全文获取类型
收费全文 | 310932篇 |
免费 | 31837篇 |
国内免费 | 10900篇 |
专业分类
电工技术 | 15414篇 |
技术理论 | 15篇 |
综合类 | 15517篇 |
化学工业 | 60330篇 |
金属工艺 | 16977篇 |
机械仪表 | 18135篇 |
建筑科学 | 20167篇 |
矿业工程 | 7486篇 |
能源动力 | 7577篇 |
轻工业 | 23266篇 |
水利工程 | 5335篇 |
石油天然气 | 17072篇 |
武器工业 | 1924篇 |
无线电 | 34963篇 |
一般工业技术 | 49069篇 |
冶金工业 | 18012篇 |
原子能技术 | 5915篇 |
自动化技术 | 36495篇 |
出版年
2024年 | 1213篇 |
2023年 | 4169篇 |
2022年 | 8113篇 |
2021年 | 11101篇 |
2020年 | 9460篇 |
2019年 | 9552篇 |
2018年 | 10917篇 |
2017年 | 12160篇 |
2016年 | 11829篇 |
2015年 | 13626篇 |
2014年 | 16182篇 |
2013年 | 19843篇 |
2012年 | 18897篇 |
2011年 | 19772篇 |
2010年 | 17489篇 |
2009年 | 16874篇 |
2008年 | 16191篇 |
2007年 | 15263篇 |
2006年 | 14676篇 |
2005年 | 12626篇 |
2004年 | 9264篇 |
2003年 | 8940篇 |
2002年 | 8754篇 |
2001年 | 7961篇 |
2000年 | 7212篇 |
1999年 | 6503篇 |
1998年 | 5131篇 |
1997年 | 4266篇 |
1996年 | 3862篇 |
1995年 | 3251篇 |
1994年 | 2709篇 |
1993年 | 2089篇 |
1992年 | 1901篇 |
1991年 | 1549篇 |
1990年 | 1488篇 |
1989年 | 1340篇 |
1988年 | 1153篇 |
1987年 | 1025篇 |
1986年 | 908篇 |
1985年 | 814篇 |
1984年 | 777篇 |
1982年 | 720篇 |
1981年 | 737篇 |
1979年 | 766篇 |
1978年 | 792篇 |
1977年 | 768篇 |
1976年 | 787篇 |
1975年 | 724篇 |
1974年 | 719篇 |
1973年 | 726篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
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
53.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献
54.
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
55.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
56.
57.
E. A. Gurieva P. P. Konstantinov L. V. Prokof D. A. Pshenaĭ-Severin M. I. Fedorov Yu. I. Ravich 《Semiconductors》2006,40(7):763-767
The coefficients of thermopower and electrical and thermal conductivity in the PbTe0.8Se0.1 S 0.1 solid solution with electron concentration (4.6–54) × 1018 cm?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb1?x SnxTe1?x Sex alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L0 numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L0 = 0.75 is obtained for a lightly doped sample at ~130 K. 相似文献
58.
This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver. 相似文献
59.
60.
N.S. Chen S.F. Yu 《Photonics Technology Letters, IEEE》2004,16(7):1610-1612
The effect of external optical feedback on the transient response of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) is studied. It can be shown that the proper design of ARROW can suppress the excitation of high-order transverse leaky mode as well as increase the critical feedback strength so that stable high-power single-mode operation of VCSELs can be obtained even under the influence of strong external optical feedback. 相似文献