全文获取类型
收费全文 | 327709篇 |
免费 | 18734篇 |
国内免费 | 10151篇 |
专业分类
电工技术 | 14292篇 |
技术理论 | 24篇 |
综合类 | 14280篇 |
化学工业 | 49067篇 |
金属工艺 | 17935篇 |
机械仪表 | 17547篇 |
建筑科学 | 19535篇 |
矿业工程 | 7651篇 |
能源动力 | 9252篇 |
轻工业 | 19498篇 |
水利工程 | 4255篇 |
石油天然气 | 17213篇 |
武器工业 | 1662篇 |
无线电 | 40386篇 |
一般工业技术 | 47688篇 |
冶金工业 | 37570篇 |
原子能技术 | 3580篇 |
自动化技术 | 35159篇 |
出版年
2024年 | 1047篇 |
2023年 | 4010篇 |
2022年 | 6924篇 |
2021年 | 9780篇 |
2020年 | 7577篇 |
2019年 | 6643篇 |
2018年 | 7762篇 |
2017年 | 8557篇 |
2016年 | 7819篇 |
2015年 | 9698篇 |
2014年 | 12616篇 |
2013年 | 17643篇 |
2012年 | 16616篇 |
2011年 | 19028篇 |
2010年 | 16303篇 |
2009年 | 16122篇 |
2008年 | 16021篇 |
2007年 | 15667篇 |
2006年 | 15798篇 |
2005年 | 13888篇 |
2004年 | 10264篇 |
2003年 | 9101篇 |
2002年 | 8031篇 |
2001年 | 7717篇 |
2000年 | 8020篇 |
1999年 | 9402篇 |
1998年 | 14678篇 |
1997年 | 10461篇 |
1996年 | 8806篇 |
1995年 | 6596篇 |
1994年 | 5539篇 |
1993年 | 4639篇 |
1992年 | 3123篇 |
1991年 | 2785篇 |
1990年 | 2435篇 |
1989年 | 2041篇 |
1988年 | 1692篇 |
1987年 | 1192篇 |
1986年 | 1162篇 |
1985年 | 1105篇 |
1984年 | 937篇 |
1983年 | 804篇 |
1982年 | 819篇 |
1981年 | 775篇 |
1980年 | 637篇 |
1979年 | 512篇 |
1978年 | 441篇 |
1977年 | 554篇 |
1976年 | 990篇 |
1975年 | 308篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
61.
Although cortico steroids are effective anti-inflammatory agents in ameliorating asthma symptoms and bronchial hperreactivity, their mechanism of action is unknown. Interleukin (IL)-5 is known to play a key role in regulating eosinophil proliferation and activation. Therefore, we examined the changes of IL-5 mRNA expressions in PBMC semi-quantitatively with RT-PCR as well as serum ECP levels and MCH-PC20 values in asthmatics before and after being treated with corticosteroids. The results revealed that there were significant decrease in the level of IL-5 mRNA and serum ECP concentration after therapy (P < 0.05) and there was remarkable improvement in the values of MCH-PC20 and FEV1% (P < 0.05). It was also found that the changes of serum ECP levels or MCH-PC20 values were accompanied by a reduction in IL-5 mRNA expression (r = 0.5426 or 0.4857, P < 0.05). These results suggested that the therapeutic effects of corticosteroids in asthma may result from modulation of IL-5 gene expression with consequent inhibition of eosinophil activation. 相似文献
62.
C Llanes P Gabant M Couturier Y Michel-Briand 《Canadian Metallurgical Quarterly》1994,176(11):3403-3407
The Inc A/C plasmids, like Inc P and Inc Q plasmids, have a broad host range. However, their maintenance functions remain to be studied. An autoreplicative region of 2.79 kb named RepA/C, able to replicate both in the family Enterobacteriaceae and in Pseudomonas spp., was isolated and sequenced. The stability, copy number, and incompatibility expression of this replicon were determined. RepA/C and a nonautoreplicative fragment of 16 kb of this replicon were used as probes and showed specific hybridizations with the Inc P3-A/C plasmids from Pseudomonas spp. and members of the Enterobacteriaceae. These probes could be used as tools for identification of the plasmids of this epidemiologically important Inc group. 相似文献
63.
A distributed problem solving system can be characterized as a group of individual cooperating agents running to solve common problems. As dynamic application domains continue to grow in scale and complexity, it becomes more difficult to control the purposeful behavior of agents, especially when unexpected events may occur. This article presents an information and knowledge exchange framework to support distributed problem solving. From the application viewpoint the article concentrates on the stock trading domain; however, many presented solutions can be extended to other dynamic domains. It addresses two important issues: how individual agents should be interconnected so that their resources are efficiently used and their goals accomplished effectively; and how information and knowledge transfer should take place among the agents to allow them to respond successfully to user requests and unexpected external situations. The article introduces an architecture, the MASST system architecture, which supports dynamic information and knowledge exchange among the cooperating agents. The architecture uses a dynamic blackboard as an interagent communication paradigm to facilitate factual data, business rule, and command exchange between cooperating MASST agents. The critical components of the MASST architecture have been implemented and tested in the stock trading domain, and have proven to be a viable solution for distributed problem solving based on cooperating agents 相似文献
64.
This paper analyzes probability of bit-error (Pe) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of Pe analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low Pe (< 10-3) or a prohibitively large computational complexity. The paper presents an alternate method of Pe analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P e performance, user capacity and the accuracy of the proposed method 相似文献
65.
Computing must become much more human centered--for example, by presenting personalized information to users and by respecting personal preferences when controlling multiple devices or invoking various services. Appropriate representation of the information's semantics and of the functionality of devices and services will be critical to such personalized computing. Symbolic artificial intelligence techniques provide the method of choice for the required semantic-representation and reasoning capabilities. 相似文献
66.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
67.
68.
69.
70.
Ignatius Y. Chan 《Microscopy research and technique》1987,5(2):181-188
A new transmission electron microscopy (TEM) specimen preparation procedure for high temperature experiments using a controlled atmosphere specimen holder (HTCASH) has been developed. It is designed for studying the microstructure of catalyst specimens before and after treatments in various gases. The procedure involved (1) finding a new formula for the embedding material, (2) devising a new method of making specimen supports, and (3) developing a method for removing the embedding material after the specimen has been microtomed. These techniques were then brought together to produce the ideal specimens for the HTCASH experiments. As an extra benefit, this procedure is also suitable for preparing specimens for ultrahigh resolution imaging experiments. The application of the new procedure in HTCASH experiments is illustrated through a high temperature reduction of a Co/SiO2-923 catalyst. 相似文献