全文获取类型
收费全文 | 3338篇 |
免费 | 195篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 3536篇 |
出版年
2024年 | 11篇 |
2023年 | 40篇 |
2022年 | 42篇 |
2021年 | 100篇 |
2020年 | 84篇 |
2019年 | 110篇 |
2018年 | 169篇 |
2017年 | 154篇 |
2016年 | 154篇 |
2015年 | 143篇 |
2014年 | 194篇 |
2013年 | 396篇 |
2012年 | 200篇 |
2011年 | 254篇 |
2010年 | 247篇 |
2009年 | 192篇 |
2008年 | 118篇 |
2007年 | 90篇 |
2006年 | 54篇 |
2005年 | 19篇 |
2004年 | 34篇 |
2003年 | 35篇 |
2002年 | 38篇 |
2001年 | 32篇 |
2000年 | 40篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 19篇 |
1995年 | 23篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1985年 | 20篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 37篇 |
1980年 | 26篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 32篇 |
1975年 | 23篇 |
1974年 | 16篇 |
1973年 | 22篇 |
排序方式: 共有3536条查询结果,搜索用时 15 毫秒
991.
Kelly F. Robinson Mark DuFour Michael Jones Seth Herbst Tammy Newcomb James Boase Travis Brenden Duane Chapman John Dettmers James Francis Travis Hartman Patrick Kočovský Brian Locke Christine Mayer Jeff Tyson 《Journal of Great Lakes research》2021,47(1):108-119
Decisions about invasive species control and eradication can be difficult because of uncertainty in population demographics, movement ecology, and effectiveness of potential response actions. These decisions often include multiple stakeholders and management entities with potentially different objectives, management priorities, and jurisdictional authority. We provide a case study of using multi-party, collaborative decision analysis to aid decision makers in determining objectives and control actions for invasive grass carp (Ctenopharyngodon idella) in Lake Erie. Creating this process required binational (Canada-United States) and multi-state/provincial collaboration to craft a shared problem statement, establish objectives related to ecological, economic, and social concerns, determine potential response actions, and evaluate consequences and tradeoffs of these actions. We used participatory modeling and expert elicitation to evaluate the effectiveness of control scenarios that varied in action type (i.e., removal efforts and spawning barriers) and the temporal and spatial application of these actions. Using a matrix population model parameterized for western Lake Erie grass carp, we found that removal efforts concentrated in areas of high catchability, when paired with a spawning barrier on the Sandusky River, Ohio, USA, could effectively control grass carp in Lake Erie, if all assumptions are met. We determined a set of key uncertainties regarding gear catchability and current population size that have led to the transition to an adaptive management process. In addition, our work formed the basis for grass carp management plans for the states of Michigan and Ohio and has provided a means for collaboration among agencies for effective application of control efforts. 相似文献
992.
Marta Harničárová Jan Valíček Robert Čep Hakan Tozan Jana Müllerová Radovan Grznárik 《The International Journal of Advanced Manufacturing Technology》2013,69(1-4):81-91
The contribution deals with comparing non-traditional cutting technologies from the point of view of generated surface roughness. The comparison is carried out for technologies of abrasive waterjet cutting, oxygen cutting, laser and plasma cutting. As an experimental material, EN S355J0 structural steel and titanium CP-Ti Grade 2 was used. Surface topography measurement was done using a Mitutoyo Surftest SJ-401 instrument, and an optical profilometer MicroProf FRT was used for comparison and verification of acquired surface data. The aim of the contribution is to clarify, on the basis of experimental measurements, the behaviour of a topographic function after various ways of cutting; the knowledge of the function is necessary for solving both theoretical and practical technological tasks. The topographic function, which is a basis for the prediction of quality and control of the cutting processes, was derived in an original way. The use of individual technologies depends on technical and economical possibilities and on environmental influences. The results of measurement of cut surface roughness are in good accordance with the results of theoretical analysis. 相似文献
993.
The interaction between Pd2+ ions and Cu2-xS coating formed by three cycles and containing ~30 at.% of elementary S has been investigated by the methods of cyclic voltammetry and photoelectron spectroscopy (one cycle of coating formation includes treatment of the surface with Cu(I)+Cu(II) ammoniate solution, hydrolysis of the adsorbed copper compounds and sulphidation of copper oxygen compounds in Na2Sn solution). After exposure of such a coating to Pd2+ ions (1.7 mM PdCl2’ pH-2), an exchange as well as a redox interaction between the coating components and Pd2+ ions has been shown to occur. Due to this the amount of copper in the coating decreases from 2 to 4 times and that of sulphur from 1.5 to 5 times. The coating modified in such a way has been found to contain up to 75 at.% of palladium, ~90% of it being in a metallic state.It has been determined that at the beginning So is bound into a soluble compound:2Pd2+ + So + 3H2O → 2Pdo + H2SO3 + 4H+.The Cu2S present in the coating is considered to interact with Pd2+, with the formation of Pd0 and CuPdS2’, while CuS reacts most likely according to the reaction:CuS + 3Pd2+ + 3H2O → 3Pdo; + H2SO3 + Cu2+ + 4H+.The Cu2-xS +So coating formed on a dielectric and modified with Pd2+, contrary to the initial Cu2-xS +So coating, can be plated with copper from any electrolyte for copper deposition. 相似文献
994.
Mindaugas Valinčius Mindaugas Vaišnoras Algirdas Kaliatka 《Structure and Infrastructure Engineering》2018,14(2):151-162
A district heating network (DHN) is one of the most important infrastructures in cities and towns of countries with colder weather. Citizens generally use DHN services for hot water supply all year round and also for space heating during winter. It is important that in case of an accident this service would be restored as soon as possible, causing minimal damage or inconveniences for the customers. In addition, it is important to minimise losses of the DHN operator. This study demonstrated a possibility of leak location in DHN using the data from the pressure sensors in the network, employing the negative pressure wave (NPW) method. The mass balance in the DHN is measured at the heating source, which acts as a confirmation of a leak in a closed system. The experiments in the real DHN were performed and the data was used to trace the leak location. Numerical modelling tools were used to model pressure transients during pipe break accident under various conditions in order to predict the effectiveness and limitations of the leak detection system. 相似文献
995.
Atlantic salmon (Salmo salar) (90 g) were fed four different diets for 21 weeks (final weight 344 g). The levels of n-3 highly unsaturated fatty acids
(HUFA) ranged from 11% of the total fatty acids (FA) in the low n-3 diet to 21% in the intermediate n-3 diet, to 55 and 58%
in the high n-3 diets. The high n-3 diets were enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA).
Increasing dietary levels of n-3 HUFA led to increasing percentages (from 31 to 52%) of these FA in liver lipids. The group
fed the highest level of DHA had higher expressions of peroxisome proliferator-activated receptor (PPAR) β and the FA β-oxidation
genes acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase (CPT)-II, compared to the low n-3 groups. The high n-3 groups
had reduced activity of mitochondrial cytochrome c oxidase and β-oxidation capacity, together with increased activities of
superoxide dismutase (SOD) and caspase-3 activities. In the group fed the highest level of n-3 HUFA, decreased percentages
of major phospholipids (PL) in the mitochondrial and microsomal membranes of the liver were also apparent. The percentage
of mitochondrial cardiolipin (Ptd2Gro) was 3.1 in the highest n-3 group compared to 6.6 in the intermediate group. These data clearly show an increased incidence
of oxidative stress in the liver of fish fed the high n-3 diets. 相似文献
996.
Summary The fluorescence spectra of thin films of poly(N-vinylcarbazole), PVCA, were measured at temperatures between 103 K and 535 K by constant excitation light intensity. Below 300 K, the corrected spectra were divided into bands belonging to different emitting species of PVCA. Temperature changes of the intensity of fluorescence of the two main excitation energy traps in PVCA are discussed using the simplified kinetic model of Johnson. Local anomalies on the curves of intensity of excimer fluorescence versus temperature measured at constant wavelength reflex the - and - relaxation regions in PVCA. 相似文献
997.
998.
Numan Almonasy Miloš Nepraš Šárka Hyková Antonin Lyčka Jiři Čermák Miroslav Dvořák Martin Michl 《Dyes and Pigments》2009,82(3):416-421
An alternative procedure has been described for the syntheses of several bi- and trichromophoric compounds consisting of 1-aminopyrene and 3-aminobenzanthrone chromophoric subsystems connected by an s-triazinyl ring spacer. The synthetic method used, which utilises an autoclave under autogenous pressure, is suitable for the nucleophilic substitution of both chlorine atoms within the triazinyl ring by weakly basic aromatic amines. The structures of the synthesized compounds were confirmed using elemental analysis, 1H NMR, and mass spectra. UV/vis absorption and fluorescence spectra and fluorescence quantum yields were measured. The dependence of fluorescence intensity and fluorescence quantum yields on solvent polarity was investigated. 相似文献
999.
Several critical points, where both geometry and material properties change abruptly, arise in an adhesively bonded lap joint between a metallic and a composite material. These critical points, called multimaterial corners or cross-points, at which the linear theory of elasticity predicts unbounded (singular) stresses, are potential points for failure initiation. In this work, a complete stress characterization at these multimaterial corners has been carried out to analyze, after a preliminary experimental test program, the suitability of the application of the parameters defining the singular stress state in the characterization of the failure of these joints. The comparative analysis of the numerical and experimental results obtained show that the singular stress state controlled by a series of the generalized stress intensity factors is controlling the failure path at these corners. 相似文献
1000.
The dilatation-temperature curves of the PZT-ZrO2 composites, containing 1.3–13.2 vol% ZrO2 were studied. The course of martensitic transformation (MT) of dispersed ZrO2 particles in the PZT matrix was followed. Upon cooling, a spontaneous microcrack formation occurred during the MT from tetragonal to monoclinic crystal phase of ZrO2. The phenomenon of intensive shrinkage above 800 °C upon heating is explained as a process of microcrack healing in the presence of the PbO-rich liquid phase. 相似文献