首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1547篇
  免费   14篇
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
  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.
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.
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.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号