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   7363篇
  免费   657篇
  国内免费   15篇
耳鼻咽喉   42篇
儿科学   272篇
妇产科学   180篇
基础医学   1112篇
口腔科学   129篇
临床医学   861篇
内科学   1564篇
皮肤病学   69篇
神经病学   676篇
特种医学   302篇
外科学   882篇
综合类   112篇
现状与发展   1篇
一般理论   5篇
预防医学   721篇
眼科学   158篇
药学   502篇
中国医学   2篇
肿瘤学   445篇
  2022年   42篇
  2021年   106篇
  2020年   56篇
  2019年   88篇
  2018年   142篇
  2017年   84篇
  2016年   78篇
  2015年   120篇
  2014年   158篇
  2013年   247篇
  2012年   385篇
  2011年   436篇
  2010年   272篇
  2009年   246篇
  2008年   409篇
  2007年   467篇
  2006年   410篇
  2005年   386篇
  2004年   355篇
  2003年   420篇
  2002年   331篇
  2001年   127篇
  2000年   152篇
  1999年   162篇
  1998年   113篇
  1997年   93篇
  1996年   73篇
  1995年   67篇
  1994年   81篇
  1993年   75篇
  1992年   122篇
  1991年   123篇
  1990年   118篇
  1989年   119篇
  1988年   104篇
  1987年   106篇
  1986年   89篇
  1985年   93篇
  1984年   64篇
  1983年   57篇
  1982年   48篇
  1981年   43篇
  1979年   84篇
  1978年   56篇
  1976年   43篇
  1974年   55篇
  1973年   39篇
  1972年   42篇
  1971年   46篇
  1970年   44篇
排序方式: 共有8035条查询结果,搜索用时 15 毫秒
61.
PURPOSE: Chromogenic in situ hybridization (CISH) is a new modification of the fluorescence in situ hybridization (FISH) technique for detection of oncogene amplification in archival tumor samples. In CISH, the oncogene probe is detected using a peroxidase reaction, allowing use of transmitted light microscopy. We compared detection of HER-2/neu amplification by CISH with a Food and Drug Administration-approved two-color FISH test in an interlaboratory setting. EXPERIMENTAL DESIGN: Formalin-fixed paraffin-embedded tumor samples from 197 breast cancers were analyzed for HER-2 amplification by CISH. Two-color FISH (PathVysion) CISH of 17 centromere was done if the observer considered it necessary to ascertain amplification status in tumors with borderline HER-2 CISH copy numbers. RESULTS: Paired CISH/FISH results were available from 192 (97%) of 197 cases, no clear difference in success rates of either method was observed. Centromere 17 CISH was considered necessary in seven tumors. CISH and two-color FISH results were concordant in 180 cases (93.8%). There were 92 and 88 tumors found HER-2 amplified and nonamplified, respectively, by both methods. Eight tumors were amplified by CISH but not by FISH, and four tumors exhibited the opposite condition (kappa coefficient 0.875). In 7 of 12 cases differences between the two methods could have related to a lack of CISH chromosome 17 information. The remaining cases were explained by difficult histology (ductal carcinoma in situ, poor representativity, dense lymphocytic infiltration, or intratumoral heterogeneity). CONCLUSIONS: These results indicate that CISH could provide an accurate and practical alternative to FISH for clinical diagnosis of HER-2/neu oncogene amplification in archival formalin-fixed breast cancer samples.  相似文献   
62.
A treatment portal or simulator image has traditionally been used to demonstrate the lung and heart coverage of the breast tangential portal. In many cases, these images were acquired as a planning session on the linear accelerator. The patients were also CT scanned to assess the lung/heart volume and to determine the surgical site depth for the electron‐boost energy. A study using 50 consecutive patients was performed comparing the digitally reconstructed radiograph (DRR) from the virtual simulation with treatment portal images. Modification to the patient's arm position is required when performing the planning CT scans due to the aperture size of the CT scanner. Virtual simulation was used to assess the potential variation of lung and heart measurements. The average difference in lung volume between the DRR and portal image was less than 2 mm, with a range of 0?5 mm. Arm position did not have a sig­nificant impact on field deviation; however, great care was taken to minimize any changes in arm position. The modification of the arm position for CT scanning did not lead to significant variations between the DRRs and portal images. The Advantage Sim software has proven capable of producing good quality DRR images, providing a realistic representation of the lung and heart volume included in the treatment portal.  相似文献   
63.
AIMS—To report on the epidemiology of cerebral palsy in England and Scotland, to provide information on the prevalence of cerebral palsy and the severity of the disability or any co-morbidity.METHODS—Cerebral palsy registers were compiled from multiple sources of ascertainment covering all of Scotland and the counties of Merseyside, Cheshire, Berkshire, Buckinghamshire, Northamptonshire and Oxfordshire in England. All cases of cerebral palsy born in 1984 to 1989, to mothers resident in the area, were included. Denominator number of live births and neonatal deaths for determining birthweight specific prevalence were obtained from birth and death registrations. Learning, manual, and ambulatory disabilities were graded for severity. Any co-existing sensory (hearing or visual) morbidity was also graded for severity.RESULTS—There were 789 411 live births in 1984-9, with 3651 neonatal deaths (neonatal mortality 4.6 per 1000 live births) and 1649cases of cerebral palsy—a cerebral palsy prevalence of 2.1 per 1000 neonatal survivors. The birthweight specific cerebral palsy prevalence ranged from 1.1 per 1000 neonatal survivors in infants weighing ?2500 g to 78.1 in infants weighing <1000 g. There was no significant time trend in prevalence of cerebral palsy in any of the birthweight groups, in contrast to the fall in neonatal mortality observed in all birthweight groups. Of the 1649 cases of cerebral palsy, 550 (33.4%) had severe ambulatory disability (no independent walking), 390 (23.7%) had severe manual disability (incapable of feeding or dressing unaided), 381 (23.1%) had severe learning disability (IQ <50), 146 (8.9%) had severe visual disability (vision <6/60 in the better eye) and 12 had severe hearing disability (>70 dB loss).CONCLUSIONS—Registers fill an important gap left by the lack of routine data on the prevalence of disability in children. The ability to record trends in the prevalence and the severity of the disability should inform those who have responsibility for providing services for children with disabilities.  相似文献   
64.
Purpose: Both ondansetron and cyclophosphamide are thought to be metabolized by hepatic microsomal processes. The purpose of this study was to evaluate the potential pharmacokinetic interactions between ondansetron and high-dose alkylating agent chemotherapy. Methods: A total of 54 breast cancer patients receiving high-dose cyclophosphamide, cisplatin and carmustine were treated prospectively in four sequential cohorts. Cohorts I and II received continuous infusions of both ondansetron and prochlorperazine, and cohorts III and IV received a continuous infusion of ondansetron alone at the same doses. All patients received lorazepam every 4 h. A group of 75 matched historical controls had received a continuous infusion of prochlorperazine with lorazepam. Pharmacokinetic monitoring of each drug used in the high-dose chemotherapy regimen was conducted. Results: Median AUCs of cyclophosphamide in patients receiving ondansetron (73.6 mg/ml · min) were lower than those of the control patients (88.3 mg/ml · min, n = 75, P = 0.0004), but the median cisplatin AUC was approximately 10% higher and no difference in the disposition of carmustine was demonstrated. Patients treated with ondansetron displayed a higher frequency of headaches than the controls. The frequency of achieving complete emetic control was greater in the ondansetron + prochlorperazine groups compared to the ondansetron alone groups and was greater in both these groups than in the prochlorperazine alone group on the first day of therapy only. Conclusion: Ondansetron altered the systemic exposure to cyclophosphamide when these agents were administered concomitantly. Ondansetron did not substantially improve overall emetic control when used alone but may improve control in combination with prochlorperazine. Future randomized studies are needed to delineate the effect of ondansetron on the disposition of the active cyclophosphamide metabolites so that clinical implications can be addressed. Received: 28 October 1997 / Accepted: 9 March 1998  相似文献   
65.
Tolerance is defined as a decrease in responsiveness to a drug after repeated administration. Tolerance to the behavioral effects of hallucinogens occurs in humans and animals. In this study, we used drug discrimination to establish a behavioral model of lysergic acid diethylamide (LSD) tolerance and examined whether tolerance to the stimulus properties of LSD is related to altered serotonin receptor signaling. Rats were trained to discriminate 60 microg/kg LSD from saline in a two-lever drug discrimination paradigm. Two groups of animals were assigned to either chronic saline treatment or chronic LSD treatment. For chronic treatment, rats from each group were injected once per day with either 130 microg/kg LSD or saline for 5 days. Rats were tested for their ability to discriminate either saline or 60 microg/kg LSD, 24 h after the last chronic injection. Rats receiving chronic LSD showed a 44% reduction in LSD lever selection, while rats receiving chronic vehicle showed no change in percent choice on the LSD lever. In another group of rats receiving the identical chronic LSD treatment, LSD-stimulated [35S]GTPgammaS binding, an index of G-protein coupling, was measured in the rat brain by autoradiography. After chronic LSD, a significant reduction in LSD-stimulated [35S]GTPgammaS binding was observed in the medial prefrontal cortex and anterior cingulate cortex. Furthermore, chronic LSD produced a significant reduction in 2,5-dimethoxy-4-iodoamphetamine-stimulated [35S]GTPgammaS binding in medial prefrontal cortex and anterior cingulate cortex, which was blocked by MDL 100907, a selective 5-HT2A receptor antagonist, but not SB206553, a 5-HT2C receptor antagonist, indicating a reduction in 5-HT2A receptor signaling. 125I-LSD binding to 5-HT2A receptors was reduced in cortical regions, demonstrating a reduction in 5-HT2A receptor density. Taken together, these results indicate that adaptive changes in LSD-stimulated serotonin receptor signaling may mediate tolerance to the discriminative stimulus effects of LSD.  相似文献   
66.
BACKGROUND: The aim of this study was to determine whether a polytetrafluoroethylene (PTFE) patch sutured over the religated saphenofemoral junction could reduce the rate of recurrence after operation for recurrent varicose veins. METHODS: Fifty patients who had surgery for recurrent long saphenous incompetence (81 legs had a small PTFE patch sutured over the religated saphenofemoral junction. There were no major complications following surgery. Three patients had a wound infection or delayed healing. All patients were invited for clinical examination and duplex imaging at a median of 19 (range 6-39) months after operation. RESULTS: Some 38 of 43 patients (70 legs) remained satisfied with the results of surgery; 16 (23 per cent) of 70 legs had visible veins on inspection and eight of these (11 per cent) involved symptomatic recurrence. Duplex imaging showed that recurrence was due to saphenofemoral junction incompetence in ten legs; two appeared to have a major groin connection but the other eight appeared to have neovascularization. Other causes were thigh perforator reflux (three legs) and cross-groin collaterals (three). Eleven of the 16 legs with recurrence had varicography but in two the procedure was a technical failure. Two legs had evidence of a significant connection (more than 3 mm) and two a minor connection (less than 3 mm) to the femoral vein at the level of the PTFE patch, but in the remainder recurrence was due to upper thigh perforating veins. There was good concordance between duplex imaging and varicography. CONCLUSION: PTFE patch saphenoplasty appears to be safe. Although these are early results, the technique seems potentially as effective as other barrier methods that have been investigated; in ten legs (12 per cent) recurrence was attributed to failure at the level of the PTFE patch.  相似文献   
67.
PURPOSE: To determine the incidence of second malignancies among patients with Hodgkin's lymphoma (HL) treated with autologous hematopoietic stem cell transplantation (AHSCT) compared with patients receiving conventional therapy alone and to identify potential risk factors for their occurrence. PATIENTS AND METHODS: We analyzed data on 1,732 consecutive patients with HL treated at the British Columbia Cancer Agency from 1976 to 2001, including 202 patients undergoing AHSCT. The median follow-up duration was 9.8 years for the whole cohort, 9.7 years for those patients treated with conventional therapy, and 7.8 years from AHSCT. RESULTS: The cumulative incidence of developing any second malignancy 15 years after therapy for HL was 9% (risk ratio = 3.5; P < .001); however, the incidence did not differ between those patients receiving conventional therapy alone compared with those undergoing AHSCT (10% and 8%, respectively; P = .48). In multivariate analysis, the only factor significantly associated with an increased risk of developing any second neoplasm or solid tumor was age > or = 35 years (P < .0001). An increased risk of therapy-induced acute myeloid leukemia and therapy-induced myelodysplastic syndrome was seen for patients aged > or = 35 years (P = .03) and stage III/IV (P = .04). CONCLUSION: Patients with HL are at increased risk of developing a second neoplasm. However, those patients undergoing AHSCT do not seem to be at greater risk compared with those patients receiving conventional therapy alone, at least during the first decade after therapy.  相似文献   
68.
69.

Background

Automated detection of subtle changes in peripapillary retinal nerve fibre layer thickness (RNFLT) over time using optical coherence tomography (OCT) is limited by inherent image quality before layer segmentation, stabilization of the scan on the peripapillary retina and its precise placement on repeated scans. The present study evaluates image quality and reproducibility of spectral domain (SD)-OCT comparing different rates of automatic real-time tracking (ART).

Methods

Peripapillary RNFLT was measured in 40 healthy eyes on six different days using SD-OCT with an eye-tracking system. Image brightness of OCT with unaveraged single frame B-scans was compared to images using ART of 16 B-scans and 100 averaged frames. Short-term and day-to-day reproducibility was evaluated by calculation of intraindividual coefficients of variation (CV) and intraclass correlation coefficients (ICC) for single measurements as well as for seven repeated measurements per study day.

Results

Image brightness, short-term reproducibility, and day-to-day reproducibility were significantly improved using ART of 100 frames compared to one and 16 frames. Short-term CV was reduced from 0.94?±?0.31 % and 0.91?±?0.54 % in scans of one and 16 frames to 0.56?±?0.42 % in scans of 100 averaged frames (P?≤?0.003 each). Day-to-day CV was reduced from 0.98?±?0.86 % and 0.78?±?0.56 % to 0.53?±?0.43 % (P?≤?0.022 each). The range of ICC was 0.94 to 0.99. Sample size calculations for detecting changes of RNFLT over time in the range of 2 to 5 μm were performed based on intraindividual variability.

Conclusion

Image quality and reproducibility of mean peripapillary RNFLT measurements using SD-OCT is improved by averaging OCT images with eye-tracking compared to unaveraged single frame images. Further improvement is achieved by increasing the amount of frames per measurement, and by averaging values of repeated measurements per session. These strategies may allow a more accurate evaluation of RNFLT reduction in clinical trials observing optic nerve degeneration.  相似文献   
70.
The effect of aminophylline on renin release from human chorion was investigated by perfusing the tissue with various concentrations of the drug. Buffer containing aminophylline (2 X 10(-6) mol/l) doubled the rate of active and total renin secretion, but a more concentrated solution (10(-5) mol/l) released proportionately less active and total renin although the result was statistically significant. Renin secretion was not altered by aminophylline (5 X 10(-5) mol/l). The pattern of renin release was modulated by concentrations of aminophylline which were at least a 100-fold lower than those required to inhibit cyclic adenosine 3',5'-monophosphate phosphodiesterase. However, as the methylxanthines are potent adenosine receptor antagonists, we suggest that in the human chorion adenosine is a mediator of renin release.  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