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排序方式: 共有2756条查询结果,搜索用时 40 毫秒
61.
H Tlaskalová-Hogenová R St?pánková L Tucková MA Farré DP Funda EF Verdú J Sinkora T Hudcovic Z Reháková B Cukrowska H Kozáková L Prokesová 《Canadian Metallurgical Quarterly》1998,43(5):545-550
Despite the fact that target antigens and the genetic basis of several autoimmune diseases are now better understood, the initial events leading to a loss of tolerance towards self-components remain unknown. One of the most attractive explanations for autoimmune phenomena involves various infections as possible natural events capable of initiating the process in genetically predisposed individuals. The most accepted explanation of how infection causes autoimmunity is based on the concept of "molecular mimicry" (similarity between the epitopes of an autoantigen and the epitopes in the environmental antigen). Infectious stimuli may also participate in the development of autoimmunity by inducing an increased expression of stress proteins (hsp), chaperones and transplantation antigens, which leads to abnormal processing and presentation of self antigens. Superantigens are considered to be one of the most effective bacterial components to induce inflammatory reactions and to take part in the development and course of autoimmune mechanisms. It has long been known that defects in the host defense mechanism render the individual susceptible to infections caused by certain microorganisms. Impaired exclusion of microbial antigens can lead to chronic immunological activation which can affect the tolerance to self components. Defects in certain components of the immune system are associated with a higher risk of a development of autoimmune disease. The use of animal models for the studies of human diseases with immunological pathogenesis has provided new insights into the influence of immunoregulatory factors and the lymphocyte subsets involved in the development of disease. One of the most striking conclusion arising from work with genetically engineered immunodeficient mouse models is the existence of a high level of redundancy of the components of the immune system. However, when genes encoding molecules involved in T cell immunoregulatory functions are deleted, spontaneous chronic inflammation of the gut mucosa (similar to human inflammatory bowel disease) develops. Surprisingly, when such immunocompromised animals were placed into germfree environment, intestinal inflammation did not develop. Impairment of the mucosal immune response to the normal bacterial flora has been proposed to play a crucial role in the pathogenesis of chronic intestinal inflammation. The use of immunodeficient models colonized with defined microflora for the analysis of immune reactivity will shed light on the mode of action of different immunologically important molecules responsible for the delicate balance between luminal commensals, nonspecific and specific components of the mucosal immune system. 相似文献
62.
Floral nectar phenolics as biochemical markers for the botanical origin of heather honey 总被引:1,自引:0,他引:1
Federico Ferreres Paula Andrade Maria I. Gil Francisco A. Tomás-Barberán 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,202(1):40-44
In order to find out biochemical markers for the botanical origin of heather (Erica) honey, the phenolic metabolites present in heather floral nectar, collected from the honey-stomach of bees gathering nectar from these flowers, were analysed. The flavonoid fraction of nectar contained four main flavonoids. Two of them were quercetin and kaempferol 3-rhamnosides, and the other two were tentatively identified as myricetin 3-methyl ether and isorhamnetin 3-rhamnosides. Since the natural glycosides are hydrolysed by bee enzymes to render the corresponding aglycones, which are the metabolites detected in honey, acid hydrolysis of the nectar glycosides was achieved. The aglycones quercetin, myricetin 3-methyl ether, kaempferol and isorhamnetin were identified, as well as the gallic acid derivative ellagic acid. The analysis of Portuguese heather honey samples showed that ellagic acid was present in all the samples in significant amounts ranging between 100 g and 600 g per 100 g honey. The other nectar-derived flavonoids were also present, although some of them in very variable amounts. Ellagic acid and myricetin 3-methyl ether, which have not been detected in any of the monofloral honey samples investigated so far, with the only exception being a French honey sample of the botanically relatedCalluna (Ericaceae) which also contained ellagic acid, seem to be the most useful potential markers for the floral origin of heather honey. However, more detailed and extensive investigations are needed to prove the utility of these markers. 相似文献
63.
Ward atmosphere was assessed with the help of the Ward Atmosphere Scale (WAS) by patients, nurses and physicians on 8 admission units before and after the introduction of the partial open door system. On average, on 45% of the days on which the units could have been potentially open, they were indeed at least temporarily open. Several significant changes in the WAS scores, mostly in desirable direction, were registered. However, close relationship with the partial opening of the units could be substantiated only with regard to the scale "praxis orientation"; still a positive result. No unequivocal relationships could be demonstrated between the introduction of the partial open door system and the changes in the frequency of "special events". 相似文献
64.
65.
Miguel Juliá Óscar Reinoso Arturo Gil Mónica Ballesta Luis Payá 《Engineering Applications of Artificial Intelligence》2010,23(4):473-486
In this paper we present a hybrid reactive/deliberative approach to the multi-robot integrated exploration problem. In contrast to other works, the design of the reactive and deliberative processes is exclusively oriented to the exploration having both the same importance level. The approach is based on the concepts of expected safe zone and gateway cell. The reactive exploration of the expected safe zone of the robot by means of basic behaviours avoids the presence of local minima. Simultaneously, a planner builds up a decision tree in order to decide between exploring the current expected safe zone or changing to other zone by means of travelling to a gateway cell. Furthermore, the model takes into account the degree of localization of the robots to return to previously explored areas when it is necessary to recover the certainty in the position of the robots. Several simulations demonstrate the validity of the approach. 相似文献
66.
We address the self-calibration of a smooth generic central camera from only two dense rotational flows produced by rotations
of the camera about two unknown linearly independent axes passing through the camera centre. We give a closed-form theoretical
solution to this problem, and we prove that it can be solved exactly up to a linear orthogonal transformation ambiguity. Using
the theoretical results, we propose an algorithm for the self-calibration of a generic central camera from two rotational
flows. 相似文献
67.
Many applications require teams of robots to cooperatively execute tasks. Among these domains are those in which successful
coordination must respect intra-path constraints, which are constraints that occur on the paths of agents and affect route
planning. This work focuses on multi-agent coordination for disaster response with intra-path precedence constraints, a compelling
application that is not well addressed by current coordination methods. In this domain a group of fire truck agents attempt
to address fires spread throughout a city in the wake of a large-scale disaster. The disaster has also caused many city roads
to be blocked by impassable debris, which can be cleared by bulldozer robots. A high-quality coordination solution must determine
not only a task allocation but also what routes the fire trucks should take given the intra-path precedence constraints and
which bulldozers should be assigned to clear debris along those routes. 相似文献
68.
Gil Shklarski Sivan Toledo 《Computer Methods in Applied Mechanics and Engineering》2009,198(37-40):3084-3095
We present a method for computing the null space of finite element models, including models with equality constraints. The method is purely algebraic; it requires access to the element matrices, but not to the geometry or material properties of the model.Theoretical considerations show that under certain conditions, both the amount of computation and the amount of memory required by our method scale linearly with model size; memory scales linearly but computation scales quadratically with the dimension of the null space. Our experiments confirm this: the method scales extremely well on 3-dimensional model problems. In general, large industrial models do not satisfy all the conditions that the theoretical results assume; however, experimentally the method performs well and outperforms an established method on industrial models, including models with many equality constraints.The accuracy of the computed null vectors is acceptable, but the method is usually less accurate than a more naive (and computationally much more expensive) method. 相似文献
69.
The pre-integrated volume rendering technique is widely used for creating high quality images. It produces good images even though the transfer function is nonlinear. Because the size of the pre-integration lookup table is proportional to the square of data precision, the required storage and computation load steeply increase for rendering of high-precision volume data. In this paper, we propose a method that approximates the pre-integration function proportional to the data precision. Using the arithmetic mean instead of the geometric mean and storing opacity instead of extinction density, this technique reduces the size and the update time of the pre-integration lookup table so that it classifies high-precision volume data interactively. We demonstrate performance gains for typical renderings of volume datasets. 相似文献
70.
The oxidation behaviour of the intermetallic phase Ti-50 at% Al at 900 °C was studied. It was found that the oxidation behaviour strongly depends on the composition and distribution of the and 2-phases in the alloy microstructure. As this microstructure strongly depends on the alloy cooling rate, the oxidation behaviour of TiAl-based intermetallics is significantly affected by the casting procedure and subsequent heat treatment. Rapid cooling from high temperature (T 1400 °C) has a beneficial effect on oxidation behaviour.On leave from the Academy of Mining and Metallurgy, Krakow, Poland. 相似文献