全文获取类型
收费全文 | 10175篇 |
免费 | 772篇 |
国内免费 | 321篇 |
专业分类
电工技术 | 373篇 |
综合类 | 413篇 |
化学工业 | 1628篇 |
金属工艺 | 552篇 |
机械仪表 | 646篇 |
建筑科学 | 534篇 |
矿业工程 | 178篇 |
能源动力 | 317篇 |
轻工业 | 531篇 |
水利工程 | 152篇 |
石油天然气 | 305篇 |
武器工业 | 33篇 |
无线电 | 1461篇 |
一般工业技术 | 1595篇 |
冶金工业 | 1123篇 |
原子能技术 | 101篇 |
自动化技术 | 1326篇 |
出版年
2024年 | 44篇 |
2023年 | 135篇 |
2022年 | 259篇 |
2021年 | 337篇 |
2020年 | 285篇 |
2019年 | 272篇 |
2018年 | 273篇 |
2017年 | 266篇 |
2016年 | 257篇 |
2015年 | 351篇 |
2014年 | 423篇 |
2013年 | 621篇 |
2012年 | 569篇 |
2011年 | 636篇 |
2010年 | 512篇 |
2009年 | 552篇 |
2008年 | 490篇 |
2007年 | 498篇 |
2006年 | 428篇 |
2005年 | 426篇 |
2004年 | 282篇 |
2003年 | 272篇 |
2002年 | 275篇 |
2001年 | 261篇 |
2000年 | 217篇 |
1999年 | 266篇 |
1998年 | 335篇 |
1997年 | 254篇 |
1996年 | 217篇 |
1995年 | 188篇 |
1994年 | 141篇 |
1993年 | 124篇 |
1992年 | 98篇 |
1991年 | 85篇 |
1990年 | 65篇 |
1989年 | 72篇 |
1988年 | 60篇 |
1987年 | 48篇 |
1986年 | 39篇 |
1985年 | 43篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 28篇 |
1980年 | 18篇 |
1979年 | 14篇 |
1977年 | 24篇 |
1976年 | 28篇 |
1974年 | 19篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
大型离心复合球墨铸铁轧辊的生产 总被引:1,自引:0,他引:1
简述了我公司为舞阳铜厂试制4200mm厚板轧机离心复合球墨铸铁轧辊的性能要求、内外层双重金属铸造工艺参数的选择及整个铸造生产工艺过程。 相似文献
74.
Ismail K. Meyerson B.S. Rishton S. Chu J. Nelson S. Nocera J. 《Electron Device Letters, IEEE》1992,13(5):229-231
The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm2/V-s and 2.5×1012 (1.5×1012 ) cm-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors 相似文献
75.
用傅里叶变换红外扫描光致发光方法研究了Hg1-xCdxTe体单晶样品,该方法可直接得到HgCdTe晶片组分的二维平面分布,并可得到辐射复合在复合机制中所占比重的平面分布,以及晶体中非平衡载流子寿命的分布 相似文献
76.
DR Offord MH Boyle D Campbell P Goering E Lin M Wong YA Racine 《Canadian Metallurgical Quarterly》1996,41(9):559-563
OBJECTIVE: To present the one-year prevalence of 14 psychiatric disorders in a community sample of Ontarians aged 15 to 64 years. METHOD: Data on psychiatric disorders were collected on 9953 respondents using the University of Michigan revision of the Composite International Diagnostic Interview (UM-CIDI). DSM-III-R criteria were used to define the psychiatric disorders. RESULTS: Almost 1 in 5 Ontarians (18.6%) had one or more of the disorders measured in the survey. Among 15-to 24-year-olds, 1 in 4 was affected. The distribution of individual disorders varied by sex and age. CONCLUSION: Because of the immense burden of suffering associated with psychiatric disorders, clinical and research efforts in this area should receive high priority within the health budget. 相似文献
77.
The cellular localization of protein kinase C (PKC) is intimately associated with the regulation of its biological activity. Previously we have demonstrated that the redistribution of PKC to the plasma membrane in response to physiological stimuli is followed by a rapid returning of PKC back to the cytoplasm (Feng, X., Zhang, J., Barak, L. S., Meyer, T., Caron, M. G., and Hannun, Y. A. (1998) J. Biol. Chem. 273, 10755-10762). Although the process of PKC membrane targeting has been extensively studied, the molecular mechanism underlying the dissociation of membrane-bound PKC remains unclear. In the present study, by examining the dynamic distribution of wild-type PKC betaII and its kinase-deficient mutant (K371R), we demonstrate that kinase activity is required for PKC membrane dissociation. Moreover, the inability of PKC betaII(K371R) to dissociate from the plasma membrane in cells overexpressing wild-type PKC betaII suggests that autophosphorylation activity of the kinase might be essential for its membrane dissociation. This was further supported by mutational analysis of two in vivo autophosphorylation sites on PKC betaII. The replacement of Ser660 or Thr641 by alanine (S660A or T641A) was found to synergistically reduce the reversal of PKC betaII membrane translocation, whereas the replacement of the same amino acids by glutamic acid (S660E or T641E), an amino acid commonly used to mimic phosphate, results in mutants behaving similar to wild-type PKC betaII. These findings point to an essential role for autophosphorylation in the dissociation of activated PKC from the plasma membrane and suggest that, like PKC membrane translocation, the returning of PKC to the cytoplasm after its activation is also delicately regulated. 相似文献
78.
本试验研究了ZrO2与40Cr钢在加入缓冲层前后的钎焊连接,结果表明:插入缓冲层Cu和Ti可以提高接头强度。对每一种缓冲层,存在一最佳厚度,对应的钎焊强度最大。此最佳厚度对Cu为0.4mm左右,对Ti为1mm左右。作者认为这是由缓冲层的力学性能和热膨胀系数对残余应力释放产生的两种相反影响而造成的。钎焊时,缓冲层Cu和Ti向钎料中均有程度不同的溶解,但不影响钎料对ZrO2的浸润和反应结合。ZrO2-40Cr钢连接的所有接头均断在陶瓷的近缝区,其断裂方式有三种。 相似文献
79.
Microring resonator channel dropping filters 总被引:17,自引:0,他引:17
Little B.E. Chu S.T. Haus H.A. Foresi J. Laine J.-P. 《Lightwave Technology, Journal of》1997,15(6):998-1005
Microring resonators side coupled to signal waveguides provide compact, narrow band, and large free spectral range optical channel dropping filters. Higher order filters with improved passband characteristics and larger out-of-band signal rejection are realized through the coupling of multiple rings. The analysis of these devices is approached by the novel method of coupling of modes in time. The response of filters comprised of an arbitrarily large dumber of resonators may be written down by inspection, as a continued fraction. This approach simplifies both the analysis and filter synthesis aspects of these devices 相似文献
80.