全文获取类型
收费全文 | 263161篇 |
免费 | 4767篇 |
国内免费 | 1817篇 |
专业分类
电工技术 | 5436篇 |
技术理论 | 5篇 |
综合类 | 1169篇 |
化学工业 | 42557篇 |
金属工艺 | 11061篇 |
机械仪表 | 7809篇 |
建筑科学 | 6727篇 |
矿业工程 | 1667篇 |
能源动力 | 5700篇 |
轻工业 | 26086篇 |
水利工程 | 2918篇 |
石油天然气 | 6012篇 |
武器工业 | 244篇 |
无线电 | 28021篇 |
一般工业技术 | 49563篇 |
冶金工业 | 47885篇 |
原子能技术 | 5639篇 |
自动化技术 | 21246篇 |
出版年
2021年 | 2494篇 |
2019年 | 2137篇 |
2018年 | 3419篇 |
2017年 | 3393篇 |
2016年 | 3723篇 |
2015年 | 2827篇 |
2014年 | 4637篇 |
2013年 | 11536篇 |
2012年 | 7802篇 |
2011年 | 10352篇 |
2010年 | 8246篇 |
2009年 | 8792篇 |
2008年 | 9619篇 |
2007年 | 9759篇 |
2006年 | 8568篇 |
2005年 | 7496篇 |
2004年 | 6739篇 |
2003年 | 6272篇 |
2002年 | 6278篇 |
2001年 | 6366篇 |
2000年 | 5962篇 |
1999年 | 5949篇 |
1998年 | 12926篇 |
1997年 | 9594篇 |
1996年 | 7324篇 |
1995年 | 5581篇 |
1994年 | 5146篇 |
1993年 | 5002篇 |
1992年 | 3989篇 |
1991年 | 3780篇 |
1990年 | 3865篇 |
1989年 | 3807篇 |
1988年 | 3560篇 |
1987年 | 3057篇 |
1986年 | 3083篇 |
1985年 | 3452篇 |
1984年 | 3363篇 |
1983年 | 3117篇 |
1982年 | 2721篇 |
1981年 | 2929篇 |
1980年 | 2652篇 |
1979年 | 2865篇 |
1978年 | 2745篇 |
1977年 | 2855篇 |
1976年 | 3708篇 |
1975年 | 2469篇 |
1974年 | 2293篇 |
1973年 | 2330篇 |
1972年 | 1987篇 |
1971年 | 1788篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
L. Gao P. Hrter Ch. Linsmeier J. Gstttner R. Emling D. Schmitt-Landsiedel 《Materials Science in Semiconductor Processing》2004,7(4-6):331
Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt3)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO2/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO2/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO2 substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas. 相似文献
133.
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
134.
Two models are given for determining the collision rate of inertial particles in a homogeneous isotropic turbulence. The advantages and disadvantages of the known models of particle collisions are discussed. One of the models suggested by us is based on the assumption that the joint probability density function of gas and particle velocities is a Gaussian distribution. The second model follows from the kinetic equation for the probability density of the relative velocity of two particles. These two models are compared with each other and with the available data of direct numerical simulation. 相似文献
135.
EGD级环保型润滑油及其生物降解性 总被引:2,自引:0,他引:2
经生物降解性评定和粘度测量确定了EGD级生物降解二冲程润滑油复合基础油的组成;通过发动机清净性试验确定了添加剂组成配方和总添加量。在此基础上,研制了生物降解二冲程油(Oil B),其达到了ISO EGD级二冲程油标准中规定的6个发动机性能指标和2个理化性能指标,生物降解性达到73.1%。 相似文献
136.
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
137.
A multi-level attention framework for tracking and segmentation of humans and objects under complex occlusions is investigated,
featuring an effective probabilistic appearance-based technique for pixel reclassification during object grouping and splitting.
A novel ’spatial-depth affinity metric’ is introduced in the conventional likelihood function, utilising information of both
spatial locations of pixels and dynamic depth ordering of the component objects in grouping. Depth ordering estimation is
achieved through a combination of top-down and bottom-up approach. Experiments on some realworld difficult scenarios of low
quality and highly compressed videos demonstrate the very promising results achieved. 相似文献
138.
Dell'Amico M. Maffioli F. Merani M.L. 《Wireless Communications, IEEE Transactions on》2004,3(4):1013-1017
This paper proposes some novel techniques to accommodate users with different rate requirements in a wideband code-division multiple-access system employing orthogonal variable spreading factor codes. Two simple static code assignment strategies are first considered, and an improvement based on multicode assignment. Then the new idea of tree partitioning is introduced and used to devise a dynamic code reassignment algorithm. The behavior of these different techniques is experimentally investigated, in terms of call blocking probability and number of required reassignments. The tree partitioning method exhibits very good performances. 相似文献
139.
This study investigates the citation patterns in the journal, Medical Principles and Practice from its inception in 1989 through 2000 (volumes 1-9). The data set includes 4740 references appended to the 221 original
research articles. All of the citations were entered into a ProCite database for analysis. Specifically, this study addresses:
(1) bibliometric patterns of cited works in terms of publication format, subject scatter, authorship characteristics, age
of citations, geographic distribution, and language distribution; (2) productivity of journal titles; (3) the role of self-citation;
and (4) how selected bibliometric indicators apply. Some of the findings include: journal articles are most frequently cited;
English language publications dominate the literature; there is a trend of multiple authorship; and the pattern of aging is
below the norm for medical literature. The results of the study can provide a benchmark to measure the user behavior of a
particular group of researchers as well as for the provision of collection development and management decisions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
140.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献