全文获取类型
收费全文 | 9729篇 |
免费 | 456篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 97篇 |
综合类 | 4篇 |
化学工业 | 1999篇 |
金属工艺 | 142篇 |
机械仪表 | 188篇 |
建筑科学 | 616篇 |
矿业工程 | 21篇 |
能源动力 | 321篇 |
轻工业 | 854篇 |
水利工程 | 110篇 |
石油天然气 | 28篇 |
无线电 | 729篇 |
一般工业技术 | 1969篇 |
冶金工业 | 1287篇 |
原子能技术 | 42篇 |
自动化技术 | 1798篇 |
出版年
2023年 | 70篇 |
2022年 | 137篇 |
2021年 | 216篇 |
2020年 | 177篇 |
2019年 | 212篇 |
2018年 | 235篇 |
2017年 | 234篇 |
2016年 | 258篇 |
2015年 | 228篇 |
2014年 | 337篇 |
2013年 | 666篇 |
2012年 | 559篇 |
2011年 | 794篇 |
2010年 | 506篇 |
2009年 | 480篇 |
2008年 | 600篇 |
2007年 | 519篇 |
2006年 | 441篇 |
2005年 | 389篇 |
2004年 | 333篇 |
2003年 | 308篇 |
2002年 | 285篇 |
2001年 | 149篇 |
2000年 | 161篇 |
1999年 | 139篇 |
1998年 | 146篇 |
1997年 | 155篇 |
1996年 | 139篇 |
1995年 | 115篇 |
1994年 | 93篇 |
1993年 | 95篇 |
1992年 | 84篇 |
1991年 | 69篇 |
1990年 | 79篇 |
1989年 | 64篇 |
1988年 | 44篇 |
1987年 | 63篇 |
1986年 | 52篇 |
1985年 | 57篇 |
1984年 | 52篇 |
1983年 | 67篇 |
1982年 | 49篇 |
1981年 | 41篇 |
1980年 | 36篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1976年 | 28篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Bottomley Stephen P.; Popplewell Andrew G.; Scawen Michael; Wan Tommy; Sutton Brian J.; Gore Michael G. 《Protein engineering, design & selection : PEDS》1994,7(12):1463-1470
The stability and unfolding of an immunoglobulin (Ig) G bindingprotein based upon the B domain of protein A (SpAB) from Staphylococcusaureus were studied by substituting tryptophan residues at strategiclocations within each of the three a-helical regions (al-a3)of the domain. The role of the C-terminal helix, a3, was investigatedby generating two protein constructs, one corresponding to thecomplete SpAB, the other lacking a part of ct3; the Trp substitutionswere made in both one-and two-domain versions of each of theseconstructs. The fluorescence properties of each of the single-tryptophanmutants were studied in the native state and as a function ofguanidine-HCl-mediated unfolding, and their IgG binding activitieswere determined by a competitive enzyme-linked immunosorbentassay. The free energies of folding and of binding to IgG foreach mutant were compared with those for the native domains.The effect of each substitution upon the overall structure andupon the IgG binding interface was modelled by molecular graphicsand energy minimization. These studies indicate that (i) 3 contributesto the overall stability of the domain and to the formationof the IgG binding site in l and 2, and (ii) al unfolds first,followed by 2 and 3 together. 相似文献
82.
Martel Zeldin Eric Granger Wilmer K. Fife 《Journal of Inorganic and Organometallic Polymers》1993,3(2):141-154
New silane monomers with the pendant 4-(3-pyridine)butyl group have been synthesized by hydrosilation of 3-(3-butenyl)pyridine with Me
n
Si(OEt)3-n
H (n=0, 1) using a platinum catalyst. Only -addition products were observed. The products were characterized by elemental analysis, infrared,1H- and13C-NMR spectroscopy, and gas chromatography-mass spectrometry. Hydrolysis-polycondensation of the difunctional monomer with a basic catalyst, Me4NOH, gave a mixture of cyclic oligomers, principally cyclic tetramer, and linear homopolymer. Under similar reaction conditions, the trifunctional monomer gave crosslinked material which was soluble in common organic solvents. The linear homopolymer and crosslinked polymer were trimethylsilyl end-blocked with hexamethyldisilazane. The cyclic and end-blocked polymers were characterized by elemental analysis and spectroscopic methods. Molecular weights of the polymers were obtained by end-group analysis using1H-NMR spectral data, size exclusion chromatography, and direct insertion-probe mass spectrometry. The cyclic, linear, and crosslinked materials were N-oxidized withm-chloroperoxybenzoic acid and characterized by spectroscopic methods. The polymeric N-oxide derivatives were shown to be effective transacylation catalysts in the synthesis of mixed carboxylic acid anhydrides in immiscible solvents (H2O/CH2Cl2) under phase-transfer conditions. The implications of the results on the mechanism of catalysis are discussed. 相似文献
83.
Tessa E. Smith David H. Abbott Andrew J. Tomlinson Jerzy A. Mlotkiewicz 《Journal of chemical ecology》1997,23(11):2523-2546
The hypothesis was tested that marmosets have differential displays of investigatory behavior towards circumgenital scent marks from socially dominant females based on degree of familiarity. In a series of two-choice behavioral discrimination bioassays, dominant males together with subordinate and dominant females were presented concurrently with scent secretions from familiar versus unfamiliar dominant females, and their investigative behaviors towards the scent were recorded. Test animals directed significantly different amounts of investigative behaviors towards familiar versus unfamiliar scents when the scent stimuli involved complete circumgenital scent marks, glandular secretion only, or urine only. When animals discriminated between the two scent samples, they did so by directing significantly increased amounts of behavior to scent from unfamiliar females. Chemical cues promoting differential displays of behavior to familiar versus unfamiliar scents appeared to be volatile in nature and were effective in the scent mark for at least one day following deposition. The reliable ability of marmosets to consistently discriminate between odors from familiar versus unfamiliar dominant females provides strong circumstantial evidence that individual female marmosets have distinct chemical signatures. The ability of marmosets to discriminate the odor from familiar versus unfamiliar dominant females may be important in the context of intergroup relations. 相似文献
84.
J. Richard Hall Carolyn A. L. Westerdahl Andrew T. Devine Michael J. Bodnar 《应用聚合物科学杂志》1969,13(10):2085-2096
Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm?1 in PE, and 887 and 910 cm?1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found. 相似文献
85.
Michelle?A.?Phipps Andrew?F.?A.?HoadleyfEmail author 《Korean Journal of Chemical Engineering》2003,20(4):642-648
Heat integration techniques can be used to optimize the energy requirement for both new and retrofit plant designs. Software
tools for identifying retrofit options are becoming available. This paper reports our experiences from using heat exchanger
network (HEN) optimization software for a retrofit case study of an oil refinery process. The HEN optimization software was
used to automate the search for the most beneficial retrofit designs following the twostage process proposed by Asante and
Zhu. The software provided three potential retrofit designs. Results from this analysis were used as the basis of a rigorous
mass and energy balance simulation of the plant. The simulation corroborated the energy savings, but there were some important
differences. The simulation required 20% more heat exchange area. Furthermore, the retrofit design involving one topology
change was shown to be less economic than an alternative design. These differences are discussed and a revised methodology
is proposed. 相似文献
86.
Andrew A. Sobek Vijay Rastogi Donald A. Benedetti 《Mine Water and the Environment》1990,9(1-4):133-148
In pyritic environments, the bacteriaThiobacillus ferrooxidans catalyze acid formation by increasing the oxidation rate of pyrite by a factor of one million. This acid solubilizes metals and pollutes adjacent streams and lands. Bactericide sprays during mining and waste disposal operations attack the source of the problem by preventing acid formation and metals solubilization. Used in conjunction with current water treatment systems, bactericides can dramatically reduce operating costs. Controlled release bactericides contribute to successful reclamation by providing assurance against revegetation failure and post-reclamation water quality problems that can necessitate perpetual water treatment. While inhibitingT. ferrooxidans these organic compounds aid in the establishment of beneficial heterotrophic bacteria which support vegetation. These conditions continue to persist after the bactericide is depleted from the controlled release system. Case Studies I and II show that bactericides inhibit acid generation during hard rock and coal mining operations and they are cost effective. Case Studies III and IV illustrate the improvement in water quality and vegetation after reclamation when controlled release bactericides were used. Economic analyses show cost benefits are achieved when controlled-release bactericides are part of the reclamation plan. 相似文献
87.
Ian A. Brummel Daniel E. Drury Andrew R. Kitahara Farid El Gabaly Jon F. Ihlefeld 《Journal of the American Ceramic Society》2021,104(2):711-721
Lithium zirconium phosphate (LiZr2P3O12) thin films have been prepared on platinized silicon substrates via a chemical solution deposition approach with processing temperatures between 700°C and 775°C. Films that were subject to a single high-temperature anneal were found to crystallize at temperatures above 725°C. Crystallization was observed in films annealed after each deposited layer at 700°C and above. In both cases, grain size was found to increase with annealing temperature. Ion conductivity was found to increase with annealing temperature in singly annealed films. In per-layer annealed films ion conductivity was found to initially increase then decrease with increasing annealing temperature. A maximum ion conductivity of 1.6 × 10−6 S/cm was observed for the singly annealed 775°C condition, while a maximum ion conductivity of 5.8 × 10−7 S/cm was observed for the 725°C per-layer annealed condition. These results are consistent with an increasing influence of cross-plane, internal interface resistance and vapor phase carrier loss in the per-layer annealed samples. This work demonstrates that post-deposition processing methods can strongly affect the ion conducting properties of LiZr2P3O12 thin films. 相似文献
88.
A study of 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 shows that, when it is doped with 2.5% Sm on the A-site, in addition to an almost threefold increase in piezoelectric charge coefficient and dielectric permittivity, there is a 2 order of magnitude reduction in conductivity, attributed to a decrease in oxygen vacancy concentration. An analysis of the nonlinearity of permittivity with respect to field amplitude shows that both the reversible and irreversible contributions increase significantly with Sm-doping, with simple models showing that these changes are consistent with a reduction in the concentration of dipolar defects that can inhibit both polarization rotation and domain wall translation. Contrary to the argument that doping increases heterogeneity, there is little change in the diffuseness of the peak in permittivity as a function temperature, whilst there is a 15% increase in spontaneous polarization with Sm addition. Through comparison of the Rayleigh law parameters with those published for other piezoelectric materials, it is concluded that a significant contribution to the observed increase in piezoelectric performance due to Sm-doping of PMN-PT is similar in origin to that seen in soft, donor-doped PZT and other conventional piezoelectric ceramics. 相似文献
89.
Andrew J. Steveson Waltraud M. Kriven 《Journal of the American Ceramic Society》2021,104(7):3397-3410
The K[AlSi2O6]-Cs[AlSi2O6] pseudo-binary system was synthesized by geopolymer crystallization. The thermal expansion properties of these materials were studied by in situ high-temperature X-ray diffraction to characterize thermal expansion behavior for potential application as environmental barrier coatings. Tailorable thermal expansion through changing cation stoichiometry allowed reduced thermal expansion mismatch with SiCf/SiC composites compared to rare-earth-based coatings. 相似文献
90.
Mollie B. Schear Arianna Neal Jadah S. Clarke Andrew P. Saab Carl B. Giller Riccardo Casalini Matthew Laskoski 《应用聚合物科学杂志》2021,138(12):50053
The preparation of highly aromatic elastomers from a bisphenol A-based divinyl-terminated resin and polymerization with various aromatic silane containing compounds utilizing a room temperature hydrosilylation reaction is demonstrated. The polymers exhibit high thermal and oxidative stability with 5% weight losses around 430 and 350°C and char yields ranging from 35% to 40%. The thermosets maintained their elastomeric properties with good hardness and mechanical properties as measured by elongation measurements. The toughness of the thermosets was not improved with the inclusion of aromatic moieties but the hardness did appear to increase with the addition of more aromatic groups. 相似文献