全文获取类型
收费全文 | 85785篇 |
免费 | 8284篇 |
国内免费 | 4593篇 |
专业分类
电工技术 | 6407篇 |
技术理论 | 2篇 |
综合类 | 6021篇 |
化学工业 | 13125篇 |
金属工艺 | 5306篇 |
机械仪表 | 5911篇 |
建筑科学 | 5648篇 |
矿业工程 | 2220篇 |
能源动力 | 2926篇 |
轻工业 | 5815篇 |
水利工程 | 1921篇 |
石油天然气 | 3480篇 |
武器工业 | 1016篇 |
无线电 | 11121篇 |
一般工业技术 | 10204篇 |
冶金工业 | 4177篇 |
原子能技术 | 1088篇 |
自动化技术 | 12274篇 |
出版年
2024年 | 275篇 |
2023年 | 1012篇 |
2022年 | 2074篇 |
2021年 | 3098篇 |
2020年 | 2323篇 |
2019年 | 1892篇 |
2018年 | 2161篇 |
2017年 | 2595篇 |
2016年 | 2568篇 |
2015年 | 3347篇 |
2014年 | 4381篇 |
2013年 | 5269篇 |
2012年 | 6547篇 |
2011年 | 6958篇 |
2010年 | 6451篇 |
2009年 | 6236篇 |
2008年 | 6060篇 |
2007年 | 5599篇 |
2006年 | 5142篇 |
2005年 | 4257篇 |
2004年 | 3364篇 |
2003年 | 3128篇 |
2002年 | 3253篇 |
2001年 | 2817篇 |
2000年 | 1830篇 |
1999年 | 1378篇 |
1998年 | 1001篇 |
1997年 | 774篇 |
1996年 | 624篇 |
1995年 | 460篇 |
1994年 | 392篇 |
1993年 | 269篇 |
1992年 | 203篇 |
1991年 | 167篇 |
1990年 | 149篇 |
1989年 | 125篇 |
1988年 | 79篇 |
1987年 | 83篇 |
1986年 | 56篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1983年 | 39篇 |
1982年 | 23篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 19篇 |
1976年 | 21篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Y Tamura S Takashima JM Cho W Qi K Kamiguchi T Torigoe S Takahashi I Hirai N Sato K Kikuchi 《Canadian Metallurgical Quarterly》1996,87(6):623-630
Certain MHC class I molecules on target cells are known to inhibit the cytotoxic action of NK cells. By using monoclonal antibody (mAb) Cho-1, we have found inhibitory non-MHC class I cell surface molecules that are noncovalently-associated with 200 kDa and 40 kDa antigens. Poly I-C-induced rat NK cells were not cytotoxic to rat fetus-derived fibroblast WFB cell line. In contrast, NK cells were cytotoxic to H-ras oncogene-induced transformants of WFB, W14 and W31. FACS analysis indicated that mAb Cho-1 reacts with WFB, but not with W14 and W31 cells. Thus, this antigen may disappear concomitantly with cell growth and transformation. Cho-1 antigens were also expressed on other NK-resistant lines, such as mouse BALB3T3 fibroblast, EL-4 lymphoma and human fibroblast HEPM. However, they were not expressed on NK-sensitive mouse YAC-1 and H-ras transformant (Brash) of BALB3T3 cells. Furthermore, treatment of target cells with IFN-gamma clearly induced the cell surface expression of Cho-1 antigens, and conferred a resistance to NK cytolysis on target cells. These data strongly suggest that Cho-1 antigen expression may correlate with target cell susceptibility to NK cells. Indeed, treatment of NK-resistant WFB as well as HEPM cells with F(ab')2 fragments of mAb Cho-1 resulted in the acquisition of susceptibility to NK cytolysis. Cho-1 antigens may be novel molecules that regulate the NK resistance of cells. 相似文献
42.
In arc welding processes, because of the complexity and nonlinearity of heat transfer phenomena, it is often difficult to design an effective control system based upon an exact mathematical model. In this paper, a self-organizing fuzzy control method is proposed to obtain a uniform weld quality by regulation of the surface temperature at a desired level. The proposed control system is designed to comprise a combined structure of the fuzzy SOC with conventional PD control for improving the system's stability. The control experiments show that the proposed controller guarantees a uniform weld quality for various welding conditions. 相似文献
43.
旋转式伽玛刀的辐射剂量学 总被引:4,自引:0,他引:4
旋转式伽玛刀的辐射剂量学指标的物理测试在放射性医疗设备投放医院正式临床使用前是必不可少的,是对设备及其附件的设计、加工制造、安装以及电气控制系统等的全面综合性检定。用电离室作辐射剂量学的绝对测量,用胶片法进行相对测量,给出了测量结果并进行了讨论。 相似文献
44.
45.
In this work, we designed, fabricated and tested a disposable, flow-through amperometric sensor for free chlorine determination in water. The sensor is based on the principle of an electrochemical cell. The substrate, as well as the top microfluidic layer, is made up of a polymer material. The advantages include; (a) disposability from low cost; (b) stable operation range from three-electrode design; (c) fluidic interconnections that provide on line testing capabilities; and (d) transparent substrate which provides for future integration of on-chip optics. The sensor showed a good response and linearity in the chlorine concentration ranging from 0.3 to 1.6 ppm, which applies to common chlorination process for drinking water purification. 相似文献
46.
本文研究了浸胶工艺对Nomex蜂窝性能的影响,分析探讨了提高Nomex蜂窝性能及外观质量的途径。研究结果表明:采取新的浸胶工艺制作的Nomex蜂窝,各项性能全面达到法国宇航材料标准。 相似文献
47.
Po-An Sung Kwang-Cheng Chen 《Selected Areas in Communications, IEEE Journal on》1996,14(8):1583-1594
We generalize the multiuser (CDMA spread spectrum) communication systems to the fading environments. We first extend Verdu's (1986) conventional optimum receiver to Rayleigh-fading environments and then evaluate its performance. Having no knowledge of the received power at the receiving end, we therefore need an estimator to efficiently estimate the received signal strength of each user in fading environments. A linear minimum mean square error (LMMSE) unbiased estimator is proposed to attain this goal. By using the minimum mean square error (MMSE) Bayesian estimation, we further propose the LMMSE bit estimator for efficient demodulation. Its performance is close to the optimum multiuser receiver but with a much simpler polynomial complexity. To further reduce the complexity, we extend the LMMSE estimator to the sequential LMMSE estimator. In sequential estimation, we do not need to implement the matched filter banks and to perform the matrix inversion when estimating. In addition, it converges after approximately 2k iterations, where k is the number of users. With this fast convergence property and the simple structure, the sequential LMMSE estimator provides an attractive alternative to the implementation of a multiuser system 相似文献
48.
为了提高E^2PROM中N管源漏穿通电压,用实验的方法对制造工艺进行了研究。结果表明,高能量注入是提高VPT的有效手段,但受到pn结击穿的限制,只适用于低区短沟N管;DDD工艺大幅度高VPT,但pn结击穿电压低于20V,不能应用于高压MOS管;采用适量的防穿通注入和适当增大沟道长度为最理想的工艺途径。 相似文献
49.
WJ Cho EK Kim MJ Park SU Choi CO Lee SH Cheon BG Choi BH Chung 《Canadian Metallurgical Quarterly》1998,6(12):2449-2458
In this study a series of 3-arylisoquinoline derivatives were synthesized and cytotoxicity against human melanoma tumor cell evaluated, and a three dimensional quantitative structure-activity relationship was investigated using the comparative molecular field analysis (CoMFA). The results suggested that the electrostatic, steric and hydrophobic factors of 3-arylisoquinolines were strongly correlated with the antitumor activity. Considerable predictive ability (cross-validated r2 as high as 0.721) was obtained through CoMFA. 相似文献
50.
We report a family in which three siblings developed dementia between the ages of 40 and 70 years. Two of the siblings developed symptoms of depression, abnormal behavior, and an inability to function, progressing to severe dementia. The third sibling had a severe dementia, the clinical details of which are not available. In the two deceased siblings neuropathologic examinations demonstrated severe demyelination, axon loss, and gliosis in cerebral white matter. Cerebellar and brainstem white matter were unaffected. Cerebral gray matter was negligibly affected. The disorder, histopathologically classified as a pigmented orthochromatic leukodystrophy, is extremely rare. Its etiology is unknown, but the pathology and familial occurrence imply that it represents a genetic defect in a function localized in the cerebral white matter. 相似文献