全文获取类型
收费全文 | 4807篇 |
免费 | 149篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 46篇 |
综合类 | 6篇 |
化学工业 | 984篇 |
金属工艺 | 70篇 |
机械仪表 | 90篇 |
建筑科学 | 183篇 |
矿业工程 | 41篇 |
能源动力 | 113篇 |
轻工业 | 284篇 |
水利工程 | 42篇 |
石油天然气 | 23篇 |
无线电 | 345篇 |
一般工业技术 | 688篇 |
冶金工业 | 1190篇 |
原子能技术 | 31篇 |
自动化技术 | 827篇 |
出版年
2023年 | 38篇 |
2022年 | 60篇 |
2021年 | 105篇 |
2020年 | 59篇 |
2019年 | 57篇 |
2018年 | 91篇 |
2017年 | 83篇 |
2016年 | 100篇 |
2015年 | 97篇 |
2014年 | 127篇 |
2013年 | 173篇 |
2012年 | 174篇 |
2011年 | 198篇 |
2010年 | 143篇 |
2009年 | 178篇 |
2008年 | 181篇 |
2007年 | 165篇 |
2006年 | 169篇 |
2005年 | 128篇 |
2004年 | 120篇 |
2003年 | 111篇 |
2002年 | 100篇 |
2001年 | 91篇 |
2000年 | 79篇 |
1999年 | 98篇 |
1998年 | 288篇 |
1997年 | 194篇 |
1996年 | 184篇 |
1995年 | 138篇 |
1994年 | 125篇 |
1993年 | 90篇 |
1992年 | 51篇 |
1991年 | 63篇 |
1990年 | 55篇 |
1989年 | 48篇 |
1988年 | 55篇 |
1987年 | 51篇 |
1986年 | 31篇 |
1985年 | 64篇 |
1984年 | 47篇 |
1983年 | 36篇 |
1982年 | 39篇 |
1981年 | 39篇 |
1980年 | 29篇 |
1979年 | 30篇 |
1978年 | 35篇 |
1977年 | 48篇 |
1976年 | 65篇 |
1975年 | 26篇 |
1974年 | 25篇 |
排序方式: 共有4963条查询结果,搜索用时 15 毫秒
101.
Hybrid systems are heterogeneous systems characterised by the interaction of discrete and continuous dynamics. We present a trajectory-based algebraic model for describing hybrid systems; the trajectories used are closely related to streams. The algebra is based on left quantales and left semirings and provides a new application for these algebraic structures. We show that hybrid automata, which are probably the standard tool for describing hybrid systems, can conveniently be embedded into our algebra. Moreover we point out some important advantages of the algebraic approach. In particular, we show how to handle Zeno effects, which are excluded by most other authors. The development of the theory is illustrated by a running example and a larger case study. 相似文献
102.
Marco Bakera Tiziana Margaria Clemens D. Renner Bernhard Steffen 《Innovations in Systems and Software Engineering》2009,5(3):211-228
We show on a case study from an autonomous aerospace context how to apply a game-based model-checking approach as a powerful
technique for the verification, diagnosis, and adaptation of system behaviors based on temporal properties. This work is part
of our contribution within the SHADOWS project, where we provide a number of enabling technologies for model-driven self-healing.
We propose here to use GEAR, a game-based model checker, as a user-friendly tool that can offer automatic proofs of critical
properties of such systems. Although it is a model checker for the full modal μ-calculus, it also supports derived, more user-oriented logics. With GEAR, designers and engineers can interactively investigate
automatically generated winning strategies for the games, by this way exploring the connection between the property, the system,
and the proof.
This work has been partially supported by the European Union Specific Targeted Research Project SHADOWS (IST-2006-35157), exploring a Self-Healing Approach to Designing cOmplex softWare Systems. The project’s web page is at .
This article is an extended version of Renner et al. [18] presented at ISoLA 2007, Poitiers, December 2007. 相似文献
103.
Morphology and composition of nanograde calcium phosphate needle-like crystals formed by simple hydrothermal treatment 总被引:5,自引:0,他引:5
Li Yubao K. De Groot J. De Wijn C. P. A. T. Klein S. V. D. Meer 《Journal of materials science. Materials in medicine》1994,5(6-7):326-331
Nanograde calcium phosphate needle-like crystals are prepared from wet synthesized Ca–P precipitates by simple hydrothermal treatment at 140°C and 0.3 MPa for 2 h. The morphology of these crystals is observed by transmission electron microscopy (TEM). The phase composition is tested through X-ray diffractometer (XRD) and infrared spectroscopy (IR). It is found that the morphology of these crystals is related to the activity or fresh degree of the starting Ca–P precipitates and the added fluorine ions, but is not greatly influenced by the Ca/P ratio of the precipitates. These crystals with a Ca/P ratio between 1.67 and 1.5 show a poorly crystallized apatite structure at room temperature and a biphasic (HA+–TCP) structure at 1100°C, corresponding to their Ca/P ratio. It is demonstrated that these nonstoichiometric apatite crystals contain lattice-bound water which could play an important role in the formation of bone apatite. The similarity in morphology and composition between these needle-like crystals and the apatite crystals in bone provides a possibility to make a bone-like implant consisting of these needle-like crystals and collagen, etc. 相似文献
104.
M. V. Klein Ran Liu D. Salamon S. L. Cooper W. C. Lee D. M. Ginsberg S. -W. Cheong 《Journal of Superconductivity》1994,7(2):429-433
Optical absorption at the insulating gap in the parent phase of cuprate superconductors shows a broad exciton-like peak near 1.7 eV, followed by a gradual decrease in absorption persisting 1 eV above the gap. By using ultraviolet laser lines to excite Raman spectra, we have found a Raman peak 0.2 eV below the first absorption peak in insulating cuprates. The Raman peak is much narrower than the absorption peak and hasA
2g
symmetry. We assign it to an exciton consisting of a hole transition from Cu
to a linear combination of Cud
xy
and nearest neighbor Op
orbitals. We have also studied the resonance Raman profile for two-magnon Raman scattering in the same samples. We find a sharp resonance feature at about 2.7 eV, and little Raman intensity for photon energies at the 1.7 eV absorption peak. The state created at the peak must therefore be an inappropriate intermediate state for the double spin-flip Raman process. 相似文献
105.
CD22 beta is a B cell-restricted phosphoprotein expressed on the surface of mature resting B cells. It mediates interactions with other cells partly or exclusively via recognition of alpha 2-6-linked sialic acids on glycoconjugates. The sialylated N-linked oligosaccharides recognized best by CD22 beta are common to many glycoproteins, suggesting that additional regulatory mechanisms may exist. Since the exocyclic side chain of sialic acid is required for recognition, we explored the effects of a naturally occurring modification of the side chain, 9-O-acetylation. Semisynthetic N-linked oligosaccharides terminating with 9-O-acetylated, alpha 2-6-linked sialic acids showed markedly reduced binding to CD22 beta relative to their non-O-acetylated counterparts. Murine lymphoid cells were probed for natural CD22 beta ligands that might be O-acetylated using recombinant soluble forms of CD22 beta (CD22 beta Rg) and influenza C esterase (CHE-Fc, which specifically removes 9-O-acetyl esters from sialic acids). By flow cytometry analysis, CD22 beta Rg binding to splenic B cells and a subset of T cells was increased by pretreatment with CHE-Fc, indicating that some potential CD22 beta ligands are naturally "masked" by 9-O-acetylation. Unmasking of these CD22 beta ligands by removal of 9-O-acetyl esters from intact splenocytes substantially increases their CD22 beta-dependent adhesion in an in vitro adhesion assay. Probing of murine lymphoid tissue sections by CD22 beta Rg and CHE-Fc treatment demonstrates regionally restricted and differentially expressed patterns of distribution between masked and unmasked ligands. For example, lymph node-associated follicular B cells express high levels of CD22 beta ligands, none of which are masked by 9-O-acetylation. In contrast, the ligands on lymph node-associated dendritic cells are almost completely masked by 9-O-acetylation, suggesting that masking may regulate interactions between CD22 beta-positive B cells and dendritic cells. In the thymus, only medullary cells express CD22 beta ligands, and a significant portion of these are masked by 9-O-acetylation, particularly at the cortical-medullary junction. Thus, 9-O-acetylation of sialic acids on immune cells is in a position to negatively regulate CD22 beta adhesion events in a manner depending on both cell type and tissue localization. 相似文献
106.
A method is presented for the experimental determination of refractive-index profiles for planar media of monotonically decreasing refractive index, such as those used for optical waveguides. The technique is based on a generalization of the classical experiment of Lloyd's mirror, involving the interference pattern formed by a point source and its mirage, i.e., its reflection in such a graded planar medium. 相似文献
107.
108.
109.
T. J. Niwinski F. Kraemer M. Klein M. Oechsner S. Herter M. M. Becker 《Materialwissenschaft und Werkstofftechnik》2023,54(8):945-956
Ultrasonic based bolt preload evaluation is commonly performed using the mono-wave method. This method works by measuring the time of flight of longitudinal waves. Here, a reference measurement in the unloaded condition is necessary for each bolt. In this publication the longitudinal wave is complemented by another type of ultrasonic wave - the transverse wave. This method does not require a reference measurement in the unloaded condition for each bolt. Moreover, an analytic method for determining the bolt-specific K-value is introduced, which is needed for the ultrasonic bolt preload determination. The analytically calculated K-values are compared with experimental K-values from tensile tests. The influence of material, bolt property class and surface protection system were determined with cylindrical specimens. In component tests, the bolt preload was evaluated using the bi-wave method, a possible influence of the bolt assembly method was investigated and the results were interpreted regarding their accuracy. 相似文献
110.
This study utilized a non-experimental design to obtain information on a full range of domestic violence incidents brought before the Quincy, Massachusetts District Court, a model court. One limitation of previous research on spouse assaults using more sophisticated designs is that the target population has been restricted to specific subgroups of cases thereby limiting subsequent discussions of policy/practice implications of the findings vis-a-vis all spouse assault cases. To address this research "shortfall", we obtained permission from the Quincy District Court to examine all the spouse assault cases brought before the court during a 7-month period (June, 1995, through February, 1996). The findings show that in a full enforcement environment, victims took out restraining orders only against the most violent, criminally abusive men. Most men who were arrested for domestic violence had prior criminal histories for a variety of offenses. Domestic violence offenders appeared to be of two types: those with extensive and diverse criminal histories and those with little or no such involvement. However, active criminal justice intervention against domestic violence offenders appears to be primarily directed toward offenders already active in the criminal justice system. 相似文献