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931.
Robustness, the ability of a system to function correctly in the presence of both internal and external uncertainty, has emerged as a key organising principle in many biological systems. Biological robustness has thus become a major focus of research in Systems Biology, particularly on the engineering-biology interface, since the concept of robustness was first rigorously defined in the context of engineering control systems. This review focuses on one particularly important aspect of robustness in Systems Biology, that is, the use of robustness analysis methods for the validation or invalidation of models of biological systems. With the explosive growth in quantitative modelling brought about by Systems Biology, the problem of validating, invalidating and discriminating between competing models of a biological system has become an increasingly important one. In this review, the authors provide a comprehensive overview of the tools and methods that are available for this task, and illustrate the wide range of biological systems to which this approach has been successfully applied. 相似文献
932.
J. Neal G. Schumann T. Fewtrell M. Budimir P. Bates D. Mason 《Journal of Flood Risk Management》2011,4(2):88-95
Two‐dimensional flood inundation modelling is a widely used tool to aid flood risk management. In urban areas, the model spatial resolution required to represent flows through a typical street network often results in an impractical computational cost at the city scale. This paper presents the calibration and evaluation of a recently developed formulation of the LISFLOOD‐FP model, which is more computationally efficient at these resolutions. Aerial photography was available for model evaluation on 3 days from the 24 to the 31 of July. The new formulation was benchmarked against the original version of the model at 20 and 40 m resolutions, demonstrating equally accurate simulation, given the evaluation data but at a 67 times faster computation time. The July event was then simulated at the 2 m resolution of the available airborne LiDAR DEM. This resulted in more accurate simulation of the floodplain drying dynamics compared with the coarse resolution models, although maximum inundation levels were simulated equally well at all resolutions tested. 相似文献
933.
The necessary characteristics are derived for an antenna system which is to transmit efficiently and faithfully a very wide bandwidth (of an octave or more) signal. It is demonstrated that a suitable antenna for such a system may radiate isotropically in azimuth but be focused in all vertical planes. It is shown that a phase-corrected conical monopole is a convenient approximate realization of the antenna. Results are presented of an experimental investigation (inferring frequency responses from nanosecond time-domain-reflectometer techniques) of the driving-point and far-field responses of conical monopoles phase-corrected with cylindrically symmetrical lenses. Included is an experimental verification of previous theoretical predictions of the frequency dependence of the radiation which occurs when a transient is radiated from the base and the tip of a thin cylindrical monopole. 相似文献
934.
Discrete nanopores develop in the interfacial regions of polyolefin blends and layered films under tension. They originate from crazelike structures in the early development stage, which later undergo disruption processes with an increase in strain. The disruption processes appear to be triggered by the existence of adjacent ductile polyolefins and their micromechanical deformations. The degree of nanopore development significantly varies among blends and layered systems, depending on several material parameters, such as the interfacial strength. Discrete nanopores are observed more often in metallocene systems and blends than in Ziegler–Natta systems and layered films. Macroscopically, with the development of discrete nanopores, metallocene systems show higher strain to break and significant shear yielding under tension. The disruption mechanism can be used to prepare nanoporous materials or to improve the mechanical performances of polyolefins. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 708–718, 2005 相似文献
935.
Intrauterine growth retardation (IUGR), which is defined as less than 10 percent of predicted fetal weight for gestational age, may result in significant fetal morbidity and mortality if not properly diagnosed. The condition is most commonly caused by inadequate maternal-fetal circulation, with a resultant decrease in fetal growth. Less common causes include intrauterine infections such as cytomegalovirus and rubella, and congenital anomalies such as trisomy 21 and trisomy 18. When IUGR is recognized, it is important to attempt to correct reversible causes, although many of the conditions responsible for IUGR are not amenable to antenatal therapy. Close fetal surveillance with delivery before 38 weeks of gestation is usually recommended. Some infants born with IUGR have cognitive and medical problems, although for most infants the long-term prognosis is good. 相似文献
936.
AT Hattersley PM Clark R Page JC Levy L Cox CN Hales RC Turner 《Canadian Metallurgical Quarterly》1997,40(11):1367-1368
937.
938.
Reproduction in vertebrates is regulated by internal signals such as hormone levels and by external signals such as social interactions. In an African cichlid fish, Haplochromis burtoni, the effect of social interactions is evident in the hypothalamo-pituitary-gonadal (HPG) axis of males. Territorial males, characterized by aggressive and reproductive activity, have significantly larger hypothalamic gonadotropin-releasing hormone (GnRH)-containing neurons and larger testes than nonterritorial males. Furthermore, a switch in the social status of an adult male causes a corresponding change in GnRH neuron size and testis size. Here we show that the GnRH-containing neurons in the hypothalamus of adult territorial males are also influenced by gonadal hormones. Castration of territorial males caused GnRH neurons to increase in size. This neuronal hypertrophy in castrated animals was prevented either by testosterone (T) or 11-ketotestosterone (KT) treatment. Estradiol (E2) treatment did not reduce GnRH cell size in castrated animals. These results suggest that androgens reduce the size of GnRH cells through negative feedback. Since E2 had no effect, androgen influence on GnRH cell size appears to be independent of aromatization. These data are consistent with the hypothesis that the setpoint for hypothalamic GnRH cell size is determined by social cues and that this setpoint is maintained by negative feedback from gonadal androgens. 相似文献
939.
Hippocampal cells often fire prolonged bursts of action potentials, resulting in dynamic modulation of postsynaptic responses; yet long-term potentiation (LTP) has routinely been studied using only single presynaptic stimuli given at low frequency. Recent work on neocortical synapses has suggested that LTP may cause a \"redistribution of synaptic strength\" in which synaptic responses to the first stimulus of a presynaptic burst of action potentials are potentiated with later responses depressed. We have examined whether this redistribution occurs at hippocampal synapses during LTP. Using prolonged bursts that result in maximal short-term depression of later responses within the burst, we found that LTP resulted in a uniform potentiation of individual responses throughout the burst rather than a redistribution of synaptic strength. This occurred both at Schaffer collateral-CA1 synapses and at CA3-CA3 synapses, the latter being activated and monitored using paired recordings. Thus in the hippocampus, LTP preserves the fidelity of postsynaptic responses to presynaptic bursts by a uniform increase rather than a redistribution of synaptic strength, a finding that suggests there are important differences between neocortex and hippocampus in how long-term changes in synaptic strength are used to encode new information. 相似文献
940.
EE Bates MC Dieu O Ravel SM Zurawski S Patel JM Bridon S Ait-Yahia F Vega J Banchereau S Lebecque 《Canadian Metallurgical Quarterly》1998,35(9):513-524
Using a cDNA subtraction technique, a novel member of the immunoglobulin superfamily was isolated from human Dendritic cells (DC). This cDNA which we named DORA, for DOwn-Regulated by Activation encodes a protein belonging to the CD8 family of receptors containing a single V type loop domain with an associated J chain region, a transmembrane region containing an atypical tyrosine residue and a cytoplasmic domain containing three putative tyrosine phosphorylation sites. The hDORA gene has been localised to chromosome 16. From database searches a rat cDNA was identified that encoded a polypeptide with 63% identity to hDORA. The expression of the human cDNA was studied in detail. Northern blot analysis revealed 1.0 kb and 2.5 kb mRNAs in peripheral blood lymphocytes, spleen and lymph node, while low levels were observed in thymus, appendix, bone marrow and fetal liver. No signal was noted in non-immune system tissues. By RT-PCR analysis of hDORA revealed expression in cells committed to the myeloid lineage but not in CD34+ precursors or B cells and low expression in T cells. Expression was also observed in DC, purified ex vivo or generated in vitro from either monocytes or CD34+ progenitors. This was down-regulated following activation both by PMA and Ionomycin treatment and also by CD40L engagement. In situ hybridisation performed on tonsil sections showed the presence of hDORA in cells within Germinal Centers. This structure and expression suggests a function as a co-receptor, perhaps in an antigen uptake complex, or in homing or recirculation of DC. 相似文献