全文获取类型
收费全文 | 10124篇 |
免费 | 991篇 |
国内免费 | 1277篇 |
专业分类
航空 | 5423篇 |
航天技术 | 3140篇 |
综合类 | 1244篇 |
航天 | 2585篇 |
出版年
2022年 | 102篇 |
2021年 | 102篇 |
2020年 | 146篇 |
2019年 | 69篇 |
2018年 | 133篇 |
2017年 | 128篇 |
2016年 | 99篇 |
2015年 | 210篇 |
2014年 | 410篇 |
2013年 | 469篇 |
2012年 | 472篇 |
2011年 | 578篇 |
2010年 | 634篇 |
2009年 | 673篇 |
2008年 | 674篇 |
2007年 | 565篇 |
2006年 | 481篇 |
2005年 | 435篇 |
2004年 | 301篇 |
2003年 | 288篇 |
2002年 | 256篇 |
2001年 | 342篇 |
2000年 | 343篇 |
1999年 | 453篇 |
1998年 | 436篇 |
1997年 | 363篇 |
1996年 | 361篇 |
1995年 | 310篇 |
1994年 | 318篇 |
1993年 | 260篇 |
1992年 | 252篇 |
1991年 | 176篇 |
1990年 | 168篇 |
1989年 | 177篇 |
1988年 | 115篇 |
1987年 | 98篇 |
1986年 | 69篇 |
1985年 | 143篇 |
1984年 | 96篇 |
1983年 | 87篇 |
1982年 | 71篇 |
1981年 | 119篇 |
1980年 | 28篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 26篇 |
1976年 | 24篇 |
1975年 | 40篇 |
1972年 | 34篇 |
1971年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
本文结合多年教学实践,对激发学生的创造意识,培养发散思维,运用创造技法等方面进行了探索。 相似文献
52.
介绍自行研制的VKM—5型立式捏合机的构造及工作原理,详述了该机采用液压传动和气动元件进行位置检测以及气、电、液安全联锁的特点,并说明与卧式捏合机对比试验情况。 相似文献
53.
R L Mancinelli J R Marshall M R White 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(4):111-116
Potential Martian soil components relevant to exobiology include water, organic matter, evaporites, clays, and oxides. These materials are also resources for human expeditions to Mars. When found in particular combinations, some of these materials constitute diagnostic paleobiomarker suites, allowing insight to be gained into the probability of life originating on Mars. Critically important to exobiology is the method of data analysis and data interpretation. To that end we are investigating methods of analysis of potential biomarker and paleobiomarker compounds and resource materials in soils and rocks pertinent to Martian geology. Differential thermal analysis coupled with gas chromatography is shown to be a highly useful analytical technique for detecting this wide and complex variety of materials. 相似文献
54.
了微动同步器结构原理,用数学方法找出了温度对其标度因数产生影响的主要原因,温度对激磁线圈的铜阻有影响,从而最终将影响输出电压的大小,针对这一主要原因,采用NTC物理方法进行补偿,取得了很好的实际效果。 相似文献
55.
L. B. F. M. Waters 《Space Science Reviews》1992,61(1-2):25-43
In this review the IR emission from circumstellar material is discussed, both of ionized gas and dust grains, and the astrophysical information that can be extracted from such observations. Some emphasis is placed on the possibilities of stellar IR astronomy using a large space-borne telescope, especially with respect to the much better spatial and spectral resolution of such a telescope compared to the current generation of ground-based and space IR telescopes. 相似文献
56.
57.
L.B. Tsirulnik T.V. Kuznetsova V.N. Oraevsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2369-2372
A new method of nonlinear spectral analysis (called the method of global minimum: MGM), based on the best presentation (in sense of minimal squares) of a given time data set as a sum of sinusoids whose frequencies, amplitudes and phases are to be determined, has been used to find periodicities in annual Wolf sunspot numbers (W) during the period 1700–1995. The possible future behaviour of the 11-year solar cycle (based on an extrapolation of the calculated model) is also presented. The main characteristics of the 23rd solar cycle are as follows: the W maximum occurs about 2004, with a peak of nearly 220. An unusually large value of W will occur during the 23rd cycle, which should be characterised by the longest maximum, specifically, W will be greater than 100 during the 11-year period from 1997 to 2007. The first sharp rise will occur during the period 1996–1998, the second sharp during 2002–2004. The main features of the 24 year cycle are as follows: the next minimum in W, associated with the 24th solar cycle, should occur in the year 2008 and the maximum in 2014. W is expected to peak at about 180. The minimum value for the 25th year cycle is expected to occur in the year 2019. It is shown that the accuracy of these predictions depends, first of all, on the extrapolation of the hyperlong harmonic of the calculated polyharmonic model fit of observed annual sunspot numbers during the period 1700–1995. The error bars in the definition of the maximum and minimum epochs can be as large as two years. 相似文献
58.
本文是近年来在微波聚焦热疗人体深部癌病灶研究工作推动下完成的。文中给出了光学及电磁学界感兴趣的某些结果。在人体分层媒质前的一有限口径处,置一时谐电流分布,在每一分层内的微波传输场及反射场可利用传输矩阵及并矢格林函数给出计算结果。 相似文献
59.
Eagle-Picher Energy Products (EPEP) has been manufacturing and testing large lithium ion cells (up to 100-Ah) for several years. Recently, work has focused on the testing of different chemistries at variable temperatures and designing and fabricating 100-Ah cylindrical cells. For the aircraft application the largest concern is irreversible capacity loss at elevated temperatures (70°C). In contrast, for the aerospace application shelf-life and cycle life are critical. EPEP has found that the major contributor to the loss in low temperature performance due to high temperature testing, was the positive electrode. EPEP discuss recent results of variable temperature cycling and 100-Ah cell performance 相似文献
60.
Shu-Mei Guo Shieh L.S. Guanrong Chen Coleman N.P. 《IEEE transactions on aerospace and electronic systems》2001,37(4):1406-1418
An observer-type of Kalman innovation filtering algorithm to find a practically implementable "best" Kalman filter, and such an algorithm based on the evolutionary programming (EP) optima-search technique, are proposed, for linear discrete-time systems with time-invariant unknown-but-hounded plant and noise uncertainties. The worst-case parameter set from the stochastic uncertain system represented by the interval form with respect to the implemented "best" filter is also found in this work for demonstrating the effectiveness of the proposed filtering scheme. The new EP-based algorithm utilizes the global optima-searching capability of EP to find the optimal Kalman filter and state estimates at every iteration, which include both the best possible worst case Interval and the optimal nominal trajectory of the Kalman filtering estimates of the system state vectors. Simulation results are included to show that the new algorithm yields more accurate estimates and is less conservative as compared with other related robust filtering schemes 相似文献