全文获取类型
收费全文 | 2269篇 |
免费 | 85篇 |
国内免费 | 176篇 |
出版年
2023年 | 12篇 |
2022年 | 44篇 |
2021年 | 62篇 |
2020年 | 51篇 |
2019年 | 76篇 |
2018年 | 89篇 |
2017年 | 42篇 |
2016年 | 33篇 |
2015年 | 38篇 |
2014年 | 75篇 |
2013年 | 115篇 |
2012年 | 67篇 |
2011年 | 117篇 |
2010年 | 86篇 |
2009年 | 141篇 |
2008年 | 133篇 |
2007年 | 143篇 |
2006年 | 111篇 |
2005年 | 70篇 |
2004年 | 77篇 |
2003年 | 130篇 |
2002年 | 100篇 |
2001年 | 78篇 |
2000年 | 77篇 |
1999年 | 50篇 |
1998年 | 54篇 |
1997年 | 44篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 44篇 |
1993年 | 35篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 11篇 |
1989年 | 30篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 4篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有2530条查询结果,搜索用时 31 毫秒
51.
Hermann Seim Heinz Löster Reiner Claus Hans-Peter Kleber Erich Strack 《Archives of microbiology》1982,132(1):91-95
In view of the development of al-carnitine deficiency, the metabolism ofl-carnitine and structure-related trimethylammonium compounds was studied inSalmonella typhimurium LT2 by means of thin-layer chromatography (TLC).l-Carnitine, crotonobetaine and acetyl-l-carnitine stimulated the anaerobic growth in a complex medium significantly. The stimulation depended on the formation of -butyrobetaine. The reduction ofl-carnitine proceeded in two steps: (1) Dehydration of thel-carnitine to crotonobetaine, (2) hydrogenation of crotonobetaine to -butyrobetaine. The reduction of crotonobetaine was responsible for the growth stimulation. Terminal electron acceptors of the anaerobic respiration such as nitrate and trimethylamine N-oxide, but not fumarate, suppressed the catabolism ofl-carnitine completely. Glucose fermentation, too, inhibited the reduction ofl-carnitine but optimal growth with a high carnitine catabolism was achieved byd-ribose. The esters of carnitine with medium- and long-chain fatty acids inhibited the growth considerably because of their detergent properties.Abbreviations TLC
thin-layer chromatography 相似文献
52.
53.
The fractionation of iron-phosphorus compounds in sediments studied by Mössbauer spectroscopy 总被引:1,自引:1,他引:0
Iron compounds of phosphorus form a large part of the phosphorus bound in sediments. Mössbauer spectroscopy is a technique that enables us to study, directly, chemical forms of iron in solid samples. Mössbauer spectroscopy allowed us to check, directly, the selectivity of the extraction scheme for soil phosphorus proposed by Chang &; Jackson (1957), but only as far as the iron compounds are concerned. It appears that selectivity of the extraction method leaves much to be desired.
相似文献54.
Inhibition of ADP-ribosylation of histone by diadenosine 5', 5"' -p (1), p(4)-tetraphosphate 总被引:3,自引:0,他引:3
Y Tanaka N Matsunami K Yoshihara 《Biochemical and biophysical research communications》1981,99(3):837-843
Diadenosine 5′, 5?-p1, p4-tetraphosphate (Ap4A) strongly inhibited ADP-ribosylation reaction of histone by purified bovine thymus poly(ADP-ribose) polymerase. This compound showed a relatively weak inhibitory effect on Mg2+-dependent, enzyme-bound poly(ADP-ribose) synthesis. Among various adenine nucleotides tested, including several diadenosine nucleotides with varying phosphate chain length, Ap4A was the most effective inhibitor of the histone-modification reaction. Ap5A and Ap6A showed slightly lower inhibitory effect than Ap4A. Kinetic analysis of the inhibitor (Ap4A) with varying concentration of substrate (NAD+) revealed that this compound is a “mixed type inhibitor”, with a Ki value of 5.1 μM. 相似文献
55.
56.
57.
Thymectomized, lethally irradiated mice reconstituted with syngeneic bone marrow cells are tolerant to xenogeneic Yoshida ascites sarcoma (YAS). The tolerance was abolished by an injection of syngeneic normal spleen, thymus, or lymph node cells given simultaneously with YAS. Allogeneic and semiallogeneic spleen cells were ineffective. The YAS-rejecting mice produced specific anti-tumor antibodies. The serum of these mice transferred to tolerant T-cell-deficient mice protected the latter from inoculated YAS cells. These serum-protected mice were not able to resist the reinoculum of the tumor cells as the mice restored with lymphoid cells did. The latter mice rejected the YAS at the time when donor cells were practically absent in their lymphoid tissue. The low effective ratio of injected syngeneic lymphoid to tumor cells, efficiency of injected thymus cells, and other data led to the conclusion that transferred lymphoid cells did not act directly on tumor cells but through cooperation with host lymphoid cells. The cooperation of donor T- and host B-lymphocytes enabled the activation of the latter, and YAS cells were rejected. 相似文献
58.
O. Modesto Olanya Joseph E. Sites Aaron K. Hoshide 《Biocontrol Science and Technology》2016,26(5):651-664
Published research on process-based models for biocontrol of foodborne pathogens on produce is limited. The aim of this research was to develop cost model estimates for competitive exclusion (CE) process using Pseudomonas fluorescens and Pseudomonas chlororaphis (non-plant pathogenic and non-human pathogen) as biocontrol against Salmonella enterica on tomatoes. Cost estimates were based on material inputs, equipment, facilities, and projected processing conditions of post-harvest packaging of tomatoes. The microbiological data for inactivation of S. enterica was based on published papers. The small-scale processing facility was assumed to have a processing capacity of 2000 kg of tomatoes/hour for 16 h per day, operational 6 days a week, and for 3-months /year. The large-scale facility was assumed to have a processing capacity of 100,000 kg of tomatoes/hour. Estimated initial capital investment costs for small and large-scale models (production facility) were US$391,000 and US$2.1 million. Application of CE for biocontrol of S. enterica on tomatoes was estimated at US$0.0058–0.073/kg of tomatoes during commercial processing operations. This exceeds chlorine wash technology estimated at US$0.00046/kg and is competitive with gaseous chlorine dioxide at US$0.02–0.21/kg. For high-value produce, CE may complement existing technologies increase food safety, reduce storage loses, and extend shelf life of produce. 相似文献
59.
Phytochrome induces δ-aminolevulinate dehydratase (ALAD) activity in radish seedling cotyledons under continuous far red light. Analysis of the enzymatic activity in etioplasts vs total activity shows a constant ALAD level in these organelles (10 %) in etiolated seedlings. In far red irradiated seedlings, the percentage of enzyme detected into etioplasts increases up to 45 % of the total. Comparative kinetic studies of ALAD activity detected in the cytoplasm and the etioplasts indicate an increase in both compartments with a maximum value reached respectively at 96 and 120 hr from sowing. Treatment with cycloheximide shows a very fast abolition of cytoplasmic ALAD activity which is always correlated to an etioplast decrease with a time shift of ca 24 hr. Erythromycin acts only on the cytoplasmic level of ALAD, and only for far red irradiated seedlings, with an increase of activity twice the level detected in untreated ones. This unexpected effect is discussed. 相似文献
60.
Phage therapy is considered an alternative modality in the treatment of different bacterial diseases. However, their therapeutic and preventive roles against infections caused by Salmonella Kentucky and Escherichia coli O119 were of little attention. In this study, two phages were isolated, characterized and assessed for their potential therapeutic and preventive roles against S. Kentucky and E. coli O119 infections in broilers. Commercial 1-day-old arboacres broiler chicks were assigned to seven groups: Group Ӏ was as a negative control, groups (П and Ш) were assigned as positive controls by the challenge of S. Kentucky and E. coli O119, respectively. The remaining four groups (IV, V, VI and VII) were administrated with five repeated phage doses to determine the effect of multiple doses. Phages were administrated in groups (IV and VI) after challenging with S. Kentucky and E. coli O119, respectively to assess their therapeutic role; moreover, their preventive role was evaluated through administration in groups (V and VII) before challenging with S. Kentucky and E. coli O119, respectively. Sampling was done from different organs at three time points and revealed that phage-treated groups had lower colony forming units of S. Kentucky and E. coli. Our results suggest that bacteriophages are efficient in the treatment and prevention of salmonellosis and colibacillosis in broiler farms. 相似文献