全文获取类型
收费全文 | 260159篇 |
免费 | 3192篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 5130篇 |
综合类 | 330篇 |
化学工业 | 37232篇 |
金属工艺 | 10257篇 |
机械仪表 | 8485篇 |
建筑科学 | 6106篇 |
矿业工程 | 1076篇 |
能源动力 | 6393篇 |
轻工业 | 22856篇 |
水利工程 | 2561篇 |
石油天然气 | 3908篇 |
武器工业 | 68篇 |
无线电 | 34725篇 |
一般工业技术 | 50074篇 |
冶金工业 | 46574篇 |
原子能技术 | 5418篇 |
自动化技术 | 22981篇 |
出版年
2021年 | 2038篇 |
2019年 | 2033篇 |
2018年 | 3467篇 |
2017年 | 3534篇 |
2016年 | 3728篇 |
2015年 | 2320篇 |
2014年 | 4048篇 |
2013年 | 11287篇 |
2012年 | 6564篇 |
2011年 | 8878篇 |
2010年 | 6982篇 |
2009年 | 7850篇 |
2008年 | 8680篇 |
2007年 | 8614篇 |
2006年 | 7804篇 |
2005年 | 7141篇 |
2004年 | 6886篇 |
2003年 | 6732篇 |
2002年 | 6372篇 |
2001年 | 6470篇 |
2000年 | 6171篇 |
1999年 | 6256篇 |
1998年 | 14251篇 |
1997年 | 10274篇 |
1996年 | 8114篇 |
1995年 | 6415篇 |
1994年 | 5712篇 |
1993年 | 5584篇 |
1992年 | 4553篇 |
1991年 | 4214篇 |
1990年 | 4050篇 |
1989年 | 3779篇 |
1988年 | 3625篇 |
1987年 | 3171篇 |
1986年 | 3066篇 |
1985年 | 3611篇 |
1984年 | 3385篇 |
1983年 | 3031篇 |
1982年 | 2852篇 |
1981年 | 2952篇 |
1980年 | 2761篇 |
1979年 | 2648篇 |
1978年 | 2504篇 |
1977年 | 2945篇 |
1976年 | 3558篇 |
1975年 | 2319篇 |
1974年 | 2315篇 |
1973年 | 2318篇 |
1972年 | 1850篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Person identification using multiple cues 总被引:6,自引:0,他引:6
Brunelli R. Falavigna D. 《IEEE transactions on pattern analysis and machine intelligence》1995,17(10):955-966
This paper presents a person identification system based on acoustic and visual features. The system is organized as a set of non-homogeneous classifiers whose outputs are integrated after a normalization step. In particular, two classifiers based on acoustic features and three based on visual ones provide data for an integration module whose performance is evaluated. A novel technique for the integration of multiple classifiers at an hybrid rank/measurement level is introduced using HyperBF networks. Two different methods for the rejection of an unknown person are introduced. The performance of the integrated system is shown to be superior to that of the acoustic and visual subsystems. The resulting identification system can be used to log personal access and, with minor modifications, as an identity verification system 相似文献
992.
KV Shah TD Kessis F Shah JW Gupta D Shibata RW Jones 《Canadian Metallurgical Quarterly》1996,15(2):127-130
Unstable expansion of the CTG repeats in the 3' untranslated region encoding a member of the protein kinase family in the q13.3 band on chromosome 19 is a mutation specific for myotonic dystrophy. To examine the correlation between clinical expression and CTG trinucleotide repeat length, we carried out Southern blot analysis in a family with myotonic dystrophy. In this pedigree, the expanded CTG repeats were transmitted maternally. The mother had three female children. The mother had about 200 CTG repeats, and the number of repeats for each child was about 800, 1500 and 1600 in birth order. The mother and the patient with 800 repeats were unaware of muscle weakness or myotonia. Symptoms were present from age 3 years in the patient with 1500 repeats and from birth in the one with 1600 repeats. Although the mother menstruated regularly, the patients with 800 and 1500 repeats both menstruated irregularly, and the one with 1600 repeats has never menstruated. The age of onset and severity of the disease were correlated with the size of the expanded repeats. Endocrinological studies revealed that the basal levels of the gonadotropins, PRL and E2 were within normal range, and a pituitary response to LHRH was observed. These data suggest that the amenorrhea and menstrual irregularities were caused by a suprahypophyseal dysfunction. When expanded CTG repeats are transmitted maternally, abnormal products resulting from the metabolic disturbance in the affected mother may harm the fetus in utero. A heterozygous fetus, who has more CTG repeats, may be unable to metabolize the pathologic products sufficiently and therefore may become more severely affected. This may explain the exclusive maternal transmission of congenital myotonic dystrophy. 相似文献
993.
M Schietroma A Risetti F Carlei MV Santirocco F Muzi G Maggi C De Santis CL Recchia D Iannucci R Rampa M Simi 《Canadian Metallurgical Quarterly》1996,48(4):43-46
Adhesions have been suggested as a possible cause of chronic abdominal pain, but the reports of their etiological role conflict. Lysis of adhesions has been proposed as the therapeutic modality of choice, although the reports of success are controversial. The aim our prospective study was to determine whether laparoscopic adhesiolysis ameliorates chronic abdominal pain in patients with abdominal adhesions. Forty-one patients with chronic abdominal pain lasting for more than 6 months, but with no abnormal findings other than adhesions found at laparoscopy, underwent laparoscopic adhesiolysis. 37 patients (90.2%) were available for follow-up after a median time interval of 18 months (range: 12-41 months). Twenty-two patients (59.4%) were free from abdominal pain and 9 (24.3%) patients reported significant amelioration of their pain. Six (16.2%) patients had no amelioration. In conclusion the laparoscopy is an effective tool for the evaluation of patients with chronic abdominal pain, and laparoscopic adhesiolysis cures of ameliorates chronic abdominal pain in more than 80% of patients. 相似文献
994.
Mason G.M. Hamilton D.C. Walpole P.H. Heuerman K.F. James T.L. Lennard M.H. Mazur J.E. 《Geoscience and Remote Sensing, IEEE Transactions on》1993,31(3):549-556
The SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) LEICA instrument is designed to measure ~0.5-5-MeV/nucleon solar and magnetospheric ions over the range from He-Ni. The instrument is a time-of-flight (TOF) mass spectrometer, which measures particle TOF over an ~0.5-m path and the residual energy deposited in an array of Si solid state detectors. Large-area microchannel plates are used, resulting in a large geometrical factor for the instrument (0.6 cm2 sr), which is essential for accurate compositional measurements in small solar flares and in studies of precipitating magnetospheric heavy ions 相似文献
995.
In the present paper a new method is presented for the evaluation of torsional stressing of diesel-generator sets consisting of components with uncertain torsional characteristics. A frequency scanning technique is implemented for eigenvalue analysis of the elastic system. Due to the uncertainty of the values of stiffness and damping coefficients, a sensitivity analysis method is also presented, suitable for the evaluation of the range of the mechanical stresses. Special consideration is given to the correct simulation of the coupling to the electric network, including the influence of generator regulators and possible network interactions. An exact formula is extracted for the synchronizing and damping torque coefficients. The method presented was checked in a diesel power station of the autonomous electric system of a Greek island 相似文献
996.
The authors present an original analysis of an aperture-coupled microstrip antenna. The theory is based on the segmentation method, which considers the patch as a multiport network whose impedance matrix is deduced from a hybrid matrix, and the use of analytical expressions of the cavity admittance at the slot centre. The theory is presented for the first time, and the theoretical results are in good agreement with previous published measurements 相似文献
997.
Dotti D. Lombardi R. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(5):864-869
Correlation functions, calculated on the ultrasonic echoes scattered by blood, provide a rich harvest of information concerning the local speed, which has often been underestimated; in particular, blood flow measurement usually yields only the longitudinal component of the velocity, even if significant information about the speed direction can be extracted. In this paper it is shown how correlation functions, calculated on the dependency of both time and space displacements, allow us to evaluate the angle Θ between ultrasound beam and blood flow; when straight vessels are considered, this single parameter, combined with the longitudinal velocity profile, permits the complete hemodynamic characterization. The underlying theory is developed and preliminary experimental results are presented 相似文献
998.
The optimization of wet granulation in a 10-liter high-shear mixer was investigated using a nonclassical experimental mixture design. Hydroxypropylmethylcellulose, lactose, cornstarch, and microcrystalline cellulose were used as excipients of the granulate, while polyvinylpyrrolidone was used as binder. Besides the minimization of the number of experiments, the strategy applied takes into account the cost of each experiment. The introduction of such a modification allowed us to select an experimental matrix giving enough information with a relatively low number of experiments and at a minimum cost. 相似文献
999.
The feasibility of using a thick ground plane with an aperture coupled microstrip patch antenna while maintaining reasonable antenna performance is demonstrated using moment method and reciprocity analyses in the spectral domain. The thick ground plane, which may serve as a heatsink for active MMIC circuitry, or as a mechanical support for thin substrates, is particularly advantageous in millimetre wave phased array applications. It is found that the effect of ground plane thickness is to reduce the level of coupling from the feed line to the patch 相似文献
1000.
Two layer frequency selective surfaces (FSS) comprised of aperture elements on a single dielectric substrate are used to produce extremely narrow and angularly stable passband transmission responses. Experimental results are compared with predictions to verify a computer model which is based on solving a pair of coupled aperture integral equations. Reductions in bandwidth of up to a factor of seven have been achieved 相似文献