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81.
The paper considers the problem of density estimation and clustering in distributed sensor networks. It is assumed that each node in the network senses an environment that can be described as a mixture of some elementary conditions. The measurements are thus statistically modeled with a mixture of Gaussians, where each Gaussian component corresponds to one of the elementary conditions. The paper presents a distributed expectation-maximization (EM) algorithm for estimating the Gaussian components, which are common to the environment and sensor network as a whole, as well as the mixing probabilities that may vary from node to node. The algorithm produces an estimate (in terms of a Gaussian mixture approximation) of the density of the sensor data without requiring the data to be transmitted to and processed at a central location. Alternatively, the algorithm can be viewed as a distributed processing strategy for clustering the sensor data into components corresponding to predominant environmental features sensed by the network. The convergence of the distributed EM algorithm is investigated, and simulations demonstrate the potential of this approach to sensor network data analysis. 相似文献
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Bipolar meiotic spindle formation without chromatin 总被引:1,自引:0,他引:1
S Brunet Z Polanski MH Verlhac JZ Kubiak B Maro 《Canadian Metallurgical Quarterly》1998,8(22):1231-1234
Establishing a bipolar spindle is an early event of mitosis or meiosis. In somatic cells, the bipolarity of the spindle is predetermined by the presence of two centrosomes in prophase. Interactions between the microtubules nucleated by centrosomes and the chromosomal kinetochores enable the formation of the spindle. Non-specific chromatin is sufficient, however, to promote spindle assembly in Xenopus cell-free extracts that contain centrosomes [1,2]. The mouse oocyte represents an excellent model system in which to study the mechanism of meiotic spindle formation because of its size, transparency and slow development. These cells have no centrioles, and their multiple microtubule-organizing centers (MTOCs) are composed of foci of pericentriolar material [3,4]. The bipolarity of the meiotic spindle emerges from the reorganization of these randomly distributed MTOCs [4]. Regardless of the mechanisms involved in this reorganization, the chromosomes seem to have a major role during spindle formation in promoting microtubule polymerization and directing the appropriate rearrangement of MTOCs to form the two poles [5]. Here, we examined spindle formation in chromosome-free mouse oocyte fragments. We found that a bipolar spindle can form in vivo in the absence of any chromatin due to the establishment of interactions between microtubule asters that are progressively stabilized by an increase in the number of microtubules involved, demonstrating that spindle formation is an intrinsic property of the microtubule network. 相似文献
84.
L Nogowski P Ma?kowiak K Kandulska T Szkudelski KW Nowak 《Canadian Metallurgical Quarterly》1998,42(6):360-366
The effect of the isoflavone, genistein, on the lipid metabolism of ovariectomized rats was studied. Three types of experiments were performed. In the first one, the rats were fed diets supplemented with 0.01 or 0.1% of genistein for 14 days. In the second and third experiments, the direct effect of genistein on the liver and fat tissue were measured respectively by means of liver perfusion or incubation of isolated adipocytes with the isoflavone. Genistein in food significantly decreased blood serum and muscle triglyceride concentrations and increased the level of free fatty acids in serum. Serum free cholesterol was diminished and liver cholesterol was enhanced after genistein ingestion. When genistein acted directly on the liver during perfusion, a smaller incorporation of 14C-glucose into lipids was observed, and in parallel a greater output of free fatty acids into the medium was noticed. These changes were accompanied by diminution of the liver triglyceride contents. Genistein, acting on the adipocytes strongly depressed both basal and insulin-induced lipid synthesis, when glucose was used as a substrate. The effect of the isoflavone alone on the lipolysis in the adipocytes was negligible. However, it intensified lipolysis induced by epinephrine. The results obtained let us conclude that genistein in food can reduce the fattening processes in ovariectomized rats. This effect of genistein may be attributed, at least in part, to its direct influence on lipid metabolism in the liver and adipose tissue. 相似文献
85.
MF Nitschke UH Melchert C Hahn V Otto H Arnold HD Herrmann G Nowak M Westphal K Wessel 《Canadian Metallurgical Quarterly》1998,140(12):1223-1229
Intracranial lesions may compromise structures critical for motor performance, and mapping of the cortex, especially of the motor hand area, is important to reduce postoperative morbidity. We investigated nine patients with parietal lobe tumours and used functional MRI sensitized to changes in blood oxygenation to define the different motor areas, especially the primary sensorimotor cortex, in relation to the localization of the tumour. Activation was determined by pixel-by-pixel correlation of the signal intensity time course with a reference waveform equivalent to the stimulus protocol. All subjects showed significant activation of the primary sensorimotor cortex while performing a finger opposition task with the affected and unaffected side. In five patients the finger opposition task additionally activated the ipsilateral sensorimotor cortex and the supplementary motor area (SMA). Extension and flexion of the foot, additionally performed in two patients, also activated the sensorimotor cortex, in one case within the perifocal oedema of the tumour. Tumour localization near the central sulcus induced displacement of the sensorimotor cortex as compared to the unaffected side in all patients with a relevant mass effect. The results of our study demonstrate that functional MRI at 1.5 T with a clinically used tomograph can reproducibly localize critical brain regions in patients with intracranial lesions. 相似文献
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L Wolska-Goszka A Nowak E Jassem J Galiński JM S?omiński 《Canadian Metallurgical Quarterly》1997,3(16):206-207
At the beginning of 80-ties new system BACTEC for mycobacteria culture has been introduced. So time of this culture has been shortened to 1-3 weeks. At the end 80-ties Polymerase Chain Reaction (PCR) technique was started and at present it is used in many laboratories in order to get information about genetic material of mycobacteria in different biological samples. Most often insertive factor IS 6110, located in chromosome Myc. tub. complex, is used. DNA amplification occurs in three stages: 1) DNA denaturation. 2) addition of starters (primers): 3) elongation of starter with d NTP synthesis. PCR technique identifies genetic material (DNA) of mycobacterium which is presented in a given biological sample. Positive PCR result not necessarily means that active disease takes place. 相似文献
89.
JZ Ayanian E Guadagnoli BJ McNeil PD Cleary 《Canadian Metallurgical Quarterly》1997,157(22):2570-2576
BACKGROUND: Both cardiologists and generalist physicians care for patients with acute myocardial infarction, but little is known about their patients' characteristics, treatments, and outcomes. METHODS: We identified attending and consulting physicians, patient characteristics, drugs, procedures, and mortality from clinical and administrative records of 1620 Medicare beneficiaries aged 65 to 79 years who were treated for acute myocardial infarction at 285 hospitals in Texas during 1990. RESULTS: Patients treated by attending cardiologists were younger, had prior congestive heart failure less frequently, and were initially treated in hospitals offering coronary angioplasty or bypass surgery more often than patients treated by attending generalist physicians (for each, P<.004). Adjusting for patient and hospital characteristics, cardiologists were more likely than generalist physicians to prescribe thrombolytic therapy and aspirin (P<.05) but not beta-adrenergic blocking agents (beta-blockers). Cardiologists used coronary angiography and angioplasty more often (P<.003), but not echocardiography or exercise testing. Adjusted 1-year mortality did not differ significantly between patients of attending cardiologists and generalist physicians (odds ratio, 1.01; 95% confidence interval, 0.76-1.35) or between patients of generalist physicians with and without a consulting cardiologist (odds ratio, 0.83; 95% confidence interval, 0.60-1.16). However, patients initially admitted to hospitals offering coronary angioplasty and bypass surgery had lower adjusted 1-year mortality than patients admitted to other hospitals (odds ratio, 0.68; 95% confidence interval, 0.47-0.98). CONCLUSIONS: Compared with generalist physicians, cardiologists used some, but not all, effective drugs more frequently, as well as coronary angiography and angioplasty. Although these differences were not associated with lower adjusted mortality among cardiologists' patients, cardiologists were more likely to treat patients in hospitals with better outcomes. Future studies should identify organizational factors that improve outcomes of myocardial infarction. 相似文献
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