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排序方式: 共有1440条查询结果,搜索用时 703 毫秒
941.
Bartosz Jan Pachno Magorzata Kapusta Piotr
witek Krzysztof Bana Vitor F. O. Miranda Anna Bogucka-Kocka 《International journal of molecular sciences》2021,22(11)
In most angiosperms, the female gametophyte is hidden in the mother tissues and the pollen tube enters the ovule via a micropylar canal. The mother tissues play an essential role in the pollen tube guidance. However, in Utricularia, the female gametophyte surpasses the entire micropylar canal and extends beyond the limit of the integument. The female gametophyte then invades the placenta and a part of the central cell has direct contact with the ovary chamber. To date, information about the role of the placenta and integument in pollen tube guidance in Utricularia, which have extra-ovular female gametophytes, has been lacking. The aim of this study was to evaluate the role of the placenta, central cell and integument in pollen tube pollen tube guidance in Utricularia nelumbifolia Gardner and Utricularia humboldtii R.H. Schomb. by studying the production of arabinogalactan proteins. It was also determined whether the production of the arabinogalactan proteins is dependent on pollination in Utricularia. In both of the examined species, arabinogalactan proteins (AGPs) were observed in the placenta (epidermis and nutritive tissue), ovule (integument, chalaza), and female gametophyte of both pollinated and unpollinated flowers, which means that the production of AGPs is independent of pollination; however, the production of some AGPs was lower after fertilization. There were some differences in the production of AGPs between the examined species. The occurrence of AGPs in the placental epidermis and nutritive tissue suggests that they function as an obturator. The production of some AGPs in the ovular tissues (nucellus, integument) was independent of the presence of a mature embryo sac. 相似文献
942.
Multibody modeling of human body for the inverse dynamics analysis of sagittal plane movements 总被引:1,自引:0,他引:1
A multibody methodology for systematic construction of a two-dimensional biomechanical model of a human body is presented,
aimed at effective determination of the muscle forces and joint reaction forces in the lower extremities during sagittal plane
movements such as vertical jump, standing long jump or jumping down from a height. While the hip, knee and ankle joints are
modeled as enforced directly by the muscle forces applied to the foot, shank, thigh and pelvis at the muscle attachment points,
the actuation of the other joints is simplified to the torques representing the respective muscle action. The developed formulation
is applicable to both the flying and support phases, enhanced by an effective scheme for the determination of reaction forces
exclusively in the lower extremity joints. The determination of reactions from the ground is also provided. The problem of
muscle force redundancy in the lower extremities is solved by applying the pseudoinverse method, with post-processing procedures
used to assure the muscle being tensile. Results of the inverse dynamics analysis of vertical jump are reported. 相似文献
943.
A solution to the problem of recovering and tracking the signal configuration at the receiver side for digital optical transmission systems employing the modulation of polarization (POLSK) is proposed. The tracking algorithm for signal configuration is based on analysis of torsion and curvature of three dimensional curve segments. Impact of polarization effects on presented method is investigated. The only impairments considered in this paper are: frequency-independent birefringence and one lumped PDL element. The numerical simulations and experiments shows that the presented method is resistant to change of fiber optics birefringence; and is sensitive to depolarization effect and state of polarization location fluctuations which are equal or faster than the data rate. 相似文献
944.
Krzysztof Kosowski Karol Tucki Adrian Kosowski 《Expert systems with applications》2009,36(9):11536-11542
We propose a general, efficient system for designing turbine cascades and stages in real 3D-flow conditions. The presented algorithms involve application of evolutionary algorithms, as well as Artificial Neural Networks. Results of the design process are shown to be highly optimised in terms of efficiency, whereas computation time is reduced by several orders of magnitude in comparison to methods relying on Computational Fluid Dynamics calculations. 相似文献
945.
This paper deals with the problem of modelling current mode PWM controllers with the use of SPICE. The monolithic integrated circuit UC3842 is considered in the paper. Two isothermal models of UC3842 known in the literature are compared, tested and discussed. A new electrothermal model (ETM), including selfheating, of the considered controller is proposed and described in detail. The experimental verification of the ETM showed its much greater accuracy compared to the isothermal models of the investigated device. 相似文献
946.
Russell S. Drago Krzysztof Jurczyk Nicholas Kob Alak Bhattacharyya Joseph Masin 《Catalysis Letters》1998,51(3-4):177-181
Claims for the partial oxidation of methane to CO and H2 have been clouded by the possibility of the indirect reaction sequence occurring at hot spots in the catalyst bed. In this
report, we claim that the direct reaction occurs on NiO/silica at 500°C with methane conversions as high as 80% and selectivities
for H2 of 80% and CO of 70%. Arguments are presented to show that the amount of diluent gas employed prevents formation of local
hot spots with temperatures high enough for the indirect reaction to occur. Consequently, this study constitutes one of the
most convincing reports for the conversion of CH4 to syngas by the partial oxidation of methane. The catalyst deactivates in 10 h. Surface studies show coke formation and
aggregation of NiO contribute to the loss of activity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
947.
Krzysztof Majewski 《Information Processing Letters》2009,109(4):233-237
A Boolean function is symmetric if it is invariant under all permutations of its arguments; it is quasi-symmetric if it is symmetric with respect to the arguments on which it actually depends. We present a test that accepts every quasi-symmetric function and, except with an error probability at most δ>0, rejects every function that differs from every quasi-symmetric function on at least a fraction ε>0 of the inputs. For a function of n arguments, the test probes the function at O((n/ε)log(n/δ)) inputs. Our quasi-symmetry test acquires information concerning the arguments on which the function actually depends. To do this, it employs a generalization of the property testing paradigm that we call attribute estimation. Like property testing, attribute estimation uses random sampling to obtain results that have only “one-sided” errors and that are close to accurate with high probability. 相似文献
948.
Ofelia Márquez Krzysztof N. Waliszewski 《International Journal of Food Science & Technology》2008,43(11):1993-1999
The conditions for enzyme activity (pH and temperature) and kinetic parameters for the thermal inactivation of β‐glucosidase enzyme in vanilla beans have been investigated. The maximum enzyme activity was detected at pH 6.5 and 38 °C. The values obtained for Vmax and Km were 62.05 units and 2.07 mm, respectively. When hot water treatment (the most practical method of vanilla bean killing) was applied, β‐glucosidase treated at pH 6.0 and 60 °C for 3 min lost 51% of activity, while at 70 °C for 90 s the enzyme lost 60% of activity and at 80 °C for 30 s the enzyme lost 48% of its activity. When vanilla beans were cured in an oven at 60 °C for 36 to 48 h all β‐glucosidase activity was lost. 相似文献
949.
950.