全文获取类型
收费全文 | 1389篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 85篇 |
综合类 | 4篇 |
化学工业 | 324篇 |
金属工艺 | 32篇 |
机械仪表 | 23篇 |
建筑科学 | 19篇 |
能源动力 | 44篇 |
轻工业 | 107篇 |
水利工程 | 2篇 |
无线电 | 93篇 |
一般工业技术 | 186篇 |
冶金工业 | 296篇 |
原子能技术 | 67篇 |
自动化技术 | 146篇 |
出版年
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 22篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 30篇 |
2013年 | 64篇 |
2012年 | 44篇 |
2011年 | 74篇 |
2010年 | 44篇 |
2009年 | 67篇 |
2008年 | 52篇 |
2007年 | 48篇 |
2006年 | 48篇 |
2005年 | 48篇 |
2004年 | 41篇 |
2003年 | 37篇 |
2002年 | 49篇 |
2001年 | 27篇 |
2000年 | 34篇 |
1999年 | 29篇 |
1998年 | 120篇 |
1997年 | 73篇 |
1996年 | 59篇 |
1995年 | 47篇 |
1994年 | 31篇 |
1993年 | 30篇 |
1992年 | 21篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1967年 | 7篇 |
排序方式: 共有1428条查询结果,搜索用时 46 毫秒
101.
The motility pattern of mammalian spermatozoa changes during migration in the female genital tract and during incubation in vitro. This change in motility is termed hyperactivation. Hyperactivated spermatozoa swim vigorously in 'whiplash', 'figure-8' or 'small circle' trajectories. In this study, a quantitative analysis was carried out of the changes in the motility pattern of hamster spermatozoa during incubation to investigate the mechanism regulating hyperactivation. In the culture system used in this study, hyperactivation occurred 4 h after incubation. Several parameters in the analysis of sperm movement pattern were examined. Curvilinear velocity, average path velocity and straightness abruptly increased between 2 and 4 h. However, linearity, amplitude of lateral head displacement, beat cross frequency and average wavelength gradually changed with time. In the analysis of flagellar bending, the bend angles were measured after dividing images of the flagellum into short lengths. Flagellar bending changed in different manners in each region during incubation. The asymmetry in the direction of the curve of the head gradually increased with time in the first half of the flagellum. The flexibility, which was determined using the amplitude of bending and the rate of change in bend angles, abruptly decreased between 10 min and 1 h, and then increased between 2 and 4 h in the first half of flagellum. These results indicate that complex physiological changes occur before hyperactivation. 相似文献
102.
Sonochemical degradation of chlorinated hydrocarbons using a batch and continuous flow system 总被引:1,自引:0,他引:1
The sonochemical degradation of chlorinated hydrocarbons such as 1,1,1-trichloroethane, trichloroethylene and tetrachloroethylene in aqueous solution was carried out in the batch and continuous flow systems at an ultrasonic frequency of 100kHz under an air atmosphere. In the batch experiment, the rate of degradation follows the order 1,1,1-trichloroethane>tetrachloroethylene>trichloroethylene, and the chlorinated hydrocarbon were readily degraded by ultrasonic irradiation. The experiments in the continuous flow system were performed in the range of volumetric flow rate from 7 to 30 x 10(-3)lmin(-1). The conversion of the chlorinated hydrocarbons at a steady-state of reactor depended on the volumetric flow rate. The yield of Cl(-) (as a measurement of mineralization of chlorinated hydrocarbons) was 70-90% of the chlorine atoms in the parent chlorinated hydrocarbon molecules. From the viewpoint of the scale-up process, the sonochemical degradation of trichloroethylene was simulated in a three stage reactor, and the conversion (>99%) in a third stage reactor was showed the good results that can be satisfied a desired water quality standard. 相似文献
103.
Among passerines, Bengali finches are known to sing extremely complex courtship songs with three hierarchical structures:
namely, the element, the chunk, and the syntax. In this work, we theoretically studied the mechanism of the song of Bengali
finches in aides to provide a dynamic view of the development of birdsong learning. We first constructed a model of the Elman
network with chaotic neurons that successfully learned the supervisor signal defined by a simple finite-state syntax. Second,
we focused on the process of individual-specific increases in the complexity of song syntax. We propose a new learning algorithm
to produce the intrinsic diversification of song syntax without a supervisor on the basis of the itinerant dynamics of chaotic
neural networks and the Hebbian learning rule. The emergence of novel syntax modifying the acquired syntax is demonstrated.
This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January
23–25, 2006 相似文献
104.
Miyuki Hayashi Hirokage Yamada Naozumi Nabeshima Kazuhiro Nagata 《International Journal of Thermophysics》2007,28(1):83-96
The temperature dependences of the velocity of sound in liquid Pb, Sn, Ge, and Si have been measured by means of the pulse
transmission technique over temperature ranges of 610–1078 K, 608–1463 K, 1215–1443 K, and 1723–1888 K, respectively. In both
liquid Pb and Sn, the velocities of sound decrease linearly with increasing temperature, which is the same temperature dependence
as shown in many other liquid metals. On the other hand, the velocities of sound in liquid Ge and Si exhibit anomalous temperature
dependences. In Ge, the velocity of sound has a distinct maximum around 1280 K and decreases linearly at higher temperatures.
In Si, the velocity of sound increases monotonically with increasing temperature in the temperature range investigated. It
is considered that these results predict that the coordination numbers of liquid Ge and Si increase with increasing temperature. 相似文献
105.
Shujun Zhang Thomas R Shrout Hajime Nagata Yuji Hiruma Tadashi Takenaka 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(5):910-917
Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na0.5Bi0.5)TiO3-y(K0.5Bi0.5)TiO3-zBaTiO3 [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing. Dielectric maximum temperatures of 280 degrees C and 262 degrees C were found for tetragonal 0.79(Na0.5Bi0.5)TiO3-0.14(K0.5Bi0.5)TiO3-0.07BaTiO3 (BNBK79) and MPB composition 0.88(Na0.5Bi0.5)TiO3-0.08(K0.5Bi0.5)TiO3-0.04BaTiO3 (BNBK88), with depolarization temperatures of 224 degrees C and 162 degrees C, respectively. Piezoelectric coefficients d33 were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d31 was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy. Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively. The remanent polarization of BNBK88 (approximately 40 microC/cm2) was larger than that of BNBK79 (approximately 29 microC/cm2). The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed. 相似文献
106.
Yuji Hiruma Hajime Nagata Tadashi Takenaka 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(12):2493-2499
The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a. 相似文献
107.
In this paper, we develop computational methods for obtaining Stackelberg solutions to two-level mixed zero-one programming problems in which the decision maker at the upper level controls zero-one variables and the decision maker at the lower level controls real variables. To illustrate two-level mixed zero-one programming problems, we formulate a facility location and transportation problem as a two-level mixed zero-one programming problem. We develop computational methods through genetic algorithms for obtaining Stackelberg solutions. To demonstrate the feasibility and efficiency of the proposed methods, computational experiments are carried out and comparisons between the methods based on the branch-and-bound techniques and the proposed methods are provided. 相似文献
108.
In this article, we focus on two-level linear programming problems involving random variable coefficients in objective functions and constraints. Following the concept of chance constrained programming, the two-level stochastic linear programming problems are transformed into deterministic ones based on the fractile criterion optimization model. After introducing fuzzy goals for objective functions, interactive fuzzy programming to derive a satisfactory solution for decision makers is presented as a fusion of a stochastic approach and a fuzzy one. An illustrative numerical example is provided to demonstrate the feasibility of the proposed method. 相似文献
109.
Cooling load is a heat value of cold water used for air conditioning in a district heating and cooling system. Cooling load prediction in a district heating and cooling system is one of the key techniques for smooth and economical operation. In this article, cooling load prediction in such a district heating and cooling system is considered. Unfortunately, since actual cooling load data usually involve measurement noises, outliers, and missing data for several reasons, a prediction method considering the effect of the outliers and missing data is desirable. In this article, a new prediction method using a simplified robust filter to improve a numerical stability problem of a robust filter and a three-layered neural network, is proposed. Applications of the proposed method and some other methods to actual cooling load data in a district heating and cooling system involving outliers and missing data show the usefulness of the proposed method. 相似文献
110.
Convex mirrors are universally used as rear-view mirrors in automobiles. However, the ocular accommodative responses during the use of these mirrors have not yet been examined. This study investigated the effects of a convex mirror on the ocular accommodative systems. Seven young adults with normal visual functions were ordered to binocularly watch an object in a convex or plane mirror. The accommodative responses were measured with an infrared optometer. The average of the accommodation of all subjects while viewing the object in the convex mirror were significantly nearer than in the plane mirror, although all subjects perceived the position of the object in the convex mirror as being farther away. Moreover, the fluctuations of accommodation were significantly larger for the convex mirror. The convex mirror caused the 'false recognition of distance', which induced the large accommodative fluctuations and blurred vision. Manufactures should consider the ocular accommodative responses as a new indicator for increasing automotive safety. 相似文献