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The small (116 amino acids) inner membrane protein MerT encoded by the transposon Tn501 has been overexpressed under the control of the bacteriophage T7 expression system. Random mutants of MerT were made and screened for loss of mercuric ion hypersensitivity. Several mutantmerT genes were selected and sequenced: Cys24Arg and Cys25Tyr mutations abolish mercury resistance, as do charge-substitution mutations in the first predicted transmembrane helix (Glyl4Arg, Glyl5Arg, Gly27Arg, Ala18Asp), and the termination mutations Trp66Ter and Cys82Ter. 相似文献
996.
L. Zavalova S. Lukyanov I. Baskova E. Snezhkov S. Akopov S. Berezhnoy E. Bogdanova E. Barsova E. D. Sverdlov 《Molecular & general genetics : MGG》1996,253(1-2):20-25
We previously detected in salivary gland secretions of the medicinal leech (Hirudo medicinalis) a novel enzymatic activity, endo-ɛ(γ-Glu)-Lys isopeptidase, which cleaves isopeptide bonds formed by transglutaminase (Factor
XIIIa) between glutamine γ-carboxamide and the ɛ-amino group of lysine. Such isopeptide bonds, either within or between protein
polypeptide chains are formed in many biological processes. However, before we started our work no enzymes were known to be
capable of specifically splitting isopeptide bonds in proteins. The isopeptidase activity we detected was specific for isopeptide
bonds. The enzyme was termed destabilase. Here we report the first purification of destabilase, part of its amino acid sequence,
isolation and sequencing of two related cDNAs derived from the gene family that encodes destabilase proteins, and the detection
of isopeptidase activity encoded by one of these cDNAs cloned in a baculovirus expression vector. The deduced mature protein
products of these cDNAs contain 115 and 116 amino acid residues, including 14 highly conserved Cys residues, and are formed
from precursors containing specific leader peptides. No homologous sequences were found in public databases.
Received: 9 April 1996 / Accepted: 17 May 1996 相似文献
997.
Development of microsatellite markers and characterization of simple sequence length polymorphism (SSLP) in rice (Oryza sativa L.) 总被引:26,自引:0,他引:26
Microsatellite markers containing simple sequence repeats (SSR) are a valuable tool for genetic analysis. Our objective is to augment the existing RFLP map of rice with simple sequence length polymorphisms (SSLP). In this study, we describe 20 new microsatellite markers that have been assigned to positions along the rice chromosomes, characterized for their allelic diversity in cultivated and wild rice, and tested for amplification in distantly related species. Our results indicate that the genomic distribution of microsatellites in rice appears to be random, with no obvious bias for, or clustering in particular regions, that mapping results are identical in intersubspecific and interspecific populations, and that amplification in wild relatives ofOryza sativa is reliable in species most closely related to cultivated rice but becomes less successful as the genetic distance increases. Sequence analysis of SSLP alleles in three relatedindica varieties demonstrated the clustering of complex arrays of SSR motifs in a single 300-bp region with independent variation in each. Two microsatellite markers amplified multiple loci that were mapped onto independent rice chromosomes, suggesting the presence of duplicated regions within the rice genome. The availability of increasing numbers of mapped SSLP markers can be expected to increase the power and resolution of genome analysis in rice. 相似文献
998.
T. Zhu L. Shi P. Keim R. P. Funke P. M. Gresshoff 《Molecular & general genetics : MGG》1996,252(4):483-488
Yeast artificial chromosomes (YACs) are widely used in the physical analysis of complex genomes. In addition to their value in chromosome walking for map-based cloning, YACs represent excellent probes for chromosome mapping using fluorescence in situ hybridization (FISH). We have screened such a library for low-copy-number clones by hybridization to total genomic DNA. Four clones were chosen for chromosome tagging based upon their low or moderate signal. By using degenerate oligonucleotide-primed PCR (DOP-PCR), we were able to use relatively small amounts of soybean YAC DNA, isolated directly by preparative pulsed-field gel electrophoresis, as FISH probes for both metaphase chromosome spreads and interphase nuclei. FISH chromosomal analysis using the three of the clones as probes resulted in relatively simple hybridization patterns consistent with a single homologous locus or two homoeologous loci. The fourth YAC probe resulted in a diffuse hybridization pattern with signal on all metaphase chromosomes. We conclude that YACs represent a valuable source of probes for chromosomal analysis in soybean. 相似文献
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1000.
J. Xu D. M. Gooler A. S. Feng 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(4):435-445
Single-unit recordings were made from 143 neurons in the frog (Rana p. pipiens) inferior colliculus (IC) to investigate how free-field sound direction influenced neural responses to sinusoidal-amplitude-modulated (SAM) tone and/or noise. Modulation transfer functions (MTFs) were derived from 3 to 5 sound directions within 180° of frontal field. Five classes of MTF were observed: low-pass, high-pass, band-pass, multi-pass, and all-pass. For 64% of IC neurons, the MTF class remained unchanged when sound direction was shifted from contralateral 90° to ipsilateral 90°. However, the MTFs of more than half of these neurons exhibited narrower bandwidths when the loudspeaker was shifted to ipsilateral azimuths. There was a decrease in the cut-off frequency for neurons possessing low-pass MTFs, an increase in cut-off frequency for neurons showing high-pass MTFs, or a reduction in the pass-band for neurons displaying bandpass MTFs. These results suggest that sound direction can influence amplitude modulation (AM) frequency tuning of single IC neurons.Since changes in periodicity of SAM tones alter both the temporal parameters of sounds as well as the sound spectrum, we examined whether directional effects on spectral selectivity play a role in shaping the observed direction-dependent AM selectivity. The directional influence on AM selectivity to both SAM tone and SAM noise was measured in 62 neurons in an attempt to gain some insight into the mechanisms that underlie directionally-induced changes in AM selectivity. Direction-dependent changes in the shapes of the tone and noise derived MTFs were different for the majority of IC neurons (55/62) tested. These data indicate that a spectrally-based and a temporally-based mechanism may be responsible for the observed results.Abbreviations
AM
amplitude modulation
-
CF
characteristic frequency
-
DI
direction index
-
FR
isointensity frequency response
-
GABA
gamma-aminobutyric acid
-
IC
inferior colliculus
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ICc
central nucleus of the inferior colliculus
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ITD
interaural time difference
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MTF
modulation transfer function
-
PSTH
peri-stimulus time histogram
-
SAM
sinusoidal-amplitude-modulated
-
SC
synchronization coefficient
-
CN
cochlear nucleus 相似文献