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   289篇
  免费   26篇
  国内免费   4篇
  319篇
  2024年   1篇
  2022年   6篇
  2021年   10篇
  2020年   5篇
  2019年   9篇
  2018年   4篇
  2017年   6篇
  2016年   14篇
  2015年   23篇
  2014年   19篇
  2013年   23篇
  2012年   23篇
  2011年   26篇
  2010年   20篇
  2009年   12篇
  2008年   12篇
  2007年   17篇
  2006年   13篇
  2005年   13篇
  2004年   17篇
  2003年   13篇
  2002年   10篇
  2001年   2篇
  2000年   3篇
  1999年   1篇
  1998年   2篇
  1997年   4篇
  1995年   1篇
  1991年   1篇
  1987年   1篇
  1985年   1篇
  1981年   1篇
  1974年   1篇
  1973年   1篇
  1971年   2篇
  1968年   1篇
  1966年   1篇
排序方式: 共有319条查询结果,搜索用时 15 毫秒
111.
We have recently identified in Drosophila melanogaster a new gene encoding a nuclear protein, DIP1. Here we report the developmental expression and the finding that DIP1 subcellular localization is in the nucleus and at the nuclear periphery during interphase in embryos. Interestingly, in humans, DIP1 antibody identified signals in nuclei from cultured cells and reacted with a rough 30kDa protein in Western blotting experiments, demonstrating evolutionary conservation.  相似文献   
112.
113.
OBJECTIVE: To investigate the changing prognosis for babies of less than 28 weeks'' gestation. DESIGN: A prospective, collaborative, population based survey. SETTING: The former Northern Regional Health Authority. SUBJECTS: All the births between 1983 and 1994 at 22 to 27 completed weeks'' gestation to women normally resident in the region. MAIN OUTCOME MEASURES: Miscarriage, stillbirth, death in the first year of life, and disability in survivors. RESULTS: There were 479070 registered births in the study period. No baby of 22 weeks'' gestation survived; only eight (4%) of the 197 babies of 23 weeks who were alive at the onset of labour survived for a year-a proportion that did not change during the study period. Survival among other babies of less than 28 weeks improved progressively between 1983-6 and 1991-4, but administration of artificial surfactant to babies requiring ventilation from mid-1990 was associated with further improvement in survival only in those over 25 weeks'' gestation. Babies of 24 weeks required three times as much high dependency care per survivor as babies of 27 weeks (76 v 26 days). The rate of severe disability in the one year survivors of less than 26 weeks'' gestation (30/123; 24%) was similar to that seen in the sampled survivors of 26 and 27 weeks (29/108; 27%); the proportion disabled did not change significantly during the study period. All the children born in 1983, 1987, and 1991 were later reassessed in greater detail: 10% (13/136) seemed destined for a continuing life of total dependency. CONCLUSIONS: Gestation, if accurately assessed, can give a woman facing very preterm delivery a clear indication of the prognosis for her baby and help her judge the appropriateness of accepting obstetric intervention and sustained perinatal support.  相似文献   
114.
Bacteria regulate their pathogenicity and biofilm formation through quorum sensing (QS), which is an intercellular communication system mediated by the binding of signaling molecules to QS receptors such as LasR. In this study, a range of dihydropyrrolone (DHP) analogues were synthesized via the lactone-lactam conversion of lactone intermediates. The synthesized compounds were tested for their ability to inhibit QS, biofilm formation and bacterial growth of Pseudomonas aeruginosa. The compounds were also docked into a LasR crystal structure to rationalize the observed structure-activity relationships. The most active compound identified in this study was compound 9i, which showed 63.1% QS inhibition of at 31.25?µM and 60% biofilm reduction at 250?µM with only moderate toxicity towards bacterial cell growth.  相似文献   
115.
Species diagnosis is of the utmost importance to both pest management and plant quarantine services. Because of difficulties in the morphological diagnosis of spider mites, molecular techniques are of great value to rapidly and accurately diagnose closely related species. We examined four species of genus Tetranychus (the green and red forms of T. urticae, and T. kanzawai, T. phaselus and T. truncatus), which are found in Korea and are of significance to plant quarantine services. DNA samples isolated from a single egg, larva or adult weighed 64–188 ng. We designed species‐specific primers by performing sequence alignment for 107 sequences of the ribosomal internal transcribed spacer 2 (ITS2) region, which we obtained from GenBank, and sequences generated in this study. Specific nucleotides of each species were selected for designing primers specific for each species. Each species‐specific primer pair, when used to perform PCR analyses, detected only the species from which it originated. However, a T. urticae‐specific primer pair did not discriminate between the green and red forms of this species. These species‐specific primers can be applied in practice for the rapid and accurate diagnosis of spider mite species in plant quarantine and in agricultural fields.  相似文献   
116.
Ma, K. Y., Chan, T. ‐Y & Chu, K. H. (2011). Refuting the six‐genus classification of Penaeus s.l. (Dendrobranchiata, Penaeidae): a combined analysis of mitochondrial and nuclear genes. —Zoologica Scripta, 40, 498–508. The taxonomic revision in 1997 of the shrimps formerly classified in Penaeus s.l. has been one of the most controversial issues on systematics of the decapods in recent years. Since Pérez Farfante & Kensley (Penaeoid and Sergestoid Shrimps and Prawns of the World, 1997) split this long‐accepted taxon into six genera, much debate has been devoted to their proposed new classification scheme; this has taken place because there are serious doubts whether the said scheme could reflect the evolutionary relationships among the 29 Penaeus s.l. species. Although these shrimps can be easily separated into several groups morphologically, whether these subdivisions are truly monophyletic and warrant a generic rank continues to be hotly debated among taxonomists. This study examined a total of 2425 bp sequences from three nuclear protein genes (enolase, phosphoenolpyruvate carboxykinase and sodium–potassium ATPase α‐subunit), and the mitochondrial 16S and 12S rRNA gene of 18 Penaeus s.l. shrimps and 13 other species in the family Penaeidae. Our phylogenetic analyses strongly support the monophyly of Penaeus s.l. and, concurring with previous studies that used the mitochondrial genes alone, the paraphyly of both Penaeus s.s. (sensu Pérez Farfante & Kensley, Penaeoid and Sergestoid Shrimps and Prawns of the World, 1997) and Melicertus, rendering them non‐natural groupings. Our study reveals two lineages: Penaeus s.s. + Fenneropenaeus + Litopenaeus + Farfantepenaeus and Melicertus + Marsupenaeus, which exhibit genetic divergences comparable with those among other penaeid genera. However, all the morphological characters, which are emphasized by Pérez Farfante and Kensley and used to separate Penaeus s.l., do not correlate with the grouping revealed by the present, perhaps decisive, phylogenetic result. Such disparity may arise from selection on the morphology of genitalia and convergent evolution. Our molecular data clearly refute the six‐genus classification, and we advocate the restoration of the old Penaeus genus (=Penaeus s.l.) definition which is the only classification scheme with both the morphological and the molecular data being in agreement.  相似文献   
117.
Partial cDNA of hemolin, an insect immune protein, was cloned from indianmeal moth, Plodia interpunctella, and the rates of hemolin mRNA expression were demonstrated in each stage of development and also by bacterial injections. A deduced amino acid sequence from the cloned hemolin cDNA was approximately 44‐54% similar to hemolins of 5 other moths. During development the level of hemolin mRNA was the highest at the time of the larval‐pupal matamorphosis. Hemolin was also rapidly induced by the injection of bacteria into the 4th or the 5th instar larvae. Hemolin induction rate by bacterial challenge was higher in the 5th instar larvae than in 4th instars. Our results suggest that hemolin could have multiple roles that act both on cellular processes during development and on the immune reactions for the resistance to pathogen invasion.  相似文献   
118.
119.
The leaf anatomy of Goniothalamus andersonii, G. macrophyllus, G. malayanus and G. velutinus from the peat swamps of Sarawak is compared. Sufficient anatomical differences exist to differentiate the four species. G. velutinus has many points of difference from the other three species and G. macrophyllus is readily identified by the presence of fibre-sclereids in the lamina mesophyll. G. andersonii and G. malayanus are similar to each other, but G. andersonii can be distinguished, in particular by the more pronounced multiple projections of the outer periclinal walls of the epidermal cells and the presence of thick and cutinised outer ends of the anticlinal walls of the epidermal cells.  相似文献   
120.
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