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   2539篇
  免费   181篇
  国内免费   18篇
  2023年   28篇
  2022年   33篇
  2021年   88篇
  2020年   70篇
  2019年   72篇
  2018年   75篇
  2017年   89篇
  2016年   70篇
  2015年   116篇
  2014年   221篇
  2013年   199篇
  2012年   132篇
  2011年   199篇
  2010年   157篇
  2009年   122篇
  2008年   178篇
  2007年   138篇
  2006年   100篇
  2005年   88篇
  2004年   81篇
  2003年   62篇
  2002年   43篇
  2001年   28篇
  2000年   14篇
  1999年   26篇
  1998年   16篇
  1997年   13篇
  1996年   14篇
  1995年   8篇
  1994年   19篇
  1993年   19篇
  1992年   20篇
  1991年   23篇
  1990年   8篇
  1989年   16篇
  1988年   12篇
  1987年   9篇
  1985年   12篇
  1984年   9篇
  1983年   11篇
  1982年   7篇
  1981年   8篇
  1980年   12篇
  1979年   13篇
  1978年   8篇
  1977年   6篇
  1976年   12篇
  1974年   5篇
  1973年   6篇
  1972年   10篇
排序方式: 共有2738条查询结果,搜索用时 15 毫秒
991.
Reconstruction of early Pleistocene hominin carcass acquisition and processing behaviors are necessarily based at least in part on butchered fossil bones. This paper provides zooarchaeological and taphonomic analyses and behavioral interpretations of three approximately 1.5 million-year-old archaeofaunas from areas 1A and 103 in the Okote Member of the Koobi Fora Formation, northern Kenya: FwJj14A, FwJj14B, and GaJi14. These sites are all located in similar paleoenvironmental contexts, near shallow water with swampy, seasonally flooded areas, and some evidence for more wooded or gallery forest settings. Both individual specimen--and assemblage-level analyses of butchery-marked bones indicate that the hominins appear to have practiced similar butchery strategies at all of these sites, with butchery (defleshing, disarticulation, and marrow extraction) of both high- and low-ranked skeletal elements with no apparent preference for prey size, skeletal region, limb class, or limb portion. Only four tooth-marked specimens, including one likely crocodile-tooth-marked bone, are preserved in all three archaeofaunas. A paucity of limb epiphyses suggests that bone-crunching hyenids may have deleted these portions subsequent to hominin butchery. Strangely, there are no stone tools preserved with the 292 cut-marked and 27 percussion-marked faunal specimens (out of a total of 6,039 specimens), suggesting that raw material availability may have conditioned hominin lithic discard patterns at these locales. These assemblages increase our knowledge of the dietary behavior and ecology of Homo erectus, and provide support for variability in early Pleistocene hominin carcass foraging patterns.  相似文献   
992.
We have hypothesized that human bone marrow-derived mesenchymal stem cells (BMMSCs), that are not osteogenically differentiated prior to implantation, would regenerate bone extensively in vivo once exogenous bone morphogenetic protein-2 (BMP-2) was delivered to the implantation site. BMP-2 released from heparin-conjugated poly(lactic-co-glycolic acid) (HCPLGA) scaffolds stimulates osteogenic differentiation of cultured BMMSCs. Upon implantation, undifferentiated BMMSCs on BMP-2-loaded HCPLGA scaffolds induce far more extensive bone formation than either undifferentiated BMMSCs or osteogenically differentiated BMMSCs on HCPLGA scaffolds. These BMP-2-loaded HCPLGA scaffolds could prove invaluable for in vivo regeneration of bone from undifferentiated human BMMSCs.  相似文献   
993.
We proposed a novel combined gene therapy of human vascular endothelial growth factor 165 gene (hVEGF165) and human bone morphogenetic protein 2 gene (hBMP2) for bone regeneration by lentivirus-mediated co-transfection of both genes into rat bone marrow-derived mesenchymal stromal cells (MSCs). Both genes were successfully co-expressed in MSCs confirmed by real-time PCR and ELISA. And the alkaline phosphatase activity of MSCs was significantly augmented by the co-transfection with both genes than any single gene transfection (P < 0.01). These results demonstrated the feasibility of the combined gene therapy by using MSCs lentivirally co-transfected with hVEGF165 and hBMP2 for bone regeneration.  相似文献   
994.
In order to examine the effect of polysaccharides from morinda officinalis (MOP) on bone quality of osteoporosis rats. The osteoporosis in rats was induced by ovariectomy, and MOP (100 or 300mg/kg) was orally administrated once daily. The animals were assessed 30 days after the operation for bone mineral density, serum cytokines level and mineral element concentration. MOP administration in rats resulted in an increase in bone mineral density and mineral element concentration, a decrease in serum cytokines level, which indicated that MOP administration may play an important role in the development of osteoporosis.  相似文献   
995.
To determine whether increased Ca intakes can prevent rickets in a susceptible group of children living in a rickets-endemic area of Bangladesh, we conducted a 13-month long, double-blind, clinical trial with 1-to 5-year-old children who did not present with rickets but ranked in the upper decile of plasma alkaline phosphatase (AP) activity of a screening cohort of 1,749 children. A total of 158 children were randomized to a milk-powder-based dietary supplement given daily, 6 days/week, and providing either 50, 250, or 500 mg Ca, or 500 mg Ca plus multivitamins, iron, and zinc. Upon initial screening, 194 healthy children presented with no rachitic leg signs and had serum AP in the upper decile (>260 u/dl) of the cohort. When 183 of those subjects were re-screened after a 7-month pre-trial period, 23 (12.6%) had developed rachitic leg signs, suggesting an annual risk of 21.5% in this cohort. Of those still not presenting with leg signs and completing 13 months of dietary intervention, none showed rachitic leg signs, none showed significant radiological evidence of active rickets, and all showed carpal ossification normal for age after that intervention. These results are consistent with even the lowest amount of supplemental Ca (50 mg/day) being useful in supporting normal bone development in this high-risk population.  相似文献   
996.
目的:观察放疗和博宁对骨转移癌的止痛效果。方法:对100例骨转移癌患者进行回顾性分析,单纯放疗30例,博宁加放疗14例,博宁加放化疗56例。结果:全组总有效率为89%,显效率达51%。各组有效率:单放组为83-3%,博宁加放疗组为92.9%,博宁加放化组为91.1%。三组间止痛效果无显著性差异(P>0.05)。在应用博宁治疗组中有一例出现类似过敏反应症状,其他无明显毒副反应发生。结论:放射治疗骨转移癌止痛迅速而有效。博宁治疗骨转移癌止痛效果明显,尤其适合应用于多发性骨转移癌患者。二者联合应用效果更加。  相似文献   
997.
998.
目的:构建乳腺癌体外骨转移瘤3D模型。方法:新生CD-1小鼠的颅骨单独孵育为正常组,新生CD-1小鼠的颅骨与MDA-MB-231细胞低氧共孵育四天为模型组。通过扫描电镜(SEM)鉴定骨转移瘤模型,中性红染色法鉴定骨组织中的破骨细胞,硝酸银复染法观察骨的溶解,结晶紫染色法观察骨转移瘤模型中肿瘤细胞的生长。结果:正常组骨表面光滑完整;模型组骨组织表面黏附大量肿瘤细胞,破骨细胞活性增强,产生严重的溶骨,表面出现骨陷窝,骨纤维发生断裂。结论:成功建立了乳腺癌骨转移瘤体外3D模型,该模型能够模拟体内骨转移瘤微环境。  相似文献   
999.
目的:探讨手术治疗盖氐骨折术后骨不连合并下尺桡关节炎的方法和临床疗效。方法:对2010年1月至2015年6月收治的9例盖氐骨折术后骨不连合并下尺桡关节炎患者的临床资料进行回顾性分析,评价其骨不连愈合率、前臂旋转活动度,采用DASH问卷评估上肢功能,记录术中及术后并发症的发生情况。结果:9例患者随访13-78个月,平均45.4个月所有骨不连在24周都获得愈合,愈合时间12-24周;术后前臂旋转功能平均115.56±26.74°,显著高于术前(P0.01);而DASH评分从术前48.56±8.71分降至20.11±8.08分(P0.05);根据Anderson前臂功能评分标准,优2例,良5例,中2例,优良率为77.8%所有患者均对手术效果十分满意。结论:尺骨头切除术联合桡骨切开植骨内固定术操作简单有效,可显著改善盖氐骨折术后骨不连合并下尺桡关节炎患者的上肢功能。  相似文献   
1000.
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