全文获取类型
收费全文 | 22087篇 |
免费 | 960篇 |
国内免费 | 319篇 |
专业分类
电工技术 | 487篇 |
综合类 | 543篇 |
化学工业 | 4215篇 |
金属工艺 | 526篇 |
机械仪表 | 761篇 |
建筑科学 | 895篇 |
矿业工程 | 180篇 |
能源动力 | 601篇 |
轻工业 | 2247篇 |
水利工程 | 254篇 |
石油天然气 | 179篇 |
武器工业 | 28篇 |
无线电 | 2477篇 |
一般工业技术 | 2970篇 |
冶金工业 | 3721篇 |
原子能技术 | 185篇 |
自动化技术 | 3097篇 |
出版年
2023年 | 121篇 |
2022年 | 424篇 |
2021年 | 542篇 |
2020年 | 302篇 |
2019年 | 368篇 |
2018年 | 420篇 |
2017年 | 385篇 |
2016年 | 439篇 |
2015年 | 381篇 |
2014年 | 581篇 |
2013年 | 1111篇 |
2012年 | 884篇 |
2011年 | 1060篇 |
2010年 | 826篇 |
2009年 | 868篇 |
2008年 | 857篇 |
2007年 | 886篇 |
2006年 | 761篇 |
2005年 | 647篇 |
2004年 | 718篇 |
2003年 | 935篇 |
2002年 | 1218篇 |
2001年 | 1037篇 |
2000年 | 607篇 |
1999年 | 555篇 |
1998年 | 1351篇 |
1997年 | 879篇 |
1996年 | 648篇 |
1995年 | 439篇 |
1994年 | 332篇 |
1993年 | 363篇 |
1992年 | 204篇 |
1991年 | 155篇 |
1990年 | 149篇 |
1989年 | 138篇 |
1988年 | 133篇 |
1987年 | 114篇 |
1986年 | 116篇 |
1985年 | 152篇 |
1984年 | 94篇 |
1983年 | 95篇 |
1982年 | 88篇 |
1981年 | 103篇 |
1980年 | 104篇 |
1979年 | 65篇 |
1978年 | 54篇 |
1977年 | 104篇 |
1976年 | 194篇 |
1975年 | 53篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
There are several damping phenomena in quantum optics. Such phenomena have been usually explained by open systems. In statistical physics, open system dynamics have been used to study the irreversibility and the approach to equilibrium. In this paper, the dynamical change of the mutual entropy for an open system, frequently studied in the quantum optics literature, is rigorously computed through a model of quantum Markov chain. In particular, the concrete formula of Stinespring expression for such a model is obtained and applied to the derivation of the mutual entropy, and some computational results are presented. 相似文献
32.
Evaluation of hydroxylapatite/poly(l-lactide) composites: physico-chemical properties 总被引:7,自引:0,他引:7
C. C. P. M. Verheyen C. P. A. T. Klein J. M. A. De Blieck-Hogervorst J. G. C. Wolke C. A. Van Blitterswijn K. De Groot 《Journal of materials science. Materials in medicine》1993,4(1):58-65
The aim of this in vitro study was to examine the physico-chemical behaviour of hydroxylapatite/poly(l-lactide) (HA/PLLA) composites in solution tests. The polymer PLLA, the composites 30 wt% HA/PLLA (C30) and 50 wt% HA/PLLA (C50) and a one-side HA-coated PLLA (HAcP) were evaluated. Rectangular specimens were incubated in various acellular aqueous buffer solutions [citrate, Gomori's and phosphate-buffered saline (PBS)] up to 24 weeks. Data for cumulative release of calcium, phosphate and l-lactate release in solutions containing C30 or C50 showed linear patterns. Release data for solutions containing HAcP combined with scanning micrographs, X-ray microanalysis and X-ray diffraction patterns of the specimens in time showed that the plasma-sprayed HA coating on PLLA dissolves significantly, progressively in the first weeks and almost completely within the tested period of 24 weeks in vitro. A precipitate of scaly crystallites (calcium phosphates) was observed at the HA coating-PBS interface. After 24 weeks incubation all materials were still above their initial weight, indicating that swelling still exceeded dissolution. Application of C30, C50 and HAcP as implant materials seems interesting where initial stabilization through bone bonding is needed or where the linear release of constituents is a requirement. HAcP has the advantage that the HA coating acts as a hydrolysis barrier and consequently delays the degradation of PLLA in vitro. 相似文献
33.
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
34.
35.
G Chessa Ricotti R Cutrì A De Bernardi M Funis S Frediani 《Canadian Metallurgical Quarterly》1995,17(3):271-273
The authors describe 5 cases, 3 boys and 2 girls, with idiopathic growth hormone deficiency in prepubertal age, treated with human growth hormone. In four of five cases the response to treatment with GH was relevant. Only in one case (F1) the response was negative. The results of this study confirm that rhGH is a safe and effective therapy in children with GHD. 相似文献
36.
Photocyclovoltammetric experiments with films of poly(3-methylthiophene) under polychromatic light irradiation show a p-type semiconductor behavior in the reduced state, with a flat band potential of 0.18 V. The photocurrent depends on film thickness and surface morphology. Films with different thickness were characterized by scanning electron microscopy, indicating a globular morphology with globule sizes changing according to the charge density used during polymer deposition. The highest photocurrent is observed for the lowest globule diameter. These films were also irradiated with monochromatic light from the electrolyte side and from the substrate side. A higher photocurrent and a photocurrent spectrum matching the absorption spectrum of the reduced form of the polymer is observed on irradiation from the electrolyte side of a 0.7 μm thick film. In contrast, for irradiation from the electrode side, the photocurrent is lower and the spectrum shows a peak at lower energy. These results were interpreted in terms of a delocalized space charge zone, different kinetics for charge transfer and mass transport across the solvent swollen polymer film and different depth of penetration of the light as a function of wavelength. 相似文献
37.
38.
39.
40.
Ⅰ线光致抗蚀剂可以同时实用电子束和光学系统曝光,在50kV加速电压下,其曝光剂量为50-100μC/cm^2,曝光后在0.7%NaOH溶液内显影1分钟。其灵敏度比PMMA快5倍,分辩率为0.5μm。采用两方法制备CaAsPHEMT:一种用Ⅰ线光致抗蚀剂,对源、漏及栅全部都采用电子束曝光,制备了0.5μm栅长的GaAs PHEMT;另一种将源、漏及栅分割成两部分,其中精细部分由电子束曝光,其余部分由光学系统曝光,用这种方法制备了0.25μm栅长的GaAs PHEMT。Ⅰ 相似文献