全文获取类型
收费全文 | 67890篇 |
免费 | 6256篇 |
国内免费 | 4482篇 |
专业分类
电工技术 | 6598篇 |
技术理论 | 4篇 |
综合类 | 6065篇 |
化学工业 | 5187篇 |
金属工艺 | 5205篇 |
机械仪表 | 10094篇 |
建筑科学 | 3512篇 |
矿业工程 | 2604篇 |
能源动力 | 1784篇 |
轻工业 | 3651篇 |
水利工程 | 820篇 |
石油天然气 | 1275篇 |
武器工业 | 591篇 |
无线电 | 5225篇 |
一般工业技术 | 7084篇 |
冶金工业 | 2989篇 |
原子能技术 | 478篇 |
自动化技术 | 15462篇 |
出版年
2024年 | 368篇 |
2023年 | 1129篇 |
2022年 | 1881篇 |
2021年 | 2131篇 |
2020年 | 2247篇 |
2019年 | 1914篇 |
2018年 | 1679篇 |
2017年 | 2054篇 |
2016年 | 2307篇 |
2015年 | 2665篇 |
2014年 | 4029篇 |
2013年 | 3780篇 |
2012年 | 4621篇 |
2011年 | 5244篇 |
2010年 | 3802篇 |
2009年 | 3867篇 |
2008年 | 3726篇 |
2007年 | 4544篇 |
2006年 | 4299篇 |
2005年 | 3671篇 |
2004年 | 3060篇 |
2003年 | 2648篇 |
2002年 | 2293篇 |
2001年 | 1877篇 |
2000年 | 1590篇 |
1999年 | 1330篇 |
1998年 | 1000篇 |
1997年 | 888篇 |
1996年 | 735篇 |
1995年 | 644篇 |
1994年 | 560篇 |
1993年 | 429篇 |
1992年 | 338篇 |
1991年 | 241篇 |
1990年 | 224篇 |
1989年 | 177篇 |
1988年 | 154篇 |
1987年 | 69篇 |
1986年 | 71篇 |
1985年 | 37篇 |
1984年 | 47篇 |
1983年 | 41篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1974年 | 8篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
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
42.
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
43.
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
44.
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
45.
46.
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
47.
N. N. Radaev A. D. Daragan A. M. Agapov S. P. Voronov D. V. Klopov 《Measurement Techniques》2005,48(3):211-214
Neuronets are considered for processing data on the state of a potentially hazardous object after an emergency. An example is given of processing the data on the state of a potentially hazardous object in increments.Translated from Izmeritel’naya Tekhnika, No. 3, pp. 6–8, March, 2005. 相似文献
48.
水生生物环境诊断(AOD)技术应用研究 总被引:4,自引:0,他引:4
介绍一种新型的毒性试验方法——水生生物环境诊断(AOD)技术,该方法将冷冻浓缩和生物测试技术有机地相结合,较好地解决了低毒性水体的毒性测试问题。应用本项技术以红鳍鱼为受试生物,分别对湖北武汉马伧湖、墨水湖、广东深圳河、长江干流寸滩等几个断面、丹江口水库白河、丹江河口、老灌河等不同水体进行AOD测试,所得48hr-LC\-50结果与实际水质状况基本相符。 相似文献
49.
50.
The application of the eXtended finite element method (X-FEM) to thermal problems with moving heat sources and phase boundaries
is presented. Of particular interest is the ability of the method to capture the highly localized, transient solution in the
vicinity of a heat source or material interface. This is effected through the use of a time-dependent basis formed from the
union of traditional shape functions with a set of evolving enrichment functions. The enrichment is constructed through the
partition of unity framework, so that the system of equations remains sparse and the resulting approximation is conforming.
In this manner, local solutions and arbitrary discontinuities that cannot be represented by the standard shape functions are
captured with the enrichment functions. A standard time-projection algorithm is employed to account for the time-dependence
of the enrichment, and an iterative strategy is adopted to satisfy local interface conditions. The separation of the approximation
into classical shape functions that remain fixed in time and the evolving enrichment leads to a very efficient solution strategy.
The robustness and utility of the method is demonstrated with several benchmark problems involving moving heat sources and
phase transformations.
Received 20 May 2001 / Accepted 19 December 2001 相似文献