全文获取类型
收费全文 | 43717篇 |
免费 | 6643篇 |
国内免费 | 3001篇 |
学科分类
工业技术 | 53361篇 |
出版年
2024年 | 402篇 |
2023年 | 1010篇 |
2022年 | 1990篇 |
2021年 | 2219篇 |
2020年 | 2288篇 |
2019年 | 1756篇 |
2018年 | 1637篇 |
2017年 | 1896篇 |
2016年 | 1995篇 |
2015年 | 2022篇 |
2014年 | 2824篇 |
2013年 | 2696篇 |
2012年 | 3121篇 |
2011年 | 3445篇 |
2010年 | 2553篇 |
2009年 | 2501篇 |
2008年 | 2134篇 |
2007年 | 2470篇 |
2006年 | 2269篇 |
2005年 | 1967篇 |
2004年 | 1613篇 |
2003年 | 1375篇 |
2002年 | 1217篇 |
2001年 | 1027篇 |
2000年 | 896篇 |
1999年 | 766篇 |
1998年 | 559篇 |
1997年 | 435篇 |
1996年 | 416篇 |
1995年 | 349篇 |
1994年 | 273篇 |
1993年 | 232篇 |
1992年 | 169篇 |
1991年 | 170篇 |
1990年 | 136篇 |
1989年 | 102篇 |
1988年 | 66篇 |
1987年 | 55篇 |
1986年 | 44篇 |
1985年 | 31篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1980年 | 28篇 |
1979年 | 9篇 |
1966年 | 10篇 |
1965年 | 7篇 |
1964年 | 17篇 |
1959年 | 12篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
葡北3-12注气井位于吐哈盆地葡北构造带中断葡北1号构造.井深为3610m。针对该区块地层承压能力低,易漏失,油气水窜严重,常规固井方法无法满足固井要求的问题,该井采用三段三凝制、常规水泥浆和泡沫水泥浆体系固井,并采用重钻井液顶替技术.降低施工压力。该技术能保证固井候凝过程中井底压力平衡,施工安全。现场应用表明,采用常规水泥浆和泡沫水泥浆固井技术.提高了低压易漏井、长封固井段的固井质量,解决了水泥返高不足的问题;并通过一次常规固井工艺实现了全井封固,简化了施工工艺,节约了成本,经济效益和社会效益十分显著。该井封固优质段累计达2600m,优质率达85%,固井结果良好。 相似文献
83.
84.
85.
Effect of the absence of lipoxygenase isoenzymes on the storage characteristics of rice grains 总被引:1,自引:0,他引:1
Three varieties of paddy rice with and three varieties without lipoxygenase (LOX) isoenzymes were stored at room temperature, in dark conditions for 42 months. Insect damage and viability were investigated during that time. Varieties without LOX-1,2 and their offspring were screened with a rapid method of estimating LOX isoenzymes, and subjected to an accelerated-ageing experiment. The results indicated that in varieties without LOX-1,2, after long storage, rice quality was normal, but for varieties with LOX-1,2, rice quality deteriorated. With increase of storage time, the germination rate of the seed of most varieties decreased greatly except for varieties without LOX-1,2 where there was almost no change in the germination rate. In varieties without LOX-1,2 and their offspring, after an accelerated ageing experiment the germination rate of some varieties changed slowly, but with others, the germination rate changed quickly. This indicated that a definitive factor, which influenced the life of seeds, may be the loss of LOX-1,2. During storage, there was also a significant difference in the degree of insect damage. In varieties without LOX-3 insect damage was lower, but in varieties with LOX-3 insect damage was higher. Therefore, the absence of LOX-3 may be very important in insect resistance in rice grain. 相似文献
86.
埕岛油田东部斜坡带下第三系油藏以三角洲、浊积扇砂体隐蔽油气藏为主,储层埋藏深、厚度变化大,油气成藏复杂。通过对该带的沉积特征、沉积体系和沉积物源的研究,指出其东下段砂体的分布主要受物源和沉积相带两方面控制,砂体只有在有效圈闭情况下才能成藏,并且从构造上总结了三种油藏类型。最后指出该带下一步勘探重点是沿主物源方向展布的、成藏条件良好的各种砂体。 相似文献
87.
钢纤维聚合物混凝土抗压本构关系 总被引:2,自引:0,他引:2
钢纤维聚合物混凝土是由聚合物混凝土基体和钢纤维共同组成的纤维增强复合材料,它的力学行为不仅依赖于聚合物混凝土基体的行为,而且与钢纤维的掺量、分散特征以及钢纤维的几何尺寸有关,本文将基于损伤力学原理研究在不同纤维掺量下的钢纤维聚合物混凝土的全程压力-应变曲线及其本构模型。 相似文献
88.
An optical nondestructive strain measurement technique was performed to analyze the mechanical deformation induced by an electrical field within the insulating materials. Poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) films were then subjected to constant electrical fields right up to their electrical breakdown. The experimental technique made it possible to follow the various stages of the mechanical behavior of PEN in real time. The final breakdown occurred in the observation zone and the related mechanical deformation was captured. A “margarita” structure was observed with a hole at the center. The experimental results indicated that the level of the induced‐mechanical deformations depended on the local environment. We defined two different zones representing the inside and the outside of the damaged area. The induced‐deformations were larger in the damaged zone. It was also observed that deformations increased when the sample had a lower degree of crystallinity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
89.
Tooru Tanaka Toshiyuki Yamaguchi Akihiro Wakahara Akira Yoshida Ryoichi Taniguchi Yatsuka Matsuda Masatoshi Fujishiro 《Solar Energy Materials & Solar Cells》2003,75(1-2):115-120
Radiation damages due to 8 MeV electron irradiation in electrical properties of CuInSe2 thin films have been investigated. The n-type CuInSe2 films in which the carrier concentration was about 3×1016 cm−3, were epitaxially grown on a GaAs(0 0 1) substrate by RF diode sputtering. No significant change in the electrical properties was observed under the electron fluence <3×1016 e cm−2. As the electron fluence exceeded 1017 e cm−2, both the carrier concentration and Hall mobility slightly decreased. The carrier removal rate was estimated to be about 0.8 cm−1, which is slightly lower than that of III–V compound materials. 相似文献
90.
L. F. Fitzgerald, C. L. Hulin. and F. Drasgow (1995) proposed that victim characteristics, such as race, might moderate the relationships between sexual harassment and its job, psychological, and health status outcomes. This study describes 2 theoretical positions, tokenism and double jeopardy, that could account for this possible moderation by race, as well as the alternative view that no moderating effects exist. The effects of race are empirically examined through simultaneous path analysis. Results indicate that whereas, mean levels of harassment differ across race, the phenomenon of sexual harassment unfolds similarly across races; race is not a moderator of the relationships between sexual harassment and the variables proposed as its antecedents and outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献