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61.
El-Laithy HM 《AAPS PharmSciTech》2003,4(1):80-89
The performance of dioctyl sodium sulfosuccinate (aerosol OT) in the development of a pharmaceutically acceptable, stable,
self-emulsifying water continuous microemulsion with high dilution efficiency was assessed. A pseudoternary microemulsion
system was constructed using aerosol OT/medium-chain triglycerides with oleic acid/glycerol monooleate and water. The model
microemulsion was characterized with regard to its electroconductive behavior, eosin sodium absorption, interfacial tension,
and droplet size measurements after dilution with water. The percolation transition law, which makes it possible to determine
the percolation threshold and to identify bicontinuous structures, was applied to the system. The interfacial tension changes
associated with the microemulsion formation revealed ultralow values up to 30% oil at a surfactant/cosurfactant ratio of 3∶1.
Moreover, the investigated particle size and polydispersity using photon correlation spectroscopy after dilution with excess
of the continuous phase proved the efficiency of the microemulsion system as a drug carrier that ensures an infinitely dilutable,
homogeneous, and thermodynamically stable system. 相似文献
62.
Martínez-Ballesta MC Diaz R Martínez V Carvajal M 《Journal of plant physiology》2003,160(12):1487-1492
In this study we have compared the short-term effects of both NaCl and HgCl2 on aquaporins of Capsicum annuum L. plants, in order to determine whether or not they are similar. Stomatal conductance, turgor, root hydraulic conductance and water status were measured after 0.5, 2, 4 and 6 h of NaCl (60 mmol/L) or HgCl2 (50 μmol/L) treatment. When 60 mmol/L NaCl was added to the nutrient solution, a large decrease in stomatal conductance was observed after 2 h. However, when HgCl2 (50 μmol/L) was added, the decrease occurred after 4 h. The number of open stomata closed was always lower in plants treated with HgCl2 than in plants treated with NaCl. The water content of the Hg2+-treated plants was decreased, compared with controls and NaCl-treated. The root hydraulic conductance decreased after HgCl2 and NaCl treatment plants. Turgor of leaf epidermal cells was greatly reduced in plants treated with HgCl2, but remained constant in the NaCl treatment, compared with control plants. The fact that the stomatal conductance was reduced more rapidly after NaCl addition, followed by the stomatal closure, and that both water content and turgor did not differ from the control suggests that in NaCl-treated plants there must be a signal moving from root to shoot. Therefore, the control of plant homeostasis through a combined regulation of root and stomatal exchanges may be dependent on aquaporin regulation. 相似文献
63.
Improvement of phage defence in Lactococcus lactis by introduction of the plasmid encoded restriction and modification system LlaAI 总被引:1,自引:0,他引:1
AIMS: To study the ability of the plasmid-encoded restriction and modification (R/M) system LlaAI to function as a bacteriophage resistance mechanism in Lactococcus lactis during milk fermentations. METHODS AND RESULTS: Plasmid pAIcat4, carrying the R/M system LlaAI and a chloramphenicol resistance cassette, was introduced into the plasmid-free strain L. lactis MG1614 and the industrial strain L. lactis 964. By measuring changes in conductivity the influence of different phage on the growth was determined. CONCLUSIONS: The plasmid-encoded R/M system LlaAI significantly improves the bacteriophage resistance of L. lactis during milk fermentations. SIGNIFICANCE AND IMPACT OF THE STUDY: It is essential to determine the potential of a phage defence mechanism in L. lactis starter culture strains during growth in milk before steps are taken to improve starter cultures. This study shows that LlaAI is useful for improvement of starter cultures. 相似文献
64.
The exotic temperate liana (woody vine) Celastrus orbiculatus has become a weed in Michigan, occurring in many of the same habitats as the native liana Vitis riparia. However, C. orbiculatus frequently develops into extensive monospecific infestations, while V. riparia does not. Freezing-induced embolism may be responsible for limiting liana distribution. Root pressure has been observed in numerous tropical lianas and temperate species of Vitis and has been implicated as vital to the recovery of xylem function in wide vessels following winter freezes. For both of these co-occurring lianas we investigated root pressure and water conductance as possible explanatory factors for their differential spread. According to our hypothesis, C. orbiculatus should have produced greater or more frequent root pressures than V. riparia. However, the reverse proved true, indicating that root pressure is not a prerequisite for weedy proliferation of C. orbiculatus. Additionally, the seasonal patterns of specific conductivity of stem xylem indicate that each species responds differently to environmental constraints. Vitis riparia establishes conductivity early in the growing season, before the leaves emerge, using root pressure to reverse embolism, but loses conductivity with the first freeze in early autumn. Celastrus orbiculatus is slow to establish conductivity, depending on new wood production, but leafs out sooner than V. riparia and maintains green leaves after the first freeze. Vulnerability curves of xylem to cavitation caused by water stress for the two species indicate that they respond similarly to dehydration. These results indicate that root pressures are not responsible for the invasive success of C. orbiculatus and suggest that other factors must be key to its prolific invasion. 相似文献
65.
66.
Electrical breakdown of erythrocytes induces hemoglobin release which increases markedly with decreasing conductivity of
the pulse medium. This effect presumably results from the transient, conductivity-dependent deformation forces (elongation
or compression) on the cell caused by Maxwell stress. The deformation force is exerted on the plasma membrane of the cell,
which can be viewed as a transient dipole induced by an applied DC electric field pulse. The induced dipole arises from the
free charges that accumulate at the cell interfaces via the Maxwell-Wagner polarization mechanism. The polarization response
of erythrocytes to a DC field pulse was estimated from the experimental data obtained by using two complementary frequency-domain
techniques. The response is very rapid, due to the highly conductive cytosol. Measurements of the electrorotation and electrodeformation
spectra over a wide conductivity range yielded the information and data required for the calculation of the deformation force
as a function of frequency and external conductivity and for the calculation of the transient development of the deformation
forces during the application of a DC-field pulse. These calculations showed that (i) electric force precedes and accompanies
membrane charging (up to the breakdown voltage) and (ii) that under low-conductivity conditions, the electric stretching force
contributes significantly to the enlargement of ``electroleaks' in the plasma membrane generated by electric breakdown.
Received: 12 December 1997/Revised: 13 March 1998 相似文献
67.
José M. Quintero José M. Fournier José Ramos Manuel Benlloch 《Physiologia plantarum》1998,102(2):279-284
Twenty‐day‐old sunflower plants ( Helianthus annuus L. cv. Sun‐Gro 380) grown in nutrient solutions with different KCl levels were used to study the effects of K+ status of the root and of abcisic acid (ABA) on the exudation rate (Jv ), the hydraulic conductivity of the root (Lp ), the fluxes of exuded K+ and Na+ (JK and JNa ), and the gradient of osmotic pressure between the xylem and the external medium. Jv and Lp increased in direct proportion to the K+ starvation of the root. Also addition of ABA (4 µ M ) at the onset of exudation in the external medium made Jv and Lp rise, and this effect also increased with the degree of K+ starvation. Similarly, K+ starvation and ABA promoted both the flux of exuded Na+ and the accumulation of Na+ in the root. We suggest that ABA acts as a regulating signal for the radial transport of water across the root, and that potassium may be an effector of this mechanism. 相似文献
68.
The aim of this study was the evaluation of membrane permeability of callus cells of several Polish meadow fescue cultivars,
which were treated with toxins of two leaf spot pathogens Bipolaris sorokiniana and Drechslera dictyoides. Fungus metabolites were obtained by the method described by Lepoivre et al. (1986). Calli of cultivars ‘Skrzeszowicka’, ‘Skawa’, ‘Westa’, POB 282, POB 383, KOA 186 have been selected on medium with
metabolites for two weeks. Next the conductivity test of electrolyte leakage and of total ion contents in the examined tissue
was done. On the base of this data the membrane permeability coefficients for each cultivar were calculated. Toxins of B. sorokiniana damaged the cell membranes more strongly than metabolites of D. dictyoides. The significant differences of several objects sensitivity to the influence of B. sorokiniana metabolites were stated. These differences were not observed in the case of the influence of D. dictyoides metabolites on the examined tissue. 相似文献
69.
Palmitic acid increased the conductivity of BLM from mitochondrial phospholipids when they were dissolved in a mixture of decane and chlorodecane, and was ineffective when phospholipids were dissolved in decane. Lauric acid produced an increase in the membrane conductivity independently of the phospholipid type in the membrane-forming solutions (mitochondrial phospholipids, asolectin, lecithin with cholesterol) and their solvents (decane or decane with chlorodecane). The results show that discrepancies between published data concerning fatty acid effects on the BLM conductivity may be explained by differences in phospholipids, their solvents and fatty acid used. 相似文献
70.
Limits to water transport in Juniperus osteosperma and Pinus edulis: implications for drought tolerance and regulation of transpiration 总被引:9,自引:0,他引:9
1. An air-injection method was used to study loss of water transport capacity caused by xylem cavitation in roots and branches of Pinus edulis (Colorado Pinyon) and Juniperus osteosperma (Utah Juniper). These two species characterize the Pinyon–Juniper communities of the high deserts of the western United States. Juniperus osteosperma can grow in drier sites than P. edulis and is considered the more drought tolerant.
2. Juniperus osteosperma was more resistant to xylem cavitation than P. edulis in both branches and roots. Within a species, branches were more resistant to cavitation than roots for P. edulis but no difference was seen between the two organs for J. osteosperma . There was also no difference between juveniles and adults in J. osteosperma ; this comparison was not made for P. edulis .
3. Tracheid diameter was positively correlated with xylem cavitation pressure across roots and stems of both species. This relation suggests a trade-off between xylem conductance and resistance to xylem cavitation in these species.
4. During summer drought, P. edulis maintained higher predawn xylem pressures and showed much greater stomatal restriction of transpiration, consistent with its greater vulnerability to cavitation, than J. osteosperma .
5. These results suggest that the relative drought tolerance of P. edulis and J. osteosperma results in part from difference in their vulnerability to xylem cavitation. 相似文献
2. Juniperus osteosperma was more resistant to xylem cavitation than P. edulis in both branches and roots. Within a species, branches were more resistant to cavitation than roots for P. edulis but no difference was seen between the two organs for J. osteosperma . There was also no difference between juveniles and adults in J. osteosperma ; this comparison was not made for P. edulis .
3. Tracheid diameter was positively correlated with xylem cavitation pressure across roots and stems of both species. This relation suggests a trade-off between xylem conductance and resistance to xylem cavitation in these species.
4. During summer drought, P. edulis maintained higher predawn xylem pressures and showed much greater stomatal restriction of transpiration, consistent with its greater vulnerability to cavitation, than J. osteosperma .
5. These results suggest that the relative drought tolerance of P. edulis and J. osteosperma results in part from difference in their vulnerability to xylem cavitation. 相似文献