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31.
Andrew N. Webber Kathryn A. Platt-Aloia Robert L. Heath William W. Thomson 《Physiologia plantarum》1988,72(2):288-297
The detergent Tween-20 solubilized preferentially portions of the marginal regions of Spinacea oleracea L. thylakoid membranes and, thus, opened the inside of the grana to the external media. Differential centrifugation. following Tween-20 solubilization. enabled separate fractions of grana and stromal-exposed membranes to be isolated. Analysis of Tween-20 solubilized material, after pelleting all membrane material by centrifugation at 100 000 g, revealed polypeptides associated with the coupling factor (CF1 ) particles, cytochrome b6 /f and photosystem II complexes, suggesting that the marginal membranes contain these proteins. Concomitantly, the 100 000 g pellet was depleted in cytochrome b6 /f and P700, determined spectroscopically, Thus. our results reveal the margin to be a distinct membrane region, which does not contain the light-harvesting centers of photosystem II (LHC II). The implication of these results, in terms of the energetic interaction of components of granal and stromalexposed membrane regions, is discussed. 相似文献
32.
Chloroplasts with high rates of photosynthetic O2 evolution (up to 120 mol O2· (mg Chl)-1·h-1 compared with 130 mol O2· (mg Chl)-1·h-1 of whole cells) were isolated from Chlamydomonas reinhardtii cells grown in high and low CO2 concentrations using autolysine-digitonin treatment. At 25° C and pH=7.8, no O2 uptake could be observed in the dark by high- and low-CO2 adapted chloroplasts. Light saturation of photosynthetic net oxygen evolution was reached at 800 mol photons·m-2·s-1 for high- and low-CO2 adapted chloroplasts, a value which was almost identical to that observed for whole cells. Dissolved inorganic carbon (DIC) saturation of photosynthesis was reached between 200–300 M for low-CO2 adapted chloroplasts, whereas high-CO2 adapted chloroplasts were not saturated even at 700 M DIC. The concentrations of DIC required to reach half-saturated rates of net O2 evolution (Km(DIC)) was 31.1 and 156 M DIC for low- and high-CO2 adapted chloroplasts, respectively. These results demonstrate that the CO2 concentration provided during growth influenced the photosynthetic characteristics at the whole cell as well as at the chloroplast level.Abbreviations Chl
chlorophyll
- DIC
dissolved inorganic carbon
- Km(DIC)
coneentration of dissolved inorganic carbon required for the rate of half maximal net O2 evolution
- PFR
photon fluence rate
- SPGM
silicasol-PVP-gradient medium 相似文献
33.
P L Black H Phillips H R Tribble R Pennington M Schneider J E Talmadge 《Journal of cellular biochemistry》1988,36(4):377-392
The mechanism of therapeutic activity of recombinant murine interferon-gamma (rMu IFN-gamma) and the IFN inducer polyinosinic-polycytidylic acid solubilized with poly-L-lysine in carboxy methyl cellulose (pICLC) in treating metastatic disease was investigated by comparing effector cell augmentation with therapeutic activity in mice bearing experimental lung metastases (B16-BL6 melanoma). Effector cell functions in spleen, peripheral blood, and lung (the organ with tumor) were tested after 1 and 3 weeks of rMu IFN-gamma or pICLC administration (intravenous, three times a week). In these studies, natural killer (NK), lymphokine-activated killer (LAK), cytolytic T lymphocytes (CTL) (against specific and nonspecific targets), and macrophage tumoricidal and tumoristatic activities were measured. rM IFN-gamma and pICLC had therapeutic activity and immunomodulatory activity in most assays of immune function examined. Specific CTL activity of pulmonary parenchymal mononuclear cells (PPMC), but not in splenocytes or peripheral blood lymphocytes (PBL), during week 3 and not during week 1, correlated with the therapeutic activity of rMu IFN-gamma and of pICLC. Macrophage tumoricidal activity in PPMC, but not in alveolar macrophages, also correlated with the therapeutic activity of rMu IFN-gamma, but the opposite was true for the therapeutic activity of pICLC. NK activity of PPMC, but not of splenocytes or PBL, during week 1 correlated with the therapeutic activity of pICLC; in contrast, NK activity at any site did not correlate with the therapeutic activity of rMu IFN-gamma. LAK activity at any site did not correlate with the therapeutic activity of either agent. 相似文献
34.
Usually the toxicity of superoxide is attributed lo its ability to reduce metal ions and subsequently reoxidation of the metal by hydrogen peroxide yields deleterious oxidizing species. As many other nontoxic biological reductants reduce metal compounds, we suggest that part of the mechanism of superoxide toxicity results from its ability to oxidize metal ions bound to biological targets, which subsequently degrade the target via an intramolecular electron Transfer reaction. 相似文献
35.
Recent crystallographic studies on the mutant human hemoglobin Ypsilanti (beta 99 Asp-->Tyr) have revealed a previously unknown quaternary structure called "quaternary Y" and suggested that the new structure may represent an important intermediate in the cooperative oxygenation pathway of normal hemoglobin. Here we measure the oxygenation and subunit assembly properties of hemoglobin Ypsilanti and five additional beta 99 mutants (Asp beta 99-->Val, Gly, Asn, Ala, His) to test for consistency between their energetics and those of the intermediate species of normal hemoglobin. Overall regulation of oxygen affinity in hemoglobin Ypsilanti is found to originate entirely from 2.6 kcal of quaternary enhancement, such that the tetramer oxygenation affinity is 85-fold higher than for binding to the dissociated dimers. Equal partitioning of this regulatory energy among the four tetrameric binding steps (0.65 kcal per oxygen) leads to a noncooperative isotherm with extremely high affinity (pmedian = .14 torr). Temperature and pH studies of dimer-tetramer assembly and sulfhydryl reaction kinetics suggest that oxygenation-dependent structural changes in hemoglobin Ypsilanti are small. These properties are quite different from the recently characterized allosteric intermediate, which has two ligands bound on the same side of the alpha 1 beta 2 interface (see ref. 1 for review). The combined results do, however, support the view that quaternary Y may represent the intermediate cooperativity state of normal hemoglobin that binds the last oxygen. 相似文献
36.
A step leading to the formation of the covalent complexes between porcine pancreatic elastase (PPE) and 7-[(alkylcarbamoyl)amino]-4-chloro-3-ethoxyisocoumarins (alkylHNCO-EICs) is the formation of the noncovalent Michaelis complex. No average structures are available for the Michaelis complexes of PPE with alkylHNCO-EICs. We present the results of an initial step in obtaining these structures and have determined kinetic constants as well. The kinetic results indicate that formation of the Michaelis complex is what differentiates the effectiveness of these inhibitors in inactivating PPE. The structural and kinetic results together suggest that the structure of the Michaelis complex is necessary for the design of potent alkylHNCO-EIC inhibitors of PPE. Two novel alkylHNCO-EICs are predicted to be the best inhibitors of this series. An alternate mechanism for serine protease inhibition is also proposed. Evidence for, and studies that may add support to, the hypothesized mechanism are discussed. 相似文献
37.
Mechanisms of action of abscisic acid at the cellular level 总被引:11,自引:2,他引:9
38.
Current perspectives on plasmodesmata: structure and function 总被引:2,自引:0,他引:2
Recent studies on plasmodesmata have shown that these important intercellular passages for communication and transport are much more sophisticated in both structure and regulatory abilities than previously imagined. A complex, but not well understood, substructure has been revealed by a variety of increasingly reliable ultrastructural techniques. Proteinaceous particles are seen within the cytoplasmic sleeve surrounding the desmotubule. Dye-coupling studies have provided experimental evidence for the physical pathway of solute movement, supporting conclusions about substructural dimensions within plasmodesmata drawn from the ultrastructural studies. Calcium has been identified as a major factor in the regulation of intercellular communication via plasmodesmata. Evidence from studies on virus movement through plasmodesmata suggests a direct interaction between virallycoded movement proteins and plasmodesmata in the systemic spread of many viruses. There is increasing evidence, albeit indirect, that in some plant species phloem loading may involve transport of photoassimilate entirely within the symplast from mesophyll cells to the sieve element-companion cell complexes of minor veins. 相似文献
39.
Vladimir P. Skulachev 《Bioscience reports》1991,11(6):387-444
The development of membrane bioenergetic studies during the last 25 years has clearly demonstrated the validity of the Mitchellian chemiosmotic H+ cycle concept. The circulation of H+ ions was shown to couple respiration-dependent or light-dependent energy-releasing reactions to ATP formation and performance of other types of membrane-linked work in mitochondria, chloroplasts, some bacteria, tonoplasts, secretory granules and plant and fungal outer cell membranes. A concrete version of the direct chemiosmotic mechanism, in which H+ potential formation is a simple consequence of the chemistry of the energy-releasing reaction, is already proved for the photosynthetic reaction centre complexes.Recent progress in the studies on chemiosmotic systems has made it possible to extend the coupling-ion principle to an ion other than H+. It was found that, in ceertain bacteria, as well as in the outer membrane of the animal cell, Na+ effectively substitutes for H+ as the coupling ion (the chemiosmotic Na+ cycle). A precedent is set when the Na+ cycle appears to be the only mechanism of energy production in the bacterial cell. In the more typical case, however, the H+ and Na+ cycles coexist in one and the same membrane (bacteria) or in two diffeerent membranes of one and the same cell (animals). The sets of
and
generators as well as
and
consumers found in different types of biomembranes, are listed and discussed. 相似文献
40.
Summary A simple E.COSY type technique is described for measurement of two-bond JCOH coupling constants in proteins that are uniformly enriched with13C. The method has been used to measure2JCOH for 132 residues in the proteins calmodulin and staphylococcal nuclease having non-overlapping H–C correlations. Measured2JCOH coupling constants fall in the 0 to –9.5 Hz range. A separate experiment, measuring the accuracy of these values, indicates a root-mean-square error of 1 Hz. Comparison of the J couplings with the dihedral back bone angles from crystallographic studies confirms a weak but statistically significant correlation between the dihedral angle and the magnitude of2JCOH, but also indicates that parameters other than have a significant effect on the value of the coupling. 相似文献