首页 | 官方网站   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   19068篇
  免费   1604篇
  国内免费   984篇
医药卫生   21656篇
  2024年   41篇
  2023年   267篇
  2022年   386篇
  2021年   824篇
  2020年   632篇
  2019年   584篇
  2018年   652篇
  2017年   545篇
  2016年   502篇
  2015年   817篇
  2014年   1058篇
  2013年   1032篇
  2012年   1457篇
  2011年   1591篇
  2010年   1034篇
  2009年   833篇
  2008年   1023篇
  2007年   1060篇
  2006年   1026篇
  2005年   948篇
  2004年   671篇
  2003年   633篇
  2002年   509篇
  2001年   445篇
  2000年   454篇
  1999年   522篇
  1998年   311篇
  1997年   316篇
  1996年   223篇
  1995年   196篇
  1994年   145篇
  1993年   109篇
  1992年   120篇
  1991年   98篇
  1990年   86篇
  1989年   69篇
  1988年   93篇
  1987年   79篇
  1986年   53篇
  1985年   45篇
  1984年   23篇
  1983年   21篇
  1982年   14篇
  1981年   13篇
  1980年   8篇
  1979年   28篇
  1978年   9篇
  1975年   8篇
  1974年   8篇
  1972年   7篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
971.
G6PD-deficient adults are reported to be susceptible to severe infection, and decreased cytokine responses have been postulated as the underlying mechanism. However, investigating the association of G6PD deficiency and cytokine responses during infancy is lacking. The current study aims to determine whether cytokine responses of tumor necrosis factor ()-α, interleukins (IL)-6, and IL-10 are impaired in the G6PD-deficient infants. Upon agreements with informed consents, peripheral blood mononuclear cells (PBMCs) of enrolled infants were collected twice at 1 month and 1 year of age. PBMCs were then stimulated with toll-like receptor (TLR) agonists—including PAM3csk4 for TLR1–2, poly (I:C) for TLR3, and lipopolysaccharide for TLR4—to analyze the expression of TNF-α, IL-6, and IL-10. Males (P = .004) and phototherapy during neonatal period (P = .008) were more common among G6PD-deficient infants than G6PD-normal subjects. After the stimulation of TLR agonists, there was no significant difference in the expression of TNF-α, IL-6, and IL-10 between PBMCs of G6PD-deficient and -normal infants at both 1 month and 1 year of age. In conclusion, the clinical characteristics of G6PD-deficient infants are different from those of G6PD-normal subjects. The data suggest that the innate immune responses to TLR agonists in G6PD-deficienct infants are not different from those of G6PD-normal infants.  相似文献   
972.
目的了解我院早产儿视网膜病(refinopathy of prematurity,ROP)的发病状况,并对其高危因素进行分析。方法对2010年1月至2012年12月在我院新生儿科住院的早产儿(胎龄≤36周,体重≤2.5kg),于生后2周进行ROP筛查,并定期随访。将患儿全身状况及吸氧、母孕期吸氧、先兆子痫、胎盘早剥等因素进行分析。结果255例患儿全部完成了眼底筛查,在周边视网膜血管化或病变退化后终止随访,发现ROP16例(26只眼),ROP患病率为6.3%(5.1%),其中Ⅰ期12例,Ⅱ期3例,Ⅲ期1例。高危因素分析示胎龄、出生体重、吸氧时间,吸氧浓度、机械通气与ROP相关(P〈0.05);母孕期吸氧、先兆子痫、胎盘早剥等因素与ROP发病无关。结论早产、吸氧浓度高、机械通气是ROP的主要危险因素。对早产儿适时进行ROP筛查,并对发现的ROP早期进行有效视网膜激光光凝术,可控制病变,降低早产儿的致盲率。  相似文献   
973.
目的:探讨川芎嗪( ligustrazine,LIG)对离体豚鼠气道平滑肌( airway smooth muscle,ASM)的效应及机制。方法取正常豚鼠支气管,制作成气管螺旋条,随机分成LIG组、LIG+普萘洛尔组、LIG+阿托品组、LIG+硝苯地平组、LIG+格列苯脲组、对照组。分别观察ASM在静息张力下以及组胺所致的高张力下,各组不同LIG浓度对ASM的效应并比较各组间ASM舒张率。结果(1) LIG对离体豚鼠ASM静息张力以及组胺所致的高张力均具有舒张作用。(2)离体豚鼠ASM在静息张力下,与LIG组比较,LIG+普萘洛尔组在LIG浓度10-7~10-6.5 mol/L时,舒张作用明显受到拮抗( P <0.05)。 LIG +阿托品组、LIG+格列苯脲组在LIG浓度10-7.5~10-3 mol/L时,舒张作用没有明显差别(P>0.05)。 LIG+硝苯地平组在LIG浓度10-6~10-4 mol/L时,舒张作用明显加强( P<0.05)。(3)离体豚鼠ASM在组胺所致的高张力下,与LIG组比较,LIG+普萘洛尔组在LIG浓度10-6.5~10-5 mol/L时,舒张作用明显受到拮抗( P<0.05);LIG+阿托品组、LIG+格列苯脲组在LIG浓度10-8~10-3 mol/L时,舒张作用没有明显差别( P>0.05);LIG+硝苯地平组在LIG浓度10-6.5~10-5 mol/L时,舒张作用明显加强(P<0.05)。结论 LIG可对离体豚鼠ASM静息张力以及组胺所致的高张力产生明显的舒张作用,其效应的产生可能与竞争性激动β2受体以及抑制Ca2+内流有关,这为临床应用川芎嗪治疗支气管哮喘提供了理论依据。  相似文献   
974.
Periodontal ligament stem cells (PDLSCs) show a multi-differentiation potential, however, the mechanism of its neural differentiation is still unclear. We aim to explore the potential role of Erk1/2 signalling pathway in the differentiation of PDLSCs to Schwann cells (SCs).  相似文献   
975.
目的 以改良的壳聚糖、胶原等生物大分子作为矿化模板,引导釉质实现类似自生长的再矿化。方法 通过对天然聚阳离子多糖--壳聚糖进行磷酸化本体改性,生成其聚阴离子衍生物磷酸化壳聚糖;以京尼平为交联剂将磷酸化壳聚糖与聚阳离子的Ⅰ型胶原交联改性,构建双性聚电解质复合物水凝胶作为生物矿化的大分子模板,以紫外光辐射激发其在惰性牙体表面的化学组装,仿生唾液提供矿化离子,调控磷灰石晶体在牙体原位的形成与组装,生成羟磷灰石。结果 红外光谱检测证实,PO43−官能团(3 446 cm-1)成功引入壳聚糖,扫描电子显微镜下双性聚电解质复合物水凝胶呈现多孔并存,孔孔交通的级联结构。水凝胶原位接枝能够生成白色晶体,X射线衍射证实新生的晶体为羟磷灰石,该沉积层与原有釉质同质结合,类似釉柱平行排列;新生晶体直径30~60 nm,硬度接近牙本质。结论 取材容易、操作便利的双性聚离子凝胶能够在一定程度上模仿釉质矿化模板,实现羟磷灰石的自生长,这对釉质结构仿生的发展有重要意义。  相似文献   
976.

Introduction

We conducted a meta-analysis to dissect the association between PIK3CA mutations (exon 9 and exon 20) and resistance to anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (MoAbs) in KRAS wild-type metastatic colorectal cancer (mCRC) patients.

Material and methods

In 11 previously published studies, 864 cancer patients were treated with cetuximab or panitumumab-based therapy. Primary outcomes included objective response (complete response + partial response vs. stable disease + progressive disease), progression-free survival (PFS), and overall survival (OS). We calculated the odds ratio (OR) or hazard ratio (HR) with 95% confidence intervals (CIs) to estimate the risk or hazard. We found consistent and clinically substantial risk or hazard for objective response, PFS, and OS in the cetuximab or panitumumab-treated mCRC patients.

Results

PIK3CA mutations as a whole were associated with reduced response and poor PFS and OS in KRAS wild-type mCRC patients (objective response: OR = 0.42 and 95% CI 0.23–0.75; PFS: HR = 1.54 and 95% CI 1.13–2.09; and OS: HR = 1.4 and 95% CI 1.02–1.91). PIK3CA exon 9 mutations had no effect, whereas exon 20 mutations were associated with a worse outcome compared with wild types, with an OR of 0.21 (95% CI 0.05–0.93).

Conclusions

PIK3CA mutations as a whole might be useful prognostic factors for assessing clinical outcomes of anti-EGFR MoAb-based chemotherapies in KRAS wild-type mCRC patients. In particular, PIK3CA exon 20 mutations were significantly associated with lack of response.  相似文献   
977.
978.
Microtubule‐associated protein light chain 3 (LC3A) is a reliable marker of autophagy that displays three distinct patterns of immunohistochemical staining in solid tumors: diffuse cytoplasmic staining, juxtanuclear staining, and staining of “stone‐like” structures. These three patterns have a different prognostic significance in many solid tumors, but little is known about their influence in gastric cancer (GC). This study was a retrospective analysis of 188 GC patients from stages I to IV. The pattern of LC3A expression was examined in tumor and nontumor tissues by immunohistochemistry. Then, the association between the pattern of LC3A expression in GC and the prognosis was investigated by Kaplan‐Meier analysis and the Cox proportional hazards model. Two distinct patterns of LC3A immunostaining (diffuse cytoplasmic expression and “stone‐like” structures) were observed in GC tissues. LC3A‐positive “stone‐like” structures were found only in the tumors, and the number of such structures was correlated with both the tumor type and tumor stage. In addition, a high number of LC3A‐positive “stone‐like” structures was closely associated with an increased risk of recurrence after radical resection of stages I–III cancer (P < 0.001; HR = 0.205) and was associated with a lower overall survival rate for stage IV cancer (P < 0.001; HR = 0.364). Taken together, our data demonstrate that LC3A‐positive “stone‐like” structures can be used as an independent biomarker for an adverse prognosis of GC, suggesting that “stone‐like” structures are correlated with the malignancy of this disease. Anat Rec, 297:653–662, 2014. © 2014 The Authors The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology Published by Wiley Periodicals, Inc.  相似文献   
979.
Endometrial preparation with exogenous estrogen is a common practice in frozen-thawed embryo transfer (FET) cycles. The objective of this study was to compare the clinical outcomes of two endometrial preparation groups, oral estradiol valerate tablets (OEV) group versus vaginal estradiol (VE) tablets group, in inadequate endometrium patients. This retrospective, single-center, cohort study of patients undergoing FET treatment between Jan. 2012 and Jun. 2013, at an academic IVF center, included 247 patients (cycles) with endometrial thickness < 8 mm on day 13 of the hormone replacement cycle: OEV group included 69 patients (cycles) who received continuous OEV from day 1 onwards up to the day of progesterone supplement, while VE group included 178 patients (cycles) who taken OEV from day 1 to day 12, and used VE tablets from day 13 till the day of progesterone supplement. Patients in VE group required more days and higher dosage of estradiol, but had thinner endometrium on the day of transfer. However, the increase of endometrial thickness was more, when compared to OEV-treated patients. The implantation rate and pregnancy rate were, though not significantly, higher in VE group. Conclusions: Longer time of administration and higher dosage of estradiol usage did not have adverse effects on the clinical pregnancy rate. VE tablets may promote endometrial development and pregnancy success in FET cycles could not verify. Further study is needed to confirm the vaginal estradiol action on frozen-thawed embryo transfer cycles.  相似文献   
980.
A new kind of multicolor phosphor Ba2La3(GeO4)3F:0.15Tb3+,xEu3+ (BLGOF:0.15Tb3+,xEu3+) has been acquired through the traditional high temperature solid phase synthesis method. The structural information of the phosphor was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rietveld refinement. The optical properties of the phosphor have also been studied in detail, including its photoluminescence spectra (PL), photoluminescence excitation spectra (PLE), fluorescence decay curves, energy transfer mechanism and thermal quenching spectra. It has been found that the optimum concentration of Eu3+ in BLGOF:0.15Tb3+,xEu3+ is 0.24 mol and the energy transfer mechanism from Tb3+ to Eu3+ in BLGOF is quadrupole–quadrupole. The color of BLGOF:0.15Tb3+,xEu3+ phosphors can be changed from green to yellow/orange to red. Some details of the energy transfer are reviewed and the effect of complex anion regulation on thermal stability has also been studied. All the properties are good and can contribute to the promotion from the laboratory to practical application for the phosphor.

Single-phase Ba2La3(GeO4)3F:Tb3+,Eu3+ phosphors were obtained for the first time.  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-23

京公网安备 11010802026262号