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   3440篇
  免费   363篇
  国内免费   279篇
  2024年   9篇
  2023年   93篇
  2022年   100篇
  2021年   142篇
  2020年   149篇
  2019年   154篇
  2018年   155篇
  2017年   127篇
  2016年   169篇
  2015年   136篇
  2014年   191篇
  2013年   244篇
  2012年   134篇
  2011年   227篇
  2010年   119篇
  2009年   196篇
  2008年   169篇
  2007年   166篇
  2006年   143篇
  2005年   123篇
  2004年   131篇
  2003年   96篇
  2002年   93篇
  2001年   84篇
  2000年   57篇
  1999年   55篇
  1998年   54篇
  1997年   50篇
  1996年   50篇
  1995年   54篇
  1994年   41篇
  1993年   49篇
  1992年   28篇
  1991年   32篇
  1990年   25篇
  1989年   24篇
  1988年   19篇
  1987年   11篇
  1986年   13篇
  1985年   17篇
  1984年   27篇
  1983年   23篇
  1982年   26篇
  1981年   12篇
  1980年   11篇
  1979年   12篇
  1977年   9篇
  1976年   7篇
  1975年   6篇
  1973年   7篇
排序方式: 共有4082条查询结果,搜索用时 484 毫秒
91.
In this work, an integrated one-step alkaline–extrusion process was tested as pretreatment for sugar production from barley straw (BS) biomass. The influence of extrusion temperature (T) and the ratio NaOH/BS dry matter (w/w) (R) into the extruder on pretreatment effectiveness was investigated in a twin-screw extruder at bench scale. A 23 factorial design of experiments was used to analyze the effect of process conditions [T: 50–100 °C; R: 2.5–7.5% (w/w)] on composition and enzymatic digestibility of pretreated substrate (extrudate). The optimum conditions for a maximum glucan to glucose conversion were determined to be R = 6% and T = 68 °C. At these conditions, glucan yield reached close to 90% of theoretical, while xylan conversion was 71% of theoretical. These values are 5 and 9 times higher than that of the untreated material, which supports the great potential of this one-step combined pre-treatment technology for sugar production from lignocellulosic substrates. The absence of sugar degradation products is a relevant advantage over other traditional methods for a biomass to ethanol production process since inhibitory effect of such product on sugar fermentation would be prevented.  相似文献   
92.
93.
Abstracts     
《Anthrozo?s》2013,26(2):123-126
ABSTRACT

The normal development of empathy has been proposed to be imperative to the healthy emotional and social functioning of youths. In contrast, compromised levels of empathy have been linked to an increased propensity to engage in antisocial behaviors, including animal cruelty. Previous findings have revealed parent attachment to be intrinsically linked to the development of empathy. This association has been shown to play a role in predicting the expression of various outcome behaviors, including both those which are prosocial in nature, and those which are antisocial, and potentially aggressive. This study examines these associations in a sample of 281 12- to 18-year-old students. The aims included the investigation of the direct predictive roles played by attachment and empathy for prosocial and antisocial behaviors directed at both humans and animals. We also investigated the mediating role played by empathy in these relationships. Attachment and empathy significantly predicted prosocial and antisocial behaviors, both individually, and in combination. Furthermore, empathy was found to serve a mediating role in the associations between attachment and: human-directed prosocial behavior, the humane treatment of animals, and animal cruelty. These findings expand upon existing literature by demonstrating that it is, at least partially, through empathy that attachment to parents predicts prosocial and antisocial behaviors during adolescence. This is in contrast to the direction of relationships implied by some previous findings and proposals, which have suggested that treating animals humanely fosters the normal development of empathy, for example. Notwithstanding the promising findings revealed by the current study, we recommend that replicating this research using a larger sample will assist in addressing the limited generalizability identified in the current study. It is further proposed that the use of a lie scale could limit the influence of social desirability responding. Future research is also needed to determine the direction of the demonstrated relationships.  相似文献   
94.
Cancer is the second leading cause of death worldwide. Research on the relationships between trace elements (TE) and the development of cancer or its prevention is a field that is gaining increasing relevance. This review provides an evaluation of the effects of TE (As, Al, B, Cd, Cr, Cu, F, I, Pb, Li, Mn, Hg, Mo, Ni, Se, Si, Sn, V and Zn) intake and supplementation in cancer risk and prevention, as well as their interactions with oncology treatments. Advancements in the knowledge of TE, their dietary interactions and their main food sources can provide patients with choices that will help them to improve their quality of life and therapy outcomes. This approach could open new opportunities for treatments based on the integration of conventional therapies (chemotherapy, radiotherapy, and immunotherapy) and dietary interventions that provide advanced personalized treatments.  相似文献   
95.
Conditionally replicative adenoviruses (CRAds) were promising approach for solid tumour treatment, but its oncolytic efficiency and toxicity are still not satisfactory for further clinical application. Here, we developed the CAIX promotor (CAIXpromotor)‐controlled CRAd armed with a tumour suppressor absent in melanoma 2 (AIM2) to enhance its oncolytic potency. The CAIXpromotor‐AIM2 adenoviruses (Ad‐CAIXpromotor‐AIM2) could efficiently express E1A and AIM2 in renal cancer cells. Compared with Ad‐CAIXpromotor, Ad‐CAIXpromotor‐AIM2 significantly inhibited cell proliferation and enhanced cell apoptosis and cell killing, thus resulting in the oncolytic efficiency in 786‐O cells or OSRC‐2 cells. To explore the therapeutic effect, various Ads were intratumourally injected into OSRC‐2‐xenograft mice. The tumour growth was remarkably inhibited in Ad‐CAIXpromotor‐AIM2‐treated group as demonstrated by reduced tumour volume and weight with a low toxicity. The inflammasome inhibitor YVAD‐CMK resulted in the reduction of anti‐tumour activity by Ad‐CAIXpromotor‐AIM2 in vitro or in vivo, suggesting that inflammasome activation response was required for the enhanced therapeutic efficiency. Furthermore, lung metastasis of renal cancer mice was also suppressed by Ad‐CAIXpromotor‐AIM2 treatment accompanied by the decreased tumour fossil in lung tissues. These results indicated that the tumour‐specific Ad‐CAIXpromotor‐AIM2 could be applied for human renal cancer therapy. The therapeutic strategy of AIM2‐based CRAds could be a potential and promising approach for the therapy of primary solid or metastasis tumours.  相似文献   
96.
97.
The photoelectrochemical performance of the WO3 photoanode is limited by the severe charge recombination in the bulk phase and at the WO3/electrolyte interface. Herein, In2S3 nanosheets are integrated onto the surface of the WO3 nanowall array photoanode, followed by a facile polyvinylpyrrolidone (PVP) solution treatment. The PVP treatment results in sulfur vacancies and a gradient oxygen doping into In2S3 from surface to interior, which induces the formation of a gradient energy band distribution. The gradient band structured In2S3 and type II band alignment at the WO3/In2S3 interface simultaneously create a channel that favors photogenerated electrons to migrate from the surface to the conductive substrate, thereby suppressing bulk carrier recombination. Meanwhile, the sulfur vacancies and oxygen doping contribute to increased charge carrier concentration, prolonged carrier lifetime, more active sites, and small interfacial transfer impedance. As a consequence, the PVP treated WO3/In2S3 heterostructure photoanode exhibits a significantly enhanced photocurrent of 1.61 mA cm?2 at 1.23 V versus reversible hydrogen electrode (RHE) and negative onset potential of 0.02 V versus RHE.  相似文献   
98.
摘要 目的:探究结直肠癌血清生长分化因子-15(GDF-15)、粒细胞集落刺激因子(G-CSF)水平与患者临床病理参数、预后的关系,并分析其对结直肠癌的诊断价值。方法:采集结直肠癌患者、结直肠腺瘤患者及健康体检志愿者的血清样本,酶联免疫吸附测定(ELISA)实验检测血清GDF-15、G-CSF;分析结直肠癌患者血清GDF-15、G-CSF水平与患者临床病理参数的关系;Kaplan Meier生存曲线分析血清GDF-15、G-CSF水平与患者预后的关系;受试者工作特征曲线(ROC)分析血清GDF-15、G-CSF水平对结直肠癌的诊断价值。结果:结直肠癌患者血清GDF-15、G-CSF水平高于结直肠腺瘤患者及健康体检志愿者(均P<0.05);血清GDF-15水平与肿瘤直径、分化程度、远处转移及TNM分期相关(均P<0.05);血清G-CSF水平与肿瘤分化程度、远处转移及TNM分期相关(均P<0.05);Kaplan Meier生存曲线结果显示,血清GDF-15低表达、G-CSF低表达患者的术后5年总生存率及中位生存时间均分别高于血清GDF-15高表达、G-CSF高表达患者(均P<0.05);ROC分析结果表明,血清GDF-15、G-CSF有较好的诊断结直肠癌的价值,血清GDF-15、G-CSF联合应用的敏感度、特异度分别为0.876、0.863。结论:结直肠癌患者血清GDF-15、G-CSF水平升高,且均与患者病情恶性进展、不良预后相关;血清GDF-15、G-CSF是诊断结直肠癌的潜在指标。  相似文献   
99.
摘要 目的:总结原发性子宫恶性淋巴瘤的临床表现、影像及病理学特点,以期提高对原发性子宫恶性淋巴瘤的认识及诊治水平。方法:通过PubMed、万方、维普、中国知网数据库检索2001年1月至2019年12月报道的原发性子宫恶性淋巴瘤的文献,结合首都医科大学附属北京妇产医院收治的1例原发性子宫大B细胞淋巴瘤的病例资料,对此类患者临床表现、影像及病理学特点、治疗方案及预后进行总结。结果:患者女,64岁,发现盆腔肿物半月伴有绝经后阴道流血,盆腔CT提示:宫体与宫颈局部巨大团块状软组织密度灶,宫底及宫体上段可见内膜。宫腔镜下组织活检病理:(宫内物)符合低分化恶性肿瘤,结合免疫组化结果,诊断原发性子宫大B细胞淋巴瘤。行开腹全子宫及双侧附件、大网膜及腹膜后淋巴结清扫术,术后接受CHOP方案化疗六程,现治疗后随访17月,未发现复发。结论:原发性子宫恶性淋巴瘤极少见,组织学上以大B 细胞淋巴瘤为主,临床表现缺乏特异性。最终需要结合免疫组化确诊。该疾病恶性程度高,治疗上以根治性手术联合化疗为主,预后较差。  相似文献   
100.
PurposeThis study compared the positioning accuracy between cone-beam CT (CBCT) and ExacTrac (ETX) for a single-isocenter multiple target stereotactic radiosurgery (SRS) on two TrueBeam STx systems.MethodsA single-isocenter treatment plan was simulated on an anthropomorphic head phantom with six spherical steel ball bearings (BBs). One of the BBs was chosen to be the isocenter. The five off-isocenter targets were located at various distances from the isocenter. MV portal images were generated to evaluate the deviations between the expected and the real center of the targets after CBCT and ETX positioning, respectively.ResultsThe evaluation of the positioning accuracy for the isocenter target showed that CBCT and ETX positioning provided comparable, sub-millimetric results. Deviations in positioning accuracy were also calculated for all other targets, also showing comparable results for CBCT and ETX. Moreover, our study showed that the deviation between CBCT and ETX positioning were in better agreement for TBSTx1 and deviated slightly higher on TBSTx2 (maximum: 1.23 mm at S/I direction), due to a less perfect alignment between the CBCT coordinate system and the ETX coordinate system on TBSTx2 compared to TBSTx1. This study also showed a correlation between the target positioning accuracy and the distance to the isocenter.ConclusionThe positioning accuracy of ETX and CBCT for targets located at isocenter and off-isocenter locations was compared on two treatment machines and found comparable. Our study highlights the importance of a proper calibration procedure, to ensure correct alignment between the CBCT, ETX and machine coordinate systems.  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