全文获取类型
收费全文 | 1547篇 |
免费 | 14篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 54篇 |
金属工艺 | 9篇 |
机械仪表 | 4篇 |
建筑科学 | 28篇 |
能源动力 | 4篇 |
轻工业 | 86篇 |
石油天然气 | 1篇 |
无线电 | 80篇 |
一般工业技术 | 69篇 |
冶金工业 | 1165篇 |
原子能技术 | 8篇 |
自动化技术 | 45篇 |
出版年
2022年 | 4篇 |
2019年 | 8篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 4篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 15篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 19篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 23篇 |
1999年 | 48篇 |
1998年 | 360篇 |
1997年 | 185篇 |
1996年 | 135篇 |
1995年 | 71篇 |
1994年 | 80篇 |
1993年 | 82篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 36篇 |
1976年 | 71篇 |
1975年 | 5篇 |
1973年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有1561条查询结果,搜索用时 0 毫秒
991.
In limbs with combined shortening with angulation or malrotation, deformity may be quickly or slowly corrected before lengthening with external fixation. We examined a series of 35 patients with 40 limbs that underwent acute deformity correction and subsequent gradual lengthening. The average deformity corrected was 19 degrees, with subsequent average lengthening of 4.1 cm. Good radiographic callus formation was noted in 34 of the 40 segments studied. The magnitude of deformity correction had no effect on the quality of lengthened bone, incidence of complications, or the healing index. Skeletally mature segments had statistically significant decreased bone formation (p = 0.001), increased prevalence of callus complications (p = 0.001), and a higher healing index (p = 0.003). Based on this experience, it is our conclusion that immediate correction and lengthening is suitable in children and adolescents who have malaligned and shortened lower extremities. Because of poorer results in older patients, we believe that other techniques should be considered in adults. 相似文献
992.
Li H.Y. Southern E.P. Crossley P.A. Potts S. Pickering S.D.A. Caunce B.R.J. Weller G.C. 《Power Delivery, IEEE Transactions on》1997,12(3):1090-1099
This paper describes a new technique for sampling synchronisation in a numerical differential feeder protection relay. The protection uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder. The EMTP/ATP power system simulator was used to simulate a typical distribution feeder with faults at various locations. The current signals generated at both ends of feeder were used to evaluate the performance of the protection. These tests were carried out using a protection simulator. The results illustrate the effect of current transformer saturation on the sensitivity and stability of the protection. Finally it is shown that a precisely synchronized differential protection is fast, selective and accurate. On an internal fault it provides a high operating sensitivity, whilst it remains stable on all external faults 相似文献
993.
The conformation of L-malate bound at the active site of Ascaris suum malic enzyme has been investigated by electron spin echo envelope modulation spectroscopy. Dipolar interactions between Mn2+ bound to the enzyme active site and deuterium specifically placed at the 2-position, the 3R-position, and the 3S-position of L-malate were observed. The intensities of these interactions are related to the distance between each deuterium and Mn2+. Several models of possible Mn-malate complexes were constructed using molecular graphics techniques, and conformational searches were conducted to identify conformers of malate that meet the distance criteria defined by the spectroscopic measurements. These searches suggest that L-malate binds to the enzyme active site in the trans conformation, which would be expected to be the most stable conformer in solution, not in the gauche conformer, which would be more similar to the conformation required for oxidative decarboxylation of oxalacetate formed from L-malate at the active site of the enzyme. 相似文献
994.
Use of the laryngeal mask airway as an alternative to the tracheal tube during ambulatory anesthesia
GP Joshi Y Inagaki PF White L Taylor-Kennedy LI Wat C Gevirtz JM McCraney DA McCulloch 《Canadian Metallurgical Quarterly》1997,85(3):573-577
Apoptosis is a major determinant of the effectiveness of antitumor chemotherapy since most of the drugs used in cancer treatment provoke cell death by this process. We selected L1210/0.7R (7-fold) and L1210/3R (16-fold) murine leukemia cells resistant to cisplatin (CDDP) by adaptation of parental L1210/S cells to increasing drug concentration. L1210/0.7R exhibited a decreased apoptosis response to CDDP compared to parental L1210/S, while it was totally defective in L1210/3R as analyzed by cell morphology, DNA fragmentation, and poly(ADP-ribose) polymerase cleavage. This default in apoptosis did not result from differential expression of the antiapoptotic protein bcl-2 or from altered expression of p53. L1210/3R was resistant to other cross-linking agents and sensitive to topoisomerase II inhibitors and microtubule poisons. Whatever the drug sensitivity phenotype to these agents, L1210/3R was totally defective in apoptosis in response to drug treatment, showing that apoptosis control cannot be directly involved in the resistance process of these cell lines. 相似文献
995.
We consider irregular quasi-cyclic low-density parity-check (LDPC) codes derived from difference families. The resulting codes can be encoded with low complexity and perform well when iteratively decoded with the sum-product algorithm. 相似文献
996.
PURPOSE: Study purpose was to develop a theoretical framework that will explain pharmacists' behavior relative to the provision of pharmaceutical care. The model was developed from four attitude models by testing their predictive validity relative to pharmaceutical care implementation. Four hypotheses and one research question were investigated to identify determinants of behavioral intention and behavior. METHODS: 617 community pharmacists in the state of Florida, U.S.A., were surveyed twice using mail survey methodology to collect data. The first survey assessed community pharmacists' attitude, subjective norm, perceived behavioral control, past behavior recency, self-efficacies, instrumental beliefs and affect. The second survey assessed pharmacists' behavior relative to the implementation of pharmaceutical care. After establishing reliability and validity of measures, regression analysis was used to test hypotheses and research question investigated. RESULTS: The Pharmacists' Implementation of Pharmaceutical Care (PIPC) model developed postulates that (i) behavior is directly determined by past behavior recency, behavioral intention and perceived behavioral control; (ii) psychological appraisal processes-instrumental beliefs, self-efficacies, and affect toward means-influence behavior through past behavior recency; and (iii) behavioral intention is determined by attitude, social norm and perceived behavioral control. CONCLUSIONS: The PIPC model provides a formal scientifically validated theoretical framework which can be used to design successful intervention for pharmaceutical care implementation. 相似文献
997.
OBJECTIVE: To determine the accuracy with which cervico-vaginal fetal fibronectin predicts preterm delivery using systematic quantitative overview of the available literature. DESIGN: Online searching of MEDLINE database (1966 to April 1996), scanning of bibliography of known primary and review articles and review of recent journal issues. Study selection, assessment of study quality and data extraction were performed in duplicate under masked conditions. Likelihood ratios were generated in subgroups of symptomatic and asymptomatic pregnant women by pooling data from different studies. An LR of > 10 or < 0.1 indicated conclusive changes in the pretest probability of preterm delivery while an LR of 5-10 or 0.2-0.1 indicated only moderate changes. PARTICIPANTS: Seven hundred and twenty-three symptomatic women with threatened preterm labour included in nine studies and 847 asymptomatic women (635 low risk and 212 high risk) included in six studies selected for meta-analyses. MAIN OUTCOME MEASURES: Likelihood ratios for positive and negative test results using delivery at < 37 and < 34 weeks of gestation, and within one week of testing as outcome measures. RESULTS: In symptomatic women a positive test predicted delivery < 37 weeks of gestation with a pooled likelihood ratio (LR) of 4.6 (95% CI 3.5-6.1) while a negative test had a pooled LR of 0.5 (95% CI 0.4-0.6). For delivery < 34 weeks of gestation, the pooled LR was 2.6 (95% CI 1.8-3.7) for a positive test and 0.2 (95% CI 0.1-0.5) for a negative test. For delivery within one week of testing, the pooled LR was 5.0 (95% CI 3.8-6.4) for a positive test and 0.2 (95% CI 0.1-0.4) for a negative test. In asymptomatic women at low risk of delivery < 37 weeks of gestation the pooled LR was 3.2 (95% CI 2.2-4.8) for a positive test and 0.8 (95% CI 0.7-0.9) for a negative test. In high risk asymptomatic women using delivery < 37 weeks of gestation as an outcome measure the pooled LR was 2.0 (95% CI 1.5-2.6) for a positive test and 0.4 (95% CI 0.2-0.8) for a negative test. For delivery < 34 weeks of gestation in high risk, asymptomatic women the pooled LR was 2.4 (95% CI 1.8-3.2) for a positive test and 0.6 (95% CI 0.4-0.9) for a negative test. CONCLUSION: The presence of fetal fibronectin in cervico-vaginal mucus has limited accuracy in predicting preterm delivery as the likelihood ratios for positive and negative test results generated only minimal to moderate changes in the pretest probability of preterm birth. 相似文献
998.
999.
The authors hypothesized that children's perceptions of their parents' job insecurity mediate the effects of parental job insecurity and layoffs on children's work beliefs and work attitudes. Male and female undergraduate students (N = 134; M age = 18.9 years), as well as their mothers (M age = 47.0 years) and fathers (M age = 49.1 years), participated voluntarily. With structural equation modeling as implemented by LISREL VIII, support for the proposed model was obtained, whereas no support was obtained for a competing model. Moreover, identification with fathers moderated the influence of perceived paternal job insecurity on children's humanistic work beliefs, but no comparable effect emerged for mothers. 相似文献
1000.