全文获取类型
收费全文 | 274163篇 |
免费 | 6423篇 |
国内免费 | 2672篇 |
专业分类
电工技术 | 7085篇 |
技术理论 | 1篇 |
综合类 | 2253篇 |
化学工业 | 40609篇 |
金属工艺 | 12593篇 |
机械仪表 | 9075篇 |
建筑科学 | 8745篇 |
矿业工程 | 1449篇 |
能源动力 | 7131篇 |
轻工业 | 26480篇 |
水利工程 | 2408篇 |
石油天然气 | 2978篇 |
武器工业 | 274篇 |
无线电 | 34839篇 |
一般工业技术 | 48776篇 |
冶金工业 | 51354篇 |
原子能技术 | 4268篇 |
自动化技术 | 22940篇 |
出版年
2022年 | 1928篇 |
2021年 | 3051篇 |
2020年 | 2212篇 |
2019年 | 2363篇 |
2018年 | 3362篇 |
2017年 | 3393篇 |
2016年 | 3401篇 |
2015年 | 3254篇 |
2014年 | 4860篇 |
2013年 | 12640篇 |
2012年 | 7496篇 |
2011年 | 9895篇 |
2010年 | 8066篇 |
2009年 | 8756篇 |
2008年 | 9317篇 |
2007年 | 9199篇 |
2006年 | 8632篇 |
2005年 | 7833篇 |
2004年 | 7098篇 |
2003年 | 7120篇 |
2002年 | 7050篇 |
2001年 | 7090篇 |
2000年 | 6524篇 |
1999年 | 7192篇 |
1998年 | 17179篇 |
1997年 | 12127篇 |
1996年 | 9409篇 |
1995年 | 7106篇 |
1994年 | 6219篇 |
1993年 | 5962篇 |
1992年 | 4272篇 |
1991年 | 4136篇 |
1990年 | 3705篇 |
1989年 | 3615篇 |
1988年 | 3513篇 |
1987年 | 2955篇 |
1986年 | 2869篇 |
1985年 | 3441篇 |
1984年 | 3067篇 |
1983年 | 2760篇 |
1982年 | 2570篇 |
1981年 | 2572篇 |
1980年 | 2438篇 |
1979年 | 2277篇 |
1978年 | 2241篇 |
1977年 | 2813篇 |
1976年 | 4173篇 |
1975年 | 1902篇 |
1974年 | 1796篇 |
1973年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
101.
Li Lei Limin Li Shasha Wang Gaoyang Zhao Yoshifumi Oshima Yang Ren Lei Zhao Lihua Jin Yao Wang Chengshan Li Pingxiang Zhang 《Journal of the European Ceramic Society》2018,38(14):4694-4700
Highly (100)-oriented Ce1-x(Y0.2Zr0.8)xOδ (CYZO) films were prepared on biaxially textured NiW substrates by a chemical solution deposition approach using metal inorganic salts as starting materials. It has been found that both the preferential orientation and surface roughness of CYZO films decrease gradually with increasing of the doping percentage of Y3+ and Zr4+ ions. The epitaxial growth relationship of (220)CYZO//(200)NiW and [00?l]CYZO//[001]NiW was demonstrated by XRD texture measurement as well as atomic resolution STEM observation. XRD, Raman and XPS spectra results indicate that Y3+ and Zr4+ ions were indeed introduced into CeO2 lattice to substitute Ce4+ ions and form cubic fluorite CYZO solid solution. Moreover, CeO2 buffer layer can be endowed a strong enough capability to prevent element diffusion through co-doping of yttrium and zirconium, provided that an optimal doping ratio of them is adopted. This will provide a new approach to fabricating strong-barrier single buffer layer for coated conductor. 相似文献
102.
Yao Dajie Liu Xiaofei Wu Jian 《International Journal of Control, Automation and Systems》2020,18(9):2251-2258
International Journal of Control, Automation and Systems - In this paper, the tracking problem for a class of uncertain nonlinearly parameterized systems with input delay based the adaptive... 相似文献
103.
H.C. Weigele L. Gygax A. Steiner B. Wechsler J.-B. Burla 《Journal of dairy science》2018,101(3):2370-2382
Lameness is one of the most prevalent diseases affecting the welfare of cows in modern dairy production. Lameness leads to behavioral changes in severely lame cows, which have been investigated in much detail. For early detection of lameness, knowledge of the effects of moderate lameness on cow behavior is crucial. Therefore, the behavior of nonlame and moderately lame cows was compared on 17 Swiss dairy farms. On each farm, 5 to 11 nonlame (locomotion score 1 of 5) and 2 to 7 moderately lame (locomotion score 3 of 5) cows were selected for data collection in two 48-h periods (A, B) separated by an interval of 6 to 10 wk. Based on visual locomotion scoring, 142 nonlame and 66 moderately lame cows were examined in period A and 128 nonlame and 53 moderately lame cows in period B. Between these 2 periods, the cows underwent corrective hoof trimming. Lying behavior, locomotor activity, and neck activity were recorded by accelerometers (MSR145 data logger, MSR Electronics GmbH, Seuzach, Switzerland), and feeding and rumination behaviors by noseband sensors (RumiWatch halter, ITIN + HOCH GmbH, Liestal, Switzerland). Furthermore, visits to the brush and the concentrate feeder, and the milking order position were recorded. In comparison with nonlame cows, moderately lame cows had a longer lying duration, a longer average lying bout duration, and a greater lateral asymmetry in lying duration. Average locomotor activity, locomotor activity during 1 h after feed delivery or push-ups, and average neck activity were lower in moderately lame cows. Eating time and the number of eating chews (jaw movements) were reduced in moderately lame compared with nonlame cows, whereas no effect of moderate lameness was evident for ruminating time, number of ruminating chews and boluses, and average number of ruminating chews per bolus. Moderately lame cows visited the concentrate feeder and the brush less frequently, and they were further back in the milking order compared with nonlame cows. In conclusion, nonlame and moderately lame cows differed in a biologically relevant way in many of the behavioral variables investigated in this study. Therefore, the use of these behavioral changes seems to be promising to develop a tool for early lameness detection. 相似文献
104.
105.
To minimize the mass and increase the bearing failure load of composite doublelap bolted joints, a three-step optimization strategy including feasible region reduction,
optimization model decoupling and optimization was presented. In feasible region
reduction, the dimensions of the feasible design region were reduced by selecting dominant
design variables from numerous multilevel parameters by sensitivity analyses, and the
feasible regions of variables were reduced by influence mechanism analyses. In model
decoupling, the optimization model with a large number of variables was divided into
various sub-models with fewer variables by variance analysis. In the third step, the
optimization sub-models were solved one by one using a genetic algorithm, and the
modified characteristic curve method was adopted as the failure prediction method. Based
on the proposed optimization method, optimization of a double-lap single-bolt joint was
performed using the ANSYS® code. The results show that the bearing failure load increased
by 13.5% and that the mass decreased by 8.7% compared with those of the initial design of
the joint, which validated the effectiveness of the three-step optimization strategy. 相似文献
106.
In this paper, the development of the models for the prediction of rock mass P wave velocity is presented. For model development, the database of 53 cases including widely used and recorded drilling parameters and P wave velocity was constructed from the field studies conducted in 13 open pit lignite mines. Both conventional linear, non-linear multiple regression and Adaptive Neuro Fuzzy Inference System (ANFIS) were used for model development. Prediction performance indicators showed that ANFIS model presented the best performance and it can successfully be used for the preliminary prediction of P wave velocities of rock masses. 相似文献
107.
Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano‐biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles—from self‐assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models. 相似文献
108.
Y.K. Yang F.L. Liu Y.W. Zhang M.F. Li F. Ling H.T. Wu 《Ceramics International》2018,44(11):12238-12244
In this work, ultra-low loss Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics were successfully prepared via the conventional solid-state method. X-ray photoelectron spectroscopy (XPS), thermally stimulated depolarization current (TSDC) and bond energy were used to determine the distinction between intrinsic and extrinsic dielectric loss in (Mg1/3Nb2/3)4+ ions substituted ceramics. The addition of (Mg1/3Nb2/3)4+ ions enhances the bond energy in unit cell without changing the crystal structure of Li2MgTiO4, which results in high Q·f value as an intrinsic factor. The extrinsic factors such as porosity and grain size influence the dielectric loss at lower sintering temperature, while the oxygen vacancies play dominant role when the ceramics densified at 1400?°C. The Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: εr =?16.19, Q·f?=?160,000?GHz and τf =??3.14?ppm/°C. In addition, a certain amount of LiF can effectively lower the sintering temperature of the matrix, and the Li2MgTi0.7(Mg1/3Nb2/3)0.3O4-3?wt% LiF ceramics sintered at 1100?°C possess balanced properties with εr?=?16.32, Q·f?=?145,384?GHz and τf =??16.33?ppm/°C. 相似文献
109.
The reported point centromeres of Scheffersomyces stipitis are retrotransposon long terminal repeats
Point centromeres, found in some ascomycete yeasts such Saccharomyces cerevisiae, are very different in structure from the centromeres of other eukaryotes. They are tiny and nonrepetitive and contain only two short conserved sequence motifs. Until recently, point centromeres were thought to have a single evolutionary origin, in the budding yeast family Saccharomycetaceae. Most yeasts outside this family have centromeres that are many kilobases in size. Some have centromeres consisting of a large inverted repeat sequence, others have centromeric clusters of retrotransposons, and a third group including Candida albicans has centromeres with no conserved sequence features. It was recently reported that Scheffersomyces stipitis has point centromeres with a strongly conserved 125-bp core sequence, which is unexpected because S. stipitis is only distantly related to the known point-centromere species. We show here that the 125-bp core sequence is actually part of the long terminal repeat (LTR) of the Ty5-like retrotransposon Tps5, which forms a cluster in the centromeric region of each S. stipitis chromosome. Thus, the LTR of a centromere-associated retrotransposon confers centromere-like mitotic stability when cloned into a plasmid. The centromeric regions of S. stipitis contain three types of Tps5 element (Tps5a, Tps5b, and Tps5c) and a noncoding nonautonomous large retrotransposon derivative. 相似文献
110.
Antti Voss Niko Hänninen Mohammad Pour-Ghaz Marko Vauhkonen Aku Seppänen 《Materials and Structures》2018,51(3):68
The development of visualizing tools to monitor unsaturated moisture flow in cement-based materials is of great importance, as most degradation processes in cement-based materials are connected to and take place in the presence moisture. This paper investigates the ability of electrical capacitance tomography (ECT) to image two-dimensional (2D) unsaturated moisture flow in cement-based materials. In ECT, the electrical permittivity distribution within an object is reconstructed based on measured capacitances between electrodes attached on the object’s surface. In a series of experiments, mortar specimens with and without discrete cracks were imaged with ECT during a 2D moisture ingress. The results show that ECT is able to monitor the evolution of the moisture flow, and to approximate the shape and position of the moisture front. These findings indicate that ECT is a viable method for monitoring and visualizing 2D unsaturated moisture flow in cement-based materials in the presence and absence of discrete cracks. 相似文献