全文获取类型
收费全文 | 44504篇 |
免费 | 16800篇 |
国内免费 | 852篇 |
专业分类
62156篇 |
出版年
2024年 | 36篇 |
2023年 | 222篇 |
2022年 | 479篇 |
2021年 | 1054篇 |
2020年 | 2574篇 |
2019年 | 4163篇 |
2018年 | 4300篇 |
2017年 | 4534篇 |
2016年 | 4748篇 |
2015年 | 5050篇 |
2014年 | 4820篇 |
2013年 | 5452篇 |
2012年 | 3508篇 |
2011年 | 3121篇 |
2010年 | 4004篇 |
2009年 | 2715篇 |
2008年 | 1796篇 |
2007年 | 1307篇 |
2006年 | 1258篇 |
2005年 | 1138篇 |
2004年 | 1060篇 |
2003年 | 929篇 |
2002年 | 890篇 |
2001年 | 485篇 |
2000年 | 347篇 |
1999年 | 326篇 |
1998年 | 208篇 |
1997年 | 168篇 |
1996年 | 132篇 |
1995年 | 118篇 |
1994年 | 96篇 |
1993年 | 109篇 |
1992年 | 99篇 |
1991年 | 105篇 |
1990年 | 91篇 |
1989年 | 63篇 |
1988年 | 62篇 |
1987年 | 58篇 |
1986年 | 49篇 |
1985年 | 75篇 |
1984年 | 53篇 |
1983年 | 31篇 |
1982年 | 31篇 |
1981年 | 38篇 |
1980年 | 34篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 27篇 |
1976年 | 22篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
C. Benito M. P. Romero N. Henriques-Gil F. Llorente A. M. Figueiras 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(5-6):926-931
The variation in recombination frequency (rf) is important to plant breeders since their major objective is to obtain favorable recombinants of linked genes. One source of variation in rf is sex. Sex differences for recombination frequencies were studied in four of the seven chromosomes of Secale cereale L. cv Ailés using isozyme and storage protein loci and were determined on the basis of reciprocal crosses between heterozygous plants of cv. Ailés and homozygous plants of the inbred line Riodeva. The differences were found to be strongly segmentspecific. In some cases the level of crossing-over in male and female meiosis was about the same (between Pgm1 and Ndh1 loci on chromosome arm 4RS). However, for most of the chromosome segments in 1R, 3RL and 6RL the male rf was significantly higher than the female rf. Different hypotheses about the mechanisms of plant sex differences for recombination are discussed. 相似文献
32.
33.
Juan José R. Coque Juan F. Martín Paloma Liras 《Molecular genetics and genomics : MGG》1993,236(2-3):453-458
34.
Marcelo J. Yanovsky Jorge J. Casal Juan P. Luppi 《The Plant journal : for cell and molecular biology》1997,12(3):659-667
Phytochromes play a key role in the perception of light signals by plants. In this study, the three classical phytochrome action modes, i.e. very-low-fluence responses (VLFR), low-fluence responses (LFR) and high-irradiance responses (HIR), were genetically dissected using phyA and phyB mutants of Arabidopsis thaliana (respectively lacking phytochrome A or phytochrome B) and a polymorphism between ecotypes Landsberg erecta and Columbia. Seed germination and potentiation of greening, hypocotyl growth inhibition and cotyledon unfolding in etiolated seedlings of the ecotype Landsberg erecta showed biphasic responses to the calculated proportion of active phytochrome established by one light pulse or repeated light pulses. The first phase, i.e. the VLFR, was absent in the phyA mutant, normal in the phyB mutant (both in the Landsberg erecta background) and severely deficient in Columbia. The second phase, i.e. the LFR, was present in the phyA mutant, deficient in the phyB mutant and normal in Columbia. Under continuous far-red light, HIR of etiolated seedlings were absent in phyA and normal in phyB and Columbia. The segregation of VLFR in recombinant inbred lines derived from a cross between Landsberg erecta and Columbia was analysed by MAPMAKER/QTL. Two quantitative trait loci, one on chromosome 2 ( VLF1 ) and another on chromosome 5 ( VLF2 ), were identified as responsible for the polymorphism. Phytochrome A is proposed to initiate two transduction pathways, VLFR and HIR, involving different cells and/or different molecular steps. This is the first application of the analysis of quantitative trait loci polymorphic between ecotypes to dissect transduction chains of environmental signals. 相似文献
35.
Two groups of male rats were treated orally for 60 days with ebrotidine and cimetidine, used as reference standard, respectively. The dose used of both drugs was 500mg/kg. A third group, used as control, received 10 ml/kg of an aqueous agar suspension. After receiving the last dose, the animals were killed by inhalation of CO2 in a sealed chamber and the stomachs were removed for histological preparation. The purpose of this study was to count antral G-cells throughout the gastric mucosa by light microscope. A PAP system-associated antigastrin immunohistochemical method was used for cell identification. Cell density, with respect to their location in the gastric mucosa and the treatments given, was calculated using image analysis techniques. The results showed that ebrotidine did not cause any significant differences in the density of the population of these cells compared with the control group, while cimetidine induced a significant proliferation of antral G-cells. 相似文献
36.
37.
Danley A. S. Callieri Carlos G. Núñez Juan C. Díaz Ricci Luis Scidá 《Applied microbiology and biotechnology》1984,19(4):267-271
Summary
Candida utilis var. major NRRL-Y-1084 was grown in a defined medium without a phosphorous (P) source. During the exponential phase, cells divided according to a specific growth rate of 0.32 h-1, which is lower than the usual rate for a balanced medium (0.4–0.6 h-1). The relative P content of the biomass decreased from 2.70% to 0.75% over a period of 6 h, including 2 h of cell division arrest. At the end of this period there was another interruption of cell division. After that, multiplication restarted at a considerably lower rate and it deviated slightly from the exponential pattern. The stationary phase began when biomass P content reached 0.4%–0.5%, slowly decreasing afterwards to 0.25–0.20%. Biomass synthesis was less affected than cell division by the relative decrease of endogenous P, the two processes differing partially in their kinetics. Cell lysis started shortly before the stationary phase and affected about 20% of the population by the end of the assay. RNA and P content of the resulting biomass were 2.4% and 0.25% respecitvely, P being mainly incorporated to RNA.The relationship of biomass production to glucose uptake was very low, probably because the marked P deficiency called for an increase in energy consumption for growth and specially for maintenance. Compared with yeasts grown in a balanced medium, 40% increase in glycogen was observed, whereas no mean changes in the content of cell wall carbohydrates (glucan and mannan) and that of true protein were found.Member of the Scientific Researcher's Career of the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET). Agrentina 相似文献
38.
Juan Alberto Claver Irene von Lawzewitsch Orestes Jorge Colillas 《Primates; journal of primatology》1984,25(3):362-371
The microscopic structure of theAlouatta caraya ovary is studied in different ages and reproductive stages. The most significant feature seems to be the presence in adult
ovaries of abundant glandular interstitial tissue which occupies both the cortex and medulla. It seems to be derived from
the theca interna of atretic follicles. Discrete luteinized masses are present in the medulla in all the ovaries observed.
Invaginations of the surface epithelium are seen only in infant and juvenile ovaries. The development of cystic follicles
seems to be a common pathway of atresia. 相似文献
39.
Summary We present a quantitative theory that relates the fluorescence intensityvs. temperature (I vs. T) profile of a fluorescent-labeled two-component lipid bilayer to the phase diagram of the bilayer and the partition coefficientK of the fluorophore between fluid and solid phases of the bilayer. We show how the theory can be used to evaluateK from experimentalI vs. T profiles and the appropriate phase diagrams as well as to understand the different shapes ofI vs. T profiles obtained with particular fluorophores and phase diagrams. Using calculatedI vs. T graphs, we discuss the meaning of parameters, such as midpoint of the phase transition and onset and termination of a transition, which are often used to characterize phase transitions on the basis of fluorescence intensityvs. temperature profiles. 相似文献
40.
Summary Intermediate filaments of toad oxyntic cells were isolated and analysed by SDS-PAGE. The major proteins of the residue were identified as actin and a 51,000 dalton polypeptide. Immunological crossreactivity between toad oxyntic cell intermediate filament components and anti-prekeratin, was shown by double immunodiffusion tests and indirect immunofluorescence. The immunofluorescent decoration of oxyntic cells and the electron microscope images are coincident in locating the intermediate filaments mainly at the cortical and perinuclear basal zones. Furthermore, the cortical zone appears especially rich in prekeratin-like material at its adluminal third. This results in a cup-like structure that encloses the cell portion occupied by the tubulovesicular system, which does not contain intermediate filaments. The translocation of membranes occurring during the secretory cycle of the oxyntic cell, has been attributed to a system of contractile proteins. The disposition of the prekeratin-like material suggests a role for intermediate filaments in the generation of movement, produced by actin and myosin interaction, by providing a fixed plane for the anchoring of actin microfilaments. 相似文献