全文获取类型
收费全文 | 2416篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 26篇 |
综合类 | 2篇 |
化学工业 | 158篇 |
金属工艺 | 26篇 |
机械仪表 | 11篇 |
建筑科学 | 74篇 |
能源动力 | 60篇 |
轻工业 | 210篇 |
水利工程 | 20篇 |
石油天然气 | 2篇 |
武器工业 | 1篇 |
无线电 | 109篇 |
一般工业技术 | 121篇 |
冶金工业 | 1431篇 |
原子能技术 | 30篇 |
自动化技术 | 166篇 |
出版年
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 26篇 |
2014年 | 38篇 |
2013年 | 57篇 |
2012年 | 48篇 |
2011年 | 72篇 |
2010年 | 46篇 |
2009年 | 63篇 |
2008年 | 72篇 |
2007年 | 44篇 |
2006年 | 46篇 |
2005年 | 46篇 |
2004年 | 37篇 |
2003年 | 35篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 25篇 |
1999年 | 49篇 |
1998年 | 434篇 |
1997年 | 238篇 |
1996年 | 162篇 |
1995年 | 105篇 |
1994年 | 99篇 |
1993年 | 103篇 |
1992年 | 29篇 |
1991年 | 37篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 32篇 |
1976年 | 68篇 |
1975年 | 4篇 |
1971年 | 4篇 |
1968年 | 5篇 |
排序方式: 共有2447条查询结果,搜索用时 15 毫秒
61.
The TR1C fragment of turkey skeletal muscle TnC (residues 12-87) comprises the two regulatory calcium binding sites of the protein. Complete assignments of the 1H-NMR resonances of the backbone and amino acid side chains of this domain in the absence of metal ions have been obtained using 2D 1H-NMR techniques. Sequential (i,i+1) and short-range (i,i+3) NOE connectivities define two helix-loop-helix calcium binding motifs, and long-range NOE connectivities indicate a short two-stranded beta-sheet formed between the two calcium binding loops. The two calcium binding sites are different in secondary structure. In terms of helix length, site II conforms to a standard "EF-hand" motif with the first helix ending one residue before the first calcium ligand and the second helix starting one residue after the beta-sheet. In site I, the first helix ends three residues before the first calcium ligand, and the second helix starts three residues after the beta-sheet. A number of long-range NOE connectivities between the helices define their relative orientation and indicate formation of a hydrophobic core between helices A, B, and D. The secondary structure and global fold of the TR1C fragment in solution in the calcium-free state are therefore very similar to those of the corresponding region in the crystal structure of turkey skeletal TnC [Herzberg, O., & James, M.N.G. (1988) J. Mol. Biol. 203, 761-779]. 相似文献
62.
SR Poole BD Schmitt T Carruth A Peterson-Smith M Slusarski 《Canadian Metallurgical Quarterly》1993,92(5):670-679
BACKGROUND: After-hours telephone calls are a stressful and frustrating aspect of pediatric practice. At the request of private practice pediatricians in Denver, a metropolitan area-wide system was created to manage after-hours pediatric telephone calls and after-hours patient care. This system, the After-Hours Program (AHP), uses specially trained pediatric nurses with standardized protocols to provide after-hours telephone triage and advice for the patients of 92 Denver pediatricians, representing 56 practices. OBJECTIVES: This report describes the AHP, presents data from 4 years' experience with the program, and describes results of our evaluation of the following aspects of the program: subscribing physician satisfaction, parent satisfaction, the accuracy and appropriateness of telephone triage, and program costs. METHODS: After-Hours Program records (including quality assurance data) for all 4 years of operation were retrospectively reviewed, tabulated, and analyzed. The results of two subscribing physician surveys and one parent caller satisfaction survey are presented. A retrospective review of after-hours patient care encounter forms assessed the necessity for after-hours visits triaged by the AHP. An analysis of the total cost of this program to 10 randomly selected subscribing physicians was conducted using current AHP data and a survey of the 10 physicians. RESULTS: In 4 years, 107,938 calls have been successfully managed without an adverse clinical outcome. Minor errors in using protocols occurred in one call out of 1450 after-hours calls. After-hours phoen calls necessitated an after-hours patient visit 20% of the time and generated one after-hours hospital admission out of every 88 calls. Just over half of the patients were managed with home care advice only, and 28% were given home care advice after-hours and seen the next day in the primary physician's office. Of all patients directed by the telephone triage nurses to be seen after hours, 78% were determined to have a condition necessitating after-hours care. Data are presented regarding call volumes by time of day, day of week, patient age, and patient's initial complaint. The 6 most common complaints accounted for more than one half of the calls, and 38 complaints accounted for more than 95% of all after-hours calls. Utilization by subscribing physicians is described. Satisfaction among subscribing pediatricians was 100%, and among parents was 96% to 99% on a variety of issues. The total cost to participating Denver pediatricians (which includes revenues "given up" as a result of not seeing patients after hours) ranged from 1% to 12% of their annual net income, depending on a variety of factors. CONCLUSIONS: Large-scale after-hours telephone coverage systems can be effective and well-received by patients, parents, and primary physicians. Data presented in this report can assist in planning the training of personnel who provide after-hours telephone advice and triage. Controversies associated with this type of program are discussed. Suggestions are made regarding the direction of future programs and research. 相似文献
63.
WL George BD Kirby VL Sutter DM Citron SM Finegold 《Canadian Metallurgical Quarterly》1981,3(3):599-626
Twenty infrequently reported species of gram-negative anaerobic bacilli other than Fusobacterium nucleatum, Fusobacterium necrophorum, and members of the genus Bacteroides were studied with regard to their role in infection and their susceptibility to antimicrobial agents. In addition, the literature regarding the recovery of these organisms from both the normal flora and infections of humans was reviewed. During a six-year period at the Wadsworth Clinical Anaerobic Bacteriology Research Laboratory (Veterans Administration Wadsworth Medical Center, Los Angeles, Calif.), 39 (6%) of 679 specimens obtained from anaerobic infections yielded "other gram-negative anaerobic bacilli" (OGNAB). Fusobacterium naviforme, Fusobacterium gonidiaformans, Fusobacterium varium, Fusobacterium mortiferum, and Fusobacterium russii were the most commonly isolated OGNAB. Most of the OGNAB tested were resistant to erythromycin, and most strains, except for F. varium, were susceptible to beta-lactam antibiotics and clindamycin. Chloramphenicol and metronidazole were active against all strains of OGNAB tested. Certain Fusobacterium species are undoubtedly previously unrecognized members of the normal flora of the oropharynx, upper respiratory tract, or urogenital tract and may be present in infections derived from these floras. 相似文献
64.
"Stimulus-secretion" processes, and notably those in which the stimulus is provided by the formation of an antigen-antibody complex at the cell surface, require the presence of external Ca++. To test the possiblity that effector cells, in non-T cell mediated cytolysis, might be triggered to release a cytolytic product by a similar mechanism, we investigated the requirements of this phenomenon for divalent cations. We found that Ca++ is not sufficient, not necessary, and not inhibitory, whereas Mg++ is necessary and sufficient. Other cations were tested, and we found that Mn++ behaved like Mg++. The Ca++ data suggest that no conventional "stimulus-secretion" process is operative in non-T cell mediated cytolysis of antibody-coated sheep red blood cells. 相似文献
65.
Hanne Larsen 《Packaging Technology and Science》2004,17(4):187-192
The ambient oxygen ingress rate (AOIR) method is an alternative or supplementary method to Ox‐Tran for measuring the oxygen transmission rate (OTR) of packages. The method has high capacity, requires relatively inexpensive equipment and measures OTR at different temperatures and humidity conditions. The aim of this study was, on the one hand, to study the effect of temperature on the OTR for packages produced from different polymer materials and laminates, and on the other hand to evaluate the suitability of the AOIR method at freezing temperature conditions. The OTR for 10 packages with different polymer compositions was measured at 23°C, 6°C and ?25°C. The AOIR method was shown to be a reliable test method for measuring OTR of packages at all the applied test conditions, also at frozen storage temperature. The OTR for the packages decreased with lower temperatures, especially for the packages with the highest OTR values at 23°C. In order to avoid higher packaging expenses than necessary to obtain the required shelf‐life for different food products, the OTR for alternative packages should be measured at the temperature and humidity conditions of intended use. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
66.
Housing preweaned dairy calves in pairs rather than individually has been found to positively affect behavioral responses in novel social and environmental situations, but concerns have been raised that close contact among very young animals may impair their health. In previous studies, the level of social contact permitted in individual housing has been auditory, visual, or physical contact. It is unclear how these various levels of social contact compare with each other and to pair housing, when their effects on behavior and health are considered, and whether the timing of pair housing has an effect. To investigate this, 110 Holstein calves (50 males, 60 females) in 11 blocks were paired according to birth date. Within 60 h of birth, each pair of calves was allocated to 1 of 5 treatments: individual housing with auditory contact (I), individual housing with auditory and visual contact (V), individual housing with auditory, visual, and tactile contact (T), pair housing (P), or individual housing with auditory and visual contact the first 2 wk followed by pair housing (VP). At 6 wk of age, calves were subjected to a social test and a novel environment test. In the social test, all pair-housed calves (P and VP) had a shorter latency to sniff an unfamiliar calf than did individually housed calves (I, V, and T), whereas calves with physical contact (T, P, and VP) sniffed the unfamiliar calf for longer than calves on the remaining treatments (I and V). In the novel environment test, calves with physical contact (T, P, and VP) had a lower heart rate, and more of these calves vocalized during the test compared with calves without physical contact (I and V). No effect of treatment was found for clinical scores, levels of the 5 most common pathogens in feces, or in development of serum antibodies against the 3 most common respiratory pathogens. Calves housed individually are more fearful of unfamiliar calves than are pair-housed calves. Contrary to common belief, the allowance of physical contact and pair housing had no effects on the health of the calves. 相似文献
67.
Comparison of the performance of masterbatch and liquid color concentrates for mass coloration of polypropylene
下载免费PDF全文
![点击此处可从《Color research and application》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sonja Haastrup Donghong Yu Thomas Broch Kim Lambertsen Larsen 《Color research and application》2016,41(5):484-492
The properties of polypropylene (PP) mixed with masterbatch (MB) and liquid color concentrates (LCC), respectively, were compared by preparing samples of PP with MB and PP with LCC and neat PP as a reference material using 1–4 extrusion cycles. Two colors were examined, i.e., a white color consisting of pigment white 6, and a green color consisting of pigment white 6, pigment blue 15:3, and pigment green 7. The color difference between PP prepared with MB and LCC was determined and the mechanical, rheological, and crystalline properties of PP prepared with MB and LCC were found to be generic. The color of PP obtained from MB and LCC were comparable. Further, it was found that the tensile strength, the viscosity, and the crystal structure obtained were similar when using LCC instead of MB. The viscosity of the treated PP generally decreased with increasing extruder retention time due to thermal degradation. The tensile strength and the crystal structure were independent of increased extruder retention time. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 484–492, 2016 相似文献
68.
J.J. Yu X.S. Qin L.C. LarsenO. Larsen A. JayasooriyaX.L. Shen 《Advances in Engineering Software》2012,45(1):360-369
There has been an increasing awareness that large-scale datasets of earth-system model results would be produced and accumulated rapidly within the next few decades with extensive usage of numerical models. The successful exploration of these data for scientific research and engineering applications requires the capability of efficient storage, retrieval, integration and visualization of these large datasets. Robust publication methods are also needed to enable data exchange through the web to increase global research collaborations. In this study, a comprehensive GIS-based data management and publication framework (GMPF) was developed and applied to the use, representation, and analysis of hydrodynamic modeling results of Hamburg Port, Germany. Linking with GIS, a desktop- and a web-based model-results data atlas were developed to provide an interactive environment for various cartography and time series plots. The implementation of the framework was based on modular software design, open specifications and reuse of open source projects. The study results showed that the project life-cycle was shortened and development efforts were reduced through applying GMPF. The developed system could be integrated into commercial hydrodynamics software platforms to enhance the capability of model-results management and publication. 相似文献
69.
The ability to control the formation and chemistry of alkenes is of central importance to organic synthesis in both industry and academia. Progress in using catalysts with bifunctional (heteroaryl)phosphines to control positional and/or geometric selectivity in alkene isomerization and related chemistry is summarized. 相似文献
70.
Tamara G. Oberti Diego Larsen M. Susana Cortizo 《Polymer-Plastics Technology and Engineering》2019,58(4):443-453
New copolymers of dioctyl fumarate (DOF) and styrene (S) were synthetized by radical polymerization and used to modify bitumen. The poly(dioctyl fumarate-co-styrene) copolymers, PFS, were characterized by 1H-NMR and FTIR spectroscopies and size exclusion chromatography (SEC) in order to determine their monomer composition and weight average molecular weights, respectively. The polymer-bitumen blending conditions were optimized and the samples analyzed by different methodologies. Fluorescence microscopy, rotational viscosity and differential scanning calorimetry (DSC) were used to study the morphological changes of blends during their manufacturing and the rheological and thermal behavior, respectively. All modified bitumen (MB) exhibited higher viscosity than the based bitumen (BB) under studied conditions and this effect was more evident for the MB containing the higher molecular weight polymer. The addition of polymers to BB enhances the bitumen viscosity and thus increased the energy required for the flowing (activation energy calculated by Arrhenius equation). Thermal and morphological analysis showed that all MB exhibited good polymer- bitumen compatibility, which could be consider as a good starting point for a potential applications of this new material in road engineering. 相似文献