全文获取类型
收费全文 | 4118篇 |
免费 | 344篇 |
国内免费 | 1篇 |
专业分类
4463篇 |
出版年
2023年 | 40篇 |
2022年 | 81篇 |
2021年 | 139篇 |
2020年 | 106篇 |
2019年 | 111篇 |
2018年 | 116篇 |
2017年 | 111篇 |
2016年 | 134篇 |
2015年 | 218篇 |
2014年 | 213篇 |
2013年 | 283篇 |
2012年 | 301篇 |
2011年 | 295篇 |
2010年 | 232篇 |
2009年 | 181篇 |
2008年 | 168篇 |
2007年 | 158篇 |
2006年 | 142篇 |
2005年 | 124篇 |
2004年 | 112篇 |
2003年 | 101篇 |
2002年 | 84篇 |
2001年 | 59篇 |
2000年 | 77篇 |
1999年 | 40篇 |
1998年 | 22篇 |
1997年 | 34篇 |
1996年 | 33篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 43篇 |
1991年 | 30篇 |
1990年 | 36篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 22篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1977年 | 25篇 |
1975年 | 17篇 |
1972年 | 16篇 |
1970年 | 15篇 |
排序方式: 共有4463条查询结果,搜索用时 15 毫秒
101.
Claudia K. Herrmann Lucas Bukata Luciano Melli M. Ines Marchesini Julio J. Caramelo Diego J. Comerci 《Journal of bacteriology》2013,195(3):493-501
Phosphatidylcholine (PC), a common phospholipid of the eukaryotic cell membrane, is present in the cell envelope of the intracellular pathogen Brucella abortus, the etiological agent of bovine brucellosis. In this pathogen, the biosynthesis of PC proceeds mainly through the phosphatidylcholine synthase pathway; hence, it relies on the presence of choline in the milieu. These observations imply that B. abortus encodes an as-yet-unknown choline uptake system. Taking advantage of the requirement of choline uptake for PC synthesis, we devised a method that allowed us to identify a homologue of ChoX, the high-affinity periplasmic binding protein of the ABC transporter ChoXWV. Disruption of the choX gene completely abrogated PC synthesis at low choline concentrations in the medium, thus indicating that it is a high-affinity transporter needed for PC synthesis via the PC synthase (PCS) pathway. However, the synthesis of PC was restored when the mutant was incubated in media with higher choline concentrations, suggesting the presence of an alternative low-affinity choline uptake activity. By means of a fluorescence-based equilibrium-binding assay and using the kinetics of radiolabeled choline uptake, we show that ChoX binds choline with an extremely high affinity, and we also demonstrate that its activity is inhibited by increasing choline concentrations. Cell infection assays indicate that ChoX activity is required during the first phase of B. abortus intracellular traffic, suggesting that choline concentrations in the early and intermediate Brucella-containing vacuoles are limited. Altogether, these results suggest that choline transport and PC synthesis are strictly regulated in B. abortus. 相似文献
102.
Expression of a chitinase transgene in rose (Rosa hybrida L.) reduces development of blackspot disease (Diplocarpon rosae Wolf) 总被引:12,自引:0,他引:12
Marchant Robert Davey Michael R. Lucas John A. Lamb Chris J. Dixon Richard A. Power J. Brian 《Molecular breeding : new strategies in plant improvement》1998,4(3):187-194
Blackspot, caused by the Ascomycete fungus Diplocarpon rosae, is the most widespread and pernicious disease of cultivated roses. While some species of rose possess resistance to D. rosae, none of the modern-day rose cultivars are fully resistant to the pathogen. In the current study, Biolistic gene delivery was used to introduce a rice gene, encoding a basic (Class I), chitinase into embryogenic callus of the blackspot-susceptible rose (Rosa hybrida L.) cv. Glad Tidings. The plasmid used for transformation carried the neomycin phosphotransferase (nptII) gene facilitating the selection and regeneration of transgenic plants on medium containing 250 mg/l kanamycin. Southern analysis confirmed integration of 2–6 copies of the chitinase gene into the rose genome; gene expression was confirmed by enzyme assay. Bioassays demonstrated that expression of the chitinase transgene reduced the severity of blackspot development by 13–43%. This degree of resistance to the pathogen correlated with the level of chitinase expression in the transgenic rose plants. The introduction of disease defence genes into rose provides a method of producing blackspot-resistant rose cultivars sought by breeders and growers. 相似文献
103.
Bhavna Bhasin Bryan Lau Mohamed G. Atta Derek M. Fine Michelle M. Estrella George J. Schwartz Gregory M. Lucas 《PloS one》2013,8(12)
Background
Serum creatinine and cystatin C are used as markers of glomerular filtration rate (GFR). The performance of these GFR markers relative to exogenously measured GFR (mGFR) in HIV-positive individuals is not well established.Methods
We assessed the performance of the chronic kidney disease epidemiology collaboration equations based on serum concentrations of creatinine (eGFRcr), cystatin C (eGFRcys) and both biomarkers combined (eGFRcr-cys) in 187 HIV-positive and 98 HIV-negative participants. Measured GFR was calculated by plasma iohexol clearance. Bias and accuracy were defined as the difference between eGFR and mGFR and the percentage of eGFR observations within 30% of mGFR, respectively. Activated CD4 and CD8 T-cells (CD38+ HLA-DR+) were measured by flow cytometry.Results
The median mGFR was >100 ml/min/1.73 m2 in both groups. All equations tended to be less accurate in HIV-positive than in HIV-negative subjects, with eGFRcr-cys being the most accurate overall. In the HIV-positive group, eGFRcys was significantly less accurate and more biased than eGFRcr and eGFRcr_cys. Additionally eGFRcys bias and accuracy were strongly associated with use of antiretroviral therapy, HIV RNA suppression, and percentages of activated CD4 or CD8 T-cells. Hepatitis C seropositivity was associated with larger eGFRcys bias in both HIV-positive and HIV-negative groups. In contrast, eGFRcr accuracy and bias were not associated with HIV-related factors, T-cell activation, or hepatitis C.Conclusions
The performance of eGFRcys relative to mGFR was strongly correlated with HIV treatment factors and markers of T-cell activation, which may limit its usefulness as a GFR marker in this population. 相似文献104.
O Kuperman G W Fortner Z J Lucas 《Journal of immunology (Baltimore, Md. : 1950)》1975,115(5):1282-1287
Measurement of the development of cytolytic activity by mammary tumor primed or unprimed syngeneic spleen cells on in vitro monolayers of the 13762 rat mammary tumor operationally defined several subpopulations of lymphoid cells involved in the cytotoxic response. In vitro sensitization of cells from Fischer 344 animals injected 2 to 10 days earlier with 2 x 10(7) viable tumor cells always resulted in a higher and earlier lytic response than cells from non-inoculated animals. Adoptive transfer of the same in vivo primed cells for 5 days in irradiated syngeneic hosts removed any cytotoxic cells originally present but subsequent in vitro sensitization still resulted in a higher and earlier cytolytic response. We defined such cells as "memory" cells for cytotoxicity. Memory cells were radiosensitive and specific for the immunizing target cell. In contrast to cells from animals inoculated for 3 to 10 days, cells obtained 11 and 12 days after immunization had a lower response than unprimed cells on vitro sensitization. The anamnestic response could be restored either by culturing 12-day primed cells in vitro for 2 days without antigen or by adoptive transfer for 5 days into irradiated syngeneic rats. This suggests that another population of cells is present in spleen and suppresses the conversion of memory to cytotoxic cells. A more direct measurement of suppressor cell function was obtained by coincubating tumor-primed and unprimed cells on monolayers during in vitro sensitization. Cells from animals bearing tumors for 5 to 10 days always caused an increase in the response of the mixed lymphocyte groups, whereas 11- to 13-day tumor primed cells always caused a marked decrease in the cytolytic response. These results suggest the following interpretation of the kinetics of cell-mediated cytotoxicity to syngeneic tumor inoculation. Cytotoxic cells appear about 6 days after immunization, reach peak levels 2 days later, and then decrease rapidly. Memory cells are generated at a faster rate, reach peak levels before maximum cytolytic activity, but are then functionally inhibited from converting into differentiated cytotoxic cells by a new population of suppressor cells which reach peak activity about 12 days after immunization. 相似文献
105.
Sadly, Prof. Ko Shimamoto died on September 28, 2013, aged 63. He was born in Wakayama, Japan, on October 19, 1949, received his bachelor's degree in Agriculture from Kyoto University in 1974 and his PhD in Genetics from the University of Wisconsin- Madison in 1980. After his postdoctoral training at the Friedrich Miescher Institute in Basel, Switzerland, 相似文献
106.
107.
Lambers Hans Wright Ian J. Guilherme Pereira Caio Bellingham Peter J. Bentley Lisa Patrick Boonman Alex Cernusak Lucas A. Foulds William Gleason Sean M. Gray Emma F. Hayes Patrick E. Kooyman Robert M. Malhi Yadvinder Richardson Sarah J. Shane Michael W. Staudinger Christiana Stock William D. Swarts Nigel D. Turner Benjamin L. Turner John Veneklaas Erik J. Wasaki Jun Westoby Mark Xu Yanggui 《Plant and Soil》2021,461(1-2):43-61
Plant and Soil - Root-released carboxylates enhance the availability of manganese (Mn), which enters roots through transporters with low substrate specificity. Leaf Mn concentration ([Mn]) has been... 相似文献
108.
Hepatic nuclear factor 3- and hormone-regulated expression of the phosphoenolpyruvate carboxykinase and insulin-like growth factor-binding protein 1 genes. 总被引:7,自引:4,他引:7 下载免费PDF全文
109.