全文获取类型
收费全文 | 125篇 |
免费 | 1篇 |
专业分类
系统科学 | 4篇 |
理论与方法论 | 1篇 |
现状及发展 | 20篇 |
研究方法 | 15篇 |
综合类 | 86篇 |
出版年
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2013年 | 2篇 |
2012年 | 12篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有126条查询结果,搜索用时 31 毫秒
21.
22.
Neurodegenerative diseases of the central nervous system are often associated with impaired learning and memory, eventually leading to dementia. An important aspect in pre-clinical research is the exploration of strategies to re-establish learning ability and access to long-term memories. By using a mouse model that allows temporally and spatially restricted induction of neuronal loss, we show here that environmental enrichment reinstated learning behaviour and re-established access to long-term memories after significant brain atrophy and neuronal loss had already occurred. Environmental enrichment correlated with chromatin modifications (increased histone-tail acetylation). Moreover, increased histone acetylation by inhibitors of histone deacetylases induced sprouting of dendrites, an increased number of synapses, and reinstated learning behaviour and access to long-term memories. These data suggest that inhibition of histone deacetylases might be a suitable therapeutic avenue for neurodegenerative diseases associated with learning and memory impairment, and raises the possibility of recovery of long-term memories in patients with dementia. 相似文献
23.
强酸促进的Mo/HZSM-5基催化剂上甲烷脱氢芳构化研究 总被引:3,自引:0,他引:3
研制出一种强酸促进的甲烷非氧化脱氢芳构化催化剂Mo-A/HZSM-5.在可比的实验条件下,其对甲烷的转化活性和苯收率比非促进的Mo/HZSM-5催化剂均提高约40%,且催化剂稳定性大为提高.实验结果揭示表面酸度,主要是表面B-酸位浓度,与甲烷的转化活性密切相关.本文认为在强酸促进的Mo-A/HZSM-5催化剂上,甲烷活化脱氢主要系经由B-酸助的C-H键异裂的反应途径,即:低价Mo物种则可能在稳定卡宾中间态,以及后续的齐聚、芳构化过程中起重要作用. 相似文献
24.
研究了一元MoO_3/SiO_2体系中新电氧物种O~-和O_2~-的形成,说明气相氧和晶格氧都能产生这类氧物种,二元体系MoO_3-Bi_2O_3/SiO_2上丙烯催化氧化的选择性随着O~-、O_2~-自旋浓度的降低而提高的实验事实说明O~-、O_2~-是导致非选择性氧化的表面物种.在MoO_3-Bi_2O_3/SiO_2中添加磷组份可能促进氧吸附态的转化O_2?O_?~-?2O?2O~(2-)(晶格)向右进行,因而提高反应的选择性,铁作为第三组份引入时,可使体系中产生氧化还原偶Fe~(3 )/Fe~(2 ),这有利于提高丙烯氧化的选择性。 相似文献
25.
蔡禄 《内蒙古大学学报(自然科学版)》1988,(1)
从信息论角度入手,进一步对13类、约1200个核酸非编码序列进行研究。对信息指标作了长度修正,找到了一些非编码区的特殊结构。得到非编码区遵守与编码区一样的进化规律,非编码区进化水平低于编码区的结论。 相似文献
26.
27.
Wu Xiong-bin Xu Ji-sheng Ma Shu-ying Tian Mao Yu Shen-bing K C Yeh W H Tsai K H Lin 《武汉大学学报:自然科学英文版》1999,4(2):186-192
The design and operation features of the automatic data acquisition system for the low-latitude ionospheric tomography along
the 120°E meridian are presented. The system, automatically collects the differential Doppler phase data, and GPS satellite
beacon signal is simultaneously collected to achieve time synchronization of all recelvers in whole station-chain. An improved
reconstruction algorithm of computerized ionospheric tomography is also proposed, in which calculating of the integral phase
constant and choosing of the initial guess are integrated in the procedure of reconstruction and evaluated by the reconstructed
image. Both numerical simulation examples and reconstructed results from observed data show that the new algorithm works reasonably
and effectively with ionospheric CT problems.
Foundation item: Supported by the National Natural Science Foundation of China (49584006)
Biography: WU Xiong-bin (1968-), male, Ph. D candidate. Research direction: computerized ionospheric tomography. 相似文献
28.
低温催化裂解烷烃法制备碳纳米管 总被引:12,自引:2,他引:12
实验发现,甲烷可在较低温度(723K)下,在一种Ni催化剂上分解生成碳纳米管.透射电镜测试结果显示,通过此法制得的碳纤维几乎都具有管状结构.碳纳米管的外径,管长及产率明显地受催化剂的结构、性能,反应温度和原料气流速所支配.将所制得的产物浸泡在稀硝酸溶液中,溶去催化剂颗粒,经水洗,并于473K温度下烘干,可达到将碳纳米管产物与催化剂分离、纯化的目的. 相似文献
29.
催化剂分子设计专家系统推理机的设计 总被引:3,自引:1,他引:3
承接前文关于催化剂分子设计专家系统的数据库与知识库的建造.详细沦述了本系统推理机的设计与实现.针对特定催化领域的知识体系,初步建立起相应的推理机制,主要包括对合适的知识推理技术的采用和推理的搜索、控制策略的选择确定. 相似文献
30.
Template-imprinted nanostructured surfaces for protein recognition 总被引:18,自引:0,他引:18
Synthetic materials capable of selectively recognizing proteins are important in separations, biosensors and the development of biomedical materials. The technique of molecular imprinting creates specific recognition sites in polymers by using template molecules. Molecular recognition is attributed to binding sites that complement molecules in size, shape and chemical functionality. But attempts to imprint proteins have met with only limited success. Here we report a method for imprinting surfaces with protein-recognition sites. We use radio-frequency glow-discharge plasma deposition to form polymeric thin films around proteins coated with disaccharide molecules. The disaccharides become covalently attached to the polymer film, creating polysaccharide-like cavities that exhibit highly selective recognition for a variety of template proteins, including albumin, immunoglobulin G, lysozyme, ribonuclease and streptavidin. Direct imaging of template recognition is achieved by patterning a surface at the micrometre scale with imprinted regions. 相似文献