全文获取类型
收费全文 | 355037篇 |
免费 | 4761篇 |
国内免费 | 1215篇 |
专业分类
电工技术 | 6398篇 |
综合类 | 243篇 |
化学工业 | 53879篇 |
金属工艺 | 14858篇 |
机械仪表 | 10506篇 |
建筑科学 | 8822篇 |
矿业工程 | 2063篇 |
能源动力 | 9297篇 |
轻工业 | 31373篇 |
水利工程 | 3757篇 |
石油天然气 | 6656篇 |
武器工业 | 10篇 |
无线电 | 40362篇 |
一般工业技术 | 69003篇 |
冶金工业 | 66763篇 |
原子能技术 | 8533篇 |
自动化技术 | 28490篇 |
出版年
2021年 | 2753篇 |
2019年 | 2630篇 |
2018年 | 4384篇 |
2017年 | 4444篇 |
2016年 | 4721篇 |
2015年 | 3199篇 |
2014年 | 5450篇 |
2013年 | 15828篇 |
2012年 | 8991篇 |
2011年 | 12545篇 |
2010年 | 9975篇 |
2009年 | 11537篇 |
2008年 | 11596篇 |
2007年 | 11627篇 |
2006年 | 9946篇 |
2005年 | 9277篇 |
2004年 | 8902篇 |
2003年 | 8495篇 |
2002年 | 8157篇 |
2001年 | 8263篇 |
2000年 | 8027篇 |
1999年 | 8309篇 |
1998年 | 20448篇 |
1997年 | 14638篇 |
1996年 | 11362篇 |
1995年 | 8462篇 |
1994年 | 7481篇 |
1993年 | 7250篇 |
1992年 | 5498篇 |
1991年 | 5335篇 |
1990年 | 5029篇 |
1989年 | 5123篇 |
1988年 | 4934篇 |
1987年 | 4281篇 |
1986年 | 4127篇 |
1985年 | 4860篇 |
1984年 | 4458篇 |
1983年 | 4156篇 |
1982年 | 3776篇 |
1981年 | 3924篇 |
1980年 | 3652篇 |
1979年 | 3692篇 |
1978年 | 3684篇 |
1977年 | 4216篇 |
1976年 | 5617篇 |
1975年 | 3215篇 |
1974年 | 3125篇 |
1973年 | 3188篇 |
1972年 | 2648篇 |
1971年 | 2469篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
F.T. Munna Vidhya Selvanathan K. Sobayel Ghulam Muhammad Nilofar Asim Nowshad Amin Kamaruzzaman Sopian Md. Akhtaruzzaman 《Ceramics International》2021,47(8):11003-11009
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell. 相似文献
5.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical... 相似文献
6.
Prof. Andrea Baier Dr. Anne Kokel Dr. William Horton Ewa Gizińska Dr. Garima Pandey Prof. Ryszard Szyszka Prof. Béla Török Prof. Marianna Török 《ChemMedChem》2021,16(12):1927-1932
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays. 相似文献
7.
Kravchenko V. F. Konovalov Ya. Yu. 《Journal of Communications Technology and Electronics》2022,67(8):952-964
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically... 相似文献
8.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
9.
Chemical engineering systems often involve a functional porous medium, such as in catalyzed reactive flows, fluid purifiers, and chromatographic separations. Ideally, the flow rates throughout the porous medium are uniform, and all portions of the medium contribute efficiently to its function. The permeability is a property of a porous medium that depends on pore geometry and relates flow rate to pressure drop. Additive manufacturing techniques raise the possibilities that permeability can be arbitrarily specified in three dimensions, and that a broader range of permeabilities can be achieved than by traditional manufacturing methods. Using numerical optimization methods, we show that designs with spatially varying permeability can achieve greater flow uniformity than designs with uniform permeability. We consider geometries involving hemispherical regions that distribute flow, as in many glass chromatography columns. By several measures, significant improvements in flow uniformity can be obtained by modifying permeability only near the inlet and outlet. 相似文献
10.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献