全文获取类型
收费全文 | 1348篇 |
免费 | 131篇 |
国内免费 | 1篇 |
专业分类
1480篇 |
出版年
2022年 | 8篇 |
2021年 | 21篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 24篇 |
2016年 | 45篇 |
2015年 | 48篇 |
2014年 | 64篇 |
2013年 | 80篇 |
2012年 | 82篇 |
2011年 | 76篇 |
2010年 | 53篇 |
2009年 | 44篇 |
2008年 | 64篇 |
2007年 | 58篇 |
2006年 | 60篇 |
2005年 | 59篇 |
2004年 | 66篇 |
2003年 | 65篇 |
2002年 | 63篇 |
2001年 | 38篇 |
2000年 | 38篇 |
1999年 | 36篇 |
1998年 | 22篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 9篇 |
1971年 | 5篇 |
1969年 | 6篇 |
1968年 | 14篇 |
1967年 | 9篇 |
1966年 | 8篇 |
1965年 | 5篇 |
排序方式: 共有1480条查询结果,搜索用时 15 毫秒
81.
Kemming GI Messick JB Enders G Boros M Lorenz B Muenzing S Kisch-Wedel H Mueller W Hahmann-Mueller A Messmer K Thein E 《Comparative medicine》2004,54(4):404-409
Mycoplasma haemocanis (formerly Haemobartonella canis) is a red blood cell parasite that causes disease mainly in immunosuppressed and splenectomized dogs. Clinical outbreak of the disease resulted in failure of a large experimental project. We aimed to identify whether M. haemocanis has increased prevalence in kennel-raised dogs. In a prospective study, we compared the prevalence of M. haemocanis in whole blood (anti-coagulated by use of EDTA) collected from pet dogs (University of Illinois, Urbana Champaign, Ill.; n = 60) with that in blood from dogs raised in three distinct kennels in western Europe (WE; n = 23), eastern Europe (EE; n = 20), and North America (NA; n = 20). Screening included antibody testing and microscopy of blood smears. The presence of M. haemocanis was identified using a polymerase chain reaction (PCR) assay for specific DNA of the organism. None of the pet dogs (0%) was test positive for M. haemocanis DNA. Mycoplasma haemocanis was found in dogs tested at all of the kennels. Infection rate in the three kennels was 30, 35, and 87%, respectively (all P < 0.001 versus control, chi2-test). Latent infection with M. haemocanis was not a single observation in kennel-raised dogs. Prevalence may be higher than that in a pet dog population. The potential exists for these latent infections to adversely affect or confound research results. 相似文献
82.
Transmission electron microscopy was used to examine the ultrastructure of the allantoplacenta of garter snakes during the last half of gestation. This placenta occupies the dorsal hemisphere of the egg and is formed through apposition of the chorioallantois to the inner lining of the uterus. The uterine epithelium consists of flattened cells with short, irregular microvilli and others that bear cilia. The lamina propria is vascularized and its capillaries lie at the base of the uterine epithelial cells. The chorionic epithelium consists of a bilayer of squamous cells that are particularly thin superficial to the allantoic capillaries. Neither the chorionic epithelium nor the uterine epithelium undergoes erosion during development. Although a thin remnant of the shell membrane intervenes between fetal and maternal tissue at mid-gestation, it undergoes fragmentation by the end of gestation. Thus, uterine and chorionic epithelial are directly apposed in some regions of the allantoplacenta, forming continuous cellular boundaries at the placental interface. During development, capillaries proliferate in both the uterine and chorioallantoic tissues. By late gestation, the interhemal diffusion distance has thinned in some areas to less than 2 microm through attenuation of the uterine and chorionic epithelia. Morphologically, the allantoplacenta is well adapted for its function in gas exchange. However, the presence of cytoplasmic vesicles, ribosomal ER, and mitochondria in the chorionic and uterine epithelial cells are consistent with the possibility of additional forms of placental exchange. 相似文献
83.
Makino Y Nakamura H Ikeda E Ohnuma K Yamauchi K Yabe Y Poellinger L Okada Y Morimoto C Tanaka H 《Journal of immunology (Baltimore, Md. : 1950)》2003,171(12):6534-6540
Peripheral T lymphocytes undergo activation by antigenic stimulation and function in hypoxic areas of inflammation. We demonstrated in CD3-positive human T cells accumulating in inflammatory tissue expression of the hypoxia-inducible factor-1alpha (HIF-1alpha), indicating a role of hypoxia-mediated signals in regulation of T cell function. Surprisingly, accumulation of HIF-1alpha in human T cells required not only hypoxia but also TCR/CD3-mediated activation. Moreover, hypoxia repressed activation-induced cell death (AICD) by TCR/CD3 stimulation, resulting in an increased survival of the cells. Microarray analysis suggested the involvement of HIF-1 target gene product adrenomedullin (AM) in this process. Indeed, AM receptor antagonist abrogated hypoxia-mediated repression of AICD. Moreover, synthetic AM peptides repressed AICD even in normoxia. Taken together, we propose that hypoxia is a critical determinant of survival of the activated T cells via the HIF-1alpha-AM cascade, defining a previously unknown mode of regulation of peripheral immunity. 相似文献
84.
85.
Muschner VC Lorenz AP Cervi AC Bonatto SL Souza-Chies TT Salzano FM Freitas LB 《American journal of botany》2003,90(8):1229-1238
Passiflora, a genus with more than 400 species, exhibits a high diversity of floral and vegetative structures and a complex taxonomy, which includes 23 subgenera and many sections and series. To better understand Passiflora's variability and interspecific relationships, the phylogeny of 61 species, classified in 11 of 23 suggested subgenera, was investigated. Three molecular markers were used, the nuclear ribosomal internal transcribed spacers (nrITS), the plastid trnL-trnF spacer regions (~1000 bp), and the rps4 plastid gene (~570 bp). Three major clades were highly supported, independent of the marker and phylogenetic method used; one included the subgenera Distephana, Dysosmia, Dysosmioides, Passiflora, and Tacsonioides, a second, the subgenera Adopogyne, Decaloba, Murucuja, and Pseudomurucuja, and a third, the subgenus Astrophea. We call these the Passiflora, Decaloba, and Astrophea clades, respectively. The position of subgenus Deidamioides is undefined. The monophyly of Passiflora could not be statistically corroborated, and the relationships among the major clades and of these clades with the related genera remain unresolved. Our results indicate that a reevaluation of the monophyly of Passiflora and its infrageneric classification is necessary. 相似文献
86.
Middelboe M Hagström A Blackburn N Sinn B Fischer U Borch NH Pinhassi J Simu K Lorenz MG 《Microbial ecology》2001,42(3):395-406
Viral lysis of specific bacterial populations has been suggested to be an important factor for structuring marine bacterioplankton
communities. In the present study, the influence of bacteriophages on the diversity and population dynamics of four marine
bacterial phage-host systems was studied experimentally in continuous cultures and theoretically by a mathematical model.
By use of whole genome DNA hybridization toward community DNA, we analyzed the dynamics of individual bacterial host populations
in response to the addition of their specific phage in continuous cultures of mixed bacterial assemblages. In these experiments,
viral lysis had only temporary effects on the dynamics and diversity of the individual bacterial host species. Following the
initial lysis of sensitive host cells, growth of phage-resistant clones of the added bacteria resulted in a distribution of
bacterial strains in the phage-enriched culture that was similar to that in the control culture without phages after about
50-60 h incubation. Consequently, after a time frame of 5-10 generations after lysis, it was the interspecies competition
rather than viral lysis of specific bacterial strains that was the driving force in the regulation of bacterial species composition
in these experiments. The clonal diversity, on the other hand, was strongly influenced by viral activity, since the clonal
composition of the four species in the phage-enriched culture changed completely from phage-sensitive to phage-resistant clones.
The model simulation predicted that viral lysis had a strong impact on the population dynamics, the species composition, and
the clonal composition of the bacterial community over longer time scales (weeks). However, according to the model, the overall
density of bacteria in the system was not affected by phages, since resistant clones complemented the fluctuations caused
by viral lysis. Based on the model analysis, we therefore suggest that viral lysis can have a strong influence on the dynamics
of bacterial populations in planktonic marine systems. 相似文献
87.
88.
89.
Roggo L Bernard V Kovacs AL Rose AM Savoy F Zetka M Wymann MP Müller F 《The EMBO journal》2002,21(7):1673-1683
Here we present a detailed genetic analysis of let-512/vps34 that encodes the Caenorhabditis elegans homologue of the yeast phosphatidylinositol 3-kinase Vps34p. LET-512/VPS34 has essential functions and is ubiquitously expressed in all tissues and developmental stages. It accumulates at a perinuclear region, and mutations in let-512/vps34 result in an expansion of the outer nuclear membrane as well as in a mislocalization and subsequent complete lack of expression of LRP-1, a C.elegans LDL receptor normally associated with the apical surface of hypodermal cells. Using a GFP::2xFYVE fusion protein we found that the phosphatidylinositol 3-phosphate (PtdIns 3-P) product of LET-512/VPS34 is associated with a multitude of intracellular membranes and vesicles located at the periphery, including endocytic vesicles. We propose that LET-512/VPS34 is required for membrane transport from the outer nuclear membrane towards the cell periphery. Thus, LET-512/VPS34 may regulate the secretory pathway in a much broader range of compartments than was previously suggested for the yeast orthologue. 相似文献
90.
Mitochondrial death protein Nix is induced in cardiac hypertrophy and triggers apoptotic cardiomyopathy 总被引:14,自引:0,他引:14
Yussman MG Toyokawa T Odley A Lynch RA Wu G Colbert MC Aronow BJ Lorenz JN Dorn GW 《Nature medicine》2002,8(7):725-730
Loss of cardiomyocytes through programmed cell death is a key event in the development of heart failure, but the inciting molecular mechanisms are largely unknown. We used microarray analysis to identify a genetic program for myocardial apoptosis in Gq-mediated and pressure-overload cardiac hypertrophy. A critical component of this apoptotic program was Nix/Bnip3L. Nix localized to mitochondria and caused release of cytochrome c, activation of caspase-3 and apoptotic cell death, when expressed in HEK293 fibroblasts. A previously undescribed truncated Nix isoform, termed sNix, was not targeted to mitochondria but heterodimerized with Nix and protected against Nix-mediated apoptosis. Forced in vivo myocardial expression of Nix resulted in apoptotic cardiomyopathy and rapid death. Conversely, sNix protected against apoptotic peripartum cardiomyopathy in G(alpha)q-overexpressors. Thus, Nix/Bnip3L is upregulated in myocardial hypertrophy, and is both necessary and sufficient for Gq-mediated apoptosis of cardiomyocytes and resulting hypertrophy decompensation. 相似文献