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991.
The rhizosphere of Trifolium repens and Lolium perenne was divided into three fractions: the bulk soil, the soil adhering to the roots and the washed roots (rhizoplane and endorhizosphere). After isolation and purification of DNA from these fractions, 16S rDNA was amplified by PCR and cloned to obtain a collection of 16S rRNA genes representative of the bacterial communities of these three fractions. The genes were then characterized by PCR restriction analysis. Each different profile was used to define an operational taxonomic unit (OTU). The numbers of OTUs and the numbers of clones among these OTUs allowed to calculate a diversity index. The number of OTUs decreased as root proximity increased and a few OTUs became dominant, resulting in a lower diversity index. In the root fraction of T. repens, the restriction profile of the dominant OTU matched the theoretical profile of the 16S rRNA gene of Rhizobium leguminosarum. This study showed that plant roots create a selective environment for microbial populations. 相似文献
992.
Identification of a STS marker linked to the Aegilops speltoides-derived leaf rust resistance gene Lr28 in wheat 总被引:7,自引:0,他引:7
S. Naik K. S. Gill V. S. Prakasa Rao V. S. Gupta S. A. Tamhankar S. Pujar B. S. Gill P. K. Ranjekar 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(4):535-540
A sequence-tagged-site (STS) marker is reported linked to Lr28, a leaf rust resistance gene in wheat. RAPD (random amplified polymorphic DNA) analysis of near-isogenic lines (NILs) of
Lr28 in eight varietal backgrounds was carried out using random primers. Genomic DNA enriched for low-copy sequences was used
for RAPD analysis to overcome the lack of reproducibility due to the highly repetitive DNA sequences present in wheat. Of
80 random primers tested on the enriched DNA, one RAPD marker distinguished the NILs and the donor parent from the susceptible
recurrent parents. The additional band present in resistant lines was cloned, sequenced, and STS primers specific for Lr28 were designed. The STS marker (Indian patent pending: 380 Del98) was further confirmed by bulk segregation analysis of F3 families. It was consistently present in the NILs, the resistant F3 bulk and the resistant F3 lines, but was absent in recurrent parents, the susceptible F3 bulk and the susceptible F3 lines.
Received: 20 February 1998 / Accepted: 4 March 1998 相似文献
993.
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996.
†Wiebke Sihver Karl-Johan Fasth Mattias Ögren ‡Håkan Bivehed Mats Bergström §Agneta Nordberg †Yasuyoshi Watanabe Bengt Långström 《Journal of neurochemistry》1998,71(4):1750-1760
Abstract: The binding characteristics of the novel 11C-labeled nicotinic ligands (R,S)-1-methyl-2-(3-pyridyl) azetidine (MPA) and (S)-3-methyl-5-(1-methyl-2-pyrrolidinyl)isoxazole (ABT-418) were investigated in comparison with those of (S)-[11C]nicotine in vitro in the rat brain to be able to predict the binding properties of the new ligands for positron emission tomography studies in vivo. The data from time-resolved experiments for all ligands indicated fast binding kinetics, with the exception of a slower dissociation of [11C]MPA in comparison with (S)-[11C]nicotine and [11C]ABT-418. Saturation experiments revealed for all ligands two nicotinic receptor binding sites with affinity constants (KD values) of 2.4 and 560 nM and binding site densities (Bmax values) of 65.5 and 223 fmol/mg of protein for (S)-[11C]nicotine, KD values of 0.011 and 2.2 nM and Bmax values of 4.4 and 70.7 fmol/mg of protein for [11C]MPA, and KD values of 1.3 and 33.4 nM and Bmax values of 8.8 and 69.2 fmol/mg of protein for [11C]ABT-418. In competing with the 11C-ligands, epibatidine was most potent, followed by cytisine. A different rank order of potencies was found for (?)-nicotine, (+)-nicotine, MPA, and ABT-418 displacing each of the 11C-ligands. Autoradiograms displayed a similar pattern of receptor binding for all ligands, whereby [11C]MPA showed the most distinct binding pattern and the lowest nonspecific binding. We conclude that the three 11C-labeled nicotinic ligands were suitable for characterizing nicotinic receptors in vitro. The very high affinity of [11C]MPA to nicotinic acetylcholine receptors, its low nonspecific binding, and especially the slower dissociation kinetics of the [11C]MPA from the putative high-affinity nicotinic acetylcholine receptor binding site compared with (S)-[11C]nicotine and [11C]ABT-418 raise the level of interest in [11C]MPA for application in positron emission tomography. 相似文献
997.
Matthijs G. P. Feenstra Margriet H. A. Botterblom Johanna F. M. van Uum 《Journal of neurochemistry》1998,70(3):1104-1113
Abstract: On-line in vivo microdialysis was used to determine the effects of a 16-min handling period on release of dopamine (DA) in the nucleus accumbens and of DA and noradrenaline (NA) in the medial prefrontal cortex of awake, freely moving rats. DA and NA were determined in one HPLC run. Handling resulted in an immediate and strong increase of both catecholamines in the prefrontal cortex. Maximal values for DA were 295%, and for NA 225%, of controls. DA in the nucleus accumbens was also increased (to 135% of controls) but only after a short delay. Local inhibition of ionotropic glutamate receptors by continuous reversed dialysis of the drugs 6-cyano-7-nitroquinoxaline, d -2-amino-5-phosphonopentanoic acid, or dizocilpine did not significantly affect handling-induced increases in cortical DA and NA release. Neither did the agonist of metabotropic glutamate receptors, trans -(1 S ,3 R )-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), or the GABA-B agonist baclofen. Reversed dialysis of dizocilpine in the nucleus accumbens was equally ineffective, but ACPD inhibited the increase in DA release in this area. Stimulation of metabotropic glutamate receptors in the nucleus accumbens was previously reported to inhibit activation of DA release in that area after stimulation of glutamatergic or dopaminergic afferents. It is concluded that metabotropic receptors in the nucleus accumbens are important for the control of activation of DA release in the accumbens by physiological stimuli but that a similar mechanism is lacking in the prefrontal cortex. 相似文献
998.
Delphine S. Dupuis Christiane Palmier Francis C. Colpaert Petrus J. Pauwels 《Journal of neurochemistry》1998,70(3):1258-1268
Abstract: G protein activation mediated by serotonin 5-HT1A and 5-HT1B/D receptors in guinea pig brain was investigated by using quantitative autoradiography of agonist-stimulated [35S]GTPγS binding to brain sections. [35S]GTPγS binding was stimulated by the mixed 5-HT1A/5-HT1B/D agonist L694247 in brain structures enriched in 5-HT1A binding sites, i.e., hippocampus (+140 ± 14%), dorsal raphe (+70 ± 8%), lateral septum (+52 ± 12%), cingulate (+36 ± 8%), and entorhinal cortex (+34 ± 5%). L694247 caused little or no stimulation of [35S]GTPγS binding in brain regions with high densities of 5-HT1B/D binding sites (e.g., substantia nigra, striatum, central gray, and dorsal subiculum). The [35S]GTPγS binding response was antagonized by WAY100635 (10 µM) and methiothepin (10 µM). In contrast, the 5-HT1B inverse agonist SB224289 (10 µM) did not affect the L694247-mediated [35S]GTPγS binding response, and the mixed 5-HT1B/D antagonist GR127935 (10 µM) yielded a partial blockade. The distribution pattern of the [35S]GTPγS binding response and the antagonist profile suggest the L694247-mediated response in guinea pig brain to be mediated by 5-HT1A receptors. In addition to L694247, 8-hydroxy-2-(di-n-propylamino)tetralin, and flesinoxan also stimulated [35S]GTPγS binding; their maximal responses varied between 46 and 52% compared with L694247, irrespective of the brain structure being considered. Sumatriptan, rizatriptan, and zolmitriptan (10 µM) stimulated [35S]GTPγS binding in the hippocampus by 20–50%. Naratriptan, CP122638, and dihydroergotamine stimulated [35S]GTPγS binding to a similar level as L694247 in hippocampus, lateral septum, and dorsal raphe. It appears that under the present experimental conditions, G protein activation through 5-HT1A but not 5-HT1B/D receptors can be measured in guinea pig brain sections. 相似文献
999.
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
1000.
We document the phylogenetic behavior of the 18S rRNA molecule in 67 taxa from 28 metazoan phyla and assess the effects of
among-site rate variation on reconstructing phylogenies of the animal kingdom. This empirical assessment was undertaken to
clarify further the limits of resolution of the 18S rRNA gene as a phylogenetic marker and to address the question of whether
18S rRNA phylogenies can be used as a source of evidence to infer the reality of a Cambrian explosion. A notable degree of
among-site rate variation exists between different regions of the 18S rRNA molecule, as well as within all classes of secondary
structure. There is a significant negative correlation between inferred number of nucleotide substitutions and phylogenetic
information, as well as with the degree of substitutional saturation within the molecule. Base compositional differences both
within and between taxa exist and, in certain lineages, may be associated with long branches and phylogenetic position. Importantly,
excluding sites with different degrees of nucleotide substitution significantly influences the topology and degree of resolution
of maximum-parsimony phylogenies as well as neighbor-joining phylogenies (corrected and uncorrected for among-site rate variation)
reconstructed at the metazoan scale. Together, these data indicate that the 18S rRNA molecule is an unsuitable candidate for
reconstructing the evolutionary history of all metazoan phyla, and that the polytomies, i.e., unresolved nodes within 18S
rRNA phylogenies, cannot be used as a single or reliable source of evidence to support the hypothesis of a Cambrian explosion.
Received: 9 December 1997 / Accepted: 23 March 1998 相似文献