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911.
Dockendorff TC Robertson SE Faulkner DL Jongens TA 《Molecular & general genetics : MGG》2000,263(1):137-143
We have performed an F2 genetic screen to identify lethal mutations that map to the 44D-45B region of the Drosophila melanogaster genome. By screening 8500 mutagenized chromosomes for lethality over Df(2R)Np3, a deficiency which encompasses nearly 1% of the D. melanogaster euchromatic genome, we recovered 125 lines with lethal mutations that represent 38 complementation groups. The lethal mutations
have been mapped to deficiencies that span the 44D-45B region, producing an approximate map position for each complementation
group. Lethal mutations were analyzed to determine the phase of development at which lethality occurred. In addition, we have
linked some of the complementation groups to P element-induced lethals that map to 44D-45B, thus possibly providing new alleles of a previously tagged gene. Some of the
complementation groups represent potentially novel alleles of previously identified genes that map to the region. Several
genes have been mapped by molecular means to the 44D-45B region, but do not have any reported mutant alleles. This screen
may have uncovered mutant alleles of these genes. The results of complementation tests with previously identified genes in
44D-45B suggests that over half of the complementation groups identified in this screen may be novel.
Received: 13 July 1999 / Accepted: 4 November 1999 相似文献
912.
913.
To study the evolution of mtDNA and the intergeneric relationships of New World Jays (Aves: Corvidae), we sequenced the entire
mitochondrial DNA control region (CR) from 21 species representing all genera of New World jays, an Old World jay, crows,
and a magpie. Using maximum likelihood methods, we found that both the transition/transversion ratio (κ) and among site rate
variation (α) were higher in flanking domains I and II than in the conserved central domain and that the frequency of indels
was highest in domain II. Estimates of κ and α were much more influenced by the density of taxon sampling than by alternative
optimal tree topologies. We implemented a successive approximation method incorporating these parameters into phylogenetic
analysis. In addition we compared our study in detail to a previous study using cytochrome b and morphology to examine the effect of taxon sampling, evolutionary rates of genes, and combined data on tree resolution.
We found that the particular weighting scheme used had no effect on tree topology and little effect on tree robustness. Taxon
sampling had a significant effect on tree robustness but little effect on the topology of the best tree. The CR data set differed
nonsignificantly from the tree derived from the cytochrome b/morphological data set primarily in the placement of the genus Gymnorhinus, which is near the base of the CR tree. However, contrary to conventional taxonomy, the CR data set suggested that blue and
black jays (Cyanocorax sensu lato) might be paraphyletic and that the brown jay Psilorhinus (=Cyanocorax) morio is the sister group to magpie jays (Calocitta), a phylogenetic hypothesis that is likely as parsimonious with regard to nonmolecular characters as monophyly of Cyanocorax. The CR tree also suggests that the common ancestor of NWJs was likely a cooperative breeder. Consistent with recent systematic
theory, our data suggest that DNA sequences with high substitution rates such as the CR may nonetheless be useful in reconstructing
relatively deep phylogenetic nodes in avian groups.
Received: 10 November 1999 / Accepted: 16 March 2000 相似文献
914.
A new, model-based method was devised to locate nucleotide changes in a given phylogenetic tree. For each site, the posterior
probability of any possible change in each branch of the tree is computed. This probabilistic method is a valuable alternative
to the maximum parsimony method when base composition is skewed (i.e., different from 25% A, 25% C, 25% G, 25% T): computer
simulations showed that parsimony misses more rare → common than common → rare changes, resulting in biased inferred change
matrices, whereas the new method appeared unbiased. The probabilistic method was applied to the analysis of the mutation and
substitution processes in the mitochondrial control region of mouse. Distinct change patterns were found at the polymorphism
(within species) and divergence (between species) levels, rejecting the hypothesis of a neutral evolution of base composition
in mitochondrial DNA.
Received: 15 March 1999 / Accepted: 7 October 1999 相似文献
915.
Takashi Ebihara Yasuko Yanagida Tetsuya Haruyama Eiry Kobatake Masuo Aizawa 《Biotechnology letters》2000,22(1):59-63
A novel cap-independent translation has been performed where the ribosome entry is regulated by the 5-noncoding region (NCR) of L-A virus mRNA. Despite L-A virus mRNA containing neither cap structure nor a poly(A) tail, the reconstructed mRNA encoding the 5 NCR of L-A virus mRNA and a reporter gene (luciferase) was translated, in yeast lysate, 60 times more efficiently than control mRNA. The 5 NCR from L-A virus was effective in regulating the recruitment of ribosome in vitro. A possible mechanism in Saccharomyces cerevisiae is also suggested, whereby the ribosome entry is regulated by the 5 NCR of L-A virus mRNA. 相似文献
916.
Chronic toxicity of rare-earth elements on human beings 总被引:3,自引:0,他引:3
Zhang H Feng J Zhu W Liu C Xu S Shao P Wu D Yang W Gu J 《Biological trace element research》2000,73(1):1-17
Blood analyses for rare-earth element (REE)-high background regions in South Jiangxi show that the population averages of
many of the biochemical indices deviate markedly from normal values in the normal region. These deviations are thought to
be caused by prolonged intake of REE through food chains in view of that the toxicity of other harmful metals such as Pb and
Cd can be neglected because of their insignificant amounts in the environment. In comparison with the normal region, blood
biochemical indices abnormal in the REE-high regions are manifested as low total serum protein (TSP), albumin, β-globulin,
glutamic pyruvic transitanase, serium triglycerides, and immunoglobulin, but high cholesterol. These deviations may be related
to the REE concentration and composition of food chains, and are sex dependent. Certain blood indices (such as TSP) of different
age groups in the LREE-high region indicate that the influence of REE on males is a one-way irreversible process, whereas
females show a strong ability of restoration. 相似文献
917.
918.
This study was designed to characterize further the nontranscribed intergenic spacers (NTSs) of the 5S rRNA genes of fish
and evaluate this marker as a tool for comparative studies. Two members of the closely related North American Great Lakes
cisco species complex (Coregonus artedi and C. zenithicus) were chosen for comparison. Fluorescence in situ hybridization found the ciscoes to have a single multicopy 5S locus located
in a C band-positive region of the largest submetacentric chromosome. The entire NTS was amplified from the two species by
polymerase chain reaction with oligonucleotide primers anchored in the conserved 5S coding region. Complete sequences were
determined for 25 clones from four individuals representing two discrete NTS length variants. Sequence analysis found the
length variants to result from presence of a 130-bp direct repeat. No two sequences from a single fish were identical. Examination
of sequence from the coding region revealed two types of 5S genes in addition to pseudogenes. This suggests the presence of
both somatic and germline (oocyte) forms of the 5S gene in the genome of Coregonus. The amount of variation present among NTS sequences indicates that accumulation of variation (mutation) is greater in this
multicopy gene than is gene conversion (homogenization). The high level of sequence variation makes the 5S NTS an inappropriate
DNA sequence for comparisons of closely related taxa.
Received: 22 August 1997 / Accepted: 31 October 1997 相似文献
919.
Eduardo Eizirik Sandro L. Bonatto Warren E. Johnson Peter G. Crawshaw Jr. Jean Cristophe Vié Dulce M. Brousset Stephen J. O'Brien Francisco M. Salzano 《Journal of molecular evolution》1998,47(5):613-624
The ocelot (Leopardus pardalis) and margay (L. wiedii) are sister-species of Neotropical cats which evolved from a lineage that migrated into South America during the formation
of the Panamanian land bridge 3–5 million years ago. Patterns of population genetic divergence of each species were studied
by phylogenetic analyses of mitochondrial DNA (mtDNA) control region sequences in individuals sampled across the distribution
of these taxa. Abundant genetic diversity and remarkably concordant phylogeographic partitions for both species were observed,
identifying parallel geographic regions which likely reflect historical faunal barriers. Inferred aspects of phylogeography,
population genetic structure, and demographic history were used to formulate conservation recommendations for these species.
In addition, observed patterns of sequence variation provided insight into the molecular evolution of the mtDNA control region
in closely related felids.
Received: 26 January 1998 / Accepted: 14 May 1998 相似文献
920.
Andres M Lozano Anthony E Lang William D Hutchison Jonathon O Dostrovsky 《Current opinion in neurobiology》1998,8(6):783-790
Important recent advances have been made in understanding the etiology and pathogenesis of Parkinson's disease, as well as in developing novel treatments. Two newly identified genes, α-synuclein and parkin, have been linked to parkinsonism. In addition, disturbances to the normal basal ganglia circuits in Parkinson's patients are being described at both anatomical and physiological levels. These developments provide a strong scientific basis for novel medical and surgical strategies to treat the profound motor disturbances in patients with Parkinson's disease. 相似文献