全文获取类型
收费全文 | 358833篇 |
免费 | 14054篇 |
国内免费 | 6639篇 |
专业分类
电工技术 | 11954篇 |
技术理论 | 9篇 |
综合类 | 8853篇 |
化学工业 | 56857篇 |
金属工艺 | 18972篇 |
机械仪表 | 16224篇 |
建筑科学 | 13731篇 |
矿业工程 | 5878篇 |
能源动力 | 8267篇 |
轻工业 | 22369篇 |
水利工程 | 5812篇 |
石油天然气 | 15905篇 |
武器工业 | 1068篇 |
无线电 | 37911篇 |
一般工业技术 | 68079篇 |
冶金工业 | 44135篇 |
原子能技术 | 10147篇 |
自动化技术 | 33355篇 |
出版年
2023年 | 2750篇 |
2022年 | 5842篇 |
2021年 | 8077篇 |
2020年 | 6069篇 |
2019年 | 5787篇 |
2018年 | 8276篇 |
2017年 | 8789篇 |
2016年 | 8598篇 |
2015年 | 7633篇 |
2014年 | 10654篇 |
2013年 | 17162篇 |
2012年 | 14735篇 |
2011年 | 16967篇 |
2010年 | 14073篇 |
2009年 | 14563篇 |
2008年 | 14571篇 |
2007年 | 13927篇 |
2006年 | 12580篇 |
2005年 | 11116篇 |
2004年 | 9164篇 |
2003年 | 8990篇 |
2002年 | 8871篇 |
2001年 | 8533篇 |
2000年 | 7642篇 |
1999年 | 7357篇 |
1998年 | 12695篇 |
1997年 | 9269篇 |
1996年 | 7367篇 |
1995年 | 5766篇 |
1994年 | 4971篇 |
1993年 | 4965篇 |
1992年 | 4038篇 |
1991年 | 3893篇 |
1990年 | 3768篇 |
1989年 | 3655篇 |
1988年 | 3536篇 |
1987年 | 3132篇 |
1986年 | 3119篇 |
1985年 | 3371篇 |
1984年 | 3215篇 |
1983年 | 3027篇 |
1982年 | 2786篇 |
1981年 | 2759篇 |
1980年 | 2794篇 |
1979年 | 2885篇 |
1978年 | 2916篇 |
1977年 | 3010篇 |
1976年 | 3432篇 |
1975年 | 2680篇 |
1973年 | 2665篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The hydrocarbon-group composition and distribution of naphthenoaromatic hydrocarbons of West Siberian oils were studied by the technique of mass spectrometry. Naphthenoaromatic hydrocarbons of the general formula CnH2n?z , where z is 8, 10, 12, 14, 16, or 18, containing from one to six saturated cycles are present in oils in significant concentrations. Naphthenomonoarenes with one saturated cycle dominate in all oils. An increase in the amount of compounds containing 3–6 saturated cycles in their molecule with the occurrence depth was noted. Naphthenobiarenes of the general formula CnH2n?z , where z is 14, 16, 18, 20, 22, or 24 containing from one to six saturated cycles are present in oils in concentrations from 20.0 to 54.0 wt % of the biaromatic fraction. Most oils are characterized by the prevalence of structures with one and two saturated cycles in their molecule. The dependence of the number of cycles in naphthenobiarenes on the nature of original organic matter (OM) was not traced. The lack of correlation between the number of cycles and the OM type is presumably due to the fact that, for the most part, fused polycyclic naphthenobiarenes reflect the degree of catagenetic alteration of organic matter. 相似文献
42.
Extraction of Cs, Sr, Eu, U, Np, and Am with mixtures of dipicolinic acid diamides with chlorinated cobalt dicarbollide was studied. A synergistic effect was revealed. 相似文献
43.
Albul V. I. Bychkov V. B. Gusev K. E. Demidov V. S. Demidova E. V. Kurchanov A. F. Luk'yashin V. E. Sokolov A. Yu. 《Measurement Techniques》2003,46(8):810-814
A monitor is proposed based on ultrasonic production when ionizing radiation passes through a medium. The recording element is a 0.2 mm aluminum plate mounted in a ceramic acoustic converter AC in the form of a wedge of thickness 2 mm. The low plate thickness minimizes the beam parameter distortion, while special technology used in the AC provides high sensitivity. The device has been calibrated in the proton beam from the ITEP accelerator at 200 MeV with 2·109–6·1010 particles in a pulse and a pulse length of 70 nsec. 相似文献
44.
Mutoh N. Nakashima J. Kanesaki M. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1085-1094
Electromagnetic interference (EMI) noises generated in power converters are diffused on the surface of conductors. This means influences occur from radiated EMI noises emitted from power transmission lines as well as conducted EMI noises transmitted from them. EMI noises diffusing on the surface of conductors are generally difficult to control using conventional concentrated constant theory. Thus, a new approach based on distributed constant circuit theory is needed in order to control EMI noises. A power converter structure to control EMI noises using multilayer power printed circuit technology is studied in this paper. A structure which can control EMI noises should simultaneously satisfy two conditions, i.e., one to shut down and one to attenuate EMI noises. The structure satisfying these conditions is studied through simulations using the Transmission-Line Modeling Method. The simulations show that the diffusion of EMI noises is controlled by dividing the flow of currents produced by EMI noises into the horizontal and perpendicular directions. That is, the horizontal current flow is controlled inside using the differences in the resistance produced from differences between inner and outer diameter of power transmission lines and the perpendicular current flow can be controlled by properly designing the thickness of the dielectric layer sandwiched between P-and N-power transmission lines with the symmetrical structure. Moreover, it is confirmed by simulations and experiments that the attenuation of EMI noises is affected by the width of the power transmission lines. It is expected that the results obtained in this paper can provide important rules when designing power converters with EMI noise control functions which use the multilayer power printed circuit technology. 相似文献
45.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
46.
The studies show that in the combined use of biological and chemisorption stages of treatment, a deeper degree of removal of industrial pollutants from wastewaters is attained. The chemisorption stage allows stabilizing the treatment process in different concentration-temperature drops and increasing the degree of removal of synthetic surfactants (SSF), petroleum products, and nitrogen compounds. The possibility of regulating the selectivity of the treatment process by varying the composition of the chemisorption material is demonstrated. 相似文献
47.
N. Jongen M. Donnet P. Bowen J. Lemaître H. Hofmann R. Schenk C. Hofmann M. Aoun‐Habbache S. Guillemet‐Fritsch J. Sarrias A. Rousset M. Viviani M.T. Buscaglia V. Buscaglia P. Nanni A. Testino J.R. Herguijuela 《化学工程与技术》2003,26(3):303-305
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production. 相似文献
48.
We have analyzed degradation of N-channel thin-film-transistor (TFT) under dynamic stress using a pico-second time-resolved emission microscope. We have successfully detected emission at pulse fall edge for the first time. Emission intensity increased with the decrease of pulse fall time. As the degradation depended on the pulse fall time, this dependence clearly illustrates that hot electrons are the dominant cause of the degradation under dynamic stress. Based on these dependences, we proposed a model considering electron traps in the poly-Si. 相似文献
49.
50.
Previously unknown compounds AI
I(BUO5)2·nH2O (AI
I = Mg, Ca, Sr, Ba; n = 0-7) were synthesized. Their structure and thermal decomposition were studied by X-ray diffraction, IR spectroscopy, and thermal analysis. 相似文献