全文获取类型
收费全文 | 464887篇 |
免费 | 5151篇 |
国内免费 | 1272篇 |
专业分类
电工技术 | 8578篇 |
综合类 | 443篇 |
化学工业 | 71331篇 |
金属工艺 | 17783篇 |
机械仪表 | 13996篇 |
建筑科学 | 10966篇 |
矿业工程 | 2164篇 |
能源动力 | 11787篇 |
轻工业 | 42350篇 |
水利工程 | 4411篇 |
石油天然气 | 7714篇 |
武器工业 | 47篇 |
无线电 | 55357篇 |
一般工业技术 | 88789篇 |
冶金工业 | 89176篇 |
原子能技术 | 10097篇 |
自动化技术 | 36321篇 |
出版年
2021年 | 3974篇 |
2019年 | 3672篇 |
2018年 | 6264篇 |
2017年 | 6254篇 |
2016年 | 6641篇 |
2015年 | 4190篇 |
2014年 | 7310篇 |
2013年 | 20592篇 |
2012年 | 11538篇 |
2011年 | 15874篇 |
2010年 | 12694篇 |
2009年 | 14230篇 |
2008年 | 15052篇 |
2007年 | 15026篇 |
2006年 | 13357篇 |
2005年 | 11742篇 |
2004年 | 11336篇 |
2003年 | 11390篇 |
2002年 | 11009篇 |
2001年 | 11301篇 |
2000年 | 10599篇 |
1999年 | 10926篇 |
1998年 | 27391篇 |
1997年 | 19203篇 |
1996年 | 14784篇 |
1995年 | 11280篇 |
1994年 | 10038篇 |
1993年 | 9930篇 |
1992年 | 7315篇 |
1991年 | 6956篇 |
1990年 | 7010篇 |
1989年 | 6691篇 |
1988年 | 6396篇 |
1987年 | 5584篇 |
1986年 | 5555篇 |
1985年 | 6208篇 |
1984年 | 5808篇 |
1983年 | 5429篇 |
1982年 | 5102篇 |
1981年 | 5078篇 |
1980年 | 4911篇 |
1979年 | 4693篇 |
1978年 | 4497篇 |
1977年 | 5245篇 |
1976年 | 7022篇 |
1975年 | 3869篇 |
1974年 | 3746篇 |
1973年 | 3805篇 |
1972年 | 3241篇 |
1971年 | 2885篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. S. Han S. R. Hahn H. C. Kwon Y. Bin T. W. Kang J. H. Leem Y. B. Hou H. C. Jeon J. K. Hyun Y. T. Jeoung H. K. Kim J. M. Kim T. W. Kim 《Journal of Electronic Materials》1998,27(6):680-683
Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100Å/100Å) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment. 相似文献
992.
Hebb J.P. Jensen K.F. Thomas J. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(4):607-614
The radiative properties of patterned silicon wafers have a major impact on the two critical issues in rapid thermal processing (RTP), namely wafer temperature uniformity and wafer temperature measurement. The surface topography variation of the die area caused by patterning and the roughness of the wafer backside can have a significant effect on the radiative properties, but these effects are not well characterized. We report measurements of room temperature reflectance of a memory die, logic die, and various multilayered wafer backsides. The surface roughness of the die areas and wafer backsides is characterized using atomic force microscopy (AFM). These data are subsequently used to assess the effectiveness of thin film optics in providing approximations for the radiative properties of patterned wafers for RTP applications 相似文献
993.
V. N. Polupanov N. F. Dakhov V. K. Kiselyev V. N. Seleznev 《Journal of Infrared, Millimeter and Terahertz Waves》1995,16(6):1167-1172
Antiferromagnetic resonance (AFMR) in iron borate at the frequency of 300 GHz at the room temperature in weak (down to 0.1T) external magnetic fieldH has been studied. The loss in AFMR line increased or decreased depending on the direction and magnitude ofH. Such properties ofFeBO 3 monocrystals allows to design undirectional and modulation devices. 相似文献
994.
Attempts have been made to extend SQL to work with multimedia databases. We are reserved on the representation ability of extended SQL to cope with the richness in content of multimedia data. In this paper we present an example of a multimedia database system, Computer Aided Facial Image Inference and Retrieval system (CAFIIR). The system stores and manages facial images and criminal records, providing necessary functions for crime identification. We would like to demonstrate some core techniques for multimedia database with CAFIIR system. Firstly, CAFIIR is a integrated system. Besides database management, there are image analysis, image composition, image aging, and report generation subsystems, providing means for problem solving. Secondly, the richness of multimedia data urges feature-based database for their management. CAFIIR is feature-based. A indexing mechanism,iconic index, has been proposed for indexing facial images using hierarchical self-organization neural network. The indexing method operates on complex feature measures and provides means for visual navigation. Thirdly, special retrieval methods for facial images have been developed, including visual browsing, similarity retrieval, free text retrieval and fuzzy retrieval. 相似文献
995.
The paper presents a review of results concerning the aspartic proteinase cathepsin D and its role in tumor invasion and metastasis. Special attention was paid to the clinical prognostic value of cathepsin D determination in the breast cancer cytosol. 相似文献
996.
T Omland T Aarsland A Aakvaag RT Lie K Dickstein 《Canadian Metallurgical Quarterly》1993,72(3):255-259
Case reports from the United Kingdom (UK) in 1989 have suggested that the introduction of human insulin in 1985 was associated with an increased risk of sudden death in insulin-treated diabetic patients. If human insulin increases the risk of sudden death, the number of these should have increased during the period where human insulin was introduced. We therefore identified all cases of sudden death in Denmark in younger insulin-treated diabetic patients, age at death below 50 years. During this period the consumption of human insulin went from 0.2% to 70% of the total consumption in Denmark. The total number of cases fulfilling the inclusion criteria was 226, and the annual number of sudden deaths did not change during the study period (p = 0.14). The number of deaths due to hypoglycaemia and cases with unexplained cause of death also remained constant (test for trend: p = 0.44). Chronic alcohol abuse or acute alcohol intoxication was found in 50% of the 135 patients dying from hypoglycaemia, ketoacidosis or unknown cause of death (including found dead in bed), while this was the case in only 16% of the remaining 91 cases dying from other natural causes. We conclude that introduction of human insulin in Denmark was not followed by an increase in sudden deaths among younger insulin-treated diabetic patients. 相似文献
997.
R Kürzl 《Canadian Metallurgical Quarterly》1993,53(1):15-19
OBJECTIVE: To analyze HLA-DR4 alleles in New Zealand Polynesians with rheumatoid arthritis (RA). METHODS: Thirty Polynesians and 30 Caucasians with RA, as well as 65 Polynesian and 60 Caucasian healthy blood donors, were DR4 subtyped using the polymerase chain reaction and sequence-specific oligonucleotide probes. RESULTS: The frequency of DR4 (DRB1*04) was increased in both Polynesian (P < 0.001) and Caucasian (P < 0.005) RA patients compared with race-matched controls. Dw4 (DRB1*0401) was detected in 15 of 30 Caucasian patients but only 2 of 30 Polynesian patients (P < 0.001). In Polynesians, RA was associated with Dw15 (DRB1*0405), which was present in 11 of 30 patients and 3 of 65 controls (P < 0.001). Dw13 (DRB1*0403) was the most frequent DR4 allele in healthy Polynesians, but was not significantly associated with RA. CONCLUSION: The predominance of the Dw13 subtype in Polynesians may explain in part the low prevalence of RA in this population. The association of Dw15 with RA in Polynesians supports the hypothesis that the third hypervariable region of DR beta determines susceptibility to RA. 相似文献
998.
L Struillou M Fiks-Sigaud JH Barrier E Blat G Magadur-Joly 《Canadian Metallurgical Quarterly》1993,60(7-8):524-526
The authors report an exceedingly rare complication of rheumatoid arthritis, i.e. acquired hemophilia due to anti-factor VIII autoantibody production. Treatment with intravenous immune globulin ensured control of hemorrhagic manifestations by inducing a transient rise in factor VIII level. 相似文献
999.
A 21-year-old man presented to our hospital on June 7, 1990, asymptomatic but with an abnormal shadow in his chest roentgenogram. A well-demarcated tumorous shadow was seen in the left hilum of the lung in the frontal view of the chest X-ray, and adjacent to the posterior chest wall in the lateral view. A percutaneous needle biopsy was performed, and since there were no malignant findings, the tumor was left untreated for future examinations. However, since the tumor was observed to be enlarging gradually in subsequent chest X-rays, it was resected surgically on June 18, 1991. The tumor was fist-sized and its surface smooth, and was protruding into the thoracic cavity. At surgery, the tumor was separated from the chest wall. The tumor, weighing 170 grams, was diagnosed pathologically as a liposarcoma (myxoid type). It was confirmed that there was no infiltration into the surrounding tissue and that total resection had been performed. There are few reports of liposarcomas within the thoracic cavity developing in the extra-mediastinal chest wall. As our case is the second in Japan occurring in a young patient, we present it here together with a review of the literature. 相似文献
1000.