全文获取类型
收费全文 | 4148篇 |
免费 | 831篇 |
国内免费 | 661篇 |
专业分类
航空 | 2601篇 |
航天技术 | 1062篇 |
综合类 | 536篇 |
航天 | 1441篇 |
出版年
2024年 | 21篇 |
2023年 | 54篇 |
2022年 | 138篇 |
2021年 | 189篇 |
2020年 | 165篇 |
2019年 | 131篇 |
2018年 | 150篇 |
2017年 | 164篇 |
2016年 | 148篇 |
2015年 | 192篇 |
2014年 | 238篇 |
2013年 | 221篇 |
2012年 | 262篇 |
2011年 | 265篇 |
2010年 | 340篇 |
2009年 | 335篇 |
2008年 | 248篇 |
2007年 | 241篇 |
2006年 | 197篇 |
2005年 | 189篇 |
2004年 | 129篇 |
2003年 | 149篇 |
2002年 | 184篇 |
2001年 | 130篇 |
2000年 | 136篇 |
1999年 | 132篇 |
1998年 | 108篇 |
1997年 | 106篇 |
1996年 | 97篇 |
1995年 | 106篇 |
1994年 | 80篇 |
1993年 | 62篇 |
1992年 | 64篇 |
1991年 | 53篇 |
1990年 | 45篇 |
1989年 | 34篇 |
1988年 | 28篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 21篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有5640条查询结果,搜索用时 15 毫秒
851.
852.
K. Hornung Yu.G. Malama K. Thoma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):77-86
This overview deals with very high impact velocities, where complete vaporization of an impacting cosmic dust particle is to be expected upon expansion from the high pressure high temperature state behind the stopping shock (v > 15 km/s). The topics discussed are the mechanics and thermodynamics of compression, adiabatic release, equation of state and nonequilibrium states upon expansion. The case of very high particle porosity (ρ 1 g/cm3) and the case of very small dust masses (m < 10−17 g) are discussed from what one presently knows. The possibility of three body collisions in the expanding gas phase is discussed briefly. The effect of oblique impact is discussed with respect to its relevance to the ionization process. The numbers communicated are up to the highest “experimental” impact velocities (80 km/s, Halley mission). As one goes to lower impact velocities (20 < v < 30 km/s) there is still complete vaporization of the dust particle but ionization out of the bulk of the particle becomes low. Other than thermal processes may become important. Ideas are outlined to understand their physical nature. 相似文献
853.
多媒体煤矿安全监测管理系统研究 总被引:1,自引:0,他引:1
介绍了现有的煤矿安全监测和安全考勤管理系统的特点及缺陷,探讨了如何将多媒体计算机技术应用于煤矿安全监测管理系统。该系统具有实时监视、紧急救援和事故分析三大特点。 相似文献
854.
保证高校教职工、大学生的身心健康,是高校医院义不容辞的责任.为此,应探索一条更适合高校实际情况的医疗模式.本文就高校医院应如何为师生员工提供全方位的医疗保健服务进行了初步探讨. 相似文献
855.
A N Boyandin T I Lobova L Yu Popova N S Pechurkin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(7):1763-1768
It has been demonstrated that the transgenic microorganism Escherichia coli Z905/pPHL7 (AprLux+) can exist for a long time at an elevated concentration of mineral salts. The microorganism was introduced into microcosms with sterile brackish water (salinity variable from 21 to 22 g l-1) taken from Lake Shira (Khakasia, Russia). The survival of the microorganism was estimated both by measuring the growth of the colonies on solid nutrient media and by the bioluminescence exhibited by the transgenic strain in samples from the microcosms and in the enrichment culture with the added selective factor-ampicillin (50 micrograms/ml). In the enrichment culture, the bioluminescent signal was registered through the 160-day experiment. It has been shown that in the closed microcosms with brackish water the E. coli strain becomes heterogeneous in its ampicillin resistance. The populations of the transgenic strain were mainly represented by isolates able to persist in the medium containing 50 micrograms/ml, but there were also the cells (about 10%) with the threshold of ampicillin resistance not more than 0.05 micrograms/ml. Thus, it was shown that in the microcosms with brackish water and in the absence of the selective factor the transgenic strain survives and retails the recombinant plasmid. 相似文献
856.
857.
E.I. Daibog Yu.I. Logachev S. Kahler K. Kecskemty S. McKenna-Lawlor 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(12):2661-2666
The values of the characteristic decay time of particle fluxes in SEP events vary, as a rule, considerably from event to event. We point out, however, that at times sequences of events having similar decay times were observed over long time intervals (up to one month, and even longer in a few cases). The values of the decay times, however, differed among different sequences. The constancy of the decay phase in each consecutive event of these series suggests that the interplanetary medium was in steady state during the event series, and, because of solar rotation, its uniformity within sectors extended to 90–180° in heliolongitude. The very rarely observed long series (up to 2–3 solar rotations) indicate the steadiness and homogeneity of the plasma and the interplanetary magnetic field (IMF) in the entire inner solar system in the course of this time span. It is pointed out that the neutral current sheet of the IMF does not represent a substantial obstacle for energetic charged particles. Both hemispheres are (above and below the current sheet), at least during the series of solar events, invariant with time, uniform and alike from the viewpoint of the propagation of charged particles. The investigation of such sequences of events can also be useful for forecasting characteristics of SEP events. 相似文献
858.
通过对Linux2.4.20版内核路由模块代码的分析和研究,详尽地阐述了Linux路由机制的实现思想和技术特点,对于更好地使用Linux的路由功能和在Linux路由上进行二次开发都具有实际的指导意义。 相似文献
859.
I. Yu. Skriabysheva 《Cosmic Research》2005,43(6):432-441
The main problems concerning the electric polarization of low-orbit spacecraft are considered, including the results of studying the structure of the Earth's upper ionosphere, the methods of calculating the electrophysical characteristics of construction materials for spacecraft, and the elaboration of recommendations to mitigate the negative effects due to processes of charging and discharging. 相似文献
860.
A Class of TVD Type Combined Numerical Scheme for MHD Equations With a Survey About Numerical Methods in Solar Wind Simulations 总被引:3,自引:0,他引:3
It has been believed that three-dimensional, numerical, magnetohydrodynamic (MHD) modelling must play a crucial role in a
seamless forecasting system. This system refers to space weather originating on the sun; propagation of disturbances through
the solar wind and interplanetary magnetic field (IMF), and thence, transmission into the magnetosphere, ionosphere, and thermosphere.
This role comes as no surprise to numerical modelers that participate in the numerical modelling of atmospheric environments
as well as the meteorological conditions at Earth. Space scientists have paid great attention to operational numerical space
weather prediction models. To this purpose practical progress has been made in the past years. Here first is reviewed the
progress of the numerical methods in solar wind modelling. Then, based on our discussion, a new numerical scheme of total
variation diminishing (TVD) type for magnetohydrodynamic equations in spherical coordinates is proposed by taking into account
convergence, stability and resolution. This new MHD model is established by solving the fluid equations of MHD system with
a modified Lax-Friedrichs scheme and the magnetic induction equations with MacCormack II scheme for the purpose of developing
a combined scheme of quick convergence as well as of TVD property. To verify the validation of the scheme, the propagation
of one-dimensional MHD fast and slow shock problem is discussed with the numerical results conforming to the existing results
obtained by the piece-wise parabolic method (PPM). Finally, some conclusions are made.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献