全文获取类型
收费全文 | 2751篇 |
免费 | 343篇 |
国内免费 | 2篇 |
出版年
2022年 | 21篇 |
2021年 | 38篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 37篇 |
2017年 | 36篇 |
2016年 | 43篇 |
2015年 | 98篇 |
2014年 | 86篇 |
2013年 | 143篇 |
2012年 | 155篇 |
2011年 | 154篇 |
2010年 | 87篇 |
2009年 | 94篇 |
2008年 | 132篇 |
2007年 | 110篇 |
2006年 | 106篇 |
2005年 | 101篇 |
2004年 | 120篇 |
2003年 | 111篇 |
2002年 | 96篇 |
2001年 | 62篇 |
2000年 | 84篇 |
1999年 | 63篇 |
1998年 | 44篇 |
1997年 | 24篇 |
1996年 | 26篇 |
1995年 | 19篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 46篇 |
1991年 | 43篇 |
1990年 | 89篇 |
1989年 | 78篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 29篇 |
1978年 | 21篇 |
1976年 | 17篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 23篇 |
1971年 | 18篇 |
排序方式: 共有3096条查询结果,搜索用时 15 毫秒
51.
Chlamydomonas reinhardtii Dangerad 11–32(90) (−), which exhibits C3 properties, and Anacystis nidulans (Strain no. UTEX 625), which exhibits C4 properties, were used to study the effects of triacontanol on growth, photosynthesis and photorespiration. Photosynthetic rate was measured as CO2 uptake and the O2 inhibition of photosynthesis was used as a measure of photorespiration. Triacontanol dissolved in chloroform and dispersed in Tween-20 and triacontanol colloidally dispersed in an aqueous solution of sodium tallow alkyl sulfate were tested. Chlamydomonas cultures increased significantly in cell number after 4 days, and in chlorophyll content after 3 days of treatment with 2.3 × 10−8 M TRIA in chloroform/Tween-20. In cultures of Anacystis the chlorophyll content became significantly higher 3 days after treatment with 2.3 × 10−9 M TRIA and the cell number was noticeably higher than the controls.
CO2 uptake by triacontanol-treated Chlamydomonas cultures was about the same in both 2 and 21% O2, and the O2 inhibition was significantly reduced as compared with the controls. Photosynthesis in Anacystis was O2-insensitive under the experimental condition used. When Anacystis was treated with triacontanol there was no change in the rate of CO2 uptake and no change in the O2 sensitivity of its CO2 uptake. It appears that triacontanol affects some process which regulated the balance between photosynthesis and photorespiration, but other processes which result in increased growth are probably also affected. 相似文献
CO
52.
53.
Replication of repeated DNA in human cells 总被引:1,自引:0,他引:1
The replication pattern of the repeated sequence families of human DNA has been studied by means of DNA reassociation curves. Early- and late-replicating DNA fractions were obtained from synchronized cultures of KB cells by labeling cells with bromodeoxyuridine (BUdR) early or late in the DNA synthesis period and isolating the BUdR-containing DNA by CsCl density-gradient centrifugation. Highly repeated and moderately repeated sequence classes labeled with either early or late in the DNA synthesis period were also prepared. The effect of the isolated early- or late-replicating BUdR-DNA on the rate of reassociation of the repeated sequences was then tested. Increasing concentrations of early- or late-replicating BUdR-DNA were added to a constant amount of either early- or late-replicating repeated sequences, and the fraction of label in double-stranded DNA was determined. Analysis of the DNA reassociation curves so obtained indicates that some repeated sequence families are replicated throughout the DNA synthesis period whereas others are replicated primarily in the second half. This is true for both the highly-repeated and moderately-repeated sequence classes. 相似文献
54.
55.
56.
From 1964 to 1967, 6,646 monkeys, representing 10 primate species, were examined for Shigella and Salmonella infections upon arrival at the National Center for Primate Biology. Of these animals, 12% were infected with Shigella, and 75% of the Shigella isolates were S. flexneri 4. The incidence of Salmonella infections decreased from 12 to 3% during the period of study. Epidemiological studies of animals in the colony for 90 days or more indicated no seasonal variation in the occurrence of Shigella and Salmonella. Many of the isolates from incoming monkeys as well as from laboratory-conditioned animals were resistant to chloramphenicol, dihydrostreptomycin, and tetracycline. The possible operation of drug-resistance factors in these infections is discussed. 相似文献
57.
Aerobic Bacterial Flora of the Bahama Bank 总被引:1,自引:1,他引:0
May F. McCallum 《Journal of applied microbiology》1970,33(3):533-542
58.
Survival of Aerobic and Anaerobic Bacteria in Chicken Meat During Freeze-Dehydration, Rehydration, and Storage 下载免费PDF全文
Total and anaerobic counts were ascertained on boneless, cooked, cubed, frozen chicken meat. We determined survival of aerobes and anaerobes in the natural flora after the meat was freeze-dehydrated and rehydrated at room temperature for 30 min and at 50, 85, and 100 C for 10 min. Total and anaerobic counts of bacteria in the rehydrated meat were established during storage of samples at 4, 22, and 37 C-until a spoilage odor was detected. Samples were also inoculated with Clostridium sporogenes and were dried and rehydrated at 100 C and stored at 37 C. Approximately 21% of the aerobes and 37% of the anaerobes survived drying and rehydration at room temperature. Many genera of aerobes, anaerobes, and facultative anaerobes survived drying and rehydration at 50 C; only sporeformers survived rehydration at 85 or 100 C. Low-temperature (4 C) storage of rehydrated meat produced ample shelf life (over 20 days), whereas storage at the higher temperature resulted in a shelf life of less than 30 hr. Approximately 81% of the C. sporogenes cells survived rehydration at 100 C and grew to over 10(7) cells within 40 hr. Our study presents additional data for adequate microbiological control in processing of freeze-dehydrated meat. Also, it points out the natural selection for sporeformers at high temperature of rehydration, stressing the need for consumer education in product handling for safety purposes. 相似文献
59.
60.