全文获取类型
收费全文 | 1974篇 |
免费 | 9篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 32篇 |
金属工艺 | 5篇 |
机械仪表 | 5篇 |
建筑科学 | 8篇 |
能源动力 | 8篇 |
轻工业 | 20篇 |
石油天然气 | 2篇 |
无线电 | 9篇 |
一般工业技术 | 30篇 |
冶金工业 | 1825篇 |
原子能技术 | 1篇 |
自动化技术 | 30篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 61篇 |
1998年 | 559篇 |
1997年 | 336篇 |
1996年 | 228篇 |
1995年 | 115篇 |
1994年 | 104篇 |
1993年 | 110篇 |
1992年 | 13篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 30篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 34篇 |
1976年 | 90篇 |
1975年 | 4篇 |
1972年 | 1篇 |
1965年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有1983条查询结果,搜索用时 15 毫秒
101.
STUDY DESIGN: The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae. OBJECTIVES: To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation. SUMMARY OF BACKGROUND DATA: The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision. METHODS: Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure. RESULTS: The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws. CONCLUSIONS: Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing. 相似文献
102.
103.
104.
Notes that documentation of the reversibility of posthypnotic amnesia has been hampered by the correlation of hypnotizability with the initial level of response to amnesia suggestions. 691 college students were placed in groups differing in hypnotic susceptibility that could be matched for initial amnesia recall, thereby eliminating the ceiling effect. At virtually every point along the distribution of initial amnesia response, hypnotizable Ss were significantly better able than insusceptible Ss to recapture the previously blocked memories after the amnesia suggestion was lifted. Conversely, those Ss who showed reversibility of amnesia were more responsive overall to hypnosis than those who did not. It is concluded that reversibility is of value in distinguishing between amnesia and pseudoamnesia and between partial amnesia and nonamnesia. Furthermore, reversibility helps define posthypnotic amnesia as a process involving the disruption of retrieval processes in memory. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
106.
107.
108.
A method for the isolation of polytene nuclei from salivary glands cells of the Diptera Rhynchosciara americana is described. The stage-specific morphological pattern of the chromosome is maintained during the isolation. The isolated nuclei show two distinct RNA polymerase activities, namely I and II, characterized on the basis of ionic requirements and alpha-amanitin sensitivity. Studies of the product under the incubation conditions show that the system allows the synthesis of high-molecular weight RNA, beside a low molecular weight peak which may comprise pre-4S and 5S RNAs. Autoradiographic studies carried out in the presence or absence of the toxin alpha-amanitin showed that micronucleoli contain products of RNA polymerase type I activity (ribosomal RNA) and that the DNA puffs are engaged in alpha-amanitin sensitive RNA synthesis and thus are sites of polymerase type II activity. 相似文献
109.
Nurok D Koers JM Novotny AL Carmichael MA Kosiba JJ Santini RE Hawkins GL Replogle RW 《Analytical chemistry》2004,76(6):1690-1695
Pressurized planar electrochromatography (PPEC) is a new planar chromatographic technique in which the mobile phase is driven by electroosmotic flow, while the sorbent layer is pressurized in a manner that allows heat to flow from the layer through an electrically insulating, thermally conducting, sheet of aluminum nitride ceramic. A prototype apparatus for performing PPEC is described. Separation by PPEC is faster than by conventional TLC, and an example is presented of a 24-fold enhancement in the speed of separation. PPEC was performed on both regular and high-performance C18 layers, and the latter yield substantially faster separation. The sorbent layer requires conditioning at elevated temperature before use, and solute migration velocity increases with this temperature. The flow rate increases in a linear manner with increasing voltage and diminishes in a nonlinear manner with increasing pressure. Both electrical current and Joule heating diminish with increasing pressure, and the diminution of flow at high pressure can be compensated by an increase in voltage. PPEC is more efficient than classical TLC. Theoretical plate heights diminish with increasing Rf and are in the range 29-21 and 55-27 microm for the high-performance and regular plates, respectively. PPEC retains the advantages of classical TLC but has the ability to separate a substantially higher number of samples simultaneously. An example is presented on the separation of nine samples in 1 min on a 2.5 cm x 10 cm sorbent layer. 相似文献
110.
RF DeLuca FJ Tedesco K Ballan E Wortzel AI Rogers 《Canadian Metallurgical Quarterly》1977,67(4):362-365
A case of esophageal perforation occurring in a 75-year-old man is presented. The clinical presentation was benign and the diagnosis of esophageal perforation was made incidental to an upper gastrointestinal barium examination. Conservative management consisting of nasogastric suctioning, antibiotics and antacids was effective in minimizing the clinical course. This represents a rare instance of a successful nonsurgical approach to esophageal perforation. 相似文献