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   1766篇
  免费   88篇
  国内免费   2篇
  2023年   3篇
  2022年   7篇
  2021年   9篇
  2020年   9篇
  2019年   19篇
  2018年   21篇
  2017年   17篇
  2016年   49篇
  2015年   47篇
  2014年   81篇
  2013年   138篇
  2012年   110篇
  2011年   141篇
  2010年   81篇
  2009年   62篇
  2008年   94篇
  2007年   88篇
  2006年   114篇
  2005年   123篇
  2004年   113篇
  2003年   114篇
  2002年   110篇
  2001年   13篇
  2000年   13篇
  1999年   12篇
  1998年   33篇
  1997年   26篇
  1996年   18篇
  1995年   21篇
  1994年   24篇
  1993年   6篇
  1992年   17篇
  1991年   9篇
  1990年   11篇
  1989年   12篇
  1988年   11篇
  1987年   9篇
  1986年   16篇
  1985年   6篇
  1984年   4篇
  1983年   10篇
  1982年   13篇
  1981年   6篇
  1980年   4篇
  1979年   2篇
  1976年   2篇
  1975年   1篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
排序方式: 共有1856条查询结果,搜索用时 78 毫秒
101.
Since it is known that androstenediol (ADIOL) has potent immunoregulatory effects, changes in ADIOL levels during and after pregnancy might affect the maternal immune system. We examined serum concentrations of ADIOL and androstenediol 3-sulfate (ADIOLS) together with IFN-gamma and IL-4 production levels during pregnancy and after delivery up to 10-11 months postpartum. The subjects were 73 normal pregnant, 76 normal postpartum, and 28 normal non-pregnant women. ADIOL and ADIOLS were measured using EIA and GC/MS, respectively. The cytokine levels in the supernatant of whole-blood cultures stimulated with phorbol 12-myristate 13-acetate and ionomycin were measured using ELISA. ADIOL levels significantly decreased compared to non-pregnant levels in the first trimester (P < 0.05) and were reversed in the third trimester (P < 0.05). After pregnancy, ADIOL levels gradually declined, and a significant decrease was observed at 10-11 months postpartum (P < 0.05). ADIOLS levels were significantly lower in the third trimester (P < 0.05) and significantly higher at the first month postpartum (P < 0.001) compared to non-pregnant women. IFN-gamma and IL-4 levels decreased during pregnancy and subsequently increased postpartum. On the other hand, we found significant negative correlations between ADIOL concentrations and production levels of IFN-gamma (P < 0.05) or IL-4 (P < 0.05). These findings suggest that ADIOL may be involved in modifying the maternal immune response during and after pregnancy.  相似文献   
102.
103.
104.
Minamoto N 《Uirusu》2004,54(2):213-222
Since rabies has not been reported in Japan for nearly the past 50 years, it has been relegated to the status of a forgotten infectious disease in this country. However,in the neighboring Asian countries, Africa, America, the number fo rabies cases had not decrease but on the contrary, seen an increasing trend. In Russia and the former Soviet Union countries (CIS countries), the number of information. Between 30,000 approximately 20,000 fatal cases of rabies in both humans and animals had been reported yearly butit was thought that the number might run up to hundred of thousands.japan, Taiwan, UK, Australia and New Zealand are rabies-free countries and should be considered the exception rather than the norm. Due to the long Lull in which rabies has not occurred in Japan,people tend to forget that the disease can infect all mammals including humans, with a mortality rate of 100% after manifestation of debilitating nervous symptoms and that is one of the most dangerous zoonotic viral diseases on earth.  相似文献   
105.
Previously, we introduced the RPLKPW sequence, a highly potent hypotensive peptide designed based on ovokinin (2-7), into three homologous sites in the soybean beta-conglycinin alpha' subunit by site-directed mutagenesis. The modified protein expressed in Escherichia coli reduced blood pressure of spontaneously hypertensive rats (SHRs) after oral administration at a dose of 10 mg/kg, which suggested about 30% of the introduced peptide was released in vivo. In this study amino acid residues around the RPLKPW sequence were optimized with a use of synthetic peptides to facilitate release of RPLKPW by gastrointestinal proteases. Then, fourth RPLKPW was also introduced into the extension domain of the protein. The newly modified protein, which was produced in E. coli, significantly lowered blood pressure in SHRs at a dose of 2.5 mg/kg 4 h after oral administration. Furthermore, we produced an extension domain that corresponds to residues 1-143 of the modified alpha' subunit containing four RPLKPW sequences by introducing a termination codon. The minimum effective dose of the modified extension domain was 1.0 mg/kg, which is 1/2000 that of ovalbumin.  相似文献   
106.
Novel nonsteroidal C(17,20)-lyase inhibitors were synthesized using de novo design based on its substrate, 17 alpha-hydroxypregnenolone, and several compounds exhibited potent C(17,20)-lyase inhibition. However, in vivo activities were found to be short-lasting, and in order to improve the duration of action, a series of benzothiophene derivatives were evaluated. As a result, compounds 9h, (S)-9i, and 9k with nanomolar enzyme inhibition (IC(50)=4-9 nM) and 9e (IC(50)=27 nM) were identified to have powerful in vivo efficacy with extended duration of action. The key structural determinants for the in vivo efficacy were demonstrated to be the 5-fluoro group on the benzothiophene ring and the 4-imidazolyl moiety. Superimposition of 9k and 17 alpha-hydroxypregnenolone demonstrated their structural similarity and enabled rationalization of the pharmacological results. In addition, selected compounds were also identified to be potent inhibitors of human enzyme with IC(50) values of 20-30 nM.  相似文献   
107.
An efficient asymmetric synthesis of the chiral N-(3-chloro-2-hydroxypropyl)anilines (2a and 2b) was achieved through the regioselective ring-opening reaction of chiral epichlorohydrin with aniline. This was applied to an asymmetric synthesis of the enantiomers of 1-[4,4-bis(4-fluorophenyl)butyl]-4-[2-hydroxy-3-(phenylamino)propyl]piperazine 1 as a novel potent dopamine uptake inhibitor. Both enantiomers as trihydrochlorides, 4a.3HCl and 4b.3HCl, could be synthesized in good total yields and optical purities of 100% ee in three steps synthesis, respectively. The absolute configurations of 4a.3HCl and 4b.3HCl were determined using the modified Mosher's method with the related compounds, the intermediates (2a and 2b) and the free bases (4a and 4b). The analytical results indicated that 4a.3HCl and 4b.3HCl have the (S)- and (R)-configuration, respectively, and a series of reactions to provide them proceeded without the apparent influence on the stereochemistry at the chiral centers. In in vitro pharmacological evaluations, 4a.3HCl and 4b.3HCl showed potent dopamine transporter binding affinities, high dopamine, moderate serotonin, and weak norepinephrine uptake inhibitory activities, and 4a.3HCl exhibited a more potent and selective dopamine uptake inhibition over the serotonin or norepinephrine uptake inhibition as compared with 4b.3HCl. An ex vivo evaluation revealed that the oral administrations of both enantiomers at a dose of 30 mg/kg in rats displayed apparent dopamine uptake inhibitory activities and 4a.3HCl had a stronger tendency to inhibit dopamine uptake compared with 4b.3HCl.  相似文献   
108.
Abstract To investigate the phylogenetic relationships and molecular evolution of α-amylase (Amy) genes in the Drosophila montium species subgroup, we constructed the phylogenetic tree of the Amy genes from 40 species from the montium subgroup. On our tree the sequences of the auraria, kikkawai, and jambulina complexes formed distinct tight clusters. However, there were a few inconsistencies between the clustering pattern of the sequences and taxonomic classification in the kikkawai and jambulina complexes. Sequences of species from other complexes (bocqueti, bakoue, nikananu, and serrata) often did not cluster with their respective taxonomic groups. This suggests that relationships among the Amy genes may be different from those among species due to their particular evolution. Alternatively, the current taxonomy of the investigated species is unreliable. Two types of divergent paralogous Amy genes, the so-called Amy1- and Amy3-type genes, previously identified in the D. kikkawai complex, were common in the montium subgroup, suggesting that the duplication event from which these genes originate is as ancient as the subgroup or it could even predate its differentiation. Thc Amy1-type genes were closer to the Amy genes of D. melanogaster and D. pseudoobscura than to the Amy3-type genes. In the Amy1-type genes, the loss of the ancestral intron occurred independently in the auraria complex and in several Afrotropical species. The GC content at synonymous third codon positions (GC3s) of the Amy1-type genes was higher than that of the Amy3-type genes. Furthermore, the Amy1-type genes had more biased codon usage than the Amy3-type genes. The correlations between GC3s and GC content in the introns (GCi) differed between these two Amy-type genes. These findings suggest that the evolutionary forces that have affected silent sites of the two Amy-type genes in the montium species subgroup may differ.  相似文献   
109.
In order to investigate any effect of truncated mutant huntingtin (tNhtt) aggregation on protein kinase C (PKC) signaling in Huntington's disease (HD), we studied a possible association of PKC isoforms with the aggregates using cellular and transgenic models of HD. In this report we describe an association of mutant tNhtt with at least three PKC isoforms (alpha, delta, zeta), as revealed by co-immunoprecipitation assays and immunocytochemistry in a cellular model of HD (Neuro2a cells expressing tNhtt-150Q-EGFP), as well as a specific association of PKC delta with intranuclear aggregates in a transgenic model (R6/2 mice). Immunoblot analysis of isolated nuclear fractions shows an elevation of nuclear PKC delta in transgenic brain tissue. The observed elevation has a strong similarity with the apoptotic translocation of PKC delta detected in experiments with the mouse neuroblastoma Neuro2a cells. Using a Neuro2a cell line expressing tNhtt with the nuclear localization signal, we demonstrate the association of PKC delta with intranuclear aggregates and present evidence that accumulation of PKC delta in cell nuclei does not depend on mutant htt nuclear translocation. Our results suggest that the association of PKC delta with intranuclear htt-aggregates may affect its apoptotic function in a transgenic model of HD.  相似文献   
110.
Sclerosteosis is a progressive sclerosing bone dysplasia. Sclerostin (the SOST gene) was originally identified as the sclerosteosis-causing gene. However, the physiological role of sclerostin remains to be elucidated. Sclerostin was intensely expressed in developing bones of mouse embryos. Punctuated expression of sclerostin was localized on the surfaces of both intramembranously forming skull bones and endochondrally forming long bones. Sclerostin-positive cells were identified as osteoclasts. Recombinant sclerostin protein produced in cultured cells was efficiently secreted as a monomer. We examined effects of sclerostin on the activity of BMP2, BMP4, BMP6, and BMP7 for mouse preosteoblastic MC3T3-E1 cells. Sclerostin inhibited the BMP6 and BMP7 activity but not the BMP2 and BMP4 activity. Sclerostin bound to BMP6 and BMP7 with high affinity but bound to BMP2 and BMP4 with lower affinity. In conclusion, sclerostin is a novel secreted osteoclast-derived BMP antagonist with unique ligand specificity. We suggest that sclerostin negatively regulates the formation of bone by repressing the differentiation and/or function of osteoblasts induced by BMPs. Since sclerostin expression is confined to the bone-resorbing osteoclast, it provides a mechanism whereby bone apposition is inhibited in the vicinity of resorption. Our findings indicate that sclerostin plays an important role in bone remodeling and links bone resorption and bone apposition.  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