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21.
Radioiodination of highly purified human follicle-stimulating hormone (hFSH) (4000 IU/mg) was performed every other week for 23 weeks using 2 mCi carrier free Na 125I (Amersham Corp., 15 mCi/μg I2) in the presence of lactoperoxidase. Incorporation of 125I into hFSH was determined by the method of [7.]Biochem. J. 89, 114). Hormone binding was studied in vitro under steady-state conditions (16 h, 20°C) using different calf testis membrane preparations having similar receptor characteristics. Each 125I-hFSH preparation was characterized for maximum bindability, specific activity of bindable radioligand as determined by self-displacement analysis, and by determination of Ka and Rt. Incorporation of 125I into FSH was relatively constant over the large number of experiments (62.4 ± 6.4 μCi/μg; n = 23). By comparison, however, specific radioactivity of the receptor bindable fraction of 125I-hFSH was related to the lot of 125I utilized, and was significantly (P ≤ 0.01) lower and more variable (28.7 ± 10.5 μCi/μg). Maximum bindability of 125I-hFSH was not correlated to specific activity (r = 0.06) but was negatively correlated to hFSH 125I incorporation (r = −0.47; P ≤ 0.05). These observations demonstrate the need to assess the quality of each batch of radioligand before undertaking radioligand-receptor assays and suggest that differences in Na125I lots affect specific radioactivity of the radioligand and its receptor binding characteristics. 相似文献
22.
Transport across the outer membrane of Escherichia coli K12 via the FhuA receptor is regulated by the TonB protein of the cytoplasmic membrane 总被引:40,自引:0,他引:40
Summary Point mutations in the “TonB box” offhuA were suppressed by point mutations in thetonB gene, suggesting both a functional and physical interaction between the FhuA receptor protein in the outer membrane and the
TonB protein in the cytoplasmic membrane ofEscherichia coli K12. Mutations influA were classified into four types according to the extent by which they impaired mutant cells in their growth on ferrichrome
as sole iron source and in their sensitivity to the antibiotic albomycin and to colicin M. ThetonB mutation with a glutamine to leucine replacement at position 165 was less efficient in restoring the FhuA functions than
the glutamine to lysine exchange at the same position. The better the coupling between FhuA and TonB the poorer was the inhibition
of phage T1 binding to FhuA by ferrichrome. A working model is proposed in which the TonB protein assumes different conformations
in response to the energized state of the cytoplasmic membrane and thereby allosterically regulates the activity of the FhuA
receptor. This model implies an intermembrane coupling between two proteins in adjacent membranes. 相似文献
23.
At inflammatory sites neutrophils are stimulated to produce a variety of toxic agents, yet rarely harm the endothelium across which they migrate. We have recently found that endothelium releases adenosine which, acting via receptors on the surface of human neutrophils, inhibits generation of toxic metabolites by stimulated neutrophils but, paradoxically, promotes chemotaxis. Agents which diminish plasma membrane viscosity affect neutrophil function similarly, possibly by modulating chemoattractant receptor number or affinity. We therefore determined whether adenosine receptor agonists modulate neutrophil function by decreasing membrane viscosity and/or chaning the affinity of chemoattractant (N-fMet-Leu-Phe, FMLP) receptors. Surprisingly, 5′-(N-ethylcar☐amido)adenosine (NECA, 10 μM), the most potent agonist at neutrophil adenosine receptors, increased plasma membrane viscosity, as measured by fluorescence anisotropy of the plasma membrane specific probe 1-(4-trimethylaminophenyl)-6-diphenyl-1,3,5-hexatriene (TMA-DPH), in unstimulated neutrophils from a mean microviscosity of 1.67 ± 0.02 (S.E.) to 1.80 ± 0.02 (p < 0.001) while inosine (10 μM), a poor adenosine receptor agonist, had no effect (1.73 ± 0.04, p =n.s. vs. control, p < 0.01 vs. NECA). Adenosine receptor agonists increased plasma membrane viscosity in neutrophils with the same order of potency previously seen for inhibition of superoxide anion generation and enhancement of chemotaxis (NECA > adenosine = N6-phenylisopropyladenosine). The adenosine receptor antagonist 8-(p-sulfophenyl)theophylline reversed the effect of NECA on plasma membrane viscosity. Unlike other agents which modulate plasma membrane viscosity, NECA (10 μM) did not significantly change the number or affinity of [3H]FMLP binding sites on neutrophils. In contrast to the hypothesis of Yuli et al. these results indicate that occupancy of adenosine receptors on neutrophils increases plasma membrane viscosity without affecting chemoattractant receptor display. 相似文献
24.
Relative importance of temporal and spatial heterogeneity in the zooplankton community of an artificial reservoir 总被引:1,自引:1,他引:0
Jotaro Urabe 《Hydrobiologia》1989,184(1-2):1-6
Zooplankton samples were collected monthly at three stations in Ogochi Reservoir during 1980, and the temporal and horizontal
variations in the density of dominant taxa were evaluated by a standard 2-way ANOVA with random effects. The analysis revealed
that horizontal is greater than temporal variation in the warm water season (> 18 °C), whereas temporal variation is greater
in the cold water season (< 18 °C). Horizontal heterogeneity of the zooplankton community found in the warm water season seems
to be associated with differences in site-specific conditions. 相似文献
25.
Günter Kämper Hans-Ulrich Kleindienst 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,167(2):193-200
1. | Filiform hairs of various lengths on the cerci of adult crickets vibrate in a sound field. These movements were measured with a photodetector for sound frequencies from 10 Hz to 200 Hz in the species Acheta domestica, Gryllus bimaculatus and Phaeophilacris spectrum. |
2. | With low air-particle velocities, the hair shafts were deflected sinusoidally from their resting position, without bending or secondary oscillations (Figs. 2 A, 3 A). At higher velocities (from ca. 80 mm/s peak velocity, depending on the properties of the individual hairs), the shaft struck the cuticular rim of the socket in which the base of the hair is seated (Fig. 2B). This contact was made at an average angular displacement from the resting position of 5.16°±1.0°. |
3. | The best frequencies of the hairs were found to be between 40 Hz and 100 Hz (Fig. 5A). The slope of the amplitude curve for constant peak air-particle velocity at frequencies below the best frequencies was between 0 and 6 dB/octave. Long hairs had smaller slope values than short hairs (Fig. 5C). |
4. | At its best frequency the ratio of maximal tip displacement of a hair to the displacement of the air particles in the sound field was between 0.2 and 2. Only a small number of hairs (2 out of 36) showed tip displacements exceeding twice the air-particle displacement. The values of maximal angular displacement were not correlated to hair length (Fig. 5 B). |
5. | The angular displacement of the hairs was phase shifted with respect to the air-particle velocity by 0° to +45° (phase lead) at sound frequencies around 10 Hz and by -45° to -120° (phase lag) at 200 Hz (Figs. 3C, 4B). At a particular frequency long hairs tended to have larger phase lags than shorter hairs (Fig. 5D). |
26.
GABAA-receptors, the major synaptic targets for the neutotransmitter GABA, are gated chloride channels. By their allosteric drug-induced modulation they serve as molecular control elements through which the levels of anxiety, vigilance, muscle tension and epileptiform activity can be regulated. Despite their functional prominence, the structural requirements of fully functional GABAA-receptors are still elusive. Expression of cDNAs coding for the 1- and 1-subunits of rat brain yielded GABA-gated chloride channels which were modulated by barbiturates but displayed only agonistic responses to ligands of the benzodiazepine receptor. GABAA-receptors with fully functional benzodiazepine receptor sites were formed when the 1- and 1-subunits were coexpressed with the 2-subunit of rat brain. These receptors, however, failed to show cooperativity of GABA in gating the channel. In order to determine the subunit repertoire available for receptor assembly in different neuronal populations in vivo, the sites of subunit gene expression were (1, 2, 3, 5, 6, 1, 2, 3, 2) mapped by in situ hybridization histochemistry in brain sections. The mRNAs of the 1-, 1- and 2-subunits were co-localized e.g. in mitral cells of olfactory bulb, pyramidal cells of hippocampus as well as granule cells of dentate gyrus and cerebellum. The lack of colocalization in various other brain areas points to an extensive receptor heterogeneity. The presence of multiple GABAA-receptors in brain may contribute to synaptic plasticity, differential responsiveness of neurons to GABA and to variations in drug profiles.Special issue dedicated to Dr. Erminio Costa 相似文献
27.
Nicotinic Agonists Regulate α-Bungarotoxin Binding Sites of TE671 Human Medulloblastoma Cells 总被引:1,自引:1,他引:0
The TE671 human medulloblastoma cell line expresses a variety of characteristics of human neurons. Among these characteristics is the expression of membrane-bound high-affinity binding sites for alpha-bungarotoxin, which is a potent antagonist of functional nicotinic acetylcholine receptors on these cells. These toxin binding sites represent a class of nicotinic receptor isotypes present in mammalian brain. Treatment of TE671 cells during proliferative growth phase with nicotine or carbamylcholine, but not with muscarine or d-tubocurarine, induced up to a five-fold increase in the density of radiolabeled toxin binding sites in crude membrane fractions. This effect was blocked by co-incubation with the nicotinic antagonists d-tubocurarine and decamethonium, but not by mecamylamine or by muscarinic antagonists. Following a 10-13 h lag phase upon removal of agonist, recovery of the up-regulated sites to control values occurred within an additional 10-20 h. These studies indicate that the expression of functional nicotinic acetylcholine receptors on TE671 cells is subject to regulation by nicotinic agonists. Studies of the murine CNS have consistently indicated nicotine-induced up-regulation of nicotinic acetylcholine receptors, thereby supporting the identification of the toxin binding site on these cells as the functional nicotinic receptor. Although a mechanism for this effect is not apparent, nicotine-induced receptor blockade does not appear to be involved. 相似文献
28.
The kinetics of dissociation of [3H]methyl beta-carboline-3-carboxylate (beta-CCM) binding was studied in a synaptosomal membrane preparation of rat cerebral cortex. Dissociation was biphasic: a faster phase (10-30% contribution) was followed by a slower phase. Picrotoxin pretreatment at 22 degrees C enhanced the equilibrium binding of [3H]beta-CCM. The half-life of the slower phase of beta-CCM dissociation (t1/2II) was increased by 60 muM picrotoxin from 1.7 min to 3.3 min. The dissociation of [3H]beta-CCM was identical when initiated by an excess of either diazepam or beta-CCM. Quasi-equilibrium Scatchard analysis of [3H]beta-CCM binding was performed by a kinetic separation of the rapid and slow phases of dissociation. The slow and rapid phases represented beta-CCM binding sites of high and low affinity, respectively. The dissociation of [3H]beta-CCM (control t1/2II = 2.0 min) was decelerated by the gamma-aminobutyric acid (GABA) antagonist 3-alpha-hydroxy-16-imino-5 beta-17-aza-androstan-11-one (R 5135) (t1/2II = 2.5 min) and accelerated by GABA (t1/2II = 1.6 min). GABA inhibited both high- and low-affinity beta-CCM bindings. 相似文献
29.
Cytogenetic patterns from primary short-term culture of breast cancer, renal carcinoma, and tumors of the central nervous system are presented to illustrate the range of karyotypic diversity of human solid tumors as well as their biologic differences in culture systems that support their growth. These studies have illustrated several major issues. 1) Results vary with the tissue of origin: primary cultures from breast are almost uniformly diploid, while renal tumors are near-diploid, mosaic, and show clonal aberrations; and CNS tumors are heterogeneous: some diploid, some near-diploid and some highly aneuploid. 2) Results after short-term culture are selective, representing subpopulations from the heterogeneous cells that are detected on direct analysis of fresh tumors by cytogenetics or flow cytometry (FCM). It is not yet clear whether prognosis depends on the dominant population of the primary tumor or alternatively should be influenced by detection of small aneuploid subpopulations. 3) Evidence from all three tumor types supports the interpretation that cytogenetically normal diploid cells constitute part of some tumor populations, and may be better adapted to routine growth in culture than aneuploid subpopulations from the same primary tumors. These cells may also compose a major portion of the viable population of tumors in vivo and, therefore, could represent a useful model for studies of tumorigenesis and therapeutic regimens. 相似文献
30.
Richard C. Woodman John T. Curnutte Bernard M. Babior 《Free radical biology & medicine》1988,5(5-6):355-361
We examined the effects of the recombinant human colony stimulating factors GM-CSF and G-CSF, cycloheximide (a protein synthesis inhibitor) and dihydrocytochalasin B (a microfilament disrupting agent) upon FMLP (N-formyl-methionyl-leucylphenylalanine)-stimulated O2 − production by neutrophils. We confirmed a time dependent augmentation of O2 − production following preincubation of neutrophils either alone or with colony stimulating factors. Furthermore, we found that GM-CSF, but not G-CSF, increased O2 − production at some concentrations of the stimulus. Preincubation of neutrophils with cycloheximide in the absence of CSF caused a marked fall in O2−-production that was first evident at 2 hours. The fall in O2−-forming capacity caused by cycloheximide was much less pronounced if dihydrocytochalasin B was also included in the preincubation buffer. These findings suggest a previously unrecognized role for de novo protein synthesis in maintaining the ability of neutrophils to manufacture O2−, and support earlier studies indicating that the cycling of FMLP receptors between the cell membrane and an intracellular compartment is important in determining the magnitude of the respiratory burst in FMLP-stimulated neutrophils. 相似文献