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   399056篇
  免费   26858篇
  国内免费   4371篇
耳鼻咽喉   5407篇
儿科学   8501篇
妇产科学   10397篇
基础医学   55778篇
口腔科学   12164篇
临床医学   32808篇
内科学   81469篇
皮肤病学   8794篇
神经病学   28328篇
特种医学   14615篇
外国民族医学   97篇
外科学   62859篇
综合类   13164篇
现状与发展   7篇
一般理论   66篇
预防医学   18711篇
眼科学   9970篇
药学   33204篇
  14篇
中国医学   3164篇
肿瘤学   30768篇
  2021年   3240篇
  2020年   2426篇
  2019年   3383篇
  2018年   5291篇
  2017年   4094篇
  2016年   4145篇
  2015年   4978篇
  2014年   6938篇
  2013年   8402篇
  2012年   11674篇
  2011年   11893篇
  2010年   7192篇
  2009年   6675篇
  2008年   10640篇
  2007年   11449篇
  2006年   11371篇
  2005年   10559篇
  2004年   9533篇
  2003年   9250篇
  2002年   8832篇
  2001年   28743篇
  2000年   29364篇
  1999年   24234篇
  1998年   5437篇
  1997年   4515篇
  1996年   4014篇
  1995年   3797篇
  1994年   3351篇
  1993年   3021篇
  1992年   16291篇
  1991年   15022篇
  1990年   14358篇
  1989年   14147篇
  1988年   12737篇
  1987年   12171篇
  1986年   11211篇
  1985年   10435篇
  1984年   6950篇
  1983年   5639篇
  1982年   2730篇
  1979年   5495篇
  1978年   3355篇
  1977年   2971篇
  1975年   2643篇
  1974年   3083篇
  1973年   2876篇
  1972年   2844篇
  1971年   2784篇
  1970年   2519篇
  1969年   2556篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.

Background

Previous studies suggest that dexmedetomidine has a protective effect against local anaesthetic-induced nerve injury in regional nerve blocks. Whether this potentially protective effect exists in the context of diabetes mellitus is unknown.

Methods

A diabetic state was established in adult male Sprague–Dawley rats with intraperitoneal injection of streptozotocin. Injections of ropivacaine 0.5%, dexmedetomidine 20 μg kg?1 (alone and in combination), or normal saline (all in 0.2 ml) were made around the sciatic nerve in control and diabetic rats (n=8 per group). The duration of sensory and motor nerve block and the motor nerve conduction velocity (MNCV) were determined. Sciatic nerves were harvested at post-injection day 7 and assessed with light and electron microscopy or used for pro-inflammatory cytokine measurements.

Results

Ropivacaine and dexmedetomidine alone or in combination did not produce nerve fibre damage in control non-diabetic rats. In diabetic rats, ropivacaine induced significant nerve fibre damage, which was enhanced by dexmedetomidine. This manifested with slowed MNCV, decreased axon density, and decreased ratio of inner to outer diameter of the myelin sheath (G ratio). Demyelination, axon disappearance, and empty vacuoles were also found using electron microscopy. An associated increase in nerve interleukin-1β and tumour necrosis factor-α was also seen.

Conclusions

Ropivacaine 0.5% causes significant sciatic nerve injury in diabetic rats that is greatly potentiated by high-dose dexmedetomidine. Although the dose of dexmedetomidine used in this study is considerably higher than that used in clinical practice, our data suggest that further studies to assess ropivacaine (alone and in combination with dexmedetomidine) use for peripheral nerve blockade in diabetic patients are warranted.  相似文献   
82.
83.

Background

In cardiothoracic surgery, little data exist on the transition to operative independence. We aimed to compare current perceptions of operative autonomy of junior cardiothoracic surgeons and senior colleagues who oversee transitional years.

Methods

An anonymous online survey was sent to currently practicing North American board-certified/eligible cardiothoracic surgeons to assess reported time to operative independence and comfort with cardiothoracic operations. The χ2 test, Fisher exact test, and Mann-Whitney U test were used to compare junior surgeons’ self-reported experience to the junior experience as reported by the midcareer and senior surgeons with whom they practiced. Logistic regression was performed to assess factors associated with operative independence.

Results

Responses from 436 completed surveys were analyzed (82 juniors and 354 midcareer/seniors). Two hundred fifty-four midcareer/senior surgeons reported on the experience of 531 junior partners. Juniors reported high immediate posttraining comfort with basic cardiac cases and moderate comfort with all other categories. Time to operative independence was significantly different between juniors' self-report and midcareer/senior reports of junior partners except for complex thoracic cases. In multivariable logistic regression analysis, senior, and not midcareer, surgeon status was independently associated with junior operative independence status for cardiac cases and for basic thoracic cases.

Conclusions

Most junior surgeons perceived operative independence with basic thoracic, basic cardiac, and complex cardiac operations earlier in their surgical career than that reported by senior colleagues. Objective measures of operative independence may clarify this discrepancy. This study establishes a baseline by which to compare the effects of integrated 6-year programs on operative independence. The discrepant perceptions may have implications for how training programs prepare graduates for the transition to independent practice.  相似文献   
84.

Introduction

Breast cancer incidence increases from the age of 30 years. As this age range coincides with that in which women usually pursue pregnancy, undergoing medical examinations for conditions such as breast cancer is a concern, especially when pregnancy is uncertain during the first eight weeks. Moreover, in this age range, breast often exhibits a high density, thus compromising diagnosis. For such density, digital breast tomosynthesis (DBT) provides a more accurate diagnosis than 2D mammography given its higher sensitivity and specificity. However, radiation exposure increases during DBT, and it should be determined.

Methods

We determined the entrance surface dose, scattered radiation dose, and average glandular dose (AGD), which can be mutually compared following an international protocol. Using our proposed method, the distribution of scattered radiation can be easily and quickly obtained with a minor load to the equipment. Then, we can determine the indoor scattered radiation and surface dose on patients during DBT.

Results

We obtained a maximum AGD of 2.32 mGy. The scattered radiation was distributed over both sides with maximum of approximately 40 μGy, whereas the maximum dose around the eye was approximately 10 μGy.

Conclusion

By measuring doses using the proposed method, a correct dose information can be provided for patients to mitigate their concerns about radiation exposure. Although the obtained doses were low, their proper management is still required. Overall, the results from this study can help to enhance dose management for patients and safety management regarding indoor radiation.  相似文献   
85.
86.
Objective: This cross-sectional study assessed the effect of food donations on total nutrient intake of clients of a food pantry in Central Texas.

Methods: Nutrient intakes of total, base and food donation diets were estimated for 112 food pantry recipients using specific questionnaires; and then compared to the dietary reference intakes (DRI) and 2015–2020?US Dietary Guidelines.

Results: Food donations accounted for more than half of the client’s daily intake of energy, carbohydrates, vitamin B6, phosphorus, copper and selenium. Yet, daily total intake remained less than their DRIs for carbohydrates, poly-unsaturated fats, dietary fiber, fat soluble vitamins and vitamin C, and was even lower for calcium, magnesium and potassium. Total food intake of clients almost met the US Dietary Guidelines for refined grains, fruits, vegetables, and meat; however, the amount of whole grains and dairy was inadequate.

Conclusions: Supplemental foods offered at food pantries are an important resource for improving nutrient intake of low-income populations.  相似文献   

87.
88.
89.
目的:以自发性2型糖尿病GK大鼠为研究对象,应用全基因组表达谱芯片技术,旨在探讨参芪复方调节胰岛细胞功能的分子机制,为中医药防治2型糖尿病提供理论依据。方法:GK大鼠每日给予高脂饲料喂养,连续4周,随机从GK大鼠中选取大鼠检测随机血糖,验证2型糖尿病模型成功。实验分为4组,空白组,模型组,参芪复方组(1.44 g?kg~(-1)),西格列汀组(16 mg·kg~(-1)),于灌胃前、灌胃4周、灌胃8周测早上8:00各组大鼠尾尖血糖;灌胃8周后,运用酶联免疫吸附测定(ELISA)检测大鼠血清胰岛素(INS)水平;采用原位末端标记(TUNEL)荧光法定量检测并观察胰岛β细胞凋亡情况;运用全基因组表达谱芯片技术对各组大鼠胰腺组织进行差异基因检测;采用实时荧光定量聚合酶链式反应(Real-time PCR)检测关键差异基因的mRNA转录水平。结果:与空白组比较,灌胃前、灌胃4周、灌胃8周,GK大鼠各组血糖显著升高(P0.01);灌胃4,8周,与模型组比较,各药物干预组大鼠血糖均显著较低(P0.01)。灌胃8周,与空白组比较,模型组大鼠INS水平显著较低(P0.01);与模型组比较,参芪复方组具有INS水平更高的趋势,西格列汀组INS水平显著较高(P0.01)。灌胃8周,与空白组比较,模型组大鼠胰岛β细胞凋亡数明显升高(P0.05);与模型组比较,参芪复方组、西格列汀组大鼠胰岛β细胞凋亡数均明显较低(P0.05,P0.01)。基因芯片及Real-time PCR检测均显示磷脂酰肌醇3-激酶受体1(PIK3R1)在参芪复方组/模型组中表达上调,在西格列汀组/模型组、模型组/空白组中表达下调;蛋白激酶B1(Akt1)在参芪复方组/模型组、西格列汀组/模型组中表达上调,在模型组/空白组中表达下调。结论:参芪复方可减少胰岛β细胞凋亡,增加胰岛素分泌,上调基因PIK3R1,Akt1的表达,推测具有养阴益气活血功效的参芪复方可能通过上调基因PIK3R1,Akt1的表达,抑制胰岛β细胞凋亡,改善胰岛β细胞功能,调节胰岛素分泌,从而防治2型糖尿病。  相似文献   
90.
Protein homeostasis is critical for maintaining eukaryotic cell function as well as responses to intrinsic and extrinsic stress. The proteasome is a major portion of the proteolytic machinery in mammalian cells and plays an important role in protein homeostasis. Multiple myeloma (MM) is a plasma cell malignancy with high production of immunoglobulins and is especially sensitive to treatments that impact protein catabolism. Therapeutic agents such as proteasome inhibitors have demonstrated significant benefit for myeloma patients in all treatment phases. Here, we demonstrate that the 11S proteasome activator PA28α is upregulated in MM cells and is key for myeloma cell growth and proliferation. PA28α also regulates MM cell sensitivity to proteasome inhibitors. Downregulation of PA28α inhibits both proteasomal load and activity, resulting in a change in protein homeostasis less dependent on the proteasome and leads to cell resistance to proteasome inhibitors. Thus, our findings suggest an important role of PA28α in MM biology, and also provides a new approach for targeting the ubiquitin-proteasome system and ultimately sensitivity to proteasome inhibitors.Subject terms: Myeloma, Translational research  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