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   43409篇
  免费   3732篇
  国内免费   2027篇
耳鼻咽喉   828篇
儿科学   1075篇
妇产科学   212篇
基础医学   5605篇
口腔科学   7156篇
临床医学   3903篇
内科学   3862篇
皮肤病学   188篇
神经病学   921篇
特种医学   2127篇
外国民族医学   20篇
外科学   9484篇
综合类   6363篇
现状与发展   6篇
预防医学   1350篇
眼科学   196篇
药学   2013篇
  26篇
中国医学   1333篇
肿瘤学   2500篇
  2024年   114篇
  2023年   713篇
  2022年   1228篇
  2021年   1732篇
  2020年   1708篇
  2019年   1565篇
  2018年   1465篇
  2017年   1530篇
  2016年   1493篇
  2015年   1683篇
  2014年   2754篇
  2013年   3785篇
  2012年   2236篇
  2011年   2584篇
  2010年   2281篇
  2009年   2104篇
  2008年   2019篇
  2007年   2073篇
  2006年   1860篇
  2005年   1778篇
  2004年   1603篇
  2003年   1421篇
  2002年   1195篇
  2001年   1063篇
  2000年   881篇
  1999年   777篇
  1998年   645篇
  1997年   635篇
  1996年   586篇
  1995年   423篇
  1994年   432篇
  1993年   303篇
  1992年   315篇
  1991年   263篇
  1990年   208篇
  1989年   208篇
  1988年   168篇
  1987年   134篇
  1986年   130篇
  1985年   156篇
  1984年   115篇
  1983年   108篇
  1982年   125篇
  1981年   92篇
  1980年   86篇
  1979年   87篇
  1978年   93篇
  1977年   62篇
  1976年   60篇
  1975年   36篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
52.
本实验采用~(45)Ca液闪技术,测定骨折后不同天数的幼年小鼠和成年小鼠在注射~(45)Ca-氯化钙后24 h,各骨段~(45)Ca沉积量,发现:1.幼年小鼠各骨段中钙的沉积量均高于成年小鼠;2.右股骨中段骨折后,骨折股骨中段的钙沉积量急剧升高;健侧股骨上、中、下三段,骨折股骨上段及左右胫骨上段的钙沉积量则逐渐下降而骨折股骨下段的骨转换增加。说明骨折部位以外的各骨段均最大限度地调动了一切可以调动的钙,以满足骨折修复的需要。  相似文献   
53.
In recent years, bone grafts and bone substitutes have been increasingly utilized underneath barrier membranes to optimize the treatment outcome of bone reconstructive therapy for defects in the alveolar process. In the present study, 4 different filling materials were evaluated in bone defects of similar dimensions in the mandible of miniature pigs. Blood clots and autografts were used as controls. The defects were covered with barrier membranes and allowed to heal for 4, 12 or 24 weeks. Histologic examination demonstrated that bone repair progressed through a programmed sequence of maturation steps closely resembling the pattern of bone development and growth regardless of whether bone grafts or substitutes were present or not. Histomorphometric analysis showed that autologous bone grafts (autografts) had the best osteoconductive properties during the initial healing period, with 39% of newly formed bone inside the membrane-covered defects at 4 weeks of healing. In addition, 87% of the graft surfaces were already covered by bone at this time. Both values were significantly higher for autografts than for the 4 alternative bone fillers (P < or = 0.05). At 12 weeks, these differences were no longer apparent, with all 5 filling materials showing similar values. Among the tested bone substitutes, tricalcium phosphate (TCP) showed a significantly higher percentage of bone fill at 24 weeks of healing. It can be concluded that sites filled with autografts clearly demonstrated the best results underneath barrier membranes in the early phase of healing. As far as degradation and substitution are concerned, TCP showed the most promising results. This filler, however, needs to be tested further in a more demanding animal model. Less favorable results were obtained for coral-derived hydroxyapatite granules and for demineralized freeze-dried bone allografts.  相似文献   
54.
In most of the studies on long-term radiographic evaluations of crestal bone levels adjacent to dental implants, no baseline radiographs taken immediately post-surgically had been obtained.The aim of this study was to test the reproducibility of a simple radiographic method for linear measurements of changes in bone levels and to evaluate changes in crestal bone levels adjacent co non-submerged ITI® implants 1 year following the surgical procedure. From 128 patients enrolled in a clinical and radiographic longitudinal study 40 patients also had radiographs taken immediately postsurgically. They were, however, not obtained as “identical” images. The radiographs were mounted onto slides and projected on a screen. Mesially and distally from 57 implants triplicate linear measurements of the distance implant shoulder to bone crest were taken, using known dimensions of the implants as internal reference distances. The median difference of 213 (out of 228 possible) duplicate measurements was 0.00 mm (ranging from ?1.72 mm to +1.47 mm when comparing the second co the third reading). Some 81% of the double measurements were within ±0.5 mm and the precision was 0.30 mm. In the immediate postoperative radiographs the median mesial bone level was located at 2.07 mm (distally 2.19 mm) from the implant shoulder. A statistically significant amount of bone loss in the first year was observed mesially (median=?0.78 mm) and distally (0.85 mm)(Wilcoxon matched pairs signed rank test ±0.001). No statistically significant influence of the implant location, the implant length, type of the implant (screw; cylinder) was observed (Kruskal-Wallis P>0.05).The age of the patients was not correlated significantly to the amount of bone loss observed. In conclusion, methodological limitations existed when evaluating linear bone changes in non-identical radiographs using reference dimensions of the implants. The amount of postsurgical bone loss estimated in other studies was confirmed when using an immediate postoperative radiograph as a baseline.  相似文献   
55.
K. Wester 《Acta neurochirurgica》1994,131(3-4):223-225
Summary The results of a total of 25 cranioplasties are reported. In 10 patients, a reinforced acrylic prosthesis was utilized. In the remaining 15 cases, the patient's own autoclaved bone flap was re-implanted. Six of these bone flaps were autoclaved to kill tumour cells, and was re-implanted during the same surgical procedure. In the remaining 9 patients, the flaps were removed to allow brain swelling, preserved in a freezer and re-implanted several months later. All the prostheses and re-implanted flaps were accepted by the patients without complications such as infections or resorption, and with cosmetically satisfying results. The tumour infiltrated flaps remained tumour free for the entire period of observation.  相似文献   
56.
Since it covers the lateral wall of the mastoid air system, the suprameatal triangle is of importance to otologic surgeons during mastoidectomy. Because of this clinical importance, topographic anatomy of the suprameatal spine and depression was studied on Anatolian skulls. In all, 363 male and 231 female skulls were studied. The most prevalent type of suprameatal spine resembled a crest and was found in both sexes on the right (77.6%) and left (80%) sides. The absence of a suprameatal depression was significantly higher in females (right 9.1%; left 8.7%) than in males (right 1.7%; left 2.5%). Suprameatal depressions were mostly shallow in female subjects, but were mostly observed in males to be at a medium depth or deep. Received: 5 January 1998 / Accepted: 19 March 1998  相似文献   
57.
Inanimate structures cannot detect and repair their fatigue damage or microdamage, so to minimize it they need more structural material and strength. Living bone handles this matter differently. Bone modeling drifts adapt bone architecture and strength to the loads on bones in ways that tend to keep strains from exceeding a “modeling threshold” range. Strains (or equivalent features) above that threshold switch mechanically controlled modeling ON. Where strains stay below that threshold, this modeling goes OFF. Repeatedly loading-deloading a bone causes microdamage in it, and basic multicellular unit (BMU)-based bone remodeling normally repairs it. Where strains stay below an operational “microdamage threshold,” remodeling can repair whatever microdamage happens for as long as it happens. Strains above that threshold can cause too much microdamage to repair completely and lead to fatigue fractures of trabeculae or whole bones. The modeling threshold normally lies comforably below the microdamage threshold. Since modeling normally adjusts bone architecture to keep strains from exceeding the modeling threshold, this keeps strains below the microdamage threshold, too, and voluntary activities do not cause more microdamage than remodeling can repair. Therefore, long-distance runners do not need more bone mass and strength than nonrunners of comparable age, sex, and body size.  相似文献   
58.
Improving Femoral Bone Density Measurements   总被引:1,自引:0,他引:1  
Femoral bone density measurements are clinically important because of their strong relationship with hip fracture. However, current densitometers have not improved upon femoral densitometry since the introduction of dual-energy X-ray absorptiometry (DXA) systems. Recently, several advances in DXA measurement of the proximal femur have been proposed by various published studies. These advances can be added to existing DXA systems, while maintaining the conventional femoral regions of interest. Both upper neck bone mineral density (BMD) and hip axis length have been reported to be associated with hip fractures. With newer technology that enables a rapid assessment of both hips, bilateral femur measurements are now clinically practical and are of importance in those with T-scores approaching, yet not reaching, diagnostic or therapeutic thresholds. Bilateral femur measurements also reduce precision error compared to a single femur measurement, yielding precision errors less than observed at the spine. With this decrease in precision error, monitoring of bone changes is now possible at the femur with the utility comparable to the spine.  相似文献   
59.
Phosphorus was imaged in vivo in human cortical and trabecular bone and the T(1) and T(2) (*) were measured. An ultrashort TE (UTE) pulse sequence (TE = 70 microm) was used with half pulse excitation and radial mapping of k-space from the center out. T(2) (*) was measured using multiple echo times and T(1) was measured both by saturation recovery and by a method using different RF pulse amplitudes. Seven normal subjects (32-85 years) were examined. Phosphorus was imaged, with a true in-plane resolution of 2.9 x 2.9 mm and a signal-to-noise ratio (SNR) of 19:1, in both cortical and trabecular bone. The mean T(2) (*) value was 207 +/- 12 micros, and the mean T(1) value was 8.6 +/- 3.0 sec. Images and measurements were obtained in realistic times on a clinical MR system. This may provide a new approach to characterizing disease of bone.  相似文献   
60.
The aim of the present study was to evaluate the combined application of different bioabsorbable materials for healing of residual peri‐implant defects after placement of non‐submerged implants into fresh extraction sockets. Second and third mandibular premolars were extracted from 10 Beagle dogs, the coronal part of the distal sockets were surgically enlarged and this was followed by immediate placement of specially designed hollow‐screw non‐submerged dental implants. For each animal, the coronal peri‐implant defects were further treated with one of the 4 following procedures: 1) no treatment, control site: 2) grafting with porous hydroxyapatite (HA); 3) collagen membrane tightly secured around the implant and over the defect and 4) grafting with HA covered with a collagen membrane. After 16 weeks of healing, specimens were removed from the mandibule and prepared for a histomorphometric evaluation. The bone-to-implant contact length (BIC) was measured and compared amongst the different treatment modalities. In the defect area, the irregular bone regeneration was similar between all the treatment procedures ( P >0.10). In the sites covered with a collagen membrane alone, the total BIC (47%) was greater than in control sites (28.7%. P <0.05) or sites grafted with HA (22.2%, P <0.02). Total BIC in sites treated with the HA‐membrane combination (43%) was only significantly different from sites treated with HA ( P <0.10). It is concluded that the use of bioabsorbable materials results in a limited increase of osseointegration when used in conjunction with immediate placement of non-submerged implants, although the principle of the one stage surgical approach can be maintained.  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