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   86135篇
  免费   6121篇
  国内免费   3816篇
耳鼻咽喉   378篇
儿科学   1591篇
妇产科学   876篇
基础医学   13457篇
口腔科学   1778篇
临床医学   7191篇
内科学   14698篇
皮肤病学   1073篇
神经病学   8018篇
特种医学   1423篇
外国民族医学   15篇
外科学   5527篇
综合类   14491篇
现状与发展   22篇
预防医学   5405篇
眼科学   986篇
药学   11014篇
  10篇
中国医学   2672篇
肿瘤学   5447篇
  2024年   152篇
  2023年   870篇
  2022年   2257篇
  2021年   3102篇
  2020年   2486篇
  2019年   2146篇
  2018年   2116篇
  2017年   2407篇
  2016年   2750篇
  2015年   3110篇
  2014年   5270篇
  2013年   5965篇
  2012年   5567篇
  2011年   6206篇
  2010年   4913篇
  2009年   4789篇
  2008年   4925篇
  2007年   4802篇
  2006年   4312篇
  2005年   4043篇
  2004年   3304篇
  2003年   2833篇
  2002年   2195篇
  2001年   1882篇
  2000年   1650篇
  1999年   1408篇
  1998年   1311篇
  1997年   1156篇
  1996年   1010篇
  1995年   800篇
  1994年   748篇
  1993年   634篇
  1992年   557篇
  1991年   507篇
  1990年   446篇
  1989年   350篇
  1988年   326篇
  1987年   313篇
  1986年   275篇
  1985年   390篇
  1984年   346篇
  1983年   231篇
  1982年   266篇
  1981年   211篇
  1980年   182篇
  1979年   118篇
  1978年   99篇
  1977年   85篇
  1976年   73篇
  1975年   62篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
周丽媛  施喆  刘悦君  李静霞  崔志利  安欣 《安徽医学》2023,44(11):1334-1337
目的 探讨肿瘤坏死因子诱导蛋白8样蛋白2(TIPE2)、细胞增殖核抗原Ki67在子宫内膜癌组织中的表达及对患者预后的评估价值。方法 选取2018年1月至2020年1月河北工程大学附属医院妇科收治的子宫内膜癌患者120例作为观察组,另选取同期收治的非子宫内膜癌患者130例作为对照组,所有入组患者均接受手术治疗。回顾性收集患者的临床及病理资料,比较两组患者子宫内膜组织中TIPE2、Ki67的表达水平。同时定期对观察组患者进行随访,分析患者2年生存情况,通过Cox比例风险回归模型分析子宫内膜癌患者预后的影响因素。结果 观察组、对照组子宫内膜组织中TIPE2阳性率分别为28.33%、71.54%。与对照组相比,观察组子宫内膜组织TIPE2阳性率降低(P<0.05);观察组、对照组子宫内膜组织中Ki67阳性率分别为33.33%、5.38%。观察组子宫内膜组织Ki67阳性率高于对照组(P<0.05)。对120例子宫内膜癌患者随访2年,至随访结束,93例患者存活,生存率77.50%。Cox模型分析结果显示,TIPE2阴性(HR=3.736,95%CI=1.016~13.157)为子宫内膜...  相似文献   
992.
硫氧还蛋白相互作用蛋白(thioredoxin-interacting protein, TXNIP)主要调节胰岛β细胞中葡萄糖的稳态,是治疗糖尿病的新颖靶点。本研究以4-羟基苯并嘧啶为原料,通过不同长度的碳链,引入吡唑、甲基哌嗪、咪唑、吗啡啉等4种含氮杂环,设计合成靶向TXNIP的苯并嘧啶骨架拼合含氮杂环的衍生物,并考察化合物对棕榈酸(palmitate acid, PA)刺激的胰岛β细胞损伤的保护作用。共设计合成20个苯并嘧啶衍生物,结构经1H NMR、ESI-MS确证;药理活性表明大部分化合物对胰岛β细胞有保护作用,其中化合物C-1、C-2、C-4、D-2保护作用较强,相较PA模型组细胞活力为38.3%,这4个化合物细胞活力高于70%,其中化合物D-2细胞活力最高,达到87.2%;化合物D-2可以作为潜在的抗糖尿病新化学实体。  相似文献   
993.
An immunohistochemical assessment of the endometrium was carried out in a group of IVF patients on stimulated cycles, in order to evaluate this technique against standard histological methods and to consider its application in a clinical situation. Monoclonal antibodies to the two cycle-dependent proteins: pregnancy associated endometrial alpha 2-globulin (alpha 2-PEG) and 24K (a protein originally isolated from an oestrogen-dependent breast tumour line, MCF-7) were used in the experiment. Immunohistochemical results concerning the effect of drug stimulation, age and date of biopsy on the secretory state of the endometrium revealed trends which were consistent with previous histological data, helping to confirm the value of this new technique. In addition, several specimens were found to have a normal, i.e. in phase, histological appearance but to have an atypical pattern of protein secretion. These observations suggest that biochemical monitoring of the uterus should be used in conjunction with routine histological dating.  相似文献   
994.
Summary Immunochemical analyses revealed that a monclonal antibody Am-3 recognized amyloid precursor protein (APP) in senile plaques extracted from Alzheimer's brain, but did not recognize amyloid protein. Immunohistochemically, however, the staining pattern of Am-3 in frozen section of Alzheimer's brain was almost the same with that of rabbit polyclonal antibody to amyloid peptide which could recognize both amyloid protein and APP. In other words, APP was present in senile plaques of various types, cerebrovascular amyloid and granular deposits. The granular deposits were 5–10 m in size and laminarily distributed in the 1st, 3rd and 4th layers of cerebral cortex. They were especially abundant in 1st and 4th layers where senile plaques were usually fewer in number. Although the distribution in the cerebral cortex was different between the senile plaques and the granular deposits, the number of the granular deposits was well correlated with that of senile plaques. The granular deposits were negative in Congo-red birefringence, but contained amyloid protein as well as APP fragment judging from positive staining by both Am-3 and polyclonal antibody to synthetic amyloid peptide. Thus, they could be regarded as pre-amyloid.  相似文献   
995.
Summary The immunohistochemical distribution of S-100 protein in patients with Down's syndrome was investigated as part of a study aimed at ascertaining a possible involvement in the syndrome (trisomy 21) of this protein, which has recently been shown to be coded in chromosome 21. No appreciable differences in the cell distribution of the antigen could be observed between patients with Down's syndrome and normal subjects. The possibility of an overexpression or abnormal expression of the molecule as a consequence of chromosome 21 triplication, not detectable by immunocytochemical methods alone, remains to be investigated.Supported in part by grants from Consiglio Nazionale delle Ricerche and Ministero della Pubblica Istruzione to F. M. and L. L.  相似文献   
996.
The following integrodifferential equation is proposed as the basis for a generalized treatment of pharmacokinetic systems in which nonlinear binding occurs $$\phi '(c_u )c'_u = - q(c_u ) + g*c_u + f$$ where cu≡unbound plasma drug concentration, f≡drug input rate,'indicates the derivative of a function, and * indicates the convolution operation: (g* cu)(t)=∫ 0 t g(t?u)cudu.Possible physical interpretations of the functions q, g and f are: q (cu)≡ rate at which drug leaves the sampling compartment, g * cu ≡ rate at which drug returns to the sampling compartment from the peripheral system (tissues that are kinetically distinct from the sampling compartment), and φ(cu) ≡ amount of drug in the sampling compartment. The approach assumes that drug binding is sufficiently rapid that it may be treated as an equilibrium process. It may be applied to systems in which nonlinear binding occurs within the sampling compartment, i.e., in the systemic circulation or in tissues to which drug is rapidly distributed. The proposed relationship is a generalization of most existing models for drugs with nonlinear binding. It can serve as a general theoretical framework for such models or as the basis for “model-independent” methods for analyzing the pharmacokinetics of drugs with nonlinear binding. Computer programs for the numerical solution of the integrodifferential equation are presented. Methods for pharmacokinetic system characterization, prediction and bioavailability are presented and demonstrated.  相似文献   
997.
We recently described the cloning of a fifth member of the 5-hydroxytryptamine (5-HT)1 (serotonin1) receptor class that inhibits adenylyl cyclase, namely the human 5-HT1F receptor (Adham et al. 1993 a). In the present study we have examined in greater detail the functional coupling of the 5-HT1F receptor in two different cell lines, NIH-3T3 and LM(tk) fibroblasts (receptor densities of 1.7 and 4.4 pmol/mg protein, respectively). The maximal inhibitory response elicited by 5-HT was significantly greater in NIH-3T3 as compared to LM(tk) cells, whereas the EC50 values were comparable.To investigate the relationship between receptor occupancy and inhibition of cAMP accumulation mediated by 5-HT1F receptors in NIH-3T3 cells (and hence the degree of receptor reserve), we used the irreversible receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). The half-maximal response required only about 10% receptor occupancy, consistent with a receptor reserve of 90% (88±2.1%, n = 4) for 5-HT-induced inhibition of FSCA. Despite the presence of such a high degree of receptor reserve, a range of intrinsic activities was displayed by structurally diverse classes of compounds. For example, sumatriptan and lysergol were as efficacious as 5-HT itself and thus acted as full agonists, whereas metergoline and 1-NP behaved as partial agonists and as shown previously (Adham et al. 1993a), methiothepin was a silent antagonist (Kb = 438 nM).We have also investigated activation of additional signal transduction pathways by the 5-HT1F receptor and found that the responses differ in the two cell lines with respect to stimulation of phospholipase C. For example, in NIH-3T3 cells no elevation of inositol phosphates (IP) of [Ca2+]i was observed even at very high agonist concentrations (100 M). In contrast, in LM(tk) cells concentrations of 5-HT as low as 10 nM induced stimulation of IP and a rapid increase of [Ca2+]i. The 5-HT1F receptor failed to alter arachidonic acid release in either cell line.The maximal increase in IP accumulation in LM(tk) cells was modest, averaging about 100% above basal. The increases of IP and [Ca2+]i required 5-HT concentrations less than one order of magnitude greater than those inhibiting FSCA (EC50 = 17, 55 and 8 nM, respectively), and both responses were blocked by 100 M methiothepin. All three responses (cAMP, IP, and [Ca2+]i) were sensitive to pertussis toxin pre-treatment, suggesting the involvement of Gi/Go protein(s) in these signal transduction pathways. [Ca2+]i was also elevated by sumatriptan, which may provide a mechanism by which this drug causes constriction of the vasculature. In conclusion, these data indicate that the human 5-HT1F receptor can couple to multiple effectors, and that this coupling is cell-type dependent.Abbreviations FSCA forskolin-stimulated cAMP accumulation - [Ca2+] intracellular free calcium concentration - AA arachidonic acid - EEDQ N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline - CHO chinese hamster ovary cell - LM(tk) mouse fibroblast cell - Bmax maximal binding site density - Ki apparent dissociation constant obtained from competition binding studies - G protein guanine nucleotide-binding protein - HBS HEPES-buffered saline - IP inositol phosphates - IP3 inositol 1,4,5 trisphosphate - PLC phospholipase C - Kb antagonist dissociation constant - Kd equilibrium dissociation constant - N-1F-6 stable NIH-3T3 cells expressing the cloned 5-HT1F receptor - L-1F-3 stable LM(tk) cells expressing the cloned 5-HT1F receptor - PTX pertussis toxin - BSA bovine serum albumin - METH methiothepin - SUMA sumatriptan - 5-MeO-DMT 5-methoxy-N,N-dimethyltryptamine - 1-NP 1-(1-napthyl)piperazine - 5-CT 5-carboxyamidotryptamine Correspondence to: N. Adham at the above address  相似文献   
998.
The natural killer (NK) activity of peripheral blood mononuclear cells and serum immunosuppressive acidic protein (IAP) levels were examined in patients with esophageal or gastric cancer, before and after surgery. Patients with stage IV esophageal or stage IV gastric cancer had significantly lower NK activity (39.5±14.8% and 37±11.6%, respectively), and also higher serum IAP levels (778±264 g/mL and 633±156 g/mL, respectively), than the corresponding control values (50±5.6% and 375±26 g/mL, respectively). Patients with esophageal or gastric cancer who underwent curative resection had high NK activity (54.8±11.6% and 54.8±8.0%, respectively), and low IAP levels (471±116 g/mL and 490±42 g/mL, respectively), compared with those who underwent non-curative resection. Patients who underwent non-curative resection had lower NK activity and higher serum IAP levels than those who underwent curative resection, even 1 month after surgery. Mononuclear cells in the regional lymph nodes and tumor specimens showed significantly lower NK activity than those in the peripheral blood and spleen. Thus, NK activity and the IAP level reflected the immunocompetence, clinical course, and surgical curability of those patients. NK cells appeared not to have any significant antitumor activity in the regional lymph nodes or in the tumor itself, although they were still active in the peripheral blood.  相似文献   
999.
The binding characteristics of valproic acid (VPA) and its pharmacologically active monounsaturated metabolite, E-2-VPA, to rat plasma proteins were compared. The plasma free fraction was determined by a rapid equilibrium procedure, which minimizes the interfering effects of nonesterified fatty acids liberated by in vitro lipolysis. Nonlinear binding behavior was observed with both compounds over their respective pharmacologic concentration range. Multiple binding-site models were invoked to explain the binding isotherm. The 2-unsaturated compound has a much higher affinity for the rat plasma proteins (mainly albumin) than its saturated precursor. The equilibrium association constants for the high- and intermediate-affinity sites were more than an order of magnitude higher with E-2-VPA than with VPA (104–106 versus 103 M –1). This difference in binding affinity was also reflected by a lower plasma free fraction for E-2-VPA compared with VPA (<<10 versus >20% at total concentrations of less than 100 µg/ml). A more pronounced dose- and concentration-dependent variation in the distribution and clearance kinetics is predicted for the 2-unsaturated analogue compared to VPA. Also, the structural dependency in plasma protein binding observed with these branched-chain fatty acids may provide insights into the mechanism of interaction between fatty acyl molecules and albumin.  相似文献   
1000.
目的 阐明鼻咽癌细胞中EB病毒编码的潜伏膜蛋白 1(LMP1)活化核转录因子NF κB的机制。方法 利用强力霉素Dox诱导表达LMP1的鼻咽癌细胞株Tet on LMP1 HNE2为实验模型 ,首先应用免疫印迹方法测定Dox诱导后不同时相LMP1的表达动力学以及IκBs蛋白量及功能的改变。进而用间接免疫荧光法检测NF κB的亚细胞定位。最后采用瞬间共转染及报道基因活性分析分析NF κB的活性。结果 在鼻咽癌细胞Tet on LMP1 HNE2中 ,Dox处理 15分钟后LMP1的表达迅速升高并维持与较高水平直至 12 0分钟。LMP1的诱导性表达导致IκBα的磷酸化并降解 ,但IκBα蛋白总量无改变。继IκBα的磷酸化并降解 ,NF κB(P6 5 )自胞浆易位至胞核且活性升高。IκBα的显性负性突变子抑制NF κB(P6 5 )的核易位及报道活性。LMP1的诱导性表达并未引起IκBβ蛋白水平变化。结论 在鼻咽癌细胞Tet on LMP1 HNE2中 ,EB病毒LMP1通过IκBα的磷酸化并降解激活核转录因子NF κB的活性 ,并且 ,LMP1诱导的NF κB活性能被IκBα的显性负性突变子完全抑制。IκBβ在此信号传导途径中无改变。LMP1表达前后IκBα蛋白总量维持恒定可能是由于NF κB的活化迅速启动了IκBα的重头合成这一自身调节环路所致。  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