全文获取类型
收费全文 | 9097篇 |
免费 | 699篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 61篇 |
综合类 | 15篇 |
化学工业 | 2254篇 |
金属工艺 | 131篇 |
机械仪表 | 175篇 |
建筑科学 | 391篇 |
矿业工程 | 58篇 |
能源动力 | 189篇 |
轻工业 | 1954篇 |
水利工程 | 59篇 |
石油天然气 | 42篇 |
无线电 | 478篇 |
一般工业技术 | 1353篇 |
冶金工业 | 1506篇 |
原子能技术 | 41篇 |
自动化技术 | 1100篇 |
出版年
2023年 | 77篇 |
2022年 | 147篇 |
2021年 | 241篇 |
2020年 | 209篇 |
2019年 | 214篇 |
2018年 | 312篇 |
2017年 | 300篇 |
2016年 | 357篇 |
2015年 | 318篇 |
2014年 | 330篇 |
2013年 | 803篇 |
2012年 | 521篇 |
2011年 | 574篇 |
2010年 | 400篇 |
2009年 | 355篇 |
2008年 | 356篇 |
2007年 | 435篇 |
2006年 | 279篇 |
2005年 | 263篇 |
2004年 | 220篇 |
2003年 | 227篇 |
2002年 | 212篇 |
2001年 | 121篇 |
2000年 | 88篇 |
1999年 | 122篇 |
1998年 | 192篇 |
1997年 | 147篇 |
1996年 | 146篇 |
1995年 | 128篇 |
1994年 | 99篇 |
1993年 | 94篇 |
1992年 | 72篇 |
1991年 | 44篇 |
1990年 | 81篇 |
1989年 | 67篇 |
1988年 | 60篇 |
1987年 | 63篇 |
1986年 | 62篇 |
1985年 | 48篇 |
1984年 | 64篇 |
1983年 | 52篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 52篇 |
1979年 | 66篇 |
1978年 | 55篇 |
1977年 | 54篇 |
1976年 | 56篇 |
1975年 | 39篇 |
1974年 | 53篇 |
排序方式: 共有9807条查询结果,搜索用时 15 毫秒
61.
Jung-Han Kimn Marcus Sarkis 《Computer Methods in Applied Mechanics and Engineering》2007,196(8):1507-1514
Overlapping balancing domain decomposition methods and their combination with restricted additive Schwarz methods are proposed for the Helmholtz equation. These new methods also extend previous work on non-overlapping balancing domain decomposition methods toward simplifying their coarse problems and local solvers. They also extend restricted Schwarz methods, originally designed to overlapping domain decomposition and Dirichlet local solvers, to the case of non-overlapping domain decomposition and/or Neumann and Sommerfeld local solvers. Finally, we introduce coarse spaces based on partitions of unity and planes waves, and show how oblique projection coarse problems can be designed from restricted additive Schwarz methods. Numerical tests are presented. 相似文献
62.
Mou Weimin; Biocca Frank; Owen Charles B.; Tang Arthur; Xiao Fan; Lim Lynette 《Canadian Metallurgical Quarterly》2004,10(4):238
In 3 experiments, the authors investigated spatial updating in augmented reality environments. Participants learned locations of virtual objects on the physical floor. They were turned to appropriate facing directions while blindfolded before making pointing judgments (e.g., "Imagine you are facing X. Point to Y"). Experiments manipulated the angular difference between the learning heading and the imagined heading and between the actual heading and the imagined heading. The effect of actual-imagined on pointing latency was observed for naive users but not for users with brief training or instructions concerning the fact that objects can move with body movements. The results indicated that naive users used an environment-stabilized reference frame to access information arrays, but with experience and instruction the nature of the representation changed from an environment stabilized to a body stabilized reference frame. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
63.
Levent Onal Sophie Cozien‐Cazuc I. Arthur Jones Christopher D. Rudd 《应用聚合物科学杂志》2008,107(6):3750-3755
The moisture uptake of polymers and composites has increasing significance where these materials are specified for invasive, long‐term medical applications. Here we analyze mass gain and the ensuing degradation mechanisms in phosphate glass fiber reinforced poly‐?‐caprolactone laminates. Specimens were manufactured using in situ polymerization of ?‐caprolactone around a bed of phosphate glass fibers. The latter were sized with 3‐aminopropyltriethoxysilane to control the rate of modulus degradation. Fiber content was the main variable in the study, and it was found that the moisture diffusion coefficient increased significantly with increasing fiber volume fraction. Diffusion, plasticization, and leaching of constituents appear to be the dominant aspects of the process over these short‐term tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
64.
María Esther Diupotex-Chong Néstor J Cazzaniga Alejandra Hernández-Santoyo José Miguel Betancourt-Rule 《Biocell》2004,28(3):279-285
Mitotic chromosomes of the freshwater snail Pomacea patula catemacensis (Baker 1922) were analyzed on gill tissue of specimens from the type locality (Lake Catemaco, Mexico). The diploid number of chromosomes is 2n = 26, including nine metacentric and four submetacentric pairs; therefore, the fundamental number is FN = 52, No sex chromosomes could be identified. The same chromosome number and morphology were already reported for P. flagellata, i.e., the other species of the genus living in Mexico. The basic haploid number for family Ampullariidae was reported to be n = 14 in the literature; so, its reduction to n = 13 is probably an apomorphy of the Mexican Pomacea snails. Lanistes bolteni, from Egypt, also shows n = 13, but its karyotype is much more asymmetrical, and seems to have evolved independently from P. flagellata and P. patula catemacensis. The nominotypical subspecies, P. patula patula (Reeve 1856), is a poorly known taxon, whose original locality is unknown. A taxonomical account is presented here, and a Mexican origin postulated as the most parsimonious hypothesis. 相似文献
65.
66.
67.
68.
Reduction of optical proximity effects (OPE), at deep uv wavelength of 248nm, caused by the variation of stepper lens operating conditions is investigated. It is shown that many of these effects, which increase as the Rayleigh limit is approached, can be minimised, and in many cases eliminated, by suitable choice of lens numerical aperture (NA) and partial coherence (sigma, σ).
Application of these results should enable the user of advanced wafer steppers to carry out high resolution lithography with a minimum of time consuming optical proximity correction (OPC). 相似文献
69.
A structural model of science achievement and attitude: An extension to high school. 总被引:1,自引:0,他引:1
A previous structural model of Walberg's theory of educational productivity (A. J. Reynolds and H. J. Walberg, 1991) was tested with a national probability sample of 2,535 10th graders for science achievement and attitude. Using data from the Longitudinal Study of American Youth, a 3-wave design incorporated information from students, teachers, and parents. Results indicate that a revised mediated-effects model fit the data best and accounted for substantial variance in Grade 11 science achievement (56%) and attitude (44%). The variables prior achievement, home environment, exposure to mass media through reading, and instructional time had the greatest total effects on science achievement. Prior attitude, home environment, motivation, and prior achievement made the greatest total contributions to science attitude. Although there were different weightings of the factors between the present study and Reynolds and Walberg (1991), both studies support a mediated-effects model of educational productivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.