全文获取类型
收费全文 | 109019篇 |
免费 | 1954篇 |
国内免费 | 440篇 |
专业分类
电工技术 | 1092篇 |
综合类 | 2357篇 |
化学工业 | 17100篇 |
金属工艺 | 5171篇 |
机械仪表 | 3503篇 |
建筑科学 | 3492篇 |
矿业工程 | 660篇 |
能源动力 | 1757篇 |
轻工业 | 5623篇 |
水利工程 | 1502篇 |
石油天然气 | 412篇 |
无线电 | 11143篇 |
一般工业技术 | 20756篇 |
冶金工业 | 7719篇 |
原子能技术 | 464篇 |
自动化技术 | 28662篇 |
出版年
2023年 | 222篇 |
2022年 | 369篇 |
2021年 | 591篇 |
2020年 | 353篇 |
2019年 | 455篇 |
2018年 | 14849篇 |
2017年 | 13742篇 |
2016年 | 10508篇 |
2015年 | 1172篇 |
2014年 | 995篇 |
2013年 | 1667篇 |
2012年 | 4292篇 |
2011年 | 10837篇 |
2010年 | 9306篇 |
2009年 | 6525篇 |
2008年 | 7877篇 |
2007年 | 8821篇 |
2006年 | 1117篇 |
2005年 | 2000篇 |
2004年 | 1907篇 |
2003年 | 1842篇 |
2002年 | 1129篇 |
2001年 | 569篇 |
2000年 | 566篇 |
1999年 | 486篇 |
1998年 | 934篇 |
1997年 | 665篇 |
1996年 | 545篇 |
1995年 | 468篇 |
1994年 | 427篇 |
1993年 | 419篇 |
1992年 | 305篇 |
1991年 | 238篇 |
1990年 | 288篇 |
1989年 | 284篇 |
1988年 | 248篇 |
1987年 | 252篇 |
1986年 | 242篇 |
1985年 | 290篇 |
1984年 | 247篇 |
1983年 | 250篇 |
1982年 | 229篇 |
1981年 | 201篇 |
1980年 | 185篇 |
1979年 | 204篇 |
1978年 | 178篇 |
1977年 | 199篇 |
1976年 | 256篇 |
1975年 | 192篇 |
1974年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Freddy A. Bernal Dr. Marcel Kaiser Prof. Dr. Bernhard Wünsch Prof. Dr. Thomas J. Schmidt 《ChemMedChem》2020,15(1):68-78
Protozoal infections are still a global health problem, threatening the lives of millions of people around the world, mainly in impoverished tropical and sub-tropical regions. Thus, in view of the lack of efficient therapies and increasing resistances against existing drugs, this study describes the antiprotozoal potential of synthetic cinnamate ester analogues and their structure-activity relationships. In general, Leishmania donovani and Trypanosoma brucei were quite susceptible to the compounds in a structure-dependent manner. Detailed analysis revealed a key role of the substitution pattern on the aromatic ring and a marked effect of the side chain on the activity against these two parasites. The high antileishmanial potency and remarkable selectivity of the nitro-aromatic derivatives suggested them as promising candidates for further studies. On the other hand, the high in vitro potency of catechol-type compounds against T. brucei could not be extrapolated to an in vivo mouse model. 相似文献
22.
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
23.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
24.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
25.
26.
27.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
28.
The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows. 相似文献
29.
Interactions of hexamethylenetetramine ligand in atom transfer radical polymerization initiated by activator generated by electron transfer were studied. Polymerization of methyl methacrylate was done using two-step experimental procedure in 2 L emulsion batch reactor at 50, 60, and 80°C. The selection of reactant ratios was quite challenging for a reactor of this size. Replicate runs were conducted for data reproducibility purpose. Gravimetry method and gel permeation chromatography were used to determine monomer conversion, Mn, and PDI of polymer samples. PMMA produced was also characterized by means of dynamic light scattering, Fourier-transform infrared spectroscopy and nuclear Magnetic Resonance spectroscopy. Results showed high monomer conversion up to 93% and Mn ranging 243–274 kg/mol with PDI from 1.45 to 1.60. Besides, combining HMTA with sodium dodecyl sulfate, an anionic surfactant, a well-controlled polymer with a lower Mn of 201 kg/mol and PDI of 1.56 was obtained in 3 hr reaction time. 相似文献
30.
We demonstrate that alkali-halide salts, particularly potassium bromide, can reduce the photothermal emission (PTE) from single walled carbon nanotubes (SWNT). PTE is a prominent spectral feature in Raman spectroscopy when a near infrared laser is used to analyze a dark colored sample. We subsequently show that trapping salts inside SWNT and coating SWNT with the salt has a more pronounced impact on not only reducing PTE, but also enhancing the intensity of the Raman spectral features. The effect, which we have called nanotube enhanced Raman spectroscopy (NERS), has differences and similarities to the widely studied surface enhanced Raman spectroscopy (SERS). 相似文献