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   8055篇
  免费   865篇
  国内免费   2篇
  2023年   42篇
  2021年   187篇
  2020年   110篇
  2019年   133篇
  2018年   166篇
  2017年   158篇
  2016年   234篇
  2015年   376篇
  2014年   421篇
  2013年   475篇
  2012年   629篇
  2011年   626篇
  2010年   406篇
  2009年   338篇
  2008年   474篇
  2007年   463篇
  2006年   395篇
  2005年   383篇
  2004年   404篇
  2003年   341篇
  2002年   311篇
  2001年   122篇
  2000年   87篇
  1999年   106篇
  1998年   88篇
  1997年   76篇
  1996年   53篇
  1995年   54篇
  1994年   43篇
  1993年   38篇
  1992年   70篇
  1991年   73篇
  1990年   47篇
  1989年   57篇
  1988年   44篇
  1987年   40篇
  1986年   44篇
  1985年   54篇
  1984年   59篇
  1983年   43篇
  1982年   43篇
  1981年   31篇
  1980年   31篇
  1979年   34篇
  1978年   33篇
  1977年   40篇
  1976年   31篇
  1974年   29篇
  1972年   30篇
  1971年   25篇
排序方式: 共有8922条查询结果,搜索用时 203 毫秒
61.
Chromosomes and sex determination of 9 species of Haemaphysalis assigned to 4 subgenera are described. H. (tAlloceraea) kitaokai possesses an XX∶XO sex chromosome system with 18 autosomes plus XX in females; 18 plus X in males. H. (Kaiseriana) hystricis has 18 +XX and 18 + XY in females and males, respectively, in most specimens, but a supernumerary chromosome is present in some individuals. A supernumerary chromosome was also observed in 1 male H. (Aborphysalis) formosensis. These two species are the second and third species of ticks reported to have supernumerary chromosomes. H. formosensis, H. (Kaiseriana) bispinosa, H. (Haemaphysalis) campanulata, H. (H.) flava, H. (H.) megaspinosa, H. (H.) japonica, and H. (H.) pentalagi possess 20 autosomes plus 2 sex chromosomes in females and 20+1 sex chromosomes in males. Phylogenetic relationships within the genus Haemaphysalis are briefly discussed.  相似文献   
62.
The final phase of spermiogenesis in the hard tick Dermacentor andersoni occurs in the seminal receptacle of engorged females. This phase is characterized mainly by rupture of the outer sheath of advanced spermatids at their pointed tips, and subsequent elongation as the internal column of these cells evaginates. The sheath invaginates at the opposite end to form the narrow posterior half of the sperm cell. Rupture of the endospermatophoric wall releases the large mass of contained spermatozoa, which begin migration up one or both oviducts. During the migration to the ovarian lumen, spermatozoa exhibit a propensity for active penetration of epithelial cells lining the oviducts. This phenomenon is also observed with spermatozoa in the ovarian lumen. Penetration of epithelial cells by spermatozoa is interpreted to be a response by the latter in seeking eggs for penetration and fertilization.  相似文献   
63.
Phenol oxidase activity of activated A1 and A2 (A3) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A1 band and then in the A2 (A3) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.  相似文献   
64.
65.
66.
A man presented with the sudden onset of pernicious anaemia at the age of 21. He had been treated for hypothyroidism since the age of 6. His father and only paternal aunt were also found to have pernicious anaemia. Gastric and thyroid antibody studies showed one or more antibodies to be present in all three subjects, as well as in the patient''s mother.  相似文献   
67.
It is possible to stabilize foot-and-mouth disease antiserum by either freeze-drying in bottles or air-drying on paper for periods of 7 months.  相似文献   
68.
Results of the use of ampicillin, penicillin G and symptomatic therapy in the treatment of acute otitis media in 142 children were compared. Antibiotic therapy conveyed significant benefit. No major differences were observed between penicillin and ampicillin, except in the age group under 3 years where ampicillin was associated with the best results. Ampicillin appears to be the drug of choice. Its superiority over symptomatic therapy was statistically significant. Long-term sequelae were not observed in any of the three treatment groups. The relative merits of erythromycin and ampicillin require further study.  相似文献   
69.
The cystine-containing peptides of horse growth hormone were isolated and their amino acid sequences determined. Four unique half-cystine residues occur in two peptides, one containing 11 and the other, at the C-terminus of the protein, 15 amino acids. These sequences are compared with published data on growth hormones from other species.  相似文献   
70.
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