全文获取类型
收费全文 | 9130篇 |
免费 | 309篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 89篇 |
综合类 | 12篇 |
化学工业 | 1840篇 |
金属工艺 | 135篇 |
机械仪表 | 167篇 |
建筑科学 | 540篇 |
矿业工程 | 18篇 |
能源动力 | 218篇 |
轻工业 | 687篇 |
水利工程 | 74篇 |
石油天然气 | 27篇 |
武器工业 | 1篇 |
无线电 | 526篇 |
一般工业技术 | 1690篇 |
冶金工业 | 1929篇 |
原子能技术 | 126篇 |
自动化技术 | 1366篇 |
出版年
2023年 | 47篇 |
2022年 | 100篇 |
2021年 | 145篇 |
2020年 | 109篇 |
2019年 | 136篇 |
2018年 | 179篇 |
2017年 | 173篇 |
2016年 | 196篇 |
2015年 | 160篇 |
2014年 | 243篇 |
2013年 | 612篇 |
2012年 | 388篇 |
2011年 | 528篇 |
2010年 | 364篇 |
2009年 | 411篇 |
2008年 | 430篇 |
2007年 | 457篇 |
2006年 | 433篇 |
2005年 | 362篇 |
2004年 | 311篇 |
2003年 | 294篇 |
2002年 | 247篇 |
2001年 | 171篇 |
2000年 | 174篇 |
1999年 | 179篇 |
1998年 | 164篇 |
1997年 | 150篇 |
1996年 | 154篇 |
1995年 | 166篇 |
1994年 | 133篇 |
1993年 | 128篇 |
1992年 | 138篇 |
1991年 | 84篇 |
1990年 | 90篇 |
1989年 | 109篇 |
1988年 | 103篇 |
1987年 | 101篇 |
1986年 | 98篇 |
1985年 | 104篇 |
1984年 | 103篇 |
1983年 | 97篇 |
1982年 | 62篇 |
1981年 | 76篇 |
1980年 | 60篇 |
1979年 | 57篇 |
1978年 | 76篇 |
1977年 | 52篇 |
1976年 | 48篇 |
1975年 | 46篇 |
1974年 | 43篇 |
排序方式: 共有9445条查询结果,搜索用时 15 毫秒
81.
Stephen D. Brignac 《乙烯基与添加剂工艺杂志》1996,2(2):147-157
EPDM rubber is an important ingredient in thermoplastic polyolefin elastomers (TPOs). Such key properties as impact strength, flexibility, and flow are significantly affected by EPDM polymer properties. In this work, a set of EPM and EPDM polymer is used to produce via melt processing a series of TPOs, consisting of simple binary blends of rubber and polypropylene of varying composition. Various structural and thermal properties of the EPDM are correlated with the TPO compound properties. Significant property relationships are explored. 相似文献
82.
Philip E. Sonnet Thomas A. Foglia Stephen H. Feairheller 《Journal of the American Oil Chemists' Society》1993,70(4):387-391
The fatty acid selectivity of several commercial lipases was evaluated in the hydrolysis of high-erucic acid rapeseed oil
(HEARO). The lipase ofPseudomonas cepacia catalyzed virtually complete hydrolysis of the oil (94–97%), while that ofGeotrichum candidum discriminated strongly against erucic acid, especially in esterification. A two-step process is suggested for obtaining a
highly enriched erucic acid in which theG. candidum lipase is employed to selectively esterify the fatty acid residues of unsaturated C-18, and shorter chain acids, from a mixture
of HEARO fatty acids obtained from total hydrolysis of the oil withP. cepacia lipase. 相似文献
83.
Career visual searchers such as radiologists and airport security screeners strive to conduct accurate visual searches, but despite extensive training, errors still occur. A key difference between searches in radiology and airport security is the structure of the search task: Radiologists typically scan a certain number of medical images (fixed objective), and airport security screeners typically search X-rays for a specified time period (fixed duration). Might these structural differences affect accuracy? We compared performance on a search task administered either under constraints that approximated radiology or airport security. Some displays contained more than one target because the presence of multiple targets is an established source of errors for career searchers, and accuracy for additional targets tends to be especially sensitive to contextual conditions. Results indicate that participants searching within the fixed objective framework produced more multiple-target search errors; thus, adopting a fixed duration framework could improve accuracy for career searchers. 相似文献
84.
In this Account, we explore the role constant curvature structures play in amphiphilic small molecule crystals and extended coordination solids. A constant curvature structure is one in which there is a surface or interface that has the same curvature throughout its surface. Simple examples of such structures contain spheres (micelles), columns, or layers. Yet another family are cubic as is found in the gyroid topology. For amphiphilic systems, there are two domains, one generally hydrophobic and the other hydrophilic. We find that the interfaces between these two domains in small molecule structures resemble those in larger scale systems and adopt topologies related to constant curvature structures. The hydrophobic-to-total volume ratio, a molecular parameter, can be used to predict which type of constant curvature structure is adopted. In the case of three coordinate extended solids, constant curvature plays a role both in the extended net topology and in the hydrophobic-to-hydrophilic interface. 相似文献
85.
Fei Yan Josef Kittler David Windridge William Christmas Krystian Mikolajczyk Stephen Cox Qiang Huang 《Image and vision computing》2014
Fully automatic annotation of tennis game using broadcast video is a task with a great potential but with enormous challenges. In this paper we describe our approach to this task, which integrates computer vision, machine listening, and machine learning. At the low level processing, we improve upon our previously proposed state-of-the-art tennis ball tracking algorithm and employ audio signal processing techniques to detect key events and construct features for classifying the events. At high level analysis, we model event classification as a sequence labelling problem, and investigate four machine learning techniques using simulated event sequences. Finally, we evaluate our proposed approach on three real world tennis games, and discuss the interplay between audio, vision and learning. To the best of our knowledge, our system is the only one that can annotate tennis game at such a detailed level. 相似文献
86.
An experimental study to determine the effect of copper (I) iodide (Cul) on the rate and product distribution of degradation of a model of an aliphatic–aromatic polyamide was carried out. N,N′-Dihexylisophthalamide (DHI) was reacted in both an inert argon atmosphere and a pure oxygen environment at 350°C with CuI added in amounts ranging from 0 to 20% by weight. The rate of disappearance of DHI was enhanced by an order of magnitude when 0.5% by weight of CuI was added and was an increasing function of increasing CuI loading. Reaction in pure O2 increased the rate of DHI degradation by two orders of magnitude over that for neat DHI pyrolysis. The rate of disappearance of DHI in O2 was relatively unchanged when 5% CuI by weight was added. The transformations of DHI and its products are organized in terms of a set of reaction rules. This “reaction operator” formalism allowed computer generation of the reaction network and facilitated estimation of kinetic parameters. © 1995 John Wiley & Sons, Inc. 相似文献
87.
A series of polyurethane (PU) films was prepared from chain-extended hydroxypropyl lignins (CEHPL). In appearance, these films ranged from brittle and dark brown to rubbery and bronze. The thermal, mechanical, and network properties of these PUs were investigated by DMTA and DSC analysis. All films exhibited single Tg's which varied between ?53° and 101°C, depending on lignin content. From swelling experiments, molecular weight between crosslinks (M c) was determined and found to vary over 2.5 orders of magnitude. The M c's were related to the change in Tg that accompanied network formation. Stress–strain experiments showed a variation in Young's modulus between 7 and 1300 MPa. Most of the variation in material properties was related to lignin content and to a lesser extent to diisocyanate type, hexamethylene diisocyanate, or toluene diisocyanate. The source of the CEHPL had no effect on the observed properties. From these results it was concluded that the properties of PUs can be controlled and engineered for a wide variety of practical uses. 相似文献
88.
Stephen Q. Zhou Liming Wang Xiugao Liao Georges Manuel William P. Weber 《Journal of Inorganic and Organometallic Polymers and Materials》1991,1(2):199-210
High molecular weight poly(1,1-dimethyl-1-germa-cis-pent-3-ene), poly(1,1-diphenyl-1-germa-cis-pent-3-ene), poly(1,1-dimethyl-1-sila-cis-pent-3-ene), and poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) have been prepared. The thermal stability of these polymers is found to increase with their molecular weight. 相似文献
89.
This paper reviews the brittle fracture behavior of dielectric ceramics such as barium titanate, and describes some of the relationships between defects such as cracks and electrical degradation and failure of multilayer capacitors. Stresses arising from the ferroelectric phase transformation in these dielectric materials are shown to play a part as a driving force for crack growth. In addition, possible contributions to failure from stresses arising from thermal excursions in the capacitor are discussed. Low-voltage failures arising from a short between the electrodes in multilayer capacitors are shown to be related to the growth of cracks in the dielectric. A technique for predicting the onset of these types of failures based upon fracture mechanics techniques is described. Possible effects of the electric field itself in promoting or retarding the growth of cracks are discussed. 相似文献
90.
An elimination strategy for solving sparse linear systems in bordered triangular form is presented. This strategy is designed to exploit certain common structural properties of the borders of such a system. It may also be interpreted as a recursive application of block elimination. The technique is numerically efficient and provides significant reductions in fill-in compared to routine Gaussian elimination. It is applicable in the iterative solution of the large systems of nonlinear equations that arise in the equation-oriented approach to process simulation and design calculations, as well as in other problems of interest to the chemical engineer. 相似文献