全文获取类型
收费全文 | 78180篇 |
免费 | 5789篇 |
国内免费 | 3370篇 |
专业分类
电工技术 | 3932篇 |
技术理论 | 8篇 |
综合类 | 3674篇 |
化学工业 | 11924篇 |
金属工艺 | 5099篇 |
机械仪表 | 4203篇 |
建筑科学 | 4443篇 |
矿业工程 | 1551篇 |
能源动力 | 2601篇 |
轻工业 | 4617篇 |
水利工程 | 1244篇 |
石油天然气 | 3192篇 |
武器工业 | 651篇 |
无线电 | 9642篇 |
一般工业技术 | 13277篇 |
冶金工业 | 6718篇 |
原子能技术 | 983篇 |
自动化技术 | 9580篇 |
出版年
2024年 | 260篇 |
2023年 | 958篇 |
2022年 | 1922篇 |
2021年 | 2627篇 |
2020年 | 1954篇 |
2019年 | 1765篇 |
2018年 | 2097篇 |
2017年 | 2191篇 |
2016年 | 2065篇 |
2015年 | 2626篇 |
2014年 | 3247篇 |
2013年 | 4928篇 |
2012年 | 4459篇 |
2011年 | 5148篇 |
2010年 | 4379篇 |
2009年 | 4467篇 |
2008年 | 4370篇 |
2007年 | 4196篇 |
2006年 | 4072篇 |
2005年 | 3478篇 |
2004年 | 2690篇 |
2003年 | 2394篇 |
2002年 | 2411篇 |
2001年 | 2247篇 |
2000年 | 1996篇 |
1999年 | 2051篇 |
1998年 | 2617篇 |
1997年 | 2026篇 |
1996年 | 1693篇 |
1995年 | 1230篇 |
1994年 | 946篇 |
1993年 | 799篇 |
1992年 | 565篇 |
1991年 | 507篇 |
1990年 | 338篇 |
1989年 | 348篇 |
1988年 | 261篇 |
1987年 | 172篇 |
1986年 | 146篇 |
1985年 | 135篇 |
1984年 | 69篇 |
1983年 | 57篇 |
1982年 | 63篇 |
1981年 | 63篇 |
1980年 | 39篇 |
1979年 | 29篇 |
1977年 | 24篇 |
1976年 | 38篇 |
1975年 | 24篇 |
1973年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
112.
113.
介绍新型低压抽屉式开关柜的结构性能和特点,并与早期低压柜作了比较。阐述了新型低压抽屉式开关柜在冶金系统应用中的几点改进情况。 相似文献
114.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献
115.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
116.
Z. Yu Y. F. Hsia X. Z. You H. Spiering P. Gutlich 《Journal of Materials Science》1997,32(24):6579-6581
A light-induced excited spin state trapping (LIESST) experiment for a thermal gradual spin crossover complex, Fetris (2-pyridylmethyl)
amine(NCS)2 or Fe(tpa) (NCS)2, was attempted for the first time. The high spin (HS) state after light inducement stayed metastable
over a period of days without relaxation at 10 K. Intersystem relaxation from a high to a low spin (LS) complex occurred at
50 K after bleaching at 10 K. Investigation of the Mossbauer spectra of the LIESST and relaxation experiment indicated that
the Debye–Waller factor was a correlation parameter of the HS fraction and that the co-operative effect played a role in the
relaxation process for such a solid compound.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
117.
X. Wang S. B. Lambert 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(12):1637-1655
Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%. 相似文献
118.
119.
OBJECTIVE: To investigate the inhibitory effect in vivo of ganciclovir (GCV) on the growth of human ovarian cancer cells (AO) transducted with the thymidine kinase gene of herpes simplex virus I type (HSV1-tk). METHODS: Tumors were induced in nude mice by subcutaneous injection of AO cells and AO cells carried with HSV1-tk gene from China strain (AO/HSV1-tk cells). When the growing tumors were visible, GCV was injected daily into the peritoneum of the nude mice. RESULTS: The average weights of survived AO/HSV1-tkc tumors and AO tumors treated with GCV were 0.087 +/- 0.036 g and 0.661 +/- 0.260 g respectively. Most of the survived AO/HSV1-tkc cells treated with GCV were characterized by hypertrophy and necrosis, but their nuclear chromatins predominantely took the forms of heterchromatins. CONCLUSIONS: GCV could effectively inhibit the growth of HSV1-tk positive human ovarian cancer cells in vivo, but the nuclei of the survival tumor cells appeared to proliferate actively. As the same results of in vitro experiments, this may suggest that HSV1-tk/GCV gene therapeutic system might be combined with S-phase chemotherapy to increase the long-term effect. 相似文献
120.
In order to build models that relate thematic mapper (TM) imagery to field forest variables, several regression techniques, such as the ones based on the Mallows' Cp and the adjusted R2 statistics, were applied. Nevertheless, although the best created models had good fittings (R2>0.65) apparently supported by a clear statistical significance (p<0.0001), later trials tested with additional plots showed that these models were, in fact, nonrobust models (models with very low-predictive capabilities). Two factors were pointed out as causes of these inconsistencies between predicted and observed values: a relatively small number of available field plots and a relatively high number of possible independent variables. Actually, different trials suggested much lower fittings for the expected “really” predictive models. Some restrictions of TM satellite data, such as its radiometric, spectral, and spatial limitations, together with restrictions arising from gathering and processing of field data, might have led to these poor relations. This study shows the need for guarantees stronger than the usual ones before concluding that there is a clear possibility of using satellite information to estimate forest parameters by means of regression techniques 相似文献