全文获取类型
收费全文 | 158085篇 |
免费 | 2153篇 |
国内免费 | 670篇 |
专业分类
电工技术 | 3186篇 |
综合类 | 194篇 |
化学工业 | 25513篇 |
金属工艺 | 5882篇 |
机械仪表 | 5082篇 |
建筑科学 | 4730篇 |
矿业工程 | 385篇 |
能源动力 | 4161篇 |
轻工业 | 17809篇 |
水利工程 | 1195篇 |
石油天然气 | 645篇 |
武器工业 | 7篇 |
无线电 | 21038篇 |
一般工业技术 | 29870篇 |
冶金工业 | 24656篇 |
原子能技术 | 2372篇 |
自动化技术 | 14183篇 |
出版年
2019年 | 949篇 |
2018年 | 1249篇 |
2017年 | 1286篇 |
2016年 | 1457篇 |
2015年 | 1215篇 |
2014年 | 2010篇 |
2013年 | 6967篇 |
2012年 | 3543篇 |
2011年 | 5013篇 |
2010年 | 3892篇 |
2009年 | 4501篇 |
2008年 | 4980篇 |
2007年 | 5250篇 |
2006年 | 4593篇 |
2005年 | 4345篇 |
2004年 | 4197篇 |
2003年 | 4067篇 |
2002年 | 4073篇 |
2001年 | 4083篇 |
2000年 | 3846篇 |
1999年 | 3790篇 |
1998年 | 6760篇 |
1997年 | 5334篇 |
1996年 | 4538篇 |
1995年 | 3804篇 |
1994年 | 3444篇 |
1993年 | 3251篇 |
1992年 | 2841篇 |
1991年 | 2719篇 |
1990年 | 2674篇 |
1989年 | 2676篇 |
1988年 | 2502篇 |
1987年 | 2198篇 |
1986年 | 2166篇 |
1985年 | 2604篇 |
1984年 | 2358篇 |
1983年 | 2235篇 |
1982年 | 2102篇 |
1981年 | 2025篇 |
1980年 | 1890篇 |
1979年 | 1898篇 |
1978年 | 1789篇 |
1977年 | 2100篇 |
1976年 | 2589篇 |
1975年 | 1609篇 |
1974年 | 1452篇 |
1973年 | 1461篇 |
1972年 | 1204篇 |
1971年 | 1122篇 |
1970年 | 952篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
In the editorial by J.C. Bezdek (ibid., p.1), an example is presented to demonstrate differences between fuzzy membership and probability. The authors argue that probability can be used in a way much more closely analogous to this use of fuzzy membership, weakening the argument for the latter 相似文献
62.
A generalized fuzzy Petri net model 总被引:14,自引:0,他引:14
The paper proposes a new model of Petri nets based on the use of logic based neurons. In contrast to the existing generalizations, this approach is aimed at neural-type modeling of the entire concept with a full exploitation of the learning capabilities of the processing units being used there. The places and transitions of the net are represented by OR and AND-type and DOMINANCE neurons, respectively. A correspondence between this model and the previous two-valued counterpart is also revealed. The learning aspects associated with the nets are investigated 相似文献
63.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献
64.
Robotica is a computer aided design package for robotic manipulators developed in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. It encapsulates over 30 functions into a Mathematica package allowing efficient symbolic and numeric calculation of kinematic and dynamic equations for multi-degree-of-freedom manipulators. An X-Windows front end that utilizes the interprocess communication features of Mathematica 2.1 has also been created for ease of use. This paper describes the most important features of the package and how they are used 相似文献
65.
Twenty-six patients with an intracardiac myxoma underwent surgical resection at our institution from 1977 through 1992. Left atrial myxoma was diagnosed in 22 patients, left ventricular in 1, right atrial in 2, and right ventricular in 1. Six patients were asymptomatic; preoperative symptoms included dyspnea, arrhythmias, embolic episodes, and syncope. The diagnosis was established with transthoracic echocardiography in all cases but one. Surgery was performed in all cases with the aid of cardiopulmonary bypass with moderate hypothermia and cold crystalloid cardioplegia. One patient with a left ventricular myxoma died in a comatose state during the immediate postoperative period. Long-term clinical and echocardiographic evaluation was performed in 19 patients; results were excellent (all the patients were in New York Heart Association functional class I or II), and no recurrences were documented. The clinical characteristics, diagnostic methods, and surgical approach are presented and discussed. 相似文献
66.
A clear understanding of the concept and consequences of diversity in science and technology is a key issue for Europe, when considering the current debate on cohesion Put forward within the Single European Act. According to Article 130B of the Single Act, all European policies, including technological policies must contribute to the achievement of a greater cohesion throughout the EC. The European market is generally presented as mainly a patchwork of national or even regional characteristics, with compartmentalized niches, and specific regulations. But does cohesion mean decreasing disparities between regions, which in such case signifies a passive policy of reallocation of resources within the EC, at the risk of generating uniformity? Or, does cohesion mean integration of all innovative and creative efforts, which implies a more complex policy of stimulation, under the condition to maintain a certain diversity? Must the governments systematically reduce diversity, or on the contrary must they enlarge diversity? How can they distinguish between negative and positive aspects of diversity? How do they operate a trade off between economies of scale and economies of diversity? To try to answer these political issues and to set up a coherent industrial policy at the EC level, a careful analysis of the sources of diversity, of the mechanisms that generate or reduce diversity, of the ways to valorize diversity are discussed in this paper 相似文献
67.
During the 1980s, the ecologic association of conjugated estrogens with endometrial cancer changed from positive to negative in a prepaid health plan. During the same period, use of progestins increased dramatically. We investigated whether the latter increase could explain the reversal of the estrogen-cancer association. Endometrial cancer incidence was estimated from cases recorded in the health plan registry divided by the number of women over age 45 years. Conjugated estrogens usage was measured as milligrams prescribed per woman per year and progestin was measured as tablets per woman per year, both based upon pharmacy records. Graphical and regression methods were used to analyze the resulting ecologic data. In a log-linear regression of incidence on conjugated estrogens and medroxyprogesterone usage, estrogen usage had a strong positive association with incidence, while medroxyprogesterone had a strong negative association with incidence. The change in the direction of the ecologic association between estrogen and endometrial cancer that occurred in 1984 continued until 1993, suggesting that the decline in endometrial cancer incidence and concomitant increase in conjugated estrogens usage since 1984 is explained by the increasing use of progestins. The data are entirely consistent with the hypothesis that progestins can protect against most of the excess risk conferred by conjugated estrogens, although the ecologic nature of the data prohibits drawing further inferences. 相似文献
68.
Surveyed 70 practicing attorneys and 150 law students to determine the extent to which they felt it was their responsibility to inform clients they referred for psychological testing about the testing process and about the validity scales on tests. Results showed that almost 50% of the attorneys and over 33% of the students believe that clients referred for testing always or usually should be informed of validity scales on tests. These results suggest that many test takers, particularly in forensic settings, may have information about validity scales that facilitates their giving biased responses without detection. Psychologists doing forensic evaluations should be alert to this possibility and should consider using more than one approach to detect response distortions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
69.
70.