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   18495篇
  免费   1197篇
  国内免费   249篇
耳鼻咽喉   246篇
儿科学   207篇
妇产科学   227篇
基础医学   3144篇
口腔科学   367篇
临床医学   1635篇
内科学   3677篇
皮肤病学   585篇
神经病学   1357篇
特种医学   1338篇
外科学   2213篇
综合类   69篇
一般理论   6篇
预防医学   697篇
眼科学   324篇
药学   2113篇
中国医学   277篇
肿瘤学   1459篇
  2024年   14篇
  2023年   171篇
  2022年   592篇
  2021年   827篇
  2020年   412篇
  2019年   582篇
  2018年   691篇
  2017年   563篇
  2016年   745篇
  2015年   996篇
  2014年   1156篇
  2013年   1258篇
  2012年   1725篇
  2011年   1743篇
  2010年   1047篇
  2009年   798篇
  2008年   1122篇
  2007年   1055篇
  2006年   903篇
  2005年   857篇
  2004年   745篇
  2003年   576篇
  2002年   453篇
  2001年   194篇
  2000年   158篇
  1999年   112篇
  1998年   78篇
  1997年   58篇
  1996年   41篇
  1995年   27篇
  1994年   23篇
  1993年   14篇
  1992年   30篇
  1991年   23篇
  1990年   22篇
  1989年   25篇
  1988年   8篇
  1987年   12篇
  1986年   13篇
  1985年   11篇
  1984年   9篇
  1983年   8篇
  1981年   4篇
  1980年   4篇
  1978年   4篇
  1976年   4篇
  1974年   3篇
  1971年   4篇
  1970年   6篇
  1967年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Although adenocarcinoma is a well known complication of chronic inflammatory bowel disease, primary gastrointestinal lymphoma occurring in Crohn's disease is rare. A 40-year-old man with 10 year-history of Crohn's disease had multiple longitudinal ulcerative lesions on descending colon in follow-up colonoscopic examination. Microscopic examination of proximal descending colon revealed peripheral T cell lymphoma and other site of the descending colon was consistent with Crohn's disease. The patient reached complete remission of malignant lymphoma after three cycles of combined chemotherapy. He has been well for 10 months with sulfasalazine maintenance therapy but was admitted to the hospital due to spontaneous bowel perforation of ascending colon. Right hemicolectomy was done, but the patient died of post-surgical recurrent mesenteric abscess and sepsis. To the best of our knowledge, this is the first case of Non-Hodgkin's lymphoma complicating Crohn's disease in Korea which was confirmed by immunohistochemical studies.  相似文献   
22.
Increased expression of the sodium iodide symporter (NIS) is required for effective radioiodine treatment and reporter gene imaging of breast cancer. We investigated the effect of retinoic acid on adenovirus-mediated expression of the human NIS gene in the MCF-7 breast cancer cell line. METHODS: The MCF-7 cell line was infected with recombinant adenovirus carrying the human NIS gene (Rad-NIS). Levels of NIS messenger RNA (mRNA) and protein expression and radioiodine ((125)I) uptake were measured to evaluate adenovirus-mediated NIS gene expression in wild-type and Rad-NIS-infected MCF-7 cells after treatment with all-trans-retinoic acid (ATRA; 10(-8)-10(-6) mol/L). RESULTS: The transduction efficiency of adenovirus in MCF-7 cells at a multiplicity of infection (MOI) of 50 was >60%. After incubation with 10(-6) mol/L ATRA, the mRNA level in Rad-NIS-infected MCF-7 cells increased to 118.5 times that of wild-type MCF-7 cells, whereas the mRNA level in wild-type MCF-7 cells showed only a 2.1-fold increase. Western blot, immunocytochemical staining, and flow cytometry analyses showed that NIS protein expression in MCF-7 cells infected with Rad-NIS increased after ATRA treatment. With ATRA treatment, the amount of (125)I uptake increased in a dose-dependent manner (P < 0.001). The (125)I uptake in wild-type MCF-7 cells increased 3.1-, 5.5-, and 7.6-fold with treatment with 10(-8), 10(-7), and 10(-6) mol/L ATRA, respectively. Rad-NIS-infected cells showed a 4.0-fold increase in (125)I uptake. Treatment of Rad-NIS-infected cells with 10(-8), 10(-7), and 10(-6) mol/L ATRA increased (125)I uptake by 4.9-, 8.2-, and 27.6-fold, respectively, compared with wild-type MCF-7 cells. The level of NIS expression in Rad-NIS-infected MCF-7 cells treated with 10(-6) mol/L ATRA (245.0 +/- 13.7 pmol/10(6) cells) was much greater than the sum of the expression levels seen in ATRA-treated wild-type cells and Rad-NIS-infected wild-type cells. CONCLUSION: Retinoic acid increases adenovirus-mediated NIS expression in MCF-7 cells. Our results indicate that improved efficiency of NIS gene therapy or reporter imaging in breast cancer may be possible with retinoic acid treatment.  相似文献   
23.
To characterize apoptosis in keloids and the mechanisms responsible for this process, the expression of activated caspase-9 and -3 in fibroblasts obtained from keloids was analyzed. Immunohistochemistry revealed that the number of fibroblasts positive for terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) or activated caspase-9 or -3 was low but was significantly higher in keloid tissues than in normal scar tissues. Significant relationships between the number of caspase-positive fibroblasts and TUNEL-positive fibroblasts suggested that the activation of caspase-9 and -3 induces apoptosis in a subpopulation of keloid fibroblasts. All keloid fibroblast cell lines established in this study showed activation of caspase-9 and -3 after serum deprivation for 3 or 4 hours, as shown using Western blotting. Furthermore, serum deprivation-induced apoptosis in a keloid fibroblast line was blocked by a caspase-9 inhibitor (acetyl-Leu-Glu-His-Asp-al), indicating that activation of caspase-9 was necessary for the process of apoptosis in keloid fibroblasts. Although serum deprivation did not significantly change the level of apoptosis protease activating factor-1 in any of the lines, cytochrome c release was detected in cytosolic fractions of the lines after serum deprivation for 3 or 4 hours. These results strongly suggest that keloid fibroblasts are predisposed to apoptosis and cytochrome c release and that caspase-9 activation may underlie regulation of apoptosis in keloid fibroblasts in vivo.  相似文献   
24.
It is important to acknowledge the harmful effects of environmental chemicals in human’s lives. The toxic effects of Diethylstilbestrol (DES), one of the endocrine-disrupting chemicals (EDCs), have been documented in many studies. As expected, DES affect male gendal hormone as well as female’s; therefore, epigenetic study should be considered. In this study, microarray technology was used to study harmful effects on the level of genomics, and here, two types of microarray chips- the Agilent mouse genome 4 × 44 K array for gene expression profiling and the Agilent mouse miRNA v13 for miRNA expression profiling-was used to study the relation between gene and miRNA expression profiles. As a result, we identified 4 miRNAs (miR 203, 350, 421, and 466i) that were similarly expressed at 3 hrs and 24 hrs of DES treat times. Twenty one genes matched between predicted target for 4 miRNAs and 118 genes expressed similarly. These genes have functions related to cell differentiation and cell cycle. Therefore, DES affects cellular function and induces toxicity in TM4 cells. In future studies, it is necessary to find more related functions and mechanisms of DES in the system.  相似文献   
25.
The aim of this longitudinal study was to assess the effect of rotating shift work on perceived sleep quality and sleep duration of nurses at Queen Elizabeth Central Hospital, Blantyre, Malawi. Twenty four female nurses were recruited at random from among personnel engaged in rotating shift work. The nurses worked a three-phase schedule: five day shifts (7.00 – 17.00) followed by three night shifts (17.00 – 7.00) and five days off. Controls were 22 female nurses who did not perform night duties. Sleep quality and duration was assessed using standardized and validated questionnaires on sleep duration and subjective sleep quality (SSQ). One-way analysis of variance revealed a significant effect of shift phase on total sleep duration (F = 36.8, d.f. = 8, P < 0.000) and perceived sleep quality (F = 8.81, d.f. = 3, P < 0.000). Night shift work was associated with reduction of sleep quality and duration. The after effects of night shifts persisted during days of the recovery period indicating accumulation of fatigue.  相似文献   
26.
The prevalence of wheezing in children varies widely around the world. The reasons for this geographic variability remain unclear but may be related in part to exposures in the home environment during pregnancy and early childhood. We investigated the prenatal and early childhood risk factors for wheezing symptoms among 2127 children aged 6–8 years who were participants in the Ukrainian component of the European Longitudinal Study of Pregnancy and Childhood (ELSPAC). Cases included the 169 children whose parents answered yes to the International Study of Asthma and Allergy in Children (ISAAC) question: 'Has your child had wheezing or whistling in the chest in the past 12 months' during the ELSPAC assessment of the children at age 7. These were compared with the 1861 children in the cohort whose parents answered 'no' to this question.
Factors significantly associated with increased risk of wheezing illness at age 7 in adjusted analyses included mother's asthma [adjusted odds ratio (OR) 3.46, 95% confidence interval (CI) 1.22, 9.85]; mother's allergy problems (OR 1.43, [1.00, 2.05]); rarely playing with other children at age 3 (OR 1.84, [1.09, 3.11]); water intrusion (OR 1.62, [1.09, 2.39]) and inadequate heating of the home (OR 1.52, [1.06, 2.16]) during pregnancy. Factors protective of wheezing at age 7 included being first-born (adjusted OR 0.70, 95% CI 0.50, 0.98); living in the city of Dniprodzerzynsk as compared with Kyiv (OR 0.36, [0.24, 0.54]) and weekly contact with furry animals (OR 0.44, [0.20, 0.97]) before age 3. The constellation of risk factors for wheezing in Ukrainian children is similar to that of children in other parts of the world. Known risk factors do not account for the significant between-city variability of wheezing in Ukrainian children.  相似文献   
27.
The synthesis of boron-containing 1,3,5-triazines and 1,2,4-triazines is described. Derivatives of 1,3,5-triazine containing the o-carborane cluster have been obtained by reacting the corresponding propargyl derivatives with B(10)H(14). Derivatives of 1,2,4-triazine containing the B(12)H(12)(2-) cluster have been obtained by nucleophilic substitution of ethylsulfone derivatives with B(12)H(11)SH(2-). They have been isolated in their ring-protonated form. Reaction of RNH(2)-B(8)H(11)NH-R with stericly demanding heterocycles failed, either for steric or for solubility reasons.  相似文献   
28.
The application of molecular techniques to solid tumors   总被引:1,自引:0,他引:1  
Recent developments in the field of molecular biology including the sequencing of the human genome and related high throughput methodologies are presenting the diagnostic pathologist with new opportunities to expand our understanding of human disease. These techniques enable the comprehensive assessment of molecular alterations with cell populations of interest, including cancer. It will be necessary for the diagnostic pathologist to become familiar with these techniques to effectively translate their potential into the clinical environment.  相似文献   
29.
Calcium channel blocker is useful for a variety of purposes and is effective for preventing hepatitis elicited by different inducers, suggesting its possible clinical application for treating hepatitis. The alpha1-subunit of the dihydropyridine-sensitive L-type calcium channel is a target of calcium channel blocker. For clinical application of calcium channel blocker, it is important to analyze the expression of the L-type calcium channel in the liver. However, the subtype of the L-type calcium channel alpha1-subunit expressed in the liver was not known. In the present study, the alpha1-subunit of the calcium channel expressed in human liver was systematically analyzed. The alpha1D subunit of the dihydropyridine-sensitive L-type voltage gated calcium channel is expressed relatively strongly in the liver and may play an important role in the liver.  相似文献   
30.
Lamivudine, a nucleoside analogue, has been used widely as an effective antiviral agent for the treatment of patients with chronic hepatitis B virus (HBV) infection. However, the YMDD motif mutation of HBV polymerase resistant to lamivudine occurs very frequently after long term therapy. We developed an oligonucleotide chip for the detection of YMDD motif mutants resistant to lamivudine and investigated the prevalence of the mutants in patients with chronic HBV infection who had not been treated by lamivudine before. Forty patients who had not been treated with lamivudine were included in this study. Serum samples were tested by the oligonucleotide chips designed for detection of wild-type YMDD motif, M552V and M552I. Samples were confirmed by restriction fragment length polymorphism (RFLP) and direct sequencing. M552I mutants were detected by the oligonucleotide chips in 7.5% (3/40) of chronic HBV infected patients (2 chronic hepatitis and 1 cirrhosis). The results were in accordance with those of RFLP. YMDD motif mutants occur as natural genome variabilities in patients with chronic HBV infection who had not been treated with lamivudine before. Oligonucleotide chip technology is a reliable and useful diagnostic tool for the detection of mutants resistant to antiviral therapy in chronic HBV infection.  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