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   255篇
  免费   20篇
  2022年   2篇
  2021年   3篇
  2019年   1篇
  2018年   1篇
  2017年   5篇
  2016年   5篇
  2015年   11篇
  2014年   15篇
  2013年   23篇
  2012年   17篇
  2011年   9篇
  2010年   7篇
  2009年   13篇
  2008年   11篇
  2007年   11篇
  2006年   15篇
  2005年   9篇
  2004年   6篇
  2003年   8篇
  2002年   4篇
  2001年   10篇
  2000年   12篇
  1999年   6篇
  1998年   12篇
  1997年   7篇
  1996年   3篇
  1995年   4篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1988年   4篇
  1987年   4篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   6篇
  1978年   2篇
  1977年   1篇
  1976年   2篇
  1971年   1篇
  1967年   1篇
  1941年   1篇
  1923年   1篇
  1921年   1篇
排序方式: 共有275条查询结果,搜索用时 15 毫秒
1.
Dispersed marmoset luteal cells were incubated for 2 h and progesterone production measured after exposure to hCG, cloprostenol, dibutyryl cAMP, PGF-2 alpha, PGF-2, adrenaline or melatonin. The cells were studied on Days 6, 14 and 20 after ovulation in conception and non-conception cycles. Luteal cells from Day 14 non-pregnant marmosets were compared with human luteal cells taken in the mid-luteal phase. All the treatments stimulated progesterone production including cloprostenol, which is luteolytic when administered to the marmoset in vivo, but the degree of response varied with the stage of the cycle or pregnancy and between marmoset and human luteal cells. In the marmoset, overall analysis of the effect of the treatments showed that, on Day 6 after ovulation, there was no significant effect of any of the treatments in cells from pregnant or non-pregnant animals. In contrast, luteal cells from non-pregnant animals on Day 14 showed a significant response to the treatments (F (8,41) = 2.79, P less than 0.0145) whereas cells from pregnant Day-14 animals were responsive; in cells from pregnant animals, the control production of progesterone was high and already equivalent to the levels stimulated by the treatments. By Day 20, cells from pregnant animals produced lower control concentrations of progesterone than did those on Day 14 and there was a significant overall effect of the treatments (F (8,33) = 3.78, P less than 0.003). These results show that the marmoset CL gains responsiveness to treatment between Days 6 and 14 after ovulation in the non-pregnant cycle. In pregnancy, on Day 14, 2 days after attachment of the embryo, the high control concentrations of progesterone and absence of response to treatment suggest that an embryo message may have affected the CL, providing an endogenous stimulus.  相似文献   
2.
Eight neurologically impaired patients underwent reconstruction of chronic perineal and ischial pressure sores utilizing an inferiorly based rectus abdominis myocutaneous flap. Other local and regional flap options had been previously used or were not feasible. In six patients, healing was uncomplicated. One patient required local debridement and flap readvancement. The second involved minor separation of a suture line and healed by secondary intention. All donor sites were closed directly and healed by primary intention. There was no evidence of hernia formation, and no functional deficit was detected from removal of the rectus muscle in any of the patients. In conclusion, it was felt that the inferiorly based rectus abdominis myocutaneous flap should be considered a reconstructive option in dealing with perineal and ischial pressure sores. Furthermore, for reasons discussed, we found distinct advantages to using this flap in spinal cord injury patients.  相似文献   
3.
Epstein-Barr virus (B95-8) DNA consists of short (10 X 10(6)) and long (87 X 10(6)) unique DNA sequences joined by 10 tandem reiterations of a 1.85 X 10(6) DNA segment. The reiterated sequence contains BamI and BglII sites separated by 4 X 10(5). The 4.5 X 10(5) and 14.0 X 10(5) segments generated by cleavage of the reiterated DNA with BamI and BglII contain sequences which hybridize to each other, suggesting that the internal tandemly reiterated sequence has a direct or inverted repeat within it. The opposite ends of the linear, nicked, double-stranded DNA molecule (R. F. Pritchett, S. D. Hayward, and E. D. Kieff, J. Virol. 15:556--569, 1975) consist of from 1 to 12 direct repeats of another 3 X 10(5) sequence (D. Given and E. Kieff, J. Virol. 28:524--542, 1978; D. Given, D. Yee, K. Griem, and E. Kieff, J. Virol. 30:852--862, 1979). There is no homology between the internal reiterated sequence and either terminus. However, part of the internal reiteration (less than 5 X 10(5) is reiterated at two separate locations in the long unique region. The internal reiterations are a source of variation within EBV (B95-8) DNA preparations. Thus, although the majority of molecules contain 10 tandem reiterations, some molecules have 9, 8, 7, 6, 5, 4, or fewer tandem reiterations. A consequence of this variability is that the KpnI A fragment and the EcoRI/Hsul A fragment consist of a family of seven or more fragments differing in the number of tandem internal reiterations. The EcoRI/HsuI A fragment of EBV (W91) DNA is approximately 6 X 10(6) smaller than the largest and dominant EcoRI/HsuI A fragment of EBV (B95-8) DNA. EBV (W91 DNA also differs from EBV (B95-8) DNA by an additional 7 X 10(6) to 8 X 10(6) of DNA in the long unique DNA region (D. Given and E. Kieff, J. Virol. 28:524--542, 1978; N. Raab-Traub, R. Pritchett, and E. Kieff, J. Virol. 27:388--398, 1978). These data suggest the possibility that the smaller number of internal reiterations in EBV (W91) DNA may be a consequence of the additional unique DNA and a restriction in the overall size of EBV DNA.  相似文献   
4.
The arrangement of EcoRI, Hsu I, and Sal I restriction enzyme sites in the DNA of the B95-8 and W91 isolates of Epstein-Barr virus (EBV) has been determined from the size of the single-enzyme-cleaved fragments and from blot hybridizations that identify which fragments cut from the DNA with one enzyme contain nucleotide sequences in common with fragments cut from the DNA with a second enzyme. The DNA of the B95-8 isolate was the prototype for this study. The data indicate that (i) approximately 95 X 10(6) to 100 X 10(6) daltons of EBV (B95-8) DNA is in a consistent and unique sequence arrangement. (ii) Both termini are variable in length. One end of the molecule after Hsu I endonuclease cleavage consists of approximately 3,000 base pairs, with as many as 10 additional 500-base pair segments. The opposite end of the molecule after Sal I endonuclease cleavage consists of approximately 1,500 base pairs, with as many as 10 additional 500-base pair segments. (iii) The opposite ends of the molecule contain homologous sequences. The high degree of homology between the opposite ends of the molecule and the similarity in size of the "additional" 500-base pair segments suggests that there are identical repeating units at both ends of the DNA. The arrangement of restriction endonuclease fragments of the DNA of the W91 isolate of EBV is similar to that of the B95-8 isolate and differs from the latter in the presence of approximately 7 X 10(6) daltons of "extra" DNA at a single site. Thus, the size of almost all EcoRI, Hsu I, and Sal I fragments of EBV (W91) DNA is identical to that of fragments of EBV (B95-8) DNA. A single EcoRI fragment, C, of EBV (W91) DNA is approximately 7 X 10(6) daltons larger than the corresponding EcoRI fragment of EBV (B95-8) DNA. Digestion of EBV (W91) DNA with Hsu I or Sal I restriction endonucleases produces two fragments (Hsu I D1 and D2 or Sal I G2 and G3) which differ in total size by approximately 7 X 10(6) daltons from the fragments of EBV (B95-8) DNA. Furthermore, the EcoRI, Hsu I, and Sal I fragments of EBV (W91) and (B95-8) DNAs, which are of similar molecular weight, have homologous nucleotide sequences. Moreover, the W91 fragments contain only sequences from a single region of the B95-8 genome. Two lines of evidence indicate that the "extra" sequences present in W91 EcoRI fragment C are viral DNA and not cellular. (i) The molecular weight of the "enlarged" EcoRI C fragment of EBV (W91) DNA is identical to that of the EcoRI C fragment of another isolate of EBV (Jijoye), (ii) The HR-1 clone of Jijoye has previously been shown to contain DNA which is not present in the B95-8 strain but is present in the EcoRI C and Hsu I D2 and D1 fragments of EBV (W91) DNA (N. Raab-Traub, R. Pritchett, and E. Kieff, J. Virol. 27:388-398, 1978).  相似文献   
5.
We tested the brood-reduction hypothesis by adding three nestlingsto naturally occurring synchronous and asynchronous broods ofthe house wren (Troglodytes aedon) in order to mimic food shortagesfor the broods. Two types of controls were established in whichbrood size remained unchanged: those in which nestlings wereexchanged among broods and those in which no nestlings wereexchanged. The critical test of the hypothesis was in 1988 whenthere was a food shortage for enlarged broods. Although broodreduction occurred, enlarged synchronous broods produced asmany fledglings as did enlarged asynchronous broods, and fledgingmass was similar. Juvenile recapture 2-8 weeks after fledgingand offspring recruitment to subsequent breeding populationswere not related to treatment. The results are not consistentwith the brood-reduction hypothesis as an explanation for theoccurrence of hatching asynchrony in the house wren.  相似文献   
6.
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.  相似文献   
7.
Hormonal regulation of ripening in the strawberry,a non-climacteric fruit   总被引:1,自引:0,他引:1  
N. K. Given  M. A. Venis  D. Gierson 《Planta》1988,174(3):402-406
Anthocyanin accumulation is one measure of ripening in the strawberry (Fragaria ananassa Duch.), a non-climacteric fruit. Neither aminoethoxyvinylglycine, an inhibitor of 1-aminocyclopropane carboxylic acid synthase, nor inhibitors of ethylene action (silver, norbornadiene) affected anthocyanin accumulation in ripening fruit. When the achenes were removed from one half of an unripe fruit there was an accelerated accumulation of anthocyanin and induction of phenylalanine ammonia lyase on the de-achened portion of the ripening fruit. These effects of achene removal could be prevented by the application of the synthetic auxins 1-naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid to the de-achened surface. The introduction of 1-naphthalene acetic acid into intact unripe strawberry fruit through the peduncle delayed their subsequent ripening, as measured by the accumulation of anthocyanin, loss of chlorophyll and decrease in firmness. These findings suggest that the decline in the concentration of auxin in the achenes as strawberry fruit mature modulates the rate of fruit ripening.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - NAA 1-naphthaleneacetic acid - PA1 phenylalanine ammonia-lyase - POA phenoxyacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid  相似文献   
8.
9.
10.
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