全文获取类型
收费全文 | 1562篇 |
免费 | 135篇 |
国内免费 | 1篇 |
专业分类
1698篇 |
出版年
2021年 | 21篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 53篇 |
2014年 | 67篇 |
2013年 | 83篇 |
2012年 | 98篇 |
2011年 | 84篇 |
2010年 | 57篇 |
2009年 | 48篇 |
2008年 | 81篇 |
2007年 | 75篇 |
2006年 | 68篇 |
2005年 | 73篇 |
2004年 | 73篇 |
2003年 | 75篇 |
2002年 | 72篇 |
2001年 | 43篇 |
2000年 | 49篇 |
1999年 | 36篇 |
1998年 | 21篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1983年 | 9篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 13篇 |
1972年 | 13篇 |
1971年 | 7篇 |
1969年 | 11篇 |
1968年 | 15篇 |
1967年 | 13篇 |
1966年 | 9篇 |
排序方式: 共有1698条查询结果,搜索用时 15 毫秒
101.
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
102.
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
103.
104.
FOXL2 and BPES: mutational hotspots,phenotypic variability,and revision of the genotype-phenotype correlation 总被引:15,自引:0,他引:15
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
105.
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
106.
Pereira T Zheng X Ruas JL Tanimoto K Poellinger L 《The Journal of biological chemistry》2003,278(9):6816-6823
107.
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
108.
Aim of this study was to elaborate an efficient method for the micronization of the decapeptide cetrorelix (a GnRH-antagonist),
in order to obtain a microsuspension as basis for other pharmaceutical preparations, such as e.g. inhalation aerosols. A modified
pearl-mill coupled with a cryostat was used for the micronization of cetrorelix in fluid propellant and operated under different
conditions. The obtained cetrorelix suspensions were analyzed for particle size distribution, purity of cetrorelix, and for
metal contamination through abrasion from parts of the mill. The method allowed an effective micronization of cetrorelix.
The mean particle size of the initial cetrorelix lyophilizate bulk ware was reduced from 52.5 μ (Volume Mean Diameter, VMD)
down to 14.9, 6.1 and 3.1 μm, respectively, respectively. The HPLC analysis of all cetrorelix suspensions after micronization
did not show signs of decomposition as compared to the initial product. The elementary analysis of the suspensions performed
by inductively coupled plasma mass spectrometry revealed a negligible amount of contaminants in the suspension (Zr=max. 0.6
ppm; Fe, Cr, Ni, Ba, below limit of quantification, i.e.<0.14 ppm). The only appreciable contaminant. Aluminum (Al=1.1 ppm),
was derived from the mechanical capping of aluminum canisters prior to analysis. The Zr determination in the suspension of
0.6 ppm, is still considered to be negligible as compared to the legally tolerated limit of air contamination. By low-temperature
micronization in fluid propellant, fine drug suspensions of cetrorelix for pMDIs can be directly manufactured in one-step
procedure without destruction of the peptide structure and without appreciable product contamination.
Published: July 12, 2001. 相似文献
109.
Lorenz JN 《American journal of physiology. Regulatory, integrative and comparative physiology》2002,282(6):R1565-R1582
The development and widespread use of genetically altered mice to study the role of various proteins in biological control systems have led to a renewed interest in methodologies and approaches for evaluating physiological phenotypes. As a result, cross-disciplinary approaches have become essential for fully realizing the potential of these new and powerful animal models. The combination of classical physiological approaches and modern innovative technology has given rise to an impressive arsenal for evaluating the functional results of genetic manipulation in the mouse. This review attempts to summarize some of the techniques currently being used for measuring cardiovascular, renal, and pulmonary variables in the intact mouse, with specific attention to practical considerations useful for their successful implementation. 相似文献
110.