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   1568篇
  免费   85篇
  2023年   6篇
  2022年   23篇
  2021年   38篇
  2020年   22篇
  2019年   23篇
  2018年   32篇
  2017年   41篇
  2016年   48篇
  2015年   50篇
  2014年   70篇
  2013年   94篇
  2012年   100篇
  2011年   96篇
  2010年   49篇
  2009年   51篇
  2008年   66篇
  2007年   78篇
  2006年   62篇
  2005年   81篇
  2004年   57篇
  2003年   76篇
  2002年   61篇
  2001年   31篇
  2000年   29篇
  1999年   17篇
  1998年   13篇
  1997年   6篇
  1996年   8篇
  1995年   8篇
  1993年   8篇
  1992年   15篇
  1991年   14篇
  1990年   21篇
  1989年   13篇
  1988年   15篇
  1987年   12篇
  1986年   9篇
  1985年   9篇
  1984年   10篇
  1983年   10篇
  1979年   6篇
  1978年   7篇
  1976年   6篇
  1974年   14篇
  1972年   7篇
  1913年   8篇
  1912年   5篇
  1908年   6篇
  1904年   7篇
  1865年   5篇
排序方式: 共有1653条查询结果,搜索用时 31 毫秒
71.
72.
The phylogeny of true bugs (Hemiptera: Heteroptera), one of the most diverse insect groups in terms of morphology and ecology, has been the focus of attention for decades with respect to several deep nodes between the suborders of Hemiptera and the infraorders of Heteroptera. Here, we assembled a phylogenomic data set of 53 taxa and 3102 orthologous genes to investigate the phylogeny of Hemiptera–Heteroptera, and both concatenation and coalescent methods were used. A binode-control approach for data filtering was introduced to reduce the incongruence between different genes, which can improve the performance of phylogenetic reconstruction. Both hypotheses (Coleorrhyncha + Heteroptera) and (Coleorrhyncha + Auchenorrhyncha) received support from various analyses, in which the former is more consistent with the morphological evidence. Based on a divergence time estimation performed on genes with a strong phylogenetic signal, the origin of true bugs was dated to 290–268 Ma in the Permian, the time in Earth's history with the highest concentration of atmospheric oxygen. During this time interval, at least 1007 apomorphic amino acids were retained in the common ancestor of the extant true bugs. These molecular apomorphies are located in 553 orthologous genes, which suggests the common ancestor of the extant true bugs may have experienced large-scale evolution at the genome level.  相似文献   
73.
74.
The design of efficient and safe gene delivery vehicles remains a major challenge for the application of gene therapy. Of the many reported gene delivery systems, metal complexes with high affinity for nucleic acids are emerging as an attractive option. We have discovered that certain metallohelices—optically pure, self-assembling triple-stranded arrays of fully encapsulated Fe—act as nonviral DNA delivery vectors capable of mediating efficient gene transfection. They induce formation of globular DNA particles which protect the DNA from degradation by various restriction endonucleases, are of suitable size and electrostatic potential for efficient membrane transport and are successfully processed by cells. The activity is highly structure-dependent—compact and shorter metallohelix enantiomers are far less efficient than less compact and longer enantiomers.  相似文献   
75.
76.
Baranov VS  Baranov AN  Zelenin AV 《Genetika》2001,37(8):1046-1054
Failure of drug therapy of Duchenne muscular dystrophy (DMD) stimulated intense search for adequate methods of gene therapy (GT) which would ensure effective delivery of the dystrophin (D) gene, its long-term persistence in transfected cells, and its expression in muscle fibers. The main results of the experimental GT of DMD with the use of viral and nonviral delivery of the D gene into muscles of biological models are discussed. Delivery of a mini-gene of D with a specific muscle promoter using a modified adenoassociated virus is currently the most promising method, which will soon be available for clinical trials. The main results of the studies on the DMD GT in Russia are summarized. The results of experiments on genetic transfection of mdx mice with marker genes and various constructions with the D gene are outlined. The genes are delivered into muscles by means of gene gun, electroporation, viral oligopeptides, liposomes, microspheres, lactoferine, and other nonviral vehicles. It is emphasized that consolidation of funds and efforts of all Russian laboratories dealing with gene and cell therapy of DMD are necessary to complete the experiments and start clinical trials.  相似文献   
77.
Polymerase chain reaction with subsequent SSCP (single-strand DNA conformational polymorphism) and restriction (BselI restriction endonuclease) analyses were used to type the DNA samples of affected individuals and their relatives from 23 Russian families with high risk of spinal muscular atrophy (SMA) residing in the northwestern region of Russia. Deletions of exon 7 of the SMN gene were found in 96% of the individuals examined. The frequency of homozygous deletion of exons 7 and 8 of the SMN1 gene was 65%. The frequency of homozygous isolated deletion of the SMN1 gene exon 7 among the SMA patients was 4.3%. Homozygous deletion of exon 5 of the NAIP gene was found in 22% of SMA patients. In SMA patients, a total of seven deletion types involving the SMN1, NAIP, and SMN2 genes were detected. Deletion of exons 7 and 8 of the SMN1 gene was the most common mutation associated with SMA in patients from the northwestern Russia.  相似文献   
78.
It is well established that bicarbonate stimulates electron transfer between the primary and secondary electron acceptors, Q(A) and Q(B), in formate-inhibited photosystem II; the non-heme Fe between Q(A) and Q(B) plays an essential role in the bicarbonate binding. Strong evidence of a bicarbonate requirement for the water-oxidizing complex (WOC), both O2 evolving and assembling from apo-WOC and Mn2+, of photosystem II (PSII) preparations has been presented in a number of publications during the last 5 years. The following explanations for the involvement of bicarbonate in the events on the donor side of PSII are considered: (1) bicarbonate serves as an electron donor (alternative to water or as a way of involvement of water molecules in the oxidative reactions) to the Mn-containing O2 center; (2) bicarbonate facilitates reassembly of the WOC from apo-WOC and Mn2+ due to formation of the complexes MnHCO3+ and Mn(HCO3)2 leading to an easier oxidation of Mn2+ with PSII; (3) bicarbonate is an integral component of the WOC essential for its function and stability; it may be considered a direct ligand to the Mn cluster; (4) the WOC is stabilized by bicarbonate through its binding to other components of PSII.  相似文献   
79.
Green fluorescent protein (GFP) as a marker during pollen development   总被引:5,自引:0,他引:5  
The transient expression of three mutant forms of green fluorescent protein (GFP) genes, GFP4, GFP5ER, and GFP4S65C, under several constitutive and pollenspecific promoters throughout pollen development in Nicotianatabacum, thaliana and Antirrhinummajus is described. Immature pollen of tobacco, Arabidopsis and snapdragon, isolated at different developmental stages, were bombarded with plasmids containing the GFP and cultured in vitro for several days until maturity. The expression of GFP was monitored every day during in vitro maturation, germination and pollination, as well as after in situ pollination. The expression pattern of each construct was compared in parallel experiments to that of ßglucuronidase (GUS) constructs expressed by the same promoters. The results show that the expression level of all three GFP mutant forms was dependent on the strength of the promoter used. The strongest promoter was the DC3 promoter, and no notable differences in the intensity and brightness of all three versions of GFP were observed. GFPexpressing pollen from tobacco and snapdragon developed in vitro for several days until maturity and germinated in vitro as well as on the surface of stigmata, strongly suggesting that all three GFPs are not toxic for the development of functional pollen. Furthermore, stably transformed tobacco plants expressing GFP under the control of the strong pollenexpressed DC3 and LAT52 promoters were not impaired in reproductive function, confirming that GFP can be used as a nondestructive marker for plant reproductive biology and development.  相似文献   
80.
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