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911.
Saeed A. Khan S. S. Murty Manzoor A. Zargar M. Chakravorty 《Journal of biosciences》1991,16(3):161-174
Bacteriophage MB78 is a virulent phage ofSalmonella typhimurium. The viral DNA is 42 kb in size and seems to be circularly permuted. We show that viral DNA replication is through concatemeric
DNA formation which is subsequently converted into full length DNA through headful packaging. A restriction map of MB78 DNA
for six restriction endonucleases e.g.BgIII,PvuII, ECORI, ClaI, SalI and SmaI has been constructed. The yield of certain fragments in less than molar amount is explained in
terms of permutation and the headful mechanism of packaging. The packaging site (pac site) has been suggested. 相似文献
912.
Genetic correlations among traits alter evolutionary trajectories due to indirect selection. Pleiotropy, chance linkage, and selection can all lead to genetic correlations, but have different consequences for phenotypic evolution. We sought to assess the mechanisms contributing to correlations with size at maturity in the cyclic parthenogen Daphnia pulicaria. We selected on size in each of four populations that differ in the frequency of sex, and evaluated correlated responses in a life table. Size at advanced adulthood, reproductive output, and adult growth rate clearly showed greater responses in high‐sex populations, with a similar pattern in neonate size and r. This pattern is expected only when trait correlations are favored by selection and the frequency of sex favors the creation and demographic expansion of highly fit clones. Juvenile growth and age at maturity did not diverge consistently. The inter‐clutch interval appeared to respond more strongly in low‐sex populations, but this was not statistically significant. Our data support the hypothesis that correlated selection is the strongest driver of genetic correlations, and suggest that in organisms with both sexual and asexual reproduction, adaptation can be enhanced by recombination. 相似文献
913.
Michael Lynch Sen Xu Takahiro Maruki Xiaoqian Jiang Peter Pfaffelhuber Bernhard Haubold 《Genetics》2014,198(1):269-281
Although the analysis of linkage disequilibrium (LD) plays a central role in many areas of population genetics, the sampling variance of LD is known to be very large with high sensitivity to numbers of nucleotide sites and individuals sampled. Here we show that a genome-wide analysis of the distribution of heterozygous sites within a single diploid genome can yield highly informative patterns of LD as a function of physical distance. The proposed statistic, the correlation of zygosity, is closely related to the conventional population-level measure of LD, but is agnostic with respect to allele frequencies and hence likely less prone to outlier artifacts. Application of the method to several vertebrate species leads to the conclusion that >80% of recombination events are typically resolved by gene-conversion-like processes unaccompanied by crossovers, with the average lengths of conversion patches being on the order of one to several kilobases in length. Thus, contrary to common assumptions, the recombination rate between sites does not scale linearly with distance, often even up to distances of 100 kb. In addition, the amount of LD between sites separated by <200 bp is uniformly much greater than can be explained by the conventional neutral model, possibly because of the nonindependent origin of mutations within this spatial scale. These results raise questions about the application of conventional population-genetic interpretations to LD on short spatial scales and also about the use of spatial patterns of LD to infer demographic histories. 相似文献
914.
《Journal of biological education》2012,46(4):163-164
Understanding how people think and how people organise knowledge are always major concerns for educational researchers. Hence, educators have developed various ways of representing learners' ‘cognitive structures‘. This article provides a review of the use of five methods of representing cognitive structures - free word association, controlled word association, tree construction, concept map and flow map. Through comparing the types of analyses that are generated from these cognitive structure representation methods, this paper discusses the applications, as well as the limitations, among these methods. 相似文献
915.
A further α-protease inhibitor system, PI4, was detected in porcine sera using either 2D agarose gel, pH 5.0-PAGE, pH 9.0, or ID PAGE followed by immunoblotting with rabbit anti-porcine PI2 or PI3 antisera. PI4 inhibited chymotrypsin, but not trypsin. Seven allelic variants of PI4 were described. By haplotyping of a-protease inhibitor systems in 52 complete families it was shown that PI4 locus belongs to the PI gene cluster. The probable order of the PI loci was: PI1, PO1A, PI2, PI4, PI3. 相似文献
916.
Koorosh Mirpour James W. Bisley 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1628)
When searching for an object, we usually avoid items that are visually different from the target and objects or places that have been searched already. Previous studies have shown that neural activity in the lateral intraparietal area (LIP) can be used to guide this behaviour; responses to task irrelevant stimuli or to stimuli that have been fixated previously in the trial are reduced compared with responses to potential targets. Here, we test the hypothesis that these reduced responses have a different genesis. Two animals were trained on a visual foraging task, in which they had to find a target among a number of physically identical potential targets (T) and task irrelevant distractors. We recorded neural activity and local field potentials (LFPs) in LIP while the animals performed the task. We found that LFP power was similar for potential targets and distractors but was greater in the alpha and low beta bands when a previously fixated T was in the response field. We interpret these data to suggest that the reduced single-unit response to distractors is a bottom-up feed-forward result of processing in earlier areas and the reduced response to previously fixated Ts is a result of active top-down suppression. 相似文献
917.
918.
In the context, 2-thiosalicylic acid (TSA) is modified with two crosslinking reagents (3-chloropropyltrimethoxysilane (CTPMS), 3-(triethoxysilyl)-propyl isocyanate (TESPIC)) to achieve two kinds of sulfide bridges (abbreviated as TSA-CSi and TSA-TSi, respectively). And two organic polymers (poly acrylamide (PAM) and poly ethylene glycol (PEG)) are also functionalized with TESPIC to form their polymeric silane derivatives PAMSi and PEGSi. Then series of multi-component Eu3+/Tb3+ hybrid material have been assembled with inorganic silica covalently linking organic polymer through the sulfide bridges after co-hydrolysis and co-polycondensation with the above inorganic or organic alkoxyl compounds (TSA-CSi(TSi), PAMSi(PEGSi)) and tetraethoxysilane (TEOS). These hybrid material are characterized in details to compare with the binary hybrid material without organic polymer unit, whose results reveal that the photoluminescence properties of the hybrid system are improved with the introduction of the polymer unit. 相似文献
919.
Digitization and geo-referencing of botanical distribution maps 总被引:4,自引:0,他引:4
Christian A. Schölzel reas Hense Peter Hübl Norbert Kühl & Thomas Litt 《Journal of Biogeography》2002,29(7):851-856
920.