全文获取类型
收费全文 | 5478篇 |
免费 | 211篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 73篇 |
综合类 | 2篇 |
化学工业 | 867篇 |
金属工艺 | 130篇 |
机械仪表 | 232篇 |
建筑科学 | 95篇 |
矿业工程 | 1篇 |
能源动力 | 143篇 |
轻工业 | 343篇 |
水利工程 | 13篇 |
石油天然气 | 1篇 |
无线电 | 690篇 |
一般工业技术 | 777篇 |
冶金工业 | 1887篇 |
原子能技术 | 43篇 |
自动化技术 | 398篇 |
出版年
2023年 | 41篇 |
2022年 | 45篇 |
2021年 | 83篇 |
2020年 | 74篇 |
2019年 | 80篇 |
2018年 | 111篇 |
2017年 | 116篇 |
2016年 | 128篇 |
2015年 | 107篇 |
2014年 | 160篇 |
2013年 | 260篇 |
2012年 | 234篇 |
2011年 | 306篇 |
2010年 | 210篇 |
2009年 | 229篇 |
2008年 | 211篇 |
2007年 | 172篇 |
2006年 | 184篇 |
2005年 | 144篇 |
2004年 | 147篇 |
2003年 | 125篇 |
2002年 | 106篇 |
2001年 | 96篇 |
2000年 | 81篇 |
1999年 | 100篇 |
1998年 | 610篇 |
1997年 | 363篇 |
1996年 | 265篇 |
1995年 | 135篇 |
1994年 | 130篇 |
1993年 | 133篇 |
1992年 | 34篇 |
1991年 | 52篇 |
1990年 | 38篇 |
1989年 | 33篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 9篇 |
1982年 | 10篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 49篇 |
1976年 | 106篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1955年 | 3篇 |
排序方式: 共有5695条查询结果,搜索用时 31 毫秒
1.
Multimedia Systems - The preferences of Web information purchasers are changing. Cost-effectiveness (i.e., an emphasis on performance with respect to price) is becoming less regarded than... 相似文献
2.
3.
AbstractBuilding thermal inertia and operation control strategies have impacted on the thermal performance of a radiant floor heating system. This study conducts a two-dimensional numerical analysis of an intermittently operated radiant floor heating system using the Re-Normalization Group model with Discrete Ordinates Radiation model. A detailed numerical simulation setups and various analyses are provided, including grid independency analysis, initial condition, time step sizes and external boundary conditions. Three different weekend day intermittent operation strategies are investigated. The results showed that Case 3 designed with pre-heating of 20?h has better performance compared to Case 1 designed with pre-heating of 8?h and Case 2 designed with pre-heating of 14?h. The average indoor air temperature differences of approximate 2.1, 1.6 and 1.2 K are observed for Case 1, Case 2 and Case 3, respectively, when comparing two-time slot at 8:00am on Friday morning and Monday morning. This significantly highlights the effect of thermal inertia and the potential of energy saving due to the utilization of intermittent operation. Therefore, the current study presents numerical simulation potential in evaluating the radiant floor heating effects on indoor thermal environment, taking into account building thermal inertia and transient external climatic conditions. 相似文献
4.
Park Sangwon Nam Hyunbin Na Youngsang Kim Hyoungseop Moon Younghoon Kang Namhyun 《Metals and Materials International》2020,26(5):641-649
Metals and Materials International - This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurred from friction stir welding of... 相似文献
5.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
6.
Lead content of rice collected from various areas in the world 总被引:1,自引:0,他引:1
ZW Zhang CS Moon T Watanabe S Shimbo M Ikeda 《Canadian Metallurgical Quarterly》1996,191(1-2):169-175
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world. 相似文献
7.
PURPOSE: We investigated Sertoli cells in testicular biopsies with carcinoma in situ (CIS) in respect to cytokeratin expression to elucidate the status of Sertoli cell differentiation adjacent to CIS in human testes. Cytokeratin 18 intermediate filaments indicate a state of undifferentiation usually observed in Sertoli cells of prepubertal testes. MATERIALS AND METHODS: 29 testicular biopsies presenting CIS were investigated by means of immunohistochemistry, using a polyclonal antibody against placental-alkaline phosphatase to detect CIS cells and a monoclonal antibody against human cytokeratin 18 to show expression of cytokeratin 18 intermediate filaments in Sertoli cells. RESULTS: All tubules bearing CIS showed positive cytokeratin expression of Sertoli cells if tubules were devoid of normal germ cells. However, a total of 13 specimen revealed CIS cells together with normal germ cells. In the presence of CIS cells together with round or elongated spermatids, adjacent Sertoli cells did not express cytokeratin immunoreactivity. In the case of combined presence of CIS and spermatogonia and primary spermatocytes, Sertoli cells could be found either immunopositive or immunonegative, and were positive in tubules with CIS and spermatogonia only. CONCLUSIONS: Sertoli cells associated with CIS cells undergo a process of dedifferentiation, seen by the re-expression of cytokeratin intermediate filaments. We suggest that this dedifferentiation results in a loss of Sertoli cell function and leads to a cessation of spermatogenic activity. 相似文献
8.
DA O'Farrell HM Ridha P Keenan FW McManus M Stephens 《Canadian Metallurgical Quarterly》1997,28(5-6):377-379
Roller blading is a new and increasingly popular leisure activity in many countries. We reviewed 110 consecutive patients with roller-blade injuries between 1 January and 30 June 1996. The patients ranged from 4 to 14 years in age (mean 6.5 years). Eighty-three (75.4%) sustained injuries to the upper limb and 27 (24.5%) injured the lower limb. Fifty-six patients, were girls and 54 were boys. Of the 110 patients, 79 (72.7%) sustained fractures, 28 (25.4%) soft tissue injuries and 3 (2.7%) dislocations. Eighty-three (75.4%) of the patients wore no protective equipment on the limbs. Four months following injury 103 (93.6%) patients were fully recovered. The mean duration of school absence was 3 days. Subsequently 101 children returned to using roller-blades following injury. Seventy-three (66.3%) of these now use protective equipment. We found that injuries were unrelated to age or duration of roller-blading experience or to the brand-name of roller blades used, and that most of our patients wore no protective equipment at the time of injury. 相似文献
9.
PE Borchardt SM Quadri RS Freedman HM Vriesendorp 《Canadian Metallurgical Quarterly》1997,44(3):283-293
Sensory-perceptual abnormalities in people with autism are discussed from two perspectives: published firsthand accounts and existing psychological research evidence. A range of abnormalities, including hyper- and hyposensitivity, sensory distortion and overload, and multichannel receptivity and processing difficulties, are described in firsthand accounts and frequently portrayed as central to the autistic experience. A number of dangers are inherent in uncritically accepting these accounts at face value and in any wider generalization to the autistic population as a whole. Evidence from clinical studies suggests that unusual sensory responses are present in a majority of autistic children, that they are manifested very early in development, and that they may be linked with other aspects of autistic behavior. In addition, experimental studies using a range of indices have found evidence of unusual responses to sensory stimuli in autistic subjects. However the clinical and experimental research to date suffers from serious methodological limitations and more systematic investigation is warranted. Key issues for future psychological research in the area are identified. 相似文献
10.