全文获取类型
收费全文 | 5763篇 |
免费 | 152篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 100篇 |
综合类 | 20篇 |
化学工业 | 423篇 |
金属工艺 | 64篇 |
机械仪表 | 54篇 |
建筑科学 | 92篇 |
矿业工程 | 6篇 |
能源动力 | 27篇 |
轻工业 | 322篇 |
水利工程 | 19篇 |
石油天然气 | 15篇 |
武器工业 | 3篇 |
无线电 | 137篇 |
一般工业技术 | 420篇 |
冶金工业 | 3938篇 |
原子能技术 | 11篇 |
自动化技术 | 270篇 |
出版年
2023年 | 17篇 |
2022年 | 22篇 |
2021年 | 46篇 |
2020年 | 41篇 |
2019年 | 30篇 |
2018年 | 54篇 |
2017年 | 66篇 |
2016年 | 78篇 |
2015年 | 50篇 |
2014年 | 98篇 |
2013年 | 123篇 |
2012年 | 131篇 |
2011年 | 181篇 |
2010年 | 75篇 |
2009年 | 84篇 |
2008年 | 77篇 |
2007年 | 81篇 |
2006年 | 52篇 |
2005年 | 69篇 |
2004年 | 55篇 |
2003年 | 59篇 |
2002年 | 57篇 |
2001年 | 50篇 |
2000年 | 27篇 |
1999年 | 151篇 |
1998年 | 1311篇 |
1997年 | 761篇 |
1996年 | 465篇 |
1995年 | 244篇 |
1994年 | 221篇 |
1993年 | 258篇 |
1992年 | 26篇 |
1991年 | 48篇 |
1990年 | 39篇 |
1989年 | 53篇 |
1988年 | 53篇 |
1987年 | 43篇 |
1986年 | 33篇 |
1985年 | 50篇 |
1984年 | 24篇 |
1983年 | 20篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1978年 | 18篇 |
1977年 | 94篇 |
1976年 | 164篇 |
1972年 | 9篇 |
1943年 | 8篇 |
1940年 | 8篇 |
排序方式: 共有5921条查询结果,搜索用时 15 毫秒
11.
ME Richardson 《Canadian Metallurgical Quarterly》1998,185(7):324-327
It is probably true to say that the masticatory apparatus attracts proportionally greater attention than any other part of the body. Evidence that this is so is provided, not only by the degree of specialisation within the dental profession, but by the frequency with which references to teeth and dentistry crop up in literature. Generations of biographers, novelists, poets, playwrights and essayists have written about their dental experiences and included the dentition in describing the facial appearance of characters, factual and fictional. The literary extracts in this article, culled from an extensive collection, refer to orthodontics. They provide a fascinating insight into the patient's perspective on that speciality and make entertaining reading. 相似文献
12.
ME Stefanek 《Canadian Metallurgical Quarterly》1995,7(6):527-530
Over the past year, increasing research attention has been devoted to the issue of women at increased risk of developing breast cancer. These articles focus on a range of issues from recruiting high-risk women into breast cancer trials to recommendations for assessment and counseling women with a family history of breast cancer. In addition, continuing research attention has focused on quality of life, symptom management, and articles related to physician-patient communication. This review summarizes and critiques publications in these areas, and it includes articles reviewing the status of research in psychosocial oncology. 相似文献
13.
F. Minami A. Brückner-Foit D. Munz B. Trolldenier 《International Journal of Fracture》1992,54(3):197-210
The local approach was recently proposed by Beremin and Mudry for evaluating the statistical behaviour of toughness results of materials. This approach introduces a stress parameter
w
, termed the Weibull stress, as a measure of the fracture resistance of materials instead of the conventional toughness parameters such as K
c,
c
and J
cl (critical stress intensity factor, CTOD and J-integral, respectively). The Weibull stress
w
obeys the Weibull distribution with the two parameters m and
u
(the shape and the scale parameter, respectively). The first parameter m is normally estimated to be 22 irrespective of the kind of material. In this paper a procedure for the determination of the Weibull parameters m and
u
is developed. This procedure consists of the determination of the plastic zone ahead of the crack tip, from which cleavage fracture originates, and of the maximum likelihood estimation of the parameters m and
u
based on the stress distribution in the plastic zone. Calculations using this procedure confirm that the distribution of the Weibull stress
w
is a material property independent of specimen thickness, and in particular that the shape parameter m depends on the material, e.g. m12 for a German reactor pressure vessel steel (20 Mn Mo Ni 5 5). Using these parameters for the distribution of the Weibull stress the size effect in fracture toughness values is predicted and an improved agreement between theory and experiments is obtained compared to the Weakest Link model. 相似文献
14.
Engineers of the concrete technology are increasingly concerned with the material passing through a sieve of the size under 0.149 mm. Materials called very fine aggregate or mineral filler may affect the performance of concrete in an either positive or a negative way. Discussions on aggregate containing very fine material are vitally important. Washing the aggregate residue has been the sole way to solve this matter to date. This is mainly based on the debatable opinion that materials of this kind are regarded as clay material. The goal of the study was to determine how the content of mineral filler might affect properties of concrete. Two types of aggregates with different amounts of cement and mineral filler were used. Basically, mineral filler replaced sand. The effect of applying different amounts of mineral filler on concrete was then determined. The addition of 7-10% of mineral filler to fine aggregate (0-2 mm) was found to considerably improve the properties of concrete. 相似文献
15.
An exploratory, comparative survey design was used to describe and compare similarities and differences in perception of caring behaviors between hospitalized antepartum and short-stay postpartum patients. Forty-two patients completed the 63-item Caring Behavior Assessment instrument (CBA). The scale, based on Watson's theory of caring, contains seven categories. There were no statistically significant differences in age, education, gravida, or para between the two groups. Significantly more women in the postpartum group were married. There were no statistically significant differences or correlations in the total CBA scores and the demographic variables. No statistically significant differences in total CBA scores were found between antepartum participants and postpartum participants. These findings corroborate the results of "caring" studies in other patient populations, that satisfying basic needs--that is, evidence of technical knowledge and skills--is more important to patients than meeting higher order needs. 相似文献
16.
Pancreatic cancer is a dismal disease. The 5-year overall survival ranges from 1% to 5%. Surgery is the only curative treatment available for this cancer, but it is indicated only in selected patients with a less than 4 cm tumor. In these patients, survival rate is about 30%. We have considered several aspects: the very difficult early diagnosis, the correct diagnostic flow chart, actual surgical procedures and new trends in biologic and genetic research. It is likely that better results can be achieved by defining an "early pancreatic cancer" and establishing how to detect it. This could be the wrigth one way is to significantly improve the survival of these patients. 相似文献
17.
BACKGROUND: Clinical manifestations and course of sickle-cell anemia are variable. Knowledge about the factors, possibly geographic, that influence prognosis are still scanty. POPULATION AND METHODS: Data of hospitalization and management of children with sickle-cell disease were studied during two years (1992-1993) in the Pediatric Unit of Libreville Hospital. They concerned 205 admissions of 171 children and 131 outpatients. RESULTS: The main causes of hospitalization were: acute anemia (36 cases before the age of 5 years); painful crisis whose frequency increased with age (23% before 5 years, 35% between 5 and 10, 42% after 10 years); infections, essentially pulmonary occurring early, and bone infections at any age. Eight children died (because a complication of their disease). Among the 131 outpatients, half were detected because pyrexia, anemia and/or more often "hand-foot syndrome". More than 60% had hepatomegaly, one third still had splenomegaly after five years of age and more than one third was icteric. More than half children older than ten years had growth disorders. Mean hemoglobin level was 7 g/dL. 21 of the 83 tested children for HBsAg were positive and only one out of 79 was positive for HIV. CONCLUSIONS: Clinical manifestations and course of sickle-cell anemia in our patients are similar to those reported in Congolese children. Genetic and environmental factors may be responsible for differences with children from other, in particular French, cohorts. 相似文献
18.
E Huidovici M Artino R Carmaciu A B?d?r?u A Iancu 《Canadian Metallurgical Quarterly》1996,100(3-4):135-137
Our previous experimental studies on rats motionless for 7 to 60 days in special devices limiting their movements revealed a significantly increased activity of the fibrinolytic system (Groza, Artino) due to the "detention stress" rather then to the immobilization. Starting from these studies we have tried to observe the behaviour of the fibrinolytic system during long-term orthopedic immobilization (7-28 days) on patients having different injuries of the lower limb and submitted to orthopedic therapy (with or without osteosynthesis) to which an anticoagulant preventive treatment was added (heparin or low-molecular-weight substitutes such as Clivarine, Fraxiparine). We studied on 23 patients (11 male and 12 female) motionless for 14, 21, 28 days the plasma fibrinolytic activity (PFA) through euglobulin lysis time (ELT). Clinical investigation revealed that PFA did not change significantly during long-term orthopedic immobilization regardless of the duration of immobilization (14,21,28 days). Rosenfeld et al. (1994) described in healthy volunteers on bedrest for 36 hours an increase of PFA beginning at 24 hours of immobilization, this variation being capable of preventing stasis effects. Our results suggest that preventive anticoagulant therapy properly given during immobilization prevents thromboembolic events. 相似文献
19.
Summary A mathematical model for the cooling process of a molten drop, falling freely in a fluid, is presented. This model is used to determine the duration of the cooling stage of an urea drop. The distribution of the temperature, as function of time and radius, is determined. 相似文献
20.
DW Morck JK Merrill BE Thorlakson ME Olson LV Tonkinson JW Costerton 《Canadian Metallurgical Quarterly》1993,202(2):273-277
The prophylactic administration of injectable tilmicosin for pneumonia in weaned beef calves was investigated in 1,806 animals. Comparisons were made among calves receiving an "on-arrival" injection of tilmicosin, calves receiving a single injection of long-acting oxytetracycline, and calves receiving no prophylaxis. Morbidity and mortality attributable to pneumonia, morbidity and mortality attributable to all causes, and case fatality were significantly lower in the group of calves that received tilmicosin, compared with calves that received long-acting oxytetracycline and calves that received no prophylactic antibiotic. Mean time to initial pneumonia treatment was significantly extended in calves that received prophylaxis, compared with those that received no antibiotic on arrival at the feedlot. Calves that received tilmicosin gained significantly more weight than calves that received oxytetracycline. Calves that were not treated for pneumonia during the trial period gained significantly more weight than did those calves that were treated for pneumonia regardless of experimental group. The majority of mortalities were attributable to fibrinous pneumonia (31/34). Important bacterial isolates (Pasteurella spp, Haemophilus somnus, Actinomyces pyogenes) obtained at necropsy did not have resistance to tilmicosin in association with administration of tilmicosin as prophylaxis for pneumonia. However, bacterial resistance to trimethoprim/sulfonamide and to oxytetracycline were commonly found in these postmortem isolates. 相似文献