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991.
YS Hu H Zhou V Kartsogiannis JA Eisman TJ Martin KW Ng 《Canadian Metallurgical Quarterly》1998,12(11):1721-1732
The rat homeobox gene, rHox, was cloned from a rat osteosarcoma cDNA library. Southwestern and gel mobility shift analyses showed that rHox binds to the promoter regions of collagen (alpha1)I and osteocalcin genes while transient transfection with rHox resulted in repression of their respective promoter activities. In situ hybridization studies showed that rHox mRNA was widely expressed in osteoblasts, chondrocytes, skeletal muscle, skin epidermis, and bronchial and intestinal epithelial cells, as well as cardiac muscle in embryonic and newborn mice. However in 3-month-old mice, rHox mRNA expression was restricted to osteoblasts, megakaryocytes, and myocardium. Bone morphogenetic protein 2, a growth factor that commits mesenchymal progenitor cells to differentiate into osteoblasts, down-regulated rHox mRNA expression by 40-50% in UMR 201, a rat preosteoblast cell line, in a time- and dose-dependent manner. In contrast, PTH-related protein (PTHrP), recently shown to be a negative regulator of chondrocyte differentiation, significantly enhanced rHox mRNA expression in UMR 106-06 osteoblastic cells by 3-fold at 24 h while at the same time down-regulating expression of pro-alpha1(I) collagen mRNA by 60%. Expression of rHox mRNA in calvarial osteoblasts derived from PTHrP -/- mice was approximately 15% of that observed in similar cells obtained from normal mice. In conclusion, current evidence suggests that rHox acts as a negative regulator of osteoblast differentiation. Furthermore, down-regulation of rHox mRNA by bone morphogenetic protein 2 and its up-regulation by PTHrP support a role of the homeodomain protein, rHox, in osteoblast differentiation. 相似文献
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994.
JA Laudy MM Janssen PC Struyk T Stijnen HC Wallenburg JW Wladimiroff 《Canadian Metallurgical Quarterly》1998,12(2):93-96
The effect of all-trans retinoic acid (RA), which is known as a regulator of cell growth and differentiation, was studied during neuronal apoptosis. Apoptosis was induced in primary cultures of chick embryonic neurons by treatment with staurosporine (200 nM) for 24 h which led to a reduction of cellular viability to 40% compared to 83% in untreated cultures as well as to an increase in the number of apoptotic neurons (determined by nuclear staining with Hoechst 33258) to 60% compared to 15% in untreated cultures. RA (1 nM-10 microM) reduced the number of non-viable and apoptotic cells in a concentration-dependent manner and the maximal response was seen at 1 microM RA with 60% cellular viability and 38% apoptotic neurons. The production of mitochondrial reactive oxygen species (ROS, determined by the fluorescent indicator dihydrorhodamine) was elevated 4.4-fold after 4 h of staurosporine-treatment which was reduced to a 2-fold increase in the presence of 10 microM RA. The results indicate that RA was able to reduce apoptotic damage in staurosporine-treated chick embryonic neurons by suppressing the production of ROS. 相似文献
995.
J Hamacher S Sadallah JA Schifferli J Villard LP Nicod 《Canadian Metallurgical Quarterly》1998,11(1):112-119
The presence of epidermal-growth-factor receptors (EGFR) and of its ligands (TGFalpha and amphiregulin) in breast-cancer tissues suggests that they play a paracrine/autocrine role in tumor growth or progression. This hypothesis was tested on 3 cell lines, S2T2, NS2T2A and NS2T2A1. These epithelial cells are derived from a normal human breast-epithelial-cell culture transformed by SV40-T Ag, are of the same clonal origin, have respectively increasing levels of EGFR, TGFalpha, amphiregulin and of thymidine-kinase activity associated with increasing tumorigenic potential in nude mice (tumor intake and tumor volume). The monoclonal antibody MAb 425, which blocks ligands interaction with EGFR, reduced by more than 90% anchorage-independent growth of the most tumorigenic cells, NS2T2A1. Another anti-EGFR MAb, 528, reduced to 25% of controls the mean tumor mass after NS2T2A1 grafting in mice. Anti-sense RNA expression of EGFR in these cells confirmed the importance of this receptor in tumor progression, since it reduced significantly the tumor volume and tumor weight of NS2T2A1 cells to 16% of those in mock-transfected control cells. 相似文献
996.
MA Alexander-Miller MA Derby A Sarin PA Henkart JA Berzofsky 《Canadian Metallurgical Quarterly》1998,188(8):1391-1399
Cytotoxic T lymphocytes (CTLs) are primary mediators of viral clearance, but high viral burden can result in deletion of antigen-specific CTLs. We previously reported a potential mechanism for this deletion: tumor necrosis factor (TNF)-alpha-mediated apoptosis resulting from stimulation with supraoptimal peptide-major histocompatibility complex. Here, we show that although death is mediated by TNF-alpha and its receptor (TNF-RII), surprisingly neither the antigen dose dependence of TNF-alpha production nor that of TNF-RII expression can account for the dose dependence of apoptosis. Rather, a previously unrecognized effect of supraoptimal antigen in markedly decreasing levels of the antiapoptotic protein Bc1-2 was discovered and is likely to account for the gain in susceptibility or competence to sustain the death signal through TNF-RII. This decrease requires a signal through the TCR, not just through TNF-RII. Although death mediated by TNF-RII is not as widely studied as that mediated by TNF-RI, we show here that it is also dependent on proteolytic cleavage by caspases and triggered by a brief initial encounter with antigen. These results suggest that determinant density can regulate the immune response by altering the sensitivity of CTLs to the apoptotic effects of TNF-alpha by decreasing Bc1-2 levels. 相似文献
997.
Actin in eukaryotic cells is found in different pools, with filaments being organized into a variety of supramolecular assemblies. To investigate the assembly and functional relationships between different parts of the actin cytoskeleton in one cell, we studied the morphology and dynamics of cables and patches in yeast. The fine structure of actin cables and the manner in which cables disassemble support a model in which cables are composed of a number of overlapping actin filaments. No evidence for intrinsic polarity of cables was found. To investigate to what extent different parts of the actin cytoskeleton depend on each other, we looked for relationships between cables and patches. Patches and cables were often associated, and their polarized distributions were highly correlated. Therefore, patches and cables do appear to depend on each other for assembly and function. Many cell types show rearrangements of the actin cytoskeleton, which can occur via assembly or movement of actin filaments. In our studies, dramatic changes in actin polarization did not include changes in filamentous actin. In addition, the concentration of actin patches was relatively constant as cells grew. Therefore, cells do not have bursts of activity in which new parts of the actin cytoskeleton are created. 相似文献
998.
The use of photoconductors, especially amorphous selenium (a-Se), in x-ray imaging is currently of interest. A critical performance parameter of an imaging detector is the Swank factor for degradation of the signal to noise ratio, or DQE(0), due to variations in the detector response. The Swank factor is evaluated from measured pulse height spectra generated by the absorption of monoenergetic x-ray photons. The spectra show an additional width over previous theoretical expectations, but the Swank factor is still close to the high values previously predicted theoretically. 相似文献
999.
Whole cell patch-clamp techniques were used to study voltage-dependent sodium (Na+), calcium (Ca2+), and potassium (K+) conductances in acutely isolated neurons from cortical layer I of adult rats. Layer I cells were identified by means of gamma-aminobutyric acid (GABA) immunocytochemistry. Positive stainings for the Ca2+-binding protein calretinin in a subset of cells, indicated the presence of Cajal-Retzius (C-R) cells. All investigated cells displayed a rather homogeneous profile of voltage-dependent membrane currents. A fast Na+ current activated at about -45 mV, was half-maximal steady-state inactivated at -66.6 mV, and recovery from inactivation followed a two-exponential process (tau1 = 8.4 ms and tau2 = 858.8 ms). Na+ currents declined rapidly with two voltage-dependent time constants, reaching baseline current after some tens of milliseconds. In a subset of cells (< 50%) a constant current level of < 65 pA remained at the end of a 90 ms step. A transient outward current (Ifast) activated approximately -40 mV, declined rapidly with a voltage-insensitive time constant (tau approximately 350 ms) and was relatively insensitive to tetraethylammonium (TEA, 20 mM). Ifast was separated into two components based on their sensitivity to 4-aminopyridine (4-AP): one was blocked by low concentrations (40 microM) and a second by high concentrations (6 mM). After elimination of Ifast by a conditioning prepulse (50 ms to -50 mV), a slow K+ current (I(KV)) could be studied in isolation. I(KV) was only moderately affected by 4-AP (6 mM), while TEA (20 mM) blocked most (> 80%) of the current. I(KV) activated at about -40 mV, declined monoexponentially in a voltage-dependent manner (tau approximately 850 ms at -30 mV), and revealed an incomplete steady-state inactivation. In addition to Ifast and I(KV), indications of a Ca2+-dependent outward current component were found. When Na+ currents, Ifast, and I(KV) were blocked by tetrodotoxin (TTX, 1 microM), 4-AP (6 mM) and TEA (20 mM) an inward current carried by Ca2+ was found. Ca2+ currents activated at depolarized potentials at about -30 mV, were completely blocked by 50 microM cadmium (Cd2+), were sensitive to verapamil (approximately 40% block by 10 microM), and were not affected by nickel (50 microM). During current clamp recordings, isolated layer I neurons displayed fast spiking behaviour with short action potentials (approximately 2 ms, measured at half maximal amplitude) of relative small amplitude (approximately 83 mV, measured from the action potential threshold). 相似文献
1000.
G Fischer V Mutel G Trube P Malherbe JN Kew E Mohacsi MP Heitz JA Kemp 《Canadian Metallurgical Quarterly》1997,283(3):1285-1292
The interaction of Ro 25-6981 with N-methyl-D-aspartate (NMDA) receptors was characterized by a variety of different tests in vitro. Ro 25-6981 inhibited 3H-MK-801 binding to rat forebrain membranes in a biphasic manner with IC50 values of 0.003 microM and 149 microM for high- (about 60%) and low-affinity sites, respectively. NMDA receptor subtypes expressed in Xenopus oocytes were blocked with IC50 values of 0.009 microM and 52 microM for the subunit combinations NR1C & NR2B and NR1C & NR2A, respectively, which indicated a >5000-fold selectivity. Like ifenprodil, Ro 25-6981 blocked NMDA receptor subtypes in an activity-dependent manner. Ro 25-6981 protected cultured cortical neurons against glutamate toxicity (16 h exposure to 300 microM glutamate) and combined oxygen and glucose deprivation (60 min followed by 20 h recovery) with IC50 values of 0.4 microM and 0.04 microM, respectively. Ro 25-6981 was more potent than ifenprodil in all of these tests. It showed no protection against kainate toxicity (exposure to 500 microM for 20 h) and only weak activity in blocking Na+ and Ca++ channels, activated by exposure of cortical neurons to veratridine (10 microM) and potassium (50 mM), respectively. These findings demonstrate that Ro 25-6981 is a highly selective, activity-dependent blocker of NMDA receptors that contain the NR2B subunit. 相似文献