全文获取类型
收费全文 | 2278篇 |
免费 | 218篇 |
专业分类
2496篇 |
出版年
2021年 | 33篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 33篇 |
2017年 | 29篇 |
2016年 | 48篇 |
2015年 | 94篇 |
2014年 | 84篇 |
2013年 | 113篇 |
2012年 | 117篇 |
2011年 | 139篇 |
2010年 | 89篇 |
2009年 | 84篇 |
2008年 | 124篇 |
2007年 | 117篇 |
2006年 | 94篇 |
2005年 | 104篇 |
2004年 | 108篇 |
2003年 | 108篇 |
2002年 | 59篇 |
2001年 | 42篇 |
2000年 | 42篇 |
1999年 | 43篇 |
1998年 | 40篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 39篇 |
1992年 | 25篇 |
1991年 | 32篇 |
1990年 | 34篇 |
1989年 | 21篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 36篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 26篇 |
1982年 | 24篇 |
1981年 | 26篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1975年 | 14篇 |
1974年 | 18篇 |
1973年 | 21篇 |
1972年 | 17篇 |
1970年 | 15篇 |
排序方式: 共有2496条查询结果,搜索用时 15 毫秒
21.
22.
Rudge Simon A. Hughes Phillip J. Brown Graham R. Michell Robert H. Kirk Christopher J. 《Molecular and cellular biochemistry》1995,149(1):161-174
Molecular and Cellular Biochemistry - The testis is a complex organ in which local control is achieved by signalling between its constituent cells. Herein we describe the responses of cultured rat... 相似文献
23.
24.
25.
Vasopressin, angiotensin II and the catecholamines decreased ketogenesis from oleate but increased ketogenesis from butyrate in hepatocytes from fed rats. The hormones increase CO2 production from both oleate and butyrate. It is suggested that whereas the mitochondrial uptake of butyrate is linked to its rate of oxidation, that of oleate is independent of its intramitochondrial metabolism, and consequently the oxidation of oleate to CO2 occurs at the expense of ketogenesis. Effects of the hormones on ketogenesis from oleate or butyrate were not observed after pre-treatment of the hepatocytes with dibutyryl cyclic AMP for 1 hour. The insensitivity of ketogenesis to the hormones after this treatment (which mimics the effects of acute carbohydrate deprivation in vivo) questions the physiological significance of hormonal regulation of ketogenesis other than at the onset of starvation. 相似文献
26.
Population genetics of the vitamin D binding protein (GC) subtypes in the Asian-Pacific area: Description of new alleles at the GC locus 总被引:2,自引:1,他引:1
Isoelectric focussing (IEF) in thin layer polyacrylamide gels pH range 4-6.5 has been used to analyse the GC phenotypes of 4233 individuals from 28 different population groups in the Asian, Pacific, and Australian area. Because this technique reveals subtypes of the common GC*1 allele, there is almost a two-fold increase in the mean heterozygosity at the GC locus using IEF compared with conventional electrophoresis. The highest frequency (above 50%) of the GC*1S allele was encountered in Indian populations, reflecting genetic affinities with Europeans. By comparison, east and south east Asians are unique offing maximum values of the GC*1F allele (50%). With the exception of a few Pacific populations which show similar frequencies to east Asians, all other groups in the Pacific area, including Australia, have values of GC*1F similar to GC*1S ranging from 27% to 40%. The GC*2 frequency in most populations varies from 20% to 30%. However, some Polynesian groups have values up to 40% and Australian Aborigines less than 10%. Among other alleles, GC*1A1 is found to be widely distributed among Australian Aborigines and Melanesians and occurs sporadically in Polynesians, Micronesians, and in the Lesser Sunda Islands. Four new alleles, GC*1C24, GC*1C35 Aborigine, GC*1A21, and GC*1A22 are described. The gene frequency data at the GC locus has been used to calculate Nei genetic distances between the populations studied. 相似文献
27.
Kirk Mark D. Glantz Raymon M. 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1981,141(2):183-196
Journal of Comparative Physiology A - It is concluded that burst formation is endogenous to the motoneuron andnot strongly dependent on patterned presynaptic input. 相似文献
28.
The most common repeated nucleotide sequences of the highly repetitive satellite HS-α fraction from kangaroo rat Dipodomys ordii was determined using ribosubstitution methods. This sequence was α nucleotides long and represented about 25% of the total HS-α satellite DNA, while the remaining DNA was composed of sequence variants related to the most common sequence. The sequences of the commonest of these variants are reported. Furthermore, the most common repeated sequence was identical to that reported for the α satellite of guinea pig Cavia porcellus. The α satellites of guinea pig, Cavia porcellus, pocket gopher, Thomomys bottae and antelope ground squirrel, Ammospermophilus leucurus, are shown to have sequences in common with the kangaroo rat. This implies that the simplest repeated sequences of mammalian satellite DNAs may persist over much longer evolutionary times than previously thought.Attempts to explain the very rapid quantitative changes in satellites whose sequence is strongly conserved have led us to consider that they might have a role in sympatric speciation. Among the novel features of the model presented is that fluctuations in satellites could be due to “speciation genes.” Such genes would confer a strong selective advantage in certain situations, and could explain the many puzzling instances in which large numbers of new related species have appeared over a short evolutionary span. 相似文献
29.
Carrier-mediated Uptake of Arginine and Urea by Volvox carteri f. nagariensis 总被引:5,自引:1,他引:4 下载免费PDF全文
Volvox carteri f. nagariensis takes up arginine via a high affinity, highly specific carrier, whereas carriers for neutral and acidic amino acids cannot be detected (even in nitrogen-starved cultures). Exogenous arginine is accumulated against a steep concentration gradient and is incorporated into protein with high efficiency, but it is not catabolized to any significant extent and will not serve as a nitrogen source adequate to support growth. Urea is also taken up by a saturable carrier, but several lines of evidence indicate that the arginine and urea carriers are distinct and different. Preexposure to arginine suppresses arginine uptake while stimulating urea uptake. The Ki values observed for reciprocal, competitive inhibition of uptake by arginine and urea are orders of magnitude different from the respective Km values for uptake. The two uptake systems show entirely different patterns of sensitivity to inhibition by structural analogs. Finally, the Vmax values for arginine and urea uptake fluctuate independently (but in a regular pattern) during the asexual life cycle. The fluctuations of urea uptake activity are of considerable magnitude and appear to be linked to key phases of the developmental program. 相似文献
30.