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991.
Reservoirs Effects on the Interannual Variability of Winter and Spring Streamflow in the St-Maurice River Watershed (Quebec,Canada) 总被引:3,自引:2,他引:1
Ali A. Assani Raphaëlle Landry Jonathan Daigle Alain Chalifour 《Water Resources Management》2011,25(14):3661-3675
The aim of this study was to test three main hypotheses about the interannual variability of streamflow downstream from dams:
(1) an almost similar long-term trend in interannual variability, (2) low variability of flow, and (3) its independence (no
link) from climate variability. To test these hypotheses, the interannual variability of winter and spring streamflow downstream
from three reservoirs (Gouin, Manouane, and Matawin) which induce an inversion of the natural cycle of streamflow (maximum
flows in winter and minimum flows in spring) was compared to the interannual variability of streamflow in natural rivers (measured
at the Matawin and Vermillon stations) over the period from 1932 to 2008 in the St-Maurice River watershed. As far as the
interannual variability of flow is concerned, its long-term trend is not homogeneous downstream from the three reservoirs
in both seasons. However, downstream from two reservoirs, changes in streamflow were observed to be different from those in
natural rivers (no significant trend downstream from the Taureau reservoir, on the Matawin River, and significant decrease
in spring flow downstream from the Manouane reservoir). Finally, coefficient of variation values for minimum flows are higher
downstream from reservoirs than in natural rivers, despite the fact that watershed surface area is larger for regulated rivers
than for natural ones. As for the link with climate variability, analysis of the correlation between climate variables (temperature
and precipitation) and mean winter and spring daily streamflow reveals that winter streamflow downstream from the Taureau
reservoir is not correlated with any climate variable, whereas spring streamflow is positively correlated with rainfall and
negatively correlated with maximum temperature. Thus, downstream from reservoirs, the interannual variability of streamflow
depends on climate during the spring, but not during winter. 相似文献
992.
Towards Palm-Size Autonomous Helicopters 总被引:1,自引:0,他引:1
Samir Bouabdallah Christian Bermes Slawomir Grzonka Christiane Gimkiewicz Alain Brenzikofer Robert Hahn Dario Schafroth Giorgio Grisetti Wolfram Burgard Roland Siegwart 《Journal of Intelligent and Robotic Systems》2011,61(1-4):445-471
muFly EU project started in 2006 with the idea to build an autonomous micro helicopter, comparable in size and weight to a small bird. Several scientific and technological objectives were identified. This spanned from system-level integration, high efficiency micro-actuation, highly integrated micro vision sensors and IMUs and also low processing power navigation algorithms. This paper shows how most of these objectives were reached, describing the approach and the role of each partner during the whole project. The paper describes also the technological developments achieved like the 80 g, 17 cm micro robotic-helicopter, the 8 g omnidirectional and steady-state laser scanner, the uIMU, the highly efficient micro motors, the high power-density fuel-cell and the successful graph-based navigation algorithms. 相似文献
993.
Autonomous rigid body attitude synchronization 总被引:3,自引:0,他引:3
Control laws to synchronize attitudes in a swarm of fully actuated rigid bodies, in the absence of a common reference attitude or hierarchy in the swarm, are proposed in [Smith, T. R., Hanssmann, H., & Leonard, N.E. (2001). Orientation control of multiple underwater vehicles with symmetry-breaking potentials. In Proc. 40th IEEE conf. decision and control (pp. 4598-4603); Nair, S., Leonard, N. E. (2007). Stable synchronization of rigid body networks. Networks and Heterogeneous Media, 2(4), 595-624]. The present paper studies two separate extensions with the same energy shaping approach: (i) locally synchronizing the rigid bodies’ attitudes, but without restricting their final motion and (ii) relaxing the communication topology from undirected, fixed and connected to directed, varying and uniformly connected. The specific strategies that must be developed for these extensions illustrate the limitations of attitude control with reduced information. 相似文献
994.
Managing product availability in a cost-effective way has always been a major challenge faced by inventory managers. We study the problem of a firm selling a perishable product with short-term demand patterns and a long-term service target using the newsvendor framework. The newsvendor determines his long-term order at the first stage, and revises the order according to a short-term forecast update at the second stage. He also evaluates a long-term service target for his overall performance on product availability across all possible forecast updates. We characterise his optimal inventory policy that minimises the expected inventory cost while meeting the long-term service target. Both in-stock rate and fill rate targets are examined. 相似文献
995.
Secure Data Collection with Updates 总被引:9,自引:0,他引:9
This paper describes a protocol to protect data collected by mobile agents roaming through a set of potentially malicious hosts. This protocol is based on an original secure cryptographic technique that assures the integrity of a sequence of data segments regardless of the order of each segment in the sequence. The protocol allows each host to update the data it previously submitted in a way that is suitable for free competition scenarios like comparative shopping or distributed auction and for highly dynamic environments like stock markets. The set of hosts can be visited several times in random order and a short message digest allows for the integrity verification of all the collected data. 相似文献
996.
The minimum shift keying modulation (MSK)to which a lot of recent publications have been done,presents some advantage about linear and non-linear distortions towards common 2 or 4 Phase Shift Keying (PSK)modulations. The simplified MSK modulation described in this paper is obtained by linear filtering of a coherent 2 phase shift keying modulation. Then the demodulator can be implemented with a matched filter followed by a coherent demodulator using only one carrier recovery circuit. In the first part of this paper, the modulator and the demodulator are described. After, some theorical results in the presence of noise and other impairments are given. In CCETT laboratories at Rennes, a modem has been realized at a data rate of 2,048 Mbit/s and performs at 0,8 dB of the theoretical results. 相似文献
997.
Treatment of domestic wastewater using the nutrient film technique (NFT) to produce horticultural roses 总被引:4,自引:0,他引:4
Removal of organic matter, nitrogen and phosphorus was investigated in a pilot based on the nutrient film technique system used for horticultural production. Rosebushes producing commercial roses were set on an inclined impermeable surface over which a thin film of domestic wastewater flowed directly through the root matrix. The roses produced with wastewater as nutrient solution were qualitatively and quantitatively similar to those produced traditionally and can be marketable. In the presence of the rosebushes, the lowering of chemical oxygen demand (COD), biological oxygen demand (BOD5) and suspended solids (SS) increased with their influent strengths in a linear fashion correlation. Whatever the pollutant load of the influent, within the range studied, the level of organic pollution required to allow the discharge of the effluent into water courses was reached after 24 h of treatment. At this time, the COD reached 39 +/- 13 mg L(-1), the BOD5 7 +/- 4 mg L(-1) and the SS 8 +/- 6 mg L(-1). The removal percentages were 89, 95 and 94, respectively, whereas without plants they were 55, 33 and 53, respectively. The rosebushes had a beneficial effect on the removal of phosphorus from 20% to 23% greater in their presence than without. In presence of plants, the nitrate was the principal form of nitrogen from 48 h of treatment whereas without rosebushes, nitrite represent more than 20% of initial nitrogen whatever the treatment duration. The root matrix served not only as a filter for the organic matter, but also provided a microhabitat suitable for nitrifying bacteria and heterotrophic micro-organisms, which responded rapidly to the pollutant load. 相似文献
998.
Since the seventies, energy conservation in all its forms has grown. This mindset has lead to the addition of thermal insulation in existing buildings, without concern for the existing electric cables. The addition over-insulates the cables, inhibiting heat dissipation, and possibly creating a hazardous situation.Our laboratory performed, between 1981 and 1990, a series of technical tests to determine the effect of this additional thermal insulation on the electric cables.This paper is the result of a research program giving the risks of fires caused by cables submitted to over-insulation, as a function of the type of thermal insulation and the current.Nomenclature
L
cable life expectancy (years)
-
A
constant which depends on the specific chemical reaction
-
B
constant which depends on the specific chemical reaction
-
T
temperature (°C or °K)
-
T
I
initial conductor temperature (°C)
-
T
F
final conductor temperature (°C)
-
t
time (seconds)
-
I
current (amperes)
-
W
heat dissipation (Watt-seconds)
-
R
resistance (ohms) 相似文献
999.
北方乡村生态屋设计实践 总被引:7,自引:0,他引:7
本论文给出在恶劣条件下,改善北方乡村居民居住质量、创造舒适与生态的人居环境的设计策略与技术手段,论文通过对当地传统民居与生态屋进行的同步测试、评估与比较分析,验证了生态屋生态技术的有效性,为北方乡村住宅建设的可持续发展指明了方向。 相似文献
1000.
The adsorption of trace metals on sediments of the Meuse River was interpreted in terms of competition between metals and protons for surface sites. Surface constants (*β1surf) were determined for Cu, Zn and Cd (10−1.8, 10−3.6 and 10−3.7). The constants for Pb, Ni, Ca and Mg (10−1.7, 10−3.8, 10−6.5 and 10−5.2) were estimated using a correlation between hydrolysis and surface constants. A chemical equilibrium computer program in which surface sites (for adsorption reactions) are treated as conventional ligands was used to calculate the speciation of Cu, Pb, Ni and Zn in the Meuse River. Calculated values of the adsorbed/dissolved distribution agreed well with observed values, after some realistic data manipulation. This work indicates that dissolved trace metal concentrations in the Meuse River are controlled by adsorption and not by precipitation mechanisms. The relationship between organic matter and suspended matter greatly influences the adsorption of metals like Cu and Pb. 相似文献