全文获取类型
收费全文 | 208126篇 |
免费 | 17775篇 |
国内免费 | 75篇 |
出版年
2018年 | 1974篇 |
2016年 | 2472篇 |
2015年 | 2427篇 |
2014年 | 3305篇 |
2013年 | 4811篇 |
2012年 | 5379篇 |
2011年 | 5938篇 |
2010年 | 4155篇 |
2009年 | 3728篇 |
2008年 | 5388篇 |
2007年 | 5706篇 |
2006年 | 5387篇 |
2005年 | 5112篇 |
2004年 | 5265篇 |
2003年 | 5173篇 |
2002年 | 5153篇 |
2001年 | 10048篇 |
2000年 | 10211篇 |
1999年 | 7610篇 |
1998年 | 2429篇 |
1997年 | 2468篇 |
1996年 | 2232篇 |
1995年 | 2062篇 |
1994年 | 1978篇 |
1993年 | 2069篇 |
1992年 | 6203篇 |
1991年 | 6370篇 |
1990年 | 6126篇 |
1989年 | 6070篇 |
1988年 | 5613篇 |
1987年 | 5319篇 |
1986年 | 4794篇 |
1985年 | 4928篇 |
1984年 | 3959篇 |
1983年 | 3380篇 |
1982年 | 2270篇 |
1981年 | 2048篇 |
1980年 | 2031篇 |
1979年 | 3740篇 |
1978年 | 2963篇 |
1977年 | 2666篇 |
1976年 | 2396篇 |
1975年 | 2972篇 |
1974年 | 3336篇 |
1973年 | 3199篇 |
1972年 | 3031篇 |
1971年 | 2709篇 |
1970年 | 2363篇 |
1969年 | 2253篇 |
1968年 | 2123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
R.J. Ulvik I. Romslo F. Roland R.R. Crichton 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,677(1):50-56
Mitochondria mobilize iron from ferritin by a mechanism that depends on external FMN. With rat liver mitochondria, the rate of mobilization of iron is higher from rat liver ferritin than from horse spleen ferritin. With horse liver mitochondria, the rate of iron mobilization is higher from horse spleen ferritin than from rat liver ferritin. The results are explained by a higher affinity between mitochondria and ferritins of the same species. The mobilization of iron increases with the iron content of the ferritin and then levels off. A maximum is reached with ferritins containing about 1 200 iron atoms per molecule. The results represent further evidence that ferritin may function as a direct iron donor to the mitochondria. 相似文献
122.
The dynamics of fish populations in two African rivers are being investigated with a view to developing fishery management models for tropical non-floodplain rivers. Preliminary work was carried out in the Rufiji River, East Africa, to establish growth and mortality rates along with L ∞ and K for six species in a river where fishing mortality is zero. These parameters, derived from scale-reading and length frequency analysis, also allowed the development of phased management plans for the fishery resulting from impoundment.
A subsequent investigation has begun on a West African river, the Taia in Sierra Leone, to pursue observations over four seasons, two of which are now complete. A systematic daily sampling programme is being carried out of the whole community, to accumulate similar but more extensive data to those obtained previously. In the Taia, however, fishing mortality must also be estimated from catch surveys, and analysis is carried out using the recently developed ELEFAN programs which can be compared with results obtained by other methods such as scale-reading. 相似文献
A subsequent investigation has begun on a West African river, the Taia in Sierra Leone, to pursue observations over four seasons, two of which are now complete. A systematic daily sampling programme is being carried out of the whole community, to accumulate similar but more extensive data to those obtained previously. In the Taia, however, fishing mortality must also be estimated from catch surveys, and analysis is carried out using the recently developed ELEFAN programs which can be compared with results obtained by other methods such as scale-reading. 相似文献
123.
Z I Lebedeva E A Kabanova T T Berezov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(12):696-698
The effect of substrate analogues on glutamin-(asparagin-)ase from Pseudomonas aurantiaca-548 has been studied. The enzyme was demonstrated to be highly sensitive to the the action of 6-diazo-5-oxo-L-norleucine and azaserine. L-isomers of glutamine, aspartate, glutamate and several other substrate analogues with free alpha-amino groups protected the enzyme against the inhibitory DON effect. Thus, thorough preliminary selection of appropriate inhibitors, their dosage and treatment duration is needed for the recommendation of combined enzyme-inhibitor application in anti-tumour chemotherapy. 相似文献
124.
E. G. Korvin-Pavlovskaya I. V. Neklyudova L. V. Beloussov 《Russian Journal of Developmental Biology》2006,37(2):77-84
Circumferential and radial components of the yolk cell surface movements were measured in the loach embryos at the late blastula stage within 40–50 min after puncture or indentation by an obliquely directed glass rod. The yolk cell surface was preliminarily marked by coal particles. It was shown that even closely located regions of the surface differed markedly in the rate and direction of their movements. In the vicinity of puncture, the yolk cell surface at first contracted in both circumferential and radial directions and then widened, but did not reach the initial values. In more remote areas, this surface continued to contract in the circumferential direction, but was extended in the radial direction. The degree of its contraction along different radii was unequal. The reaction to oblique indentation was anisotropic: the closest area of the yolk cell surface, located along the direction of indentation, contracted in both circumferential and radial directions and formed a fold “leaking” onto the rod, while the opposite area contracted in the circumferential direction, but extended in the radial direction. A conclusion was drawn that the yolk cell surface is a multivariant mechanosensitive system. Its active responses to mechanical influences obey the same patterns as multicellular embryonic tissues. 相似文献
125.
Monitoring signal transduction in cancer: cDNA microarray for semiquantitative analysis. 总被引:1,自引:0,他引:1
H B Hsieh R A Lersch D E Callahan S Hayward M Wong O H Clark H U Weier 《The journal of histochemistry and cytochemistry》2001,49(8):1057-1058
This study targeted the development of a novel microarray tool to allow rapid determination of the expression levels of 58 different tyrosine kinase (tk) genes in small tumor samples. The goals were to define a reference probe for multi-sample comparison and to investigate the variability and reproducibility of the image acquisition and RT-PCR procedures. The small number of tk genes on our arrays enabled us to define a reference probe by artificially mixing all genes on the arrays. Such a probe provided contrast reference for comparative hybridization of control and sample DNA and enabled cross-comparison of more than two samples against one another. Comparison of signals generated from multiple scanning eliminated the concern of photo bleaching and scanner intrinsic noise. Tests performed with breast, thyroid, and prostate cancer samples yielded distinctive patterns and suggest the feasibility of our approach. Repeated experiments indicated reproducibility of such arrays. Up- or downregulated genes identified by this rapid screening are now being investigated with techniques such as in situ hybridization. 相似文献
126.
G. I. Novik N. I. Astapovich Zh. N. Bogdanovskaya N. E. Ryabaya 《Applied Biochemistry and Microbiology》2000,36(1):90-95
Production of Enterobifidin includes the stages of preparation of culture media, reparation of lyophilizedBifidobacterium adolescentis MS-42 culture, preparation of starters, cultivation of bacteria in fermenters, biomass conservation, and its biological control.
The preparation contains physiologically active bifidobacterium cells with high activities of growth(μ = 0.7 h−1,g = 1.0 h) and acid formation (titratable acidity is ∼120–140°T; acetate concentration, 0.50–0.75%; and lactate concentration,
0.33–0.50%). The antagonistic activity of these bacteria towardsEscherichia coli 08,E. coli 086,E. coli 015,E. coli 0115, andE. coli 0101 amounts to 98.2; toProteus vulgaris 102, to 87.2; andStaphylococcus aureus 209p, to 83.2%. The bifidobacteria (with a titer of ∼109 CFU/ml) remained viable for two to five months. 相似文献
127.
Bugreev D. V. Sinitsyna O. I. Buneva V. N. Nevinsky G. A. 《Russian Journal of Bioorganic Chemistry》2003,29(3):249-261
Data on the interaction of DNA type I topoisomerases from the murine and human placenta cells with specific and nonspecific oligonucleotides of various structures and lengths are summarized. The relative contributions of various contacts between the enzymes and DNA that have previously been detected by X-ray analysis to the total affinity of the topoisomerases for DNA substrates are estimated. Factors that determine the differences in the enzyme interactions with specific and nonspecific single- and double-stranded DNAs are revealed. The results of the X-ray analysis of human DNA topoisomerase I are interpreted taking into account data on the comprehensive thermodynamic and kinetic analysis of the enzyme interaction with the specific and nonspecific DNAs. 相似文献
128.
129.
The present study was undertaken to comparatively investigate the attachment capacities of Azospirillum brasilenseSp245 and its lipopolysaccharide-defective Omegon-Km mutants KM018 and KM252, as well as their activities with respect to the alteration of the morphology of wheat seedling root hairs. The adsorption dynamics of the parent Sp245 and mutant KM252 strains of azospirilla on the seedling roots of the soft spring wheat cv. Saratovskaya 29 were similar; however, the attachment capacity of the mutant KM252 was lower than that of the parent strain throughout the incubation period (15 min to 48 h). The mutation led to a considerable decrease in the hydrophobicity of the Azospirillumcell surface. The lipopolysaccharides extracted from the outer membrane of A. brasilenseSp245 and mutant cells with hot phenol and purified by chromatographic methods were found to induce the deformation of the wheat seedling root hairs, the lipopolysaccharide of the parent strain being the most active in this respect. The role of the carbohydrate moiety of lipopolysaccharides in the interaction of Azospirillumcells with plants is discussed. 相似文献
130.