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951.
952.
Valeria Maida Federico Bennardini Francesco Bonomi Maria Luisa Ganadu Stefania Iametti Giovanni Maria Mura 《The protein journal》2000,19(4):311-318
Conformational modifications and changes in the aggregation state of human αB-crystallin were investigated at different concentrations of SDS, KBr, urea, and NH4SCN and at different temperatures. Intrinsic fluorescence measurements indicated complete and reversible unfolding of the protein at 2 M NH4SCN, whereas the concentration of urea required for complete and irreversible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micelle-like aggregate of αB-crystallin in 2 M NH4SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated αB-crystallin recovered its chaperone-like activity upon dilution of the dissociating agent, whereas the urea-treated protein did not. 相似文献
953.
Cluster analysis plays vital role in pattern recognition in several fields of science. Silhouette width is a widely used index for assessing the fit of individual objects in the classification, as well as the quality of clusters and the entire classification. Silhouette combines two clustering criteria, compactness and separation, which imply that spherical cluster shapes are preferred over others—a property that can be seen as a disadvantage in the presence of complex, nonspherical clusters, which is common in real situations. We suggest a generalization of the silhouette width using the generalized mean. By changing the p parameter of the generalized mean between ?∞ and +∞, several specific summary statistics, including the minimum, maximum, the arithmetic, harmonic, and geometric means, can be reproduced. Implementing the generalized mean in the calculation of silhouette width allows for changing the sensitivity of the index to compactness versus connectedness. With higher sensitivity to connectedness, the preference of silhouette width toward spherical clusters should reduce. We test the performance of the generalized silhouette width on artificial data sets and on the Iris data set. We examine how classifications with different numbers of clusters prepared by different algorithms are evaluated, if p is set to different values. When p was negative, well‐separated clusters achieved high silhouette widths despite their elongated or circular shapes. Positive values of p increased the importance of compactness; hence, the preference toward spherical clusters became even more detectable. With low p, single linkage clustering was deemed the most efficient clustering method, while with higher parameter values the performance of group average, complete linkage, and beta flexible with beta = ?0.25 seemed better. The generalized silhouette allows for adjusting the contribution of compactness and connectedness criteria, thus avoiding underestimation of clustering efficiency in the presence of clusters with high internal heterogeneity. 相似文献
954.
Federico M. Winkler Beatriz F. Estévez 《Journal of experimental marine biology and ecology》2003,292(1):93-102
Argopecten purpuratus Lamarck (1819) is a functional hermaphrodite that releases successively male and female gametes during their spawning process. Because the short period between the release of both kind of gametes, the chance of self-fertilization exists, even in natural conditions. The self-fertilization rate was quantified in 10 scallops as the proportion of spontaneous (nonartificially fertilized) cleaving eggs. The existence of inbreeding depression was tested comparing families produced by self- and cross-fertilization. An average of 9.9% of spontaneous self-fertilization was detected. No differences in survival or growth in either larvae or juvenile were found between families produced by self-fertilization and pair mating. 相似文献
955.
956.
957.
Acetylcholine and Dopamine Promote the Production of Platelet Activating Factor in Immature Cells of Chick Embryonic Retina 总被引:2,自引:1,他引:1
Federico Bussolino Gianpiero Pescarmona Giovanni Camussi Fulvia Gremo† 《Journal of neurochemistry》1988,51(6):1755-1759
We have previously shown that platelet-activating factor (PAF), a naturally occurring lipid mediator of cell-to-cell communication, was produced by 3-day-old chick retina stimulated with acetylcholine (ACh) and dopamine (DA), but not with other neurotransmitters. ACh and DA stimulated PAF synthesis via a dithiothreitol (DTT)-insensitive cholinephosphotransferase, without affecting the acetyltransferase pathway, which was stimulated only by the calcium ionophore A23187. Therefore, we attempted to study the effects of neurotransmitters on PAF production and on the activities of the DTT-insensitive cholinephosphotransferase and acetyltransferase in the developing chick embryo retina up to hatching. Our results show that PAF was produced already at 8 days of development, when retinal cells are still rather immature and ganglion and Mueller cells are the only differentiated cells. The stimulation of PAF production occurred with ACh and not with other neurotransmitters. In older stages, DA also stimulated PAF production, as already described in the chick after hatching. DTT-insensitive cholinephosphotransferase and acetyltransferase activities were present in 8-day-old embryos, the earliest stage analyzed. Both enzymatic activities increased with age; DTT-insensitive cholinephosphotransferase increased rapidly from day 12 up to day 18, whereas acetyltransferase activity increased linearly up to the time of hatching. To promote PAF production, ACh and DA activate DTT-insensitive cholinephosphotransferase, but not acetyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
958.
Giacomo Grassi Francesco Ripullone Marco Borghetti Sabrina Raddi Federico Magnani 《Trees - Structure and Function》2009,23(6):1149-1161
It is still unknown whether the midday depression of photosynthesis under severe water stress, frequently observed in plants
growing in a Mediterranean-type climate, is primarily a consequence of diffusional or non-diffusional limitations. We carried
out combined measurements of gas exchanges and chlorophyll fluorescence in field-grown Arbutus unedo L. trees during late spring and mid summer, and a quantitative limitation analysis was performed to distinguish between the
different limitations to photosynthesis, i.e., diffusional [D
L = stomatal (S
L) + mesophyll (MCL)] and non-diffusional (carboxylation capacity and electron transport, B
L) limitations. Light-saturated assimilation at ambient CO2 (A
max), stomatal conductance to water vapour (g
sw) and maximum carboxylation rate (V
cmax
C
i) showed a marked midday depression during both periods. The total limitations tended to increase during the day and were
remarkably similar in June and July (50 and 48%, respectively); on a daily basis, D
L was similar to B
L (about 23%) in June; whereas, in July the former was predominant (38 and 4%, respectively). We concluded that the midday
depression in photosynthesis was largely caused by diffusional limitations, with non-diffusional limitations playing a smaller
role. Although stomatal closure was the main diffusional limitation, the decline in mesophyll conductance was not negligible
during the hottest and driest period. 相似文献
959.
Grazia Maugeri Agata Grazia D'Amico Paola Castrogiovanni Salvatore Saccone Concetta Federico Michele Reibaldi Andrea Russo Vincenza Bonfiglio Teresio Avitabile Antonio Longo Velia D'Agata 《Journal of cellular biochemistry》2019,120(6):10097-10105
The corneal endothelium is composed of a single hexagonal-shaped cells layer adherent to the Descemet's membrane. The primary function of these cells is maintaining of tissue clarity by regulating its hydration. Trauma, aging or other pathologies cause their loss, counterbalanced by enlargement of survived cells unable to guarantee an efficient fluid pumping to and from the stroma. Regenerative medicine using human corneal endothelial cells (HCECs) isolated from peripheral corneal-scleral tissue of a donor could be an attractive solution, overcoming transplantation problems. In a previous study, we have demonstrated that HCECs treatment with pituitary adenylate cyclase–activating polypeptide (PACAP) following growth factors deprivation prevents their degeneration. However, the molecular mechanism mediating this effect has not been clarified, yet. Here, we have shown for the first time the expression of PACAP and its receptor (PAC1R) in human corneal endothelium and demonstrated that this peptide, selectively binding to PAC1R, induces epidermal growth factor receptor (EGFR) phosphorylation and the MAPK/ERK1/2 signaling pathway activation. In conclusion, our data have suggested that PACAP could represent an important trophic factor in maintaining human corneal endothelial integrity through EGFR transactivation. Therefore, PACAP, as well as epidermal growth factor and fibroblast growth factor, could co-operate to guarantee tissue physiological functioning by supporting corneal endothelial barrier integrity. 相似文献
960.
In this study, we investigated the metabolic responses of potato tissue induced by pulsed electric field (PEF). Potato tissue
was subjected to field strengths ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 μs, 100 μs, or 1 ms. Metabolic
responses were monitored using isothermal calorimetry, changes on electrical resistance during the delivery of the pulse,
as well as impedance measurements. Our results show that the metabolic response involves oxygen consuming pathways as well
as other unidentified events that are shown to be insensitive to metabolic inhibitors such as KCN and sodium azide. The metabolic
response is strongly dependent on pulsing conditions and is independent of the total permeabilization achieved by the pulse.
Evidence shows that calorimetry is a simple and powerful method for exploring conditions for metabolic stimulation, providing
information on metabolic responses that can not be obtained from electrical measurements. This study set the basis for further
investigations on defense-related consequences of PEF-induced stress. 相似文献