全文获取类型
收费全文 | 36767篇 |
免费 | 3778篇 |
国内免费 | 2548篇 |
专业分类
电工技术 | 2584篇 |
技术理论 | 8篇 |
综合类 | 5226篇 |
化学工业 | 3051篇 |
金属工艺 | 1001篇 |
机械仪表 | 2330篇 |
建筑科学 | 3440篇 |
矿业工程 | 1284篇 |
能源动力 | 1294篇 |
轻工业 | 520篇 |
水利工程 | 1027篇 |
石油天然气 | 887篇 |
武器工业 | 598篇 |
无线电 | 3351篇 |
一般工业技术 | 4716篇 |
冶金工业 | 2263篇 |
原子能技术 | 334篇 |
自动化技术 | 9179篇 |
出版年
2024年 | 148篇 |
2023年 | 622篇 |
2022年 | 765篇 |
2021年 | 992篇 |
2020年 | 1156篇 |
2019年 | 1054篇 |
2018年 | 1111篇 |
2017年 | 1249篇 |
2016年 | 1333篇 |
2015年 | 1372篇 |
2014年 | 2087篇 |
2013年 | 2568篇 |
2012年 | 2292篇 |
2011年 | 2664篇 |
2010年 | 2096篇 |
2009年 | 2202篇 |
2008年 | 2281篇 |
2007年 | 2382篇 |
2006年 | 2212篇 |
2005年 | 1927篇 |
2004年 | 1564篇 |
2003年 | 1309篇 |
2002年 | 1136篇 |
2001年 | 907篇 |
2000年 | 802篇 |
1999年 | 689篇 |
1998年 | 553篇 |
1997年 | 494篇 |
1996年 | 412篇 |
1995年 | 390篇 |
1994年 | 321篇 |
1993年 | 276篇 |
1992年 | 259篇 |
1991年 | 191篇 |
1990年 | 156篇 |
1989年 | 173篇 |
1988年 | 131篇 |
1987年 | 66篇 |
1986年 | 92篇 |
1985年 | 74篇 |
1984年 | 69篇 |
1983年 | 54篇 |
1982年 | 57篇 |
1981年 | 42篇 |
1980年 | 34篇 |
1979年 | 31篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1964年 | 26篇 |
1955年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
12.
Analysis on steady-state and transient heat transfer on a flat plate at the middle of a parallel duct immersed in He II was performed for bath temperatures from 1.8 to 2.1 K at 101.3 kPa. Two-dimensional computer code named SUPER-2D developed by the authors based on the two-fluid model and the theory of mutual friction was used. Steady-state critical heat flux (CHF) and the time lag from the application of a step heat input to λ transition, that is called a lifetime, were obtained numerically for various step heat fluxes and for the channel gaps from 2 to 20 mm. Effect of the gap restriction on the CHF and the lifetime were clarified. The solutions were compared with the experimental data for the ducts with the same structures and the corresponding conditions. They agreed well with the experimental data. The heat transport mechanism in the parallel duct was clarified. 相似文献
13.
The theoretical-and-experimental investigation has been performed on the stability of smooth cylindrical shells of steel with a single local dent. All the shells manufactured using the same process were tested with the fulfillment of identical conditions for observations and measurements. Theoretical calculations were carried out by the mesh method with the use of the nonlinear theory of shells. A comparison of the experimental and theoretical values of the critical loads has been made. The theoretical-and-experimental approach proposed enables one to evaluate the quality of shells by studying local dents and other specific imperfections. 相似文献
14.
15.
We introduce a new probabilistic approach to dealing with uncertainty, based on the observation that probability theory does not require that every event be assigned a probability. For a nonmeasurable event (one to which we do not assign a probability), we can talk about only the inner measure and outer measure of the event. In addition to removing the requirement that every event be assigned a probability, our approach circumvents other criticisms of probability-based approaches to uncertainty. For example, the measure of belief in an event turns out to be represented by an interval (defined by the inner and outer measures), rather than by a single number. Further, this approach allows us to assign a belief (inner measure) to an event E without committing to a belief about its negation -E (since the inner measure of an event plus the inner measure of its negation is not necessarily one). Interestingly enough, inner measures induced by probability measures turn out to correspond in a precise sense to Dempster-Shafer belief functions. Hence, in addition to providing promising new conceptual tools for dealing with uncertainty, our approach shows that a key part of the important Dempster-Shafer theory of evidence is firmly rooted in classical probability theory. Cet article présente une nouvelle approche probabiliste en ce qui concerne le traitement de l'incertitude; celle-ci est basée sur l'observation que la théorie des probabilityés n'exige pas qu'une probabilityé soit assignée à chaque événement. Dans le cas d'un événement non mesurable (un événement pour lequel on n'assigne aucune probabilityé), nous ne pouvons discuter que de la mesure intérieure et de la mesure extérieure de l'évenément. En plus d'éliminer la nécessité d'assigner une probabilityéà l'événement, cette nouvelle approche apporte une réponse aux autres critiques des approches à l'incertitude basées sur des probabilityés. Par exemple, la mesure de croyance dans un événement est représentée par un intervalle (défini par la mesure intérieure et extérieure) plutǒt que par un nombre unique. De plus, cette approche nous permet d'assigner une croyance (mesure intérieure) à un événement E sans se compromettre vers une croyance à propos de sa négation -E (puisque la mesure intérieure d'un événement et la mesure intérieure de sa négation ne sont pas nécessairement une seule et unique mesure). II est intéressant de noter que les mesures intérieures qui résultent des mesures de probabilityé correspondent d'une manière précise aux fonctions de croyance de Dempster-Shafer. En plus de constituer un nouvel outil conceptuel prometteur dans le traitement de l'incertitude, cette approche démontre qu'une partie importante de la théorie de l'évidence de Dempster-Shafer est fermement ancrée dans la theorie classique des probabilityés. 相似文献
16.
17.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors. 相似文献
18.
Dmitri E. Nikonov George I. Bourianoff Paolo A. Gargini 《Journal of Superconductivity and Novel Magnetism》2006,19(6):497-513
Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron
in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots are
described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to
a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ∼kT per bit,
if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic
device are provided. 相似文献
19.
20.
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