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21.
Chloroplast and cytoplasmic low-molecular-weight ribonucleic acid components of the leaf of Vicia faba L 总被引:5,自引:3,他引:2 下载免费PDF全文
1. A method for the extraction of plant nucleic acids and their separation on methylated-serum-albumin-kieselguhr columns is described. It is demonstrated that the characteristics of the elution profiles of material from the same source are consistently reproducible. 2. Major dissimilarities were found in the elution profiles of nucleic acids from root and from leaves of Vicia faba L. These dissimilarities were confirmed by polyacrylamide-gel electrophoresis. 3. Four distinct types of low-molecular-weight RNA were demonstrated to be present in leaves, clearly distinguished by their behaviour when chromatographed on methylated-serum-albumin-kieselguhr columns. (a) Both cytoplasmic and chloroplast ribosomes contained a low-molecular-weight RNA, and these components were distinct from each other. (b) The chloroplast possessed a unique ;soluble' RNA (i.e. RNA that is not precipitated by centrifugal forces that sediment ribosomes) which was not present in the rest of the cell. (c) A soluble component, probably transfer RNA, was found in both the chloroplasts and in the cytoplasm. 4. The components distinguishable by methylated-serum-albumin-kieselguhr column chromatography could not be distinguished by sucrose-density-gradient centrifugation. 相似文献
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23.
Binding studies with [3H]dexamethasone identified a class of binding sites on male rat liver microsomes. The binding sites were glucocorticoid-dependent and specific for glucocorticoids and progestins. Scatchard binding parameters, competition studies with triamcinolone acetonide, a synthetic glucocorticoid which competes well for the glucocorticoid receptor, and immunoblotting with an antiglucocorticoid receptor antibody indicated that these sites are distinct from the cytosolic glucocorticoid receptor. Affinity labelling experiments with [3H]dexamethasone 21-mesylate revealed two specifically labelled peptides, one at approx. 66 kDa and a doublet at 45 kDa. The 66 kDa peptide had been previously identified in serum and may be present as a result of serum contamination of the microsomal preparation. The 45 kDa doublet, on the other hand, had been shown to be absent from rat serum. The characteristics of the 45 kDa peptide(s) were identical to those of the dexamethasone binding site identified in the binding studies. [3H]Dexamethasone binding characteristics and affinity labelling of microsomal subfractions, separated by isopycnic centrifugation, showed that the binding sites are located in the endoplasmic reticulum. The identification and role of the 45 kDa peptide doublet remain to be determined. 相似文献
24.
Yasmin H. Neggers Mary B. Dubard Robert L. Goldenberg Tsunenobu Tamura Kelley E. Johnston Rachel L. Copper John C. Hauth 《Biological trace element research》1996,55(1-2):127-135
Plasma zinc (Zn) concentrations were measured in 4376 indigent women (86% African-American), at a mean (±SD) gestational age
of 15 (±7.8) wk to determine the relationship between various maternal characteristics and plasma Zn levels during pregnancy.
Mean plasma Zn levels were lower in African-American women than in Caucasian women, in multiparous women than in primiparous
women, and in women with body weight >69.9 kg than in those with body weight ≤69.9 kg (p≤0.001 for each comparison). There were no significant differences related to maternal age, marital status, education, or
smoking habit. Multiple regression analysis, including maternal prepregnancy weight, race, age, parity, smoking habit, education,
and marital status indicated that race, parity, and pregnancy weight were significantly associated with maternal plasma Zn
levels, adjusted for gestational age. Maternal race was the best predictor of plasma Zn concentrations among the population
of pregnant women studied A significant proportion of variance in maternal plasma Zn levels remained unexplained after taking
into account various maternal characteristics. The reasons for lower plasma Zn levels in African-American women, compared
to Caucasian women, during pregnancy are unknown. 相似文献
25.
Rachel Y. Reams H. Leon Thacker Daniel D. Harrington Meliton N. Novilla Billie Wilson 《Mycopathologia》1996,135(2):115-118
Aspergillus flavus Link ex Fries and A. parasiticus Speare can invade peanut kernels and under certain environmental conditions produce unacceptable levels of the mycotoxin aflatoxin. A concerted effort is underway to reduce aflatoxin contamination in peanut and peanut products. A potentially effective method of control in peanut is the discovery and use of genes for resistance to either fungal invasion or aflatoxin formation. The objective of the present experimental study was to develop an effective and efficient procedure for screening individual plants or pods of single plants for resistance to invasion by the aflatoxigenic fungi and subsequent aflatoxin production. Methods of obtaining adequate drought-stress and fungal infection were developed through this series of experiments. By completely isolating the pods from the root zone and imposing drought-stress only on pegs and pods, high levels of fungal infection were observed. High amounts of preharvest aflatoxin accumulation were also produced by completely isolating the pods from the root zone. Mid-bloom inoculation with A. parasiticus-contaminated cracked corn and drought-stress periods of 40 to 60 days were the most effective procedures. This technique was used to assess peanut genotypes previously identified as being partially resistant to A. parasiticus infection or aflatoxin contamination, and segregating populations from four crosses. Variability in aflatoxin contamination was found among the 11 genotypes evaluated, however, none were significantly lower than the standard cultivars. Broad-sense heritability of four crosses was estimated through evaluation of seed from individual plants in the F2 generation. The heritability estimates of crosses GFA-2 × NC-V11 and Tifton-8 × NC-V11 were 0.46 and 0.29, respectively, but mean aflatoxin contamination levels were high (73,295 and 27,305 ppb). This greenhouse screening method could be an effective tool when genes for superior aflatoxin resistance are identified.Cooperative investigation of the USDA-ARS and the University of Georgia, College of Agriculture. 相似文献
26.
Measures of geographic range size: the effects of sample size 总被引:2,自引:0,他引:2
A number of methods have been used for quantifying the sizes of the geographic ranges of species. The consequences of different levels of sampling (the proportion of actual spatial occurrences) are explored for eight of these, using data on the occurrences of butterfly species on a 10 × 10 km grid across Britain. For all methods, the percentage error of estimation (PEE) decreases with the number of 10 × 10 km squares which a species occupies, most rapidly for extent measures, and more rapidly for area measures than for measures of numbers of units occupied. The rate of decline in PEE itself falls as sampling effort increases. At a given sampling level, rank correlations between range sizes measured by different methods are generally high, but there is no consistent change in the magnitude of these correlations as the level of sampling increases. The composition of the set of species with the smallest range sizes changes with the level of sampling. 相似文献
27.
Christon J. Hurst Janet C. Blannon Rachel L. Hardaway Wesley C. Jackson 《Applied microbiology》1994,60(9):3462-3465
This study examined whether the practice of incorporating either tetrazolium red or tetrazolium violet dye into plaque assay medium deleteriously influences plaque assay titers. Representative members of six different virus families were studied: Cystoviridae (ϕ6), Leviviridae (MS2), Microviridae (ϕX174), Myoviridae (T2), Podoviridae (P22), and Siphoviridae (Denver, T1, and VD13). Each of the members of the Podoviridae and Siphoviridae families appeared to be suppressed by either one or both dyes at a 300-μg/ml concentration. The chosen representatives of the other bacteriophage families were not suppressed by either dye at a 300-μg/ml concentration. Subsequent trials revealed no suppression of Podoviridae or Siphoviridae plaque assay titers when members of these virus families were tested with the same two dyes at the lower concentrations of 150 and 50 μg/ml. Interestingly, the bacteriophage families whose members were affected by the dyes have additional commonality in that they are the two bacteriophage families whose members possess both double-stranded DNA genomes and noncontractile tails. 相似文献
28.
The involvement of a vanadate-sensitive ATPase in plasma membranes of a salt tolerant cyanobacterium
Rachel Gabbay-Azaria Uri Pick Gozal Ben-Hayyim Elisha Tel-Or 《Physiologia plantarum》1994,90(4):692-698
Plasma membranes of the marine cyanobacterium Spirulina subsalsa were tested for ATPase activity, and for involvement in salt stress. Transition of cells from saline to hypersaline medium enhances the respiratory activity associated with extrusion of Na+ and Cl− , and persisting salt stress induces synthesis of respiratory enzymes in the plasma membranes. The membranes possess an ATPase, specific for ATP and Mg2+ and sensitive to orthovanadate and dicyclohexylcarbodiimide. Immunoblot analysis of plasma membrane polypeptides from Spirulina subsalsa with anti- Arabidopsis H+ -ATPase serum identified a single polypeptide of 100 kDa, which cross-reacted with the antibodies. An unusual feature of this ATPase is a specific stimulation by Na+ ions. Prolonged adaptation of S. subsals cells to hypersaline conditions induced an increase in ATPase activity in subsequent plasma membrane preparations, as well as a higher content of the 100 kDa polypeptide. It is suggested that the ATPase investigated is an H+ -pump, which is involved in extrusion of Na+ and in conferring resistance to salt stress. 相似文献
29.
The genetic code, once thought to be rigid, hag been found to be quite fiexible, permitting several different reading alternatives. One of these is translatlonal frameshifting, a process programmed in the mRNA sequence and which enables a +1 or -1 shift from the reading frame of the initiation codon. So far, the Involvement of translatlonal frameahifting in gene expression has been described mainly in viruses (particularly retroviruses), retrotransposons, and bacterial insertion elements, in this MicroReview., we present a survey of the cellular genes, mostly in Escherichia coil, which have been found to be expressed through a transiational frameshifting process, as well as a discussion of the regulatory implications of this process. 相似文献
30.
Yuval Cohen Vaishali P. Chitnis Rachel Nechushtai Parag R. Chitnis 《Plant molecular biology》1993,23(4):895-900
We studied assembly of the PsaE subunit of photosystem I into photosynthetic membranes of cyanobacterial mutant strains that lack specific photosystem I subunits. Radiolabeled PsaE was incubated with photosynthetic membranes, and their binding and assembly were assayed by resistance to removal by chaotropic agents and proteolytic digestion. PsaE incorporated into the wild-type membranes was resistant to these treatments. In the absence of PsaD, it was resistant to proteolytic digestion, but was removed by NaBr. When the membranes were isolated from a mutant strain in which the psaF and psaJ genes have been inactivated, PsaE assembled in vitro could not be removed. PsaE could associate with the membranes of the strain DF in which the psaD, psaJ and psaF genes have been mutated. However, the radiolabeled PsaE associated with these membranes was removed both by the proteolytic as well as by the chaotropic agents. Characterization of PsaE present in vivo revealed similar results. These observations suggest that PsaD and PsaF/J may interact with PsaE and stabilize it in the photosystem I complex. 相似文献