全文获取类型
收费全文 | 5198篇 |
免费 | 223篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 53篇 |
综合类 | 3篇 |
化学工业 | 987篇 |
金属工艺 | 163篇 |
机械仪表 | 156篇 |
建筑科学 | 176篇 |
矿业工程 | 7篇 |
能源动力 | 154篇 |
轻工业 | 409篇 |
水利工程 | 57篇 |
石油天然气 | 12篇 |
无线电 | 374篇 |
一般工业技术 | 984篇 |
冶金工业 | 1248篇 |
原子能技术 | 46篇 |
自动化技术 | 599篇 |
出版年
2023年 | 30篇 |
2022年 | 50篇 |
2021年 | 119篇 |
2020年 | 91篇 |
2019年 | 108篇 |
2018年 | 132篇 |
2017年 | 120篇 |
2016年 | 123篇 |
2015年 | 78篇 |
2014年 | 147篇 |
2013年 | 322篇 |
2012年 | 286篇 |
2011年 | 328篇 |
2010年 | 239篇 |
2009年 | 259篇 |
2008年 | 279篇 |
2007年 | 290篇 |
2006年 | 227篇 |
2005年 | 205篇 |
2004年 | 202篇 |
2003年 | 168篇 |
2002年 | 174篇 |
2001年 | 109篇 |
2000年 | 91篇 |
1999年 | 89篇 |
1998年 | 99篇 |
1997年 | 100篇 |
1996年 | 67篇 |
1995年 | 75篇 |
1994年 | 74篇 |
1993年 | 69篇 |
1992年 | 58篇 |
1991年 | 38篇 |
1990年 | 58篇 |
1989年 | 60篇 |
1988年 | 47篇 |
1987年 | 43篇 |
1986年 | 44篇 |
1985年 | 59篇 |
1984年 | 40篇 |
1983年 | 37篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 16篇 |
1979年 | 32篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1972年 | 8篇 |
排序方式: 共有5428条查询结果,搜索用时 15 毫秒
11.
Biodegradation of monoaromatic hydrocarbons in aquifer columns amended with hydrogen peroxide and nitrate 总被引:1,自引:0,他引:1
The ability of indigenous microorganisms to degrade benzene, toluene, ethylbenzene and xylenes (BTEX) in laboratory scale flow-through aquifer columns was tested separately with hydrogen peroxide (110 mg/l) and nitrate (330 mg/l as NO3−) amendments to air-saturated influent nutrient solution. The continuous removal of individual components from all columns relative to the sterile controls provided evidence for biodegradation. In the presence of hydrogen peroxide, the indigeneous microorganisms degraded benzene and toluene (> 95%), meta- plus para-xylene (80%) and ortho-xylene (70%). Nitrate addition resulted in 90% removal of toluene and 25% removal of ortho-xylene. However, benzene, ethylbenzene, meta- and para-xylene concentrations were not significantly reduced after 42 days of operation. Following this experiment, low dissolved oxygen (< 1 mg/l) conditions were initiated with the nitrate-amended column influent in order to mimic contaminated groundwater conditions distal from a nutrient injection well. Toluene continued to be effectively degraded (> 90%), and more than 25% of the benzene, 40% of the ethylbenzene, 50% of the meta- plus para-xylenes and 60% of the ortho-xylene were removed after several months of operation. 相似文献
12.
Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for
which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that
is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation
to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and
calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium
sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur
dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this
Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide
pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023
and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique.
The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen
reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity
decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic
of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants.
A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial
pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated
several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification,
combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported
in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part
II. 相似文献
13.
The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide
to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate
pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088
K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was
demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K
under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of
reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable
for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful
in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction
cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect
to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37. 相似文献
14.
Timothy Thomasma Kurt Hilbrecht 《International Journal of Flexible Manufacturing Systems》1991,3(3-4):231-250
Good methods are needed to specify, test, and debug material-handling control logic. This article surveys a number of representative methods for defining and describing control algorithms for programmable material-handling equipment used in flexible manufacturing systems. The methods are evaluated with regard to their suitability for communication between people and as bases for interfaces to automatic program generators. It is concluded that no single method is entirely satisfactory. Three methods (position diagrams, function block diagrams, and operation networks) have potential to be combined into an effective hybrid approach that minimizes the need for the user to switch between various conceptual models. 相似文献
15.
A unified theoretical approach is presented for the calculation of the performance of the single-phase capacitor-start permanent-magnet (PM) ac line-start motor. The earlier work of Chang and of Finch and Lawrenson on capacitor reluctance motors is extended. As far as possible, a common set of reference frame transformations for steady-state, transient, and asynchronous performance is also provided, permitting the use of all the theory developed for the analysis of the balanced polyphase PM motor. A new approximate technique is given for estimating the average asynchronous torque/speed curve from computed acceleration curves. 相似文献
16.
John E. Sohn 《The Journal of Adhesion》1985,19(1):15-27
Enhanced matrix-filler adhesion is realized after filler treatment with a surface treatment process. The hydrosol/coupling agent treatment was applied to a wide range of inorganic and organic fillers, and adhesion to a variety of matrix resins was improved. Scanning Electron Microscopy (SEM) was used to determine the locus of failure in the filled systems. The locus of failure shows the relative degree of adhesion between the filler and the polymer matrix. Significant improvement in adhesion in humid environments is also observed. 相似文献
17.
Simulated annealing is known to be an efficient method for combinatorial optimization problems. Its usage for realistic problem size, however, has been limited by the long execution time due to its sequential nature. This report presents a practical approach to synchronous simulated annealing for massively parallel distributed-memory multiprocessors. We use an n-ary speculative tree to execute n different iterations in parallel on n processors, called generalized speculative computation (GSC). Execution results of the 100- to 500-city traveling salesman problems on the AP1000 massively parallel multiprocessor demonstrate that the GSC approach can be an effective method for parallel simulated annealing as it gave over 20-fold speedup on 100 processors 相似文献
18.
The implementation of TS MAC system for KOREASAT DBS (direct broadcast satellite) system is presented. This TS MAC controls and monitors the status of the TS equipment and gathers the alarm for them. The advantage of this system is the center-concentrated, real time processing, remote control, and object oriented module decomposing 相似文献
19.
Previous research shows letter-fragment masks and non-letter-fragment fields have different effects on performance with briefly presented alphabetic targets. However, popular accounts of these differences ignore mask configuration. Over a series of experiments, configurational effects of letter-fragment (LF) and non-letter-fragment (NLF) masks were compared. When the configuration of LF masks matched word boundaries, performance with exterior letter pairs from words improved, whereas performance with illegal exterior-letter pairs and single letters was unaffected. When the same changes were made to NLF masks, only an overall drop in performance occurred, with no selective effect on target type. Although LF mask configuration selectively affected lexical processing, NLF mask configuration produced substantially different effects, indicating problems with contemporary accounts of masking differences that ignore influences of mask configuration. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.
One-dimensional mathematical modeling was used to describe the self-propagating high-temperature synthesis (SHS) process for preparing TiAl3 and Ni3Al intermetallics. The kinetic parameters (activation energies and pre-exponential factors) for the two compounds were obtained by matching experimental measurement and the numerical solution. The results thus obtained were compared with rate parameters obtained using different methods. The activation energy was 483 and 283 kJ mol?1 for the formation of TiAl3 and Ni3Al, respectively. The temperature profiles calculated using the mathematical model were compared with experimental measurements for both aluminides which indicated reasonable agreement. Fine particle size and moderate preheating increase the SHS rates. 相似文献