全文获取类型
收费全文 | 181309篇 |
免费 | 14334篇 |
国内免费 | 50篇 |
专业分类
195693篇 |
出版年
2018年 | 1807篇 |
2017年 | 1756篇 |
2016年 | 2248篇 |
2015年 | 2137篇 |
2014年 | 2936篇 |
2013年 | 4191篇 |
2012年 | 4798篇 |
2011年 | 5307篇 |
2010年 | 3715篇 |
2009年 | 3351篇 |
2008年 | 4852篇 |
2007年 | 5122篇 |
2006年 | 4822篇 |
2005年 | 4538篇 |
2004年 | 4688篇 |
2003年 | 4594篇 |
2002年 | 4574篇 |
2001年 | 8385篇 |
2000年 | 8581篇 |
1999年 | 6312篇 |
1998年 | 1990篇 |
1997年 | 2036篇 |
1996年 | 1802篇 |
1995年 | 1674篇 |
1992年 | 5198篇 |
1991年 | 5362篇 |
1990年 | 5138篇 |
1989年 | 5116篇 |
1988年 | 4732篇 |
1987年 | 4485篇 |
1986年 | 4076篇 |
1985年 | 4234篇 |
1984年 | 3408篇 |
1983年 | 2912篇 |
1982年 | 1930篇 |
1981年 | 1728篇 |
1980年 | 1718篇 |
1979年 | 3211篇 |
1978年 | 2546篇 |
1977年 | 2278篇 |
1976年 | 2081篇 |
1975年 | 2546篇 |
1974年 | 2884篇 |
1973年 | 2802篇 |
1972年 | 2651篇 |
1971年 | 2415篇 |
1970年 | 2116篇 |
1969年 | 2022篇 |
1968年 | 1906篇 |
1967年 | 1743篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
O. V. Yagodina E. B. Nikol’skaya I. Y. Shemarova A. E. Khovanskikh 《Journal of Evolutionary Biochemistry and Physiology》2000,36(3):244-248
A comparison has been performed of catalytic properties of unicellular microorganism amine oxidases (AO) from two new enzyme
sources, the bacteriumMethanosarcina barkeri and the infusoriaTetrahymena pyriformis. It was shown that the both studied AO deaminate tyramine, serotonin, and benzylamine, but do not deaminate histamine. The
AO fromMethanosarcina barkeri catalyzes deamination of all three substrates at an identical rate, while the rate of tyramine deamination under effect of
AO fromTetrahymena pyriformis is one order higher than the rate of serotonin deamination, and about two orders higher than the rate of benzylamine deamination.
Based on the data of the substrate-inhibitor analysis, a suggestion was made about the existence of one center for the substrate
binding in the AO of the studied bacterium, while several centers in the AO of the studied infusoria. 相似文献
212.
J De Coninck I Verdier-Denantes F Duyme S Bouquelet V Dumortier 《Journal of industrial microbiology & biotechnology》2000,25(1):58-61
Oxygen concentrations stimulated growth (maximum number of cells) and protease secretion by Tetrahymena thermophila. Agitation and aeration conditions for growth and protease secretion were optimised by a central composite design. The best
optimised combination was a stirrer speed of 338 rpm and an aeration of 1 vvm. Journal of Industrial Microbiology & Biotechnology (2000) 25, 58–61.
Received 24 September 1999/ Accepted in revised form 06 March 2000 相似文献
213.
Heat treatment results in a loss of transgene-encoded activities in several tobacco lines. 总被引:1,自引:0,他引:1 下载免费PDF全文
Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C. 相似文献
214.
S. P. Kharitonov D. E. Nowak A. I. Nowak N. A. Egorova S. A. Korkina D. V. Osipov O. V. Natal’skaya 《Biology Bulletin》2009,36(5):469-478
Red-breasted goose colonies have been studied near Medusa Bay (73°21′N, 80°32′E), on the northwestern Taimyr Peninsula, and
along the Agapa River (70°11′N, 86°15′E) down to its mouth (71°26′N, 89° 13′E), in the central Taimyr Peninsula. Red-breasted
geese nesting near peregrine falcons are protected by the falcons from arctic foxes; however, they are sometimes attacked
by the falcons themselves. In the colonies near peregrine falcon nests, the vast majority of goose nests were situated no
farther than 100 m from the falcon nest. When food is abundant, falcons protect a larger area around their nest. The distance
between the falcon nest and the surrounding goose nests is inversely related to the falcon’s activity. In years of higher
falcon activity, falcons prevent red-breasted geese from nesting as close to their nest as in years of lower falcon activity.
Additional stimuli are required for red-breasted geese to form colonies near rough-legged buzzard nests. The distance between
snowy owl nests and red-breasted goose nests was smaller when arctic foxes were abundant than when they were scarce. 相似文献
215.
Seasonal dynamics and demographic structure was studied in 15 dominant ground beetle species in the mountain taiga and mountain forest-steppe belts of the Eastern Sayan (Okinskoe Plateau). Life cycles of the dominant ground beetle species were classified by developmental time, seasonal dynamics, and intrapopulation groups with different reproduction timing. The strategies of carabid life cycles adapted to severe mountain conditions of the Eastern Sayan were revealed. 相似文献
216.
S E Bresler E F Davidenkova K K Gurgenidze L A Noskin E I Shvarts 《Biulleten' eksperimental'no? biologii i meditsiny》1986,101(4):414-415
Elastoviscosometric parameters of DNA from normal subjects of different age and patients with Down syndrome were assessed. Characteristics of DNA isolated from lymphocytes trisomic for chromosome 21 were studied to compare normal and pathological rates of ageing. Increased elastoviscosity was observed in normal subjects above 60. Similar changes in this parameter were noted in aberrant lymphocytes isolated from patients above 10. The established dependence of elastoviscosity on ethidium bromide concentration led to the assumption that an increase in hydrodynamic DNA volume in human leukocytes during ageing was due to accumulation of spontaneous irreparable DNA lesions. 相似文献
217.
The survival of Salmonella typhimurium LT2 and Escherichia coli was studied in situ in a tropical rain forest watershed using membrane diffusion chambers. Numbers were determined by acridine orange staining and a Coulter counter. Population activity was determined by microautoradiography, cell respiration, frequency of dividing cells, and by nucleic acid composition. Numbers of Salm. typhimurium and E. coli decreased less than 1 log unit after 105 h as measured by direct count methods. Activity as measured by respiration, acridine orange activity, frequency of dividing cells, and microautoradiography indicated that both bacteria remained moderately active during the entire study. After 24 h, E. coli was more active than Salm. typhimurium , as measured by nucleic acid composition, and frequency of dividing cells. Both E. coli and Salm. typhimurium survived and remained active in this tropical rain forest watershed for more than 5 d, suggesting that Salm. typhimurium may be of prolonged public health significance once it is introduced into tropical surface waters. As E. coli was active and survived for a long time in this natural environment, it would seem to be unsuitable as an indicator of recent faecal contamination in tropical waters. 相似文献
218.
219.
A Sólyom S Tóth I Holczinger J Vajda Z Tóth R Kálmánchey 《Applied neurophysiology》1985,48(1-6):222-225
Four thalamic and cortical recordings were carried out in 5 patients. The thalamic-evoked potentials were typical and revealed a triphasic complex, but their latencies showed a relatively high standard deviation. They could be divided into two groups according to their latencies, both of which had low SD. These data suggested that there could be two types of latency of thalamic SEP, because the 4 patients' body sizes were very similar. More detailed surface, cortical and depth recordings are needed to resolve these questions. 相似文献
220.