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   11615篇
  免费   804篇
  国内免费   340篇
耳鼻咽喉   67篇
儿科学   60篇
妇产科学   34篇
基础医学   1901篇
口腔科学   329篇
临床医学   630篇
内科学   2306篇
皮肤病学   96篇
神经病学   584篇
特种医学   263篇
外科学   521篇
综合类   1585篇
预防医学   931篇
眼科学   142篇
药学   2420篇
  8篇
中国医学   701篇
肿瘤学   181篇
  2024年   28篇
  2023年   146篇
  2022年   633篇
  2021年   673篇
  2020年   338篇
  2019年   307篇
  2018年   274篇
  2017年   326篇
  2016年   333篇
  2015年   442篇
  2014年   617篇
  2013年   802篇
  2012年   660篇
  2011年   673篇
  2010年   558篇
  2009年   563篇
  2008年   561篇
  2007年   500篇
  2006年   455篇
  2005年   458篇
  2004年   359篇
  2003年   342篇
  2002年   272篇
  2001年   242篇
  2000年   221篇
  1999年   215篇
  1998年   184篇
  1997年   150篇
  1996年   153篇
  1995年   114篇
  1994年   115篇
  1993年   104篇
  1992年   86篇
  1991年   116篇
  1990年   72篇
  1989年   92篇
  1988年   79篇
  1987年   68篇
  1986年   63篇
  1985年   58篇
  1984年   66篇
  1983年   48篇
  1982年   49篇
  1981年   32篇
  1980年   30篇
  1979年   20篇
  1978年   19篇
  1977年   11篇
  1976年   12篇
  1973年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Context Withania somnifera (L.) Dunal is traditionally used for treating various ailments, but lacks scientific evaluation.

Objective This study evaluates Withania somnifera (WS) for its effect on platelet activity and inflammatory enzymes.

Materials and methods Aqueous and ethanolic (1:1) leaf extracts were subjected to in vitro indirect haemolytic activity using Naja naja venom, human platelet aggregation was quantified for lipid peroxidation using arachidonic acid (AA) as agonist and 5-lipoxygenase (5-LOX) levels were determined using standard spectrometric assays. Further, molecular docking was performed by the ligand fit method using molegro software package (Molegro ApS, Aarhus, Denmark).

Results The study found that aqueous and ethanol extracts have very negligible effect (15%) with an IC50 value of 13.8?mg/mL on PLA2 from Naja naja venom. Further, extracts of WS also had very little effect (18%) with an IC50 value of 16.6?mg/mL on malondialdehyde (MDA) formation. However, a 65% inhibition of 5-LOX with an IC50 value of 0.92?mg/mL was observed in 1:1 ethanol extracts. The same was evident from SAR model with the active ingredient withaferin A binding predominantly on Phe 77, Tyr 98, Arg 99, Asp 164, Leu 168, Ser 382, Arg 395, Tyr 396 and Tyr 614 with an atomic contact energy value of??128.96 compared to standard phenidone (?103.61). Thus, the current study validates the application of WS for inflammatory diseases.

Conclusion This study reveals the inhibitory potential of W. somnifera on inflammatory enzymes and platelet aggregation. Thus, WS can serve as a newer, safer and affordable medicine for inflammatory diseases.  相似文献   
2.
目的:应用经食管实时三维超声心动图(RT-3D-TEE)技术,探讨房性心律失常对二尖瓣结构和功能的影响.方法:选取2018年6月~2019年6月本院收治的房性心律失常拟行射频消融的患者49例纳入观察组,另外选取21例正常窦性心律者作为对照组,所有患者均行经胸超声心电图(TTE)和经食管实时三维超声心动图(RT-3D-TEE)检查,将两组患者的瓣环投影面积(A2D)、瓣环周长(C3D)、瓣环高度(H)、瓣环前后径(DAP)、瓣环前外侧至后内侧直径(DAIPm)、左室射血分数(LVEF)、左心房前后径(Lad)等参数进行比较,并分别计算对合面积和对合指数,之后采取二项Logistic回归分析或逐步线性回归对各参数及临床因素与对合指数的相关性进行分析.结果:两组患者在LVEF和对合面积方面的比较无明显差异(P>0.05),在A2D、C3D、H、DA、PDAIPm、Lad方面的比较,房性心律失常组患者明显高于正常窦性心律组患者(P<0.05),且观察组患者的对合指数明显降低(P<0.05).将49例观察组患者以不同心律失常类型分为持续性房颤、阵发性房颤、房扑、混合型房性心律失常4个亚组,采用单因素方差分析,发现在LVEF、C3D、Lad、对合指数方面的比较,各亚组间无明显差异(P>0.05).采用二项Logistic回归分析发现,女性是导致对合指数低的危险因素,另外对合指数较低、房性心律失常是导致二尖瓣返流的重要因素.结论:房性心律失常对患者二尖瓣的A2D、C3D、H、DA、PDAIPm、Lad等都会造成较大影响,从而降低对合指数,影响二尖瓣的正常功能,导致二尖瓣返流的发生.  相似文献   
3.
目的 探讨以行为-结构化-关系(BSR)干预模式对短期住院孤独症谱系障碍(ASD)儿童的干预疗效,为改善ASD儿童的预后提供参考依据。方法 选取2015年12月-2016年12月确诊为ASD的2~6岁儿童141例,随机分为治疗组和对照组。治疗组ASD儿童均接受BSR模式的短期课程训练,训练课程包括个别辅导、游戏课、运动课、音乐课等,每天训练时间6 h,持续1个月;对照组ASD儿童处于干预等待,接受随访观察和评估。所有ASD儿童干预前、后均接受儿童心理教育评估(第三版)(PEP-3)来进行各方面能力变化的评估。结果 治疗组、对照组干预前各副测验的原积分差异无统计学意义(P>0.05)。两组ASD儿童干预后认知、语言理解、模仿、情感表达、社会互动、行为特征-非语言、适应行为的原积分比较,差异均有统计学意义(t=2.41、2.02、4.14、3.69、4.42、2.69、2.96,P<0.05);但小肌肉、大肌肉、自理的原积分比较,差异无统计学意义(t=-1.13、-1.05、-0.84,P>0.05)。结论 BSR干预模式能够有效改善短期住院ASD儿童的预后,可推广用于儿童ASD的治疗。  相似文献   
4.
Malaria, one of the most striking, re-emerging infectious diseases caused by the genus Plasmodium, places a huge burden on global healthcare systems. A major challenge in the control and eradication of malaria is the continuous emergence of increasingly widespread drug-resistant malaria, creating an urgent need to develop novel antimalarial agents. Chalcone derivatives are ubiquitous in nature and have become indispensable units in medicinal chemistry applications due to their diverse biological profiles. Many chalcone derivatives demonstrate potential in vitro and in vivo antimalarial activity, so chalcone could be a useful template for the development of novel antimalarial agents. This review covers the recent development of chalcone hybrids as antimalarial agents. The critical aspects of the design and structure–activity relationship of these compounds are also discussed.  相似文献   
5.
6.
氩氦刀的原理与应用中的优势和不足   总被引:1,自引:0,他引:1  
郑玲 《医疗卫生装备》2006,27(12):53-54
氩氯刀是目前肿瘤治疗的新方法,其原理是通过组织细胞急冻急升温的方法实现的,比手术、化疗、放疗治疗方法简单,副作用小,费用低。但也存在冷冻后的问题,其适应证也受到限制。  相似文献   
7.
粉防己碱对野百合碱致大鼠肺动脉构形重建的逆转作用   总被引:2,自引:0,他引:2  
以野百合碱复制Wistar大鼠肺动脉高压模型,用特殊染色方法观察粉防已碱对野百合碱致大鼠肺动脉构形重建的逆转作用,结果表明粉防已碱可选择性的降低野百合碱诱导的大鼠肺动脉高压的作用,并明显地逆转肺血管及肺组织损伤,降低肺动脉高压和右心室肥大,对体循环压力无影响  相似文献   
8.
To explain how the myelin proteins are involved in the organization and function of the myelin sheath requires knowing their molecular structures. Except for P2 basic protein of PNS myelin, however, their structures are not yet known. As an aid to predicting their molecular folding and possible functions, we have developed a FORTRAN program to analyze the primary sequence data for proteins, and have applied this to the myelin proteins in particular. In this program, propensities for the secondary structure conformations as well as physical-chemical parameters are assigned to the amino acids and the pattern of these parameters is examined by calculating their average values, autocorrelation functions and Fourier transforms. To compare two proteins, their sequences are aligned using a unitary scoring matrix, and homologies are searched by plotting a two-dimensional map of the correlation coefficients. Comparison of the corresponding myelin basic proteins (MBP) and P0 glycoproteins (P0) for rodent and shark showed that the conserved residues included most of the amino acids which were predicted to form the alpha or beta conformations, while the altered residues were mainly in the hydrophilic and turn or coil regions. In both rodent and shark the putative extracellular domain of P0 glycoprotein displayed consecutive peaks of beta propensity similar to that for the immunoglobulins, while the cytoplasmic domain showed alpha-beta-alpha folding. To trace the immunoglobulin fold along the P0 sequence, we compared the beta propensity curve of P0 with that of the immunoglobulin M603, whose three-dimensional structure has been determined. We propose that the flat beta-sheets of P0 are orientated parallel to the membrane surface to facilitate their homotypic interaction in the extracellular space. An extra beta-fold in the extracellular domain of shark P0 compared with rodent P0 was found, and this may result in a greater attraction between the apposed extracellular surfaces and may account for a smaller extracellular space as measured by x-ray diffraction. A computer search of the myelin protein sequences for functional motifs revealed sites for N-glycosylation, phosphorylation, nucleotide binding, and certain enzyme activities. We note especially that there are potential nucleotide binding sites in proteolipid protein (PLP), MBP and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP). This is consistent with the experimental observations that PLP acts like an ionophore or proton channel when reconstituted into planar lipid bilayers, MBP binds GTP, and CNP catalyzes in vitro the hydrolysis of 2',3'-nucleotides into corresponding 2'-nucleotides.  相似文献   
9.
本文用相转移催化方法合成了四种新颖的芳香族聚酯。对所得聚合物进行了红外光谱、热重分析、偏光显微镜、示差扫描量热仪和解偏振光强等测试,以研究它们的结构和性能。它们的热分解温度都在330℃以上。其中的聚对,对′-1,4,7-三氧杂庚撐基二苯甲酸对苯二酚酯和聚对苯二甲酸对,对′-1,8-二氧杂辛撐基二苯酚酯,呈现向列型相转变,它们的清晰点分别为237℃和327℃。其它两种含双酚A或酚酞基团的聚酯则不存在液晶行为。对实验结果进行了讨论。  相似文献   
10.
l -Valyl-l -lysine hydrochloride, C11N3O3H23 HCl, crystallizes in the monoclinic space group P2, with a = 5.438(5), b = 14.188(5), c = 9.521(5) Å, β= 95.38(2)° and Z = 2. The crystal structure, solved by direct methods, refined to R = 0.036, using full matrix least-squares method. The peptide exists in a zwitterionic form, with the N atom of the lysine side-chain protonated. The two γ-carbons of the valine side-chain have positional disorder, giving rise to two conformations, χ111= -67.3 and 65.9°, one of which (65.9°) is sterically less favourable and has been found to be less popular amongst residues branching at β-C. The lysine side-chain has the geometry of g? tgt, not seen in crystal structures of the dipeptides reported so far. Interestingly, χ32 (63.6°) of lysine side-chain has a gauche+ conformation unlike in most of the other structures, where it is trans. The neighbouring peptide molecules are hydrogen bonded in a head-to-tail fashion, a rather uncommon interaction in lysine peptide structures. The structure shows considerable similarity with that of l -Lys-l -Val HO in conformational angles and H-bond interactions [4].  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