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   8054篇
  免费   417篇
  国内免费   62篇
耳鼻咽喉   67篇
儿科学   226篇
妇产科学   192篇
基础医学   1138篇
口腔科学   196篇
临床医学   639篇
内科学   1878篇
皮肤病学   178篇
神经病学   942篇
特种医学   400篇
外科学   898篇
综合类   36篇
预防医学   384篇
眼科学   173篇
药学   534篇
中国医学   38篇
肿瘤学   614篇
  2024年   13篇
  2023年   83篇
  2022年   149篇
  2021年   237篇
  2020年   134篇
  2019年   186篇
  2018年   243篇
  2017年   179篇
  2016年   194篇
  2015年   233篇
  2014年   283篇
  2013年   353篇
  2012年   555篇
  2011年   581篇
  2010年   355篇
  2009年   328篇
  2008年   511篇
  2007年   537篇
  2006年   547篇
  2005年   491篇
  2004年   493篇
  2003年   478篇
  2002年   413篇
  2001年   88篇
  2000年   68篇
  1999年   95篇
  1998年   87篇
  1997年   71篇
  1996年   54篇
  1995年   44篇
  1994年   28篇
  1993年   36篇
  1992年   31篇
  1991年   27篇
  1990年   25篇
  1989年   37篇
  1988年   35篇
  1987年   27篇
  1986年   23篇
  1985年   13篇
  1984年   17篇
  1983年   18篇
  1982年   20篇
  1981年   10篇
  1979年   15篇
  1978年   7篇
  1977年   9篇
  1974年   7篇
  1970年   10篇
  1967年   7篇
排序方式: 共有8533条查询结果,搜索用时 15 毫秒
991.
46, XY partial gonadal dysgenesis is a rare condition characterized by a varying degree of testicular dysgenesis, ambiguous genitalia, and usually absence of regression of Müllerian structures. The management of patients with these disorders warrants revisiting, owing to recent molecular biological findings and to reports on the long-term outcome of individuals with ambiguous genitalia. We report on a patient with 46, XY chromosomes, presence of the "sex-determining region of Y chromosome" (SRY) gene, scrotal gonads, fallopain tubes, uterus, vagina, and ambiguous genitalia with a penisoid, perineal hypospadia and sinus urogenitalis. Gonadal biopsy revealed virtually normal testicular tissue in both gonads. Removal of the gonads during surgery for a cystic adnex tumor revealed clear signs of partial gonadal dysgenesis. The decision to raise the child as a male was made by parents and physicians caring for the patient. Administration of testosterone, removal of the uterus and adnexes, in addition to repair of the hypospadia permitted an almost normal penis to be formed with normal male micturition. In the management of affected patients it has to be considered that establishing the diagnosis may be extremely tricky, even with the use of gonadal biopsies. The decision on sex assignment may be even more difficult, since future gender identity, limitations of genital reconstructive surgery and the potential for development of gonadal tumors have to be taken into consideration. While in the past, female sex assignment was commonly recommended for such patients, raising them in a male gender role is now considered. Parents should be involved in the decision that is ultimately based on extensive analysis of the individual case.  相似文献   
992.
Among the many promising cancer immunotherapeutic strategies, dendritic cells (DC) have become of particular interest. This study aims to optimize a clinical grade protocol for culture and transfection of human DC. Monocytes and CD34(+) hematopoietic stem cells (HSC) from same donor were differentiated under serum-free conditions and analyzed for their susceptibility to several recently described nonviral transfection methods as compared with established virally mediated gene transfer. Nonviral gene transfer methods studied were square-wave electroporation, lipofection, and particle-mediated transfer of plasmid DNA or in vitro transcribed mRNA. We conclude that DNA is not suitable for transduction of DC using nonviral methods. In contrast, mRNA and square-wave electroporation reproducibly yields 60% and 50% transfected monocyte- and CD34(+)-derived DC, respectively, measured at protein level, without affecting the cell viability. Thus, the transfection efficiency of this method is comparable with the 40-90% transgene expression obtained using retroviral (RV) or adenoviral (AdV) vectors in CD34(+)- and monocyte-derived DC, respectively. In monocyte-derived DC, however, the amount of protein expressed per-cell basis was higher after AdV (MOI = 1000) compared with mRNA electroporation-mediated transfer. This is the first study directly demonstrating side-by-side that mRNA electroporation into DC of different origin indeed results in a comparable number of transduced cells as when using virus-mediated gene transfer.  相似文献   
993.
OBJECTIVE-Impaired endothelial function of resistance and conduit arteries can be detected in patients with type 1 diabetes. We studied whether a persistent improvement of endothelial function can be achieved by regular physical training. RESEARCH DESIGN AND METHODS-The study included 26 patients with type 1 diabetes of 20 +/- 10 years' duration and no overt angiopathy; 18 patients (42 +/- 10 years old) participated in a bicycle exercise training program, and 8 patients with type 1 diabetes (33 +/- 11 years old) served as control subjects. Vascular function of conduit arteries was assessed by flow-mediated and endothelium-independent dilation of the brachial artery and of resistance vessels by the response of ocular fundus pulsation amplitudes to intravenous N(G)-monomethyl-L-arginine (L-NMMA) at baseline, after 2 and 4 months of training, and 8 months after cessation of regular exercise. RESULTS-Training increased peak oxygen uptake (VO(2max)) by 13% after 2 months and by 27% after 4 months (P = 0.04). Flow-mediated dilation (FMD) of the brachial artery increased from 6.5 +/- 1.1 to 9.8 +/- 1.1% (P = 0.04) by training. L-NMMA administration decreased fundus pulsation amplitude (FPA) by 9.1 +/- 0.9% before training and by 13.4 +/- 1.5% after 4 months of training (P = 0.02). VO(2max), FMD, and FPA were unchanged in the control group. Vascular effects from training were abrogated 8 months after cessation of exercise. CONCLUSIONS-Our study demonstrates that aerobic exercise training can improve endothelial function in different vascular beds in patients with long-standing type 1 diabetes, who are at considerable risk for diabetic angiopathy. However, the beneficial effect on vascular function is not maintained in the absence of exercise.  相似文献   
994.
PURPOSE: To assess the effectiveness of a combined procedure (pars plana vitrectomy with temporary keratoprosthesis, vitreoretinal surgery, and penetrating keratoplasty) and to determine which factors influence corneal transplant success rates. METHODS: Records for 34 severely injured eyes of 31 consecutive patients who underwent penetrating keratoplasty in combination with vitreoretinal surgery between 1991 and 1998, with a follow-up of at least 12 months, were evaluated retrospectively. Analysis was focused on ocular history, functional and anatomic anterior and posterior segment outcome, and complications. RESULTS: Penetrating keratoplasty was performed in 10 eyes (29%) within 8 weeks of trauma and in 24 eyes (71%) as a secondary procedure. Initial improvement in visual acuity (VA) was achieved in 47% of eyes; at the end of the follow-up, 74% of the eyes had attained equal or better VA than the initial postsurgical VA. Reasons for poor final VA were hypotony or phthisis (35%) and recurrent retinal detachment (11%). Corneal grafts remained clear for 1 year in 65% of eyes. Transplant failure was less in eyes that did not need a permanent silicone oil tamponade, when the retina was attached before surgery, and in eyes that were grafted later after trauma and received no further surgery. These were some conditions that were associated with a longer mean graft survival time, but without statistical significance. There was no difference in eyes according to the trauma mechanism, preoperative intraocular pressure, or graft size. CONCLUSIONS: Penetrating keratoplasty in severely injured eyes is often complicated by ciliary body malfunction and secondary transplant failure. Although the functional outcome of a combined procedure is limited by primary and secondary tissue destruction, preserving ambulatory vision is possible and thus improves the quality of life, at least in patients with single remaining eyes.  相似文献   
995.
BACKGROUND: Cannabinoids present neurotoxic and neuroprotective properties in in vitro studies, inconsistent alterations in human neuroimaging studies, neuropsychological deficits, and an increased risk for psychotic episodes. METHODS: Proton magnetic resonance spectroscopy ((1)H-MRS), neuropsychological testing, and hair analysis for cannabinoids was performed in 13 male nontreatment-seeking recreational cannabis users and 13 male control subjects. RESULTS: A significantly diminished N-acetylaspartate/total creatine (NAA/tCr) ratio in the dorsolateral prefrontal cortex (DLPFC) was observed in cannabis users (p = .0003). The NAA/tCr in the putamen/globus pallidum region correlated significantly with cannabidiol (R(2) = .66, p = .004). Results of the Wisconsin Card Sorting test, Trail making Test, and D2 test for attention were influenced by cannabinoids. CONCLUSIONS: Chronic recreational cannabis use is associated with an indication of diminished neuronal and axonal integrity in the DLPFC in this study. As chronic cannabis use is a risk factor for psychosis, these results are interesting because diminished NAA/tCr ratios in the DLPFC and neuropsychological deficits were also reported in schizophrenia. The strong positive correlation of NAA/tCr and cannabidiol in the putamen/globus pallidum is in line with neuroprotective properties of cannabidiol, which were also observed in in vitro model studies of Parkinson's disease.  相似文献   
996.
Behavioral and physiological studies have indicated the existence of a temporal window of auditory integration (TWI), within which similar sounds are perceptually grouped. The current study exploits the combined temporal and spatial resolution of fast optical imaging (the event-related optical signal, EROS) to show that brain activity elicited by sounds within and outside the TWI differs in location and latency. In a previous event-related brain potential (ERP) study [Sable, Gratton, and Fabiani (2003) European Journal of Neuroscience, 17, 2492-2496], we found that the mismatch negativity (MMN; a brain response to acoustic irregularities) elicited by deviations in stimulus onset asynchronies (SOAs) had a unique shape when the deviant SOA was within the TWI. In the present study, we extended these ERP results using EROS. Participants heard trains of five tones. The first four tones had SOAs of 96, 192, 288 or 384 ms. The SOA of the fourth and fifth tones was either the same (standard) or one of the other three (deviant) SOAs. With a deviant SOA of 96 ms, the cortical response was approximately 2 cm anterior to responses to longer SOA deviants, and was followed by a later response that was absent in the other conditions. Similarly to the electrical MMN, the optical mismatch response amplitudes were proportional to the magnitude of interval deviance. These results, in combination with our previous findings, indicate that the temporal integration of sounds is reflected in cortical mismatch responses that differ from the typical response to interval deviance.  相似文献   
997.
Summary After the use of d,1-folinic acid (d,1-CHO-THF), pharmacokinetic measurements should take into account 1-CHO-THF and its metabolite 1-methyltetrahydrofolic acid (1-CH3-THF) as well as d-CHO-THF. For this purpose, we developed a simple and rapid assay by combining reversed-phase HPLC to determine total levels of d,1-CHO-THF and CH3-THF and chiral HPLC to separate the biologically active 1-CHO-THF from the inactive d-CHO-THF. We investigated the pharmacokinetics after short-term infusion of 300 mg d,1-CHO-THF in ten healthy volunteers. With a mean of 56.5 min, 1-CHO-THF exhibits a rapid body clearance of 222 ml/min, about 60% of which is caused by metabolism to CH3-THF and 40%, by renal excretion. CH3-THF has a terminal half-life of 208 min and a total body clearance of 88.9 ml/min, which is essentially the same as the renal clearance. Due to the lower clearance of CH3-THF, its AUC (2,132 M × min) exceeds that of 1-CHO-THF (1445 M × min) by approximately 50%. In contrast to that of the reduced 1-folates, the total body and renal clearance of d-CHO-THF is very low, with values of 13.2 and 12.9 ml/min, respectively. This results in a very high AUC of 24, 269 M × min, which is higher by factors of 17 and 11 than those of 1-CHO-THF and CH3-THF, respectively. The implications of the distinct kinetics of the reduced 1-folates and d-CHO-THF for the efficacy of folinic acid/5-fluorouracil therapy and adequate protocols for the treatment of advanced colorectal cancer are discussed.Abbreviations CH2-THF N-5,N-10-methylenetetnahydrofolic acid - CH3-THF N-5-methyltetrahydrofolic acid - CHO-THF N-5-formyltetrahydrofolic acid - 5-FU 5-fluorouracil - FBAL -fluoro--alanine - FUH2 dihydrofluorouracil - FUPA -fluoroureidopropionic acid Dedicated to Prof. Dr. W. Wilmanns on the occasion of his 60th birthdayThis study was carried out with the support of the Lederle Company, Wolfratshausen  相似文献   
998.
A longitudinal study of 1,281 women with a histological diagnosis of cervical intraepithelial neoplasia (CIN) during 1974–76 is presented. After 12 years of follow-up, 30 percent of the women had further cytological abnormalities reported. The rate of subsequent abnormality was highest during the first 12 months of follow-up; thereafter, there was no evidence of any decline in the rate of subsequent abnormality with increasing duration of follow-up. Women from the CIN cohort had twice as many later cytological abnormalities as an age-matched cohort of women who were negatively screened during 1974–76 (excluding abnormalities within 12 months of entry to the study and after adjustment for smear frequency). The CIN cohort remained at substantially greater risk for a subsequent diagnosis of squamous cell carcinoma of the cervix compared with the control group of negatively-screened women (rate ratio 19.8, 95 percent confidence interval 2.4–163.6, P < 0.01). These results indicate that women who have received surgical intervention for CIN continue to have substantial morbidity from cervical abnormalities during medium-term follow-up.Dr Mitchell is Epidemiologist and Deputy Director, Victorian Cytology (Gynaecological) Service, PO Box 253B, Melbourne 3001, Australia; Dr Medley is Director, Victorian Cytology (Gynaecological) Service: Dr Carlin is Lecturer in Statistics, Department of Commuity Medicine, University of Melbourne. Address reprint requests to Dr Mitchell. Dr Mitchell is supported in part by grants from the National Health and Medical Research Council and the Anti-Cancer Council of Victoria.  相似文献   
999.
1000.
In an in vitro study, 10 gallbladders of adult pigs and 6 gallbladders of lambs, all removed immediately after slaughtering, were stimulated in a water bath by electric means to induce active contraction. Gallbladder emptying was followed by ultrasonography employing five measurement procedures: (1) gallbladder width, (2) longitudinal planimetry, (3) transverse planimetry, (4) ellipsoid method, and (5) sum of cylinders method. In an in vivo investigation, gallbladder emptying of 30 volunteers (12 healthy subjects, 18 diabetics) was evaluated in the same way after ingestion of a fatty meal. Gallbladder width was found to be unsuitable to estimate the decrease in gallbladder volume due to a nonlinear relation of the parameters. Longitudinal planimetry tended to be less valid than transverse planimetry in assessing gallbladder volume reduction. The most valid estimation of gallbladder volume decreases was obtained by the two three-dimensional procedures. However, in neither in vitro nor in vivo could a significant difference between the sum of cylinders method and the ellipsoid method in determining relative volume reduction be established. We conclude that a three-dimensional measurement procedure should be used for valid assessments of gallbladder motility. However, according to our data there is no advantage in using the time-consuming sum of cylinders method compared to the simple ellipsoid method.  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