全文获取类型
收费全文 | 1031篇 |
免费 | 63篇 |
专业分类
电工技术 | 16篇 |
化学工业 | 374篇 |
金属工艺 | 25篇 |
机械仪表 | 31篇 |
建筑科学 | 36篇 |
能源动力 | 27篇 |
轻工业 | 45篇 |
水利工程 | 1篇 |
石油天然气 | 3篇 |
武器工业 | 1篇 |
无线电 | 67篇 |
一般工业技术 | 176篇 |
冶金工业 | 78篇 |
原子能技术 | 8篇 |
自动化技术 | 206篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 71篇 |
2021年 | 81篇 |
2020年 | 31篇 |
2019年 | 36篇 |
2018年 | 42篇 |
2017年 | 32篇 |
2016年 | 34篇 |
2015年 | 46篇 |
2014年 | 50篇 |
2013年 | 73篇 |
2012年 | 66篇 |
2011年 | 64篇 |
2010年 | 62篇 |
2009年 | 56篇 |
2008年 | 33篇 |
2007年 | 45篇 |
2006年 | 37篇 |
2005年 | 19篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1955年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有1094条查询结果,搜索用时 15 毫秒
81.
New sulfated zirconias covering a wide range of pore diameters from micropores to macropores have been prepared by a combined use of two different structure-directing templates. The catalytic performance of these sulfated zirconias for the n-butane isomerization could be improved significantly compared to a standard displaying a maximum rate of isomerization of 1490 μmol/g h at 423 K. The materials remained their high activity even at 348 K. Moreover, deactivated materials could be reactivated to the original activity in an air-flow at 673 K several times. The newly designed materials were fully characterized by XRD, XPS, TPD of ammonia, IR spectroscopy and N2 adsorption to describe the formation of active surface centres and their morphology. The formation of active pyrosulfates with sulfate bands above 1400 cm?1 was followed by DRIFTS. An increased ratio of Brønsted-to-Lewis centres could be detected which can be accounted for the unexpected high activity. 相似文献
82.
The Rengen Grassland Experiment: soil contamination by trace elements after 65 years of Ca,N, P and K fertiliser application 总被引:1,自引:0,他引:1
Michal Hejcman Jiřina Szaková Jürgen Schellberg Petr Šrek Pavel Tlustoš 《Nutrient Cycling in Agroecosystems》2009,83(1):39-50
The Rengen Grassland Experiment (RGE) was established in the Eifel Mts. (Germany) on a low productive Nardetum in 1941. Since then, the following fertiliser treatments have been applied along with a two cut system: unfertilised control,
Ca, CaN, CaNP, CaNP–KCl and CaNP–K2SO4 with basic slag (syn. Thomas phosphate) as the only P fertiliser. The effect of long-term fertilisation on plant-available
(extracted with 0.01 mol l−1 CaCl2), easily-mobilisable (extracted with 0.05 mol l−1 EDTA), potentially-mobilisable (extracted with 2 mol l−1 HNO3) and total concentrations of trace elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the top 0–10 and 10–20 cm of soil
were investigated in 2006. According to redundancy analysis (RDA), the effect of treatment on the concentrations of risk elements
was significant and explained 82.3 and 90.6% of the variability in the data in the 0–10 and 10–20 cm soil layers, respectively.
Basic slag supplied the soil with considerable amounts of As, Cr, Cu, Fe, Mn and Zn. Following 65 years of fertiliser application
the concentrations of risk elements in the soil profile had increased substantially, especially with basic slag. However,
threshold limits for total trace element concentration in soil permitted by Czech national legislation were exceeded only
in the case of As. The increase in plant-available As concentrations was most critical as it increased the potential uptake
of As by plants in plots fertilised with P. Although P treatments received more than 300 g of Cr ha−1 annually, no effect on plant-available Cr soil content was detected. This contrasted with the accumulation of total Cr in
the 0–10 and 10–20 cm soil layers. Furthermore, plant availability of Cd, Fe, Mn and Zn was affected by soil pH and generally
decreased with the application of quick lime. Plant availability of these elements was not correlated with amounts supplied
by fertilisers. 相似文献
83.
Michal Kowara Sonia Borodzicz-Jazdzyk Karolina Rybak Maciej Kubik Agnieszka Cudnoch-Jedrzejewska 《International journal of molecular sciences》2021,22(11)
Myocardial infarction is one of the major causes of mortality worldwide and is a main cause of heart failure. This disease appears as a final point of atherosclerotic plaque progression, destabilization, and rupture. As a consequence of cardiomyocytes death during the infarction, the heart undergoes unfavorable cardiac remodeling, which results in its failure. Therefore, therapies aimed to limit the processes of atherosclerotic plaque progression, cardiac damage during the infarction, and subsequent remodeling are urgently warranted. A hopeful therapeutic option for the future medicine is targeting and regulating non-coding RNA (ncRNA), like microRNA, circular RNA (circRNA), or long non-coding RNA (lncRNA). In this review, the approaches targeted at ncRNAs participating in the aforementioned pathophysiological processes involved in myocardial infarction and their outcomes in preclinical studies have been concisely presented. 相似文献
84.
Design of flexible assembly line to minimize equipment cost 总被引:8,自引:0,他引:8
In this paper we develop an optimal and a heuristic algorithm for the problem of designing a flexible assembly line when several equipment alternatives are available. The design problem addresses the questions of selecting the equipment and assigning tasks to workstations, when precedence constraints exist among tasks. The objective is to minimize total equipment costs, given a predetermined cycle time (derived from the required production rate). We develop an exact branch and bound algorithm which is capable of solving practical problems of moderate size. The algorithm's efficiency is enhanced due to the development of good lower bounds, as well as the use of some dominance rules to reduce the size of the branch and bound tree. We also suggest the use of a branch-and-bound-based heuristic procedure for large problems, and analyze the design and performance of this heuristic. 相似文献
85.
86.
87.
Liv Furuberg Michal Mielnik Anja Gulliksen Lars Solli Ib-Rune Johansen Jörg Voitel Tobias Baier Lutz Riegger Frank Karlsen 《Microsystem Technologies》2008,14(4-5):673-681
We present results from the MicroActive project which develops an instrument for molecular diagnostics. The instrument is
first tested for patient screening for a group of viruses causing cervical cancer. Two disposable polymer chips with reagents
stored on-chip are developed and will be inserted into the instrument for each patient sample analysis. The first chip will
perform nucleic acid extraction from patient epithelial cervical cells, while mRNA amplification and fluorescent detection
takes place in the second chip. This paper reports results on the amplification chip. Purified sample is inserted into the
chip and split into ten smaller droplets for simultaneous amplification and detection of ten viruses. The droplets move in
parallel channels, each with two chamber extensions containing dried reagents. Experimental results on parallel droplet movement
using one external pump combined with hydrophobic restrictions show that the parallel droplet positions can be controlled.
There are four valves with increasing burst pressures between 800 and 4,500 Pa in each parallel channel, positioning the droplets
in metering zones and reaction chambers. The re-hydration times for the dried reagents in micro chambers have been monitored.
After sample insertion, uniform concentration of the reagents in the droplet was reached after respectively 60 s and 10 min.
These times are acceptable for successful amplification. Finally we show positive amplification of HPV type 16 viruses in
a micro chamber. 相似文献
88.
Michal Hoznedl Ladislav Tajc Jaroslav Krejcik Lukas Bednar Kamil Sedlak Jiri Linhart 《Frontiers of Energy and Power Engineering in China》2009,3(3):321-329
In the past, increased attention was given to the development of an optimal shape for the inlet part of LP turbine casings
in SKODA POWER. A double-flow design is typically used for high power output turbines. An optimized shape for the internal
diffuser has been found, which transforms the kinetic energy of steam into increased pressure, thus effectively increasing
the thermodynamic efficiency of the stage. Some conclusions have been drawn from laboratory experiments, others derived directly
from on-site measurements at power plants. The conclusions from the development of double-flow turbines form the basis for
the design of the single-flow turbine arrangement. Single-flow design is typically used for lower output turbines. There are
still some limitations in applying this arrangement. The designer needs to resolve the bearing position and how to ensure
access to them. Reinforcing the ribs and supports are used, therefore, to ensure the rigidity of the entire casing. The optimization
of the single-flow diffuser shape is therefore the subject of the study presented below. 相似文献
89.
New process for the production of methanol and ammonia. The gas/solids/solids thrickle flow reactor – a new kind of reactor for chemical equilibrium processes . A new process for the production of ammonia or methanol has been developed in the high pressure laboratory of Twente Technical University. The reactants can be made to react completely in a single reactor pass, thus avoiding expensive recirculation. Complete reaction without recirculation is accomplished by a combination of two reversible processes: a chemical reaction and a selective adsorption of the reaction product on a solid in constant flow. On introduction of an inert-gas free stoichiometric mixture of reactants into the reactor, the exhaust gas outlet can be closed. If there is an excess of one of the reactants or of inert gas, it can leave from the top of the reactor. Such a process has been accomplished in a new gas/solids/solids trickle flow reactor in which a granulated adsorbent ?rains”? through a fixed bed of catalyst. The present article describes the use of this kind of reactor for methanol synthesis. Considerable savings in production costs are expected relative to the modern Lurgi low pressure process. A pilot plant is to be built to characterize and evaluate the new process. Royal Dutch Shell has registered a patent application. 相似文献
90.
The kinetics of carbide precipitation in a fully processed 2.3 wt Pct silicon, 0.66 wt Pct aluminum electrical steel with
carbon contents of 0.005 to 0.016 wt Pct were investigated over the temperature range from 150 to 760 °C and times from 30
seconds to 240 hours. The size, morphology, and distribution of the carbide phases, as functions of aging time and temperature,
were determined by optical and transmission electron microscopy. The 1.5T core loss was also evaluated and correlated with
the changes in precipitation. Distinct C curves were observed for the formation of grain-boundary cementite at temperatures
above 350 °C and a transition carbide ({100}
α
habit plane) at temperatures below 350 °C. Grain-boundary cementite had a relatively small effect on core loss. The large
increases in core loss that accompanied transition carbide precipitation peaked at specific aging temperatures depending on
the carbon content of the steel. Once a transition carbide dispersion was initially established at a given aging temperature,
particle coarsening and core loss changes were generally insensitive to aging time. The influence of a combined addition of
silicon and aluminum on the solubility of cementite and the transition carbide in iron was estimated and discussed.
This paper is based on a presentation made at the symposium “Physical Metallurgy of Electrical Steels” held at the 1985 annual
AIME meeting in New York on February 24–28, 1985, under the auspices of the TMS Ferrous Metallurgy Committee. 相似文献