全文获取类型
收费全文 | 17917篇 |
免费 | 523篇 |
国内免费 | 17篇 |
学科分类
工业技术 | 18457篇 |
出版年
2021年 | 212篇 |
2020年 | 170篇 |
2019年 | 223篇 |
2018年 | 265篇 |
2017年 | 259篇 |
2016年 | 319篇 |
2015年 | 238篇 |
2014年 | 380篇 |
2013年 | 1101篇 |
2012年 | 663篇 |
2011年 | 870篇 |
2010年 | 674篇 |
2009年 | 662篇 |
2008年 | 858篇 |
2007年 | 870篇 |
2006年 | 685篇 |
2005年 | 719篇 |
2004年 | 559篇 |
2003年 | 569篇 |
2002年 | 509篇 |
2001年 | 329篇 |
2000年 | 300篇 |
1999年 | 303篇 |
1998年 | 312篇 |
1997年 | 300篇 |
1996年 | 299篇 |
1995年 | 333篇 |
1994年 | 267篇 |
1993年 | 303篇 |
1992年 | 272篇 |
1991年 | 164篇 |
1990年 | 237篇 |
1989年 | 270篇 |
1988年 | 194篇 |
1987年 | 215篇 |
1986年 | 208篇 |
1985年 | 263篇 |
1984年 | 256篇 |
1983年 | 226篇 |
1982年 | 216篇 |
1981年 | 213篇 |
1980年 | 170篇 |
1979年 | 187篇 |
1978年 | 176篇 |
1977年 | 177篇 |
1976年 | 147篇 |
1975年 | 178篇 |
1974年 | 165篇 |
1973年 | 133篇 |
1972年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
91.
Richard Kerner 《Computational Materials Science》1994,2(3-4):500-508
92.
Richard C. Morey Donna L. Retzlaff-Roberts David J. Fine 《International Transactions in Operational Research》1994,1(3):285-292
One of the focal points of discussion among firms in the service sector concerns the level of service delivered and its value. In the hospital sector, an important aspect of the level of service relates to the level of quality of care delivered. We undertake an empirical study of 300 U.S. hospitals to evaluate their relative ‘service efficiency’ using the techniques of so-called allocative efficiency. This method estimates the potential improvement in service, estimates the ideal cost shares of the various resources, and provides the ‘peer group’ members to which the unit is being compared. Utilizing this information, the method proposed for units to improve involves two chief mechanisms. The first is a reallocation of cost shares among the various resource or input types (e.g. no increase in hospital budget). The second involves adopting the management practices used by peer group members. Over all 300 hospitals, a marked improvement potential was found for well over half. Of the poorest performers there appears to be some indication that a larger cost share was needed for face-to-face contact with patients (nursing) and a smaller share for personnel who do not deal with patients directly (lab technicians, non-physician administrators, etc.). 相似文献
93.
94.
Efforts to correlate molecular characteristics with microstructural dimensions in microphase-separated diblock and triblock copolymers have been very successful, resulting in relationships that can be utilized to design materials with a specific microstructure and, consequently, with particular thermomechanical properties. However, similar efforts in the arena of multiblock copolymers have not been nearly as extensive, despite the increasing interest and diversity of this class of materials. In the present work, energy-filtered electron microscopy (EFEM) and small-angle neutron scattering (SANS) are used in a complementary fashion to probe the phase behavior of a series of three polysiloxaneimide (PSI) multiblock copolymers with different molecular architectures. Despite their relatively short segment lengths, all three materials exhibit signs of microphase separation at ambient temperature. SANS data are obtained from chemically unaltered materials and are subsequently interpreted with the Teubner-Strey model for microemulsions. Resultant microstructural dimensions are in good agreement with those measured from EFEM micrographs. Additional insight into the intramolecular sequencing of each copolymer is obtained from scaling relationships. 相似文献
95.
Tomarken Andrew J.; Davidson Richard J.; Wheeler Robert E.; Doss Robert C. 《Canadian Metallurgical Quarterly》1992,62(4):676
Assessed whether individual differences in anterior brain asymmetry are linked to differences in basic dimensions of emotion. In each of 2 experimental sessions, separated by 3 wks, resting EEG activity was recorded from female adults during 8 60-sec baselines. Mean alpha power asymmetry across both sessions was extracted in mid-frontal and anterior temporal sites. Across both regions, groups demonstrating stable and extreme relative left anterior activation reported increased generalized positive affect (PAF) and decreased generalized negative affect (NAF) compared with groups demonstrating stable and extreme relative right anterior activation. Additional correlational analyses revealed robust relations between anterior asymmetry and PAF and NAF, particularly among Ss who demonstrated stable patterns of EEG activation over time. Anterior asymmetry was unrelated to individual differences in generalized reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
97.
The effects of hydrogen dilution on the bonding characteristics, composition, and properties of SiN films deposited from a SiH4/NH3 mixture by r.f. plasma enhanced chemical vapor deposition were studied. The addition of relatively small amounts of hydrogen increased the Si/N ratio resulting in a corresponding increase in the Si---H/N---H bonding ratio. At higher hydrogen dilutions, the Si/N ratio decreased towards stoichiometric with significant changes in the hydrogen bonding characteristics. Changes in the physical properties are discussed in terms of the measured changes in bonding structure. Changes normally associated with changes in bulk film density were found to be well correlated to the Si---N bond density. The effects of substrate temperature and NH3/SiH4 ratio on films deposited under conditions of high hydrogen dilution were similar to those widely reported in the literature for plasma-enhanced chemical vapor deposition films deposited without hydrogen. Films deposited by remote plasma using hydrogen as the excitation exhibited high Si---N bond densities and low hydrogen. Experiments are planned to clarify the mechanism responsible for the observed changes in film properties. 相似文献
98.
Bruce C. Bunker R. James Kirkpatrick Richard K. Brow Gary L. Turner Carolyn Nelson 《Journal of the American Ceramic Society》1991,74(6):1430-1438
99.
Richard D. Dick William L. Fourney Deborah J. Goodings Chaun‐Ping Lin Leonhard E. Bernold 《Canadian Metallurgical Quarterly》1992,5(1):59-69
The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity. 相似文献
100.
Neil Roberts Silas Barbosa Lance D. Blumhardt Ron A. Kawoski Richard H. T. Edwards 《Magma (New York, N.Y.)》1994,2(3):375-378
Point counting represents a convenient and efficient technique for estimating the area of transects through multiple sclerosis (MS) lesions on magnetic resonance (MR) images obtained for sections through the brain. When sectioning has been performed according to the Cavalieri method, unbiased estimates of the total volume of MR-visible MS plaques can be obtained with a precision of 3–5% in 5–10 min. 相似文献