantly (p less than 0.05) better global myocardial contractility and compliance and in significantly (p less than 0.01) greater total coronary blood flow and myocardial oxygen consumption. Trifluoperazine also increased myocardial creatine phosphate content in the distribution of the left anterior descending artery (p less than 0.01) during reperfusion, and creatine kinase release was reduced (p less than 0.05). Our results suggest that trifluoperazine improved regional myocardial function after acute occlusion of the left anterior descending artery and reperfusion and that global cardiac performance was thereby improved. The beneficial effects of trifluoperazine may be exerted by prevention of myocardial injury associated with the calcium-calmodulin complex in ischemic and reperfused myocardium.  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