全文获取类型
收费全文 | 693篇 |
免费 | 61篇 |
国内免费 | 1篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 42篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 18篇 |
2016年 | 46篇 |
2015年 | 71篇 |
2014年 | 58篇 |
2013年 | 61篇 |
2012年 | 82篇 |
2011年 | 70篇 |
2010年 | 39篇 |
2009年 | 19篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 13篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1960年 | 1篇 |
1952年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有755条查询结果,搜索用时 15 毫秒
31.
Jianing Fu Julien Zuber Mercedes Martinez Brittany Shonts Aleksandar Obradovic Hui Wang Sai-ping Lau Amy Xia Elizabeth E. Waffarn Kristjana Frangaj Thomas M. Savage Michael T. Simpson Suxiao Yang Xinzheng V. Guo Michelle Miron Takashi Senda Kortney Rogers Adeeb Rahman Megan Sykes 《Cell Stem Cell》2019,24(2):227-239.e8
32.
33.
The African Black Oystercatcher Haematopus moquini is a charismatic, southern African near-endemic, wader species, that is often seen as a flagship species for coastal bird conservation, as it was recently down-listed regionally to Least Concern on the IUCN Red List of Threatened Species. To celebrate this rare conservation success story, BirdLife South Africa named it the 2018 Bird of the Year and ran a year-long programme in collaboration with the Nature’s Valley Trust highlighting aspects of the species’ biology, current threats, and conservation success. We used data collected by the Southern African Bird Atlas Project (SABAP1 and SABAP2) to examine changes in the species’ range and relative abundance, both in the records between the two projects, as well as trends within the SABAP2 sampling period (2008–2017). This case study enabled us to assess whether such metrics can accurately reflect abundance and distributional changes in a species. We found increases in the reported range and the reporting rates between the two Atlas projects, and that the SABAP2 reporting rate was stable. Regionally, across four coastal categories, the reporting rate was lowest in KwaZulu-Natal, though this region also showed an increase in the probability of reporting during the SABAP2 period. While corroborating the recent change in the species’ conservation status, we also provide good evidence that the long-term SABAP data can be used successfully to assess population trends and range changes over time. 相似文献
34.
Production of recombinant proteins using multiple-copy gene integration in high-cell-density fermentations of Ralstonia eutropha 总被引:2,自引:0,他引:2
We have previously reported the development of a novel protein expression system based on Ralstonia eutropha. In this study we report on the influence of gene copynumber on recombinant protein expression in R. eutropha. We compare recombinant gene stability and expression levels of chromosomal integration with a plasmid-based expression system. Single, double, and triple copies of a gene encoding organophosphohydrolase (OPH), an enzyme prone to inclusion-body formation in E. coli, were integrated into the R. eutropha chromosome. A linear increase between the concentration of soluble, active OPH and gene copynumber was found. Using a triple-copy integrant, we were able to produce approximately 4.3 g/L of OPH in a high-cell-density fermentation. This represents the highest titer reported to date for this enzyme, and is approximately 30 times greater than expression levels reported in E. coli. 相似文献
35.
Lin G Tiedemann K Vollbrandt T Peters H Batge B Brinckmann J Reinhardt DP 《The Journal of biological chemistry》2002,277(52):50795-50804
Fibrillin-1 and fibrillin-2 constitute the backbone of extracellular filaments, called microfibrils. Fibrillin assembly involves complex multistep mechanisms to result in a periodical head-to-tail alignment in microfibrils. Impaired assembly potentially plays a role in the molecular pathogenesis of genetic disorders caused by mutations in fibrillin-1 (Marfan syndrome) and fibrillin-2 (congenital contractural arachnodactyly). Presently, the basic molecular interactions involved in fibrillin assembly are obscure. Here, we have generated recombinant full-length human fibrillin-1, and two overlapping recombinant polypeptides spanning the entire human fibrillin-2 in a mammalian expression system. Characterization by gel electrophoresis, electron microscopy after rotary shadowing, and reactivity with antibodies demonstrated correct folding of these recombinant polypeptides. Analyses of homotypic and heterotypic interaction repertoires showed N- to C-terminal binding of fibrillin-1, and of fibrillin-1 with fibrillin-2. The interactions were of high affinity with dissociation constants in the low nanomolar range. However, the N- and C-terminal fibrillin-2 polypeptides did not interact with each other. These results demonstrate that fibrillins can directly interact in an N- to C-terminal fashion to form homotypic fibrillin-1 or heterotypic fibrillin-1/fibrillin-2 microfibrils. This conclusion was further strengthened by double immunofluorescence labeling of microfibrils. In addition, the binding epitopes as well as the entire fibrillin molecules displayed very stable properties. 相似文献
36.
We describe the development of a novel protein expression system based on the industrial fermentation organism Ralstonia eutropha (formerly known as Alcaligenes eutrophus) NCIMB 40124. This new system overcomes some of the shortcomings of traditional Escherichia coli-based protein expression systems, particularly the propensity of such systems to form inclusion bodies during high-level expression. Using a proteomics approach, we identified promoters that can be induced by simple process parameters or medium compositions in high-density cell culture or shake flasks, respectively. By combining newly developed molecular biological tools with a high-cell-density fermentation process, we were able to produce high levels (>1 g/liter) of soluble, active organophosphohydrolase, a model enzyme prone to inclusion body formation in E. coli. 相似文献
37.
LCA of concrete and steel building frames 总被引:1,自引:0,他引:1
Asa Jonsson Thomas Bjorklund Anne -Marie Tillman 《The International Journal of Life Cycle Assessment》1998,3(4):216-224
The effects on the external environment of seven concrete and steel building frames representative of present-day building
technology in Sweden were analysed using LCA methodology. Objects of the study included frame construction and supplementary
materials. Several-storey offices and dwellings were studied. The functional unit was defined as one average m2 of floor area during the lifetime of the building. Inventory data were elaborated for concrete and steel production, the
building site, service life, demolition and final disposal. Parameters included were raw material use, energy use, emissions
to air, emissions to water and waste generation. The inventory results were presented and evaluated as such, in addition to
an interpretation by using three quantitative impact assessment methods. Parameters that weighed heavily were use of fossil
fuels, CO2, electricity, SOx
2 NOx
2 alloy materials and waste, depending on what assessment method was used. Over the life cycle, building production from cradle
to gate accounted for about the same contribution to total environmental loads as maintenance and replacement of heat losses
through external walls during service life, whereas demolition and final disposal accounted for a considerably lower contribution. 相似文献
38.
Objectives
We aimed to describe and compare the prevalence of vitamin D deficiency between HIV-negative and HIV-infected veterans in the southern United States, and to determine risk factors for vitamin D deficiency for HIV infected patients.Methods
Cross-sectional, retrospective study including all patients followed at the Atlanta VA Medical Center with the first 25-hydroxyvitamin D [25(OH)D] level determined between January 2007 and August 2010. Multivariate logistic regression analysis was used to determine risk factors associated with vitamin D deficiency (< 20 ng/ml).Results
There was higher prevalence of 25(OH)D deficiency among HIV-positive compared to HIV-negative patients (53.2 vs. 38.5%, p <0.001). Independent risk factors for vitamin D deficiency in HIV + patients included black race (OR 3.24, 95% CI 2.28–4.60), winter season (OR 1.39, 95% CI 1.05–1.84) and higher GFR (OR 1.01, CI 1.00–1.01); increasing age (OR 0.98, 95% CI 0.95–0.98), and tenofovir use (OR 0.72, 95% CI 0.54–0.96) were associated with less vitamin D deficiency.Conclusions
Vitamin D deficiency is a prevalent problem that varies inversely with age and affects HIV-infected patients more than other veterans in care. In addition to age, tenofovir and kidney disease seem to confer a protective effect from vitamin D deficiency in HIV-positive patients. 相似文献39.
40.