全文获取类型
收费全文 | 2334篇 |
免费 | 109篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 29篇 |
综合类 | 4篇 |
化学工业 | 558篇 |
金属工艺 | 89篇 |
机械仪表 | 54篇 |
建筑科学 | 42篇 |
矿业工程 | 4篇 |
能源动力 | 64篇 |
轻工业 | 77篇 |
水利工程 | 6篇 |
石油天然气 | 5篇 |
无线电 | 304篇 |
一般工业技术 | 598篇 |
冶金工业 | 273篇 |
原子能技术 | 18篇 |
自动化技术 | 331篇 |
出版年
2023年 | 32篇 |
2022年 | 40篇 |
2021年 | 66篇 |
2020年 | 56篇 |
2019年 | 61篇 |
2018年 | 74篇 |
2017年 | 79篇 |
2016年 | 83篇 |
2015年 | 64篇 |
2014年 | 81篇 |
2013年 | 143篇 |
2012年 | 96篇 |
2011年 | 115篇 |
2010年 | 86篇 |
2009年 | 98篇 |
2008年 | 88篇 |
2007年 | 80篇 |
2006年 | 74篇 |
2005年 | 47篇 |
2004年 | 61篇 |
2003年 | 59篇 |
2002年 | 49篇 |
2001年 | 33篇 |
2000年 | 35篇 |
1999年 | 39篇 |
1998年 | 71篇 |
1997年 | 36篇 |
1996年 | 61篇 |
1995年 | 43篇 |
1994年 | 43篇 |
1993年 | 38篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1977年 | 20篇 |
1976年 | 10篇 |
1973年 | 9篇 |
1968年 | 7篇 |
排序方式: 共有2456条查询结果,搜索用时 109 毫秒
11.
OBJECTIVE: The most common indication for electroconvulsive therapy (ECT) is major depression. It is less recognized that ECT is effective also in the treatment of acute mania. This article aims to provide a comprehensive and critical review of the literature on the use of ECT for manic patients. METHOD: All published papers in the English language on the use of ECT in acute mania that could be found were reviewed with regard to efficacy, frequency and number of treatments, bilateral versus unilateral electrode placement, predictors of antimanic response, stability of therapeutic response, cognitive consequences, and other relevant issues. RESULTS: The evidence indicates that ECT is associated with remission or marked clinical improvement in 80% of manic patients and that it is an effective treatment for patients whose manic episodes have responded poorly to pharmacotherapy. Manic patients do not require a high frequency or prolonged course of treatments to respond to ECT. The seizure threshold appears to be lower in manic patients than in depressed patients. The issues of relapse following response to ECT, cognitive consequences of ECT, and the relative merits of unilateral versus bilateral ECT in manic patients require further study. CONCLUSIONS: ECT is an effective and safe treatment for acute mania. Remission of mania following ECT reflects a primary therapeutic effect rather than a secondary consequence of an ECT-induced organic brain syndrome. 相似文献
12.
The computer-aided design software package DMET (Digital Microwave Engineering Tool), which has been developed to meet the needs of the telecommunication engineering community involved in the design of line-of-sight digital microwave communication routes, is described. DMET can be used either by professionals or engineering students in such a way that efforts can be concentrated on the design objectives of the link rather than on cumbersome and tedious computations. This software package is particularly useful as a tool in teaching communication engineering students the basic practical steps involved in the design of line-of-sight radio communication links. Examples of antenna height computation and radio link budget computation using DMET are presented 相似文献
13.
14.
A computer method for the calculation of the phase shift due to optically injected carriers in an InP avalanche transit time diode has been suggested using the numerically simulated negative resistance profiles in the depletion layer of the diode. The results show that the phase shift due to hole injection is larger than that due to electron injection which explains the pronounced effect of photogenerated hole leakage current in modulating the microwave properties of InP diodes 相似文献
15.
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
16.
Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality-of-service (QoS)-based protection in terms of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and the impact of the correlation on the sharing of the backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration. A simple analysis of the proposed algorithm in terms of computation time and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based backup sharing algorithms indicate that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network resource utilization. 相似文献
17.
18.
This paper first presents an unified discussion of real and complex boundary integral equations (BIEs) for two-dimensional potential problems. Relationships between real and complex formulations, for both usual and hypersingular BIEs, are discussed. Potential problems in bounded as well as in unbounded domains are of concern in this work. Quantities of particular interest are derivatives of the primary field that exhibit discontinuities across corners, as well as stress intensity factors at the tips of mode III cracks. The latter problem in an application of a recent generalization of the well-known Plemelj-Sokhotsky formulae. Numerical implementations and results for interior problems in bounded domains, as well as for crack problems in unbounded domains, are presented and discussed.C. Y. Hui is supported by the Material Science Center at Cornell University, which is funded by the National Science Foundation (DMR-MRL program). S Mukherjee acknowledges partial support from NSF grant number ECS-9321508 to Cornell University. 相似文献
19.
20.