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991.
一、概述内禀增长率(r_m)是一个最基本的种群参数,它的测定和计算在动物生态学的研究中占有十分重要的地位。从20年代开始,已发展出多种计算动物r_m值的方法,如下所述。 相似文献
992.
993.
Effin T. Graham 《Biotechnic & histochemistry》1991,66(6):279-281
Two stock solutions are composed as follows: A) aluminum sulfate, sodium iodate and acetic acid in aqueous propylene glycol and B) hematoxylin in pure propylene glycol. When combined in specified proportions the stock solutions yield aluminum-hematein dissolved in nontoxic propylene glycol. The ready-to-use stain, prepared in small volumes as needed, performs well in paraffin sections of plant tissues. 相似文献
994.
Hiroyoshi Hoshi Yuji Takagi Keizo Kobayashi Masakazu Onodera Taneaki Oikawa 《In vitro cellular & developmental biology. Animal》1991,27(7):578-584
Summary We have developed an improved serum-free medium to optimize the cell growth of bovine granulosa cells. The cells on collagen-coated
culture plates proliferated extensively in a nutrient medium supplemented with insulin, heparin binding growth factor-2 (HBGF-2),
lipoprotein, and bovine serum albumin (BSA). The cell doubling time at logarithmic phase and final cell density at confluent
cultures were equal to those of cultures grown in the presence of medium supplemented with optimal concentration (10%) of
fetal bovine serum (FBS). Whereas HBGF-2 or insulin alone had a small mitogenic effect of granulosa cells, lipoprotein or
BSA did not. When lipoprotein, BSA, or insulin was added together with HBGF-2, synergistic cell proliferation was observed
in all combinations. Insulin or lipoprotein had an additive mitogenic stimulation of these cells in the presence of BSA. After
granulosa cells were subcultivated in a serum-containing medium until three generations [8.5 cumulative population doubling
level (CPDL)], subsequent subcultivation of the cells in a complete serum-free medium could be achieved up to six generations
(14.4 CPDL). These results demonstrate that this serum-free medium can support the optimal cell growth and long-term subcultivation
of bovine granulosa cells. 相似文献
995.
Summary A serum-free culture system supplemented with neural tissue extract for normal and tumor human esophagi was applied to the
culture of mouse esophageal epithelium. Similar to mouse mesenchyme and skin epithelium, esophageal epithelial lines (MEE)
emerged after serial culture. The cells had an apparent unlimited life span but retained morphology and other characteristics
of normal epithelial cells. The cells formed a small cyst consisting of keratined squamous epithelium in syngenic hosts. A
screen for growth factors that stimulated growth of the nonmalignant MEE cells in the absence of neural extract revealed that
epidermal growth factor (EGF) and heparin-binding (fibroblast) growth factors (HBGF) were most effective. An HBGF-like activity
was apparent in extracts of rapidly proliferating but not quiescent MEE cells at low or confluent densities. A cloned cell
line (MEE/C8) was selected from MEE cell cultures in the absence of neural extract. MEE/C8 cells proliferated independent
of either EGF or HBGF at rates equal to MEE cells, cell extracts exhibited HBGF-like activity at all stages of proliferation,
and the cells formed large invasive tumors in syngenic hosts. The HBGF-like activity present in extracts of tumorigenic MEE/C8
and proliferating nonmalignant MEE cells had properties similar to HBGF-1 (acidic fibroblast growth factor). These results
constitute a cultured mouse esophageal epithelial cell model for study of conversion of immortalized premalignant cells to
malignant cells, and suggest that conversion from a state of cell cycle-dependent autocrine expression of one or more members
of the HBGF family to a state of constitutive expression correlates with and may contribute to malignancy.
The work was supported in part by grants CA37589 and DK35310 to Dr. McKeehan, from the National Cancer Institute, Bethesda,
MD. 相似文献
996.
D. Hodick S. Gilroy M. D. Fricker A. J. Trewavas 《Plant biology (Stuttgart, Germany)》1991,104(3):222-228
Rhizoids of Charafragilis Desv. were iontophoretically loaded with the Ca2+-sensitive ratio dye indo-1. After loading, the rhizoids regained their preinjection-membrane potential within 2 to 5 min and survived the procedure for more than 24 h, but their growth in length was permanently inhibited. Microfluorimetric measurements of the indo-1 fluorescence-ratio showed spontaneous fluctuations of the cytoplasmic Ca2+-concentration, usually declining from high values after loading to 425 ± 80 nM (± SD, n = 7) as determined by in-vitro calibration. Increasing the extracellular K+-concentration (0.1 mM to 10 mM) or Ca2+-concentration (1 mM to 10 mM) led to increases of 100 to 200 nM in cytoplasmic Ca2+-concentration. The spatial distribution of cytosolic Ca2+ in the rhizoid tips was visualised in ratio images computed from low-light video-pictures. These images showed a fairly homogeneous distribution of Ca2+ throughout the tip cytoplasm with concentrations being in the same range as determined by microfluorimetry. A tip-to-base gradient in cytoplasmic Ca2+, thought to be a prerequisite for cell polarity and tip growth, was found in only 1 out of 16 successfully microinjected cells. Additionally, a progressive compartmentalization of the fluorochrome indo-1, probably in the proplastids and the very abundant endoplasmic reticulum of the rhizoids, was observed. 相似文献
997.
998.
Summary We traced the development in the laboratory of 18 young colonies of the arboricolous ponerine antEctatomma tuberculatum. Colony foundation is of the partially-claustral type. During the early stages, when the colony is entirely dependent on the queen's behavior, the growth of the colony in terms of number of workers produced over time was relatively predictable. Afterwards, divergence in colony growth in function of the time increases as fast as the number of workers influences the efficiency of colony provisioning.Comparative analysis indicated clear changes in the predation behavior of foundresses and workers as colonies developed. For any stage of colony growth, all individuals provisioned the nest with dead prey or sugar-rich substances in the same way. However, prey hunting involves two different strategies. Foundresses and nanitic workers (originating from colonies with 9–15 workers) foraged actively, catching prey as the result of random encounters. Post-nanitic foragers (originating from colonies with 20–30 workers) and those from nature colonies developed an ambush strategy. Workers in these colonies gained experience at catching and handling prey during a period when they acted as nest guards, and so tended to be more efficient hunters than poorly experienced foundresses or nanitic foragers. The change in strategy was also positively correlated with an increase in the size of workers as the colony matured. A stable maximum in workers size is apparently reached only after the appearance of efficiently hunting foragers, presumably in numbers sufficient to provide adequate quantity and quality of larval food. Such a correlation between worker size and colony growth, assumed general for all ants, has not been demonstrated for Ponerinae before this work. 相似文献
999.
Previous studies from this laboratory have shown that the phosphorylation of the S6 protein of the ribosomes is catalyzed by at least two different and separable kinase activities in PC12 cells. One of these activities is increased by treatment of the cells with nerve growth factor, the other by treatment of the cells with epidermal growth factor. The present work shows that these two factors stimulate the phosphorylation of S6 with quite different kinetics, and that both the number of phosphates incorporated into S6 and the phosphopeptide pattern of S6 are different in cells treated with nerve growth factor than in cells treated with epidermal growth factor. The characteristics of the nerve growth factor-sensitive S6 kinase and of the epidermal growth factor-sensitive kinase were also clearly different. Substrate specificity and inhibitor studies indicated that neither was identical to cyclic AMP-dependent kinase, kinase C, or the calcium/calmodulin-dependent kinases. However, two major phosphopeptides produced by S6 phosphorylation in nerve growth factor-treated cells were also seen on phosphorylation of S6 by cyclic AMP-dependent kinase in vitro. In addition, when rat liver 40S ribosomal subunits were pretreated with cyclic AMP-dependent kinase in vitro, the action of the nerve growth factor-sensitive S6 kinase was increased about twofold. 相似文献
1000.
Understanding the cellular response to hypoxia may help elucidate the role of altered oxidation in neuronal death or abnormal cell function. In PC12 cells, 30 min of chemical hypoxia (i.e., KCN) reduced ATP concentrations by 92%, but diminished viability by only 10%. Ten minutes of hypoxia increased cytosolic free calcium ([Ca2+]i) 2.5-fold above control, but after 30 min of hypoxia, [Ca2+]i was slightly below that of nonhypoxic cells. Short periods of hypoxia also exaggerated the K(+)-induced elevation of [Ca2+]i, but by 30 min these ATP-depleted cells reestablished a calcium gradient that was equal to nonhypoxic, K(+)-depolarized cells. Thus, 30 min of severe ATP depletion left [Ca2+]i and viability relatively unaffected. Nerve growth factor caused slight, but significant, improvements in ATP and viability of hypoxic cells, but had no effect on [Ca2+]i. Although [Ca2+]i was equivalent in control and hypoxic cells after 30 or 60 min, hypoxia abolished the K(+)-stimulated elevation of [Ca2+]i. The nerve growth factor induction of c-fos, an indicator of the genomic response, was diminished by approximately 80%. Thus, hypoxic PC12 cells with greatly reduced ATP stores maintained normal [Ca2+]i, but their ability to respond to external stimulation was impaired. Further, the reduced oxidation that occurs in the brain in a variety of pathological conditions may interfere with the cellular response to stimulation and growth factors. 相似文献