首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2502篇
  免费   236篇
  国内免费   109篇
电工技术   71篇
综合类   153篇
化学工业   839篇
金属工艺   288篇
机械仪表   51篇
建筑科学   130篇
矿业工程   52篇
能源动力   144篇
轻工业   277篇
水利工程   14篇
石油天然气   67篇
武器工业   5篇
无线电   122篇
一般工业技术   233篇
冶金工业   229篇
原子能技术   21篇
自动化技术   151篇
  2023年   32篇
  2022年   87篇
  2021年   108篇
  2020年   107篇
  2019年   72篇
  2018年   81篇
  2017年   74篇
  2016年   81篇
  2015年   93篇
  2014年   153篇
  2013年   165篇
  2012年   165篇
  2011年   168篇
  2010年   113篇
  2009年   136篇
  2008年   120篇
  2007年   136篇
  2006年   163篇
  2005年   125篇
  2004年   114篇
  2003年   92篇
  2002年   76篇
  2001年   73篇
  2000年   51篇
  1999年   46篇
  1998年   36篇
  1997年   28篇
  1996年   34篇
  1995年   26篇
  1994年   19篇
  1993年   12篇
  1992年   17篇
  1991年   8篇
  1990年   5篇
  1989年   7篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1983年   3篇
  1982年   2篇
  1981年   2篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1975年   1篇
排序方式: 共有2847条查询结果,搜索用时 15 毫秒
1.
5G系统中,邻区的合理性、准确性、及时性等将直接影响整个5G网络的性能,也是5G网络优化的基础工作。传统的人工邻区指令的制作与下发,耗时耗力,为提升5G邻区添加效率,开展本项研究。本案依托基站集中入网流程,开发一套精准的邻区指令自动化系统,在5G新开通站点开通入网后,自动化采集规划、资管数据,对接网管系统,完成邻区指令数据制作并予以执行,实现了5G邻区指令全流程的自动化,有效提高优化工作效率,降低运营成本。  相似文献   
2.
A meso-scale jet flame model was established for the flame ports of domestic gas stoves. The influences of hydrogen addition ratio (β = 0%–25%) on the combustion limits were explored. The results show that with the increase of hydrogen addition ratio, the blow-off limit increases obviously, while the extinction limit decreases slightly, namely, the combustible range expands significantly. Quantitative analysis was carried out in terms of chemical effect and thermal effect. It was found that hydrogen addition will reduce O2 fraction in the pre-mixture for a constant equivalence ratio. Under near-extinction limit condition, since the flame is located at the nozzle exit, the external O2 cannot be entrained into or diffuse into the upstream of the flame, which leads to the decrease of reaction rate. However, for the near-blow-off cases, the external O2 can be entrained and diffuse into the flame, which compensates the difference of O2 content in the pre-mixture. Therefore, the combustion reaction is enhanced by hydrogen addition because more H radicals can be produced. In addition, as the flame is located closer to the tube with the increase of hydrogen addition ratio, heat transfer between flame and tube wall is augmented and the preheating of fresh mixture is strengthened by the inner tube wall. This heat recirculation effect becomes especially notable in low velocity cases. In conclusion, the extension of extinction limit by hydrogen addition is attributed to the thermal effect, while the increase of blow-off limit is mainly due to the intensification of chemical effect.  相似文献   
3.
4.
建立了超高效液相色谱-四极杆-飞行时间质谱(UPLC-Q-TOF/MS)快速筛查畜禽类产品中50种违禁药物残留的检测方法。畜禽类产品经β-葡萄糖醛酸酶/芳基硫酸酯酶酶解,依次用乙酸乙酯-叔丁基甲醚提取后,利用HLB净化,采用UPLC-Q-TOF/MS电喷雾正离子模式检测。通过建立在线谱库检索的方法实现50种违禁药物的快速筛选和准确定性,再结合同位素内标法实现准确定量。目标物质量浓度在2~200 μg/L范围内线性关系良好,相关系数均大于0.99,检出限为0.1~0.5 μg/kg,定量限为0.3~1.5 μg/kg,三个不同浓度的加标回收率在81.74%~114.22%之间,相对标准偏差为1.41%~8.91%。研究建立的筛查数据库在无需标准品的情况下实现了50种违禁药物的快速筛查、定性确证和定量分析。该方法适用于畜禽类产品中低浓度的违禁药物残留量的快速筛查和准确定量。  相似文献   
5.
PurposeThe purpose of this study was to compare sign identification distances and driving performance metrics in presbyopic participants while wearing multifocal contact lenses (MFCL) and while wearing progressive addition lens (PAL) spectacles.Methods19 presbyopic participants completed PAL spectacle assessments and contact lens fitting and follow up visits before driving assessments began. These assessments occurred in a simulator equipped with a full-sized sedan on a motion platform and a 260 degree screen. Participants completed the driving task with PAL and with MFCL. Participants followed a lead car and identified signs at various distances from the road. For the two wearing conditions, comparisons of the distance along the road at which signs were identified were made using repeated measures ANOVA. Paired t-tests were used to compare driving performance for the two conditions.ResultsThere was no statistical difference in sign identification distance between PAL and MFLC for signs 32.0 m from the road side of the road (182 ± 46 m for MFCL; 205 ± 45 m for PAL; P = 0.07) or 51.4 m from the side of the road (204 ± 43 m for MFCL; 216 ± 36 m for PAL; P = 0.3). Only signs 70.2 m from the roadside showed a significant difference (207 ± 42 m with MFCL; 232 ± 39 m with PAL; P = 0.01), All distances were greater than those required to safely stop a vehicle. There were no significant differences in the driving performance metrics between the refractive corrections.ConclusionDriving performance metrics were similar for MFCL and PAL spectacles. Sign identification distances with both eyewear types were well within the distances required for safe vehicle stopping.  相似文献   
6.
采用安琪小曲复配不同比例浓香型大曲酿酒,探究浓香型大曲对小曲酒出酒率、主要风味物质及酒醅微生物群落的影响。结果表明,与纯安琪小曲酿酒比较,大曲添加量为5%时,出酒率提高4.23%;大曲添加量为20%时,所产基酒感官品质最佳,异丁醇及异戊醇含量分别降低0.44 g/L、0.40 g/L;大曲添加量为10%时,基酒中乙酸乙酯及乳酸乙酯含量分别增加0.78 g/L、0.04 g/L;大曲添加使酒醅微生物群落多样性增加,且不同大曲添加量使酒醅优势菌群与丰度发生了不同程度的变化,说明浓香型大曲的添加能提升安琪小曲酒产品质量。相关性分析表明,不动杆菌属(Acinetobacter)与乳酸杆菌属(Lactobacillus)、伊萨酵母属(Issatchenkia)与根霉属(Rhizopus)间呈显著负相关(P<0.05),出酒率及乳酸乙酯含量与伊萨酵母属相对丰度呈显著正相关(P<0.05),乳酸乙酯含量与根霉属相对丰度呈显著负相关(P<0.05)。  相似文献   
7.
A simplified low-cost approach to experimentally determine transport parameters in mountain rivers is described, with an emphasis on the longitudinal dispersion coefficient (DL). The approach is based on a slug injection of table salt (NaCl) as a tracer and specific conductance readings at different locations downstream of the injection spot. Observed specific conductance readings are fit using the advection-dispersion equation with OTIS-P, yielding estimates of cross-sectional area and longitudinal dispersion coefficient for various stream reaches. Estimates of the DL are used to assess the accuracy of several empirical equations reported in the literature. This allowed the determination of complementary transport parameters related to transient storage zones. The empirical equations yielded rather high DL values, with some reaching up an order of magnitude higher to those obtained from tracer additions and OTIS-P. Overall, the proposed approach seems reliable and pertinent for river reaches of ca. 150 m in length.  相似文献   
8.
镍电解液的复杂高盐基体对其中微量铜的监测产生干扰。将旋转圆盘电极原子发射光谱(RDE-AES)与标准加入法结合,无需样品前后处理,无基体效应,采用改进后的校准曲线测定镍电解液工艺流程中不同中间液中的微量铜。根据元素蒸发曲线,确定预燃时间6 s、采集时间7~30 s,预燃激发改善了盘电极的润湿性,从而保证进样量的稳定性;合理的曝光时间可以在保证分析元素强度灵敏度的前提下提高分析速度,单次检测时间小于35 s。选用Ni 324.845 7 nm为内标,校正激发行为和进样量误差。方法检出限为0.15 mg/L。按照实验方法测定镍电解液工艺流程中不同中间液中微量铜,结果的相对标准偏差(RSD,n=6)小于12%,加标回收率为98%~110%。  相似文献   
9.
A hybrid polymer matrix composite coating, resistant to solid particle erosion inside sharp elbows, consisting interlocking chains of molecules with the ability to deflect the surface impact stress and to uniformly distribute stresses along the hard-ceramic reinforcement mixture surface was developed. Formulated mixture of ceramic reinforcement particles mixtures (alumina, tungsten carbide, and silicon carbide) with polymer coupling agents; to increase adhesion to the metal surface, led to 600–700 HVN in ternary and 500–550 HVN in binary mixtures. This behavior coincides with high shear strength of 70–76 MPa, Young's and shear modulus of 8.86 and 13.4 GPa in ternary 15%Al2O3-5%WC-10%SiC, respectively. The low erosion weight loss of 0.1% and small coefficient of friction near 0.18 indicates the significant wear resistance of the ternary sample. The electron microscopic micrographs determined the dense smooth coating surfaces with adhesive interfaces with the substrate.  相似文献   
10.
针对协同消毒工艺在水厂实际应用中存在的问题和难点,通过对水厂协同消毒工艺的控制进行升级改造及模拟实验,研究了传统控制与智慧控制协同消毒在多种因素影响下的实验结果。相较传统控制,智慧控制协同消毒可将消毒剂控制指标精度提高72%左右、消毒剂投加量减少16%左右、消毒副产物的生成量减少22%左右。在水厂协同消毒应用中智慧控制较传统控制具有更好的控制效果及推广价值。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号