全文获取类型
收费全文 | 43984篇 |
免费 | 4446篇 |
国内免费 | 2917篇 |
专业分类
电工技术 | 3099篇 |
技术理论 | 1篇 |
综合类 | 4019篇 |
化学工业 | 6577篇 |
金属工艺 | 3172篇 |
机械仪表 | 2011篇 |
建筑科学 | 3048篇 |
矿业工程 | 1973篇 |
能源动力 | 1981篇 |
轻工业 | 3443篇 |
水利工程 | 1243篇 |
石油天然气 | 2708篇 |
武器工业 | 591篇 |
无线电 | 4378篇 |
一般工业技术 | 4601篇 |
冶金工业 | 3029篇 |
原子能技术 | 1110篇 |
自动化技术 | 4363篇 |
出版年
2024年 | 171篇 |
2023年 | 578篇 |
2022年 | 1130篇 |
2021年 | 1387篇 |
2020年 | 1559篇 |
2019年 | 1300篇 |
2018年 | 1299篇 |
2017年 | 1680篇 |
2016年 | 1838篇 |
2015年 | 1858篇 |
2014年 | 2741篇 |
2013年 | 3086篇 |
2012年 | 3338篇 |
2011年 | 3424篇 |
2010年 | 2540篇 |
2009年 | 2483篇 |
2008年 | 2235篇 |
2007年 | 2758篇 |
2006年 | 2339篇 |
2005年 | 2072篇 |
2004年 | 1820篇 |
2003年 | 1557篇 |
2002年 | 1309篇 |
2001年 | 1109篇 |
2000年 | 950篇 |
1999年 | 797篇 |
1998年 | 713篇 |
1997年 | 600篇 |
1996年 | 541篇 |
1995年 | 454篇 |
1994年 | 341篇 |
1993年 | 255篇 |
1992年 | 230篇 |
1991年 | 183篇 |
1990年 | 159篇 |
1989年 | 113篇 |
1988年 | 86篇 |
1987年 | 52篇 |
1986年 | 50篇 |
1985年 | 45篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 10篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
榆树林油田砂岩储层敏感性研究 总被引:16,自引:10,他引:6
榆树林油田储层粘土矿物含量较高,各种注入条件和施工条件都会对该储层造成相应的伤害,应采取相应的防护措施,为防止速敏的发生,储层的注水速度应控制在临界流速(1.0mL/min)以下,在油井转注时,可先注入1.09PV的含粘土稳定剂的进行处理,以提高产量或注入量,注入阴离子表面活性剂配置的活性水再注入地层水,不能增加地层水的渗透率,该项试验研究对指导榆树林油田的开发具有重要的意义。 相似文献
103.
提高大直径井眼机械钻速的几项措施 总被引:1,自引:0,他引:1
随着我国西部地区石油勘探开发的进展,5000-7000m的深探井所钻数量不断增多,套管程序增加,特别是大尺寸井眼所钻深度明显加大。由于国产大尺寸钻头结构单一、型号少,破岩机械能量和水力能量不足,在易斜井段目前尚无可靠的防斜保直措施,以及钻井液性能不适宜等原因,大尺寸井眼的钻这远远低于215.9mm井眼的钻速。据此,提出了几项可以提高大尺寸井眼钻速的措施:增加大尺寸钻头的种类,采用阶梯式扩眼钻头,强化钻井参数和水力参数,选用中速动力钻具,改善钻井液性能以及采用冲击旋转钻具等。 相似文献
104.
105.
从理论上探讨了磁阻率效应,叙述了精密角位移传感器的工作原理及结构设计。传感器的分辨率已达0.01°,通过可靠性寿命试验,传感器的失效率λ(t)<1×10-7/h。 相似文献
106.
Directional solidification studies of gelatinized corn starch-water mixtures were undertaken in order to examine, in situ, the freezing behavior of this food model. The solidification rate was controlled by varying sample cell velocity as it moved from a 25°C hot stage to a -25°C cold stage. While freezing at cell velocities ≤7.5 μm/sec, starch granules were alternately pushed or entrapped by the advancing solid-liquid interface producing a segregated structure consisting of alternating high-starch and low-starch bands. At a cell velocity of 10 μm/sec, the frozen product was homogeneous. The relationship between the solid-liquid interface velocity and segregation behavior was quantified and compared to an existing model of particle-interface interactions. 相似文献
107.
108.
介绍了用于油田开采工艺的膜片式流量调节阀的结构及其特点,分析了调节阀出口压力、进口压力对其流量的影响。受力分析和现场使用表明:该阀流量恒定精度(即恒流偏差)取决于膜片有效面积S与阀心下端有效面积S′之比,此值为12,其恒流比偏差为0·03,说明该阀的流量恒定精度高;该阀不易被杂质卡死,稀油中直径1mm的砂粒能顺利通过,而不影响阀的功能;膜片式流量调节阀是没有高加工精度要求的部件,普通车床即可生产,因此造价较低。 相似文献
109.
Claus Bahlmann Author Vitae 《Pattern recognition》2006,39(1):115-125
The selection of valuable features is crucial in pattern recognition. In this paper we deal with the issue that part of features originate from directional instead of common linear data. Both for directional and linear data a theory for a statistical modeling exists. However, none of these theories gives an integrated solution to problems, where linear and directional variables are to be combined in a single, multivariate probability density function. We describe a general approach for a unified statistical modeling, given the constraint that variances of the circular variables are small. The method is practically evaluated in the context of our online handwriting recognition system frog on hand and the so-called tangent slope angle feature. Recognition results are compared with two alternative modeling approaches. The proposed solution gives significant improvements in recognition accuracy, computational speed and memory requirements. 相似文献
110.
Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout 总被引:3,自引:0,他引:3
Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies. 相似文献