全文获取类型
收费全文 | 3756篇 |
免费 | 252篇 |
出版年
2023年 | 18篇 |
2022年 | 34篇 |
2021年 | 57篇 |
2020年 | 49篇 |
2019年 | 62篇 |
2018年 | 89篇 |
2017年 | 73篇 |
2016年 | 95篇 |
2015年 | 160篇 |
2014年 | 159篇 |
2013年 | 249篇 |
2012年 | 308篇 |
2011年 | 233篇 |
2010年 | 162篇 |
2009年 | 151篇 |
2008年 | 197篇 |
2007年 | 203篇 |
2006年 | 212篇 |
2005年 | 176篇 |
2004年 | 159篇 |
2003年 | 136篇 |
2002年 | 155篇 |
2001年 | 87篇 |
2000年 | 59篇 |
1999年 | 54篇 |
1998年 | 57篇 |
1997年 | 42篇 |
1996年 | 37篇 |
1995年 | 32篇 |
1994年 | 25篇 |
1993年 | 20篇 |
1992年 | 32篇 |
1991年 | 45篇 |
1990年 | 37篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 27篇 |
1985年 | 22篇 |
1984年 | 34篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 16篇 |
1974年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有4008条查询结果,搜索用时 15 毫秒
991.
Only a limited number of bacterial pathogens evade destruction by phagocytic cells such as macrophages. Legionella pneumophila is a Gram-negative γ-proteobacterial species that can infect and replicate in alveolar macrophages, causing Legionnaires' disease, a severe pneumonia. L. pneumophila uses a complex secretion system to inject host cells with effector proteins capable of disrupting or altering the host cell processes. The L. pneumophila effectors target multiple processes but are essentially aimed at modifying the properties of the L. pneumophila phagosome by altering vesicular trafficking, gradually creating a specialized vacuole in which the bacteria replicate robustly. In nature, L. pneumophila is thought to parasitize free-living protists, which may have selected for traits that promote virulence of L. pneumophila in humans. Indeed, many effector genes encode proteins with eukaryotic domains and are likely to be of protozoan origin. Sustained horizontal gene transfer events within the protozoan niche may have allowed L. pneumophila to become a professional parasite of phagocytes, simultaneously giving rise to its ability to infect macrophages, cells that constitute the first line of cellular defence against bacterial infections. 相似文献
992.
Nicoletta Bivi Milena Romanello Richard Harrison Ian Clarke David C Hoyle Luigi Moro Fulvia Ortolani Antonella Bonetti Franco Quadrifoglio Gianluca Tell Daniela Delneri 《Genome biology》2009,10(9):R93
Background
Nitrogen-containing bisphosphonates are the elected drugs for the treatment of diseases in which excessive bone resorption occurs, for example, osteoporosis and cancer-induced bone diseases. The only known target of nitrogen-containing bisphosphonates is farnesyl pyrophosphate synthase, which ensures prenylation of prosurvival proteins, such as Ras. However, it is likely that the action of nitrogen-containing bisphosphonates involves additional unknown mechanisms. To identify novel targets of nitrogen-containing bisphosphonates, we used a genome-wide high-throughput screening in which 5,936 Saccharomyces cerevisiae heterozygote barcoded mutants were grown competitively in the presence of sub-lethal doses of three nitrogen-containing bisphosphonates (risedronate, alendronate and ibandronate). Strains carrying deletions in genes encoding potential drug targets show a variation of the intensity of their corresponding barcodes on the hybridization array over the time.Results
With this approach, we identified novel targets of nitrogen-containing bisphosphonates, such as tubulin cofactor B and ASK/DBF4 (Activator of S-phase kinase). The up-regulation of tubulin cofactor B may explain some previously unknown effects of nitrogen-containing bisphosphonates on microtubule dynamics and organization. As nitrogen-containing bisphosphonates induce extensive DNA damage, we also document the role of DBF4 as a key player in nitrogen-containing bisphosphonate-induced cytotoxicity, thus explaining the effects on the cell-cycle.Conclusions
The dataset obtained from the yeast screen was validated in a mammalian system, allowing the discovery of new biological processes involved in the cellular response to nitrogen-containing bisphosphonates and opening up opportunities for development of new anticancer drugs. 相似文献993.
Ana Paula Ribeiro Paiotti Sender Jankiel Miszputen Celina Tizuko Fujiyama Oshima Henrique de Oliveira Costa Daniel Araki Ribeiro Marcello Franco 《Journal of molecular histology》2009,40(4):317-324
Inflammatory bowel disease (IBD) is a common chronic gastrointestinal disorder characterized by alternating periods of remission
and active intestinal inflammation. Some studies suggest that antiinflammatory drugs are a promising alternative for treatment
of the disease. Thus, this study aimed to evaluate the effect of lumiracoxib, a selective-cyclooxygenase-2 (COX-2) inhibitor,
on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced experimental colitis. Wistar rats (n = 25) were randomized into four groups, as follows: Group (1) Sham group: sham induced-colitis rats; Group (2) TNBS group:
nontreated induced-colitis rats; Group (3) Lumiracoxib control group; and Group (4) Lumiracoxib-treated induced-colitis rats.
Our results showed that rats from groups 2 and 4 presented similar histopathological damage and macroscopic injury in the
distal colon as depicted by significant statistically differences (P < 0.01; P < 0.05) compared to the other two groups. Weak expression of COX-2 mRNA was detected in normal colon cells, while higher
levels of COX-2 mRNA were detected in group 2 and group 4. Therapy with lumiracoxib reduced COX-2 expression by 20–30%, but
it was still higher and statistically significant compared to data obtained from the lumiracoxib control group. Treatment
with the selective COX-2 inhibitor lumiracoxib did not reduce inflammation-associated colonic injury in TNBS-induced experimental
colitis. Thus, the use of COX-2 inhibitors for treating IBD should be considered with caution and warrants further experimental
investigation to elucidate their applicability. 相似文献
994.
995.
In direct sowing, desiccation of the cover crops with herbicides can affect N availability in agroecosystems, reducing N use efficiency by the crop in succession. In this sense, the objective of the study was to evaluate nitrogen losses in the soil–plant system after application of the herbicides glyphosate and glufosinate-ammonium on pearl millet [Pennisetum glaucum (L.) R. Brown, var. ADR500]. Plants were grown in a sandy soil, fertilized with 15N ammonium sulfate, at N dose of 135.7 mg kg?1. After herbicide application, the N distribution within the plant was changed, with an observed N reduction in leaves and increased N in stalks. The glyphosate and glufosinate reduced, by 25 and 30%, respectively, the amount of N in plant tissues and increased by 3.0 g m?2 the losses in the soil–plant system of the N provided from the fertilizer. This information can be useful in preparing management strategies that will provide greater nitrogen fertilization effectiveness and, consequently, smaller environmental impacts from the use of nitrogen fertilizers and herbicides. 相似文献
996.
Anthocyanic vacuolar inclusions (AVIs) are intra-vacuolar structures capable of concentrating anthocyanins and are present
in over 50 of the highest anthocyanin-accumulating plant species. Presence of AVIs alters pigment intensity, total anthocyanin
levels, pigment hue and causes bathochromic shifts in a spatio-temporal manner within various flowers, vegetables and fruits.
A year-long study on Vitis vinifera cell suspension cultures found a strong correlation between AVI prevalence and anthocyanin content, but not the number of
pigmented cells, growth rate or stilbene content. Furthermore, enhancement of the prevalence of AVIs and anthocyanins was
achieved by treatment of V. vinifera cell suspension cultures with sucrose, jasmonic acid and white light. A unique autofluorescence of anthocyanins was used
to demonstrate microscopically that AVIs proceed from the cytosol across the tonoplast and were able to coalesce intravacuolarly,
with fewer, larger AVIs predominating as cells mature. Purification and characterisation of these bodies were performed, showing
that they were dense, highly organic structures, with a lipid component indicative of membrane-encasement. These purified
AVIs were also shown to comprise long-chain tannins and possessed an increased affinity for binding acylated anthocyanins,
though no unique protein component was detected. 相似文献
997.
Vicente Franco Daniel Garraín Rosario Vidal 《The International Journal of Life Cycle Assessment》2010,15(8):869-882
Background, aim and scope
Several methodological shortcomings still hinder the inclusion of transport noise as an established impact category within life cycle assessment (LCA). Earlier attempts to quantify the health damages caused by traffic noise yielded valuable results from an academic point of view, but these were of limited use in the context of everyday LCA practice. An enhanced understanding of traffic noise emission models coupled with a straightforward choice of indicators could lead to faster, more accurate assessments of health impairment due to traffic noise whose results would fittingly serve the purposes of policy makers and the information needs of the general public alike. This article aims to propose the guidelines for such assessments. 相似文献998.
Rui S. Oliveira Albina R. Franco Miroslav Vosátka Paula M. L. Castro 《Symbiosis (Philadelphia, Pa.)》2010,52(2-3):125-131
The application of ectomycorrhizal (ECM) fungi on forest nursery production is regarded as part of good management practice. However, before employing large scale inoculations in a nursery the interaction between ECM symbionts, growth substrate and fertilisation input should be studied to select the most suitable nursery practices for promoting plant growth and ECM colonisation. In this study, seedlings of Quercus ilex were inoculated with Paxillus involutus, Hebeloma mesophaeum or Cenococcum geophilum and grown in three different substrates commonly used in forest nurseries: peat-based compost, forest soil or composted pine bark. The effect of various fertilisation regimes was also studied. The choice of substrate had a significant effect on plant growth and ECM colonisation. The most appropriate combination of substrate and ECM fungus for Q. ilex growth and nutrition was peat and H. mesophaeum. Plants grown on a peat-based compost and inoculated with H. mesophaeum had a significantly greater biomass and leaf phosphorus concentration without fertilisation. Composted pine bark was found not to be suitable for growth or for mycorrhization. If the appropriate growth substrate is selected, it is possible to replace the use of chemical fertilisers by inoculation with selected ECM fungi. This results in a significant increase in plant development, and thus ECM fungi can be recommended as a more environmental friendly biotechnological approach to plant management in the nursery. 相似文献
999.