全文获取类型
收费全文 | 121534篇 |
免费 | 12648篇 |
国内免费 | 8719篇 |
专业分类
电工技术 | 11149篇 |
技术理论 | 1篇 |
综合类 | 12919篇 |
化学工业 | 16501篇 |
金属工艺 | 5967篇 |
机械仪表 | 5378篇 |
建筑科学 | 12318篇 |
矿业工程 | 6056篇 |
能源动力 | 4424篇 |
轻工业 | 10516篇 |
水利工程 | 4760篇 |
石油天然气 | 5351篇 |
武器工业 | 1378篇 |
无线电 | 10249篇 |
一般工业技术 | 11220篇 |
冶金工业 | 5781篇 |
原子能技术 | 1689篇 |
自动化技术 | 17244篇 |
出版年
2024年 | 563篇 |
2023年 | 1790篇 |
2022年 | 3055篇 |
2021年 | 3595篇 |
2020年 | 4045篇 |
2019年 | 3640篇 |
2018年 | 3524篇 |
2017年 | 4216篇 |
2016年 | 4605篇 |
2015年 | 4852篇 |
2014年 | 7197篇 |
2013年 | 7734篇 |
2012年 | 8531篇 |
2011年 | 9252篇 |
2010年 | 6873篇 |
2009年 | 7532篇 |
2008年 | 6813篇 |
2007年 | 8259篇 |
2006年 | 7138篇 |
2005年 | 6264篇 |
2004年 | 5312篇 |
2003年 | 4532篇 |
2002年 | 3745篇 |
2001年 | 3287篇 |
2000年 | 2777篇 |
1999年 | 2448篇 |
1998年 | 1935篇 |
1997年 | 1702篇 |
1996年 | 1482篇 |
1995年 | 1241篇 |
1994年 | 1013篇 |
1993年 | 804篇 |
1992年 | 745篇 |
1991年 | 531篇 |
1990年 | 388篇 |
1989年 | 336篇 |
1988年 | 222篇 |
1987年 | 185篇 |
1986年 | 125篇 |
1985年 | 90篇 |
1984年 | 116篇 |
1983年 | 76篇 |
1982年 | 66篇 |
1981年 | 42篇 |
1980年 | 53篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1975年 | 15篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
叙述了二代近贴聚焦像增强器批量生产所用真空设备性能及特点,同时给出了管子工艺考核结果及管子纳秒时间响应特性。工艺考核结果表明,制管工艺可靠、性能稳定,管子批量生产合格率大于70%。 相似文献
92.
The planimetric shifts in channel location of large alluvial rivers are a critical component in the creation of diverse structures and functions in riverine habitats. Engineered management schemes must also compensate for this type of channel change to protect resources and maintain navigation channels. The stability of the Lower Mississippi River channel was assessed through an analysis of historical records of channel position produced and archived by the United States Army Corps of Engineers. Channel location was recorded for the years 1765, 1820, 1881, 1915, 1930, 1937, 1960 and 1970. Channel stability was measured by two introduced metrics on a cell‐by‐cell basis: (1) the standard deviation of Euclidean distance to a channel cell for the entire period of record, and (2) the rate of Euclidean distance change between years in the period of record. At a coarse spatial scale, channel instability increased in the downstream direction. The variability of channel stability also increased in the downstream direction. Analysis of this variability identified alternating areas of high and low stability occurring with greater frequency as distance downstream increased. These findings are validated by past studies of channel stability along the Lower Mississippi River. As a result, the proposed metrics provide a consistent, quantitative, efficient and cost‐effective means of identifying areas of channel instability at several spatial scales. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
93.
文章分析了影响地震采集系统延迟时间的因素,并根据系统延迟的理论对产生的原因进行了论证.同时对实际生产中的测试方法进行了阐述研究和分析,提出了新的测试方法,并结合实际生产提出了合理性建议. 相似文献
94.
This article addresses the computation of invariant control laws [A. Fradkov, I. Miroshnik, V. Nikiforov, Nonlinear and Adaptive Control of Complex Systems, Kluwer, 1999] for fed-batch fermenters represented by two standard models. It will be shown how to derive partial state feedbacks that, assuming ideal conditions and perfect model, keep the specific growth rate μ constant provided the initial conditions are adequate. The invariant control law is the closed loop version of the exponential feeding already suggested in several references as shown later. The paper presents an analysis of invariance and a study of global stability within the framework of partial stability. That is, stability with respect to some of the state variables. This enables us to treat the case with Haldane-like or non-monotonous kinetics. 相似文献
95.
This paper describes the implementation of a stereo-vision system using Field Programmable Gate Arrays (FPGAs). Reconfigurable hardware, including FPGAs, is an attractive platform for implementing vision algorithms due to its ability to exploit parallelism often found in these algorithms, and due to the speed with which applications can be developed as compared to hardware. The system outputs 8-bit, subpixel disparity estimates for 256× 360 pixel images at 30,fps. A local-weighted phase correlation algorithm for stereo disparity [Fleet, D. J.: {Int. Conf. Syst. Man Cybernetics 1:48–54 (1994)] is implemented. Despite the complexity of performing correlations on multiscale, multiorientation phase data, the system runs as much as 300 times faster in hardware than its software implementation. This paper describes the hardware platform used, the algorithm, and the issues encountered during its hardware implementation. Of particular interest is the implementation of multiscale, steerable filters, which are widely used in computer vision algorithms. Several trade-offs (reducing the number of filter orientations from three to two, using fixed-point computation, changing the location of one localized low-pass filter, and using L1 instead of L2 norms) were required to both fit the design into the available hardware and to achieve video-rate processing. Finally, results from the system are given both for synthetic data sets as well as several standard stereo-pair test images. 相似文献
96.
N-油酰基肌氨酸钠对除盐水缓蚀性能的探讨 总被引:1,自引:0,他引:1
梁劲翌 《石油化工腐蚀与防护》2006,23(1):17-20
对N-油酰基肌氨酸钠单体的缓蚀性能以及与常用除盐水缓蚀剂的协同作用作了探讨,发现在一定浓度下,单体对经过加氨调节后的高温除盐水(氨后除盐水)有良好的缓蚀作用,且与大多数除盐水缓蚀剂有良好的协同效应。在此基础上研制了一种复合药剂,并对其缓蚀、阻蚀性能作了研究。动电位极化曲线扫描图谱表明,该复合药剂属于抑制阳极腐蚀的阳极型缓蚀剂,其适用的水质条件为[Cl~-+SO_4~(2-)]不超过50 mg/L,pH不低于8.0;与阻垢剂复配,可以适用于含Ca~(2+)不超过45 mg/L的水质条件。 相似文献
97.
IEEE 802.11g性能分析及应用 总被引:1,自引:1,他引:0
全面介绍IEEE802.11g标准的无线局域网,详细讲述IEEE802.11g草案标准的概念、产生背景、特点、构件及其体系结构和发展前景,探讨实现IEEE802.11gWLAN所需的关键技术及其双频多模应用方式,同时分析IEEE802.11g标准的网络性能。 相似文献
98.
Cs-K混合蒸气中Cs(8D)+K(4S)碰撞能量转移 总被引:3,自引:3,他引:0
在Cs-K混合蒸气中,两步激发Cs原子到8D态,观察了Cs(8D) K(4S)→Cs(5D) K(4P)碰撞能量合并逆过程(REP,reverse energy pooling)。应用双调制技术探测K(4P)原子发射的荧光,基态K原子密度用光学吸收方法测量。得到了REP速率系数,讨论了其它过程对速率系数的影响. 相似文献
99.
100.
吐哈油田部分区块地层压力系数小于0.9,常规水基压井液对储层伤害大,若使用油基压井液成本高,环境污染严重。通过实验优选出了一种低密度水基微泡沫压井液。该压井液具有密度低、泡沫强度高、稳定性好、携砂能力强等优点。现场应用表明,低密度微泡沫压井液稳定时间大于48 h,密度在0.70~0.99 g/cm3之间可调,抗油污染能力强,抗油大于8%,抗温在100℃以上,岩心污染后渗透率恢复值大于80%;并且施工方便,成本低,具有储层保护能力,使用微泡沫压井液的井表皮系数在0.20~2.34之间。 相似文献