全文获取类型
收费全文 | 495364篇 |
免费 | 5384篇 |
国内免费 | 1489篇 |
专业分类
电工技术 | 8930篇 |
综合类 | 400篇 |
化学工业 | 77338篇 |
金属工艺 | 26003篇 |
机械仪表 | 17108篇 |
建筑科学 | 10866篇 |
矿业工程 | 4308篇 |
能源动力 | 10052篇 |
轻工业 | 34668篇 |
水利工程 | 5939篇 |
石油天然气 | 14315篇 |
武器工业 | 31篇 |
无线电 | 50378篇 |
一般工业技术 | 108674篇 |
冶金工业 | 81181篇 |
原子能技术 | 14847篇 |
自动化技术 | 37199篇 |
出版年
2021年 | 4514篇 |
2019年 | 4349篇 |
2018年 | 8126篇 |
2017年 | 8343篇 |
2016年 | 8926篇 |
2015年 | 5366篇 |
2014年 | 8905篇 |
2013年 | 21606篇 |
2012年 | 13094篇 |
2011年 | 17104篇 |
2010年 | 13959篇 |
2009年 | 15308篇 |
2008年 | 16039篇 |
2007年 | 15759篇 |
2006年 | 13483篇 |
2005年 | 12096篇 |
2004年 | 11729篇 |
2003年 | 11557篇 |
2002年 | 11369篇 |
2001年 | 11202篇 |
2000年 | 10650篇 |
1999年 | 10543篇 |
1998年 | 23282篇 |
1997年 | 17090篇 |
1996年 | 13158篇 |
1995年 | 10211篇 |
1994年 | 9203篇 |
1993年 | 9245篇 |
1992年 | 7191篇 |
1991年 | 7260篇 |
1990年 | 7000篇 |
1989年 | 6803篇 |
1988年 | 6643篇 |
1987年 | 6117篇 |
1986年 | 5959篇 |
1985年 | 6718篇 |
1984年 | 6332篇 |
1983年 | 5883篇 |
1982年 | 5522篇 |
1981年 | 5630篇 |
1980年 | 5483篇 |
1979年 | 5500篇 |
1978年 | 5709篇 |
1977年 | 6220篇 |
1976年 | 8033篇 |
1975年 | 5107篇 |
1974年 | 5071篇 |
1973年 | 5114篇 |
1972年 | 4426篇 |
1971年 | 4047篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
The problem of synthesis of an isotropic reradiator providing for the transparency of a circular perfectly conducting cylinder illuminated by a TE-polarized plane wave is investigated. A general solution to the problem of diffraction from the cylinder with a reradiator is obtained, and a system of nonlinear equations for the synthesis problem is derived. Numerical solution of the synthesis problem is illustrated by a number of examples. 相似文献
33.
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
34.
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
35.
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
36.
V. N. Durcheva S. M. Puchkova 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(2):71-78
Operation of the dam in a transitional mode is described.
__________
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 1, January 2006, pp. 8–15. 相似文献
37.
V. O. Yablonskii 《Chemical and Petroleum Engineering》2006,42(11-12):611-617
A mathematical model for separation of suspensions with a non-Newtonian disperse medium by dual-stage pressurized flotation in a cylindrical-conical hydrocyclone is developed. A system of differential equations of the convective diffusion and movement of a complex of particles-bubbles is solved by a numerical method. The concentration field is modeled, and integral separation indicators are determined. Values of structural parameters of the hydrocyclone for which the separation indicators depend heavily on the taper angle of the conical section of the housing and the rheological properties of the disperse medium are established. It is demonstrated that dual-stage pressurized flotation makes it possible to reduce considerably the residual concentration of solid-phase particles as compared with single-stage flotation. 相似文献
38.
Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results 总被引:7,自引:0,他引:7
N. Bilgin M.A. Demircin H. Copur C. Balci H. Tuncdemir N. Akcin 《International Journal of Rock Mechanics and Mining Sciences》2006,43(1):139-156
Conical picks are the essential cutting tools used especially on roadheaders, continuous miners and shearers and their cutting performance affects directly the efficiency and the cost of rock/mineral excavation. In this study, in order to better understand the effects of dominant rock properties on cutter performance, 22 different rock specimens having compressive strength values varying from 10 to 170 MPa are first subjected to a wide range of mechanical tests. Then, laboratory full-scale linear cutting tests with different depth of cut and cutter spacing values are realized on large blocks of rock specimens using one type of conical pick. Specific energy, cutting and normal force values for relieved and unrelieved cutting modes are recorded using a triaxial force dynamometer with capacity of 50 tonnes and a data acquisition system. Cutter force and specific energy values are correlated with rock properties and theoretical force and specific energy values obtained from widely used theoretical approaches.The results indicate that uniaxial compressive strength among the rock properties investigated is best correlated with the measured cutter performance values, which is in good agreement with previous studies. However, it is also emphasized in this study that Brazilian tensile strength, Schmidt hammer rebound values, static and dynamic elasticity modulus are also dominant rock properties affecting cutter performance.Theoretical specific energy defined by different researchers has a meaningful relationship with the experimental specific energy, which is an essential parameter for predicting the instantaneous cutting rates of mechanical excavation systems. It is also demonstrated that the experimental cutter forces obtained for 5 mm depth of cut are in good agreement with theoretical force values, if the friction angle between rock and cutting tool is included in the theoretical formulation. It is emphasized that, to some extend, laboratory tests can help to minimize high cost of a trial–error approach in the field. 相似文献
39.
40.
Quasi-static stress fields for a crack inclined to the property gradation in functionally graded materials 总被引:3,自引:0,他引:3
Summary. Quasi-static stress fields for a crack inclined to the direction of property gradation in functionally graded materials (FGMs)
are obtained through an asymptotic analysis coupled with Westergaard's stress function approach. The elastic modulus of the
FGM is assumed to vary exponentially along the gradation direction. The mode mixity due to the inclination of the property
gradient is accommodated in the analysis through superposition of opening and shear modes. The first four terms in the expansion
of the stress field are derived to explicitly bring out the influence of nonhomogeneity on the structure of the stress field.
Using these stress field contours of constant maximum shear stress, constant maximum principal stress, constant first stress
invariant and constant out of plane displacement are generated, and the effect of inclination of the property gradation direction
on these contours is discussed.
Received September 22, 2002
Published online: May 20, 2003
The financial support of National Science Foundation (NSF) under grant no. CMS 99000138 is gratefully acknowledged. 相似文献