全文获取类型
收费全文 | 4449篇 |
免费 | 268篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 56篇 |
综合类 | 2篇 |
化学工业 | 950篇 |
金属工艺 | 60篇 |
机械仪表 | 97篇 |
建筑科学 | 161篇 |
矿业工程 | 4篇 |
能源动力 | 130篇 |
轻工业 | 650篇 |
水利工程 | 35篇 |
石油天然气 | 8篇 |
无线电 | 358篇 |
一般工业技术 | 636篇 |
冶金工业 | 638篇 |
原子能技术 | 32篇 |
自动化技术 | 905篇 |
出版年
2024年 | 6篇 |
2023年 | 49篇 |
2022年 | 48篇 |
2021年 | 222篇 |
2020年 | 100篇 |
2019年 | 100篇 |
2018年 | 160篇 |
2017年 | 100篇 |
2016年 | 184篇 |
2015年 | 140篇 |
2014年 | 195篇 |
2013年 | 292篇 |
2012年 | 263篇 |
2011年 | 336篇 |
2010年 | 202篇 |
2009年 | 230篇 |
2008年 | 213篇 |
2007年 | 191篇 |
2006年 | 169篇 |
2005年 | 123篇 |
2004年 | 103篇 |
2003年 | 107篇 |
2002年 | 85篇 |
2001年 | 55篇 |
2000年 | 65篇 |
1999年 | 72篇 |
1998年 | 224篇 |
1997年 | 150篇 |
1996年 | 113篇 |
1995年 | 71篇 |
1994年 | 67篇 |
1993年 | 44篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 15篇 |
1976年 | 18篇 |
1973年 | 3篇 |
排序方式: 共有4722条查询结果,搜索用时 15 毫秒
21.
We hypothesized that hydrocephalus can cause death of brain cells and that generation of new brain cells might compensate for the cell loss. Hydrocephalus was induced in 3-week-old rats by injection of kaolin into the cisterna magna. The brains were studied 1 to 4 weeks later by histochemical, immunochemical, and ultrastructural methods. The ventricles enlarged progressively. Some axons in the corpus callosum were injured as early as 1 week, but axonal damage was not prevalent until 4 weeks when ventriculomegaly became severe. Dying cells detected by DNA end labeling and often identified as oligodendrocytes by electron microscopy were evident in white matter. Late-stage hydrocephalus was associated with a significant increase in the quantity of dying cells. Hydrocephalus was associated with increased Ki67 labeling and bromodeoxyuridine incorporation in the subependymal zone. Reactive changes were identified among astrocytes, oligodendroglia, and microglia. We conclude that hydrocephalus causes, in addition to axonal injury, gradual cell death in the cerebrum, particularly the white matter. The brain response includes production of new glial cells, but whether the new cells play any beneficial role remains unknown. 相似文献
22.
SL Kamholz RJ Brewer G Grijalva J Burack MJ Del Rio M Vaynblatt N Lawson S Squinto WL Fodor AJ Norin 《Canadian Metallurgical Quarterly》1997,21(9):951-955
The lack of sufficient suitable human donor lungs for the many patients requiring pulmonary transplantation as life-saving therapy for end-stage lung diseases has generated extensive interest in cross-species lung transplantation. Ethical concerns and those of animal rights advocates have prompted studies of nonprimate species as potential solid organ donors for humans. This paper provides an overview of some of the laboratory studies of cross-species pulmonary transplantation performed over the past 20 years and focuses, in particular, on more recent work (from our laboratory and others) in the area of porcine-to-primate pulmonary xenotransplantation. 相似文献
23.
24.
25.
26.
27.
Morosi S. Marabissi D. Enrico Del Re Fantacci R. Del Santo N. 《Power Delivery, IEEE Transactions on》2006,21(4):1892-1897
This paper deals with a variable rate discrete multitone modulation system for broadband power-line communications, based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable least mean square channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The system performance, expressed in terms of bit rate and bit-error rate, is derived by simulation with and without estimation errors. The propagation environment has been assumed as a frequency-selective multipath fading channel with additive colored Gaussian noise, according to the in-building networks model. 相似文献
28.
M. Del C. Ruiz J. A. González J. B. Rivarola 《Metallurgical and Materials Transactions B》2004,35(3):439-448
The mechanism and kinetics of β-Ta2O5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature
range was 500 °C to 850 °C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray
diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters
was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method,
and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature
has a marked effect on the reaction rate. In the 500 °C to 600 °C temperature interval, the apparent activation energy is
144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the
order of reaction is near zero. The kinetic contractile plate model, X=kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable
mechanism for the carbochlorination of β-Ta2O5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta2O5, (3) oxidation of carbon, and (4) recrystallization of β-Ta2O5. 相似文献
29.
The influence of the substrate nature on the structure and morphology of ITO thin films grown by thermal evaporation in vacuum is investigated. The as-prepared metal films with Sn/In molar ratio of 0.1 were subsequently annealed for 2 h at 723 K in air (to obtain tin doped indium oxide), then annealed in vacuum at 523 K, followed by UV irradiation (to reduce the electrical resistivity). Irrespective of substrate nature, XRD data evidence a (222) preferential orientation in films. Substrate nature, annealing in vacuum and UV irradiation influence the structure, morphology, optical, electrical and surface wetting properties of the films' surface. 相似文献
30.
This paper proposes a low complexity joint space-time multiuser detection algorithm for asynchronous DS/CDMA antenna array systems. The proposed multiuser detector is composed of an adaptive antenna array, used as a linear beamformer, and a sliding window decorrelator. A QPSK modulation scheme is used in order to increase bandwidth efficiency. Numerical results are given in terms of Bit Error Rate (BER) under the assumption of a frequency-selective Rayleigh slow fading channel. In particular, the proposed receiver is shown to be near-far resistant, even in worst fading cases, and to exploit completely array introduction while maintaining acceptable computational complexity. The proposed architecture avoids linear filter realization of the decorrelator, which is impractical in the case of a large number of users, and operates with relatively short data frames instead of the complete information sequence. Finally, this receiver is very flexible to changes in timing configuration. 相似文献