全文获取类型
收费全文 | 51399篇 |
免费 | 6412篇 |
国内免费 | 3701篇 |
专业分类
电工技术 | 5531篇 |
技术理论 | 9篇 |
综合类 | 6475篇 |
化学工业 | 5901篇 |
金属工艺 | 1189篇 |
机械仪表 | 2141篇 |
建筑科学 | 4961篇 |
矿业工程 | 3082篇 |
能源动力 | 1674篇 |
轻工业 | 4614篇 |
水利工程 | 2790篇 |
石油天然气 | 2416篇 |
武器工业 | 571篇 |
无线电 | 4535篇 |
一般工业技术 | 4251篇 |
冶金工业 | 2260篇 |
原子能技术 | 381篇 |
自动化技术 | 8731篇 |
出版年
2024年 | 300篇 |
2023年 | 851篇 |
2022年 | 1454篇 |
2021年 | 1776篇 |
2020年 | 2021篇 |
2019年 | 1802篇 |
2018年 | 1615篇 |
2017年 | 1908篇 |
2016年 | 2121篇 |
2015年 | 2133篇 |
2014年 | 3378篇 |
2013年 | 3293篇 |
2012年 | 3788篇 |
2011年 | 4031篇 |
2010年 | 2937篇 |
2009年 | 2782篇 |
2008年 | 2797篇 |
2007年 | 3209篇 |
2006年 | 3112篇 |
2005年 | 2569篇 |
2004年 | 2159篇 |
2003年 | 1843篇 |
2002年 | 1563篇 |
2001年 | 1277篇 |
2000年 | 1146篇 |
1999年 | 1049篇 |
1998年 | 730篇 |
1997年 | 665篇 |
1996年 | 577篇 |
1995年 | 494篇 |
1994年 | 453篇 |
1993年 | 366篇 |
1992年 | 266篇 |
1991年 | 216篇 |
1990年 | 187篇 |
1989年 | 123篇 |
1988年 | 111篇 |
1987年 | 55篇 |
1986年 | 60篇 |
1985年 | 31篇 |
1984年 | 47篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1959年 | 11篇 |
1958年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
51.
简并量子拍频三能级系统中的光场压缩效应 总被引:10,自引:1,他引:9
本文讨论了V-型简并量子拍频三能级原子与单模相干辐射场相互作用时的动力学行为,并研究了光场的压缩效应。 相似文献
52.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a. 相似文献
53.
通过引入归一化脉宽P和相对脉冲展宽因子q,提出了一个适用于IM/DD系统中各种眼图恶化量x和归一化脉宽P的色散限制改进公式。通过与其它理论的比较、计算机仿真和对实验数据的分析,验证了该公式的正确性,并给出了其它结果的限制条件。研究表明:当眼图恶化量x为1dB左右时,对2.5Gb/;外调制信号(α=0)而言,非色散位移光纤IM/DD系统的色散因子γ约等于0.79,所对应的系统再生中继距离约为900余公里。 相似文献
54.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors. 相似文献
55.
Francis E. Powell Brian W. Brooks 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1993,57(1):65-71
Dimensionless material balance equations describing an uninhibited enzyme hydrolysis process in a semi-batch reactor (i.e. fed-batch reactor) are formulated; numerical solution of these equations provided concentration profiles of the enzyme-substrate complex by using published kinetic parameters. The unrestricted values obtained are compared with estimates based separately on the reaction steady state and stationary state assumptions. Results are discussed in terms of the enzyme/substrate inventory used and it is found that the reaction steady state is a satisfactory approximation only when this ratio is sufficiently small. The stationary state may be a better approximation at other values, particularly when enzyme is added to substrate or when an empty tank is being filled. Reaction yields from semi-batch and batch operations are compared. Processing takes longer in the semi-batch operations and complete conversions are only practical in this mode when enzyme is added to substrate. 相似文献
56.
Sensitivity analysis is used to show how uncertainties in basic factors, such as heat transfer, pressure drop, compressor efficiency, and thermophysical properties, influence the result of heat pump cycle performance estimations. By comparing the results of this analysis with uncertainty levels of estimations and experimental determinations, it is established to what extent improvements in accuracy are needed. The investigation was carried out for several different applications and, as working fluids, both pure substances and non-azeotropic mixtures were examined. It was found that evaporation heat transfer and compressor efficiency are two areas where improvements are needed. It is also shown that estimates using very accurate, substance-specific, equations of state differ from those using more general types by up to 1 % for COP and 2% for capacity. 相似文献
57.
58.
59.
三江平原是我国重要的商品粮基地和粮食战略后备基地。原有规划距今已过30年,远不能适应现代发展要求。结合新的形势,提出了重新编制三江平原综合规划的现实意义、目标设想及主要修编内容。 相似文献
60.
针对当前国内长途传输光缆系统在扩容过程中,因光信号色散而影响传输质量的现象,结合实际工程建设,分析了光信号色散的危害及其成因,并提出了相应的解决办法及建议。 相似文献