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   23259篇
  免费   1013篇
  国内免费   157篇
耳鼻咽喉   221篇
儿科学   488篇
妇产科学   234篇
基础医学   2947篇
口腔科学   409篇
临床医学   1507篇
内科学   6243篇
皮肤病学   551篇
神经病学   1791篇
特种医学   927篇
外科学   3724篇
综合类   64篇
一般理论   4篇
预防医学   600篇
眼科学   731篇
药学   1554篇
中国医学   36篇
肿瘤学   2398篇
  2023年   137篇
  2022年   319篇
  2021年   551篇
  2020年   272篇
  2019年   345篇
  2018年   452篇
  2017年   351篇
  2016年   461篇
  2015年   518篇
  2014年   644篇
  2013年   783篇
  2012年   1384篇
  2011年   1446篇
  2010年   825篇
  2009年   749篇
  2008年   1288篇
  2007年   1437篇
  2006年   1342篇
  2005年   1495篇
  2004年   1470篇
  2003年   1291篇
  2002年   1317篇
  2001年   461篇
  2000年   403篇
  1999年   445篇
  1998年   374篇
  1997年   266篇
  1996年   285篇
  1995年   233篇
  1994年   209篇
  1993年   202篇
  1992年   245篇
  1991年   240篇
  1990年   243篇
  1989年   235篇
  1988年   182篇
  1987年   160篇
  1986年   172篇
  1985年   134篇
  1984年   137篇
  1983年   107篇
  1982年   75篇
  1981年   68篇
  1980年   56篇
  1979年   78篇
  1978年   66篇
  1977年   57篇
  1974年   43篇
  1971年   36篇
  1970年   43篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.

Background

Photosensitizers used for photodynamic therapy (PDT) to treat dermatologic disease are metabolized into mainly protoporphyrin IX (PpIX), which has five absorption wavelength peaks: 410?nm, 510?nm, 545?nm, 580?nm, and 630?nm. Although only red light around 635?nm and blue light around 400?nm are used as light sources for PDT, the efficiency of PDT might be improved by using multiple wavelengths, including those that correspond to the other absorption peaks of PpIX. Furthermore, because the target disease often occurs on the face, a flexible-type light-source unit that can be fitted to the lesion without unnecessarily exposing the mucous membranes, e.g., the eyes, nostrils, and mouth, is preferred.

Objective

We investigated the efficacy of a flexible light-emitting diode (LED) unit that emits multiple wavelengths to improve PDT effects.

Methods

HaCaT cells were incubated with 5-ALA and subsequently irradiated with either a single wavelength or sequentially with two wavelengths. Cell viability and reactive oxygen species were analyzed. Nude mice were implanted with COLO679 cells by subcutaneous injection into the flank. 5-ALA was subcutaneously injected into the tumor. The tumor was irradiated with 50?J/cm2 (day 0) and assessed daily until day 21.

Results

The synergistic PDT effects of dual-wavelength irradiation and reactive oxygen species production were highest with the 405-nm and 505-nm wavelength combination. This dual wavelength combination was also the most effective in vivo.

Conclusion

We could therefore conclude that dual-wavelength PDT is an efficient strategy for improving the therapeutic effects of PDT. Using a flexible LED unit is expected to achieve more uniform irradiation of uneven areas.  相似文献   
2.
Purpose: Mouse double-stranded DNA-dependent protein kinase (DNA-PK) activity is heat sensitive. Recovery of heat-inactivated DNA repair activity is a problem after combination therapy with radiation and heat. We investigated the mechanism of recovery of heat-inactivated DNA-PK activity.

Methods: Hybrid cells containing a fragment of human chromosome 8 in scid cells (RD13B2) were used. DNA-PK activity was measured by an in vitro assay. Immunoprecipitation of the nuclear extract was performed with an anti-Ku80 antibody. Proteins co-precipitated with Ku80 were separated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and detected by Western blotting using anti-heat shock protein (HSP)72 and anti-heat shock cognate protein (HSC)73 antibodies. HSC73 was overexpressed with the pcDNA3.1 vector. Short hairpin (sh)RNA was used to downregulate HSC73 and HSP72.

Results: The activity of heat-inactivated DNA-PK recovered to about 50% of control during an additional incubation at 37?°C after heat treatment at 44?°C for 15?min in the presence of cycloheximide (which inhibits de novo protein synthesis). Maximal recovery was observed within 3?h of incubation at 37?°C after heat treatment. Constitutively expressed HSC73, which folds newly synthesized proteins, reached maximal levels 3?h after heat treatment using a co-immunoprecipitation assay with the Ku80 protein. Inhibiting HSC73, but not HSP72, expression with shRNA decreased the recovery of DNA-PK activity after heat treatment.

Conclusions: These results suggest that de novo protein synthesis is unnecessary for recovery of some heat-inactivated DNA-PK. Rather, it might be reactivated by the molecular chaperone activity of HSC73, but not HSP72.  相似文献   

3.
Potassium, which is abundant in vegetables, is inversely related to blood pressure. Although the situation has changed somewhat in recent years, the Okinawan diet has generally included a large amount of vegetables, and until recently Okinawans had the lowest rates of mortality due to stroke and coronary heart disease in Japan. Based on the hypothesis that these low mortality rates are partly attributable to increased potassium intake resulting from the high vegetable consumption, this study examined whether increasing the consumption of typical yellow-green Okinawan vegetables increases potassium intake. The purpose of this investigation was to determine whether increased consumption of these vegetables should be one of the dietary modifications recommended in public health promotion programs for Okinawans. The study employed 56 healthy, normotensive, free-living Japanese women aged 18-38 years living in Okinawa. They were randomized to a dietary intervention group (n=27) or a control group (n=29). Members of the dietary intervention group received an average weight of 371.4 g/day of a combination of the following vegetables twice weekly through an express home parcel deliver service for a period of 14 days: Goya (Momordica charantia), green papaya (Carica papaya), Handama (Gynura bicolor), Karashina (Brassica juncea), Njana (Crepidiastrum lanceolatium), Fuchiba (Artemisia vulgaris) and Fudanso (Beta vulgaris); and they consumed an average of 144.9 g/day, resulting in a 20.5% increase in their urinary potassium excretion over the baseline (p=0.045). The members of the control group were asked to avoid these vegetables, and the change in potassium excretion in this group was not significant (p=0.595). Urinary sodium and magnesium excretions, systolic and diastolic blood pressures, folic acid, triglycerides and serum high density lipoprotein cholesterol, low density lipoprotein cholesterol and total cholesterols changed non-significantly in both groups. Also, post-intervention urinary potassium excretion correlated positively with vegetable consumption in both the dietary intervention (p<0.0001) and control (p=0.008) groups and with Okinawan vegetable intake in the dietary intervention group (p=0.0004).  相似文献   
4.
Background: Although bleeding is an unavoidable complication of endoscopic submucosal dissection (ESD), endoscopic hemostasis using an insulation‐tipped electrosurgical knife (IT) knife is impossible because an insulator is mounted at the tip of the knife. We have developed a new type of hood which could perform both coagulation and irrigation simultaneously. Methods: Our new device was fabricated by drilling a side hole in the cap portion of a conventional transparent hood followed by attaching a machined papillotomy knife to the exterior surface of the hole. Results: Our new hood was useful for hemorrhage during ESD using IT knife. Conclusions: With this method, endoscopic hemostasis using IT knife is easy, as hemostatic procedure can be performed under irrigation and coagulation using conventional endoscopy.  相似文献   
5.
Summary Novel derivatives of K-252a, (8R*,9S*,11S*)-(–)-9-hydroxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo [a,g]-cycloocta[cde]trinden-1-one, an inhibitor of protein kinases and calmodulin-dependent phosphodiesterase, were synthesized and evaluated for their antitumor activity in vitro and in vivo. Of ten derivatives tested, four were active against the P388 murine leukemia i. p.-i. p. system, although K-252a was inactive. Among these derivatives, KT6124 was selected for further biological evaluation studies because its efficacy was the highest. KT6124 was also active against sarcoma 180 and B16 melanoma. It exerted a relatively broad spectrum of antiproliferative activity against 20 human tumor cell lines in vitro. To determine the mechanism(s) of action underlying the antitumor activity of KT6124, we tested the drug for inhibition of protein kinases, including Ca2+-and phospholipid-dependent protein kinase (PKC), in intact A431 human epidermoid carcinoma cells in comparison with the PKC-inhibitory activity of K-252a. KT6124 did not antagonize the action of phorbol 12-myristate 13-acetate (PMA) in A431 cells, whereas K-252a did, suggesting that KT6124 may not act on protein kinases in the cells. The interaction of KT6124 with DNA in living cells was examined by the alkaline elution method. KT6124 apparantly exhibited DNA scission both dose-and time-dependently in the target cells. The DNA breakage was dependent on proteinase K treatment, suggesting its possible interaction with DNA-related enzyme(s). These results indicate that KT6124 exerts antitumor activity by acting on DNA or on DNA-related enzyme(s) in tumor cells rather than via the inhibition of protein kinases.  相似文献   
6.
7.
PURPOSE: This study evaluated the bone volume, height, and width that can be obtained in alveolar ridge augmentation using titanium mesh and autogenous bone particles in patients with cleft lip/palate. PATIENTS AND METHODS: Subjects were 15 patients with cleft lip/palate requiring tertiary bone graft for implant therapy. Computed tomography (CT) scans were taken before removing the mesh, from 1 to 21 months after bone grafting. Forty-three reconstructed images corresponding to the positions for implant placement were selected for this study. The percent defect filled with bone (%BONE), defined as the percentage of newly formed bone in the space created by the mesh, was measured for image analyses. In linear analyses, 4 parameters were used: increased bone height (IBH), percent increased bone height (%IBH), increased bone width (IBW), and percent increased bone width (%IBW). Factors influencing the quantitative data and the clinical courses of placed implants were also explored. RESULTS: The average %BONE was 91.1%. IBH averaged 4.4 mm, whereas %IBH averaged 88.5%. IBW averaged 4.6 mm, whereas %IBW averaged 86.4%. Little correlation was present between the quantitative data and patient age, or time interval. A significant correlation was identified between the data for span of the grafted area and %BONE (correlation coefficient value = -0.36). However, the diminishing rate was very low. No implants were lost postoperatively. CONCLUSIONS: Alveolar ridge augmentation with titanium mesh and autogenous bone particles from the anterior iliac crest has very high predictability as a preimplant procedure in patients with cleft lip/palate.  相似文献   
8.
OBJECTIVE: It is well described that unilateral pelviureteric junction obstruction (PUJO) is a benign condition, because the dilatation resolves spontaneously and the function does not decrease in most of the kidneys. However, there is exceptional PUJO that requires emergent treatment in neonatal periods. The aim of this article is to report the urological emergency and management in neonates with PUJO. MATERIALS AND METHODS: Nine children (seven boys and two girls) with PUJO who underwent neonatal emergent treatment during the last 13 years were reviewed. Renal function was evaluated according to decay curve of serum creatinine (SCr) levels corresponding to gestational age (GA) at delivery. Physical examination, ultrasonographic monitoring, and chest and abdominal plain radiographs were repeated in each neonate. RESULTS: Eight patients were detected prenatally. In five patients, multicystic dysplastic kidney (MCDK) was demonstrated on the contralateral side. Three patients underwent percutaneous puncture of fetal hydronephrosis. Decrease of amniotic fluid was evident in three fetuses. Indications for emergent treatment included mass effect from hydronephrosis in three patients, renal dysfunction in five, and severe urinary tract infection in one. During neonatal periods, a percutaneous nephrostomy tube was placed in seven, and open nephrostomy in one with anorectal malformation. Repeated punctures of the dilated renal pelvis were done in one patient. Renal function after pyeloplasty was stable in eight patients, while it was moderately decreased in one who was associated with oligohydramnios in utero. CONCLUSION: Indications for emergent treatment in neonates with PUJO included mass effect from giant hydronephrosis, renal dysfunction and severe urinary tract infection. At birth, respiratory and circulatory conditions must first be stabilized. In neonates with hydronephrosis of the solitary kidney or severe bilateral PUJO, serial SCr should be monitored to evaluate renal function. Decrease of amniotic fluid suggested renal functional compromise that would not recover after urological management.  相似文献   
9.
OBJECTIVES: We reviewed the results of surgical treatment for children with ureterocele, especially addressing the importance of the lower urinary tract reconstruction. METHODS: We present medical records of 91 children with ureterocele (31 with the intravesical type, and 60 with the ectopic type) treated during the last 14 years. As the initial treatment, we carried out transurethral incision of the ureterocele (TUI). In patients with persistent reflux, breakthrough urinary tract infection (UTI), or signs of bladder outlet obstruction due to a collapsed cele wall, we recommended that patients undergo lower urinary tract reconstruction irrespective of the renal function involved in ureterocele. The average follow-up period was 5 years (ranging 1 year and 6 months to 14 years). RESULTS: Transurethral incision of the ureterocele was carried out as the initial treatment on 68 patients (75%). A total of 34 patients (21 intravesical [68%] and 13 ectopic [22%]) were followed medically after TUI alone. Reconstruction of the lower urinary tract was carried out in 59 patients (65%). Nephroureterectomy combined with bladder level reconstruction was carried out in four children with single system and non-functioning kidney. Follow-up voiding cystourethrography showed that only one girl had reflux, which disappeared after the first follow-up examination. Postoperative UTI occurred in 12 patients (20%) with ectopic ureterocele. Voiding dysfunction was suspected in eight patients. CONCLUSION: We believe that the primary objective for patients with ureterocele, especially of the ectopic type, is to reconstruct the original pathology of the lower urinary tract that may give rise to reflux, obstruction, or abnormalities of urination. Although surgery at the bladder level can be challenging, the lower urinary tract reconstruction successfully corrects the vesicoureteral reflux and bladder outlet pathology under a cosmetically acceptable incision.  相似文献   
10.
The incidence of stonestreet formation after extracorporeal shock wave lithotripsy (ESWL) rises with increasing stone burden. However, stonestreet after ESWL is often experienced even in stones smaller than 20 mm. To examine whether the non-contrast helical computed tomography (CT) data could predict stonestreet formation in these stones, 53 radiopaque stones of 5-20 mm treated with ESWL were evaluated. Maximal dimension was measured on plain radiograph. From an attenuation value histogram graphed from the CT data, total stone volume and mean attenuation value were calculated. Seven stonestreets longer than 25 mm developed. There was no significant difference in maximal dimension and total stone volume between stones that did and stones that did not develop stonestreet. Mean attenuation value was the sole significant predictive factor. Application of mean attenuation value with cut-off level of 650 HU would anticipate stonestreet formation with a sensitivity of 85.7% and a specificity of 71.7%. The estimated risk of stonestreet formation is high in the treatment of stones with higher mean attenuation value.  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