全文获取类型
收费全文 | 20913篇 |
免费 | 552篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 223篇 |
综合类 | 18篇 |
化学工业 | 4426篇 |
金属工艺 | 492篇 |
机械仪表 | 366篇 |
建筑科学 | 925篇 |
矿业工程 | 88篇 |
能源动力 | 535篇 |
轻工业 | 1410篇 |
水利工程 | 261篇 |
石油天然气 | 205篇 |
武器工业 | 1篇 |
无线电 | 1424篇 |
一般工业技术 | 3375篇 |
冶金工业 | 4529篇 |
原子能技术 | 167篇 |
自动化技术 | 3044篇 |
出版年
2022年 | 147篇 |
2021年 | 241篇 |
2020年 | 198篇 |
2019年 | 263篇 |
2018年 | 297篇 |
2017年 | 302篇 |
2016年 | 366篇 |
2015年 | 293篇 |
2014年 | 457篇 |
2013年 | 1238篇 |
2012年 | 753篇 |
2011年 | 945篇 |
2010年 | 755篇 |
2009年 | 760篇 |
2008年 | 886篇 |
2007年 | 955篇 |
2006年 | 781篇 |
2005年 | 739篇 |
2004年 | 650篇 |
2003年 | 607篇 |
2002年 | 583篇 |
2001年 | 364篇 |
2000年 | 368篇 |
1999年 | 361篇 |
1998年 | 442篇 |
1997年 | 390篇 |
1996年 | 375篇 |
1995年 | 359篇 |
1994年 | 308篇 |
1993年 | 358篇 |
1992年 | 313篇 |
1991年 | 228篇 |
1990年 | 273篇 |
1989年 | 279篇 |
1988年 | 267篇 |
1987年 | 251篇 |
1986年 | 286篇 |
1985年 | 299篇 |
1984年 | 300篇 |
1983年 | 291篇 |
1982年 | 231篇 |
1981年 | 258篇 |
1980年 | 253篇 |
1979年 | 251篇 |
1978年 | 229篇 |
1977年 | 230篇 |
1976年 | 207篇 |
1975年 | 195篇 |
1974年 | 175篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
121.
研制成用LD泵浦的声光调Q的Nd:YVO4-KTP腔内倍频激光器,得到了TEM00模、频率高达100kHz的稳定的532um绿激光脉冲系列输出,阈值泵浦功率为27mW;在连续570mW的泵浦功率下,绿激光脉冲的峰值功率达1100W,脉宽为4.6us;输出功率稳定,在±5℃的工作温度变化下,输出功率变化小于±2%。此种器件可望得到广泛的应用。 相似文献
122.
The paper describes a research study on visual discrimination of textual and graphic symbols on a visual display terminal (VDT) screen when viewed at eye-lo-screen distances of 61 cm and 152 cm (24 and 60 ins). Conducted as part of a development programme at McDonnell Douglas Corporation's St. Louis Aircraft Company for an Integrated Manufacturing Composites Centre (ICC), the study investigated symbol shapes, symbol sizes, symbol colours and background colours at the two viewing distances. The longer distance is representative of required placements of the VDTs at some manufacturing workstations to avoid interference with process or control equipment. Knowledge gained from the study was incorporated in the selection of the manufacturing computer information system (CIS) terminals.
All four treatments showed significant effects on visual discrimination at both viewing distances and, particularly at the 152 cm distance, the mix of symbol and background colours was highly significant. A black screen background colour with more luminous symbols such as orange, green, yellow provided much better visual discrimination at the extended viewing distance than less luminous symbols such as red and blue on a white background. Visual discrimination at the extended viewing distance, when compared with the shorter viewing distance and using symbols of equal size, was better than the loss in visual angle would suggest.
Sex and age (to age 65) did not significantly affect visual discrimination mean scores, but the variance among individuals in the 51-65 years age group was greater than for the younger age groups.
The visual discrimination scores for symbol sizes of 4 mm2 were not significantly different from the 6 mm2 symbols at the 61 cm viewing distance. The 4 mm2 symbol size was therefore adequate for visual discrimination of standalone symbols at this distance. Although 8 mm symbols were not used in this study, projections from the data indicate that such symbol sizes at 152 cm would provide comparable discrimination scores to the 4 mm2 at 61 cm.
Improved visual discrimination of standalone symbols occurs with gaps or changes in the angles of symbols, such as sets 'C' versus 'O' and 'Xl' versus'+'. 相似文献
All four treatments showed significant effects on visual discrimination at both viewing distances and, particularly at the 152 cm distance, the mix of symbol and background colours was highly significant. A black screen background colour with more luminous symbols such as orange, green, yellow provided much better visual discrimination at the extended viewing distance than less luminous symbols such as red and blue on a white background. Visual discrimination at the extended viewing distance, when compared with the shorter viewing distance and using symbols of equal size, was better than the loss in visual angle would suggest.
Sex and age (to age 65) did not significantly affect visual discrimination mean scores, but the variance among individuals in the 51-65 years age group was greater than for the younger age groups.
The visual discrimination scores for symbol sizes of 4 mm2 were not significantly different from the 6 mm2 symbols at the 61 cm viewing distance. The 4 mm2 symbol size was therefore adequate for visual discrimination of standalone symbols at this distance. Although 8 mm symbols were not used in this study, projections from the data indicate that such symbol sizes at 152 cm would provide comparable discrimination scores to the 4 mm2 at 61 cm.
Improved visual discrimination of standalone symbols occurs with gaps or changes in the angles of symbols, such as sets 'C' versus 'O' and 'Xl' versus'+'. 相似文献
123.
Recently theories of vortex fluctuations in two-dimensional superconducting films have been compared to the experimentally determined power law dependence of voltage on current and to the temperature-dependent resistance in small applied fields. Here an alternative interpretation of the power law and a practical difficulty of flux pinning for measurements in small fields are pointed out. To illustrate these points, experimental examples are presented for very homogeneous granular aluminum films. 相似文献
124.
Ronald W. Rousseau James K. Ferrell Robert M. Kelly 《Chemical Engineering Communications》1985,34(1):27-35
Experience with the operation of a pilot-scale unit is used to outline potential difficulties in the operation of acid gas removal systems on gases produced from coal. The pilot plant has been used to condition gases produced from subbituminous coal, devolatilized char, peat and lignite. The solvent used in the acid gas removal system has been refrigerated methyl alcohol. Data from this study document accumulation of hydrocarbons, sulfur and nitrogen compounds, and mercury in the circulating solvent. 相似文献
125.
126.
In order to obtain a bonded wood product from the tree, wood must be subjected to a series of processes. These include, among others, vital processes like drying of the green wood and machining of the surfaces of the dried wood in preparation for bonding. However, when wood is machined with dull blades, thermal degradation of the wood frequently occurs. The effects of kiln drying and thermal degradation of wood on the performance of the adhesive joints subsequently formed from such wood were investigated. Tapered double cantilever beam (TDCB) test specimens obtained from hard maple and phenol–resorcinol–formaldehyde (PRF) adhesives were used in the investigations. The enhancement of fracture energy due to the reduction in the moisture content of wood, the improved performance of adhesive joints due to rejointing of wood surfaces before bonding, and the reduction of adhesive joint strength resulting from thermal degradation of wood are presented and discussed. 相似文献
127.
128.
This paper is concerned with improvement in optical image quality by image restoration. Image restoration is an ill-posed
inverse problem which involves the removal or minimization of degradations caused by noise and blur in an image, resulting
from, in this case, imaging through a medium. Our work here concerns the use of the underlying Toeplitz structure of such
problems, and associated techniques for accelerating the convergence of iterative image restoration computations. Denoising
methods, including total variation minimization, followed by segmentation-based preconditioning methods for minimum residual
conjugate gradient iterations, are investigated. Regularization is accomplished by segmenting the image into (smooth) segments
and varying the preconditioners across the segments. By taking advantage of the Toeplitz structure, our algorithms can be
implemented with computational complexity of onlyO (ln
2 logn), wheren
2 is the number of pixels in the image andl is the number of segments used. Also, parallelization is straightforward. Numerical tests are reported for atmospheric imaging
problems, including the case of spatially varying blur.
Research supported in part by a National Science Foundation Postdoctoral Research Fellowship.
Research sponsored by the U.S. Air Force Office of Scientific Research under grant F49620-97-1-1039.
Research sponsored by the U.S. Air Force Office of Scientific Research under grant F49620-97-1-0139, and by the National Science
Foundation under grant CCR-96-23356.
Research sponsored by the National Science Foundation under grant CCR-96-23356. 相似文献
129.
Phan Alex Truong Phuong Schade Christoph Vasan Aditya Friend James Talke Frank E. 《Microsystem Technologies》2021,27(6):2473-2479
Microsystem Technologies - “Zero drift” behavior of an optical intraocular pressure sensor is studied using an analytical model based on the deflection of a circular membrane. Results... 相似文献
130.
This paper is concerned with the problem of positive observer synthesis for positive systems with both interval parameter uncertainties and time delay. Conventional observers may no longer be applicable for such kind of systems due to the positivity constraint on the observers, and they only provide an estimate of the system state in an asymptotic way. A pair of positive observers with state‐bounding feature is proposed to estimate the state of positive systems at all times in this paper. A necessary and sufficient condition for the existence of desired observers is first established, and the observer matrices can be obtained easily through the solutions of a set of linear matrix inequalities (LMIs). Then, to reduce the error signal between the system state and its estimates, an iterative LMI algorithm is developed to compute the optimized state‐bounding observer matrices. Finally, a numerical example is presented to show the effectiveness and applicability of the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献