全文获取类型
收费全文 | 321296篇 |
免费 | 37550篇 |
国内免费 | 275篇 |
专业分类
359121篇 |
出版年
2018年 | 2842篇 |
2016年 | 3840篇 |
2015年 | 5172篇 |
2014年 | 6107篇 |
2013年 | 8776篇 |
2012年 | 9739篇 |
2011年 | 9913篇 |
2010年 | 6721篇 |
2009年 | 5984篇 |
2008年 | 8666篇 |
2007年 | 9082篇 |
2006年 | 8484篇 |
2005年 | 8166篇 |
2004年 | 8247篇 |
2003年 | 7973篇 |
2002年 | 7886篇 |
2001年 | 14344篇 |
2000年 | 14374篇 |
1999年 | 11522篇 |
1998年 | 4050篇 |
1997年 | 4148篇 |
1996年 | 3939篇 |
1995年 | 3806篇 |
1994年 | 3810篇 |
1993年 | 3698篇 |
1992年 | 9843篇 |
1991年 | 9424篇 |
1990年 | 9243篇 |
1989年 | 8970篇 |
1988年 | 8373篇 |
1987年 | 8013篇 |
1986年 | 7239篇 |
1985年 | 7343篇 |
1984年 | 6062篇 |
1983年 | 5320篇 |
1982年 | 4190篇 |
1981年 | 3718篇 |
1980年 | 3531篇 |
1979年 | 6114篇 |
1978年 | 4578篇 |
1977年 | 4291篇 |
1976年 | 3984篇 |
1975年 | 4311篇 |
1974年 | 4664篇 |
1973年 | 4730篇 |
1972年 | 4365篇 |
1971年 | 4073篇 |
1970年 | 3445篇 |
1969年 | 3346篇 |
1968年 | 2971篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
282.
J. Dierschke T. Krüger F. Hüttmann F. Bairlein Kerstin Müller G. Scheiffarth H. -W. Helb W. Irsch W. Lantermann B. Haubitz W. Winkel und J. Haffer 《Journal of Ornithology》2003,144(4):484-498
Ohne Zusammenfassung 相似文献
283.
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
284.
285.
286.
287.
In order to adapt to the fluctuations in soil salinity/osmolarity the bacteria of the genusAzospirillum accumulate compatible solutes such as glutamate, proline, glycine betaine, trehalose, etc. Proline seems to play a major
role in osmoadaptation. With increase in osmotic stress the dominant osmolyte inA. brasilense shifts from glutamate to proline. Accumulation of proline inA. brasilense occurs by both uptake and synthesis. At higher osmolarityA. brasilense Sp7 accumulates high intracellular concentration of glycine betaine which is taken up via a high affinity glycine betaine
transport system. A salinity stress induced, periplasmically located, glycine betaine binding protein (GBBP) of ca. 32 kDa
size is involved in glycine betaine uptake inA. brasilense Sp7. Although a similar protein is also present inA. brasilense Cd it does not help in osmoprotection. It is not known ifA. brasilense Cd can also accumulate glycine betaine under salinity stress and if the GBBP-like protein plays any role in glycine betaine
uptake. This strain, under salt stress, seems to have inadequate levels of ATP to support growth and glycine betaine uptake
simultaneously. ExceptA. halopraeferens, all other species ofAzospirillum lack the ability to convert choline into glycine betaine. Mobilization of thebet ABT genes ofE. coli intoA. brasilense enables it to use choline for osmoprotection. Recently, aproU-like locus fromA. lipoferum showing physical homology to theproU gene region ofE. coli has been cloned. Replacement of this locus, after inactivation by the insertion of kanamycin resistance gene cassette, inA. lipoferum genome results in the recovery of mutants which fail to use glycine betaine as osmoprotectant. 相似文献
288.
Spontaneous fusion of phosphatidylcholine small unilamellar vesicles in the fluid phase 总被引:2,自引:0,他引:2
Using a high-sensitivity differential scanning microcalorimeter capable of performing cooling scans, we have examined the phase behavior of small unilamellar vesicles (SUV) as a function of time of storage above their order-disorder phase transition. Vesicles composed of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) were examined. Cooling scans on fresh (5-7-h postsonication) samples revealed broad, relatively simple heat capacity peaks (peak temperatures: 19.9 degrees C for DMPC, 37.8 degrees C for DPPC) free of high-temperature spikes or shoulders. Subsequent heating scans displayed a sharp peak characteristic of previously described fusion products formed below the phase transition. SUV samples stored for 1 or more days above their phase transition displayed a moderately broad, high-temperature shoulder (23.8 degrees C for DMPC and 40.2 degrees C for DPPC) in the cooling profile. For DMPC, the enthalpy associated with this peak increased in a first-order fashion with time. Hydrolysis products were not detected until 12-20 days of storage. Both the rate and extent of shoulder appearance increased with temperature (k = 0.0017 h-1, fraction of total enthalpy = 0.1 at 36 degrees C; k = 0.0037 h-1, fraction = 0.2 at 42 degrees C). Freeze-fracture electron micrographs confirmed that an intermediate-sized vesicle population (diameters 400-500 A) appeared in SUV samples stored above their phase transition. Also, the trapped volume of DMPC SUV increased from 0.26 microL/mumol after 17 h of storage to 0.54 microL/mumol after storage for 16 days at 36 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
289.
290.