全文获取类型
收费全文 | 50653篇 |
免费 | 4317篇 |
国内免费 | 2162篇 |
专业分类
电工技术 | 2866篇 |
技术理论 | 7篇 |
综合类 | 3252篇 |
化学工业 | 8553篇 |
金属工艺 | 2951篇 |
机械仪表 | 3223篇 |
建筑科学 | 3577篇 |
矿业工程 | 1616篇 |
能源动力 | 1555篇 |
轻工业 | 3166篇 |
水利工程 | 787篇 |
石油天然气 | 3191篇 |
武器工业 | 466篇 |
无线电 | 5882篇 |
一般工业技术 | 6427篇 |
冶金工业 | 2510篇 |
原子能技术 | 693篇 |
自动化技术 | 6410篇 |
出版年
2024年 | 261篇 |
2023年 | 930篇 |
2022年 | 1561篇 |
2021年 | 2207篇 |
2020年 | 1664篇 |
2019年 | 1371篇 |
2018年 | 1560篇 |
2017年 | 1792篇 |
2016年 | 1609篇 |
2015年 | 2083篇 |
2014年 | 2666篇 |
2013年 | 3205篇 |
2012年 | 3357篇 |
2011年 | 3579篇 |
2010年 | 3024篇 |
2009年 | 2894篇 |
2008年 | 2868篇 |
2007年 | 2717篇 |
2006年 | 2618篇 |
2005年 | 2240篇 |
2004年 | 1565篇 |
2003年 | 1361篇 |
2002年 | 1354篇 |
2001年 | 1167篇 |
2000年 | 1166篇 |
1999年 | 1167篇 |
1998年 | 972篇 |
1997年 | 820篇 |
1996年 | 766篇 |
1995年 | 589篇 |
1994年 | 499篇 |
1993年 | 333篇 |
1992年 | 268篇 |
1991年 | 199篇 |
1990年 | 173篇 |
1989年 | 136篇 |
1988年 | 111篇 |
1987年 | 59篇 |
1986年 | 62篇 |
1985年 | 34篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1976年 | 6篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
通过密度测定和DSC热分析,观测了超高分子量聚乙烯的辐射效应。实验结果表明:在吸收剂量0—1.13MGy范围内,密度随吸收剂量的增加而增大,熔化热和熔点也有所增加,特别是在低剂量范围内增加十分明显。以上结果都说明,超高分子量聚乙烯在辐照过程中,结晶在完善或有新的结晶形成 相似文献
12.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
13.
Fernandez E.B. Gudes E. Haiyan Song 《Knowledge and Data Engineering, IEEE Transactions on》1994,6(2):275-292
The integration of object-oriented programming concepts with databases is one of the most significant advances in the evolution of database systems. Many aspects of such a combination have been studied, but there are few models to provide security for this richly structured information. We develop an authorization model for object-oriented databases. This model consists of a set of policies, a structure for authorization rules, and algorithms to evaluate access requests against the authorization rules. User access policies are based on the concept of inherited authorization applied along the class structure hierarchy. We propose also a set of administrative policies that allow the control of user access and its decentralization. Finally, we study the effect of class structuring changes on authorization 相似文献
14.
The formula and program for calculating the total and negative first harmonic interaction impedance from the data of “large
perturbation measurement” are given. This program is a part of the programs for CCTWT design. 相似文献
15.
高温预析出对Al-Zn-Mg系铝合金时效硬化和应力腐蚀的影响 总被引:1,自引:0,他引:1
研究了高温固溶后降温处理工艺对中强可使预析出LC52和7039铝合金的组织、时效硬化和应力腐蚀的影响。金相观察发现,高温预析出可优先在晶界处产生,并提高随后时效状态下晶界析出相的不连续分布程度,温度降低到一定程度晶内和晶界产生大量析出。合金拉伸性能和应力腐蚀结果表明,预析出在保持强度和塑性的同时,可提高抗应力腐蚀性能。而预析出温度降低,合金强度呈下降趋势。 相似文献
16.
17.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献
18.
19.
I.H. Song 《Thin solid films》2007,515(19):7598-7602
This paper is a report on the effect of a single perpendicular grain boundary on the hot-carrier and high current stability in high performance polycrystalline silicon (poly-Si) thin film transistors (TFTs). Under a hot carrier stress condition (Vg = Vth + 1 V, Vd = 12 V), the poly-Si TFT with a single grain boundary is superior to the poly-Si without any grain boundary because of the smaller free carriers available for electric conduction. The shift of transconductance in poly-Si TFT with a single grain boundary is less than 5% after hot carrier stress during a period of 1000 s. The shift of transconductance is about 25% in the case of the poly-Si TFTs without a grain boundary in the channel. On high current stress, the poly-Si TFT without the grain boundary is less degraded than the poly-Si TFT with the grain boundary because the concentrated electric field near the drain junction is lower. 相似文献
20.