全文获取类型
收费全文 | 64963篇 |
免费 | 6720篇 |
国内免费 | 4192篇 |
专业分类
电工技术 | 5068篇 |
技术理论 | 4篇 |
综合类 | 5554篇 |
化学工业 | 9236篇 |
金属工艺 | 3973篇 |
机械仪表 | 4167篇 |
建筑科学 | 5002篇 |
矿业工程 | 1911篇 |
能源动力 | 1711篇 |
轻工业 | 7389篇 |
水利工程 | 1601篇 |
石油天然气 | 2859篇 |
武器工业 | 779篇 |
无线电 | 7147篇 |
一般工业技术 | 6221篇 |
冶金工业 | 3285篇 |
原子能技术 | 726篇 |
自动化技术 | 9242篇 |
出版年
2024年 | 330篇 |
2023年 | 1056篇 |
2022年 | 2201篇 |
2021年 | 2800篇 |
2020年 | 2162篇 |
2019年 | 1660篇 |
2018年 | 1918篇 |
2017年 | 2158篇 |
2016年 | 1992篇 |
2015年 | 2982篇 |
2014年 | 3602篇 |
2013年 | 4270篇 |
2012年 | 5097篇 |
2011年 | 5480篇 |
2010年 | 4978篇 |
2009年 | 4721篇 |
2008年 | 4819篇 |
2007年 | 4400篇 |
2006年 | 3892篇 |
2005年 | 3110篇 |
2004年 | 2251篇 |
2003年 | 1858篇 |
2002年 | 1783篇 |
2001年 | 1513篇 |
2000年 | 1059篇 |
1999年 | 785篇 |
1998年 | 692篇 |
1997年 | 534篇 |
1996年 | 404篇 |
1995年 | 322篇 |
1994年 | 223篇 |
1993年 | 192篇 |
1992年 | 96篇 |
1991年 | 115篇 |
1990年 | 84篇 |
1989年 | 54篇 |
1988年 | 42篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 25篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 13篇 |
1980年 | 26篇 |
1979年 | 7篇 |
1977年 | 15篇 |
1976年 | 51篇 |
1959年 | 9篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Hui Chen D.T.K. Tong 《Photonics Technology Letters, IEEE》2005,17(4):801-803
Symmetric interference in two-dimensional multimode silicon waveguides is experimentally investigated. For a 100/spl times/100 /spl mu/m/sup 2/ cross section, 2700-/spl mu/m-long waveguide fabricated on silicon-on-insulator substrate, an 8/spl times/8 matrix of replicated images with high contrast ratio is demonstrated for 1530-1570 nm wavelength range. Symmetric interference results in reduced device length, and the actual device length is consistent with the theoretical expectation. The device also exhibits stable imaging in terms of good loss uniformity, and low wavelength and polarization dependencies among the replicated images. 相似文献
92.
We report the growth of highly C-axis orientation of Sr
x
Ba1−x
Nb2O6 (SBN) thin films on p-type (100) Si substrates by using a potassium-substituted SBN template layer with the sol–gel method. The crystallization of SBN thin films was found closely related to the potassium ion doping concentration and the postannealing temperature of the K-SBN template layer. Secondary ion mass spectrometry analysis showed that potassium elements were accumulated at the interface of the template layer and silicon substrate. SBN films postannealed at 750 °C with K-SBN template layer has a smaller full width at half maximum of X-ray rocking curve of 2.45° than that of 5.40° for the pure SBN films. By introducing a template layer, the surface morphologies of SBN films fabricated on silicon substrate were greatly improved. 相似文献
93.
94.
95.
采用水力模型研究方法 ,针对马钢 2 0t转炉进行溅渣护炉冷态模拟试验 ,得出最佳工艺参数为 :枪位 1680mm ,氮气流量为 110 0 0m3/h ,大流渣量 ,渣粘度适中。此外 ,在满足炼钢生产的条件下 ,采用夹角为 13°的喷头溅渣效果好 相似文献
96.
本文通过对压电量测系统等效电路图的逐步简化,得出矩形脉冲信号的漏电方程;并对系统在各种情况下的时间常数,漏电相对误差进行了计算,最后就系统在校准和现场测试中经常碰到的几种情况,进行了定量估算,从而解决了压电量测系统在使用中的一些具体问题。 相似文献
97.
一种新型陶瓷材料及其耐磨性 总被引:5,自引:0,他引:5
对新型Al2O3-TiC-Co陶瓷的磨粒磨损,冲蚀磨损及其在单颗粒作用下的摩擦磨损行为进行了研究。与AT30(70wt%Al2O3-30wt%TiC)陶瓷相比,Al2O3-TiC-Co陶瓷具有更为良好的耐磨性,金属钴的存在提高了基体的韧性,细化了晶粒,其综合力学性能得到了显著提高,ATC陶瓷样品耐磨性与其强韧化水平和细致的组织结构有关。 相似文献
98.
There has been an increasing interest in the use of code-division multiple access (CDMA) in cellular mobile and wireless personal communications. The choice of such multiaccess technique is attractive because of its potential capacity increases and other technical factors such as privacy and multipath rejection capabilities. However, it is well known that the performance of CDMA can be significantly degraded due to cochannel interference (CI) and the near-far effects. We consider the performance of direct-sequence (DS)-based CDMA over fading channels that are modeled as slowly varying Rayleigh-fading discrete multipath channels. Specifically, we propose and analyze an adaptive multistage interference cancellation strategy for the demodulation of asynchronous DS spread-spectrum multiple-access signals. Numerical results show that the proposed multistage detector, which alleviates the detrimental effects of the near-far problem, can significantly improve the system performance 相似文献
99.
EB Poluéktova NK Khitrov VI Andreev SG Pak BK Danilkin 《Canadian Metallurgical Quarterly》1997,69(11):14-16
Changes in the activity of acid phosphatase (AP) and its isoenzymes (tartrate-insensitive AP and formalin-insensitive AP) were investigated in patients with food poisoning in the course of the disease. The activity of AP and its isoenzymes in the serum started to grow in early convalescence and reached maximum in late convalescence. Total activity of AP in food toxic infections consists primarily of the activity of its platelet fraction. AP activity may serve as an additional criterion to predict vascular platelet involvement of hemostasis. 相似文献
100.
A novel monoclonal antibody to 6 beta-hydroxycortisol (6 beta-OHC) was generated and incorporated into an antigen-coated indirect enzyme-linked immunosorbent assay (ELISA) using 6 beta-OHC-protein conjugate as the steroid-coating antigen. The monoclonal antibody is specific to 6 beta-OHC and 6 beta-OHC-3-carboxymethyloxime. Cross-reactivity with other structurally related steroids such as cortisol, cortisone, and 6 beta-hydroxycortisone was less than 10%. Two different clones (clone 5C1 and 19F) of the monoclonal anti-6 beta-OHC antibody have been developed, each with slightly different sensitivity and specificity. The sensitivity of the MAb clones was not significantly improved when compared to the rabbit polyclonal antibodies in this study, but still within the accepted detection limit for 6 beta-OHC in both human and laboratory animals. The assay had a detection limit of 200 ng/ml, an intraassay variation of 6.4% and an interassay variation of 7.3%. The application of the anti-6 beta-OHC-MAb-based-ELISA was tested by measuring the urinary output of 6 beta-OHC in human before and after enzyme induction by rifampicin treatment. The mean 24-h urine output of 6 beta-OHC in human subjects was 485 +/- 100 micrograms and 1478 +/- 281 micrograms before and after rifampicin administration, respectively. In conclusion, the monoclonal anti-6 beta-OHC antibody developed in this study has the required specificity and sensitivity as an alternative method for measuring urinary 6 beta-OHC in the detection of enzyme induction or enzyme inhibition of CYP3A in humans and laboratory animals. 相似文献