全文获取类型
收费全文 | 200708篇 |
免费 | 2192篇 |
国内免费 | 635篇 |
专业分类
电工技术 | 4108篇 |
综合类 | 125篇 |
化学工业 | 27253篇 |
金属工艺 | 7570篇 |
机械仪表 | 5499篇 |
建筑科学 | 4144篇 |
矿业工程 | 765篇 |
能源动力 | 4728篇 |
轻工业 | 14636篇 |
水利工程 | 1716篇 |
石油天然气 | 2844篇 |
武器工业 | 7篇 |
无线电 | 27620篇 |
一般工业技术 | 37826篇 |
冶金工业 | 46119篇 |
原子能技术 | 3611篇 |
自动化技术 | 14964篇 |
出版年
2021年 | 1282篇 |
2019年 | 1317篇 |
2018年 | 2160篇 |
2017年 | 2141篇 |
2016年 | 2219篇 |
2015年 | 1546篇 |
2014年 | 2667篇 |
2013年 | 8053篇 |
2012年 | 4544篇 |
2011年 | 6225篇 |
2010年 | 5006篇 |
2009年 | 5872篇 |
2008年 | 6255篇 |
2007年 | 6267篇 |
2006年 | 5712篇 |
2005年 | 5361篇 |
2004年 | 5303篇 |
2003年 | 5152篇 |
2002年 | 4967篇 |
2001年 | 5367篇 |
2000年 | 4966篇 |
1999年 | 5493篇 |
1998年 | 15845篇 |
1997年 | 10468篇 |
1996年 | 8031篇 |
1995年 | 5864篇 |
1994年 | 5093篇 |
1993年 | 5099篇 |
1992年 | 3434篇 |
1991年 | 3328篇 |
1990年 | 3259篇 |
1989年 | 3083篇 |
1988年 | 2826篇 |
1987年 | 2268篇 |
1986年 | 2327篇 |
1985年 | 2650篇 |
1984年 | 2351篇 |
1983年 | 2093篇 |
1982年 | 1921篇 |
1981年 | 2065篇 |
1980年 | 1811篇 |
1979年 | 1678篇 |
1978年 | 1669篇 |
1977年 | 2047篇 |
1976年 | 2754篇 |
1975年 | 1441篇 |
1974年 | 1382篇 |
1973年 | 1331篇 |
1972年 | 1141篇 |
1971年 | 973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Weijia Shang O'Keefe M.T. Fortes J.A.B. 《Parallel and Distributed Systems, IEEE Transactions on》1994,5(2):193-204
This paper describes several loop transformation techniques for extracting parallelism from nested loop structures. Nested loops can then be scheduled to run in parallel so that execution time is minimized. One technique is called selective cycle shrinking, and the other is called true dependence cycle shrinking. It is shown how selective shrinking is related to linear scheduling of nested loops and how true dependence shrinking is related to conflict-free mappings of higher dimensional algorithms into lower dimensional processor arrays. Methods are proposed in this paper to find the selective and true dependence shrinkings with minimum total execution time by applying the techniques of finding optimal linear schedules and optimal and conflict-free mappings proposed by W. Shang and A.B. Fortes 相似文献
42.
Neural network control of communications systems 总被引:1,自引:0,他引:1
Neural networks appear well suited to applications in the control of communications systems for two reasons: adaptivity and high speed. This paper describes application of neural networks to two problems, admission control and switch control, which exploit the adaptivity and speed property, respectively. The admission control problem is the selective admission of a set of calls from a number of inhomogeneous call classes, which may have widely differing characteristics as to their rate and variability of traffic, onto a network. It is usually unknown in advance which combinations of calls can be simultaneously accepted so as to ensure satisfactory performance. The approach adopted is that key network performance parameters are observed while carrying various combinations of calls, and their relationship is learned by a neural network structure. The network model chosen has the ability to interpolate or extrapolate from the past results and the ability to adapt to new and changing conditions. The switch control problem is the service policy used by a switch controller in transmitting packets. In a crossbar switch with input queueing, significant loss of throughput can occur when head-of-line service order is employed. A solution can be based on an algorithm which maximizes throughput. However since this solution is typically required in less than one microsecond, software implementation policy is infeasible. We will carry out an analysis of the benefits of such a policy, describe some existing proposed schemes for its implementation, and propose a further scheme that provides this submicrosecond optimization. 相似文献
43.
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
44.
Variations in lipid profile and incidence of vascular events were evaluated. Group 1 had a 29.3% reduction of total and a 38.3% reduction of LDL cholesterol as against reductions of 9% and 9.6% respectively in group 2. No significant difference was observed between the two groups as far as the vascular events considered were concerned. Pravastatin is an effective and safe drug. The lack of influence on the evolution of vascular disease would appear to be correlated to the small number of subjects studied and the short follow-up. 相似文献
45.
Studies static-state feedback control of discrete-event systems under partial observation. The authors present a necessary and sufficient condition for the existence of a static-state feedback controller. A static controller is a special case of a dynamic controller studied by Kumar et al. The authors' condition, however, has computational advantage in contrast to those obtained by Kumar et al. The authors also present a necessary and sufficient condition under which the modular feedback synthesis is possible 相似文献
46.
47.
J Botling F Oberg H T?rm? P Tuohimaa M Bl?uer K Nilsson 《Canadian Metallurgical Quarterly》1996,7(9):1239-1249
48.
Closed-loop expressions for the minimum energy control of a single-input linear digital system are described. They are obtained by two different methods. The optimal inputs are given by state feedback with the bounded variable gains. The gains are independent of the initial state of the system 相似文献
49.
50.
T Takikawa H Hayashi N Nishimura M Yano T Isomura N Sakamoto 《Canadian Metallurgical Quarterly》1994,29(5):593-597
Chronic hepatitis C has been demonstrated to be associated with hepatic iron overload, and the hypothesis that the disease activity of hepatitis C is associated with iron cytotoxicity was tested in male volunteer blood donors. Sera with either antibody to hepatitis C virus or hepatitis B surface antigen were selected for determination of ferritin concentration and alanine aminotransferase activity. A correlation between serum ferritin concentration (Y; microgram/l) and alanine aminotransferase activity (X; IU/l) was found in donors with antibody to hepatitis C (log Y = 0.65 x log X + 0.98, r = 0.53, and P < 0.01). The correlation was lower in donors with hepatitis B surface antigen (r = 0.37; P < 0.01). Hepatitis C virus infection probably induces time-dependent iron accumulation associated with the progression of disease activity, while hepatitis B virus infection results in a variety of iron loads with different clinical features. The high disease activity related to hyperferritinemia suggests the presence of iron-induced liver damage in donors with hepatitis C. 相似文献