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   124520篇
  免费   10421篇
  国内免费   5762篇
耳鼻咽喉   1016篇
儿科学   2445篇
妇产科学   2054篇
基础医学   14257篇
口腔科学   2624篇
临床医学   12235篇
内科学   19038篇
皮肤病学   1802篇
神经病学   8509篇
特种医学   3183篇
外国民族医学   32篇
外科学   11486篇
综合类   20975篇
现状与发展   16篇
预防医学   9598篇
眼科学   3133篇
药学   11464篇
  42篇
中国医学   4504篇
肿瘤学   12290篇
  2024年   330篇
  2023年   1530篇
  2022年   3475篇
  2021年   4442篇
  2020年   4022篇
  2019年   3528篇
  2018年   3451篇
  2017年   4026篇
  2016年   4382篇
  2015年   4323篇
  2014年   7917篇
  2013年   8553篇
  2012年   8073篇
  2011年   8835篇
  2010年   7392篇
  2009年   7013篇
  2008年   7222篇
  2007年   7159篇
  2006年   6426篇
  2005年   5660篇
  2004年   4747篇
  2003年   4148篇
  2002年   3353篇
  2001年   3026篇
  2000年   2522篇
  1999年   2197篇
  1998年   1861篇
  1997年   1597篇
  1996年   1427篇
  1995年   1302篇
  1994年   1077篇
  1993年   828篇
  1992年   716篇
  1991年   574篇
  1990年   540篇
  1989年   406篇
  1988年   345篇
  1987年   269篇
  1986年   229篇
  1985年   346篇
  1984年   305篇
  1983年   174篇
  1982年   235篇
  1981年   152篇
  1980年   170篇
  1979年   126篇
  1978年   76篇
  1977年   52篇
  1976年   47篇
  1975年   32篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Objective: To explore the expression level and its clinical significance of hypoxia inducible factor 1α (HIF-1α) in non-small lung cancer. Methods: The expression of HIF-1α was detected in 68 human non-small lung cancer samples by immunohistochemistry. Results: (1) Thirty-nine (57.35%) out of the 68 human non-small lung cancer samples was positive for HIF-1α; (2) The positive rate of HIF-1α in adenocarcinoma and squamous carcinoma was 54.76% (23/42) and 61.54% (16/26) respectively. No significant difference was found between adenocarcinoma and squamous carcinoma of non-small lung cancer in the expression of HIF-1α (P>0.05). The positive rate of HIF-1α in middle-high differentiation was 74.28% (26/35), significantly higher than in low differentiation (39.39%, 13/33) (P<0.05); (3) The positive expression of HIF-1α was not correlated to the sexes, ages, tumor stage and lymph node status. Conclusion: The expression of HIF-1α is higher in non-small lung cancer and is correlated to differentiation.  相似文献   
52.
AIM: The aim of this study was to investigate the nature and organization of maternal needs and priorities in a neonatal unit. BACKGROUND: The relationship between maternal needs and priorities appears to be an under studied area in neonatal nursing. METHODS: A quantitative survey was carried out based on 209 mothers with premature infants. Two self-assessment schedules were used: critical care maternal needs inventory (J. Leske, Heart and Lung 15, 27-42) and a ranking scale. The data were analysed with multivariate analysis. FINDINGS: Data analysis revealed clear priorities in maternal needs. In particular the need for accurate infant related information was a priority for 93% of the mothers. Good communication practices with professionals were also valued. The mothers displayed altruistic behaviour, and self-related needs took second place. It is proposed that maternal needs demonstrate a hierarchical organization. CONCLUSION: It is important for nurses to consider the individual needs of the mothers, simply because the satisfaction of these needs is essential for maternal well-being.  相似文献   
53.
目的 探讨产后出血的原因与影响因素。方法 回顾分析收治的产后出血 15 9例 ,数据处理采用χ2 检验。结果 产后出血发生率 3.5 % ,产后 2小时内出血者 88.6 7% ,出血原因宫缩乏力为 6 6 .6 7% ,影响因素有手术产、流产史、分娩史、妊娠合并症及产程延长等 ,统计学处理P <0 .0 1。结论 重视产后出血的影响因素 ,正确评估出血量及产妇产后 2小时留置产房观察是产后出血早期诊断的关键 ,其预防重点在于早期发现并针对不同原因及时正确处理  相似文献   
54.
通过观察益肾化浊注射液对5/6肾切除大鼠残余肾中细胞因子含量的影响,益肾化浊注射液延缓慢性肾功能衰竭(CRF)模型大鼠肾功能减退的作用机理。结果显示:益肾化浊注射液可以降低5/6肾切在鼠血清肌,尿素氮(P<0.01),下调肾组织中白细胞介素-1(IL-1)(P<0.05),白细胞介素-8(IL-8)(P<0.05)及肿瘤坏死因子(TNF)(P<0.05)的总体水平,说明益肾化浊注射液可以通过下调5/6肾切除大鼠残余肾中相关细胞因子含量,抑制促炎细胞因子对肾脏的损害,从而延缓CRF的进展。  相似文献   
55.
Our previous work indicated that in E14 embryonic rat spinal cord cultures ciliary neuronotrophic factor (CNTF) exerted (1) a survival-promoting effect on motor neurons and on a large population of unidentified neurons, and (2) a regulatory role on the expression of ChAT and low affinity NGF receptor (LNGFR) in a population of small/medium-sized neurons. In the present study, we examined the effect of CNTF on the expression of LNGFR in cultures of different regions from the E18 embryonic rat brain, namely cortex, septum, striatum, mesencephalon, hippocampus, brainstem, and cerebellum. The number of LNGFR-positive neurons (stained with the 192-IgG monoclonal antibody) was determined in untreated cultures and in cultures treated for 6 days (0-6) with human recombinant CNTF. To distinguish between effects on survival and on LNGFR expression, experiments were performed in which CNTF was administered only for the last 48 h of the culture (from days 4-6). LNGFR positive neurons were found in the cultures of all the regions examined. In each one of them, CNTF increased the number of LNGFR-positive neurons by three- to fourfold after 6 days of treatment. In the striatum, septum, mesencephalon, and cerebellum, the effect of CNTF was shown to be on the regulation of LNGFR expression and not on survival. In cultures from the cortex, hippocampus and brainstem, a survival-promoting role of CNTF could be demonstrated. The effect of CNTF was dose dependent, with half-maximal effects (ED50) achieved at 2-4.5 TU/ml for all the brain regions. Maximal effects were reached at 100-250 TU/ml. From these results, we conclude that (1) there exists a wide spectrum of CNTF-responsive neurons in the central nervous system, and (2) CNTF plays an important and widespread role in regulating the expression of the LNGFR in neurons.  相似文献   
56.
Magnetic resonance (MR) imaging may be a noninvasive method for assessing perfusion of vascularized bone grafts placed for treatment of avascular necrosis. One proximal femur of seven beagles was devascularized, with insertion of a vascularized fibular graft. MR imaging at 1 week (seven dogs) and 6 weeks (five dogs) after surgery included pre- and postcontrast spin-echo sequences, unenhanced twodimensional time-of-flight (TOF) vascular imaging, and dynamic gradient-echo imaging during infusion of gadolinium. Relative signal intensity values of selected regions obtained from the dynamic gradientecho images were plotted as percent enhancement versus time. In the operated hip, MR imaging did not show enhancement in six of seven femoral heads and greater trochanters at 1 week after surgery, with similar results after 6 weeks. MR imaging of fibular grafts 6 weeks after surgery showed an initial rapid increase in enhancement and a subsequent slower increase in five of five dogs, although no enhancement was seen in six of seven dogs at 1 week. These findings contrasted with a rapid initial increase in enhancement followed by slow decline in non-operated hips. Two-dimensional TOP imaging did not show the vascular pedicle of the graft in any dog. Findings of radionuclide bone scanning performed 1 week after surgery were consistent with devascularization of the operated femur and fibular graft. However, tetracycline distribution and histologic findings confirmed the viability of five of five grafts within the devascularized femurs 6 weeks after surgery. Thus, dynamic contrast-enhanced MR imaging at 6 weeks after surgery is valuable for assessing vascular bone graft perfusion, while similar imaging at 1 week may suggest otherwise.  相似文献   
57.
58.
BACKGROUND: The serum circulatory levels of apoptosis related molecules measured in patients with oral lichen planus (OLP) and healthy individuals in order to investigate possible alterations associated with the clinical forms of OLP. METHODS: Serum levels of tumor necrosis factor (TNF)-alpha, soluble Fas (sFas) and Bcl-2 studied by enzyme-linked immunosorbent assay in whole blood samples in 13 OLP reticular, 13 OLP atrophic-erosive form patients and 26 healthy subjects. RESULTS: Significantly elevated levels of TNF-alpha and sFas detected in OLP patients as compared with controls. Serum concentrations of Bcl-2 although increased in 17/26 patients, they were not statistically significant. Reticular OLP exhibited slightly elevated TNF-alpha and significantly elevated Bcl-2 serum levels, compared with erosive OLP. CONCLUSIONS: These data suggest that a putative dysfunction in the Fas/FasL mediated apoptosis might be involved in the OLP pathogenesis. A downregulation of Bcl-2 serum levels in the atrophic-erosive OLP may be associated with promotion of the disease activity.  相似文献   
59.
The treatment times for the fabrication of Extensive Amalgam Restorations (EAR) as recorded in a longitudinal clinical trial at the Dental School in Nijmegen were analyzed. 269 EAR's with different retention methods were made on molars by three operators. A mean total treatment time of 60 min was found. The factor operator had a significant influence on all treatment phases resulting in a 26% difference in total treatment time between operators. Also significant influences were found in some treatment phases for the factor retention, side location of the tooth and extension of the restoration. The results of this study with regard to treatment times must be considered from the perspective of the quality of the care provided.  相似文献   
60.
目的 探讨脑囊虫病患者各期脑脊液中的一氧化氮 (NO)、肿瘤坏死因子α(TNF α)的变化规律及它们在脑囊虫病中的作用机制。方法 检测 4 9例明确诊断并依据MR分期 ,单发脑实质内囊虫的脑囊虫病患者和 2 0名对照者脑脊液中NO、TNF α水平。结果 NO在脑囊虫病的Ⅰ期显著降低而TNF α水平呈显著升高 ,NO、TNF α于Ⅱ期、Ⅲ期 (整个退变死亡期 )均表现为高水平 ,Ⅳ期恢复正常 ,NO和TNF α存在高度正相关关系。结论 在单发脑实质内囊虫病中NO、TNF α可能参与杀虫作用 ,其免疫调节与杀虫机制存在着动态平衡 ,参与感染控制  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