全文获取类型
收费全文 | 302830篇 |
免费 | 7386篇 |
国内免费 | 1859篇 |
专业分类
电工技术 | 5714篇 |
技术理论 | 5篇 |
综合类 | 1181篇 |
化学工业 | 51652篇 |
金属工艺 | 11714篇 |
机械仪表 | 8666篇 |
建筑科学 | 8139篇 |
矿业工程 | 1745篇 |
能源动力 | 6804篇 |
轻工业 | 33881篇 |
水利工程 | 3309篇 |
石油天然气 | 6131篇 |
武器工业 | 246篇 |
无线电 | 29846篇 |
一般工业技术 | 56019篇 |
冶金工业 | 53836篇 |
原子能技术 | 5829篇 |
自动化技术 | 27358篇 |
出版年
2022年 | 2038篇 |
2021年 | 3816篇 |
2020年 | 2650篇 |
2019年 | 3211篇 |
2018年 | 4957篇 |
2017年 | 4896篇 |
2016年 | 5394篇 |
2015年 | 4186篇 |
2014年 | 6275篇 |
2013年 | 14756篇 |
2012年 | 10425篇 |
2011年 | 13082篇 |
2010年 | 10290篇 |
2009年 | 10721篇 |
2008年 | 11458篇 |
2007年 | 11326篇 |
2006年 | 9780篇 |
2005年 | 8551篇 |
2004年 | 7737篇 |
2003年 | 7142篇 |
2002年 | 7058篇 |
2001年 | 6877篇 |
2000年 | 6463篇 |
1999年 | 6413篇 |
1998年 | 15078篇 |
1997年 | 11025篇 |
1996年 | 8281篇 |
1995年 | 6111篇 |
1994年 | 5569篇 |
1993年 | 5429篇 |
1992年 | 4122篇 |
1991年 | 3917篇 |
1990年 | 3935篇 |
1989年 | 3913篇 |
1988年 | 3668篇 |
1987年 | 3152篇 |
1986年 | 3154篇 |
1985年 | 3539篇 |
1984年 | 3427篇 |
1983年 | 3150篇 |
1982年 | 2794篇 |
1981年 | 3017篇 |
1980年 | 2752篇 |
1979年 | 2910篇 |
1978年 | 2792篇 |
1977年 | 3002篇 |
1976年 | 4004篇 |
1975年 | 2516篇 |
1974年 | 2336篇 |
1973年 | 2387篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A. V. Kurdyumov V. F. Britun V. B. Zelyavskii S. N. Gromyko T. S. Bartnitskaya L. A. Lyudvinskaya 《Powder Metallurgy and Metal Ceramics》1997,36(7-8):425-429
The structure of SiC–AlN powders is investigated by x-ray diffraction and transmission electron microscopy methods. The powders
were produced by joint carbon reduction and nitriding of silicon and aluminum oxide mixtures. The results show that a mixture
of solid solutions forms during joint SiC and AlN synthesis at 1700°C, with SiC forming β (3C) and α (2H) modifications with
different grain morphology. The fiber form is characteristic of β-SiC, whereas the grains of the solid solution based on SiC
have a predominantly equiaxed form. α-SiC grain dimensions are considerablys smaller than those of AlN.
Institute of Materials Science, National Academy of Sciences of Ukraine. Kiev Translated from Poroshkovaya Metallurgiya, Nos.
7–8, pp. 81–86, July–August, 1997. 相似文献
992.
The changes of nitric oxide synthase (NOS) activity and nitrite level in rat brain regions after spatial learning were investigated. NOS activity was assayed by conversion of [3H]L-arginine to [3H]L-citrulline, and a sensitive fluorometric assay for quantification of nitrite was used. Compared with sham-trained rats, NOS activity and nitrite level in hippocampus and cortex, and also the nitrite level in cerebellum, was elevated significantly one day after rats had learnt a water-rewarded spatial alteration task. These results suggest a spatial memory-related changes of endogenous NO in rat brain, and support the idea that NO participates in learning and memory processes. 相似文献
993.
994.
LA Pérula de Torres J Martínez de la Iglesia J Espejo Espejo MV Rubio Cuadrado I Enciso Berge FJ Fonseca del Pozo JM Aranda Lara 《Canadian Metallurgical Quarterly》1997,20(8):425-434
OBJECTIVE: To describe the health status of a population over 60 years and to study their relationship with several socio-demographic variables. DESIGN: A cross-sectional study, population based. SETTINGS: A community. PARTICIPANTS: A randomized sample of 1,103 non institutionalized people over 60 years living in the city of Cordoba (Spain). MEASUREMENTS AND MAIN RESULTS: By mean of a personal interview at home we used the OARS-MFAQ-VE questionnaire. Low self-rated health was associated with the age, to be female sex, a low cultural background, and a low income. Only 5.2% of the study people do not suffered any illness and 56% state that their health problems are major problems for doing their current activities. 4.9% declared to have some degree of physical incapacity. 3.7% of elderly population has an important cognitive deficit. CONCLUSIONS: The majority of elderly people has good health. Age is related with a poor health. Women have more health problems than men. 相似文献
995.
FJ Couch ML DeShano MA Blackwood K Calzone J Stopfer L Campeau A Ganguly T Rebbeck BL Weber 《Canadian Metallurgical Quarterly》1997,336(20):1409-1415
BACKGROUND: To define the incidence of BRCA1 mutations among patients seen in clinics that evaluate the risk of breast cancer, we analyzed DNA samples from women seen in this setting and constructed probability tables to provide estimates of the likelihood of finding a BRCA1 mutation in individual families. METHODS: Clinical information, family histories, and blood for DNA analysis were obtained from 263 women with breast cancer. Conformation-sensitive gel electrophoresis and DNA sequencing were used to identify BRCA1 mutations. RESULTS: BRCA1 mutations were identified in 16 percent of women with a family history of breast cancer. Only 7 percent of women from families with a history of breast cancer but not ovarian cancer had BRCA1 mutations. The rates were higher among women from families with a history of both breast and ovarian cancer. Among family members, an average age of less than 55 years at the diagnosis of breast cancer, the presence of ovarian cancer, the presence of breast and ovarian cancer in the same woman, and Ashkenazi Jewish ancestry were all associated with an increased risk of detecting a BRCA1 mutation. No association was found between the presence of bilateral breast cancer or the number of breast cancers in a family and the detection of a BRCA1 mutation, or between the position of the mutation in the BRCA1 gene and the presence of ovarian cancer in a family. CONCLUSIONS: Among women with breast cancer and a family history of the disease, the percentage with BRCA1 coding-region mutations is less than the 45 percent predicted by genetic-linkage analysis. These results suggest that even in a referral clinic specializing in screening women from high-risk families, the majority of tests for BRCA1 mutations will be negative and therefore uninformative. 相似文献
996.
997.
Bez R. Cantarelli D. Moioli L. Ortolani G. Servalli G. Villa C. Dallabora M. 《Electron Device Letters, IEEE》1998,19(2):37-39
A new method to erase a standard (double-poly, stacked-gate NOR-type) flash cell is proposed. The method, still using the tunneling mechanism to extract electrons from the floating gate, is based on the concept of keeping the electric field constant during the whole erasing operation. The new method has two main advantages with respect to the conventional one: (1) it does not depend on the supply voltage variation and (2) it allows a better reliability in terms of endurance-induced stress. Results have shown that flash device performances are greatly improved in terms of stability and endurance reliability up to one million cycles 相似文献
998.
Kang W.P. Wisitsora-at A. Davidson J.L. Kerns D.V. 《Electron Device Letters, IEEE》1998,19(10):379-381
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters 相似文献
999.
1000.
V Darsonval V Berthet P Hubault C Crouzet L Fernandez 《Canadian Metallurgical Quarterly》1997,42(6):594-602
Enucleation frequently and progressively causes an enophtalmus and atrophia of the inferior eyelid, thereby leading to a height deficiency. Buccal mucous grafts give rise to phenomena such as secondary retraction. This may have complex and painful post-operative outcomes. However, when a septal chondromucous graft is performed, the height in the inferior palpebral part becomes more aesthetic, more retentive and quickly allows the wearing of a more voluminous prosthesis. Thus, the notinable enophtalmus can be corrected and the aesthetic quality of the looking is substantially restored. The authors report this surgical procedure and the results obtained with 21 patients which appear to be particularly promising. 相似文献