全文获取类型
收费全文 | 310155篇 |
免费 | 3566篇 |
国内免费 | 1108篇 |
专业分类
电工技术 | 5701篇 |
综合类 | 320篇 |
化学工业 | 50052篇 |
金属工艺 | 12304篇 |
机械仪表 | 9909篇 |
建筑科学 | 7015篇 |
矿业工程 | 1913篇 |
能源动力 | 6800篇 |
轻工业 | 30206篇 |
水利工程 | 3252篇 |
石油天然气 | 6977篇 |
武器工业 | 74篇 |
无线电 | 31366篇 |
一般工业技术 | 60045篇 |
冶金工业 | 56362篇 |
原子能技术 | 8186篇 |
自动化技术 | 24347篇 |
出版年
2021年 | 2824篇 |
2019年 | 2624篇 |
2018年 | 5118篇 |
2017年 | 5152篇 |
2016年 | 5473篇 |
2015年 | 3185篇 |
2014年 | 5196篇 |
2013年 | 13155篇 |
2012年 | 8289篇 |
2011年 | 10926篇 |
2010年 | 8557篇 |
2009年 | 9471篇 |
2008年 | 9800篇 |
2007年 | 9877篇 |
2006年 | 8741篇 |
2005年 | 9562篇 |
2004年 | 8462篇 |
2003年 | 7917篇 |
2002年 | 7223篇 |
2001年 | 6995篇 |
2000年 | 6817篇 |
1999年 | 6640篇 |
1998年 | 15714篇 |
1997年 | 11140篇 |
1996年 | 8531篇 |
1995年 | 6652篇 |
1994年 | 5873篇 |
1993年 | 5821篇 |
1992年 | 4526篇 |
1991年 | 4316篇 |
1990年 | 4509篇 |
1989年 | 4374篇 |
1988年 | 4118篇 |
1987年 | 3652篇 |
1986年 | 3698篇 |
1985年 | 4202篇 |
1984年 | 3882篇 |
1983年 | 3557篇 |
1982年 | 3334篇 |
1981年 | 3423篇 |
1980年 | 3292篇 |
1979年 | 3183篇 |
1978年 | 3216篇 |
1977年 | 3631篇 |
1976年 | 4638篇 |
1975年 | 2883篇 |
1974年 | 2739篇 |
1973年 | 2856篇 |
1972年 | 2407篇 |
1971年 | 2248篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
METHODS FOR BRAZING CERAMIC AND METAL-CERAMIC JOINTS 总被引:5,自引:0,他引:5
Owing to improved manufacturing processes technical ceramics on the basis of oxide as well as nonoxide ceramics have gained an increasing technical potential. Among other joining techniques brazing has proved to be the most flexible joining process that can easily be adapted to various ceramic-metal-combinations. In order to induce a wetting reaction there are two different approaches. The more complicated process encircles a pre-metallization process and a subsequent brazing process. The less sophisticated process is the 'active brazing process' where special brazing alloys are employed that are able to wet ceramic base materials. Although both joining processes are very flexible there are restrictions regarding the filler metals to be used, the premetallization process and the actual (active-) brazing process. 相似文献
992.
Girgis A.A. Makram E.B. Cline M.L. Jr. Fortson H.S. Jr. 《Power Systems, IEEE Transactions on》1992,7(4):1584-1590
The authors present a successful model of industry/university cooperation in establishing a strong power system curriculum in both the graduate and undergraduate level. Numerous long-term and short-term research projects have been developed to satisfy the university mission and to tackle challenging problems facing the power industry. A unique structure for the Clemson University Electric Power Research Association (CUEPRA) has been established to promote electric power system research and to meet the need for a working communication link between the power industry and the academic community. The power industries involvements in the power program at Clemson University and the strategic improvements that have been accomplished in research and education are outlined 相似文献
993.
Neuramide (NMD), a substance found in crude preparations of porcine stomach extract, is a viral inhibitor that also has putative immunostimulatory effects. The effects of NMD on stress-hormone (ACTH and prolactin-PRL) release were assessed in in vivo and in vitro studies. In the former, blood levels of corticosterone and PRL were measured in NMD-treated male rats. In vitro experiments were performed to evaluate the effects of NMD and three of its fractions (obtained with high performance liquid chromatography) on ACTH and PRL release from perfused rat pituitary slices. NMD increased plasma corticosterone levels in vivo and produced dose-dependent increases in in vitro pituitary release of ACTH. No effects on PRL secretion were observed in vivo or in vitro. The stimulatory effects on ACTH release were caused by the NMD fraction with a molecular weight of > 5000 < 10000 Da. 相似文献
994.
Replies to comments by H. W. Marsh and L. A. Roche (see record 1997-43129-003) on the author's article (Educational Policy Analysis Archives, 1997) on student evaluation and academic freedom. The author expresses his dismay that Marsh and Roche misrepresented (not misinterpreted) the article without documenting their misrepresentation. A documented response to this undocumented misrepresentation is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
J Langhorne C Cross E Seixas C Li T von der Weid 《Canadian Metallurgical Quarterly》1998,95(4):1730-1734
B cell knockout mice are unable to clear a primary erythrocytic infection of Plasmodium chabaudi chabaudi. However, the early acute infection is controlled to some extent, giving rise to a chronic relapsing parasitemia that can be reduced either by drug treatment or by adoptive transfer of B cells. Similar to mice rendered B-cell deficient by lifelong treatment with anti-mu antibodies, B cell knockout mice (muMT) retain a predominant CD4+ Th1-like response to malarial antigens throughout a primary infection. This contrasts with the response seen in control C57BL/6 mice in which the CD4+ T-cell response has switched to that characteristic of Th2 cells at the later stages of infection, manifesting efficient help for specific antibodies in vitro and interleukin 4 production. Both chloroquine and adoptive transfer of immune B cells reduced parasite load. However, the adoptive transfer of B cells resulted in a Th2 response in recipient muMT mice, as indicated by a relative increase in the precursor frequency of helper cells for antibody production. These data support the idea that B cells play a role in the regulation of CD4+ T subset responses. 相似文献
996.
997.
998.
999.
BA Cunningham PJ Quinn DH Wolfe W Tamura-Lis LJ Lis O Kucuk MP Westerman 《Canadian Metallurgical Quarterly》1995,1233(1):68-74
A questionnaire survey was carried out to examine the attitudes and practices of Australian and New Zealand intensivists with regard to brain death and organ donation. A return rate of 82.5% was achieved. Fifty-eight per cent had written evidence of their own wishes to donate organs and 94% would agree to donation from a dependent. At least one intensivist is involved in certifying brain death on 95% of occasions. Intensivists are involved in the request for organ donation over 90% of the time although one-third do not believe that it is their role to request organ donation. Although two-thirds believe that the family should always be approached for organ donation, another 52 out of 254 indicated that it was their (the intensivist's) role to decide if families should be asked for organ donation. Possible reasons for not requesting are language or other communication problems, perceptions of cultural differences and degrees of family distress. Twenty per cent of respondents do not provide haemodynamic support before brain death confirmation. Australian and New Zealand intensivists overwhelmingly support the concept of brain death, current methods of confirmation of brain death, organ donation and transplantation. Possible reasons behind loss of potential donors include decisions not to resuscitate both before and after brain death is confirmed. Perceptions of family grief and cultural differences clearly inhibit requests for organ donation. A very few units have an effective policy on approaching families about organ donation. Intensivists have almost exclusive control over requests for organ donation and thus bear a full professional responsibility for this element of hospital practice. 相似文献
1000.
J Kongerud KI Myhre OA Hauge H Kjuus E Melbostad TB Aasen 《Canadian Metallurgical Quarterly》1996,116(6):759-763
The Norwegian Societies of Thoracic Medicine and Occupational Medicine established a working group to standardise diagnostic procedures and evaluation of work-related respiratory disorders. In cases of suspected work-related diseases the physician may be asked by the National Insurance Administration or an insurance company to make a statement which will be one of the documents used to decide the patient's right to compensation benefit. We discuss the role of the physician as an independent expert. This is different from his role as clinician. The statement should include a balanced presentation of information from different sources, including health and occupational history, and the employer's information about the work environment (quantitative and qualitative exposure data). The statement must also include the results of a clinical examination and an assessment of functional status based on objective tests. The paper contains recommendations for evaluation of permanent impairment in light of the present Norwegian laws and regulations. 相似文献