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   2728篇
  免费   382篇
  3110篇
  2021年   27篇
  2019年   42篇
  2018年   27篇
  2016年   40篇
  2015年   89篇
  2014年   74篇
  2013年   138篇
  2012年   129篇
  2011年   116篇
  2010年   82篇
  2009年   83篇
  2008年   114篇
  2007年   100篇
  2006年   120篇
  2005年   98篇
  2004年   88篇
  2003年   107篇
  2002年   91篇
  2001年   67篇
  2000年   62篇
  1999年   70篇
  1998年   41篇
  1997年   33篇
  1996年   34篇
  1995年   31篇
  1994年   27篇
  1993年   32篇
  1992年   48篇
  1991年   41篇
  1990年   48篇
  1989年   43篇
  1988年   39篇
  1987年   48篇
  1986年   38篇
  1985年   38篇
  1984年   44篇
  1983年   33篇
  1981年   26篇
  1980年   39篇
  1979年   38篇
  1978年   34篇
  1977年   25篇
  1976年   32篇
  1975年   27篇
  1974年   29篇
  1973年   27篇
  1972年   31篇
  1971年   27篇
  1970年   24篇
  1968年   32篇
排序方式: 共有3110条查询结果,搜索用时 0 毫秒
41.
Previous studies with transfected cells have shown that the herpes simplex virus type 1 (HSV-1) and bovine herpesvirus 1 (BHV-1) UL47 proteins shuttle between the nucleus and the cytoplasm. HSV-1 UL47 has also been shown to bind RNA. Here we examine the BHV-1 UL47 protein in infected cells using a green fluorescent protein-UL47-expressing virus. We show that UL47 is detected in the nucleus early in infection. We use fluorescence loss in photobleaching to show that nuclear UL47 undergoes rapid nucleocytoplasmic shuttling. Furthermore, we demonstrate that actinomycin D inhibits the reaccumulation of UL47 in the nuclei of infected cells. These results suggest that UL47 exhibits behavior similar to that of previously characterized RNA-transporting proteins.  相似文献   
42.
43.

Background

Although 5-HTTLPR has been shown to influence the risk of life stress-induced depression in the majority of studies, others have produced contradictory results, possibly due to weak effects and/or sample heterogeneity.

Methods

In the present study we investigated how age, type and intensity of life-stressors modulate the effect of 5-HTTLPR on depression and anxiety in a European population cohort of over 2300 subjects. Recent negative life events (RLE), childhood adversity (CHA), lifetime depression, Brief Symptoms Inventory (BSI) depression and anxiety scores were determined in each subject. Besides traditional statistical analysis we calculated Bayesian effect strength and relevance of 5-HTTLPR genotypes in specified models.

Results

The short (s) low expressing allele showed association with increased risk of depression related phenotypes, but all nominally significant effects would turn to non-significant after correction for multiple testing in the traditional analysis. Bayesian effect strength and relevance analysis, however, confirmed the role of 5-HTTLPR. Regarding current (BSI) and lifetime depression 5-HTTLPR-by-RLE interactions were confirmed. Main effect, with other words direct association, was supported with BSI anxiety. With more frequent RLE the prevalence or symptoms of depression increased in ss carriers. Although CHA failed to show an interaction with 5-HTTLPR, in young subjects CHA sensitized towards the depression promoting effect of even mild RLE. Furthermore, the direct association of anxiety with the s allele was driven by young (≤30) individuals.

Limitations

Our study is cross-sectional and applies self-report questionnaires.

Conclusions

Albeit 5-HTTLPR has only weak/moderate effects, the s allele is directly associated with anxiety and modulates development of depression in homogeneous subgroups.  相似文献   
44.
North American women have a one in eight lifetime risk of developing breast cancer, and approximately one in three women with breast cancer will die of metastases. We, and others, have recently shown that high levels of expression of hepatocyte growth factor (HGF) and its receptor Met are associated with invasive human breast cancer and may be causally linked to metastasis. This high level of HGF and Met expression has been considered as a possible indicator of earlier recurrence and shortened survival in breast cancer patients. In contrast, HGF expression (but not Met) is strongly suppressed in normal breast epithelial cells. HGF and Met are therefore candidate targets for therapeutic intervention in the treatment of breast cancer. We have recently demonstrated that sustained activation or hyper-activation of c-Src and Stat3, which occurs in invasive breast cancer, can stimulate strong expression of HGF in carcinoma cells. In contrast, transient induction of Stat3 occurs in normal epithelium and promotes mammary tubulogenesis. We hypothesize that increased autocrine HGF-Met signaling is a critical downstream function of c-Src-Stat3 activation in mammary tumorigenesis. Future studies will identify novel Stat3 consensus sites that regulate HGF promoter activity and HGF expression preferentially in carcinoma cells and could lead to novel therapeutic drugs that specifically block HGF expression in mammary carcinoma cells, and which could be used in combined treatments to abrogate metastasis.  相似文献   
45.
Kallikrein gene families have been identified previously in genomes of the human, the mouse, and the rat, and individual kallikrein-like genes have been found in many more species. This study presents the in silico identification of kallikrein gene families in the recently sequenced genomes of four additional mammalian species, the chimpanzee, the dog, the pig, and the opossum. Phylogenies were constructed with gene sequences from all seven mammalian families, using Bayesian analysis, which clarified the evolutionary relationships between these genes. Individual gene sequences, as well as concatenated constructs of multiple sequences, were used. Fifteen kallikrein genes were located in the chimpanzee (Pan troglodytes) genome, while only 14 were identified in the canine (Canis familiaris) genome as no orthologue to human KLK3 was found. Thirteen genes were identified from the pig (Sus scrofa) genome, which lacked homologues to KLK2 and KLK3, and 11 genes, orthologous to human KLK5 through KLK15, were found in the opossum (Monodelphis domestica) genome. No kallikrein genes were identified from the available genome sequences of the chicken (Gallus gallus) or African clawed frog (Xenopus tropicalis). Within the family of kallikreins several subfamilies were suggested by phylogenetic analysis. One consisted of KLK4, KLK5, and KLK14; another of KLK9, KLK11, and KLK15; a third of KLK10 and KLK12; a fourth of KLK6 and KLK13; and finally one of KLK8 and the classical kallikreins (KLK1, KLK2, and KLK3).  相似文献   
46.
Domesticated lettuce varieties encompass much morphological variation across a range of crop type groups, with large collections of cultivars and landrace accessions maintained in genebanks. Additional variation not captured during domestication, present in ancestral wild relatives, represents a potentially rich source of alleles that can deliver to sustainable crop production. However, these large collections are difficult and costly to screen for many agronomically important traits. In this paper, we describe the generation of a diversity collection of 96 lettuce and wild species accessions that are amenable to routine phenotypic analysis and their genotypic characterization with a panel of 682 newly developed expressed sequence tag (EST)-linked KASP? single nucleotide polymorphism (SNP) markers that are anchored to the draft Lactuca sativa genome assembly. To exemplify the utility of these resources, we screened the collection for putative sources of resistance to currant-lettuce aphid (Nasonovia ribisnigri) and carried out association analyses to look for potential SNPs linked to resistance.  相似文献   
47.
Plant and Soil - Understanding limitations to plant recruitment is a key element in devising effective restoration of semi-arid ecosystems: only when these limitations are identified can management...  相似文献   
48.
In neonatal and young adult SH and WK rats, maturation of a functional unit consisting of sympathetic nerve terminals and smooth muscle (levator palpebrae) was assessed in vivo by measuring the contractile response to tyramine, an agent which releases endogenous norepinephrine from sympathetic nerve terminals. Responses in SH are comparable to WK at 5–6 days postnatally, smaller from the 8th through 19th day and larger in young adults (41–46 days old). Results indicate that functional maturation of the nerve terminal-smooth muscle complex is retarded in SH relative to WK during the 2nd and 3rd postnatal weeks. It is suggested that retardation in the neonatal SH rat is an expression of a genetic defect in the growth of the complex and that the enhanced response in young adult SH is a consequence of the neonatal abnormality.  相似文献   
49.
Typically, studies on indoor fungal growth in buildings focus on structures with known or suspected water damage, moisture, and/or indoor fungal growth problems. Reference information on types of culturable fungi and total fungal levels are generally not available for buildings without these problems. This study assessed 50 detached single-family homes in metropolitan Atlanta, Ga., to establish a baseline of “normal and typical” types and concentrations of airborne and dustborne fungi in urban homes which were predetermined not to have noteworthy moisture problems or indoor fungal growth. Each home was visually examined, and samples of indoor and outdoor air and of indoor settled dust were taken in winter and summer. The results showed that rankings by prevalence and abundance of the types of airborne and dustborne fungi did not differ from winter to summer, nor did these rankings differ when air samples taken indoors were compared with those taken outdoors. Water indicator fungi were essentially absent from both air and dust samples. The air and dust data sets were also examined specifically for the proportions of colonies from ecological groupings such as leaf surface fungi and soil fungi. In the analysis of dust for culturable fungal colonies, leaf surface fungi constituted a considerable portion (>20%) of the total colonies in at least 85% of the samples. Thus, replicate dust samples with less than 20% of colonies from leaf surface fungi are unlikely to be from buildings free of moisture or mold growth problems.  相似文献   
50.
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