全文获取类型
收费全文 | 794篇 |
免费 | 59篇 |
国内免费 | 4篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 28篇 |
2014年 | 40篇 |
2013年 | 41篇 |
2012年 | 46篇 |
2011年 | 31篇 |
2010年 | 27篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 35篇 |
2006年 | 26篇 |
2005年 | 28篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 33篇 |
2001年 | 21篇 |
2000年 | 28篇 |
1999年 | 21篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1969年 | 4篇 |
1950年 | 5篇 |
1928年 | 4篇 |
1876年 | 2篇 |
排序方式: 共有857条查询结果,搜索用时 328 毫秒
21.
Effect of acetic acid on astaxanthin production by Phaffia rhodozyma 总被引:10,自引:0,他引:10
Summary Low concentrations of acetic acid decreased the growth rate of and astaxanthin production by Phaffia rhodozyma on glucose, with growth completely inhibited by 2 g acetic acid/l. Using H2SO4 for pH control after sugar depletion caused a decline in the biomass concentration, whereas using acetic acid as titrant resulted in an increase in the biomass with a high astaxanthin content of 1430 g/g cells. An extended culture with a continuous glucose feed failed to maintain a high astaxanthin content. 相似文献
22.
Polystoma testimagna n. sp. is described as a new species of the Polystomatidae, parasitic in the urinary bladder of the striped stream frog Strongylopus f. fasciatus collected in the Vernon Crookes Nature Reserve, Natal, South Africa. Parasite prevalence was found to be 50.0% and 27.7% in two successive years, and the mean intensity was 1.5 and 1.6, respectively. The species occurs together with another Polystoma species in the same water body and within one kilometre from a third species. Aspects of host specificity are discussed and data on the ecology and distribution of the host presented. 相似文献
23.
White rhinoceros range size was ascertained telemetrically in the south-western Kruger National Park. The mean annual range size of territorial males was 9.86 km2 compared to 22.83 km2 for adult females. White rhinoceros females' summer wet season range was larger (21.44 km2 ) than the winter dry season range (11.64 km2 ). It is argued that abundant field-water during the wet season enables animals to range further from permanent water supplies and to utilize larger foraging areas. White rhinoceros have core areas in their individual ranges that usually are situated along riverbanks in the preferred grazing regions. These core areas also include some favourite resting spots on high-lying areas. White rhinoceros range sizes in the south-western Kruger National Park were similar to those of other reserves with comparable white rhinoceros densities. In the Umfolozi Game Reserve, which has a higher white rhinoceros density than the Kruger National Park, the individual ranges are much smaller. 相似文献
24.
S.-S. Yang H.-D. Jang C.-M. Liew J. C. du Preez 《World journal of microbiology & biotechnology》1993,9(2):258-264
The degree of protein enrichment of sweet potato residue by different amylolytic moulds in solid-state cultivation was much greater than that obtained using amylolytic yeasts. The optimum initial moisture content for protein enrichment was about 65% (w/w). Adding nitrogen sources to the culture twice (at the start of the incubation and after 24 h) considerably improved the final protein content. A co-culture of amylolytic mycelial fungi yielded a product with 32% (w/w) crude protein after 4 days' incubation at 30°C. In a column reactor, the highest temperatures reached were 42°C and 40°C and the minimum O2 concentrations were 1.5% and 2.5% of full saturation in the central and bottom layers, respectively. 相似文献
25.
S. G. Kilian B. A. Prior J. C. du Preez 《World journal of microbiology & biotechnology》1993,9(3):357-360
Low-affinity (K
m=67.6±3.2 mM) and high-affinity (K
m=1.9±1.2 mM) D-xylose transport occur in Candida utilis grown, respectively, on D-glucose or D-xylose. Starvation of glucose-grown cells decreases the K
m value (10.5±2.6 mm). The high-affinity system appearing during starvation required protein synthesis and it was inactivated when cells were exposed to glucose, by a process independent of protein synthesis. High-affinity transport was accompanied by transient alkalinization of yeast suspensions, indicating that it is a proton symport, whereas low-affinity transport was not. Both systems, however, were inhibited by metabolic inhibitors and by replacing H2O in the transport assay with D2O, indicating that both may be proton symports. Glucose and acetic acid also inhibited both high-and low-affinity xylose transport.S.G. Kilian, B.A. Prior and J.C. du Preez are with the Department of Microbiology and Biochemistry, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, Republic of South Africa 相似文献
26.
27.
J. C. du Preez M. Immelman J. L. F. Kock S. G. Kilian 《World journal of microbiology & biotechnology》1997,13(1):81-87
The effect of different initial acetic acid concentrations on the growth of and lipid and gamma-linolenic acid (GLA) production
byMucor circinelloides CBS 203.28 was determined in a 14 litre stirred tank reactor operated in a fedbatch, pH-stat mode with acetic acid as carbon
source and pH titrant. Increased acetic acid concentrations in the culture resulted in a significant increase in the crude
oil content of the biomass. By contrast, all the other parameters such as the biomass concentration, GLA and oil yield on
acetic acid, the GLA content of the biomass and oil, the growth rate and volumetric rate of GLA production decreased with
an increase in acetic acid concentration. The best results were obtained with acetic acid at 2 g/1, which gave 39.8 mg GLA/g
biomass and 15.6% GLA in the neutral lipid fraction, amounting to 340 mg GLA/1 culture. A decrease in the glyco- and phospho-lipid
fractions during the cultivation coincided with an increase in the neutral lipid fraction. The GLA content of the biomass
remained within rather narrow limits of 3.5% to 4% of the biomass, irrespective of the oil content of the biomass. The fatty
acid profile was not greatly affected by the acetic acid concentration. The hyphae of the fungus were characterized by the
accumulation of large intracellular oil droplets and some septa delimited the hyphae. 相似文献
28.
E L du Brul 《American journal of physical anthropology》1977,47(2):305-320
Three predominant influences mark the evolution of human head form: big brain, erect bipedalism, modified oral apparatus. Confusing interplay between different adaptive requirements of each feature has made explanation of skull structure extremely difficult in the past. It now seems possible to isolate each influence in early fossil forms. A model of mammalian modes of feeding adaptation is proposed in the form of a “Natural Experiment” for tighter analysis of fossil forms. Two forms of australopithecines are recognized, “gracile” and “robust.” Both had closely similar brains, both had erect bipedalism, but each had different masticatory construction. Separation of the first two similar influences isolates the adaptive differences in oral mechanics. The gracile form had a projecting oral apparatus, distinct canine and zygomatic buttresses, moderate jaw-lever development, jaw joint not unlike most higher primates, large unusual anterior teeth, moderately sized posterior teeth. The robust form had a retruded, greatly deepened oral apparatus, “dished-in” face with fused canine and zygomatic buttresses, powerful jaw-lever development, distinctively different joint construction, remarkably small anterior teeth, enormous posterior teeth. Striking evidence for extraordinary jaw movements emerges from these features in the robust form. This is strongly supported by remarkably close parallels in Ursidae: grizzly bear and giant panda. 相似文献
29.
30.