全文获取类型
收费全文 | 404009篇 |
免费 | 4212篇 |
国内免费 | 995篇 |
专业分类
电工技术 | 7275篇 |
综合类 | 445篇 |
化学工业 | 59997篇 |
金属工艺 | 18412篇 |
机械仪表 | 13052篇 |
建筑科学 | 8771篇 |
矿业工程 | 2792篇 |
能源动力 | 8752篇 |
轻工业 | 30315篇 |
水利工程 | 5008篇 |
石油天然气 | 11375篇 |
武器工业 | 78篇 |
无线电 | 46222篇 |
一般工业技术 | 82717篇 |
冶金工业 | 70924篇 |
原子能技术 | 11120篇 |
自动化技术 | 31961篇 |
出版年
2021年 | 3252篇 |
2019年 | 3238篇 |
2018年 | 5819篇 |
2017年 | 5986篇 |
2016年 | 6357篇 |
2015年 | 3699篇 |
2014年 | 6436篇 |
2013年 | 16646篇 |
2012年 | 10123篇 |
2011年 | 13424篇 |
2010年 | 10693篇 |
2009年 | 11960篇 |
2008年 | 12742篇 |
2007年 | 12723篇 |
2006年 | 11273篇 |
2005年 | 10329篇 |
2004年 | 9912篇 |
2003年 | 9719篇 |
2002年 | 9314篇 |
2001年 | 9375篇 |
2000年 | 9018篇 |
1999年 | 8994篇 |
1998年 | 20475篇 |
1997年 | 14825篇 |
1996年 | 11496篇 |
1995年 | 8994篇 |
1994年 | 8001篇 |
1993年 | 7983篇 |
1992年 | 6505篇 |
1991年 | 6208篇 |
1990年 | 6153篇 |
1989年 | 5822篇 |
1988年 | 5640篇 |
1987年 | 5104篇 |
1986年 | 5039篇 |
1985年 | 5597篇 |
1984年 | 5286篇 |
1983年 | 4921篇 |
1982年 | 4568篇 |
1981年 | 4853篇 |
1980年 | 4556篇 |
1979年 | 4655篇 |
1978年 | 4615篇 |
1977年 | 5077篇 |
1976年 | 6315篇 |
1975年 | 4277篇 |
1974年 | 4294篇 |
1973年 | 4350篇 |
1972年 | 3723篇 |
1971年 | 3372篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
941.
942.
A method to control the resonant or operating frequencies of circular patch antennas has been investigated experimentally and theoretically. It consists of the placement of passive metallic or tuning posts at approximate locations within the input region of the antenna. Comparison of measured and analytical results seems to establish the validity of a theoretical model proposed to determine the input performance of such circular patch antennas. 相似文献
943.
Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting. 相似文献
944.
Growth rates of spherulites were measured in poly(p-phenylene sulphide) crystallized from the melt and the quenched glass over the temperature range 100°C–280°C, possibly the most extensive overall range yet reported for any polymer and, as such, most propitious for study of régime III crystallization. For a medium M.wt. polymer, a régime II → III transition was obtained at 208°C using values of transport parameters common to many polymers (, T∞ ? Tg = 30°C) together with experimentally determined values of T0m(315°C) and Tg(92°C). Under these conditions, the régime III/II slope ratio was found to be 2.07 (i.e. only 3.5% higher than predicted by régime theory), and reasonable estimates of surface free energies and of the work of chain folding were obtained. Other choices of the transport terms, including WLF and zero values, did not allow successful kinetic analyses. Although a régime I → II transition is predicted to occur at the high-temperature end of our growth-rate data, we found no experimental evidence for it. For a low M.wt. polymer, our analysis showed that régime III kinetics is obeyed at low temperatures, while at higher ones there is a continuous departure from that behaviour without, however, full attainment of régime II kinetics. 相似文献
945.
Juan Carlos Benítez Carlos A. Giúdice Vicente J. D. Rascio 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(8):387-394
This paper discusses the bioactivity of antifouling paints based on organotin toxicants, such as tributyltin fluoride (TBTF) and triphenyltin fluoride (TPTF). These compounds were used alone or mixed as the main toxicant in formulations. The use of TPTF or mixtures of TPTF and TBTF, with vinyl binders, led to paints with satisfactory bioactivity during a 24 months immersion period. With the same binders, TBTF alone provided only 12 months of antifouling protection. The correlation coefficients calculated from the fouling attachment values and the rosin content in the binder showed that the bioactivity of the tested formulations depended on the solubility of the toxicant in sea water and on the composition and solubility of the binders. 相似文献
946.
A. I. Ivaneshkin 《Cybernetics and Systems Analysis》1991,27(6):833-840
The paper considers integrated optimization of a single-server semi-Markov queue with input conflicts, controllable message size, and a finite buffer with different types of storage organization. The optimization is based on an additive performance criterion.Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 45–53, November–December, 1991. 相似文献
947.
The application of reflex optoelectronic switching matrices (ROSM) to signal processing in the gigahertz region is analyzed. Various signal processing functions such as delay generation, loop filtering, word generation/detection, integration, and digital to analog conversion are identified and their respective realizations in a ROSM are presented. It is found that for dedicated signal processing functions, simpler submatrices instead of full matrices can be employed with significant reduction in complexity and cost. The performance of ROSM's using currently commercially available components confirms the feasibility of gigahertz signal processing with ROSM's. 相似文献
948.
We have used x-ray phase analysis to study the composition of the products of reaction between oxygen and nanocrystalline
powders with particle sizes 15, 40, 55, and 80 nm, and also specimens pressed (and sintered) from them. The powders were oxidized
in air at 100°C (400 h) to 500°C (5 min), while the sintered specimens were oxidized at 600–900°C for 15, 120, and 240 min.
In all cases, in the initial oxidation step the oxynitride Ti(OxNy) is formed, which over time is oxidized to TiO, Ti2O3, Ti3O5, TiO2 (anatase) and TiO2 (rutile). In the range 600–800°C, formation of a continuous oxide layer and conversion of anatase to rutile slows down diffusion
of oxygen in the scale. We have established that at 900°C, the growth rate of the scale thickness increases and so the reflections
from the oxynitride are barely noticeable on the diffraction patterns taken from the surface of the oxidized specimen. In
these diffraction patterns, along with strong reflections from the rutile, we also observed weak reflections from lower oxides
and anatase, which may be due to reaction between oxygen and the titanium ions diffused to the scale surface. We have concluded
that at T > 850°C, the mechanism for oxidation of TiN changes. This is due to superposition of counterdiffusion of titanium
ions on the diffusion of oxygen.
__________
Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 72–78, March–April, 2006. 相似文献
949.
Entrained double oxide films have been held responsible for reductions in mechanical properties in aluminum casting alloys.
However, their behavior in the liquid metal, once formed, has not been studied directly. It has been proposed that the atmosphere
entrapped in the double oxide film defect will continue to react with the liquid metal surrounding it, perhaps leading to
its elimination as a significant defect. A silicon-nitride rod with a hole in one end was plunged into liquid aluminum to
hold a known volume of air in contact with the liquid metal at a constant temperature. The change in the air volume with time
was recorded by real-time X-ray radiography to determine the reaction rates of the trapped atmosphere with the liquid aluminum,
creating a model for the behavior of an entrained double oxide film defect. The results from this experiment showed that first
oxygen, and then nitrogen, was consumed by the aluminum alloy, to form aluminum oxide and aluminum nitride, respectively.
The effect of adding different elements to the liquid aluminum and the effect of different hydrogen contents were also studied.
This article is based on a presentation made in the John Campbell Symposium on Shape Casting, held during the TMS Annual Meeting,
February 13–17, 2005, in San Francisco, CA. 相似文献
950.
A Platform-Based Taxonomy for ESL Design 总被引:3,自引:0,他引:3
This article presents a taxonomy for ESL tools and methodologies that combines UC Berkeley's platform-based design terminologies with Dan Gajski's Y-chart work. This is timely and necessary because in the ESL world we seem to be building tools without first establishing an appropriate design flow or methodology, thereby creating a lot of confusion. This taxonomy can help stem the tide of confusion. 相似文献