全文获取类型
收费全文 | 10171篇 |
免费 | 340篇 |
国内免费 | 169篇 |
专业分类
电工技术 | 193篇 |
综合类 | 252篇 |
化学工业 | 743篇 |
金属工艺 | 223篇 |
机械仪表 | 204篇 |
建筑科学 | 336篇 |
矿业工程 | 128篇 |
能源动力 | 111篇 |
轻工业 | 248篇 |
水利工程 | 86篇 |
石油天然气 | 149篇 |
武器工业 | 46篇 |
无线电 | 678篇 |
一般工业技术 | 684篇 |
冶金工业 | 5997篇 |
原子能技术 | 51篇 |
自动化技术 | 551篇 |
出版年
2024年 | 20篇 |
2023年 | 72篇 |
2022年 | 141篇 |
2021年 | 195篇 |
2020年 | 109篇 |
2019年 | 120篇 |
2018年 | 138篇 |
2017年 | 147篇 |
2016年 | 116篇 |
2015年 | 179篇 |
2014年 | 179篇 |
2013年 | 223篇 |
2012年 | 230篇 |
2011年 | 286篇 |
2010年 | 250篇 |
2009年 | 241篇 |
2008年 | 279篇 |
2007年 | 212篇 |
2006年 | 197篇 |
2005年 | 151篇 |
2004年 | 104篇 |
2003年 | 105篇 |
2002年 | 94篇 |
2001年 | 104篇 |
2000年 | 117篇 |
1999年 | 292篇 |
1998年 | 1876篇 |
1997年 | 1049篇 |
1996年 | 746篇 |
1995年 | 395篇 |
1994年 | 380篇 |
1993年 | 392篇 |
1992年 | 68篇 |
1991年 | 86篇 |
1990年 | 100篇 |
1989年 | 93篇 |
1988年 | 89篇 |
1987年 | 103篇 |
1986年 | 85篇 |
1985年 | 71篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 46篇 |
1981年 | 42篇 |
1980年 | 47篇 |
1979年 | 10篇 |
1978年 | 21篇 |
1977年 | 151篇 |
1976年 | 369篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
1.
Feng Wenran Li Zhen Chen Yingying Chen Jinyang Lang Haoze Wan Jianghong Gao Yan Dong Haitao 《Journal of Materials Science》2022,57(3):1881-1889
Journal of Materials Science - Although chalcogenide materials continue to generate considerable interest due to great potentials for various optoelectronic devices, annealing for a long time in... 相似文献
2.
3.
Shanquan Chen Sicong Wei Fei Jin Shanming Ke Xierong Zeng Lang Chen Chuanwei Huang 《Ceramics International》2018,44(12):13695-13698
From the perspectives of scientific researches and practical applications, it is desirable to explore high operating temperature ferromagnetic films. The effect of biaxial strain on magnetic properties of (110)-oriented La0.7Sr0.3MnO3 films was studied. High quality La0.7Sr0.3MnO3 films were grown on (110)-oriented perovskite single crystal substrates using pulsed laser deposition, varying substrate-induced misfit strains from ??2.27–0.75%. A remarkable enhancement of Curie temperature has been achieved for (110)-oriented La0.7Sr0.3MnO3 films clamped with small misfit strains (i.e., grown on LAST (110)). The enhanced Curie temperature of (110)-oriented La0.7Sr0.3MnO3 films could be attributed to the misfit strain between the films and the underlying substrates and may have technological implication for applications at high temperature environments. 相似文献
4.
5.
6.
7.
BJ Conway OH Suleiman FG Rueter RG Antonsen RJ Slayton 《Canadian Metallurgical Quarterly》1994,191(2):323-330
PURPOSE: To determine trends in mammography in the United States. MATERIALS AND METHODS: A sample of mammographic facilities was selected for each year of the Nationwide Evaluation of X-ray Trends. The same protocol was followed for the 1985, 1988, and 1992 surveys. Data were collected with use of the same imaging phantom for all three surveys and also with a different phantom in the 1988 and 1992 surveys. RESULTS: Of the 356 facilities surveyed in 1992, 59% claimed to be in compliance with the Health Care Financing Administration (HCFA) mammography requirements, 42% were accredited by the American College of Radiology (ACR), and 23% did not hold credentials from either the HCFA or the ACR. Since 1985, there has been a 34% improvement in acceptable phantom image quality score and a 20% decrease in the mean glandular dose. CONCLUSION: Mammography as practiced today is essentially a screen-film technique. Mammographic phantom image quality has improved considerably. The overall mean glandular dose has decreased primarily because of the elimination of xeroradiography. 相似文献
8.
CA Piantadosi J Zhang ED Levin RJ Folz DE Schmechel 《Canadian Metallurgical Quarterly》1997,147(1):103-114
Delayed neurological damage after CO hypoxia was studied in rats to determine whether programmed cell death (PCD), in addition to necrosis, is involved in neuronal death. In rats exposed to either air or CO (2500 ppm), microdialysis in brain cortex and hippocampus was performed to determine the extent of glutamate release and hydroxyl radical generation during the exposures. Groups of control and CO-exposed rats also were tested in a radial maze to assess the effects of the CO exposures on learning and memory. At 3, 7, and 21 days after CO exposure brains were perfusion-fixed and hematoxylin-eosin (H&E) was used to assess injury and to select regions for further examination. DNA fragmentation was sought by examining cryosections with the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) reaction. We found significant increases in glutamate release and .OH generation during and immediately after CO hypoxia. CO-exposed rats showed learning and memory deficits after exposure associated with heterogeneous cell loss in cortex, globus pallidus, and cerebellum. The frontal cortex was affected most seriously; the damage was slight at Day 3, increased at Day 7, and persistent at Day 21 after CO exposure. TUNEL staining was positive at all three time points, and TUNEL-labeled cells were distributed similarly to eosinophilic cells. The number of cells stained by TUNEL was less than by H&E and amounted to 2 to 5% of all cell nuclei in regions of injury. Ultrastructural features of both neuronal necrosis and apoptosis also were observed readily by electron microscopy. These findings indicate that both necrosis and apoptosis (PCD) contribute to CO poisoning-induced brain cell death. 相似文献
9.
10.
VB Lang P Langguth C Ottiger H Wunderli-Allenspach D Rognan B Rothen-Rutishauser JC Perriard S Lang J Biber HP Merkle 《Canadian Metallurgical Quarterly》1997,86(7):846-853
Due to the low effective permeabilities of peptides at many absorption sites, their structure-permeation relations are of high interest. In this work structure-permeation relations of Met-enkephalin analogues are presented using confluent Caco-2 cells as an in vitro permeation model. Four model peptides (Met-enkephalin, [D-Ala2]Met-enkephalin, [D-Ala2]Met-enkephalinamide, and metkephamid) were tested in terms of permeability, lipophilicity, charge, and molecular size. Permeability coefficients (P(eff)) across Caco-2 cells were low, 3.3 x 10(-8) to 9.5 x 10(-8) cm s-1, and were similar to typical paracellular markers. No correlation of permeability and the log(apparent octanol/buffer partition coefficient) was observed. A 40-fold increase of the permeability of metkephamid in the presence of 10 mM EDTA suggested a significant contribution of paracellular transport. Independent support for this conclusion was obtained by visualizing the pathway of the fluorescein isocyanate isomer I 1-metkephamid by confocal laser scanning microscopy (CLSM). The fluorophore-labeled peptide was observed in the intercallular space only. Metkephamid permeabilities were found to be direction-specific. Permeabilities from basolateral to apical (b-to-a) were significantly higher (ca. 4-fold) than in the opposite (a-to-b) direction. The addition of verapamil equalized the permeabilities in the a-to-b and b-to-a directions, suggesting the involvement of a P-glycoprotein-mediated secretion mechanism. Similar observations were obtained with [D-Ala2]Met-enkephalinamide, but not with Met-enkephalin and [D-Ala2]Met-enkephalin. In contrast to the other analogues, metkephamid and [D-Ala2]Met-enkephalinamide are positively charged at neutral pH, as demonstrated by their isoelectric points (pl = 8.6 for [D-Ala2]Met-enkephalinamide and metkephamid and 5.3 for [D-Ala2]Met-enkephalin and Met-enkephalin). The data is in agreement with the literature showing that most compounds secreted by the P-glycoprotein transporter carry a positive charge. 相似文献