全文获取类型
收费全文 | 13030篇 |
免费 | 1482篇 |
国内免费 | 569篇 |
专业分类
电工技术 | 565篇 |
综合类 | 908篇 |
化学工业 | 2153篇 |
金属工艺 | 193篇 |
机械仪表 | 385篇 |
建筑科学 | 847篇 |
矿业工程 | 343篇 |
能源动力 | 360篇 |
轻工业 | 4733篇 |
水利工程 | 453篇 |
石油天然气 | 1167篇 |
武器工业 | 41篇 |
无线电 | 598篇 |
一般工业技术 | 853篇 |
冶金工业 | 555篇 |
原子能技术 | 167篇 |
自动化技术 | 760篇 |
出版年
2024年 | 47篇 |
2023年 | 223篇 |
2022年 | 380篇 |
2021年 | 607篇 |
2020年 | 535篇 |
2019年 | 541篇 |
2018年 | 479篇 |
2017年 | 524篇 |
2016年 | 537篇 |
2015年 | 556篇 |
2014年 | 837篇 |
2013年 | 1004篇 |
2012年 | 1045篇 |
2011年 | 1099篇 |
2010年 | 708篇 |
2009年 | 679篇 |
2008年 | 586篇 |
2007年 | 709篇 |
2006年 | 658篇 |
2005年 | 502篇 |
2004年 | 437篇 |
2003年 | 361篇 |
2002年 | 309篇 |
2001年 | 293篇 |
2000年 | 203篇 |
1999年 | 198篇 |
1998年 | 181篇 |
1997年 | 127篇 |
1996年 | 114篇 |
1995年 | 117篇 |
1994年 | 79篇 |
1993年 | 69篇 |
1992年 | 51篇 |
1991年 | 50篇 |
1990年 | 37篇 |
1989年 | 24篇 |
1988年 | 25篇 |
1987年 | 9篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1961年 | 5篇 |
1960年 | 6篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Don Kelleher 《Information Systems Journal》1995,5(2):137-157
Abstract. An Information Systems Methodology is usually presented as a sequential set of tasks — planning, analysis, design and construction — resulting in a new business application. This classical 'forward-engineering' approach must be adapted to changing business needs — business process redesign, quality management, process and systems templates, advanced technologies, application packages, the reuse of existing information systems resources, and rapid delivery cycles. Using the most general concept of a Business Programme, this paper describes a methodological approach incorporating these modern themes that is qualitatively and quantitatively different from the classical model. It provides a framework for the integration of otherwise independent methodologies, and shows how an entire programme can be formulated, planned and executed. An example is provided, and the approach is justified. 相似文献
42.
Claes-Gran Johansson 《Journal of the Institute of Brewing》1996,102(4):249-250
A combustion method, relying on the Dumas principle, for the determination of total nitrogen in barley and malt, has been collaboratively tested by the Analysis Committee of the European Brewery Convention. Repeatability, r95, and reproducibility, R95, values were 0.063 and 0.116% of dry matter, respectively, for samples with nitrogen contents in the range 1.23 to 1.86% N of dry matter. There was no significant difference between these values for barley and malt. The Analysis Committee approved the adoption of the combustion method for inclusion in Analytica EBC as an alternative method. 相似文献
43.
Analysis of lipid classes by solid-phase extraction and high-performance size-exclusion chromatography 总被引:1,自引:0,他引:1
Anu I. Hopia Vieno I. Piironen Pekka E. Koivistoinen Lea E. T. Hyvönen 《Journal of the American Oil Chemists' Society》1992,69(8):772-776
An improved method to analyze lipid classes of edible oils and fats by solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) is presented. A mixture of lipid standards was fractionated by the solid-phase extraction procedure (NH2 phase) into polar and nonpolar fractions; these were then submitted to analysis by HPSEC. The size-exclusion chromatographic columns were three styrene/divinylbenzene columns with pore sizes of 100 Å and 50 Å. Light-scattering was used for the detection system, and the parameters of the detector were optimized to minimize the difference between the responses of the compounds studied. With this procedure it was possible to separate the following lipid classes: triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids, sterols, sterol esters, tocopherols and carotenoids. Quantitative analysis was studied for a light-scattering detector with several lipid standards of different molecular weights and unsaturation levels. 相似文献
44.
45.
MPC系统模块结构中的流场研究 总被引:5,自引:0,他引:5
本研究中,应用Simple数值计算方法开发了求解MPC系统模块结构中二维流场分布的计算软件。为了验证计算结果的精确性,用多普勒测速仪实测了用有机玻璃制成的MPC模块二维模型的流场,模拟计算结果与实测值对比取得了较好的一致性。四种不同流出角的MPC模块平均总压损失计算结果表明,已开发的软件可作为设计低流阻MPC模块的良好工具。 相似文献
46.
47.
Kenji Imura 《Color research and application》2007,32(3):195-200
In this article, a new method for measuring a total spectral radiance factor of a FWA‐treated sample illuminated by a specific standard illuminant is introduced. The method replaces an unstable real fluorescent standard by a bi‐spectral luminescent radiance factor data, which works as a virtual fluorescent standard (VFS) by knowing spectral intensity distributions of illuminations applied to the sample. The method utilizes two illuminations I1 and I2 whose relative spectral intensity distributions are different from each other and synthesizes a virtual illumination presenting the identical fluorescent spectral radiance factor to that presented by the standard illuminant with the VFS of the specific bi‐spectral luminescent radiance factor by linearly combining I1 and I2 with the suitable weighting factors. The applicability of the method is examined in principle by comparing ISO brightness and CIE whiteness index of fluorescent standard paper as a test sample obtained by this new method to the assigned values. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 195–200, 2007 相似文献
48.
Suitability of sweet sorghum in Greece, where irrigation supply during crop development is limited as rainfall is scarce and
evapotranspiration loss is high, is examined in relation with radiation availability. A two-year field experiment was conducted,
in central Greece, imposing four soil water regimes via different irrigation treatments: (1) Highly irrigated, (2) Highly
irrigated till anthesis when irrigation stopped, (3) Medium irrigated, and (4) Low irrigated. It was found that above-ground
dry biomass production from non-water-stressed sweet sorghum plants suggests a high productivity potential among C4 crops. Under water shortage, radiation use efficiency may be significantly lower. Radiation use efficiency seems to be linearly
related to water consumption. Stressed plants (probably except severely stressed) seem to use available water more efficiently
than unstressed plants. The slope of the line relating dry matter produced and water evapotranspired increases the sooner
the stress is sensed. Yield reduction resulting from post-anthesis irrigation stopage is very little. High water use efficiency
values tend to be related with low radiation use efficiency values. 相似文献
49.
射孔水平井中地层流体的流动是符合达西定律的,但水平井射孔工艺、完井方式以及井位等因素的影响,比垂直井复杂。本文将射孔后的流动看成线源,根据Newman乘积原理,用Green函数的方法得到井底压力解析解。在此基础上,将射孔时的地层压实和井壁污染用表皮来表示,并考虑井筒存储,得Laplace空间上的表达,最后用Laplace数值反演得到时空间上的解,利用该解可以有效预测水平井的产能。 相似文献
50.