全文获取类型
收费全文 | 36995篇 |
免费 | 4620篇 |
国内免费 | 2286篇 |
专业分类
电工技术 | 2764篇 |
技术理论 | 10篇 |
综合类 | 5384篇 |
化学工业 | 2860篇 |
金属工艺 | 925篇 |
机械仪表 | 2476篇 |
建筑科学 | 3540篇 |
矿业工程 | 1343篇 |
能源动力 | 1313篇 |
轻工业 | 530篇 |
水利工程 | 1052篇 |
石油天然气 | 902篇 |
武器工业 | 621篇 |
无线电 | 3544篇 |
一般工业技术 | 4587篇 |
冶金工业 | 2216篇 |
原子能技术 | 378篇 |
自动化技术 | 9456篇 |
出版年
2024年 | 579篇 |
2023年 | 741篇 |
2022年 | 841篇 |
2021年 | 1027篇 |
2020年 | 1206篇 |
2019年 | 1137篇 |
2018年 | 1157篇 |
2017年 | 1309篇 |
2016年 | 1404篇 |
2015年 | 1406篇 |
2014年 | 2101篇 |
2013年 | 2583篇 |
2012年 | 2322篇 |
2011年 | 2640篇 |
2010年 | 2088篇 |
2009年 | 2203篇 |
2008年 | 2261篇 |
2007年 | 2366篇 |
2006年 | 2217篇 |
2005年 | 1908篇 |
2004年 | 1553篇 |
2003年 | 1293篇 |
2002年 | 1125篇 |
2001年 | 896篇 |
2000年 | 778篇 |
1999年 | 685篇 |
1998年 | 537篇 |
1997年 | 476篇 |
1996年 | 406篇 |
1995年 | 386篇 |
1994年 | 315篇 |
1993年 | 272篇 |
1992年 | 254篇 |
1991年 | 181篇 |
1990年 | 149篇 |
1989年 | 169篇 |
1988年 | 129篇 |
1987年 | 66篇 |
1986年 | 91篇 |
1985年 | 68篇 |
1984年 | 66篇 |
1983年 | 47篇 |
1982年 | 53篇 |
1981年 | 41篇 |
1980年 | 31篇 |
1979年 | 31篇 |
1978年 | 29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 0 毫秒
1.
This article deals with the kinetics of two-step anionic polymerization by way of a non-steady state method. Several molecular parameters can be evaluated using the formulae developed. A bimodal molecular weight distribution function for the resulting polymer is derived from the set of kinetic differential equations, which is in agreement with the experimental data reported. 相似文献
2.
Inaki Arrazola Agn s Plainfoss Henri Prade Claudette Testemale 《Information Systems》1989,14(6):487-492
This paper presents different approaches which enable a data base management system to obtain a plausible fuzzy estimate for an attribute value of an item for which the information is not explicitly stored in the data base. This can be made either by a kind of analogical reasoning from information about particular items or by means of expert rules which specify the (fuzzy) sets of possible values of the attribute under consideration, for various classes of items. Another kind of expert rules enables the system to compute an estimate from the attribute value of another item provided that, in other respects, this latter item sufficiently resembles the item, the value of which we are interested in; then these expert rules are used either for controlling the analogical reasoning process or for enlarging the scope of application of the first kind of expert rules. The different approaches are discussed in the framework of possibility theory. 相似文献
3.
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
4.
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
5.
This paper reports the findings of a detailed study of Web-based systems design (WBSD) practices in Ireland based on data
collected over a 3-year period (2002–2005), the objectives of which were to (1) contribute towards a richer understanding
of the current “real-world” context of WBSD by characterising the profile of a typical project (team size, timeframe, nature
of requirements, etc.) and identifying the key challenges, constraints, and imperatives (i.e. “mediating factors”) faced by
Web-based system designers, and (2) understand how those contextual parameters and mediating factors influence the activity
of WBSD as regards the selection and enactment of whatever design practices are therefore engaged (i.e. the use of methods,
procedures, etc.). Data was gathered through a survey which yielded 165 usable responses, and later through a series of semi-structured
qualitative interviews. Using grounded theory, an explanatory conceptual framework is derived, based on an extension of the
“method-in-action” model, the application of which to WBSD has not been previously investigated in depth. It is proposed that
this framework of WBSD issues is valuable in a number of ways to educators, researchers, practitioners, and method engineers. 相似文献
6.
郝建民 《导弹与航天运载技术》1997,(2)
推导证明了作为通信理论基石之一的采样定理及其公式存在着两个矛盾:内在不自洽性,即采样定理与其公式的推导前提条件相矛盾;采样定理在工程实际应用时的严重局限性 相似文献
7.
8.
9.
To confirm the reliability of the theory of phase equibria of multicomponent polymer 1/multicomponent polymer 2 systems (i.e. quasi-binary systems) and the method of computer experiment based on this theory (Brit. Polym. J., 23 (1990)285; 23 (1990)299; Polym. Int., 29 (1992)219), could point curves (CPC), two-phase volume ratios ( R ) and critical solution points (CSP) have been determined experimentally for the quasi-binary mixtures of poly(ethylene oxide) (M¯w = 647, M¯w/M¯n = 1.15; M¯w and M¯n, the weight-average and numberaverage molecular weights, respectively) and poly(propylene oxide) (M¯w = 2028, M¯w/M¯n = 1.08; and Mw = 2987, Mw/Mn = 1.13). The hydroxyl end groups of both polymers were methoxylated in advance by the Cooper & Booth method (Polymer, 18 (1977)164). The thermodynamic interaction parameter between both polymers, χ12, and the concentration dependence parameters for the above quasi-binary systems were determined by the method proposed in a previous paper (Brit. Polym. J., 23 (1990)299). CPC, R and CSP values calculated on the basis of the theory are in good agreement with the values determined experimentally. 相似文献
10.
Reviews the book, The concept of structure in psychoanalysis by Theodore Shapiro (see record 1991-97355-000). The present volume is a hardcover edition of a previous supplement to the Journal of the American Psychoanalytic Association based on a series of panels presented at meetings of the American on the role of the concept of structure in current psychoanalytic theory and practice. The result can be taken as a more or less authoritative expression of current thinking about structure in orthodox analytic circles. As such, the volume is informative and in many regards thought provoking. But if readers are looking for a coherent, consistent, and consensually endorsed presentation of the idea of structure, or for a uniform conceptualization of the nature of psychic structure and its role in psychoanalytic praxis, they will have to look elsewhere. The volume is more remarkable for its diversity and often contradictory views on the nature of structure and the relevance of structure to clinical work in the analytic setting. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献