全文获取类型
收费全文 | 433861篇 |
免费 | 3784篇 |
国内免费 | 651篇 |
专业分类
电工技术 | 7515篇 |
综合类 | 454篇 |
化学工业 | 67452篇 |
金属工艺 | 21935篇 |
机械仪表 | 15550篇 |
建筑科学 | 9081篇 |
矿业工程 | 3452篇 |
能源动力 | 7988篇 |
轻工业 | 32911篇 |
水利工程 | 5596篇 |
石油天然气 | 12611篇 |
武器工业 | 42篇 |
无线电 | 41691篇 |
一般工业技术 | 90642篇 |
冶金工业 | 72816篇 |
原子能技术 | 11894篇 |
自动化技术 | 36666篇 |
出版年
2021年 | 3256篇 |
2019年 | 3189篇 |
2018年 | 11868篇 |
2017年 | 12254篇 |
2016年 | 9851篇 |
2015年 | 3936篇 |
2014年 | 6248篇 |
2013年 | 15369篇 |
2012年 | 11414篇 |
2011年 | 18672篇 |
2010年 | 16057篇 |
2009年 | 16039篇 |
2008年 | 16563篇 |
2007年 | 18218篇 |
2006年 | 10214篇 |
2005年 | 11581篇 |
2004年 | 10222篇 |
2003年 | 9830篇 |
2002年 | 9059篇 |
2001年 | 8477篇 |
2000年 | 8251篇 |
1999年 | 7977篇 |
1998年 | 18573篇 |
1997年 | 13270篇 |
1996年 | 10159篇 |
1995年 | 7858篇 |
1994年 | 7032篇 |
1993年 | 7002篇 |
1992年 | 5535篇 |
1991年 | 5321篇 |
1990年 | 5604篇 |
1989年 | 5398篇 |
1988年 | 5228篇 |
1987年 | 4716篇 |
1986年 | 4826篇 |
1985年 | 5295篇 |
1984年 | 5049篇 |
1983年 | 4693篇 |
1982年 | 4414篇 |
1981年 | 4626篇 |
1980年 | 4418篇 |
1979年 | 4520篇 |
1978年 | 4671篇 |
1977年 | 4957篇 |
1976年 | 6433篇 |
1975年 | 4225篇 |
1974年 | 4161篇 |
1973年 | 4292篇 |
1972年 | 3772篇 |
1971年 | 3439篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
O. A. Lambri J. I. Prez-Landazbal J. A. Cano V. Recarte 《Materials Science and Engineering: A》2004,370(1-2):459-463
Mechanical spectroscopy, neutron diffraction and differential scanning calorimetry (DSC) were performed on commercial Fe–6 wt.% Si alloy after quenching from high temperature. The damping spectrum shows a peak at around 800 K and an associated modulus defect. The modulus shows an increase during the second and subsequent heating runs. In addition, an anomaly in the modulus behavior has been found at around 400 K. Different thermal treatments allows to obtain two different recovery degrees of the quenched-in defects. The influence of the recovery degree on the 800 K internal friction peak and on the anelastic modulus has been evaluated and confirm the validity of the grain boundary mechanism associated to this peak. Experimental results are discussed on the basis of recovery and ordering processes. 相似文献
82.
J.M. Roth T.G. Ulmer N.W. Spellmeyer S. Constantine M.E. Grein 《Photonics Technology Letters, IEEE》2004,16(9):2009-2011
We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty. 相似文献
83.
I. Budić-Leto T. Lovrić J. Gajdoš Kljusurić I. Pezo U. Vrhovšek 《European Food Research and Technology》2006,222(3-4):397-402
Identification of anthocyanins in the wine made of the Croatian autochthonous grape variety of Babić (Vitis vinifera L.) was carried out and their profile was determined by means of high-performance liquid chromatography with diode array
and mass spectrometric detection. Dependence of anthocyanins content and profile on maceration treatment conditions was investigated.
Statistically significant differences of anthocyanins concentration in wines Babić produced by various maceration treatments
were confirmed by the use of multivariate analysis of variances. The investigation results indicated that the maceration temperature
exerts higher influence on anthocyanins concentration than the duration of maceration. In addition, on the basis of anthocyanin
composition and using different multivariate statistical analyses, differentiation of wines Babić according to maceration
treatments was procured. 相似文献
84.
Extraction of Cs, Sr, Eu, U, Np, and Am with mixtures of dipicolinic acid diamides with chlorinated cobalt dicarbollide was studied. A synergistic effect was revealed. 相似文献
85.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献
86.
87.
88.
M. Kaiarov E. Rudnayov J. Koval
ík J. Dusza M. Hnatko P. ajgalík A. Merstallinger 《Materialwissenschaft und Werkstofftechnik》2003,34(4):338-342
In the presented work some properties of a recently developed Si3N4/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si3N4 pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si3N4+SiC disc revealed that mechanical fracture was the wear controlling mechanism. Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism. 相似文献
89.
Combining ideal beamforming and Alamouti space-time block codes 总被引:3,自引:0,他引:3
The simplest Alamouti space-time block code is coupled with a larger number of transmit antennas via ideal beamforming to achieve higher diversity gain. It is shown that the combined system can remain both full diversity and full code rate without orthogonality loss. Simulation results show a significant performance gain over the conventional space-time block codes. 相似文献
90.
Remanufacturing facilities usually face a trade-off between limited information about remanufacturing yields and potentially long supplier lead times. To improve production performance, these firms may attempt to acquire more timely and accurate information about remanufacturing yields or alternatively, to reduce the lead times of purchased parts. We develop four decision-making models to evaluate the impact of yield information and supplier lead time on manufacturing costs. We identify the operating conditions under which these capabilities are valuable, along with their relative impact on facility performance. Each model is formulated as an infinite horizon, stochastic dynamic program (Markov decision process). Our results indicate that the yield information is generally quite valuable, while investments in supplier responsiveness provide trivial returns to products with few parts. However, as product complexity increases with large number of target parts, the value of short lead times increases. 相似文献