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911.
Mahmood Vahedian Liang Shi Tong Zhu Ronald Okimoto Kathleen Danna Paul Keim 《Plant molecular biology》1995,29(4):857-862
Repetitive DNA sequences comprise a large percentage of plant genomes, and their characterization provides information about both species and genome evolution. We have isolated a recombinant clone containing a highly repeated DNA element (SB92) that is homologous to ca. 0.9% of the soybean genome or about 105 copies. This repeated sequence is tandemly arranged and is found in four or five major genomic locations. FISH analysis of metaphase chromosomes suggests that two of these locations are centromeric. We have determined the sequence of two cloned repeats and performed genomic sequencing to obtain a consensus sequence. The consensus repeat size was 92 bp and exhibited an average of 10% nucleotide substitution relative to the two cloned repeats. This high level of sequence diversity suggests an ancient origin but is inconsistent with the limited phylogenetic distribution of SB92, which is found an high copy number only in the annual soybeans. It therefore seems likely that this sequence is undergoing very rapid evolution. 相似文献
912.
We have purified and characterized poly(A) polymerases (PAPs) from Pisum sativum, Brassica juncea, and Zea mays. Through chromatography on DEAE-Sepharose and heparin-Sepharose, these PAPs copurified as a single enzyme along with RNPs that could provide RNA substrates for the enzyme. More extensive purification by chromatography on MonoQ resulted in the resolution of the PAPs into as many as three fractions. One of these (PAP-I) contained a 43-kDa polypeptide immunologically related to the yeast PAP, and two others (PAP-II and PAP-III) contained RNAs that could serve as substrates for polyadenylation. These fractions by themselves possessed little PAP activity, but mixtures containing combinations of these displayed substantial activity. Similar PAP factors (PAP-I and PAP-III) were identified after fractionation of extracts prepared from Brassica juncea and Zea mays. The factors from one plant were completely interchangeable with those from different plants. We conclude that the poly(A) polymerases present in vegetative plant tissues consist of more than one component. In this respect, they are substantially different from other reported plant, mammalian, and yeast PAPs. 相似文献
913.
RFLP tagging of a salt tolerance gene in rice 总被引:10,自引:0,他引:10
A salt tolerant rice mutant (M-20) was obtained through selection in vitro. Its tolerance was stably inherited over eight generations and most traints between M-20 and its sensitive original 77–170 (Oryza sativa) were very similar. By deriving an F2 population of M-20 × 77–170 and splitting every F2 individual into two parts, with one part planted in normal conditions and another part in saline conditions, the inheritance of salt tolerance in rice was studied. Under normal conditions, there was no apparent segregation among F2 individuals. Under saline conditions, however, the segregation of traits was obvious. According to our standards, the ratio of salt sensitive:moderately-tolerant:tolerant plants was 25:42:18, in accordance with a 1:2:1 ratio. It suggested that the improvement of salt tolerance in our materials was induced by the mutation of a major tolerant gene which showed incomplete dominance. By use of 130 RFLP probes distributed throughout the rice genome, the gene was tagged by a single copy DNA probe, RG4, which was located on chromosome 7. The genetic distance between the salt tolerant gene and RG4 was 7.0 ± 2.9 cM. Based on the split method, a method which could be currently used to evaluate the damage of salt stress in rice was proposed. 相似文献
914.
X. Song G. Körtner F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1995,165(4):291-297
Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r
2=0.74). The Q
10 for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r
2=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r
2=0.61). Nevertheless, the Q
10 for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.Abbreviations
BM
body mass
-
BMR
basal metabolic rate
-
C
apparent conductance
-
MR
metabolic rate
-
RMR
resting metabolic rate
-
RQ
respiratory quotient
-
T
a
air temperature
-
T
b
body temperature
-
T
lc
lower critical temperature
-
T
tc
critical air temperature during torpor
-
TMR
metabolic rate during torpor
-
TNZ
thermoneutral zone
- T
difference between body temperature and air temperature
- VO2
rate of oxygen consumption 相似文献
915.
916.
云南普通马矮型马蛋白多态性及其品种分化关系 总被引:3,自引:1,他引:2
本文运用蛋白电泳技术对来自云南省文山州马关县和麻栗坡县的21匹普通马和14匹矮型马进行了分析。共分析遗传座位44个,其中有10个座位检测到多态性。根据分子钟假说和相应的公式,推算两者的分歧时间约为18.5万年。 相似文献
917.
The kinetics of substitution reactions of [η-CpFe(CO)3]PF6 with PPh3 in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)4, 4-Ph, 3-Me, 2,3-(CH)4, 2,6-Me2, 2-Me), the reactions yeild the same product [η5-CpFe(CO)2PPh3]PF6, according to a second-order rate law that is first order in concentrations of [η5-CpFe(CO)3]PF6 and of R-PyO but zero order in PPh3 concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH≠ = 13.4 ± 0.4 kcal mol−1, ΔS≠ = −19.1 ± 1.3 cal k−1 mol−1 for 4-PhPyO; ΔH≠ = 12.3 ± 0.3 kcal mol−1, ΔS≠ = 24.7 ±1.0 cal K−1 mol−1 for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing 17O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed. 相似文献
918.
Nutrients and heavy metal contamination of plants and sediments in Futian mangrove forest 总被引:2,自引:1,他引:1
An ecological survey was carried out to determine the levels of nutrients and heavy metals in the sediments and leaf tissues of two dominant mangrove plant species, Kandelia candel and Aegiceras corniculatum, in Futian mangrove forest, Shenzhen, the People's Republic of China. The spatial and seasonal variations of these elements were also investigated. The results show that there was no major difference between two sampling sites 150 m apart. In both sites, the sediment concentrations of total and NH4
+-N, total and extractable P, total and extractable K, total organic carbon were consistently higher in the landward locations and decreased gradually towards the sea. The sediment sample collected at the seaward edge of the mangrove plant community had the lowest levels of nutrient and organic matter. The vertical variations (from the land to the sea) of sediment heavy metals were less obvious and no particular trend could be identified. Extremely high contents of Cu, Cd, Pb, Cr and Zn were found at certain locations, suggesting the occurrence of some local contamination. The mean total metal concentrations in sediments decreased in the order Mn > Zn > Cu > Cr = Pb > Cd for the sample locations. Most of the heavy metals were not in a bioavailable form as the concentrations of extractable metals were relatively low (< 1% of total metals). Pb, Cr and Cd were not detected in leaf samples. Leaf C, N, P and K contents were similar between the two species and no significant difference was found among locations, although A. corniculatum seemed to have lower Mn concentrations than K. candel. With reference to temporal variations, no significant difference in sediment concentrations of some nutrients and metals was found between the spring and autumn seasons. 相似文献
919.
The ars operon of Escherichia coli confers arsenical and antimonial resistance. 总被引:4,自引:2,他引:2 下载免费PDF全文
The chromosomally encoded arsenical resistance (ars) operon subcloned into a multicopy plasmid was found to confer a moderate level of resistance to arsenite and antimonite in Escherichia coli. When the operon was deleted from the chromosome, the cells exhibited hypersensitivity to arsenite, antimonite, and arsenate. Expression of the ars genes was inducible by arsenite. By Southern hybridization, the operon was found in all strains of E. coli examined but not in Salmonella typhimurium, Pseudomonas aeruginosa, or Bacillus subtilis. 相似文献
920.
The twisting and writhing during growth of single-cell filaments of Bacillus subtilis which lead to macrofiber formation was studied in both left- and right-handed forms of strains FJ7 and RHX. Filament bending, touching, and loop formation (folding), followed by winding up into a double-strand fiber, were documented. Subsequent folds that produced multistrandedness were also examined. The rate of loop rotation during winding up was measured for 26 loops from 16 clones. In most cases, the first loop formed turned at a lower rate than those produced by the following cycles of folding. The sequence of folding topologies differed in FJ7 and RHX strains and in left- versus right-handed structures. Right-handed FJ7 routinely gave rise to four-stranded helices at the second fold, whereas left-handed FJ7 and both left-handed and right-handed forms of RHX made structures with predominantly two double-stranded helical regions. Left-handed RHX structures frequently produced second folds within the initial loop itself, resulting in T- or Y-shaped fibers. Sixteen cases in which the initial touch of a filament to itself produced a loop that snapped open before it could wind up into a double-strand fiber were found. The snap motions were used to obtain estimates of the forces generated by helical growth of single filaments and to investigate theoretical models involving the material properties of cell filaments. In general, the mechanical behavior of growing single-cell filaments and fibers consisting of two-, three-, or four-strand helices was similar to that described for larger, mature, multifilament macrofibers. The behavior of multicellular macrofibers can be understood, therefore, in terms of individual cell growth. 相似文献