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   3698篇
  免费   311篇
  国内免费   2篇
  4011篇
  2024年   3篇
  2023年   16篇
  2022年   57篇
  2021年   89篇
  2020年   74篇
  2019年   84篇
  2018年   127篇
  2017年   110篇
  2016年   171篇
  2015年   226篇
  2014年   268篇
  2013年   311篇
  2012年   346篇
  2011年   327篇
  2010年   231篇
  2009年   192篇
  2008年   254篇
  2007年   220篇
  2006年   173篇
  2005年   181篇
  2004年   134篇
  2003年   100篇
  2002年   77篇
  2001年   46篇
  2000年   29篇
  1999年   26篇
  1998年   21篇
  1997年   16篇
  1996年   12篇
  1995年   10篇
  1994年   5篇
  1993年   8篇
  1992年   9篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   4篇
  1987年   7篇
  1986年   2篇
  1984年   5篇
  1983年   2篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1975年   3篇
  1974年   2篇
  1968年   3篇
  1965年   3篇
  1960年   2篇
  1959年   1篇
排序方式: 共有4011条查询结果,搜索用时 15 毫秒
11.
Venomous snakes have various types of phospholipase A(2) inhibitory proteins (PLIs) in their circulatory system to protect them from attack by their own phospholipase A(2)s (PLA(2)s). Here we show the first evidence for the existence of circulating PLI against secretory PLA(2)s (sPLA(2)s) in mammals. In mouse serum, we detected specific binding activities of group IB and X sPLA(2)s, which was in contrast with the absence of binding activities in serum prepared from mice deficient in PLA(2) receptor (PLA(2)R), a type I transmembrane glycoprotein related to the C-type animal lectin family. Western blot analysis after partial purification with group IB sPLA(2) affinity column confirmed the identity of serum sPLA(2)-binding protein as a soluble form of PLA(2)R (sPLA(2)R) that retained all of the extracellular domains of the membrane-bound receptor. Both purified sPLA(2)R and the recombinant soluble receptor having all of the extracellular portions blocked the biological functions of group X sPLA(2), including its potent enzymatic activity and its binding to the membrane-bound receptor. Protease inhibitor tests with PLA(2)R-overexpressing Chinese hamster ovary cells suggested that sPLA(2)R is produced by cleavage of the membrane-bound receptor by metalloproteinases. Thus, sPLA(2)R is the first example of circulating PLI that acts as an endogenous inhibitor for enzymatic activities and receptor-mediated functions of sPLA(2)s in mice.  相似文献   
12.
The complete genome sequence of human respiratory syncytial virus genotype A (HRSV-A) with a 72-nucleotide duplication in the C-terminal part of the attachment protein G gene was determined and analyzed. The genome was 15,277 bp in length, and 0.46 to 6.03% variations were identified at the nucleotide level compared with the previously reported complete genome of HRSV-A. Characterization of the genome will improve understanding of the diversity of the HRSV-A major antigens and enable an in-depth analysis of its genetics.  相似文献   
13.
Various physiological and psychological functions are influenced by circadian typology (CT), which was reported to be related to resilience. However, few studies have assessed the effects of CT in relation to resilience. The aim of the present study was to assess the influence of CT on sleep-related symptoms, physical fatigue and psychological well-being in relation to resilience. The present study included a total of 1794 healthy hospital employees, and they completed the Morningness–Eveningness Questionnaire, Connor–Davidson Resilience Scale, Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, Fatigue Severity Scale, Hospital Anxiety and Depression Scale and World Health Organization Quality of Life Scale Abbreviated Version. Subjects with evening type showed lower sleep quality, more daytime sleepiness and physical fatigue than neither types and morning types. Additionally, evening types were more depressed and anxious and reported a poorer quality of life. CT was found to be a significant predictor of sleep quality, but CT was minimally associated with physical fatigue and psychological well-being in the regression analysis. Instead, resilience was substantially related to all of the variables measured. In conclusion, CT independently predicts sleep quality, but the effects of CT on physical fatigue and psychological well-being are negligible compared to those of resilience.  相似文献   
14.
Lee KJ  Bae SM  Lee MR  Yeon SM  Lee YH  Kim KS 《Proteomics》2006,6(4):1274-1282
Streptococcus pneumoniae is an important human pathogen that causes a variety of diseases, such as pneumonia, bacteremia, meningitis, otitis media, and sinusitis, in both adults and children. The global pattern of growth phase-dependent protein expression of S. pneumoniae during in vitro culture was analyzed using 2-DE combined with MALDI-TOF MS and LC/ESI-MS/MS. Several protein production patterns were observed at four time points throughout the growth stage, although some protein levels did not change significantly. We focused on the switch in protein expression at the transition from log growth phase to stationary phase. Proteins that were significantly induced or repressed at this point are likely to be involved in central intermediary metabolism, amino acid synthesis, nucleotide, and fatty acid metabolism, cell wall synthesis, protein degradation, and stress responses. This global expression profiling approach has revealed previously unrecognized relationships between proteins in the life of this pathogen.  相似文献   
15.
The threat of a highly pathogenic avian influenza (HPAI) H5N1 virus causing the next pandemic remains a major concern. In this study, we evaluated the immunogenicity and efficacy of an inactivated whole-virus H5N1 pre-pandemic vaccine (MG1109) formulated by Green Cross Co., Ltd containing the hemagglutinin (HA) and neuraminidase (NA) genes of the clade 1 A/Vietnam/1194/04 virus in the backbone of A/Puerto Rico/8/34 (RgVietNam/04xPR8/34). Administration of the MG1109 vaccine (2-doses) in mice and ferrets elicited high HI and SN titers in a dose-dependent manner against the homologous (RgVietNam/04xPR8/34) and various heterologous H5N1 strains, (RgKor/W149/06xPR8/34, RgCambodia/04xPR8/34, RgGuangxi/05xPR8/34), including a heterosubtypic H5N2 (A/Aquatic bird/orea/W81/05) virus. However, efficient cross-reactivity was not observed against heterosubtypic H9N2 (A/Ck/Korea/H0802/08) and H1N1 (PR/8/34) viruses. Mice immunized with 1.9 μg HA/dose of MG1109 were completely protected from lethal challenge with heterologous wild-type HPAI H5N1 A/EM/Korea/W149/06 (clade 2.2) and mouse-adapted H5N2 viruses. Furthermore, ferrets administered at least 3.8 μg HA/dose efficiently suppressed virus growth in the upper respiratory tract and lungs. Vaccinated mice and ferrets also demonstrated attenuation of clinical disease signs and limited virus spread to other organs. Thus, this vaccine provided immunogenic responses in mouse and ferret models even against challenge with heterologous HPAI H5N1 and H5N2 viruses. Since the specific strain of HPAI H5N1 virus that would potentially cause the next outbreak is unknown, pre-pandemic vaccine preparation that could provide cross-protection against various H5 strains could be a useful approach in the selection of promising candidate vaccines in the future.  相似文献   
16.
Hong MY  Lee EM  Jo YH  Park HC  Kim SR  Hwang JS  Jin BR  Kang PD  Kim KG  Han YS  Kim I 《Gene》2008,413(1-2):49-57
The 15,360-bp long complete mitogenome of Caligula boisduvalii possesses a gene arrangement and content identical to other completely sequenced lepidopteran mitogenomes, but different from the common arrangement found in most insect order, as the result of the movement of tRNA(Met) to a position 5'-upstream of tRNA Ile. The 330-bp A+T-rich region is apparently capable of forming a stem-and-loop structure, which harbors the conserved flanking sequences at both ends. Dissimilar to what has been seen in other sequenced lepidopteran insects, the initiation codon for C. boisduvalii COI appears to be TTG, which is a rare, but apparently possible initiation codon. The ATP8, ATP6, ND4L, and ND6 genes, which neighbor another PCG at their 3' end, all harbored potential sequences for the formation of a hairpin structure. This is suggestive of the importance of such structures for the precise cleavage of the mRNA of mature PCGs. Phylogenetic analyses of available sequenced species of Bombycoidea, Pyraloidea, and Tortricidea supported the morphology-based current hypothesis that Bombycoidea and Pyraloidea are monophyletic (Obtectomera). As previously suggested, Bombycidae (Bombyx mori and B. mandarina) and Saturniidae (Antheraea pernyi and C. boisduvalii) formed a reciprocal monophyletic group.  相似文献   
17.

Background and Methods

In this study, we utilized a combination of low oxygen tension and a novel anti-oxidant, 4-(3,4-dihydroxy-phenyl)-derivative (DHP-d) to directly induce adipose tissue stromal cells (ATSC) to de-differentiate into more primitive stem cells. De-differentiated ATSCs was overexpress stemness genes, Rex-1, Oct-4, Sox-2, and Nanog. Additionally, demethylation of the regulatory regions of Rex-1, stemnesses, and HIF1α and scavenging of reactive oxygen species were finally resulted in an improved stem cell behavior of de-differentiate ATSC (de-ATSC). Proliferation activity of ATSCs after dedifferentiation was induced by REX1, Oct4, and JAK/STAT3 directly or indirectly. De-ATSCs showed increased migration activity that mediated by P38/JUNK and ERK phosphorylation. Moreover, regenerative efficacy of de-ATSC engrafted spinal cord-injured rats and chemical-induced diabetes animals were significantly restored their functions.

Conclusions/Significance

Our stem cell remodeling system may provide a good model which would provide insight into the molecular mechanisms underlying ATSC proliferation and transdifferentiation. Also, these multipotent stem cells can be harvested may provide us with a valuable reservoir of primitive and autologous stem cells for use in a broad spectrum of regenerative cell-based disease therapy.  相似文献   
18.
Hyaluronic acid (HA) hydrogel beads were prepared by photopolymerization of methacrylated HA and N-vinylpyrrolidone using alginate as a temporal spherical mold. Various fabrication conditions for preparing the hydrogel beads, such as the concentration of methacrylated HA and UV irradiation time, were optimized to control swelling properties and enzymatic degradability. A new concept for cell encapsulation is proposed in this paper. Viable cells were directly injected into the hydrogel beads using a microinjection technique. When bovine articular chondrocytes were injected into HA hydrogel beads and cultivated for 1 week, the cells could proliferate well within the HA beads. HA hydrogel beads could be potentially used as injectable cell delivery vehicles for regenerating tissue defects.  相似文献   
19.
The present study explores the dietary effect of pectin on the MLN lymphocyte functions of mice with dextran sulfate sodium (DS)-induced colitis. We found that the immunoglobulin (Ig)A level in mesenteric lymph node (MLN) lymphocytes was high, while the IgE level was lower, in mice fed with pectin than in those fed with cellulose. Interestingly, the fecal IgA concentration of the pectin-fed mice was significantly higher than that of the cellulose-fed mice. The concentrations of interferon-gamma and interleukin (IL)-2 treated with concanavalin A (ConA) were significantly higher in the pectin-fed group than in the cellulose-fed group. Although dietary pectin did not affect the IL-4 and IL-10 levels, the activation-induced IL-4 and IL-10 secretion was lower in MLN cells of the pectin-fed mice than of the cellulose-fed mice following DS-induced colitis. Based on these findings, we propose that the effect of dietary pectin on mice with DS-induced colitis is mediated by the manipulation of Th1 cells. Furthermore, the inhibitory effect of IL-4 and IL-10 by dietary pectin may play an important role in promoting a change in Th1/Th2 balance toward Th1-dominant immunity.  相似文献   
20.
The artificial gene coding for anticoagulant hirudin was placed under the control of theGAL10 promoter and expressed in the galactokinase-deficient strain (Δgal1) ofSaccharomyces cereivisiae, which uses galactose only as a gratuitous inducer in order to avoid its consumption. For efficient production of recombinant hirudin, a carbon source other than galactose should be provided in the medium to support growth of the Δgal1 strain. Here we demonstrate the successful use of glucose in the fed-batch fermentation of the Δgal1 strain to achieve efficient production of recombinant hirudin, with a yield of up to 400 mg hirudin/L.  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