全文获取类型
收费全文 | 1986篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 113篇 |
金属工艺 | 9篇 |
机械仪表 | 19篇 |
建筑科学 | 63篇 |
能源动力 | 32篇 |
轻工业 | 120篇 |
水利工程 | 5篇 |
石油天然气 | 13篇 |
无线电 | 114篇 |
一般工业技术 | 130篇 |
冶金工业 | 1224篇 |
原子能技术 | 9篇 |
自动化技术 | 139篇 |
出版年
2022年 | 10篇 |
2021年 | 9篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 21篇 |
2013年 | 18篇 |
2012年 | 30篇 |
2011年 | 38篇 |
2010年 | 41篇 |
2009年 | 37篇 |
2008年 | 51篇 |
2007年 | 37篇 |
2006年 | 40篇 |
2005年 | 32篇 |
2004年 | 36篇 |
2003年 | 32篇 |
2002年 | 23篇 |
2001年 | 26篇 |
2000年 | 35篇 |
1999年 | 60篇 |
1998年 | 350篇 |
1997年 | 220篇 |
1996年 | 155篇 |
1995年 | 96篇 |
1994年 | 77篇 |
1993年 | 87篇 |
1992年 | 22篇 |
1991年 | 30篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 35篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1977年 | 24篇 |
1976年 | 62篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 4篇 |
排序方式: 共有2016条查询结果,搜索用时 15 毫秒
91.
J Jordan JR Shannon BK Black SY Paranjape J Barwise D Robertson 《Canadian Metallurgical Quarterly》1998,32(4):699-704
We examined the gelatinolytic activity in human oral squamous-cell carcinoma tissues in order to evaluate the capability of intravasation and extravasation of cancer cells. By a microdissection-zymography, we demonstrated separately the gelatinolytic activities in cancer cell nests and stroma adjacent to the cancer cells. The gelatinolytic activities, such as pro-matrix metalloproteinase (MMP)9 and active-MMP2 in most of cancer cell nests were much higher than those of normal gingival epithelium. Moreover, the activities of active-MMP2 in cancer cell nests of metastatic cancers were significantly higher than those of non-metastatic cancers (p<0.05). These results suggest that active-MMP2 in cancer cells can be a predictive marker for metastasis formation in oral squamous-cell carcinoma patients. 相似文献
92.
BK Patnaik 《Canadian Metallurgical Quarterly》1994,40(2-4):200-220
Like in fishes, the reptiles appear to show three types of senescence. The African skink, Mabuya buettneri, shows rapid senescence similar to death at mating observed in Salmon and marsupial mouse. Most of the lizards and snakes undergo gradual senescence comparable to the pattern exhibited by a majority of vertebrates. On the other hand, turtles, tortoises and crocodiles continue to grow throughout life and are thus credited with slow or negligible senescence. Evidences and mechanisms of rapid or negligible senescence in reptiles are still fragmentary and unclear. Findings in a few species of lizards (Calotes versicolor) and snakes (Natrix natrix) showing gradual senescence support the concept of commonalities in ageing phenomena in vertebrates. An age-related increase in the stability of collagen and accumulation of altered enzyme molecules, a decrease in metabolism and response to stress-enhanced anti-oxidative defence mechanisms and the nature of responses to hormones, restricted diet and lower environmental temperature corroborate the concept. On the other hand neither the increase in mortality rate and accumulation of lipofuscin nor the reproductive senility have been shown conclusively in ageing reptile populations. It is likely that there are multiple mechanisms of senescence in reptiles. Further studies on selected species from among the 6,000 living species are necessary to unravel the phenomena. 相似文献
93.
E Au PT Ang F Seow-Choen KC Soo CH Low HC Chng BK Ng 《Canadian Metallurgical Quarterly》1998,27(5):733-737
Carcinoma of the large bowel is the second leading cause of cancer mortality in Singapore. Although the great majority of patients are discovered at a stage where resection with curative intent is possible, almost half of the patients afflicted will die of it. The combination of 5-fluorouracil + levamisole used in patients with curatively resected high risk Dukes B2 and all Dukes' C colon cancers has been shown to reduce cancer recurrence rate and improve overall survival. Since 1990 adjuvant chemotherapy has been recommended for this group of patients. This report describes patients treated in Singapore, their toxicities and their outcome. A total of 341 patients were treated between 1990 and 1996. Treatment compliance was 71.8%. Toxicity was moderate with mainly grade 1-2 nausea and vomiting, diarrhoea, stomatitis, alopecia, and neutropenia. There was 1 treatment-related death. Median recurrence-free interval was 81 months and median survival was not reached at 90 months. This regimen is tolerable. Until further randomised reports comparing 5-fluorouracil + levamisole to other combinations are available, this combination chemotherapy is recommended to patients after surgical resection of the high risk Dukes' B2 and Dukes' C colon cancer to reduce cancer recurrence and improve overall survival. 相似文献
94.
95.
BK Teboul JL Jacob M Barsoum-Homsy I Brunette L Chevrette J Milot J Orquin RC Polomeno MG Quigley 《Canadian Metallurgical Quarterly》1995,102(11):1646-1653
PURPOSE: The purpose of this study is to determine the incidence of secondary hemorrhage after traumatic hyphema in children and to evaluate the efficacy of epsilon aminocaproic acid in reducing this incidence. METHODS: In a prospective, randomized, double-blind study performed between November 1987 and February 1994, 94 children admitted for traumatic hyphema were assigned to receive either aminocaproic acid (n = 48) (100 mg/kg every 4 hours; maximum, 30 g daily) or placebo (n = 46) for 5 days. Patients who had ingested aspirin in the week preceding admission were excluded from the study. RESULTS: Mean age of the patients was 9.4 years. Black patients comprised 4% of the study population. Secondary hemorrhage occurred in only three patients (3.2%), two from the placebo group and one from the aminocaproic acid group, none of whom had any complications. The duration of hospital stay and the clot resorption times were increased significantly in the aminocaproic acid group (P < 0.001). CONCLUSIONS: The authors report a very low incidence of secondary hemorrhage compared with most previous studies. This difference is likely related to the small proportion of black patients in our study and to the exclusion of patients having ingested aspirin, two factors that seem to be associated with higher rates of rebleeding. The efficacy of aminocaproic acid could not be determined due to the low incidence of hemorrhage. The results of this study, however, suggest that the incidence of secondary hemorrhage in white patients without prior ingestion of aspirin is insufficient to justify routine use of aminocaproic acid in managing traumatic hyphema. Rather, an individualized decision based on the risk factors of each patient would seem more appropriate to avoid a slower clot resorption time and possible side effects of this medication. 相似文献
96.
The purpose of the study was to evaluate palpation of the regional lymph nodes in control examinations of patients with malignant disease. A retrospective review of the medical records of 188 cases in which the patients had had an extirpation of the regional lymph nodes was performed. We have compared the preoperative findings through palpation with the histological diagnosis. The patients were grouped according to the region in which the lymph node removal had been done. The specificity of palpation when the histological diagnosis was malignant was (with 95% confidence limits), in the axilla 0.65 (0.54-0.75), in the inguinal region 0.86 (0.75-0.94) on the neck 0.83 (0.52-0.98) and in the suprahyoid region 0.58 (0.28-0.85). In conclusion, palpation of regional lymph nodes is not a sufficient control examination in the estimation of the course of malignant disease. Supplementary examination methods are recommended. 相似文献
97.
Blue nevus may rarely appear in plaque form. It seems to be a benign and asymptomatic lesion, but because of its rarity, no definite prognosis can be given. Only through reporting of additional cases and their follow-up will the prognosis become clear. 相似文献
98.
The primary aim of this study was to evaluate the phenotypic and genetic trends for stillbirth in Danish Holsteins. Trends of calving difficulty and calf size were also evaluated. The second aim was to compare predicted transmitting abilities (PTA) of sires for stillbirth using a linear and a threshold model. Direct and maternal genetic effects were modeled by fitting correlated additive genetic effects of the sire and the maternal grandsire (MGS). For both the calf and the dam, covariates of breed proportions of Holstein-Friesian (HF) and the heterozygosity between HF and the original Danish Black and White (ODBW) were included. Records from 1.8 million first-calving Danish Holstein cows calving from 1985 to 2002 were used. In this period, the overall frequency of stillbirth increased from 0.071 to 0.090. An unfavorable genetic trend of stillbirth was found for both the direct and maternal effect. The background for the genetic trends was an intense use of HF sires as sires of sons, which increased the proportion of HF genes to 94% in the Danish Holstein calves born in 2002. The effect of the imported HF genes was higher direct effects of calf size, calving difficulty, and stillbirth compared with the ODBW genes. The maternal effect of stillbirth was poorer for HF than for ODBW even though HF had a better maternal calving performance than ODBW. The threshold and the linear models showed almost similar predictions of transmitting abilities of sires. 相似文献
99.
A new method for designing holographic optical elements is presented. The method is based on matching the grating-spacing profile of the recording light interference pattern to the desired grating-spacing profile. We show that for designing near-field holograms, in which the optical images involved are close to the hologram aperture, the grating-matching technique is superior to the well-established aberration-balancing method introduced by Latta [Appl. Opt. 10, 609 (1971)]. 相似文献
100.
Multidimensional data modeling for location-based services 总被引:5,自引:0,他引:5
Christian?S.?JensenEmail author Augustas?Kligys Torben?Bach?Pedersen Igor?Timko 《The VLDB Journal The International Journal on Very Large Data Bases》2004,13(1):1-21
With the recent and continuing advances in areas such as wireless communications and positioning technologies, mobile, location-based services are becoming possible.Such services deliver location-dependent content to their users. More specifically, these services may capture the movements and requests of their users in multidimensional databases, i.e., data warehouses, and content delivery may be based on the results of complex queries on these data warehouses. Such queries aggregate detailed data in order to find useful patterns, e.g., in the interaction of a particular user with the services.The application of multidimensional technology in this context poses a range of new challenges. The specific challenge addressed here concerns the provision of an appropriate multidimensional data model. In particular, the paper extends an existing multidimensional data model and algebraic query language to accommodate spatial values that exhibit partial containment relationships instead of the total containment relationships normally assumed in multidimensional data models. Partial containment introduces imprecision in aggregation paths. The paper proposes a method for evaluating the imprecision of such paths. The paper also offers transformations of dimension hierarchies with partial containment relationships to simple hierarchies, to which existing precomputation techniques are applicable.Received: 28 September 2002, Accepted: 5 April 2003, Published online: 12 August 2003Edited by: J. Veijalainen
Correspondence to: I. Timko 相似文献