全文获取类型
收费全文 | 43195篇 |
免费 | 4334篇 |
国内免费 | 3096篇 |
专业分类
电工技术 | 2444篇 |
技术理论 | 1篇 |
综合类 | 3921篇 |
化学工业 | 6594篇 |
金属工艺 | 3310篇 |
机械仪表 | 1947篇 |
建筑科学 | 2814篇 |
矿业工程 | 1924篇 |
能源动力 | 1852篇 |
轻工业 | 3313篇 |
水利工程 | 1190篇 |
石油天然气 | 2497篇 |
武器工业 | 580篇 |
无线电 | 5277篇 |
一般工业技术 | 5026篇 |
冶金工业 | 3000篇 |
原子能技术 | 1074篇 |
自动化技术 | 3861篇 |
出版年
2024年 | 183篇 |
2023年 | 580篇 |
2022年 | 1132篇 |
2021年 | 1380篇 |
2020年 | 1556篇 |
2019年 | 1289篇 |
2018年 | 1311篇 |
2017年 | 1689篇 |
2016年 | 1810篇 |
2015年 | 1832篇 |
2014年 | 2699篇 |
2013年 | 3025篇 |
2012年 | 3324篇 |
2011年 | 3391篇 |
2010年 | 2530篇 |
2009年 | 2478篇 |
2008年 | 2251篇 |
2007年 | 2758篇 |
2006年 | 2335篇 |
2005年 | 2022篇 |
2004年 | 1717篇 |
2003年 | 1483篇 |
2002年 | 1249篇 |
2001年 | 1098篇 |
2000年 | 929篇 |
1999年 | 763篇 |
1998年 | 668篇 |
1997年 | 563篇 |
1996年 | 507篇 |
1995年 | 424篇 |
1994年 | 333篇 |
1993年 | 251篇 |
1992年 | 236篇 |
1991年 | 182篇 |
1990年 | 155篇 |
1989年 | 115篇 |
1988年 | 78篇 |
1987年 | 46篇 |
1986年 | 46篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 22篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1975年 | 10篇 |
1959年 | 8篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness. 相似文献
12.
The effect of biochar substituted for anthracite as reductant on magnetizing-roasting pyrite cinder was investigated.The key of magnetizing-roasting is the gasification reaction between reductants and CO2.Since biochar could react with CO2 more rapidly at lower temperature,the reactivity of biochar is better than that of anthracite.The gasification of biochar could produce reducing condition ofφCO/(φCO+φCO2)about 10%-20% between 700-800 ℃,which is in accord with the atmosphere and temperature of Fe2O3 reduction.So it is beneficial to the reduction of iron mineral of pyrite cinder.Compared with anthracite,biochar could decrease the roasting temperature from825 to 750 ℃ and roasting time from 20 to 15min,which shows that a better effect of magnetization could be obtained in the condition of lower temperature and shorter time.Using biochar as reductant,iron concentrate extracted from pyrite cinder as about 64%iron grade could be produced,and the recovery is over 90% under the condition of above 90% grinding particle less than 0.045 mm and magnetic intensity of 0.124-0.194 T. 相似文献
13.
Fresh and frozen-thawed (F-T) pork meats were classified by Vis–NIR hyperspectral imaging. Eight optimal wavelengths (624, 673, 460, 588, 583, 448, 552 and 609 nm) were selected by successive projections algorithm (SPA). The first three principal components (PCs) obtained by principal component analysis (PCA) accounted for over 99.98% of variance. Gray-level-gradient co-occurrence matrix (GLGCM) was applied to extract 45 textural features from the PC images. The correct classification rate (CCR) was employed to evaluate the performance of the partial least squares-discriminate analysis (PLS-DA) models, by using (A) the reflected spectra at full wavelengths and (B) those at the optimal wavelengths, (C) the extracted textures based on the PC images, and (D) the fused variables combining spectra at the optimal wavelengths and textures. The results showed that the best CCR of 97.73% was achieved by applying (D), confirming the high potential of textures for fresh and F-T meat discrimination. 相似文献
14.
15.
Ben-Jye Chang 《Telecommunication Systems》2006,33(4):333-352
3G Wideband CDMA systems adopt the Orthogonal Variable Spreading Factor code tree as the channelization codes management for
achieving high data rate transmission in personal multimedia communications. It assigns a single channelization code for each
accepted connection. Nevertheless, it wastes the system capacity when the required rate is not powers of two of the basic
rate. One good solution is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long
handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost
of using more number of rake combiners. Especially, long handoff delay may result in more call dropping probability and higher
Grade of Service, which will degrade significantly the utilization and revenue of the 3G cellular systems. Therefore, we propose
herein an adaptive efficient codes determination algorithm based on the Markov Decision Process analysis approach to reduce
the waste rate and reassignments significantly while providing fast handoff. Numerical results demonstrate that the proposed
approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments.
Meanwhile, the optimal number of rake combiners is also analyzed in this paper.
This research was supported in part by the National Science Council of Taiwan, ROC, under contract NSC-93-2213-E-324-018. 相似文献
16.
国产风机盘管空调系统常见问题分析 总被引:2,自引:1,他引:1
分析了国产风机盘管使用中常见的问题,指出机组因风量不足、冷量风量匹配不合理以及风机盘管某些设备故障,导致了风机盘管精度低、舒适性差、能耗高等一系列问题。指出应引起空调设计和运行维护人员的注意。 相似文献
17.
18.
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
19.
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
20.
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