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   9349篇
  免费   760篇
  国内免费   673篇
  10782篇
  2024年   28篇
  2023年   126篇
  2022年   286篇
  2021年   494篇
  2020年   336篇
  2019年   386篇
  2018年   428篇
  2017年   273篇
  2016年   399篇
  2015年   587篇
  2014年   659篇
  2013年   654篇
  2012年   847篇
  2011年   781篇
  2010年   437篇
  2009年   383篇
  2008年   465篇
  2007年   372篇
  2006年   349篇
  2005年   298篇
  2004年   236篇
  2003年   181篇
  2002年   175篇
  2001年   179篇
  2000年   154篇
  1999年   168篇
  1998年   78篇
  1997年   83篇
  1996年   73篇
  1995年   89篇
  1994年   86篇
  1993年   58篇
  1992年   87篇
  1991年   77篇
  1990年   68篇
  1989年   44篇
  1988年   55篇
  1987年   36篇
  1986年   42篇
  1985年   53篇
  1984年   26篇
  1983年   17篇
  1982年   21篇
  1981年   11篇
  1979年   11篇
  1978年   14篇
  1977年   10篇
  1974年   11篇
  1969年   5篇
  1968年   8篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Alien species are brought into countries world wide on a massive scale for agricultural production, ex situ conservation, landscape aesthetics, gardens, and ecosystem restoration. Unfortunately, some of these species have escaped and adversely impacted on regional as well as global biodiversity conservation and agricultural production. To reduce such risks, it is necessary to implement specific and effective measures. Since various government departments and institutions are involved in the management of alien species, it is difficult to prevent native and agroecosystems from being invaded by invited species. We propose the establishment of a supervision and inspection continuum over intentional species introduction, similar to that which exists in some countries over unintentional species introductions. Namely, a justification of the necessity to import, a risk assessment, assurances as to provision of an adequate containment facility assessment, and a damage-limitation protocol should that need to be invoked. These requirements should be satisfied before an alien species is knowingly imported, and the necessary follow-up supervision is important post- importation.  相似文献   
32.
本文通过从污水处理厂活性污泥中分离得到一株高效降解轻油(煤油)细菌5092-2,通过形态学、16S rRNA鉴定该菌为Mangroveibacter sp.。进一步对其生长条件进行了研究,发现该菌在23℃到38℃、pH为5.0到9.0范围内生长无明显差异。在温度为35℃,pH 7.2~7.4,160 r/min培养7 d,菌株降解煤油的能力达到52.3%,具有进一步研究的价值。  相似文献   
33.
In this study, we characterized the intratumoral expression of IL-17 and CD8(+) TILs in gastric adenocarcinoma patients after resection and determined the correlation between the survival probability of gastric adenocarcinoma patients and the expression of IL-17 in tumor. Expression of IL-17 and CD8 was assessed by immunohistochemistry, and the prognostic effects of intratumoral IL-17 expression and CD8(+) TILs were evaluated by Cox regression and Kaplan-Meier analysis. Immunohistochemical detection revealed the presence of IL-17 and CD8(+) cells in gastric adenocarcinoma tissue samples (90.6%, 174 out of 192 patients and 96.9%, 186 out of 192 patients, respectively). We have also found that intratumoral IL-17 expression was significantly correlated with age (p=0.004) and that the number of CD8(+)TILs was significantly correlated with UICC staging (p=0.012) and the depth of tumor invasion (p=0.022). The five-year overall survival probability among patients intratumorally expressing higher levels of IL-17 was significantly better than those expressing lower levels of IL-17 (p=0.036). Multivariate Cox proportional hazard analyses revealed that intratumoral IL-17 expression (HR: 0.521; 95% CI: 0.329-0.823; p=0.005) was an independent factor affecting the five-year overall survival probability. We conclude that low levels of intratumoral IL-17 expression may indicate poor prognosis in gastric adenocarcinoma patients.  相似文献   
34.
35.
Zeng L  Wang Y  Baba O  Zheng P  Liu Y  Liu Y 《The FEBS journal》2012,279(14):2467-2478
Mutations in either EPM2A, the gene encoding a dual-specificity phosphatase named laforin, or NHLRC1, the gene encoding an E3 ubiquitin ligase named malin, cause Lafora disease in humans. Lafora disease is a fatal neurological disorder characterized by progressive myoclonus epilepsy, severe neurological deterioration and accumulation of poorly branched glycogen inclusions, called Lafora bodies or polyglucosan bodies, within the cell cytoplasm. The molecular mechanism underlying the neuropathogenesis of Lafora disease remains unknown. Here, we present data demonstrating that in the cells expressing low levels of laforin protein, overexpressed malin and its Lafora disease-causing missense mutants are stably polyubiquitinated. Malin and malin mutants form ubiquitin-positive aggregates in or around the nuclei of the cells in which they are expressed. Neither wild-type malin nor its mutants elicit endoplasmic reticulum stress, although the mutants exaggerate the response to endoplasmic reticulum stress. Overexpressed laforin impairs the polyubiquitination of malin while it recruits malin to polyglucosan bodies. The recruitment and activities of laforin and malin are both required for the polyglucosan body disruption. Consistently, targeted deletion of laforin in brain cells from Epm2a knockout mice increases polyubiquitinated proteins. Knockdown of Epm2a or Nhlrc1 in neuronal Neuro2a cells shows that they cooperate to allow cells to resist ER stress and apoptosis. These results reveal that a functional laforin-malin complex plays a critical role in disrupting Lafora bodies and relieving ER stress, implying that a causative pathogenic mechanism underlies their deficiency in Lafora disease.  相似文献   
36.
The localization of beta-actin mRNA to the leading lamellae of chicken fibroblasts and neurite growth cones of developing neurons requires a 54-nt localization signal (the zipcode) within the 3' untranslated region. In this study we have identified and isolated five proteins binding to the zipcode. One of these we previously identified as zipcode binding protein (ZBP)1, a 4-KH domain protein. A second is now investigated in detail: a 92-kD protein, ZBP2, that is especially abundant in extracts from embryonic brain. We show that ZBP2 is a homologue of the human hnRNP protein, KSRP, that appears to mediate pre-mRNA splicing. However, ZBP2 has a 47-amino acid (aa) sequence not present in KSRP. Various portions of ZBP2 fused to GFP indicate that the protein most likely shuttles between the nucleus and the cytoplasm, and that the 47-aa insert promotes the nuclear localization. Expression of a truncated ZBP2 inhibits the localization of beta-actin mRNA in both fibroblast and neurons. These data suggest that ZBP2, although predominantly a nuclear protein, has a role in the cytoplasmic localization of beta-actin mRNA.  相似文献   
37.
To achieve long-term increases in soil organic carbon (SOC) storage, it is essential to understand the effects of carbon management strategies on SOC formation pathways, particularly through changes in microbial necromass carbon (MNC) and dissolved organic carbon (DOC). Using a 14-year field study, we demonstrate that both biochar and maize straw lifted the SOC ceiling, but through different pathways. Biochar, while raising SOC and DOC content, decreased substrate degradability by increasing carbon aromaticity. This resulted in suppressed microbial abundance and enzyme activity, which lowered soil respiration, weakened in vivo turnover and ex vivo modification for MNC production (i.e., low microbial carbon pump “efficacy”), and led to lower efficiency in decomposing MNC, ultimately resulting in the net accumulation of SOC and MNC. In contrast, straw incorporation increased the content and decreased the aromaticity of SOC and DOC. The enhanced SOC degradability and soil nutrient content, such as total nitrogen and total phosphorous, stimulated the microbial population and activity, thereby boosting soil respiration and enhancing microbial carbon pump “efficacy” for MNC production. The total C added to biochar and straw plots were estimated as 27.3–54.5 and 41.4 Mg C ha−1, respectively. Our results demonstrated that biochar was more efficient in lifting the SOC stock via exogenous stable carbon input and MNC stabilization, although the latter showed low “efficacy”. Meanwhile, straw incorporation significantly promoted net MNC accumulation but also stimulated SOC mineralization, resulting in a smaller increase in SOC content (by 50%) compared to biochar (by 53%–102%). The results address the decadal-scale effects of biochar and straw application on the formation of the stable organic carbon pool in soil, and understanding the causal mechanisms can allow field practices to maximize SOC content.  相似文献   
38.
Biomarkers of neurodegenerative disorders: How good are they?   总被引:11,自引:0,他引:11  
Rachakonda V  Pan TH  LE WD 《Cell research》2004,14(5):347-358
Biomarkers are very important indicators of normal and abnormal biological processes. Specific changes in pathologies,biochemistries and genetics can give us comprehensive information regarding the nature of any particular disease. A good biomarker should be precise and reliable, distinguishable between normal and interested disease, and differentiable between different diseases. It is believed that biomarkers have great potential in predicting chances for diseases, aiding in early diagnosis, and setting standards for the development of new remedies to treat diseases. New technologies have enabled scientists to identify biomarkers of several different neurodegenerative diseases. The followings, for instance,are only a few of the many new biomarkers that have been recently identified: the phosphorylated tau protein and aggregated β-amyloid peptide for Alzheimer‘s disease (AD), α-synuclein contained Lewy bodies and altered dopamine transporter (DAT) imaging for Parkinson‘s disease (PD), SOD mutations for familial amyotrophic lateral sclerosis (ALS), and CAG repeats resulted from Huntington‘s gene mutations in Huntington‘s disease (HD). This article will focus on the most-recent findings of biomarkers belonging to the four mentioned neurodegenerative diseases.  相似文献   
39.
To determine whether genetic heterogeneity exists in patients with Graves'' disease (GD), the cytotoxic T-lymphocyte associated 4 (CTLA-4) gene, which is implicated a susceptibility gene for GD by considerable genetic and immunological evidence, was used for association analysis in a Chinese Han cohort recruited from various geographic regions. Our association study for the SNPs in the CTLA4 gene in 2640 GD patients and 2204 control subjects confirmed that CTLA4 is the susceptibility gene for GD in the Chinese Han population. Moreover, the logistic regression analysis in the combined Chinese Han cohort revealed that SNP rs231779 (allele frequencies p = 2.81×10−9, OR = 1.35, and genotype distributions p = 2.75×10−9, OR = 1.42) is likely the susceptibility variant for GD. Interestingly, the logistic regression analysis revealed that SNP rs35219727 may be the susceptibility variant to GD in the Shandong population; however, SNP, rs231779 in the CTLA4 gene probably independently confers GD susceptibility in the Xuzhou and southern China populations. These data suggest that the susceptibility variants of the CTLA4 gene varied between the different geographic populations with GD.  相似文献   
40.
Chimonanthus salicifolius, a member of the Calycanthaceae of magnoliids, is one of the most famous medicinal plants in Eastern China. Here, we report a chromosome‐level genome assembly of Csalicifolius, comprising 820.1 Mb of genomic sequence with a contig N50 of 2.3 Mb and containing 36 651 annotated protein‐coding genes. Phylogenetic analyses revealed that magnoliids were sister to the eudicots. Two rounds of ancient whole‐genome duplication were inferred in the Csalicifolious genome. One is shared by Calycanthaceae after its divergence with Lauraceae, and the other is in the ancestry of Magnoliales and Laurales. Notably, long genes with > 20 kb in length were much more prevalent in the magnoliid genomes compared with other angiosperms, which could be caused by the length expansion of introns inserted by transposon elements. Homologous genes within the flavonoid pathway for Csalicifolius were identified, and correlation of the gene expression and the contents of flavonoid metabolites revealed potential critical genes involved in flavonoids biosynthesis. This study not only provides an additional whole‐genome sequence from the magnoliids, but also opens the door to functional genomic research and molecular breeding of Csalicifolius.  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