首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2940篇
  免费   55篇
  国内免费   13篇
电工技术   194篇
化学工业   639篇
金属工艺   99篇
机械仪表   71篇
建筑科学   50篇
矿业工程   1篇
能源动力   118篇
轻工业   195篇
水利工程   9篇
石油天然气   2篇
无线电   295篇
一般工业技术   599篇
冶金工业   439篇
原子能技术   85篇
自动化技术   212篇
  2023年   7篇
  2022年   38篇
  2021年   42篇
  2020年   21篇
  2019年   24篇
  2018年   35篇
  2017年   37篇
  2016年   47篇
  2015年   31篇
  2014年   66篇
  2013年   136篇
  2012年   83篇
  2011年   146篇
  2010年   102篇
  2009年   102篇
  2008年   128篇
  2007年   131篇
  2006年   115篇
  2005年   114篇
  2004年   87篇
  2003年   93篇
  2002年   92篇
  2001年   60篇
  2000年   61篇
  1999年   81篇
  1998年   199篇
  1997年   145篇
  1996年   102篇
  1995年   66篇
  1994年   64篇
  1993年   59篇
  1992年   35篇
  1991年   40篇
  1990年   34篇
  1989年   24篇
  1988年   40篇
  1987年   31篇
  1986年   26篇
  1985年   34篇
  1984年   30篇
  1983年   19篇
  1982年   18篇
  1981年   23篇
  1980年   20篇
  1979年   27篇
  1978年   21篇
  1977年   13篇
  1976年   18篇
  1974年   6篇
  1973年   8篇
排序方式: 共有3008条查询结果,搜索用时 15 毫秒
1.
2.
3.
On an earthspace propagation path with the low elevation angle of 10 deg, the phase between co- and crosspolar signals occasionally showed rapid and irregular fluctuations during fine weather. These fluctuations were generally significant during the daytime, and were strongly in phase with the occurrence of the copolar amplitude scintillations. This could be attributed to the combined effects of the crosspolar phase pattern of the receiving antenna and small fluctuations of the angle of arrival of the radiowaves.  相似文献   
4.
We constructed and tested a prototype gas sampling electromagnetic calorimeter of the Pb-proportional tube sandwich type. The calorimeter uses conductive plastic tubes and cathode pad readout with a tower structure which resulted in reasonable energy and spatial resolutions for electrons in the momentum range 0.5–4.0 GeV/c; σEE = 21%(E(GeV))12, σx = 6 mm (at 3 GeV/c). This paper describes the test and the performance studied under various conditions.  相似文献   
5.
A rare case of hepatoblastoma in a 61-year-old Japanese housewife is described. This liver tumor mainly consisted of two tissue components: embryonal hepatocytes and primitive mesenchymal tissue. Fetal hepatocytes with alpha-fetoprotein production, gland formation, cartilage and osteoid were also found in a small portion. Molecular analysis by slot blot method revealed increased copy numbers of c-met and K-sam proto-oncogenes and cyclin D1 genes. These findings suggest that alterations of these oncogenes might play a role in the development of adult hepatoblastoma.  相似文献   
6.
A new mathematical model for study of an interface crack between two dissimilar elastic half planes is proposed. A process zone is formed along the interface between the physical crack and the continuous part. Both the crack opening (and sliding) displacement with a smooth shape and the finite magnitude of stress concentration appear in this zone. The analytical model is expressed by closed elastic solutions using complex variables, but with no oscillations at the crack tip.  相似文献   
7.
An average shell volume occupied in the adsorption layer on alumina by a polyacrylic acid ammonium salts molecule (PAA) defined as the average area occupied by an adsorbed PAA on alumina multiplied by the average thickness of the water layer at the limit of thickening, has been calculated from the adsorbed amount of PAA and from the flow points of alumina in the presence of PAA of different molecular weights. A steric effect of the PAA dispersant on the dispersion of alumina resulted in a flow with no yield stress. This was due to the change of the extension of PAA in the adsorption shell from a sphere to an ellipsoid with a long axis which exceeded the effective distance that the van der Waals attraction force reaches at a molecular weight for the PAA of between 10 000–20 000.  相似文献   
8.
A novel on-chip electrostatic discharge (ESD) protection for high-speed CMOS LSI's that operate at higher than 500 MHz has been developed. Introduction of a newly developed common discharge line (CDL) can completely eliminate the protection device influence on the inner circuit operation. This enables minimization of the I/O capacitance by shrinking the dimension of the output transistor, which also serves as a protection device in conventional devices. This new protection (CDL protection) was applied to a high-speed DRAM of which I/O pin capacitance specification is 2 pF. As a result, the ESD tolerance of 4 kV for the charged device model test, 4 kV for the human body model test, and 700 V for the machine model test were obtained. In addition, the DRAM data rate higher than 660 MHz at room temperature was achieved. The results show significant improvement for both ESD and the I/O capacitance, compared with the conventional structure  相似文献   
9.
This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material.  相似文献   
10.
We synthesized new composite particles for hydrogen storage on the basis of an idea of “particle designing”. As starting materials, powders of Mg and YNi2 were selected. Fine composite particles containing mainly Mg2Ni could be designed by repetitive hydriding and dehydriding cycles at 673 K. In the synthesis process of the composite particles, the following two points were found to be essential for this technique. The first point is that, after being activated by the sequential processes of hydrogenation, amorphization and disproportionation, YNi2 reacts effectively with Mg. The second point is that evaporated Mg, which occurs during dehydriding, adheres to the surface of the activated YNi2 and accelerates a diffusion reaction to form Mg2Ni at the interface. In these composite particles, Mg2NiH4 is formed, even at 373 K, under a hydrogen pressure of 5 MPa.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号