全文获取类型
收费全文 | 1088篇 |
免费 | 77篇 |
国内免费 | 1篇 |
专业分类
1166篇 |
出版年
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 19篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 36篇 |
2014年 | 46篇 |
2013年 | 56篇 |
2012年 | 68篇 |
2011年 | 64篇 |
2010年 | 33篇 |
2009年 | 49篇 |
2008年 | 55篇 |
2007年 | 63篇 |
2006年 | 37篇 |
2005年 | 41篇 |
2004年 | 40篇 |
2003年 | 37篇 |
2002年 | 34篇 |
2001年 | 25篇 |
2000年 | 31篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1973年 | 10篇 |
1971年 | 9篇 |
1970年 | 8篇 |
1968年 | 6篇 |
1967年 | 6篇 |
1966年 | 6篇 |
排序方式: 共有1166条查询结果,搜索用时 0 毫秒
161.
162.
Although health education has proven to be cost-effective in slowing the spread of enterobiasis, assessments of the effectiveness of health education to reduce infectious diseases specifically in children are rare. To evaluate the effect of health education on knowledge, preventative practices, and the prevalence of enterobiasis, 319 children from 16 classes were divided into experimental and control groups. Data were collected from May 2012 to March 2013. A 40-minute in-class talk was given once in the experimental group. There were significant differences over the time in the mean scores for children''s knowledge of Enterobius vermicularis infection in the intervention group compared to the control group (p<0.001). After the educational session, the score for knowledge about E. vermicularis infection increased from 60.2±2.32 to 92.7±1.19 in the experimental group; this gain was partially lost 3 months later, decreasing to 83.6±1.77 (p<0.001). Children''s enterobiasis infection prevention practice scores also increased, from 3.23±0.27 to 3.73±0.25, 1 week after the educational session, a gain that was partially lost at 3 months, decreasing to 3.46±0.36 (p<0.001). The overall E. vermicularis egg detection rate was 4.4%; the rates for each school ranged from 0% to 12.9% at screening. The infection rate at 3 months after the treatment sharply decreased from 12.3% to 0.8% in the experimental group, compared to a decrease from 8.5% to 3.7% in the control group during the same period. We recommend that health education on enterobiasis be provided to children to increase their knowledge about enterobiasis and improve prevention practices. 相似文献
163.
Neurons and glia are produced in stereotyped patterns after neuroblast cell division during development of the Drosophila central nervous system. The first cell division of thoracic neuroblast 6-4 (NB6-4T) is asymmetric, giving rise to a glial precursor cell and a neuronal precursor cell. In contrast, abdominal NB6-4 (NB6-4A) divides symmetrically to produce two glial cells. To understand the relationship between cell division and glia-neuron cell fate determination, we examined and compared the effects of known cell division mutations on the NB6-4T and NB6-4A lineages. Based on observation of expression of glial fate determination and early glial differentiation genes, the onset of glial differentiation occurred in NB6-4A but not in NB6-4T when both cell cycle progression and cytokinesis were genetically arrested. On the other hand, glial differentiation started in both lineages when cytokinesis was blocked with intact cell cycle progression. These results showed that NB6-4T, but not NB6-4A, requires cell cycle progression for acquisition of glial fate, suggesting that distinct mechanisms trigger glial differentiation in the different lineages. 相似文献
164.
Shinsaku Tokuda Young Hak Kim Hisako Matsumoto Shigeo Muro Toyohiro Hirai Michiaki Mishima Mikio Furuse 《PloS one》2015,10(12)
The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma. 相似文献
165.
Although a family of transposon, P elements, are used as tools for molecular genetics in Drosophila melanogaster, the molecular details and mechanism of their mobilization process have not been studied extensively. In particular, the relationship between excision and transposition is little understood. We have previously produced a transgenic fly with a P element insertion that is nonautonomous (stable without transposase) and is highly-transposable in the presence of transposase. Using this insertion, we traced its mobilizations following introduction of a stable transposase source. We found a strain that has a 26-bp tandem repeat at the end of the original P element insertion. The 26-bp repeat reduced the frequency of excision although the frequency of transposition was not altered. Our results indicate independence of transposition from excision and importance of terminal repeat in excision. 相似文献
166.
T Shirai C Mitsuyama Y Niwa Y Matsui H Hotta T Yamane H Kamiya C Ishii T Ogawa K Muramoto 《Structure (London, England : 1993)》1999,7(10):1223-1233
BACKGROUND: Congerin I is a member of the galectin (animal beta-galactoside-binding lectin) family and is found in the skin mucus of conger eel. The galectin family proteins perform a variety of biological activities. Because of its histological localization and activity against marine bacteria and starfish embryos, congerin I is thought to take part in the eels' biological defense system against parasites. RESULTS: The crystal structure of congerin I has been determined in both lactose-liganded and ligand-free forms to 1. 5 A and 1.6 A resolution, respectively. The protein is a homodimer of 15 kDa subunits. Congerin I has a beta-sheet topology that is markedly different from those of known relatives. One of the beta-strands is exchanged between two identical subunits. This strand swap might increase the dimer stability. Of the known galectin complexes, congerin I forms the most extensive interaction with lactose molecules. Most of these interactions are substituted by similar interactions with water molecules, including a pi-electron hydrogen bond, in the ligand-free form. This observation indicates an increased affinity of congerin I for the ligand. CONCLUSIONS: The genes for congerin I and an isoform, congerin II, are known to have evolved under positive selection pressure. The strand swap and the modification in the carbohydrate-binding site might enhance the cross-linking activity, and should be the most apparent consequence of positive selection. The protein has been adapted to functioning in skin mucus that is in direct contact with surrounding environments by an enhancement in cross-linking activity. The structure of congerin I demonstrates the emergence of a new structure class by accelerated evolution under selection pressure. 相似文献
167.
Protection of mice against Sendai virus pneumonia by non-neutralizing anti-F monoclonal antibodies 总被引:1,自引:0,他引:1
Y Mochizuki T de Ming T Hayashi M Itoh H Hotta M Homma 《Microbiology and immunology》1990,34(2):171-183
Nine monoclonal antibodies (MAbs) directed to F protein of Sendai virus were obtained and characterized for their protective ability against Sendai virus infection in mice. None of the MAbs showed hemagglutination-inhibition (HI), hemolysis-inhibition (HLI), or neutralization (NT) activities in vitro when assayed by standard methods. Some of the MAbs, however, showed complement-requiring NT (C-NT) and complement-requiring hemolysis (C-HL) activities when assayed in the presence of complement. Passive immunization experiments revealed that the MAbs with higher C-NT and C-HL activities showed protective activity against Sendai virus pneumonia in mice, and that some MAbs with IgG1 isotype having neither C-NT nor C-HL activity also showed the protective activity. Digestion of the MAbs with pepsin which split immunoglobulin molecules into F(ab')2 and Fc fragments greatly suppressed the protective activity. These results suggest that not only complement-mediated immunological responses such as immune virolysis but also antibody-dependent cellular cytotoxicity (ADCC) and/or immune phagocytosis, in which complement system is not necessarily involved, play an important role in the protection of mice from Sendai virus infection. 相似文献
168.
Le Van Phung Yuki Han Shiro Oka Hisako Hotta Michael D. Smith Prapit Theeparakun Eiko Yabuuchi Ikuya Yano 《FEMS immunology and medical microbiology》1995,12(3-4):259-264
Abstract The serodiagnosis of melioidosis is commonly performed with tests using protein or polysaccharide as antigen. However, due to the low sensitivity, specificity and difficulty in the preparation of the antigens, more simple, precise and reproducible diagnostic tests were required. A purified glycolipid antigen (GL) which is a specific lipid component of Burkholderia pseudomallei has been used in an ELISA. With this antigen, specific immunoglobulin G (IgG) was detected in 49 out of 50 melioidosis sera. IgG was also detected in 2 out of 185 (Japanese) and 16 out of 181 (Vietnamese) control sera. Thus, the sensitivity was 98.0%, and specificity was 98.9% and 91.1% in the Japanese and Vietnamese sera, respectively. When the ELISA and indirect haemagglutination (IHA) tests were combined, a sensitivity of 100% and specificity of 97.8% were achieved. The advantages of the glycolipid antigen are ease of preparation, stability, high sensitivity and specificity. 相似文献
169.
Jang SW Cho MK Park MK Kang SA Na BK Ahn SC Kim DH Yu HS 《The Korean journal of parasitology》2011,49(3):245-254
Many immune down-regulatory molecules have been isolated from parasites, including cystatin (cystain protease inhibitor). In a previous study, we isolated and characterized Type I cystatin (CsStefin-1) of the liver fluke, Clonorchis sinensis. To investigate whether the CsStefin-1 might be a new host immune modulator, we induced intestinal inflammation in mice by dextran sodium sulfate (DSS) and treated them with recombinant CsStefin-1 (rCsStefin-1). The disease activity index (DAI) increased in DSS only-treated mice. In contrast, the DAI value was significantly reduced in rCsStefin-1-treated mice than DSS only-treated mice. In addition, the colon length of DSS only-treated mice was shorter than that of rCsStefin-1 treated mice. The secretion levels of IFN-γ and TNF-α in the spleen and mesenteric lymph nodes (MLNs) were significantly increased by DSS treatment, but the level of TNF-α in MLNs was significantly decreased by rCsStefin-1 treatment. IL-10 production in both spleen and MLNs was significantly increased, and IL-10(+)F4/80(+) macrophage cells were significantly increased in the spleen and MLNs of rCsStefin-1 treated mice after DSS treatment. In conclusion, rCsStefin-1 could reduce the intestinal inflammation occurring after DSS treatment, these effects might be related with recruitment of IL-10 secreting macrophages. 相似文献
170.
Enoyl-[acyl carrier protein] (ACP) reductase (ENR) is a key enzyme in type II fatty acid synthesis that catalyzes the last step in each elongation cycle. Therefore, it has been considered as a target for antibiotics. However, recent studies indicate that some pathogens have more than one ENR; in particular, Bacillus subtilis has two ENRs, FabI and FabL. The crystal structures of the ternary complexes of BsFaBI and BsFabL are found as a homotetramer showing the same overall structure despite a sequence identity of only 24%. The positions of the catalytic dyad of Tyr-(Xaa)6-Lys in FabL are almost identical to that of FabI, but a detailed structural analysis shows that FabL shares more structural similarities with FabG and other members of the SDR (short-chain alcohol dehydrogenase/reductase) family. The apo FabL structure shows significantly different conformations at the cofactor and the substrate-binding regions, and this resulted in a totally different tetrameric arrangement reflecting the flexibility of these regions in the absence of the cofactor and substrate/inhibitor. 相似文献