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   307篇
  免费   22篇
  国内免费   1篇
  330篇
  2023年   5篇
  2022年   9篇
  2021年   17篇
  2020年   5篇
  2019年   4篇
  2018年   11篇
  2017年   13篇
  2016年   13篇
  2015年   14篇
  2014年   18篇
  2013年   17篇
  2012年   15篇
  2011年   21篇
  2010年   8篇
  2009年   3篇
  2008年   8篇
  2007年   10篇
  2006年   7篇
  2005年   17篇
  2004年   7篇
  2003年   7篇
  2002年   9篇
  2001年   7篇
  2000年   17篇
  1999年   4篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1994年   2篇
  1992年   2篇
  1991年   2篇
  1990年   4篇
  1989年   3篇
  1987年   4篇
  1986年   8篇
  1984年   1篇
  1983年   1篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   4篇
  1977年   4篇
  1976年   3篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
  1970年   2篇
  1969年   1篇
  1968年   3篇
  1967年   1篇
排序方式: 共有330条查询结果,搜索用时 3 毫秒
321.
Sulphamidase is an exoglycosidase involved in the degradation of heparan sulfate. Lack of sulphamidase activity leads to the lysosomal storage disorder Mucopolysaccharidosis type IIIA (Sanfilippo type A OMIM No. 252900). At present there are no naturally occurring small animal models of this disease that could be of fundamental importance to study the pathophysiology of the disease and to try therapeutic strategies. Cloning of the mouse gene is an important step to create a mouse model for this common mucopolysaccharidosis. We have isolated and sequenced the gene encoding mouse sulphamidase. Comparison of the deduced amino acid sequences of human and mouse sulphamidase showed 88% identity and 93% similarity. The exon-intron structure of the gene has been determined with the mouse 10-kb gene divided in 8 exons. The mouse sulphamidase gene (Sgsh) was mapped to the distal end of Chromosome (Chr) 11, in a region that is homologous with a segment of human Chr 17 containing the orthologous human gene. Received: 26 July 1999 / Accepted: 3 February 2000  相似文献   
322.
Sera from mice which have been vaccinated with BCG and challenged with old tuberculin contain gamma interferon. These same sera also express antibacterial activity. Using Staphylococcus aureus we demonstrated that its growth was inhibited at dilutions of sera as high as 1:320. A 4% concentration of sera reduced the growth rate of the S. aureus from 1.6 to 0.6 doubling times per hour. The activity was stable at 56 degrees C but destroyed by 80 degrees C. It was nondialysable and destroyed by acid conditions (pH 2.0) and by the proteolytic enzymes trypsin and chymotrypsin. Antibodies to gamma interferon neutralized the antiviral activity but not the antibacterial activity. Mitogen-induced and virus-induced interferons did not have activity. We subsequently demonstrated that the factor could be induced in mice using BCG without the secondary old tuberculin challenge. No gamma interferon was found in the sera of mice given BCG without old tuberculin. These findings indicate that the antibacterial activity of these sera is not dependent on the presence of gamma interferon. We will continue to work to characterize and identify the antibacterial component in these sera.  相似文献   
323.
Studies of the possible viral etiology of human leukemia have required large quantities of cultured cells derived from human hematopoietic tissues. Since cultures sufficiently large and free from contamination could not readily be produced according to existing methods, a pilot, cell culture plant has been constructed for the production of mammalian cells in mass quantity. 500-ml to 20-liter trophocell units have already proved to be scientifically and economically practical, as they provide good reliability, excellent growth rates, and sustained yield of human cells. 200-liter stainless steel culture units have now been added to the trophocell system. Five complete 200 liter units are now in operation. The design of the original stainless steel unit was based on that of a stainless steel, jacketed soup kettle. There are no openings in the vessel other than those in the lid, which provide convenient access points for sampling, sensor probes, etc. Environmental parameters, e.g., liquid level, temperature, and pH, are monitored and controlled with commercially available apparatus. Many initial problems connected with the new 200 liter units have been resolved, but operational and design problems remain in the areas of stable instrumentation, cell harvesting, salvaging and reuse of unspent media components, establishment of physiologic steady stale, recovery of virus-containing cells with reculture of the remaining unaffected cells, and the recovery and separation of cell components and special products such as immunoglobulins, interferons, and hormones. A definitive cell plant with culture units of 20, 50, 250, and 1250 liters is now being constructed.  相似文献   
324.
The fossil tragelaphins from the late Pliocene of Hadar are described. These are Tragelaphus lockwoodi, new species, and Tragelaphus aff. T. nakuae. Tragelaphus lockwoodi bears long horns that define one complete spiral and that are mediolaterally compressed at the base. In these and other morphological characteristics it approaches the greater kudu, T. strepsiceros, and makes a good ancestral candidate for this living species. The Hadar T. aff. T. nakuae is similar to other specimens of this species from sites >2.8 Ma in East Africa and demonstrates well the major differences between the earlier and later representatives of this taxon. The sizes and morphological variation in the large Hadar T. aff. T. nakuae sample supports the idea that female individuals of this species were horned as is the case today in the elands and the bongo. Tragelaphus lockwoodi is present only in the lower beds of the Hadar Formation, and in small numbers, while T. aff. T. nakuae is recovered in relative abundance from throughout the ca. 3.4-ca. 2.9 Ma sequence.  相似文献   
325.
KB cells grown in suspension culture were synchronized by using a double thymidine block. At various times throughout the life cycle aliquots of cells were pulsed with 14C-L-leucine, 14C-D-glucosamine and 14C-choline for one hour periods. Surface membranes, cell particulates and soluble proteins were isolated and their 14C specific activities were determined. It was found that there was a marked increase in the rate of incorporation into surface membrane just after division. The pattern of incorporation was the same for all three isotopic precursors. The rate of incorporation of isotopic precursors into soluble proteins was constant throughout the cycle. Some increase in rate of incorporation of isotope into the particulate fraction was observed during division.  相似文献   
326.
The porcine major histocompatibility complex (MHC) harbors the highly polymorphic swine leukocyte antigen (SLA) class I and II gene clusters encoding glycoproteins that present antigenic peptides to T cells in the adaptive immune response. In Austria, the majority of commercial pigs are F 2 descendants of F 1 Large White/Landrace hybrids paired with Pietrain boars. Therefore, the repertoire of SLA alleles and haplotypes present in Pietrain pigs has an important influence on that of their descendants. In this study, we characterized the SLA class I ( SLA‐1 , SLA‐2 , SLA‐3 ) and class II ( SLA‐DRB1 , SLA‐DQB1 , SLA‐DQA ) genes of 27 purebred Pietrain pigs using a combination of the high‐resolution sequence‐based typing (SBT) method and a low‐resolution (Lr) PCR‐based method using allele‐group, sequence‐specific primers (PCR‐SSP). A total of 15 class I and 13 class II haplotypes were identified in the studied cohort. The most common SLA class I haplotype Lr‐43.0 ( SLA‐1 *11XX– SLA‐3 *04XX– SLA‐2 *04XX) was identified in 11 animals with a frequency of 20%. For SLA class II, the most prevalent haplotype, Lr‐0.14 [ SLA‐DRB1 *0901– SLA‐DQB1 *0801– SLA‐DQA *03XX], was found in 14 animals with a frequency of 26%. Two class II haplotypes, tentatively designated as Lr‐Pie‐0.1 [ SLA‐DRB1 *01XX/be01/ha04– SLA‐DQB1 *05XX– SLA DQA*blank] and Lr‐Pie‐0.2 [ SLA‐DRB1 *06XX– SLA‐DQB1 *03XX– SLA‐DQA *03XX], appeared to be novel and have never been reported so far in other pig populations. We showed that SLA genotyping using PCR‐SSP‐based assays represents a rapid and cost‐effective way to study SLA diversity in outbred commercial pigs and may facilitate the development of more effective vaccines or identification of disease‐resistant pigs in the context of SLA antigens to improve overall swine health.  相似文献   
327.
Transport of the nucleoside analog cytosine-arabinoside (CAR) in transformed hamster cells in culture has been studied in conditions of minimal metabolic conversion. Uptake (zero-trans in) properties at 20 degrees C over a limited range of CAR concentrations were characterized by a Km of 350 micrometer and a maximal velocity (V) of 780 micrometer.min-1 (V/Km = 2.28 min-1). Equilibrium exhcange at 20 degrees C over a wider range of concentrations was best described by a saturable component with a Km of 500 micrometer and a v of 1230 micrometer.min-1 (V/Km = 2.26 min-1) and either a saturable component of high Km or a nonsaturable component of k = 0.3 min-1. For the saturable component, the v/Km values were similar in both procedures. CAR transport was inhibited by various metabolizable nucleosides. Uptake of some of these nucleosides was inhibited by CAR. CAR transport and uridine uptake were inhibited in a reversible but partially competitive fashion by high affinity probes like S-(p-nitrobenzyl-6-mercaptoinosine (NBMI) (Ki less than 0.5 nM) and in an irreversible fashion by SH reagents such as N-ethylmaleiimide (NEM). The organomercurial p-hydroxymercuribenzene sulfonate (pMBS) markedly stimulated transport of these nucleosides, but also markedly potentiated the inhibitory effects of either NBMI or NEM. The effects are interpreted either in terms of models which invoke allosteric properties or in terms of two transport systems which display distinct chemical susceptibilities to externally added probes.  相似文献   
328.
This study aims to compare the risk of anemia by iron deficiency in mothers and infants of twin and single pregnancy. It concerned 33 couples of twins and 31 control, all 97 being term newborns. At birth, ferritinemia is significantly lower in twins, and reticulocytes count is significantly higher; their mothers have a significantly lower hemoglobin level and higher reticulocytes percentage and count. At 3 and 6 months, hemoglobin level and mean corpuscular hemoglobin are significantly lower in twins, as at 6 months ferritinemia is significantly lower in twins. Iron stocks constituted in utero are significantly lower in twin pregnancy, and this study support the early preventive iron treatment in twins.  相似文献   
329.
330.
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