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51.
Switching yeast from meiosis to mitosis: double-strand break repair, recombination and synaptonemal complex 总被引:3,自引:0,他引:3
Drora Zenvirth Josef Loidl Shoshana Klein Ayelet Arbel Ronen Shemesh & Giora Simchen 《Genes to cells : devoted to molecular & cellular mechanisms》1997,2(8):487-498
Background:
When Saccharomyces cerevisiae cells that have begun meiosis are transferred to mitotic growth conditions (‘return-to-growth’, RTG), they can complete recombination at high meiotic frequencies, but undergo mitotic cell division and remain diploid. It was not known how meiotic recombination intermediates are repaired following RTG. Using molecular and cytological methods, we investigated whether the usual meiotic apparatus could repair meiotically induced DSBs during RTG, or whether other mechanisms are invoked when the developmental context changes.Results:
Upon RTG, the rapid disappearance of meiotic features—double-strand breaks in DNA (DSBs), synaptonemal complex (SC), and SC related structures—was striking. In wild-type diploids, the repair of meiotic DSBs during RTG was quick and efficient, resulting in homologous recombination. Kinetic analysis of double-strand breakage and recombination indicated that meiotic DSB formation precedes the commitment to meiotic levels of recombination. DSBs were repaired in RTG in dmc1, but not rad51 mutants, hence repair did not occur by the usual meiotic mechanism which requires the Dmc1 gene product. In haploids, DSBs were also repaired quickly and efficiently upon RTG, showing that DSB repair did not require the presence of a homologous chromosome. In all strains examined, SC and related structures were not required for DSB repair or recombination following RTG.Conclusions:
At least two pathways of DSB repair, which differ from the primary meiotic pathway(s), can occur during RTG: One involving interhomologue recombination, and another involving sister-chromatid exchange. DSB formation precedes commitment to recombination. SC elements appear to prevent sister chromatid exchange in meiosis.52.
The mitochondrial DNA of Podospora anserina is complex, consisting of a characteristic set of genes with a large number of introns and a substantial amount of sequence of unknown function and origin. In addition, as indicated by various types of reorganization, this genome is highly flexible. Here we report the identification of three unassigned mitochondrial open reading frames (ORF P', ORF Q', ORF 11) as remnants of a rearranged viral-type RNA polymerase gene. These ORFs are not transcribed and may be derived from the integration of a linear plasmid of the type recently identified in a mutant of P. anserina. 相似文献
53.
Gerhild Küper Josef Hormes Klaus Sommer 《Macromolecular chemistry and physics.》1994,195(5):1741-1753
We present a new method for studying the influence of flame retardants as a function of time and temperature by measuring the X-ray absorption spectra of the corresponding additive. Here, red phosphorus in polyamide 6,6 was investigated at the phosphorus K-edge using synchrotron radiation. The thermo-oxidative degradation of the polymer was simulated by heating the sample up to 300°C. XANES 1 XANES, EXAFS: X-ray absorption spectroscopy investigating the near edge structure or the fine structure of the extended region, respectively. spectra were monitored during the degradation process at different temperatures and at a constant reaction temperature as a function of time. The degradation reaction was analyzed by comparing the XANES spectra of red phosphorus and orthophosphoric acid, and the reaction was identified as an oxidation of red phosphorus to H3PO4. The results so obtained are confirmed by the EXAFS spectra of the additive in the polymer sample recorded before and after the thermo-oxidative degradation process, and by the EXAFS spectra of suitable reference compounds. 相似文献
54.
55.
Manouchehr Javidan Josef Elek Dr. Arthur Prochazka 《Annals of biomedical engineering》1992,20(2):225-236
In this study we evaluated a technique for tremor suppression with functional electrical stimulation (FES), the technical
details of which were described in the previous paper. Three groups of patients were investigated: those with essential tremor,
parkinsonian tremor, and cerebellar tremor associated with multiple sclerosis. In each group, tremor was attenuated by significant
amounts (essential tremor: 73%; parkinsonian tremor: 62%; cerebellar tremor: 38%). These attenuations were in good accord
with predictions based on the dynamic analyses and filter designs derived in the previous paper. With filters “tuned” to the
lower mean tremor frequency encountered in the cerebellar patients, more attenuation was possible in this group as well. We
identified some practical limitations in the clinical application of the technique in its present form. The most important
was that in daily use, only one antagonist pair of muscles can realistically be controlled. At first sight, this restricts
the usefulness of the system to patients with single-joint tremors. However, the concomitant use of mechanical orthoses may
broaden the scope of application. 相似文献
56.
Šimurda Jiří Šimurdova Milena Braveny Pavel Šumbera Josef 《Pflügers Archiv : European journal of physiology》1976,362(3):209-218
1. | The relationship of the contractile response of cat papillary muscles and of the slow inward current, recorded under voltage clamp conditions (single sucrose gap), has been studied. The preparations were driven at a rate of 30 per min at 31° C. Both variables were recorded during a train of 7 identical clamp depolarizations (for 1 s from resting potential to –15 to +40 mV). The contractility increased severalfold and reached the steady state within 5–6 consecutive depolarizations. |
2. | The voltage-dependence of slow inward current was confirmed: maximum was found at depolarizations near 0 mV. On repetition of clamp pulses the slow current gradually diminished in amplitude and was more slowly activated and inactivated. The shift of the current-voltage curve indicated a decrease of the reversal potential. |
3. | Under non-steady state conditions the amplitude of the slow current was found to correlate closely with the magnitude of the contractile response at any given level of depolarization. The relation was linear with negative slope. The largest contractile response was not found at voltages which elicited maximum slow current. |
4. | The progressive decrease of the slow current during repetition of voltage clamp depolarizations is not significantly affected by inadequate time for recovery of slowly changing conductances, since it occurs also at stimulation frequency 15 per min and the slow current remains virtually unaltered after 20 s period of quiescence. |
5. | The course of total ionic current during phase 1 and 2 of action potential was reconstructed from a family of current curves obtained as a response to clamp depolarizations to various voltages, respecting the contractility-dependence of the current. The resulting course was correlated with the first derivative of action potential. A general conformity was ascertained. |
6. | The correlation of slow inward current with action potential configuration indicates that the rate of its activation determines the depth of the notch separating spike and plateau, its magnitude determines the voltage of the plateau phase and its rate of inactivation affects repolarization. |
7. | It is concluded that the described simultaneous changes of mechanical and electrical phenomena might be due to increased [Ca]i, which is responsible for more intense activation of the contractile proteins on the one hand, and decreased driving force of the slow inward current, carried by Ca ions, on the other. |
57.
The molecular characterization of an additional DNA species (pAL2-1) which was identified previously in a long-lived extrachromosomal mutant (AL2) of Podospora anserina revealed that this element is a mitochondrial linear plasmid. pAL2-1 is absent from the corresponding wild-type strain, has a size of 8395 bp and contains perfect long terminal inverted repeats (TIRs) of 975 bp. Exonuclease digestion experiments indicated that proteins are covalently bound at the 5 termini of the plasmid. Two long, non-overlapping open reading frames, ORF1 (3,594 bp) and ORF2 (2847 bp), have been identified, which are located on opposite strands and potentially encode a DNA and an RNA polymerase, respectively. The ORF1-encoded polypeptide contains three conserved regions which may be responsible for a 3–5 exonuclease activity and the typical consensus sequences for DNA polymerases of the D type. In addition, an amino-acid sequence motif (YSRLRT), recently shown to be conserved in terminal proteins from various bacteriophages, has been identified in the amino-terminal part of the putative protein. According to these properties, this first linear plasmid identified in P. anserina shares all characteristics with invertrons, a group of linear mobile genetic elements. 相似文献
58.
Josef Wimmers 《Pflügers Archiv : European journal of physiology》1941,245(2):189-197
Zusammenfassung Die Empfindlichkeit des Froschlungenpräparates, das im Winter auf Acetylcholinkonzentrationen von 11016 und darunter anspricht, nimmt in den Sommermonaten um mehrere Zehnerpotenzen ab. Da für die Verwertung des Präparates zur Bestimmung derartig kleiner A.Ch.-Konzentrationen die genaue Kenntnis dieser Empfindlichkeitsänderung notwendig ist, wurde die Umstellung des Präparates während der Monate September und Oktober durch tägliche Versuche verfolgt. Es zeigte sich, daß die Umstellung im September beginnt, besonders rasch in der zweiten Oktoberhälfte fortschreitet und Ende Oktober bereits beendet ist. Dabei steigt die Kontraktionshöhe bei der A.Ch.-Konzentration 1104 auf das Doppelte, bei 11012 auf das Zehnfache. Die Konzentration 11016, die im Sommer keine sichtbare Wirkung hatte, bewirkt noch eine Verkürzung der Lungen um fast 10%. Auch die Verhältniszahlen, d. h. das Verhältnis der Kontraktionshöhe einer A.Ch.-Konzentration 110x zur Kontraktionshöhe auf einen Prüfreiz 1104, die im Sommer recht niedrig lagen, wuchsen stetig an. Die ursprüngliche Größe und Konstanz der Verhältniszahlen ist im letzten Drittel des Oktober wieder erreicht. 相似文献
59.
Herink J Krejcová G Bajgar J Svoboda Z Kvĕtina J Zivnú P Palicka V 《Neuroscience letters》2003,339(3):251-253
Cyclosporine A (CsA) is the major immunosuppressive drug used for organ and neural transplantation and the therapy of selected autoimmune diseases. We investigated the effect of CsA on the activity of acetylcholinesterase (AChE) in the frontal cortex, hippocampus, septum, and basal ganglia. AChE was determined spectrophotometrically with acetylthiocholine as substrate and 5,5-bis-2-nitrobenzoic acid as chromogen. CsA was administered in single doses of 20 or 45 mg/kg perorally; in the case of the higher dose we also performed a repeated administration of CsA in three consecutive doses separated by 24 h intervals. Both lower and higher doses of CsA decreased AChE activity in the frontal cortex and hippocampus to practically the same extent. On the contrary, AChE activity was more diminished in the case of the higher dose of CsA used in the septum and basal ganglia. Repeated administration of the higher dose of CsA did not lead, with the exception of the hippocampus, to a further decrease in AChE activity in the brain structures observed. These findings contribute to rare evidence concerning the interaction of CsA and the cholinergic system in the brain. 相似文献
60.