全文获取类型
收费全文 | 3473篇 |
免费 | 57篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 37篇 |
综合类 | 2篇 |
化学工业 | 448篇 |
金属工艺 | 110篇 |
机械仪表 | 57篇 |
建筑科学 | 140篇 |
矿业工程 | 8篇 |
能源动力 | 49篇 |
轻工业 | 293篇 |
水利工程 | 18篇 |
石油天然气 | 5篇 |
无线电 | 254篇 |
一般工业技术 | 405篇 |
冶金工业 | 1316篇 |
原子能技术 | 27篇 |
自动化技术 | 364篇 |
出版年
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 36篇 |
2016年 | 27篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 128篇 |
2012年 | 57篇 |
2011年 | 102篇 |
2010年 | 76篇 |
2009年 | 84篇 |
2008年 | 103篇 |
2007年 | 100篇 |
2006年 | 87篇 |
2005年 | 96篇 |
2004年 | 76篇 |
2003年 | 71篇 |
2002年 | 86篇 |
2001年 | 59篇 |
2000年 | 60篇 |
1999年 | 108篇 |
1998年 | 318篇 |
1997年 | 205篇 |
1996年 | 138篇 |
1995年 | 99篇 |
1994年 | 109篇 |
1993年 | 105篇 |
1992年 | 56篇 |
1991年 | 46篇 |
1990年 | 56篇 |
1989年 | 52篇 |
1988年 | 46篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 39篇 |
1982年 | 35篇 |
1981年 | 45篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 32篇 |
1977年 | 49篇 |
1976年 | 77篇 |
1975年 | 26篇 |
1974年 | 26篇 |
1973年 | 18篇 |
1972年 | 21篇 |
排序方式: 共有3533条查询结果,搜索用时 15 毫秒
61.
This article discusses a longitudinal study of change in disruptive behaviors among nursing home residents treated with neuroleptics compared with those not treated with neuroleptics. Observations were made of 201 participants on admission to and after 1 year in eight skilled nursing facilities. Nine disruptive behaviors were measured using the Psychogeriatric Dependency Rating Scale with nursing assistants. Neuroleptic use was documented from medication records. Odds ratios are reported for the association of behavior at baseline and use of neuroleptics on nine problem behaviors. For those who received neuroleptics during the year, there was greater change in both developing and resolving disruptive behaviors than for those not receiving neuroleptics. For both groups, restless or pacing behavior and belligerent behavior manifested by refusing instructions changed the most, both in developing and in apparently resolving. Our results show that change in disruptive behaviors occurs among nursing home residents regardless of neuroleptic use, but it occurs more frequently among those who receive neuroleptic medication. Knowledge of which disruptive behaviors are most likely to resolve or develop is important in training nursing home staff to cope with the behaviors as well as in planning interventions that may modify such behaviors. 相似文献
62.
63.
64.
"A reevaluation of cross-sectional versus longitudinal models of residential mobility...casts doubt on the study by Davies and Pickles in 1985 in which it was argued that cross-sectional analysis is inadequate.... With the use of data from the [U.S.] Panel Study of Income Dynamics (PSID), the conclusion of this reevaluation is that longitudinal analysis increases our understanding of the processes and provides a richer understanding of migration and mobility but does not undermine the work that has been produced from cross-sectional analysis." 相似文献
65.
A. V. Clark C. M. Fortunko M. G. Lozev S. R. Schaps M. C. Renken 《Research in Nondestructive Evaluation》1992,4(3):165-182
An electromagnetic-acoustic transducer (EMAT) system was used in conjunction with a sampled CW signal-processing method to generate, receive, and process longitudinal and shear waves in thin steel sheets. Using the system, swept-frequency measurements were made up to 7.5 MHz. To relate the measurements to sheet steel formability, a dimensionless frequency ratio,K, was computed from the resonant frequencies. From theoretical considerations,K should be related to a measure of steel sheet formability,
. This parameter is traditionally measured by plastically deforming uniaxial tension specimens. Good correlation was found betweenK and
for a set of steel sheet representative of those typically used to produce automobile body parts.Contribution of NIST; not subject to copyright.NIST Guest Researcher; on leave from Technical University of Plovdiv, Bulgaria. 相似文献
66.
67.
As part of a study of the chemistry of the steam-stimulated recovery of heavy oils, the hydrolysis and subsequent desulphurization of tetrahydrothiophene and thiophene by aqueous solutions of vanadyl and nickel salts was investigated. Vanadyl sulphate and vanadyl chloride were shown to behave very differently, emphasizing that these salts have different molecular species in aqueous solutions. 相似文献
68.
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
69.
High resolution 13C n.m.r. proton noise decoupled (75.5 MHz) spectra have been recorded for a series of nitrated celluloses and denitrated cellulose nitrates. From the detailed spectral assignments an analysis of the partial degrees of substitution and distribution of nitrate groups in the β-D-glucopyranose residues is presented. The data are compared with the predictions of a model based on the constancy of ratio of three equilibrium constants for nitration—denitration at the C2, C3 and C6 positions for differently substituted β-D-glucopyranose residues and it is shown that the situation is considerably more complex than provided for by the model. Analysis of the anomeric 13C carbon region produces some sequence information which indicates non-random distribution of nitrate ester groups. 相似文献
70.
Human milk and infant formula containing coconut/soy oil were infused into the duodenum of rats to determine the incorporation
of capric, lauric, myristic and palmitic acids into lymphatic triacylglycerol (TAG). The proportion of capric and lauric acids
in the lymphatic TAG reflected the fatty acid composition of the diet. Based on positional analysis, it appears that more
than 50% of the capric and lauric acids could have been absorbed from the intestine assn-2 monoacylglycerols. In the rats fed human milk, 50% of palmitic acid in lymphatic TAG was in thesn-2 position. Because of the nonrandom distribution of palmitic acid in the lymphatic TAG, the nonspecific lipase in human
milk, i.e., bile salt-stimulated lipase, did not appear to be a factor in milk lipid digestion. 相似文献