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   323篇
  免费   10篇
  国内免费   43篇
  2024年   2篇
  2022年   5篇
  2021年   8篇
  2020年   3篇
  2019年   5篇
  2018年   8篇
  2017年   14篇
  2016年   18篇
  2015年   8篇
  2014年   19篇
  2013年   13篇
  2012年   17篇
  2011年   20篇
  2010年   16篇
  2009年   18篇
  2008年   17篇
  2007年   22篇
  2006年   17篇
  2005年   12篇
  2004年   12篇
  2003年   17篇
  2002年   8篇
  2001年   6篇
  2000年   4篇
  1999年   5篇
  1998年   5篇
  1997年   4篇
  1996年   2篇
  1995年   4篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1990年   2篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   9篇
  1985年   4篇
  1984年   5篇
  1983年   2篇
  1982年   2篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1976年   4篇
  1973年   4篇
  1970年   3篇
  1969年   3篇
  1967年   2篇
排序方式: 共有376条查询结果,搜索用时 31 毫秒
71.
This paper probes into the feasibility of increasing expression level of hFIX gene with endogenous intron 1 sequence.hFIX minigene was obtained with middle sequence truncated intron 1 inserted into the relative site of hFIX cDNA,and plasmid vector pKG5i‘IX,retroviral vector G1NaCi‘IX were constructed.These vectors were transduced into target cells of PA317,C2C12,primary rabbit skin fibroblasts (RSF) and primary human skin fibroblasts (HSF).The expression level of mixed colonies are PA317/pKG5i‘IX,151 ng/10^6 cells/24h;PA317/G1NaCi‘IX,308 ng/10^6 cells/24 h;C2C12/G1NaCi‘IX,186 ng/10^6 cells/24 h;RSF/G1NaCi‘IX,1929 ng/10^6 cells/24 h;HSF/G1NaCi‘IX,1646 ng/10^6 cells/24 h.These results indicated that hFIX minigene with intron l is able to increase the expression level to about 3 times of that of hFIX cDNA.Meanwhile,in order to study the application of hFIX minigene in the retroviral-mediated gene transfer system and refrain from intron splicing during viral production,a retroviral vector G1NaCi‘IXR with reversely inserted hFIX minigene expression cassette was constructed.The expression level of reverse constructor in PA317 cells was 390 ng/10^6 cells/24 h with 79% of bioactivity.PCR detection of HT/G1NaCi‘IXR cells infected with PA317/G1NaCi‘IXR supernatant confirmed the existence of intron 1 sequence.These results suggested that expression vector with forward-inserted intronl-carrying hFIX expression cassette can be used in directed gene transfer,but when using the retroviral-mediated gene transfer system,reversely-inserted intronl-carrying hFIX expression cassette should be considered.  相似文献   
72.
Ventilatory acclimatization to hypoxia is a time-dependent increase in ventilation and the hypoxic ventilatory response (HVR) that involves neural plasticity in both carotid body chemoreceptors and brainstem respiratory centers. The mechanisms of such plasticity are not completely understood but recent animal studies show it can be blocked by administering ibuprofen, a nonsteroidal anti-inflammatory drug, during chronic hypoxia. We tested the hypothesis that ibuprofen would also block the increase in HVR with chronic hypoxia in humans in 15 healthy men and women using a double-blind, placebo controlled, cross-over trial. The isocapnic HVR was measured with standard methods in subjects treated with ibuprofen (400mg every 8 hrs) or placebo for 48 hours at sea level and 48 hours at high altitude (3,800 m). Subjects returned to sea level for at least 30 days prior to repeating the protocol with the opposite treatment. Ibuprofen significantly decreased the HVR after acclimatization to high altitude compared to placebo but it did not affect ventilation or arterial O2 saturation breathing ambient air at high altitude. Hence, compensatory responses prevent hypoventilation with decreased isocapnic ventilatory O2-sensitivity from ibuprofen at this altitude. The effect of ibuprofen to decrease the HVR in humans provides the first experimental evidence that a signaling mechanism described for ventilatory acclimatization to hypoxia in animal models also occurs in people. This establishes a foundation for the future experiments to test the potential role of different mechanisms for neural plasticity and ventilatory acclimatization in humans with chronic hypoxemia from lung disease.  相似文献   
73.
从康氐木霉(Trichoderma k(?)ningii)白色变异株As 3.4001的粗酶制剂中,获得了纤维素酶系中的一组C_x酶(C_(x1) C_(x2) C_(x3) C_(x4))。分离步骤包括Sephadex G-75凝胶过滤,DEAESephadex A-50离子交换层析,ConA-Sepharose亲合层析,SE-Sephadex C-50离子交换层析及聚丙烯酰胺凝胶电泳。C_(x1)与C_(x2)的分子量不同而所带电荷相同,它们的分子量各自为44,500和34,000。C_(x2)—C_(x4)的分子量相同而所带电荷不同。纯化的C_(x1)—C_(x4)经聚丙烯酰胺凝胶电泳鉴定为单带。比较它们对羧甲基纤维素钠(CMC-Na)的糖化力及液化力表明在作用方式的随机性上C_(x2)>C_(x3)>C_(x1)>C_(x4)。  相似文献   
74.
Studies on male white rats have shown that tuftsin (trelys-pro-arg) enhances the locomotion in animals as disclosed by a series of the behavioral tests. The effect is dose-dependent: a dose of 50 microgram/kg did not change any of the test parameters, while that of 150 microgram/kg induced a short-term elevation of locomotion measured with an "Animeks". Administration of tuftsin in a dose of 300 microgram/kg led to the enhancement of the animals' locomotion as measured with the "Animeks", to the increased "open field" running time and to the reduced latent period of the reaction during the training in a T-shaped maze. Also, this dose of the peptide relaxed the reactions associated with fear. It is assumed that the effects observed are consequent on the stimulant action of tuftsin on the body of white rats.  相似文献   
75.
Summary The cells ofCitrobacter intermedius (containing L-tyrosine phenol lyase which catalyses the synthesis of 3-fluoro-L-tyrosine fromo-fluorophenol, pyruvate and ammonia) were entrapped into 10% poly(vinyl alcohol) cryogel beads. Cryogenic immobilization resulted in a moderate increase of the synthetic activity of the cells. During continuous operation for one month in a packed bed column reactor the productivity of the immobilized biocatalyst decreased by 30%.  相似文献   
76.
The authors observed signs of premature maturation and activation of the hypophysio-adrenocortical system at the early postnatal period (the 70--90th hour) in the progeny of rats adrenalectomized 1 to 3 and 7 to 9 days before labour. A more pronounced in comparison with control (progeny of the sham-adrenalcetomized and intact rats) response to stress pointed to the early maturation of the suprahypophysial control mechanisms as well. Signs of functional exhaustion in the hypophysio-adrenocortical system and also in the thyroid gland were revealed in mature (6--10-month-old) rats born of adrenalectomized rats.  相似文献   
77.
The distinction of the modification of Bielschowsky's method lies in additional colouring of silver-golden sections with strong solutions of stable cresyl-violet and acetic acid, as well as in recommendations to use precise-profile cortical sections. The given modification helps to obtain preparations with definite orientation and guaranteed identification of different nerve tissue elements. The preparations obtained can be employed for quantitative analysis and for a detailed study of thin specific structures and cytologic properties of pathologically changed nerve and glial cells.  相似文献   
78.
马铃薯糖转运蛋白基因的克隆及表达分析   总被引:1,自引:0,他引:1  
植物SWEET基因家族是一类糖转运蛋白,在植物的生理活动和生长发育过程中发挥着重要功能。为了解马铃薯SWEET基因的相关信息,探究其在马铃薯不同组织以及在生物胁迫与非生物胁迫下的表达特性。该研究采用同源克隆技术从马铃薯‘青薯9号’中克隆了StSWEET5基因(GenBank登录号为MN295671),其CDS序列长度为717 bp,编码238个氨基酸。系统进化树分析结果表明,StSWEET5与番茄的氨基酸序列相似性最高(97.06%)。qRT-PCR分析表明:StSWEET5基因在马铃薯各组织(根、茎、叶、花、块茎、匍匐茎)中均有表达,且在花中的表达显著高于其他组织;糖胁迫下,StSWEET5基因在根、茎、叶中均有表达,尤其在根中的表达差异最为显著(P0.05)。在晚疫病菌(Phytophthora infestans)诱导后36 h时,表达量达到最高,随后急剧下调。推测StSWEET5基因参与了马铃薯糖胁迫以及响应了晚疫病诱导的过程。  相似文献   
79.

Background  

Adverse drug reactions (ADRs) are now recognized as an important cause of hospital admissions, with a proportion ranging from 0.9–7.9%. They also constitute a significant economic burden. We thus aimed at determining the prevalence and the economic burden of ADRs presenting to Medical Emergency Department (ED) of a tertiary referral center in India  相似文献   
80.
报道了采自内蒙古呼伦贝尔市的中国疣柄牛肝菌属1个新记录种,即假褐疣柄牛肝菌Leccinum pseudoscabrum(Kallenb.)utara.。主要特征为菌肉伤后变红到紫褐色,再到黑褐色,基部菌丝体手触后呈紫褐色;具泡状菌丝,呈栅栏状。比较和讨论了该种与相近种在伤后不同的变色反应及菌丝形态。研究标本存放于吉林农业大学菌物标本馆(HMJAU)。  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