全文获取类型
收费全文 | 178692篇 |
免费 | 2525篇 |
国内免费 | 724篇 |
专业分类
电工技术 | 3318篇 |
综合类 | 111篇 |
化学工业 | 27989篇 |
金属工艺 | 7850篇 |
机械仪表 | 5223篇 |
建筑科学 | 4463篇 |
矿业工程 | 881篇 |
能源动力 | 4968篇 |
轻工业 | 16577篇 |
水利工程 | 1720篇 |
石油天然气 | 3144篇 |
武器工业 | 2篇 |
无线电 | 20007篇 |
一般工业技术 | 33911篇 |
冶金工业 | 33227篇 |
原子能技术 | 4332篇 |
自动化技术 | 14218篇 |
出版年
2021年 | 1438篇 |
2019年 | 1360篇 |
2018年 | 2238篇 |
2017年 | 2229篇 |
2016年 | 2324篇 |
2015年 | 1654篇 |
2014年 | 2823篇 |
2013年 | 8030篇 |
2012年 | 4721篇 |
2011年 | 6548篇 |
2010年 | 5180篇 |
2009年 | 6055篇 |
2008年 | 6032篇 |
2007年 | 5973篇 |
2006年 | 5107篇 |
2005年 | 4747篇 |
2004年 | 4525篇 |
2003年 | 4198篇 |
2002年 | 4131篇 |
2001年 | 4142篇 |
2000年 | 3947篇 |
1999年 | 4081篇 |
1998年 | 10412篇 |
1997年 | 7407篇 |
1996年 | 5666篇 |
1995年 | 4288篇 |
1994年 | 3625篇 |
1993年 | 3577篇 |
1992年 | 2620篇 |
1991年 | 2547篇 |
1990年 | 2425篇 |
1989年 | 2438篇 |
1988年 | 2378篇 |
1987年 | 2097篇 |
1986年 | 2044篇 |
1985年 | 2349篇 |
1984年 | 2164篇 |
1983年 | 1984篇 |
1982年 | 1860篇 |
1981年 | 1931篇 |
1980年 | 1772篇 |
1979年 | 1798篇 |
1978年 | 1755篇 |
1977年 | 2087篇 |
1976年 | 2663篇 |
1975年 | 1543篇 |
1974年 | 1536篇 |
1973年 | 1592篇 |
1972年 | 1338篇 |
1971年 | 1245篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
Dr. Alexander Fries Dr. Laura S. Mazzaferro Dr. Björn Grüning Dr. Philippe Bisel Karin Stibal Patrick C. F. Buchholz Prof. Dr. Jürgen Pleiss Prof. Dr. Georg A. Sprenger Prof. Dr. Michael Müller 《Chembiochem : a European journal of chemical biology》2019,20(13):1672-1677
Chorismate and isochorismate constitute branch-point intermediates in the biosynthesis of many aromatic metabolites in microorganisms and plants. To obtain unnatural compounds, we modified the route to menaquinone in Escherichia coli. We propose a model for the binding of isochorismate to the active site of MenD ((1R,2S, 5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC) synthase) that explains the outcome of the native reaction with α-ketoglutarate. We have rationally designed variants of MenD for the conversion of several isochorismate analogues. The double-variant Asn117Arg–Leu478Thr preferentially converts (5S,6S)-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHD), the hydrolysis product of isochorismate, with a >70-fold higher ratio than that for the wild type. The single-variant Arg107Ile uses (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHA) as substrate with >6-fold conversion compared to wild-type MenD. The novel compounds have been made accessible in vivo (up to 5.3 g L−1). Unexpectedly, as the identified residues such as Arg107 are highly conserved (>94 %), some of the designed variations can be found in wild-type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %). This raises the question for the possible natural occurrence of as yet unexplored branches of the shikimate pathway. 相似文献
52.
Waheed Iqbal Mariam Batool Arslan Hameed Saghir Abbas Muhammad Arif Nadeem 《International Journal of Hydrogen Energy》2021,46(49):25050-25059
Transition metal oxyhydroxides have been used as promising electrocatalysts for water splitting however, their catalytic activity is restricted due to low surface area and poor conductivity. Herein, we report novel composite FeOOH@ZIF-12/graphene composite as electrocatalyst for water oxidation, whereby ZIF-12 provide extra surface for the FeOOH dispersion whilst graphene act as excellent electron mediator. The composite shows a low overpotential value of 291 mV to attain a current density of 10 mA cm?2 and a low Tafel slope value of 78 mV dec?1. The catalyst offers a maximum current density of 101 mA cm?2, while it gives a turnover frequency (TOF) value of 0.031 s?1 at an overpotential of 291 mV only. The excellent activity and remarkable stability of composite is attributed to highly conductive and porous support. 相似文献
53.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for... 相似文献
54.
55.
A. A. Babenko V. I. Zhuchkov L. A. Smirnov A. V. Sychev A. A. Akberdin A. S. Kim M. F. Vitushchenko A. A. Dobromilov 《Steel in Translation》2015,45(11):883-886
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite. 相似文献
56.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
57.
Nidhi Nandu Mustafa Salih Hizir Neil M. Roberston Dr. Birol Ozturk Prof. Dr. Mehmet V. Yigit 《Chembiochem : a European journal of chemical biology》2019,20(14):1861-1867
Two-dimensional MoS2 nanoparticles (2D-nps) exhibit artificial enzyme properties that can be regulated at bio-nanointerfaces. We discovered that protein lipase is able to tune the peroxidase-like activity of MoS2 2D-nps, offering low-nanomolar, label-free detection and identification in samples with unknown identity. The inhibition of the peroxidase-like activity of the MoS2 2D-nps was demonstrated to be concentration dependent, and as low as 5 nm lipase was detected with this approach. The results were compared with those obtained with several other proteins that did not display any significant interference with the nanozyme behavior of the MoS2 2D-nps. This unique response of lipase was characterized and exploited for the successful identification of lipase in six unknown samples by using qualitative visual inspection and a quantitative statistical analysis method. The developed methodology in this approach is noteworthy for many aspects; MoS2 2D-nps are neither labeled with a signaling moiety nor modified with any ligands for signal readout. Only the intrinsic nanozyme activity of the MoS2 2D-nps is exploited for this detection approach. No analytical equipment is necessary for the visual detection of lipase. The synthesis of the water-soluble MoS2 2D-nps is low costing and can be performed in bulk scale. Exploring the properties of 2D-nps and their interactions with biological materials reveals highly interesting yet instrumental features that offer the development of novel bioanalytical approaches. 相似文献
58.
Arif Karademir Cem Aydemir Semiha Yenidogan Emine Arman Kandırmaz Rukiye G. Kıter 《Color research and application》2020,45(6):1170-1178
Alkyd resins are generally used in the production of printing inks. All industries look for alternative raw materials in the production of ink with the growing inclination toward using natural products. Resins forming the vehicle of the ink to be obtained from natural resources will provide benefits for the environment, nature, and living creatures. The aim of the study was to promote the use of natural resin in the ink system. Natural Pinus pinaster resin was added into vegetable and mineral oil-based solvents in pure form with alkyd resin in different amounts and ink varnishes of different combinations were prepared. Then, printing inks were produced from these varnishes in pure and hybrid form. Following the assessment of the rheological properties of the inks prepared, printing tests were conducted to assess the printing quality parameters. Ideal mixing ratios of the natural resins in the ink were determined for printability. The environmental importance and advantages of the use of natural resins were discussed. Recommendations were given in line with the results to encourage widespread use of natural resins in near future. 相似文献
59.
D. M. Mukhammadiev F. Kh. Ibragimov T. D. Mukhammadiev 《Journal of Machinery Manufacture and Reliability》2020,49(3):256-262
The dynamic characteristics of a saw gin as a subsystem with lumped and distributed parameters are considered in the paper. On the basis of investigation of the machine assembly, graphs are drawn that allow establishing the maximum values of the angle of relative rotation and the angle of rotation of the saw cylinder shaft under torsion. 相似文献
60.