全文获取类型
收费全文 | 2987篇 |
免费 | 176篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 3164篇 |
出版年
2023年 | 35篇 |
2022年 | 175篇 |
2021年 | 187篇 |
2020年 | 92篇 |
2019年 | 90篇 |
2018年 | 110篇 |
2017年 | 90篇 |
2016年 | 137篇 |
2015年 | 93篇 |
2014年 | 119篇 |
2013年 | 205篇 |
2012年 | 171篇 |
2011年 | 219篇 |
2010年 | 160篇 |
2009年 | 189篇 |
2008年 | 132篇 |
2007年 | 133篇 |
2006年 | 110篇 |
2005年 | 89篇 |
2004年 | 69篇 |
2003年 | 60篇 |
2002年 | 61篇 |
2001年 | 36篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 44篇 |
1997年 | 34篇 |
1996年 | 42篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有3164条查询结果,搜索用时 0 毫秒
1.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
2.
A.G. Berkovski G. Chiodi J.-P. Fabre A. Frenkel S.V. Golovkin Yu.I. Gubanov G.N. Kislizkai E.N. Kozarenko I.E. Kreslo A.E. Kushnirenko G. Martellotti D. Mazza A.M. Medvedkov G. Penso 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,380(3):537-543
We present the performance of a high-speed gateable vacuum image pipeline, which permits individual images to be delayed and selected from continuous non-repetitive image stream. This device is composed of a vacuum tube equipped with a photocathode at one end, a phosphor screen at the other end, and a system of metal grids in between. Photoelectrons produced by the images focused on the photocathode, are guided by a uniform magnetic field, parallel to the tube axis. By changing the grid potentials, the drift time of the photoelectrons inside the tube can be varied from 0.35 to 1.5 μs. An image can then be selected by an external trigger with a time resolution in the range of 4–30 ns, depending on the delay time. The selected photoelectrons are finally accelerated onto the phosphor screen, set at 10 kV, where they reproduce the desired image. With a magnetic field of 0.1 T, a spatial resolution of 33 lp/mm was obtained. The high spatial and time resolution make this device an interesting tool for high-energy physics and astrophysics experiments, and for high-speed photography. 相似文献
3.
BACKGROUND: The incidental discovery of an adrenal mass poses the problem of distinguishing between the frequent benign masses and the infrequent malignant ones that require surgery. Univocal guidelines to approach this problem are unavailable. OBJECTIVE: To perform a survey of the clinical management of incidentally discovered adrenal masses (ie, adrenal incidentalomas). DESIGN: A multicentric retrospective analysis of hospital medical records of adrenal incidentalomas diagnosed during a 5-year period; the medical records were scrutinized for demographic data and clinical details by means of a specifically tailored questionnaire. SETTING: The major surgical and medical centers of Piedmont, a northern Italian region with approximately 4 million inhabitants. The recruitment pattern of these centers was unselected. PATIENTS: The definition of adrenal incidentaloma was limited to patients with a physical examination and a clinical history unindicative of adrenal disease. Exclusion criteria also included hypertension of suspected endocrine origin and a history of neoplasms known to metastasize frequently in the adrenal glands. Two hundred twenty-four medical records were collected, and 210 were analyzed (14 excluded a posteriori). RESULTS: Most patients were in their 50s and 60s, and women were predominantly affected. The frequency of adrenocortical cancer was 13% among patients operated on. The tumor diameter was highly correlated with the risk of cancer; a cutoff at 5 cm had a sensitivity of 93% with a specificity of 64% in discriminating between benign and malignant cortical lesions. CONCLUSIONS: The occurrence of adrenocortical carcinoma among adrenal incidentalomas is not rare. The evaluation of the mass size is a simple and effective method for selecting patients at risk for cancer. The indication for surgery of masses larger than 5 cm, or of masses of any diameter that have suspicious imaging characteristics, limits unnecessary operations and costs. 相似文献
4.
A SAXS method for the quantitative assessment of the morphology of polymer layered silicate nanocomposites is proposed. Fitting the SAXS patterns, the number of clay layers, the periodicity of the layers in the tactoids, the thickness of the regions interposed between the clay platelets and their distributions can be measured. A good agreement with TEM data was obtained, avoiding the inconsistencies with microscopical observations often reported in the literature. 相似文献
5.
Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications 总被引:1,自引:0,他引:1
The slow (subcritical) crack growth (SCG) resistance of Si3 N4 and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si3 N4 sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si3 N4 without additives. 相似文献
6.
Giuseppe G. G. Manzardo Sandra Kürsteiner-Laube und Daniel Perrin 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(6):501-506
In diethyl ether extracts from celeriac (Apium graveolens L. var.rapaceum) all four stereoisomers of (3a–7a)-cis-3-butylhexahydrophthalide were found to be present. The analyses were carried out by means of GC, enantioselective GC and GC-MS. The assignment of the relative configuration of the diastereomers3 and4 was accomplished by NOE difference spectroscopy. 相似文献
7.
The present research was focused on the development of a new glass to produce glass–alumina FGMs. The glass formulation, belonging to the CaO–ZrO2–SiO2 system, was doped with cobalt, by adding a small molar percentage (about 0.1 mol%) of CoO, in order to obtain a blue glass, which could be useful to appreciate the final compositional gradient. The glass was accurately characterized, evaluating its thermal behaviour, its mechanical properties, and its attitude to crystallize during a thermal treatment. Subsequently, the glass was used to produce glass–alumina FGMs via percolation and the so obtained specimens were analysed in order to evaluate the effect of the glass infiltration. The possible development of new crystal phases, in particular, was tested via micro X-ray diffraction and the elastic properties gradient associated with the compositional gradient was measured via depth-sensing Vickers microindentation. 相似文献
8.
9.
Designing Templates for Mining Association Rules 总被引:3,自引:0,他引:3
Current approaches to data mining usually address specific userrequests, while no general design criteria for the extraction of associationrules are available for the end-user. In this paper, we propose aclassification of association rule types, which provides a general frameworkfor the design of association rule mining applications. Based on theidentified association rule types, we introduce predefined templates as ameans to capture the user specification of mining applications. Furthermore,we propose a general language to design templates for the extraction ofarbitrary association rule types. 相似文献
10.
Enrico Saggese Giuseppe Chiassarini 《International Journal of Satellite Communications and Networking》1989,7(4):295-306
One key technology, for the implementation of future on-board processing payloads, is the multicarrier demodulator (MCD). The MCD is instrumental in allowing FDMA/TDM access schemes which optimize the use of on-board and ground resources in VSAT networks. This paper deals with the analogue and digital implementations of MCD, trying to assess the fields of application of each of the two technologies. 相似文献