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   577篇
  免费   35篇
  2023年   2篇
  2022年   10篇
  2021年   21篇
  2020年   15篇
  2019年   17篇
  2018年   21篇
  2017年   16篇
  2016年   19篇
  2015年   39篇
  2014年   38篇
  2013年   46篇
  2012年   54篇
  2011年   45篇
  2010年   31篇
  2009年   20篇
  2008年   25篇
  2007年   20篇
  2006年   20篇
  2005年   20篇
  2004年   18篇
  2003年   20篇
  2002年   13篇
  2001年   7篇
  1999年   4篇
  1998年   6篇
  1997年   2篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1986年   5篇
  1985年   6篇
  1984年   7篇
  1983年   11篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1970年   1篇
  1969年   1篇
  1964年   2篇
  1963年   1篇
  1958年   1篇
排序方式: 共有612条查询结果,搜索用时 46 毫秒
191.
Birth of African Wildcat cloned kittens born from domestic cats   总被引:5,自引:0,他引:5  
In the present study, we used the African Wildcat (Felis silvestris lybica) as a somatic cell donor to evaluate the in vivo developmental competence, after transfer into domestic cat recipients, of cloned embryos produced by the fusion of African Wildcat (AWC) fibroblast cell nuclei with domestic cat cytoplasts. Cloned embryos were produced by fusion of a single AWC somatic cell to in vivo or in vitro enucleated domestic cat cytoplasts. When the two sources of oocytes were compared, fusion rate was higher using in vivo-matured oocytes as recipient cytoplasts, but cleavage rate was higher after reconstruction of in vitro-matured oocytes. To determine the number of reconstructed embryos required per domestic cat recipient to consistently establish pregnancies, AWC cloned embryos were transferred within two groups: recipients (n = 24) receiving < or =25 embryos and recipients (n = 26) receiving > or =30 embryos. Twelve recipients (46.2%) receiving > or =30 embryos were diagnosed to be pregnant, while no pregnancies were established in recipients receiving < or =25 NT embryos. Also, to determine the influence of length of in vitro culture on pregnancy rate, we compared oviductal transfer on day 1 and uterine transfer on day 5, 6, or 7. Pregnancy rates were similar after transfer of embryos on day 1 (6/12; 50.0%), day 5 (4/9; 44.4%), or day 6 (2/5; 40.0%) to synchronous recipients, but the number of fetuses developing after transfer of embryos on day 1 (n = 17), versus day 5 (n = 4) or day 6 (n = 3) was significantly different. Of the 12 pregnant recipients, nine (75%) developed to term and fetal resorption or abortion occurred in the other three (25%) from day 30 to 48 of gestation. Of a total of 17 cloned kittens born, seven were stillborn, eight died within hours of delivery or up to 6 weeks of age, and two are alive and healthy. Perinatal mortality was due to lung immaturity at premature delivery, placental separation and bacterial septicemia. Subsequent DNA analysis of 12 cat-specific microsatellite loci confirmed that all 17 kittens were clones of the AWC donor male. These AWC kittens represent the first wild carnivores to be produced by nuclear transfer.  相似文献   
192.
It is known that exogenous RNA molecules can be taken up by eukaryotic cells and can exert a variety of biological effects both in vitro and in vivo. The modulation of human lymphocytes by exogenous RNAs has medical implications. The exogenous RNA used in this study was obtained from lymphoid organs of animals immunized with the synthetic peptide p12 of HIV-1 and was referred to as p12-RNA. Human lymphocytes were transfected with the p12-RNA and the transfer of immunoreactivity of p12 was assessed by the lymphocyte proliferation and the leukocyte adherence inhibition assays. Our results indicate that the transfer of cellular immune response to the p12 occurred in 9 donors (60%) who were named responsive individuals whereas 6 donors (40%) were non-responsives. We also found that the calcium phosphate-mediated RNA uptake method is effective in converting non-responsive into responsive donors. The calcium phosphate-mediated RNA uptake may also be used to increase the efficiency of RNA transfection in other models with medical implications and to contribute to a better understanding of the molecular events involved in the uptake of RNA. Our findings give support for the use of exogenous RNAs obtained from lymphoid organs of immunized animals with synthetic peptides of HIV-1 in the immune reconstitution of individuals infected with HIV-1.  相似文献   
193.
This review reports the role of oxidative stress in impairing the function of lung exposed to particulate matter (PM). PM constitutes a heterogeneous mixture of various types of particles, many of which are likely to be involved in oxidative stress induction and respiratory diseases. Probably, the ability of PM to cause oxidative stress underlies the association between increased exposure to PM and exacerbations of lung disease. Mostly because of their large surface area, ultrafine particles have been shown to cause oxidative stress and proinflammatory effects in different in vivo and in vitro studies. Particle components and surface area may act synergistically inducing lung inflammation. In this vein, reactive oxygen species elicited upon PM exposure have been shown to activate a number of redox-responsive signaling pathways and Ca2+ influx in lung target cells that are involved in the expression of genes that modulate relevant responses to lung inflammation and disease.  相似文献   
194.

Background

Preterm birth (PTB) is a major determinant of neonatal morbimortality with adverse consequences for health. The causes are multifactorial, with intrauterine infection probably explaining most of these outcomes. It is believed that infection with Chlamydia trachomatis (CT) is also involved in PTB and premature rupture of membranes.

Objetives

To evaluate the prevalence of and associated factors for CT among cases of PTB attended at a University Hospital in Vitoria, Brazil.

Methods

A cross-sectional study performed among parturient who had preterm birth from June 2012 to August 2013 in Vitoria, Brazil. Participants answered a questionnaire including demographic, behavioral, and clinical data. A sample of urine was collected and screened for CT using polymerase chain reaction. Chi-square tests were used for proportion differences and Student’s-t tests and variance analysis were used for testing differences between mean values. Odds ratio was used as a measure of association with a 95% confidence interval.

Results

The prevalence of PTB during the period of the study was 26% and the prevalence of CT among them was 13.9%. A total of 31.6% pregnant women were younger than 25 years old and women infected by CT were even younger than women not infected by CT (p = 0.022). Most of them (76.2%) were married or had a living partner, and CT infection was more frequent among the single ones (p = 0.018); 16.7% of women reported their first sexual intercourse under 14 years old. The causes of prematurity were maternal-fetal in 40.9%; rupture of the membranes in 29.7% and premature labor in 29.4%. In multivariate analysis, being married was a protective factor for infection [OR = 0.48 (95%CI:0.24–0.97)]. None of the other characteristics were associated with CT infection.

Conclusions

This study shows a high prevalence of CT infection among parturient who have preterm birth. This high prevalence highlight the need for defining screening strategies focused on young pregnant women in Brazil.  相似文献   
195.

Aim

Fructose consumption is associated with altered hepatic function and metabolic compromise and not surprisingly has become a focus for perinatal studies. We have previously shown that maternal fructose intake results in sex specific changes in fetal, placental and neonatal outcomes. In this follow-up study we investigated effects on maternal, fetal and neonatal hepatic fatty acid metabolism and immune modulation.

Methods

Pregnant rats were randomised to either control (CON) or high-fructose (FR) diets. Fructose was given in solution and comprised 20% of total caloric intake. Blood and liver samples were collected at embryonic day 21 (E21) and postnatal day (P)10. Maternal liver samples were also collected at E21 and P10. Liver triglyceride and glycogen content was measured with standard assays. Hepatic gene expression was measured with qPCR.

Results

Maternal fructose intake during pregnancy resulted in maternal hepatic ER stress, hepatocellular injury and increased levels of genes that favour lipogenesis. These changes were associated with a reduction in the NLRP3 inflammasome. Fetuses of mothers fed a high fructose diet displayed increased hepatic fructose transporter and reduced fructokinase mRNA levels and by 10 days of postnatal age, also have hepatic ER stress, and elevated IL1β mRNA levels. At P10, FR neonates demonstrated increased hepatic triglyceride content and particularly in males, associated changes in the expression of genes regulating beta oxidation and the NLRP3 inflammasome. Further, prenatal fructose results in sex-dependant changes in levels of key clock genes.

Conclusions

Maternal fructose intake results in age and sex-specific alterations in maternal fetal and neonatal free fatty acid metabolism, which may be associated in disruptions in core clock gene machinery. How these changes are associated with hepatic inflammatory processes is still unclear, although suppression of the hepatic inflammasome, as least in mothers and male neonates may point to impaired immune sensing.  相似文献   
196.
The Adaptor Protein (AP)-3 complex is an evolutionary conserved, molecular sorting device that mediates the intracellular trafficking of proteins to lysosomes and related organelles. Genetic defects in AP-3 subunits lead to impaired biogenesis of lysosome-related organelles (LROs) such as mammalian melanosomes and insect eye pigment granules. In this work, we have performed a forward screening for genetic modifiers of AP-3 function in the fruit fly, Drosophila melanogaster. Specifically, we have tested collections of large multi-gene deletions–which together covered most of the autosomal chromosomes–to identify chromosomal regions that, when deleted in single copy, enhanced or ameliorated the eye pigmentation phenotype of two independent AP-3 subunit mutants. Fine-mapping led us to define two non-overlapping, relatively small critical regions within fly chromosome 3. The first critical region included the Atg2 gene, which encodes a conserved protein involved in autophagy. Loss of one functional copy of Atg2 ameliorated the pigmentation defects of mutants in AP-3 subunits as well as in two other genes previously implicated in LRO biogenesis, namely Blos1 and lightoid, and even increased the eye pigment content of wild-type flies. The second critical region included the ArfGAP1 gene, which encodes a conserved GTPase-activating protein with specificity towards GTPases of the Arf family. Loss of a single functional copy of the ArfGAP1 gene ameliorated the pigmentation phenotype of AP-3 mutants but did not to modify the eye pigmentation of wild-type flies or mutants in Blos1 or lightoid. Strikingly, loss of the second functional copy of the gene did not modify the phenotype of AP-3 mutants any further but elicited early lethality in males and abnormal eye morphology when combined with mutations in Blos1 and lightoid, respectively. These results provide genetic evidence for new functional links connecting the machinery for biogenesis of LROs with molecules implicated in autophagy and small GTPase regulation.  相似文献   
197.
198.
Multicellular eukaryotic organisms are attacked by numerous parasites from diverse phyla, often simultaneously or sequentially. An outstanding question in these interactions is how hosts integrate signals induced by the attack of different parasites. We used a model system comprised of the plant host Arabidopsis thaliana, the hemibiotrophic bacterial phytopathogen Pseudomonas syringae, and herbivorous larvae of the moth Trichoplusia ni (cabbage looper) to characterize mechanisms involved in systemic-induced susceptibility (SIS) to T. ni herbivory caused by prior infection by virulent P. syringae. We uncovered a complex multilayered induction mechanism for SIS to herbivory. In this mechanism, antiherbivore defenses that depend on signaling via (1) the jasmonic acid–isoleucine conjugate (JA-Ile) and (2) other octadecanoids are suppressed by microbe-associated molecular pattern–triggered salicylic acid (SA) signaling and infection-triggered ethylene signaling, respectively. SIS to herbivory is, in turn, counteracted by a combination of the bacterial JA-Ile mimic coronatine and type III virulence-associated effectors. Our results show that SIS to herbivory involves more than antagonistic signaling between SA and JA-Ile and provide insight into the unexpectedly complex mechanisms behind a seemingly simple trade-off in plant defense against multiple enemies.  相似文献   
199.
200.
Conservation Genetics - The Horvath’s rock lizard Iberolacerta horvathi (Méhely, 1904) is an understudied lacertid species, which is geographically isolated from its congeners and...  相似文献   
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