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101.
The activation by abscisic acid (ABA) of current through outward-rectifying K+ channels and its dependence on cytoplasmic pH (pHi) was examined in stomatal guard cells of Vicia faba L. Intact guard cells were impaled with multibarrelled and H+-selective microelectrodes to record membrane potentials and pHi during exposures to ABA and the weak acid butyrate. Potassium channel currents were monitored under voltage clamp and, in some experiments, guard cells were loaded with pH buffers by iontophoresis to suppress changes in pHi. Following impalements, stable pHi values ranged between 7.53 and 7.81 (7.67±0.04, n = 17). On adding 20 M ABA, pHi rose over periods of 5–8 min to values 0.27±0.03 pH units above the pHi before ABA addition, and declined slowly thereafter. Concurrent voltage-clamp measurements showed a parallel rise in the outward-rectifying K+ channel current (IK, out) and, once evoked, both pHi and IK, out responses were unaffected by ABA washout. Acid loads, imposed with external butyrate, abolished the ABA-evoked rise in IK, out. Butyrate concentrations of 10 and 30 mM (pH0 6.1) caused pHi to fall to values near 7.0 and below, both before and after adding ABA, consistent with a cytoplasmic buffer capacity of 128±12 mM per pH unit (n = 10) near neutrality. Butyrate washout was characterised by an appreciable alkaline overshoot in pHi and concomitant swell in the steady-state conductance of IK, out. The rise in pHi and iK, out in ABA were also virtually eliminated when guard cells were first loaded with pH buffers to raise the cytoplasmic buffer capacity four- to sixfold; however, buffer loading was without appreciable effect on the ABA-evoked inactivation of a second, inward-rectifying class of K+ channels (IK, in). The pHi dependence of IK, out was consistent with a cooperative binding of at least 2H+ (apparent pKa = 8.3) to achieve a voltage-independent block of the channel. These results establish a causal link previously implicated between cytoplasmic alkalinisation and the activation of IK, out in ABA and, thus, affirm a role for H+ in signalling and transport control in plants distinct from its function as a substrate in H+-coupled transport. Additional evidence implicates a coordinate control of IK, in by cytoplasmic-free [Ca2+] and pHi.Abbreviations ABA
abscisic acid
- [Ca2+]i
cytoplasmic free [Ca2+]i
- EK
K+ equilibrium potential
- IK, out, IK, in
outward-, inward-rectifying K+ channel (current)
- I-V
current-voltage (relation)
- Mes
2-(N-morpholino)ethanesulfonic acid
- pHi
cytoplasmic pH
- Tes
2-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-amino}ethanesulfonic acid
- Vm
membrane potential
We are grateful to G. Thiel (Pflanzenphysiologisches Institut, Universität Göttingen, Germany) for helpful discussions. This work was possible with equipment grants-in-aid from the Gatsby Charitable Foundation, the Royal Society and the University of London Central Research Fund. F.A. holds a Sainsbury Studentship. 相似文献
102.
A psychrotrophic toxin-producing strain of Aeromonas hydrophila grew well in a range of food slurries (scallop, prawn, fish, chicken liver paté, liverwurst, chicken luncheon slice and commercial baby food preparations) held at refrigeration temperatures. In most foods, excluding the baby food preparations, exotoxins were produced at levels comparable with production in bacteriological broth without apparent food spoilage (all but prawn and fish). Addition of ultra-heat treated (UHT) milk to toxin-containing broth culture supernatants markedly decreased or removed haemolytic and cytotoxic activities, explaining low levels of toxins found in milk in a previous study. Baby food preparations did not inactivate exotoxins under similar conditions suggesting production of toxins rather than their inactivation was inhibited in these foods. 相似文献
103.
Nanko S. Sasaki T. Fukuda R. Hattori M. Dai X. Y. Kazamatsuri H. Kuwata S. Juji T. Gill M. 《Human genetics》1993,92(4):336-338
A study of the genetic association between schizophrenia and aBalI polymorphism in exon 1 of the dopamine D3 (DRD3) gene, a candidate gene for schizophrenia, was conducted. The polymorphism was examined in 91 patients whose symptoms satisfied DSM-III-R for schizophrenia and 90 controls. There were no significant differences between the groups in allele frequencies or genotype counts. Contrary to a previous report, the patients were no more likely to be homozygous than controls. Moreover, no association with the presence of illness could be demonstrated when the patients were grouped according to sex, age of onset, history of admission to psychiatric institutions or positive family history. 相似文献
104.
Effect of heat treatment on Listeria monocytogenes and Gram-negative bacteria in sheep, cow and goat milks 总被引:1,自引:0,他引:1
Sheep milk, compared with cow and goat milk, had a protective effect on Gram-negative bacteria and Listeria spp. heated at 65°C in a test-tube method. This effect was not solely due to fat content as cow milk artificially reconstituted to 10% homologous fat was not as protective. Listeria monocytogenes in whole sheep, cow and goat milks at an inoculum level of 1 times 106 cfu ml-1 was heated at 68°C for 15 s in the plate pasteurizer and survival was only detected in whole sheep milk after heating. Whole sheep, cow and goat milks containing high levels of L. monocytogenes (1 times 106 cfu ml-1 ) could not survive the current HTST plate pasteurization protocol. 相似文献
105.
106.
Conservation of motifs within the unusually variable polypeptide sequences of type I restriction and modification enzymes 总被引:13,自引:1,他引:12
Noreen E. Murray Anne S. Daniel Gill M. Cowan Paul M. Sharp 《Molecular microbiology》1993,9(1):133-143
Type I restriction enzymes comprise three subunits encoded by genes designated hsdR, hsdM, and hsdS; S confers sequence specificity. Three families of enzymes are known and within families, but not between, hsdM and hsdR are conserved. Consequently, interfamily comparisons of M and R sequences focus on regions of putative functional significance, while both inter- and intrafamily comparisons address the origin, nature and role of diversity of type I restriction systems. We have determined the sequence of the hsdR gene for EcoA, thus making available sequences of all three hsd genes of one representative from each family. The predicted R polypeptide sequences share conserved regions with one superfamily of putative helicases, so-called ‘DEAD box’ proteins; these conserved sequences may be associated with the ATP-dependent translocation of DNA that precedes restriction. We also present hsdM and hsdR sequences for EcoE, a member of the same family as EcoA. The sequences of the M and R genes of EcoA and EcoE are at least as divergent as typical genes from Escherichia coli and Salmonella, perhaps as the result of selection favouring diversity of restriction specificities combined with lateral transfer among different species. 相似文献
107.
108.
OBJECTIVE: To examine the clinical and epidemiologic features of hepatitis C virus (HCV) infection in a gastroenterology/hepatology practice in Ottawa. DESIGN: Retrospective chart review. PATIENTS: Sixty-three consecutive patients found to be anti-HCV positive. Their charts were analysed with respect to risk factors, history of hepatitis, serum aspartate aminotransferase (AST) levels and the presence of hepatitis B markers. The long-term sexual partners of 29 patients agreed to undergo HCV antibody testing. RESULTS: Of the patients 48 (76%) had been exposed to HCV parenterally: 27 used intravenous drugs, and 21 had received blood or blood products. Eleven patients did not have any known risk factor (sporadic infection), but eight of them had lived in countries where hepatitis C may be more prevalent; the other three had locally acquired infection. The mean serum AST level at the first visit was 140 (normally less than 40) IU/L. At least one hepatitis B marker was identified in 33% of the patients. None of the sexual partners who were tested were anti-HCV positive. CONCLUSION: Most cases of hepatitis C in Ottawa are acquired through parenteral exposure; sexual transmission is rare. Sporadic infection in the Ottawa region is rare but may be more common in people from countries with a higher prevalence rate of hepatitis C. Most cases of hepatitis C are asymptomatic. 相似文献
109.
An experiment was designed to study how gut fullness and encounter with 5-mm Asellus aquaticus influenced acceptance or rejection of less profitable 8-mm Asellus . 45-mm sticklebacks were found to always accept 5-mm prey whereas 8-mm prey were accepted with an initial probability of about 0.9. This probability decreased as the gut filled. Fish of differing sizes and sex had similar daily energy intakes per unit body size, however the acceptance of 8-mm prey was related to fish size. Whenever a fish orientated to a prey it was followed by pursuit and manipulation independently of prey size. The decision to accept or reject prey occurred after one manipulation, a criterion that was more variable for the larger prey. For one feeding session per day the total energy intake was almost constant despite the changing combination of prey sizes eaten. The fish ate prey with long handling times if the energetic contents of the stomach had not reached 450 J. Calculations were made of how many of each millimetre prey size group would satisfy the 450 J demand and how long the estimated number would take to handle. This showed that the best option is to consume 5-mm prey if given the choice. 相似文献
110.
Actin-related protein 1 and cytoplasmic dynein-based motility - what's the connection? 总被引:7,自引:0,他引:7
The actin-related protein Arp1 works in conjunction with the microtubule-based motor cytoplasmic dynein to drive many types of intracellular motility. In vertebrate cells, Arp1 is present exclusively in the form of a 37-nm filament that constitutes the backbone of dynactin, a 1.2-MDa macromolecular complex containing nine other polypeptides. Dynactin has been proposed to function as the link between dynein and its cargo. Recent work indicates that the dynactin subunit p150(Glued) mediates the interaction of the dynactin molecule with dynein and microtubules, leaving the Arp1 filament as a possible cargo-binding domain. Mechanisms for binding of F-actin to membranes are discussed as models of the Arp1-membrane interaction. 相似文献