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   10740篇
  免费   905篇
  国内免费   195篇
耳鼻咽喉   38篇
儿科学   226篇
妇产科学   185篇
基础医学   1649篇
口腔科学   123篇
临床医学   665篇
内科学   1943篇
皮肤病学   206篇
神经病学   979篇
特种医学   325篇
外国民族医学   2篇
外科学   1208篇
综合类   815篇
现状与发展   1篇
预防医学   454篇
眼科学   141篇
药学   1298篇
  1篇
中国医学   471篇
肿瘤学   1110篇
  2023年   115篇
  2022年   225篇
  2021年   252篇
  2020年   246篇
  2019年   682篇
  2018年   746篇
  2017年   338篇
  2016年   270篇
  2015年   272篇
  2014年   458篇
  2013年   516篇
  2012年   440篇
  2011年   508篇
  2010年   366篇
  2009年   371篇
  2008年   311篇
  2007年   309篇
  2006年   261篇
  2005年   241篇
  2004年   225篇
  2003年   175篇
  2002年   178篇
  2001年   183篇
  2000年   168篇
  1999年   141篇
  1998年   108篇
  1997年   127篇
  1996年   104篇
  1995年   77篇
  1994年   77篇
  1993年   64篇
  1992年   47篇
  1991年   37篇
  1990年   34篇
  1989年   27篇
  1986年   21篇
  1985年   265篇
  1984年   405篇
  1983年   291篇
  1982年   289篇
  1981年   309篇
  1980年   304篇
  1979年   207篇
  1978年   178篇
  1977年   143篇
  1976年   181篇
  1975年   188篇
  1974年   142篇
  1973年   114篇
  1970年   23篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Objective Parent questionnaires of child motor and language skills are useful in many contexts. This study validates one such measure, the Preschool Child Development Inventory (PCDI), a mother‐answered standardized measure of motor (fine and gross) and language (expression and comprehension) skills of 3–6‐year‐old children. Methods Eighty‐one mothers answered the inventory and their children were concurrently tested on six verbal subtests of WPPSI‐RIS. Results The six language and motor subtests of the PCDI revealed the predicted convergent and divergent correlations with the verbal subtests of the WPPSI‐RIS. As predicted, the motor subtests diverged and the language subtests converged with the expected WPPSI‐RIS subtests. Principal components analysis of all the measures (the PCDI and the WPPSI‐RIS subtests) revealed two components, verbal and motor in content. Conclusions The findings support the validity of a mother‐answered inventory to assess language and motor development. It is pointed out that such inventories are a viable brief and cost effective alternative to individual testing, both to supplement such measures in clinical practice and as main information in research, for example on determinants of development. Some suggestions are made for future research and applications.  相似文献   
63.
Objective To optimize the extraction technology used for extracting active saponins from the roots,fibrous roots,basal part of stems,root verrucae,fruits,flowers,stems,and leaves of Panax notoginseng based on the contents of ginsengsides Rg1,Rb1,and notoginsengside R1 as evaluation indexes.Methods Different parts of P.notoginseng were extracted by smashing tissue extraction(STE),ultrasound extraction,and reflux extraction.The contents of ginsengsides Rg1,Rb1,and notoginsengside R1 in 24 kinds of extracts were determined by HPLC-UV.Hypersil C18 column(200 mm × 4.6 mm,5 μm) and acetonitrile-warter(20:80 for 30 min→45:55 for 18 min→70:30 for 2 min→80:20 for 10 min→100:0) were used;UV detector was set at 203 nm;The flow rate was set at 1.0 mL/min.Results STE was the most efficient technology with the highest yield of active saponins among the three tested extraction technologies.Conclusion STE is a fast,effective,and economical method to extract the active saponins from different parts of P.notoginseng.It could significantly shorten the extraction time and simplify the determination of the pre-processing work on identifying P.notoginseng.Such quick and effective extraction provides a powerful tool for analyzing P.notoginseng in the future.  相似文献   
64.
中药赤芍中化学成分的研究   总被引:2,自引:0,他引:2  
Two new monoterpene glycosides were isolated from the ethanolic extract of the root of Paeonia laetiflora Pall. The structure of compound (Ⅰ) has been identified as (Z)-(1S, 5R)-β-pinen-10-yl β-vicianoside; Compound (Ⅱ) is named lactiflorin and tentatively assigned as (Ⅱ).Compound (Ⅰ) is the glycoside of the enol form of an aldehyde. In compound (Ⅱ), the sugar moiety is attached to the aglycone by two ether-like linkages. Both seem to be unprecedented.  相似文献   
65.
The safety and short-term therapeutic benefit of multilesion percutaneous transluminal coronary angioplasty was assessed in 135 patients, 66 of whom had a minimum of 6 months of follow-up study. Primary success, defined as successful dilation of the most critical lesion or all lesions attempted without major in-hospital complications was obtained in 117 (87%) of the 135 patients. Cardiac complications associated with the procedure were uncommon; prolonged angina occurred in 5% and myocardial infarction in 3%; emergency coronary bypass surgery was performed in 4% of the patients. There were no deaths. Complete revascularization was achieved in 46% of the 117 patients with a primary success. Of the 66 patients eligible for 6 month follow-up, 80% had an uncomplicated course and required no further procedures. Clinical improvement by at least one angina functional class was observed in 90% of the patients. Cardiac events such as the need for a second revascularization procedure were significantly more common in patients who had incomplete versus complete revascularization (35 versus 9%; p = 0.018). Repeat coronary angiography performed an average of 5 months after angioplasty revealed restenosis in 18 of 22 symptomatic patients and 3 of 9 asymptomatic patients. Restenosis occurred at the site of a single dilation in 12 patients, at two sites in 8 patients and at three sites in 1 patient. Thus, multilesion coronary angioplasty is an important therapeutic option for selected patients with multivessel disease and can be performed with relatively low risk. Improvement in angina status can be expected even in patients who have incomplete revascularization.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
66.
The maximal aerobic exercise capacity of patients with chronic heart failure is frequently decreased because of inadequate blood flow to working skeletal muscle. To investigate whether this reduced flow is in part due to interference by angiotensin II with arteriolar dilation in working muscle, the effect of the angiotensin-converting enzyme inhibitor captopril on leg blood flow, leg vascular resistance, leg oxygen consumption (VO2) and leg lactate release during maximal upright bicycle exercise was examined in 12 patients with heart failure (maximal VO2 10.7 +/- 3.1 ml/min per kg). Captopril decreased leg resistance at rest (258 +/- 115 to 173 +/- 67 U, p less than 0.01) and maximal exercise (68 +/- 69 to 45 +/- 29 U, p less than 0.01) associated with proportionately similar decreases in systemic vascular resistance. However, maximal exercise duration and maximal VO2 were unchanged and, at identical peak exercise work times, there was no improvement in leg blood flow (2.0 +/- 0.9 to 2.0 +/- 1.1 liters/min, p = NS), leg VO2 (261 +/- 104 to 281 +/- 157 ml/min, p = NS) or leg lactate release (269 +/- 149 to 227 +/- 151 mg/min, p = NS). These data suggest that, during exercise in patients with heart failure, angiotensin II does not interfere with blood flow to working skeletal muscle.  相似文献   
67.
The occurrence of pulmonary artery obstruction in an 8 day old infant as a complication of an aneurysm of a nonpatent ductus arteriosus is reported, together with the echocardiographic and angiographic findings. To relieve the obstruction, the aneurysm and an intrapulmonary thrombus were successfully removed with the use of cardiopulmonary bypass when the infant was 3 months old.  相似文献   
68.

Background/Objective

Preconditioning has been considered promising for the treatment of ischemic flaps. In this study, the therapeutic effect of postconditioning was compared with that of preconditioning during ischemia/reperfusion (I/R) injury, and a role of inducible nitric oxide synthase (iNOS) in postconditioning treatment was also explored.

Methods

Sixty rats were randomly divided into four groups with 15 rats in each group. Ischemic injury was induced in a rat’s gracilis muscle flap model. Preconditioning and postconditioning were performed respectively on the flaps in the pre-con group and the post-con group. No treatment was given to the flaps in the control group, and flaps without I/R injury were used as a sham control. Muscle viability ratio, histology, and gene expression of iNOS were examined at different time intervals (3, 12, and 18 h).

Results

A significantly higher survival ratio was observed in both the pre-con group (78.98 ± 3.39, 62.74 ± 3.7, and 54.42 ± 4.45 %) and the post-con group (77.42 ± 4.14, 59.74 ± 6.67, and 49.52 ± 4.13 %) than the control group (45.22 ± 3.69, 42.44 ± 3.76, and 33.2 ± 3.29 %) at 3, 12, and 18 h postoperatively (P < 0.05). There was no statistical difference between the pre-con group and the post-con group (P > 0.05). Histological examination showed delayed and attenuated tissue damage in both the pre-con group and the post-con group when compared to that of the control group. A higher expression of iNOS was observed in both the pre-con group and the post-con group than the control group and the sham group (P < 0.05).

Conclusions

Significant improvement of flap survival could be achieved by both preconditioning and postconditioning treatments; however, better protection could be provided by preconditioning. The higher expression of iNOS may play an important role in the therapeutic effect of postconditioning during I/R injury.  相似文献   
69.
70.
【摘要】 目的 探讨成纤维细胞生长因子21(FGF21)对缺氧复氧(H/R)心肌细胞的保护作用及对PI3K/AKT通路的影响。方法 重组腺病毒载体Ad FGF21诱导原代心肌细胞过表达FGF21。腺病毒转染心肌细胞后构建H/R损伤模型(3h缺氧联合3h复氧)。实验分为对照组(Con组)、H/R组、H/R+Ad GFP组、H/R+Ad FGF21组4组。心肌细胞存活率评估细胞损伤程度;SOD/MDA检测联合DHE荧光染色评估氧化应激反应(ROS);流式细胞术评估细胞凋亡;Western blot检测相关蛋白水平。在机制探讨实验中给予PI3K/AKT抑制剂(LY294002)进行干预。结果 与Con组相比,H/R损伤后FGF21蛋白表达显著下调,并伴随心肌细胞活性降低、ROS与凋亡反应激活。腺病毒介导的心肌细胞过表达FGF21能够明显抑制H/R损伤,表现为细胞活力、ROS与凋亡反应均有不同程度改善。FGF21心肌细胞过表达能够增加PI3K/AKT磷酸化水平,而抑制PI3K/AKT通路后FGF21过表达介导的细胞保护功能被逆转。结论 FGF21主要通过PI3K/AKT依赖性途径改善心肌细胞H/R损伤。  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