全文获取类型
收费全文 | 5801篇 |
免费 | 169篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 74篇 |
综合类 | 8篇 |
化学工业 | 962篇 |
金属工艺 | 156篇 |
机械仪表 | 116篇 |
建筑科学 | 50篇 |
矿业工程 | 16篇 |
能源动力 | 307篇 |
轻工业 | 227篇 |
水利工程 | 36篇 |
石油天然气 | 20篇 |
无线电 | 654篇 |
一般工业技术 | 1156篇 |
冶金工业 | 1547篇 |
原子能技术 | 34篇 |
自动化技术 | 633篇 |
出版年
2023年 | 72篇 |
2022年 | 99篇 |
2021年 | 172篇 |
2020年 | 146篇 |
2019年 | 124篇 |
2018年 | 169篇 |
2017年 | 157篇 |
2016年 | 185篇 |
2015年 | 108篇 |
2014年 | 185篇 |
2013年 | 412篇 |
2012年 | 216篇 |
2011年 | 230篇 |
2010年 | 198篇 |
2009年 | 267篇 |
2008年 | 179篇 |
2007年 | 129篇 |
2006年 | 128篇 |
2005年 | 111篇 |
2004年 | 99篇 |
2003年 | 102篇 |
2002年 | 88篇 |
2001年 | 69篇 |
2000年 | 67篇 |
1999年 | 100篇 |
1998年 | 365篇 |
1997年 | 249篇 |
1996年 | 226篇 |
1995年 | 147篇 |
1994年 | 123篇 |
1993年 | 132篇 |
1992年 | 65篇 |
1991年 | 86篇 |
1990年 | 78篇 |
1989年 | 62篇 |
1988年 | 63篇 |
1987年 | 59篇 |
1986年 | 51篇 |
1985年 | 63篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 32篇 |
1978年 | 31篇 |
1977年 | 39篇 |
1976年 | 80篇 |
1975年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有5996条查询结果,搜索用时 15 毫秒
81.
The activities of guinea pig lung mitochondrial and microsomal glycerophosphate acyltransferase differed in sensitivity to
polymyxin B1. At an antibiotic concentration of 1 mg/ml, the mitochondrial enzyme activity was stimulated twofold, but the microsomal
enzyme activity was completely inhibited. Furthermore, the mitochondrial enzyme activity was stimulated by polymyxin B1 without the addition of exogenous acyl-CoA. Additional experiments ruled out the possibility of polymyxin B1 acting as a substrate for the mitochondrial acyltransferase. These results suggest either that the polymyxin B1 sensitivity of mitochondrial and microsomal glycerophosphate acyltransferase is different or that their accessibility to
substrates is different because the two isoenzymes are located differently in the different phospholipid microenvironment
of the membranes. 相似文献
82.
Features of pesticide synergism and acetylcholinesterase (AChE) inhibition (in vitro) were studied using a selected range of organotin compounds against the early 4th instar larvae of a highly resistant strain of the diamondback moth (DBM), Plutella xylostella, a major universal pest of cruciferous vegetables.Fourteen triorganotin compounds were evaluated for their ability to enhance the toxicity of the microbial insecticide, Bacillus thuringiensis (BT) and of the commercial insecticide, Malathion to Plutella xylostella larvae. Supplemental synergism was observed with triphenyl- and tricyclopentyltin hydroxides in combinations with Bacillus thuringiensis. Increased synergism was observed with an increase in the number of cyclopentyl groups on tin in the mixed series, Cyp(n) Ph(3-n) SnX, where X = OH, and 1-(1,2,4-triazolyl). The combination of (p-chlorophenyl)diphenyltin N,N-dimethyldithiocarbamate at LD(10) and LD(25) concentrations with sublethal concentrations of Malathion as well as of tricyclohexyltin methanesulphonate at the 0.01% (w/v) concentration with Malathion exerted strong synergistic effects (supplemental synergism) with toxicity index (T.I) values of 7.2, 19.8 and 10.1, respectively.Studies on the in vitro inhibition of acetylcholinesterase prepared from the DBM larvae showed that while most of the triorganotin Compounds tested were without effect on the enzyme, compounds containing the thiocarbamylacetate or the dithiocarbamylacetate moieties demonstrated appreciable levels of inhibition, being comparable in efficacy to commercial grades of Malathion and Methomyl. 相似文献
83.
A classical ionic inorganic complex Na2[Cu(mnt)2] (mnt2− = maleonitriledithiolate = 1,2-dicyanoethylenedithiolate), that acts as a template in assembling neutral [Cu(salen)] (salen = bis(salicylidene)ethylenediamine) complexes forming a framework type arrangement, is accommodated in the channel formed in the crystal structure of a new type of host–guest compound [Cu(salen)]4 · Na2[Cu(mnt)2] (1). The non-covalent supramolecular interactions among [Cu(salen)] complexes and between [Cu(salen)] and [Cu(mnt)2]2− complexes in the crystal lattice of 1 result in weak antiferromagnetic coupling. 相似文献
84.
Mahashweta Das Saravanan Thirumuruganathan Sihem Amer-Yahia Gautam Das Cong Yu 《The VLDB Journal The International Journal on Very Large Data Bases》2014,23(2):201-226
The rise of Web 2.0 is signaled by sites such as Flickr, del.icio.us, and YouTube, and social tagging is essential to their success. A typical tagging action involves three components, user, item (e.g., photos in Flickr), and tags (i.e., words or phrases). Analyzing how tags are assigned by certain users to certain items has important implications in helping users search for desired information. In this paper, we develop a dual mining framework to explore tagging behavior. This framework is centered around two opposing measures, similarity and diversity, applied to one or more tagging components, and therefore enables a wide range of analysis scenarios such as characterizing similar users tagging diverse items with similar tags or diverse users tagging similar items with diverse tags. By adopting different concrete measures for similarity and diversity in the framework, we show that a wide range of concrete analysis problems can be defined and they are NP-Complete in general. We design four sets of efficient algorithms for solving many of those problems and demonstrate, through comprehensive experiments over real data, that our algorithms significantly out-perform the exact brute-force approach without compromising analysis result quality. 相似文献
85.
The viscosity and apparent molar volume of solutions of KBrO3, NaBrO3 KIO3, NaIO3, K2SO4 and Na2SO4 in dioxane (mass fraction: 10, 20 and 30%)-water mixtures at 30, 35, 40 and 45°C have been measured. The ions appear to interact appreciably and the ion-solvent interaction is of the order BrO?3 > IO?3 > SO2?4 and K+ > Na+. 相似文献
86.
Full and semi-IPNs were prepared from epoxy and poly methyl methacrylate (PMMA), by the sequential mode of synthesis and were characterized by measurements of ultimate tensile strength (UTS), elongation at break, modulus, and toughness. Aromatic polyamine adducts and ethylene glycol dimethacrylate were used as the crosslinkers for epoxy and comonomer/crosslinker for methyl methacrylate monomer, respectively. Higher UTS and modulus of the semi-IPNs over full IPNs were attributed to the higher probability of interpenetration. The weight retention in the thermal decomposition of the IPNs and semi-IPNs were higher than the epoxy homopolymer. This enhancement was presumably related to the presence of the unzipped methyl methacrylate monomer which acted as radical scavangers in the epoxy degradation. © 1994 John Wiley & Sons, Inc. 相似文献
87.
Galvannealed coating of high strength interstitial free (IF-HS) steel was characterised by Glow Discharge Optical Emission Spectroscopy (GDOES) and colour-etching techniques. Overalloyed galvannealed coatings with considerably high amount of Γ and Γ1 phases were detected in the first set of experiments. Necessary process modifications in galvannealing furnace were made to maximise the ä phase in the galvannealed coating, which was confirmed through GDOES and colour-etching techniques. As a result, an improvement in galvannealed product quality with a better powdering resistance property during forming has been achieved. 相似文献
88.
Badal Soni Saswati Debnath Pradip K. Das 《International Journal of Speech Technology》2016,19(3):525-536
An important task of speaker verification is to generate speaker specific models and match an input speaker’s utterance with these models. This paper focuses on comparing the performance of text dependent speaker verification system using Mel Frequency Cepstral Coefficients feature and different Vector Quantization (VQ) based speaker modelling techniques to generate the speaker specific models. Speaker-specific information is mainly represented by spectral features and using these features we have developed the model which serves as an important entity for determining the claimed identity of the speaker. In the modelling part, we used Linde, Buzo, Gray (LBG) VQ, proposed adaptive LBG VQ and Fuzzy C Means (FCM) VQ for generating speaker specific model. The experimental results that are performed on microphonic database shows that accuracy significantly depends on the size of the codebook in all VQ techniques, and on FCM VQ accuracy also depend on the value of learning parameter of the objective function. Experiment results shows that how the accuracy of speaker verification system is depend on different representations of the codebook, different size of codebook in VQ modelling techniques and learning parameter in FCM VQ. 相似文献
89.
Ashwin S. Dhabale Rutuja Dive Mohan V. Aware Shantanu Das 《Asian journal of control》2015,17(6):2143-2152
In this paper a new algorithm is presented to calculate the poles and zeros to approximate a fractional order (FO) differintegral (s±α,α∈(0,1)) by a rational function on a finite frequency band ω∈(ωl,ωh). The constant phase property of the FO differintegral is the basis for development of the algorithm. Interlacing of real poles and zeros is used to achieve the constant phase. The calculations are done using the asymptotic Bode phase plot. A brief investigation is made to get a good approximation for the Bode phase plot. Two design parameters are introduced to keep the average phase close to the desired phase angle and to keep the error within the allowed bounds. A study is done to empirically understand the relationship between the error and the design parameters. The results thus obtained help in the further calculations. The algorithm is computationally simple and inexpensive, and gives a fairly good approximation of fractance frequency response on the specified frequency band. 相似文献
90.
Optimizing Safe Yield Policy Implementation 总被引:1,自引:1,他引:0
The presented method enhances groundwater-mandated safe yield management. It is useful for settings that prevent sustained
yield or integrated management. To protect hydraulically connected surface water rights, the Utah government’s Cache Valley
groundwater management plan proposes that total pumping increase not exceed 84,431 m3/day. To determine how best to spatially distribute additional allowable pumping, stakeholders quantified limits defining
acceptable impacts on selected water resource indicators. A new simulation–optimization (S–O) algorithm used these limits
while computing optimal spatially distributed perennial yield or safe yield groundwater pumping extraction strategies. The
limits prevent unacceptable decreases in: head and net flow between aquifer and surface waters (rivers, surface/subsurface
drains, springs, lakes). The optimization objective function maximizes weighted pumping to provide water for 18 growing municipalities.
For 16 perennial yield scenarios, computed optimal pumping increases differ in protectiveness toward senior water rights,
and range from 16% to 103% of the state plan-proposed increase. Implementing a protective strategy would achieve 90% of the
storage changes needed to reach equilibrium within 23 years. Indicator potentiometric heads would reach equilibrium within
10–40 years. At equilibrium, an optimal Cache Valley perennial yield strategy acceptably minimizes net annual non-pumping
discharges. By comparison, multi-period 20-year transient groundwater mining optimizations allow more pumping in early years.
Pumping then must decline to satisfy seepage and head constraints through year 20. Adverse seepage impact would increase for
years thereafter. For situations governed by safe or perennial yield policy, equilibrium-based (steady-state) optimization
is very useful. It effectively develops optimal perennial yield strategies. 相似文献