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   254篇
  免费   10篇
  国内免费   3篇
  267篇
  2021年   3篇
  2018年   3篇
  2017年   6篇
  2016年   3篇
  2015年   6篇
  2014年   7篇
  2013年   13篇
  2012年   5篇
  2011年   11篇
  2010年   9篇
  2009年   6篇
  2008年   7篇
  2007年   8篇
  2006年   9篇
  2005年   2篇
  2004年   8篇
  2003年   6篇
  2002年   13篇
  2001年   13篇
  2000年   6篇
  1999年   12篇
  1998年   5篇
  1997年   12篇
  1996年   3篇
  1995年   3篇
  1993年   4篇
  1992年   5篇
  1991年   4篇
  1990年   6篇
  1989年   3篇
  1988年   6篇
  1987年   4篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1978年   2篇
  1976年   1篇
  1974年   5篇
  1973年   4篇
  1972年   4篇
  1971年   3篇
  1970年   6篇
  1969年   2篇
  1968年   1篇
  1966年   2篇
  1965年   1篇
  1954年   1篇
排序方式: 共有267条查询结果,搜索用时 15 毫秒
231.
A resistant of the woody plants in West Siberia to toxic substances (sulfur dioxide, hydrocarbons, and carbon black) is studied by the reaction of the pigment complex, change of acidity of the leaf blade, activity of oxidative enzymes, moisture regime, and degree of damage of the leaf blade. The data of the study can be used in the landscaping of the sanitary protective zones of enterprises.  相似文献   
232.
233.
目的:研究对比三种抗癫痫药(苯妥因钠、丙戊酸钠、卡马西平)对癫痫患者脑电图的背景影响。方法:选取我院于2009年3月至2011年2月收治的60例癫痫患者,随机分为苯妥因钠(PHT)、卡马西平(CBZ)和丙戊酸钠(SVP)组各20例,动态观察各组患者于治疗期间痫样波放电的频度和EEG背景的变化。结果:EEG痫样波放电的抑制率以SVP最为明显,而CBZ在EEG背景活动影响方面均比其他两组显著。结论:三种药物对癫痫波放电的抑制顺序是SVP〉PHT〉CBZ,SVP组明显优于其他两组。  相似文献   
234.
Mitochondrial DNA (mtDNA) restriction polymorphism was examined in Turkmens, Eastern Iranians, and Ukrainians. The gene pools of all populations studied were characterized by the presence of European mtDNA lineages. Mongoloid component observed in Turkmen and Iranian populations with the frequencies of about 20% was represented by groups C, D, and E/G in Turkmens, and by M*, D, A, and B in Iranians. The relative positions of the populations studied, of populations from the Caucasus, Western Iran, and Russian populations from the Krasnodar krai and Belgorod oblast in the space of principal components revealed a geographically specific pattern of the population clustering. The data on mtDNA polymorphism indicated pronounced differentiation of Eastern and Western Iranians. The latter were characterized by a mtDNA group composition similar to that in Eastern Slavs. The historical role of the Caspian populations in the formation of the population of Southeastern Europe is discussed.  相似文献   
235.
目的:脑卒中是威胁人类健康三大疾病之一,是我国成人致残的首要原因,其中80%是缺血性卒中。本文意在研究血清胆红素水平与缺血性卒中严重程度、发病机理以及颈动脉粥样硬化斑块的关系,以进一步为防治缺血性卒中的发生、发展提供新的途径。方法:选择缺血性脑卒中患者(观察组)150例和同期健康体检者(对照组)150例,分别测定两组的血清总胆红素水平(TBIL)、间接胆红素(DBIL)、直接胆红素(IBIL),并对病例组进行TOAST分型、NIHSS评分及颈部血管超声检查。比较两组间血清胆红素,及观察组内不同分型组间血清胆红素的差异。结果:缺血性卒中患者TBIL、DBIL水平显著高于正常对照组,差异具有统计学意义(P〈0.05)。缺血性卒中患者按TOAST分型各亚型间血清TBIL、DBIL、IBIL水平差异无统计学意义(P〉0.05)。中重型脑梗死组与轻型脑梗死组比较,血清TBIL、DBIL、IBIL浓度均明显升高,差别具有统计学意义(P〈0.05)。缺血性卒中患者中有动脉粥样硬化斑块形成组血清TBIL、DBIL水平低于颈部动脉内膜光滑、完整者组,差别有统计学意义(P〉0.05)。结论:缺血性卒中患者血清胆红素升高,参与急性应激反应,可能作为衡量缺血性卒中严重程度的指标之一;高水平血清胆红素可能预防颈动脉粥样硬化斑块的形成,从而预防缺血性卒中的发生。  相似文献   
236.

Background  

To gain more insight in whether failure of intrauterine insemination (IUI) treatment in patients with idiopathic subfertility could be related to diminished fertilization, the aim of this study is to compare the fertilization of an initial IVF procedure after six cycles of IUI and the fertilization of an initial IVF procedure without preceding IUI cycles in couples with idiopathic subfertility.  相似文献   
237.
The effect of the cryoprotectants DMSO and PEG-1500 as well as freezing-thawing on the proteins of the canine erythrocyte membrane-cytoskeleton complex was studied using the cross-linking agent diamide. It was shown that the intensity of disturbances in the protein network structure correlated with the increased SH-group accessibility for oxidative bridging by this compound and accordingly, enhanced formation of high-molecular-weight protein aggregates. The maximum level of diamide-induced aggregability was revealed upon freezing of erythrocytes in liquid nitrogen without cryoprotectant. Electrophoretic analysis of the ghosts of erythrocytes incubated with cryoprotectants showed a significant increase in the aggregation level only for the cells in the polymer solution. After the freezing-thawing cycle, the diamide-induced protein aggregability in erythrocytes cryopreserved with PEG-1500 strongly increased; when DMSO was used for cell protection, the aggregation was much less pronounced than in the unprotected cells. One can suppose that the exocellular cryoprotectant PEG-1500, as distinct from the endocellular cryoprotectant DMSO, is unable to provide for preservation of the structure of the membrane-cytoskeleton protein complex at a level necessary for the maintenance of cell integrity after the return to physiological conditions.  相似文献   
238.
The vectors capable of replication in Escherichia coli and Agrobacterium tumefaciens have been constructed on the basis of the plasmid pUB5502. The constructed vectors pVA12, pVA12-2, pVA12-4 contain the mini-replicon and trimethoprim resistance gene (Tp) of a broad host-range plasmid R388 (IncW). The pVA12 vector (8.8 kb) has been constructed by insertion of a kanamycin resistance gene (Km) from the plasmid pUC-4K into a Psti site. It possesses 7 unique restriction sites for XhoI, SmaI, PvuI, PvuII, HindIII, EcoRI, BamHI and the markers for kanamycin and trimethoprim resistance (Km and Tp). The pVA12-2 and pVA12-4 vectors were obtained as a result of changing of the PvuII-EcoI fragment of pVA12 carrying the Tp gene for the PvuII-EcoRI fragment of pBR322 carrying the Tc gene. These plasmids have the same size of 9.7 kb and 8 unique sites for restriction endonucleases XhoI, SmaI, PvuI, PvuII, EcoRI, EcoRV, SalI, BalI and Km and Tc genes. No difference has been registered between the two plasmids by restriction analysis, but pVA12-4 has the dramatically increased copy number in Escherichia coli cells. All three vectors are transferable to Agrobacterium tumefaciens with the same frequencies by transformation or conjugation and do not affect the oncogenicity of pTi.  相似文献   
239.
目的:观察长期家庭氧疗配合呼吸操治疗慢性阻塞性肺疾病(COPD)的临床效果。、方法:选择本院收治的COPD患者80例,随机分为研究组和对照组,各40例,两组均给予常规治疗,研究组同时由医务人员指导给予家庭氧疗和呼吸操训练,随访1年.观察两组治疗前、治疗后6个月和1年肺功能,应用StGeorge’S呼吸问卷(SGRQ)评价生存质量、结果:研究组1年内急性发作1次5人,2次2人,3次及以上1人,对照组1年内急性发作1次9人,2次7人,3次及以上4人(P〈0.05);研究组治疗后6个月、1年用力肺活量(FVC)、第1秒用力呼气容积(FEVl)和FEVl/FVC均明显升高(P〈0.05),对照组治疗后6个月、1年FVC、FEVI/FVC与治疗前比较无统计学差异(P〉0.05);研究组治疗后6个月、1年SGRQ明显降低(P〈0.05),对照组治疗后6个月、1年SGRQ与治疗前比较无统计学差异(P〉0.05).结论:家庭氧疗配合呼吸操能明显改善COPD患者肺功能,延缓患者肺功能恶化,提高患者生存质量。  相似文献   
240.
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