全文获取类型
收费全文 | 26350篇 |
免费 | 2243篇 |
国内免费 | 1130篇 |
专业分类
电工技术 | 1454篇 |
技术理论 | 3篇 |
综合类 | 1666篇 |
化学工业 | 4396篇 |
金属工艺 | 1755篇 |
机械仪表 | 1646篇 |
建筑科学 | 2320篇 |
矿业工程 | 736篇 |
能源动力 | 715篇 |
轻工业 | 1682篇 |
水利工程 | 436篇 |
石油天然气 | 1446篇 |
武器工业 | 206篇 |
无线电 | 3032篇 |
一般工业技术 | 3365篇 |
冶金工业 | 1109篇 |
原子能技术 | 258篇 |
自动化技术 | 3498篇 |
出版年
2024年 | 95篇 |
2023年 | 421篇 |
2022年 | 697篇 |
2021年 | 1105篇 |
2020年 | 849篇 |
2019年 | 648篇 |
2018年 | 768篇 |
2017年 | 818篇 |
2016年 | 750篇 |
2015年 | 973篇 |
2014年 | 1190篇 |
2013年 | 1486篇 |
2012年 | 1627篇 |
2011年 | 1729篇 |
2010年 | 1609篇 |
2009年 | 1490篇 |
2008年 | 1426篇 |
2007年 | 1449篇 |
2006年 | 1391篇 |
2005年 | 1299篇 |
2004年 | 895篇 |
2003年 | 792篇 |
2002年 | 802篇 |
2001年 | 634篇 |
2000年 | 727篇 |
1999年 | 741篇 |
1998年 | 623篇 |
1997年 | 494篇 |
1996年 | 504篇 |
1995年 | 391篇 |
1994年 | 320篇 |
1993年 | 249篇 |
1992年 | 208篇 |
1991年 | 134篇 |
1990年 | 86篇 |
1989年 | 90篇 |
1988年 | 71篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
111.
文章讨论的基于“替换法”的汉字信息加、解密实现技术,改变了传统的汉字加密结果,使加密后的密文仍是可以识别和再利用的汉字,发送者可以在任何可编辑汉字的通讯设备上发送和接收密文,确保中文信息传输过程中的安全性。加、解密算法实现的代码语言为VFP6.0。 相似文献
112.
给出了一种用于Y7—200A运输机的隐蔽式短波天线,该天线为位于飞机垂尾前缘的回线天线,与飞机的外形共形,不影响飞机的飞行性能。在利用传输线理论与缝隙天线理论对该天线进行分析的基础上,对输入阻抗、天线与天线调谐器结合后的天线效率进行了研究,给出了该天线与KHF950电台相配合的测试试验结果,该天线能够在2.5MHz到30MHZ范围内与KHF950电台良好调谐,表明这种天线完全可以用于Y7—200A型飞机,代替原有的钢索天线。这是在国产飞机上首次使用这种天线。 相似文献
113.
A novel route was developed to prepare PbS and HgS nanocrystals in ethanol solvent in the presence of sodium hydroxide by microwave heating method. PbS and HgS nanocrystals were obtained with an average size of approximately 10 and 6 nm, respectively. In the reaction, mercury acetate and lead acetate were used as mercury and lead source; sulfur powder was employed as chalcogenide source. The products were characterized by X-ray powder analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis absorption spectroscopy. The probable mechanism was presented. 相似文献
114.
Analytical solution for the axisymmetric plane strain electroelastic dynamics of a special non-homogeneous piezoelectric hollow cylinder 总被引:1,自引:0,他引:1
By virtue of the introduction of a dependent variable and the separation of variables technique, the axisymmetric plane strain electroelastic dynamic problem of a special non-homogeneous piezoelectric hollow cylinder is transformed to a Volterra integral equation of the second kind about a function with respect to time, which can be solved successfully by means of the interpolation method. Then the solutions of displacements, stresses, electric displacements and electric potential are obtained. The present method is suitable for a piezoelectric hollow cylinder with an arbitrary thickness subjected to arbitrary mechanical and electrical loads. Numerical results are finally presented. 相似文献
115.
Soo-Chang Pei Jian-Jiun Ding 《Signal Processing, IEEE Transactions on》2004,52(7):2032-2046
The offset discrete Fourier transform (DFT) is a discrete transform with kernel exp[-j2/spl pi/(m-a)(n-b)/N]. It is more generalized and flexible than the original DFT and has very close relations with the discrete cosine transform (DCT) of type 4 (DCT-IV), DCT-VIII, discrete sine transform (DST)-IV, DST-VIII, and discrete Hartley transform (DHT)-IV. In this paper, we derive the eigenvectors/eigenvalues of the offset DFT, especially for the case where a+b is an integer. By convolution theorem, we can derive the close form eigenvector sets of the offset DFT when a+b is an integer. We also show the general form of the eigenvectors in this case. Then, we use the eigenvectors/eigenvalues of the offset DFT to derive the eigenvectors/eigenvalues of the DCT-IV, DCT-VIII, DST-IV, DST-VIII, and DHT-IV. After the eigenvectors/eigenvalues are derived, we can use the eigenvectors-decomposition method to derive the fractional operations of the offset DFT, DCT-IV, DCT-VIII, DST-IV, DST-VIII, and DHT-IV. These fractional operations are more flexible than the original ones and can be used for filter design, data compression, encryption, and watermarking, etc. 相似文献
116.
H. -C. Chiao H. -L. Lin X. -T. Li C. -X. Ding 《Journal of Thermal Spray Technology》1992,1(2):111-115
Diamond growth with rates up to 100 to 140 μm/hr was achieved using an oxygen-acetylene combustion spraying technique in an
atmospheric environment. Investigations on the processing indicated that the gas flow ratio, substrate position, substrate
temperature, temperature distribution, and substrate pretreatment were the most important factors affecting the growth of
diamond crystals. Evaluation by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and electron
probe microanalysis showed that the synthesized diamond was nearly perfect in morphology, structure, and purity. 相似文献
117.
118.
Herein a novel Dyadic Green's Function (DGF) is presented to calculate the field in ElectroMagnetic Compatibility (EMC) chamber. Due to the difficulty of simulating the whole chamber environment, the analysis combines the DGF formulation and the FEM method, with the latter deals with the reflection from absorbers. With DGF formulation for infinite periodic array structures, this paper investigates electromagnetic field in chamber with truncated arrays. The reflection from the absorber serves as the virtual source contributing to the total field. Hence the whole chamber field calculation can be separated from the work of absorber model set-up. Practically the field homogeneity test and Normal Site Attenuation (NSA) test are carried out to evaluate the chamber performance. Based on the method in this paper, the simulation results agree well with the test, and predict successfully the victim frequency points of the chamber. 相似文献
119.
以基于欧玛技术的阅卷系统为例,介绍了用Excel实现大学英语分类成绩的接口及合并计算总评成绩的基本方法与步骤. 相似文献
120.
A nonlinear stress-strain relationship of soil reinforced with flexible geofibers under static loading is derived based on a nonlinear elastic stress-strain relationship of soil and a linear elastic stress-strain relationship of geofibers in the paper. This investigation includes the following aspects: First, the homogenization technique is introduced to find the volume average stress tensor and volume average strain tensor and further an elastic incremental stress-strain relation is introduced to describe deviatoric shear stress-axial strain relationship of equivalent homogeneous geofiber-reinforced soil. Second, the relation of geofiber numbers, content, mechanical behavior, distribution, and geometrical features to shear modulus of geofiber-reinforced soil is expressed and assessed by employing an elastic energy method. Third, the deviatoric shear stress and axial strain curves of geofiber-reinforced soil are calibrated by laboratory testing data of geofiber reinforced soil samples. Finally, the theoretical computational curves of geofiber reinforced soil are compared with the curves calibrated by testing data of geofiber reinforced soil. The model prediction has a good agreement with experimental results. 相似文献