全文获取类型
收费全文 | 24313篇 |
免费 | 2361篇 |
国内免费 | 932篇 |
学科分类
工业技术 | 27606篇 |
出版年
2024年 | 69篇 |
2023年 | 331篇 |
2022年 | 694篇 |
2021年 | 1104篇 |
2020年 | 866篇 |
2019年 | 743篇 |
2018年 | 833篇 |
2017年 | 867篇 |
2016年 | 806篇 |
2015年 | 1129篇 |
2014年 | 1515篇 |
2013年 | 1886篇 |
2012年 | 2152篇 |
2011年 | 2311篇 |
2010年 | 1946篇 |
2009年 | 1833篇 |
2008年 | 1698篇 |
2007年 | 1590篇 |
2006年 | 1265篇 |
2005年 | 948篇 |
2004年 | 642篇 |
2003年 | 466篇 |
2002年 | 381篇 |
2001年 | 260篇 |
2000年 | 201篇 |
1999年 | 169篇 |
1998年 | 168篇 |
1997年 | 134篇 |
1996年 | 93篇 |
1995年 | 76篇 |
1994年 | 61篇 |
1993年 | 51篇 |
1992年 | 37篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 24篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 16篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
71.
72.
Ramirez Juan R.; Crano William D.; Quist Ryan; Burgoon Michael; Alvaro Eusebio M.; Grandpre Joseph 《Canadian Metallurgical Quarterly》2004,18(1):3
The authors investigated relationships between marijuana and inhalant use and several cultural and demographic factors in Anglo American and Hispanic American adolescents (N=1,094). Outcome measures assessed lifetime and 30-day marijuana and inhalant use. Predictors and covariates used in logistic regression analyses were region, grade, gender, knowledge, acculturation, familism, and parental monitoring. Hispanic Americans exhibited higher usage across all measures. In this group, high acculturation was associated with low marijuana, but high inhalant, use. Across all participants, positive family relations and parental monitoring were strongly associated with attenuated marijuana use hut only among those most knowledgeable about drugs. Familism and monitoring were not associated with diminished usage among the less knowledgeable. For inhalants, monitoring combined with high knowledge or high familism was associated with diminished usage. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
1 诚信对兖矿资本运营的贡献1.1 在兖矿股票发行方面 1988年4月兖矿煤业在纽约、香港打响了上市的第一炮,这次兖州煤业全球发行8.2亿股,发行总收入折合人民币2.58亿元。可是当时的背景是亚洲金融危机爆发所带来的负面影响尚未完全消除,世界各地失信现象屡屡发生。活力28集团股份有限公司股票上市申报时虚增利润1667.7万元,上市后三年虚增利润21124.3万元,1998年公司在配股时公开披露国家股股东荆州市国资局以现金2320万元认购 相似文献
74.
In the last rice harvest season, experimental results have been obtained on the efficiency and drying quality of a solar assisted heat pump drying prototype system. The system has been operated as a solar and heat pump system and drying curves for the different options have been obtained. The advantage of the low temperature and better control in the drier shows that the heat pump assisted solar drying system is an excellent alternative to traditional drying systems. 相似文献
75.
介绍了扩频通信有效的MSK信号特点及声表面波MSK抽头延迟线构成方式,给出了声表面波32位MSK抽头延迟线的实验结果。 相似文献
76.
In this work, we present a novel process to produce plasticized PVC articles. Plasticized PVC dispersion resin (dry blend) was extruded and poured into a hot mold. The mold was transferred to a rotomolding machine, where the final geometry was obtained. Formulations using commercial PVC suspension resin and three different types of plasticizers were prepared under different processing conditions. The physical appearance of the articles and the tensile properties of the materials were evaluated. 相似文献
77.
JP Grass IB Dockendorff VA Soto PH Araya CM Henriquez 《Canadian Metallurgical Quarterly》1993,18(3):336-338
A case report of a 10-year old girl with a herniated disc is presented. The most significant symptoms were progressive scoliosis with a flat back and paravertebral muscle spasm. An absent H reflex on the left and an increased latency of the somatosensory-evoked potentials of the left posterior tibial nerve were found. The computed tomographic scan of the lumbar spine showed a large central left-sided disc protrusion at the L5-S1 level. Our case presents the youngest patient with documented intervertebral disc herniation and the only one with severe scoliosis and vertebral rotation. The curve was not structural because it improved with surgery and an orthosis was not necessary. 相似文献
78.
BACKGROUND: An important agent of food intoxication is Staphylococcus aureus, that is able to produce enterotoxins. AIM: To detect Staphylococcus aureus contamination in cafeteria food handlers of a Chilean University. SUBJECTS AND METHODS: Nose, throat, hands and nail samples from 87 food handlers were obtained for microbiological examination. RESULTS: Fifty seven subjects (65.5%) were carriers of Staphylococcus aureus. Enterotoxigenic Staphylococcus aureus was found in 36 subjects (41%). The most frequently found enterotoxin was type B (18 samples) followed by type D (12 samples). Men bad a higher frequency of contamination than women (83 and 57% of positive samples respectively). CONCLUSIONS: The frequency of Staphylococcus aureus contamination among food handlers is high and should prompt personal and environmental hygienic measures. 相似文献
79.
A mixed-potential integral equation (MPIE) is formulated for the electric and magnetic currents on a multilayered aperture-coupled patch antenna. The integral equation is solved via the method of moments (MoM) using subsectional basis functions that allow the analysis of nonrectangular aperture and patch shapes. The input impedance and radiation efficiency of various aperture-coupled elements are calculated using the proposed technique and compared to measured results. The advantages and disadvantages of several aperture and patch configurations are discussed, and six methods of numerically de-embedding the element's input impedance are compared 相似文献
80.
介绍了非稳态法测试液体在低温下(-100~50℃)的热导率的测试原理、方法,测试了全氟三乙胺的低温热导率。为了提高测试的重复性,采用了相对比较法,并给出了测试装置及测试结果和误差分析。 相似文献