全文获取类型
收费全文 | 2994篇 |
免费 | 64篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 36篇 |
综合类 | 3篇 |
化学工业 | 633篇 |
金属工艺 | 34篇 |
机械仪表 | 34篇 |
建筑科学 | 197篇 |
矿业工程 | 21篇 |
能源动力 | 62篇 |
轻工业 | 160篇 |
水利工程 | 27篇 |
石油天然气 | 48篇 |
无线电 | 170篇 |
一般工业技术 | 384篇 |
冶金工业 | 815篇 |
原子能技术 | 19篇 |
自动化技术 | 418篇 |
出版年
2022年 | 27篇 |
2021年 | 35篇 |
2019年 | 34篇 |
2018年 | 36篇 |
2017年 | 54篇 |
2016年 | 48篇 |
2015年 | 42篇 |
2014年 | 42篇 |
2013年 | 179篇 |
2012年 | 71篇 |
2011年 | 104篇 |
2010年 | 83篇 |
2009年 | 93篇 |
2008年 | 105篇 |
2007年 | 109篇 |
2006年 | 95篇 |
2005年 | 110篇 |
2004年 | 74篇 |
2003年 | 96篇 |
2002年 | 68篇 |
2001年 | 74篇 |
2000年 | 51篇 |
1999年 | 64篇 |
1998年 | 97篇 |
1997年 | 65篇 |
1996年 | 69篇 |
1995年 | 45篇 |
1994年 | 40篇 |
1993年 | 40篇 |
1992年 | 38篇 |
1991年 | 32篇 |
1990年 | 53篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 52篇 |
1986年 | 35篇 |
1985年 | 49篇 |
1984年 | 39篇 |
1983年 | 35篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 34篇 |
1978年 | 34篇 |
1977年 | 30篇 |
1976年 | 49篇 |
1975年 | 30篇 |
1974年 | 32篇 |
1973年 | 42篇 |
1972年 | 23篇 |
排序方式: 共有3061条查询结果,搜索用时 15 毫秒
91.
Teresa A Morrison J Raymond Kessler Ronald D Hatfield Dwayne R Buxton 《Journal of the science of food and agriculture》1994,65(2):133-139
To ascertain the temporal relationships of phcnylpropanoid and lignin pathway enzymes, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol- NADPH dehydrogenase(CAD), with lignin concentration, PAL and CAD activities and lignin concentrations were assessed during progressive development of the 10th internode in maize (Zea mays L). Enzyme activities were quantified and lignin concentrations were determined by the detergent system of fiber fractiona- tion from lower, middle, and upper sections of the elongating internode harvested 3, 5, 7, 9, 11, 13, and 15 days after the internode had reached 10 mm in length. Over 15 days, a coordinated, sequential, and basipetal pattern of enzyme activities and lignin accumulation evolved through the internode, spanning the stages of rapid elongation, cellular differentiation, and secondary cell wall formation. PAL activity was initiated first, rising to peak activity in elongating tissue, and falling basipetally in tissues as they matured. CAD activity rose in fully elongated, maturing internode tissue where PAL activity was waning following its peak activity. Lignin accumulated in tissues with high CAD activity. CAD activity and lignin deposition patterns were similar: simultaneously increasing in activity and deposition over time while activity and deposition also shifting basipetally through the internode, keeping pace with secondary cell wall formation. Lignin concentration correlated significantly with CAD, but not with PAL. 相似文献
92.
A novel technique for the preparation of secondary fatty amides 总被引:1,自引:0,他引:1
Alexander Bilyk Raymond G. Bistline Jr. George J. Piazza Stephen H. Feairheller Michael J. Haas 《Journal of the American Oil Chemists' Society》1992,69(5):488-491
A technique for the synthesis of monosubstituted fatty amides at low temperature and ambient pressure was developed. This
method involved the condensation of an amine with a triacylglycerol. The primary amine (ethyl,n-butyl,n-hexyl andn-octyl were tested) acted as reagent and solvent for the fatty substrates. No additional organic solvent or catalyst was added.
Tallow, vegetable oils and fish oil all served well as substrates, as did pure tripalmitin. The rate of amidation was dependent
upon temperature and the ratio of fat to amine. In a series of experiments conducted with tallow andn-butylamine at a fat:amine molar ratio of 1:16, amidation could be carried out at 20°C, producingn-butyltallowamide in 83% yield in 24 hr. When the fat:amine molar ratio was reduced to 1:8, and the temperature raised to
45°C, the amide yield was 87.6% in 24 hr. When the reaction was carried out at the boiling point ofn-butylamine (78°C) and at a fat:amine ratio of 1:8, the amide yield was 93.2% in 4 hr. The reaction progressed more rapidly
with higher molecular weight amines. The identity and purity of the amides was assessed by thin-layer chromatography and confirmed
by elemental analyses and infrared and C13 nuclear magnetic resonance spectroscopy. 相似文献
93.
Synthesis, Sintering, Microstructure, and Mechanical Properties of Ceramics Made by Exothermic Reactions 总被引:6,自引:0,他引:6
Raymond A. Cutler Kevin M. Rigtrup Anil V. Virkar 《Journal of the American Ceramic Society》1992,75(1):36-43
Al2 O3 -TiC, Al2 O3 -TiC0.5 N0.5 , Al2 O3 -WC, Al2 O3 -SiC, and Al2 O3 -HfB2 powders were synthesized by the aluminothermic reduction of oxides in the presence of carbon or boron. The reacted powders were milled to reduce the size of agglomerates and subsequently densified without applied pressure to near-theoretical density. Microstructures and mechanical properties of composites made from exothermically reacted powders were compared with similar ceramics made from commercially available powders. In situ sintering was possible in the Al2 O3 -TiC system using a closed graphite crucible to contain reaction gases. The synthesis of β -SiC at temperatures above 1400°C via the direct reaction of the elements (SHS) was compared with SiC made by the magnesiothermic reduction of SiO2 in the presence of C after removing the MgO by leaching. 相似文献
94.
This work focuses on synthesizing nonlinear decoupling controllers for multivariable nonlinear systems represented by a state-space model, in the presence of deadtimes. The deadtimes appear in both the inputs and the outputs, but not in the states, and are physically associated with sensors and actuators. Simple sufficient conditions for feasibility of closed-loop deadtimes are derived, which rely only on the structural properties of the system. A control law is then derived so that the closed-loop system is input/output linear and decoupled, with deadtimes equal to the smallest ones that satisfy the feasibility conditions. The proposed method is applied to a chemical process. Its performance is evaluated through simulation in the presence of set-point and disturbance changes. 相似文献
95.
Shie Teck Tiew Yick Eu Chew Ho Yan Lee Jia Wen Chong Raymond R. Tan Kathleen B. Aviso Nishanth G. Chemmangattuvalappil 《化学,工程师,技术》2023,95(3):438-446
In this work, a novel machine learning based methodology was developed to predict fragrance from the molecular structure and the effect of the subjects attributes on odour perception. As fragrance is linked to the molecular structure and interactions, topological indices are used to develop a predictive model. Rough set-based machine learning is used to generate rule-based models that link the topology of fragrant molecules and dilution to their respective odour characteristics. The results show that the generated models are effective in determining the odour characteristic of molecules. 相似文献
96.
Anubhav Sarmah Raymond D. Mee Kailash Arole David Chi Ethan M. Harkin Smita Shivraj Dasari Aniela J. K. Wright Thang Q. Tran Ankush Rout Micah J. Green 《大分子材料与工程》2023,308(11):2300174
This work shows that radio-frequency (RF) fields can simultaneously align carbon nanotubes (CNTs) dispersed in a resin and induce Joule heating to cure the resin. The timescales of alignment and curing using RF heating are numerically computed and compared at different field strengths in order to determine a temperature where alignment happens before the matrix crosslinks. Composites are experimentally fabricated at the desired target temperature and are optically analyzed and quantified; the CNT network is successfully aligned in the direction of the applied electric field. This methodology can be used to create composites where the local alignment can be varied across the sample. Composites fabricated using RF fields have higher electrical conductivity in the direction of the aligned CNTs than an oven-cured, randomly aligned sample. Also, RF-cured nanocomposites exhibit higher tensile strength and modulus in the direction of alignment compared to an oven-cured sample. Finally, it is further demonstrated how this methodology can be coupled with a direct ink writing additive manufacturing process to induce alignment in any desired direction, even orthogonal to the shear forces in the extrusion direction. 相似文献
97.
Anne Makena Dr. Sander S. van Berkel Dr. Clarisse Lejeune Dr. Raymond J. Owens Dr. Anil Verma Ramya Salimraj Dr. James Spencer Dr. Jürgen Brem Prof. Dr. Christopher J. Schofield 《ChemMedChem》2013,8(12):1923-1929
Serine‐ and metallo‐β‐lactamases present a threat to the clinical use of nearly all β‐lactam antibiotics, including penicillins, cephalosporins, and carbapenems. Efforts to develop metallo‐β‐lactamase (MBL) inhibitors require suitable screening platforms to allow the rapid determination of β‐lactamase activity and efficient inhibition. Unfortunately, the platforms currently available are not ideal for this purpose. Further progress in MBL inhibitor identification requires inexpensive and widely applicable assays. Herein the identification of an inexpensive and stable chromogenic substrate suitable for use in assays of clinically relevant MBLs is described. (6R,7R)‐3‐((4‐Nitrophenoxy)methyl)‐8‐oxo‐7‐(2‐phenylacetamido)‐5‐thia‐1‐azabicyclo[4.2.0]oct‐2‐ene‐2‐carboxylic acid 5,5‐dioxide (CLS405) was synthesised in a three‐step protocol. CLS405 was then characterised spectroscopically, and its stability and kinetic properties evaluated. With a Δλmax value of 100 nm between the parent and hydrolysis product, a higher analytical accuracy is possible with CLS405 than with commonly used chromogenic substrates. The use of CLS405 in assays was validated by MBL activity measurements and inhibitor screening that resulted in the identification of N‐hydroxythiazoles as new inhibitor scaffolds for MBLs. Further evaluation of the identified N‐hydroxythiazoles against a panel of clinically relevant MBLs showed that they possess inhibitory activities in the mid‐ to low‐micromolar range. The findings of this study provide both a useful tool compound for further inhibitor identification, and novel scaffolds for the design of improved MBL inhibitors with potential as antibiotics against resistant strains of bacteria. 相似文献
98.
Raymond E.H. Ooi Dominic C.Y. Foo Denny K.S. Ng Raymond R. Tan 《Chemical Engineering Research and Design》2013
Carbon capture and storage (CCS) is a means for reducing carbon dioxide (CO2) emissions from fossil fuel combustion in power generation and industrial processes. It involves the capture of CO2 for subsequent storage in various geological formations. The selection and matching of the power plants and storage sites are often an issue of optimisation due to various constraints, i.e., time of availability, injection rate, and storage capacity limits. In this work, a novel graphical targeting tool based on pinch analysis is proposed to address the planning problem of the storage of captured CO2 from power generating plants into corresponding reservoirs. The main consideration for the problem is the time of availability of the latter, since reservoirs need to be developed prior to CO2 storage. The time limitation is addressed by the graphical technique where time is taken as the governing element in solving the problem. Hypothetical examples are used to elucidate the proposed approach. 相似文献
99.
Monodisperse proteins and polydisperse carbohydrates and polyenes occur in nature. The proteins are random copolymers, but no block or graft copolymers occur in nature. 相似文献
100.
Abhimanyu Jayakumar Ashay Javadekar Jacob Gissinger John M. Vohs George W. Huber Raymond J. Gorte 《American Institute of Chemical Engineers》2013,59(9):3342-3348
The long‐term stability of direct carbon fuel cells, based on solid oxide fuel cells with molten Sb and Sb–Bi anodes, was examined for operation with activated charcoal, rice starch, and bio‐oil fuels at 973 K. With intermittent stirring of the fuel–metal anode interface, the anode performance was stable, and reasonable power densities (~250 mW/cm2) were achieved for periods up to 250 h. With Sc‐stabilized zirconia, severe thinning of the electrolyte occurred in regions of high current flow. No electrolyte thinning was observed with yttria‐stabilized zirconia as the electrolyte operating at the same current densities. © 2012 American Institute of Chemical Engineers AIChE J, 59: 3342–3348, 2013 相似文献