全文获取类型
收费全文 | 281408篇 |
免费 | 4296篇 |
国内免费 | 1416篇 |
专业分类
电工技术 | 5357篇 |
综合类 | 895篇 |
化学工业 | 39967篇 |
金属工艺 | 11446篇 |
机械仪表 | 7914篇 |
建筑科学 | 7059篇 |
矿业工程 | 872篇 |
能源动力 | 6693篇 |
轻工业 | 26079篇 |
水利工程 | 2381篇 |
石油天然气 | 1382篇 |
武器工业 | 7篇 |
无线电 | 32861篇 |
一般工业技术 | 48311篇 |
冶金工业 | 67230篇 |
原子能技术 | 4037篇 |
自动化技术 | 24629篇 |
出版年
2021年 | 1694篇 |
2019年 | 1500篇 |
2018年 | 2814篇 |
2017年 | 2906篇 |
2016年 | 3511篇 |
2015年 | 2683篇 |
2014年 | 3622篇 |
2013年 | 11259篇 |
2012年 | 7488篇 |
2011年 | 10170篇 |
2010年 | 6964篇 |
2009年 | 7744篇 |
2008年 | 8188篇 |
2007年 | 8293篇 |
2006年 | 7601篇 |
2005年 | 9738篇 |
2004年 | 8724篇 |
2003年 | 8261篇 |
2002年 | 7060篇 |
2001年 | 7100篇 |
2000年 | 6068篇 |
1999年 | 6919篇 |
1998年 | 21396篇 |
1997年 | 14628篇 |
1996年 | 10938篇 |
1995年 | 7818篇 |
1994年 | 6739篇 |
1993年 | 6601篇 |
1992年 | 4238篇 |
1991年 | 4222篇 |
1990年 | 3832篇 |
1989年 | 3726篇 |
1988年 | 3678篇 |
1987年 | 3079篇 |
1986年 | 3001篇 |
1985年 | 3556篇 |
1984年 | 3106篇 |
1983年 | 2818篇 |
1982年 | 2655篇 |
1981年 | 2722篇 |
1980年 | 2601篇 |
1979年 | 2325篇 |
1978年 | 2317篇 |
1977年 | 3327篇 |
1976年 | 5276篇 |
1975年 | 1978篇 |
1974年 | 1830篇 |
1973年 | 1821篇 |
1972年 | 1492篇 |
1971年 | 1355篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
112.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
113.
Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar. 相似文献
114.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
115.
116.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献
117.
R. Urata R. Takahashi T. Nakahara K. Takahata H. Suzuki 《Photonics Technology Letters, IEEE》2006,18(1):67-69
We propose an optically clocked transistor array optoelectronic integrated circuit (OEIC) for both serial-to-parallel and parallel-to-serial conversion (demux/mux), enabling an interface between high-speed asynchronous burst optical labels and CMOS circuitry for optical label swapping. Dual functionality of the OEIC reduces size, power, and cost of the optical label swapper. The capability for greater than 20-Gb/s conversion operation is demonstrated. 相似文献
118.
Because biological wastewater treatment plants (WWTPs) involve a long time-delay and various disturbances, in general, skilled operators manually control the plant based on empirical knowledge. And operators usually diagnose the plant using similar cases experienced in the past. For the effective management of the plant, system automation has to be accomplished based upon operating recipes. This paper introduces automatic control and diagnosis based upon the operator's knowledge. Fuzzy logic was employed to design this knowledge-based controller because fuzzy logic can convert the linguistic information to rules. The controller can manage the influent and external carbon in considering the loading rate. The input of the controller is not the loading rate but the dissolved oxygen (DO) lag-time, which has a strong relation to the loading rate. This approach can replace an expensive sensor, which measures the loading rate and ammonia concentration in the reactor, with a cheaper DO sensor. The proposed controller can assure optimal operation and prevent the over-feeding problem. Case-based diagnosis was achieved by the analysis of profile patterns collected from the past. A new test profile was diagnosed by comparing it with template patterns containing normal and abnormal cases. The proposed control and diagnostic system will guarantee the effective and stable operation of WWTPs. 相似文献
119.
The objective of this study was to compare methane production and characteristics of digested material in anaerobic digestion concepts according to the Animal By-Products Regulation (ABP-Regulation) of the EC (hygienisation of biowaste for 1 hour at 70 degrees C, particle size < 12 mm) and Finnish national regulations (treatment temperature 55 degrees C, feeding interval 24 h, hydraulic retention time (HRT) 20 d, particle size < 40 mm) and with small variations in treatment methods for treating manure and biowaste. Moreover, the survival of three different salmonella bacteria in these processes was studied. Hygienisation of biowaste prior to digestion at 35 degrees C enhanced methane production by 14-18% compared to similar treatment without hygienisation. The differences in treatment temperature, HRT and hygienisation of biowaste prior to digestion did not significantly affect the characteristics of digested material. The concepts according to the ABP-Regulation and Finnish national regulations were effective in destroying salmonella bacteria to an undetectable level. 相似文献
120.
Y Terashima H Ozaki R R Giri T Tano S Nakatsuji R Takanami S Taniguchi 《Water science and technology》2006,54(8):55-63
Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater. 相似文献