全文获取类型
收费全文 | 1487696篇 |
免费 | 24524篇 |
国内免费 | 6974篇 |
学科分类
工业技术 | 1519194篇 |
出版年
2021年 | 15584篇 |
2020年 | 11876篇 |
2019年 | 14636篇 |
2018年 | 15619篇 |
2017年 | 14909篇 |
2016年 | 21328篇 |
2015年 | 17410篇 |
2014年 | 28738篇 |
2013年 | 88057篇 |
2012年 | 34766篇 |
2011年 | 47065篇 |
2010年 | 42363篇 |
2009年 | 50895篇 |
2008年 | 44103篇 |
2007年 | 41246篇 |
2006年 | 44113篇 |
2005年 | 38986篇 |
2004年 | 40985篇 |
2003年 | 40888篇 |
2002年 | 40139篇 |
2001年 | 36648篇 |
2000年 | 35169篇 |
1999年 | 33997篇 |
1998年 | 40482篇 |
1997年 | 36839篇 |
1996年 | 33799篇 |
1995年 | 29894篇 |
1994年 | 28092篇 |
1993年 | 27978篇 |
1992年 | 26032篇 |
1991年 | 23082篇 |
1990年 | 23439篇 |
1989年 | 22581篇 |
1988年 | 21106篇 |
1987年 | 19306篇 |
1986年 | 18668篇 |
1985年 | 22021篇 |
1984年 | 22280篇 |
1983年 | 20250篇 |
1982年 | 19256篇 |
1981年 | 19351篇 |
1980年 | 17956篇 |
1979年 | 18475篇 |
1978年 | 17757篇 |
1977年 | 17476篇 |
1976年 | 18316篇 |
1975年 | 16038篇 |
1974年 | 15494篇 |
1973年 | 15582篇 |
1972年 | 13076篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
E. Smith 《Journal of Materials Science》1993,28(4):880-884
The criterion for crack growth instability in an elastic-softening material that is subjected to displacement control loading conditions is examined. A theoretical analysis of the model of a solid containing two symmetrically situated deep cracks and with tensile loading of the remaining ligament, defines the criterion for crack growth instability. The criterion is expressed in terms of the material's softening characteristics and the solid's geometrical parameters. The analysis covers the complete spectrum of material behaviour from the case where the softening zone is very small to the case where instability does not occur until the softening zone traverses the ligament between the crack tips. 相似文献
972.
Commitment as a moderator of the goal-performance relation: A case for clearer construct definition.
A central assumption in the goal theory literature is that the degree of commitment to the assigned goal moderates the effectiveness of the goal-setting procedure. However, attempts to empirically verify commitment's moderating role have generally met with failure, calling into question either widely used measures of goal commitment, the moderating assumption itself, or both. Three studies are described that address this issue. Results indicate that the moderation assumption is valid but is only relevant to 1 of 3 closely related motivational concepts that are commonly discussed under the heading of commitment: prechoice attitudes, the subsequent choice of a personal goal, and the maintenance of that choice. It is suggested that a view of commitment that more clearly distinguishes these concepts can provide a better guide for future empirical research than can existing viewpoints. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
973.
The conclusions clinicians have drawn about Holocaust survivors over the last 50 yrs differ sharply from researchers' findings. It is important to evaluate these discrepancies since different perceptions of survivors affect treatment approaches. The researchers' view, stressing the survivor's resilience and resourcefulness, contrasts with clinical impressions centering on a survivor syndrome involving deep emotional disturbances as residues of the Holocaust experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
974.
975.
Studied how 26 senior managers and 47 senior professional technical staff (recently repatriated) of 4 US owned multinational organizations viewed their international posting, specifically with respect to career path satisfaction. Results of satisfaction scales indicate that many Ss felt under-prepared for their international assignment. It is suggested that a comprehensive international employee development program should assess, provide feedback, and coach individuals on career path, culture shock and adjustment, and performance issues prior, during, and on return from the expatriate assignment. Results suggest that opportunities exist for individual and organizational intervention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
976.
977.
STRONG METAL-CERAMIC JOINTS 总被引:3,自引:0,他引:3
In this paper the technology for joining metals to ceramics is reviewed. The technologies of metal powder sintering, liquid phase joining with activated brazing alloys and with ceramic frit, solid-state joining, friction welding and mechanical fixation are described. In order to put some perspective on the mechanical data given in the literature, some evaluating remarks on mechanical testing are made. 相似文献
978.
Furst C. Leitenstorfer A. Laubereau A. 《IEEE journal of selected topics in quantum electronics》1996,2(3):473-479
An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model 相似文献
979.
980.
E Campagnutta R Cannizzaro M De Cicco G De Piero G Giorda F Sopracordevole A Parin C Scarabelli 《Canadian Metallurgical Quarterly》1998,50(7-8):305-311
BACKGROUND AND AIMS: Intestinal obstruction is a frequent cause of death in patients suffering from gynecological cancer, who have undergone multiple treatment in the form of surgery and/or chemotherapy and/or radiotherapy. The usual form of rescue treatment consists in the use of a nasogastric tube to administer support and analgesic treatment. Surgical gastrostomy is not a viable proposition in these extremely weak patients with large masses compressing and displacing the stomach. Percutaneous endoscopic gastrostomy (PEG), a technique first introduced for nutritional purposes, can be beneficially used to achieve decompression in these patients. METHODS: PEG was performed in a total of 67 patients who had already undergone multiple treatment for abdominal-pelvic neoplasia with upper gastrointestinal obstruction, who could no longer be operated and who had a life expectancy of less than sixty days. In three cases positioning was not possible owing to the lack of transillumination of the gastric and abdominal wall. 54/64 patients had previously undergone at least two operations. RESULTS: Esophagogastric lesions were found in 29% of patients, some of which were attributed to the nasogastric tube. Symptomatic wellbeing was obtained in 76.5% a few days after PEG. PEG remained in situ from 4 to 472 days. Slight peristomal infection was observed in 9% of cases. In seven cases it was necessary to add octreotide owing to the reappearance of symptoms. CONCLUSIONS: PEG is relatively easy to use and allows obstructive symptoms to be resolved in the majority of patients. Special medical skills are not required and the patient may be easily managed at home together with support therapy and pain management. Once PEG has been performed, it is possible to take fluids and semi-liquid foods, offering the patient a chance to taste flavours which have often been forgotten. PEG enables neoadjuvant chemotherapy to be performed in patients with previously untreated intestinal obstruction. 相似文献