首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4881篇
  免费   0篇
  4881篇
  2016年   2篇
  2013年   1篇
  2012年   191篇
  2011年   349篇
  2010年   146篇
  2009年   2篇
  2008年   304篇
  2007年   421篇
  2006年   447篇
  2005年   433篇
  2004年   451篇
  2003年   485篇
  2002年   477篇
  2001年   302篇
  2000年   514篇
  1999年   266篇
  1998年   35篇
  1997年   15篇
  1996年   2篇
  1994年   1篇
  1992年   3篇
  1991年   1篇
  1990年   7篇
  1989年   5篇
  1988年   7篇
  1987年   6篇
  1986年   2篇
  1985年   1篇
  1983年   1篇
  1970年   2篇
  1969年   1篇
  1967年   1篇
排序方式: 共有4881条查询结果,搜索用时 15 毫秒
11.
The methods of molecular dynamics and correlation functions of coordinates were applied to investigate molecular oscillations in water solution at a variation of the amplitude of fluctuations. It was established, that the amplitude of fluctuation exceeds the threshold value (in water of the order of 0.3-0.45 A), of the force of friction sharply increases, and the vibration mode changes to the mode of limited diffusion. The consistency of the results with the theory of M?ssbauer effect and the model of Brownian oscillator for conformational mobility in biopolymers is discussed.  相似文献   
12.
Variability of egg weight, egg yolk content, neonatal growth rate and relationships of these parameters were studied in meat-type chicks. As it had been established the level of variability in neonatal growth traits was greater than variability of the egg morphology parameters. Egg weight had stronger influence on the chicks' neonatal growth rate than egg yolk content did. Low egg size was associated with limited neonatal growth rate variability, declined chick weight at hatching and increased relative growth rate throughout four days post hatch. Comparison of egg morphological parameters in two species having the same female definitive body weight--meat-type domestic fowl (precocial type) and brown pelican (altricial type) has shown, that, in contrary to predicted on the basis of avian developmental typology, egg weight to female body ratio was greater in brown pelican, egg yolk content was equal in both species.  相似文献   
13.
According to Ch. Darwin's evolutionary theory, evolutionary progress (interpreted as morpho-physiological progress or arogenesis in recent terminology) is one of logical results of natural selection. At the same time, natural selection does not hold any factors especially promoting evolutionary progress. Darwin emphasized that the pattern of evolutionary changes depends on organism nature more than on the pattern of environment changes. Arogenesis specificity is determined by organization of rigorous biological systems - integral organisms. Onward progressive development is determined by fundamental features of living organisms: metabolism and homeostasis. The concept of social Darwinism differs fundamentally from Darwin's ideas about the most important role of social instincts in progress of mankind. Competition and selection play secondary role in socio-cultural progress of human society.  相似文献   
14.
15.
Zygotic and apozygotic progenies of sugar beet exhibit high phenotypic variation with respect to cytoplasmic male sterility (CMS). There are progenies with completely sterile, semisterile, semifertile, and fertile pollen. The proportions of semifertile and fertile plants in zygotic and apozygotic progenies varied from zero to 28% and from zero to 17.8%, respectively. Comparison of the phenotypic distributions in zygotic and apozygotic progenies did not reveal significant differences in the CMS expression, although the latter is determined by the maternal S-plasmotype and both maternal and paternal (pollinator) genotypes in zygotic progenies and only by the maternal S-plasmotype and genotype in apozygotic progenies. It has been hypothesized that the instability of the CMS expression in apozygotic progenies is determined by epigenetic variation in the activities of the genes that control the maintenance of the pollen-grain sterility. Inactivated dominant alleles Rf1(0) and Rf2(0) in homozygous state may function as sterility maintenance genes, whereas activation of these alleles during ontogeny results in a partial or complete restoration of pollen-grain fertility. It was demonstrated that pollen fertility of mother plants with S cytoplasm did not affect the CMS expression in two sib progenies. Conversely, in two other progenies, the proportion of fertile plants was significantly higher in the sib progenies of mother plants with fertile pollen and S cytoplasm (inheritance of epigenetic variation).  相似文献   
16.
Population-genetic study of indigenous populations representing three ethnic Chuvash group: highland (Cheboksarsk and Morgaush district), lowland (Kanash district) and mid-lowland (Marposad district). Eight polymorphic DNA loci of the nuclear genome (VNTR/PAH, STR/PAH, VNTR/ApoB, VNTR/DAT1, APF, VNTR/eNOS, IVS6aGATT, and KM.19/PstI) were examined in the population of each district. For each of the four population, we estimated the allele and genotype frequency distributions at each polymorphic system, heterozygosities HS and between-population differences FST. In the combined Chuvash sample, HS = 0.464 and FST = 0.006. Loci VNTR(DAT) and VNTR(ApoB) showed highest between-population differentiation (0.009 < or = FST < or = 0.012), and loci IVS6aGATT, APF, VNTR/eNOS, and D7S23 (KM.19), lowest differentiation (0.001 < or = FST < or = 0.003). Analysis of genetic distances revealed somewhat higher genetic similarity between the Cheboksarsk and Morgaush populations belonging to the highland Chuvash group, whereas the highland Chuvash population from the Marposad district, which belong to the mid-lowland group, was more distant from the former populations.  相似文献   
17.
The fluorescence of the natural photosynthetic pigments beta-carotene (beta-K) and chlorophyll a (Chl) and their mixtures with bovine serum albumin (BSA) in different molar ratios has been studied. An increase in the fluorescence intensity in a pigment mixture-BSA complex was found. The highest possible (four- to sixfold) increase in the fluorescence intensity compared with fluorescence intensity of one-pigment BSA complexes BSA (beta-K) and BSA (Chl) was achieved at the ratio 11-27% beta-K/89-73% Chl in the BSA complex. A considerable overlap of fluorescence spectra of BSA (Chl) complex (lambda(max) at 690 nm) and BSA (beta-K) complex (lambda(max) at 684 nm) was observed.  相似文献   
18.
19.
The effect of N-palmitoylethanolamine (NPE, 10(-5) M) on the lipid peroxidation (LPO) processes, phospholipid and fatty acid content in the rat liver at perfusion and ischemia during the liver preservation was estimated. As early as at the 5th min of perfusion by cooled conserving solution "Eurocollins", LPO activation was determined. Simultaneously the content of lysophosphatidylcholine (LPC) and phosphatidylserine increased, the total cholesterol level decreased. The redistribution of saturated and unsaturated fatty acids quantity was detected. The addition of NPE into "Eurocollins" solution reduced the accumulation of malonedialdehyde and LPC, modified the fatty acids content. These effects, evidently, formed the basis of the protective action of NPE on the hepatic tissues under anoxia.  相似文献   
20.
Four population samples of Pacific capelin Mallotus villosus catervarius (Pennant, 1784) from geographically distant localities in the Sea of Okhotsk, Tauy Bay and the eastern coast of the Sakhalin Island, were examined using PCR-RFLP analysis of three mitochondrial DNA regions (A8/A6/COIII/ND3, ND3/ND4L/ND4, and ND5/ND6). The nucleotide divergence of mtDNA sequences among the samples, as well as the analysis of geographic heterogeneity of the haplotype frequencies and quantitative estimation of genetic differentiation performed by means of AMOVA, showed that the samples examined belonged to one panmictic population. Genealogic analysis of the mtDNA variation structure was carried out. It was demonstrated that the high level of haplotype diversity (0.9639 +/- 0.00015) along with the low level of nucleotide diversity (0.003818 +/- 0.0000003) pointed to the exponential rate of population growth of the capelin from the Sea of Okhotsk, which rather recently in its evolutionary history faced the bottleneck effect.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号