全文获取类型
收费全文 | 2239篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 67篇 |
金属工艺 | 2篇 |
机械仪表 | 6篇 |
建筑科学 | 20篇 |
能源动力 | 4篇 |
轻工业 | 79篇 |
水利工程 | 3篇 |
无线电 | 22篇 |
一般工业技术 | 45篇 |
冶金工业 | 1957篇 |
原子能技术 | 4篇 |
自动化技术 | 43篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 22篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 21篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 54篇 |
1998年 | 597篇 |
1997年 | 320篇 |
1996年 | 250篇 |
1995年 | 157篇 |
1994年 | 109篇 |
1993年 | 109篇 |
1992年 | 20篇 |
1991年 | 40篇 |
1990年 | 36篇 |
1989年 | 18篇 |
1988年 | 26篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 35篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 27篇 |
1976年 | 106篇 |
1975年 | 6篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2259条查询结果,搜索用时 15 毫秒
91.
The purpose of this in vitro study was to compare both apical and coronal dye penetration when Ketac-Endo and AH-26 sealers were used with laterally condensed gutta percha. Crowns were removed from 28 teeth and the root canals were biomechanically prepared. The teeth were divided into two groups of 12-teeth each and a control group of 4 teeth. Root canals in the two experimental groups were filled with laterally condensed gutta percha and either Ketac-Endo or AH-26 sealer. The Ketac-Endo group had the coronal 3 mm of gutta percha and sealer removed and the resultant cavity was filled with Ketac-Endo alone. After the sealers had set, the root surfaces were coated with nail varnish except at the apex and at the coronal end. Positive controls had no root fillings and were coated with nail varnish in the same manner while the negative controls were sealed apically and coronally with Cavit prior to sealing the entire external root surface with nail varnish. Specimens were placed in 2% methylene blue dye in a vacuum of 660 mm of mercury for five minutes and then left immersed for a further two days. The roots were vertically sectioned to determine the following mean levels of dye penetration: Ketac-Endo, 1.08 mm apically and 6.29 mm coronally; AH-26, 0.75 mm apically and 6.67 mm coronally. Positive controls had total leakage and negative controls had no leakage. This study demonstrated that the apical and coronal seals obtained with Ketac-Endo and AH-26 were not significantly different although the apical seal obtained with each material was significantly better than the corresponding coronal seal. 相似文献
92.
Interactions of L-triiodothyronine (T3) in adult rat cerebrocortical synaptosomes were studied in vitro. Scatchard plot analysis revealed two sets of T3 binding sites. The degree of saturation of T3 binding sites (putative receptor) correlated well with the dose-dependent inhibition of Na(+)-K(+)-ATPase activity in synaptosomes. The relative binding affinities and relative inhibition of enzyme activities for different TH analogues were L-T3 > T3-amine > TRIAC = L-T4 > r-T3 > T2 and L-T3 > T3-amine > TRIAC > L-T4 > r-T3 > T2, respectively. The present study demonstrates the nature of inhibition of synaptosomal Na(+)-K(+)-ATPase activity may be as a function of T3 occupancy of synaptosomal receptor sites in adult mammalian brain. 相似文献
93.
The purpose of this study was to evaluate the effect of redesigning the education program from individual instructional sessions to a format where the majority of instruction was provided through small group classes. Patient outcomes of lifestyle changes as evidenced by weight loss, improved glycemic control, adoption of a consistent pattern of blood glucose monitoring, and increased physical activity were evaluated using a physician satisfaction survey and a patient satisfaction and lifestyle change survey. The findings indicate that the changes in the education program accommodated a variety of needs; facilitated cost-effectiveness; were convenient for the patients, educators, and physicians; and still promoted adaptive lifestyle changes in behavior leading to improved glycemic control, increased levels of physical activity, and weight loss in persons with type 2 diabetes. 相似文献
94.
95.
R Dullerud V Graver M Haakonsen AK Haaland M Loeb B Magnaes 《Canadian Metallurgical Quarterly》1998,23(13):1464-1469
STUDY DESIGN: Prospective cohort study. OBJECTIVES: To assess the amount of scar tissue by viewing magnetic resonance images, and to evaluate the correlation between the amount of scar tissue and clinical outcome, surgical technique, and fibrinolytic factors. SUMMARY OF BACKGROUND DATA: The influence of fibrinolytic factors on magnetic resonance images has not been investigated previously. The relation between clinical outcome and findings on magnetic resonance imaging remains uncertain. METHODS: Magnetic resonance imaging at 0.5 Tesla was performed to produce sagittal and axial spin-echo T1-weighted images before and after contrast enhancement on 78 patients 7 years after traditional lumbar discectomy with partial or full laminectomy. Before surgery all patients had been tested for fibrinolytic factors. RESULTS: The overall clinical success rate of the surgery was 73%. No evidence of scar formation was seen in 19 patients, a small amount was seen in 36 patients, a moderate amount in 17 patients, and a large amount was observed in 6 patients. Ten patients who had undergone surgery at two disc levels and 18 who had been treated with full laminectomy exhibited more scar tissue than those patients who had undergone surgery on a single level (P = 0.033) and those who had undergone a partial laminectomy, respectively (P = 0.017). The amount of scar formation also was associated with a poor outcome (P = 0.017) and with low preoperative values of tissue plasminogen activator antigen (P = 0.003) and tissue plasminogen activity (P = 0.048) in samples collected after venous occlusion. The intensity of contrast enhancement, however, was not influenced by these or any other parameters. CONCLUSION: The amount of scar formation after lumbar discectomy seems to be related to the clinical outcome, the size of the surgical exposure, and some fibrinolytic factors. 相似文献
96.
SF Stamatelopoulos NS Saridakis AK Chatzis AT Kalandaridou NM Desses A Lymperidis NM Giannopoulos SD Moulopoulos 《Canadian Metallurgical Quarterly》1998,22(11):993-997
This study examines whether a catheter mounted left intraventricular balloon may prevent left ventricular (LV) dysfunction following acute experimental myocardial infarction. In 10 anesthetized pigs, multiple coronary arterial ligations were applied around the apex of the heart. LV end-diastolic pressure (LVEDP), aortic flow (AF), and LV long and short axis fractional shortening (FS) were measured before and at 15 min intervals after ligations. At the 60th min after ligation, the LV long axis FS and AF decreased by 7.2 +/- 2.6% (p < 0.05) and 13.25 +/- 2.68% (p < 0.01), respectively, and the LVEDP increased by 4.3 +/- 1.1 mm Hg (p < 0.01) while no change was noted in the LV short axis FS. An intraventricular catheter mounted nonpulsating balloon was positioned over the endocardium of the infarcted area at the LV apex. Inflation of the nonpulsating balloon to an optimal volume, which was found to be equal to 8-10% of the LV end-diastolic volume, resulted in a reduction (by 3.8 +/- 1.2 mm Hg, p < 0.01) of the already increased LVEDP and in an increase (by 6.6 +/- 2.1%, p < 0.05) in the LV short axis FS while no statistically significant change was noted in the AF and LV long axis FS. It is concluded that an intraventricular catheter mounted balloon patch positioned over the endocardium of the infarcted area may ameliorate early LV dysfunction, possibly by interfering with the functional geometry of the LV contraction. 相似文献
97.
98.
99.
Glycogen in the placenta and its appendages is important for fetal well-being. The precise location of the glycogen stores, however, is unknown. This study was initiated to quantitate glycogen levels at well-defined sampling sites in more than 641 samples from 10 uncomplicated pregnancies and to correlate these glycogen levels with clinical and morphological variables. By biochemical assay, glycogen levels were greatest in the midumbilical cord section (29.08 +/- 1.18 mg/g dry wt) and lowest in the amnionic membrane (2.31 +/- 0.08 mg/g dry wt). Within the placental disk, parenchymal glycogen levels were greatest near the cord insertion (9.31 +/- 2.68 mg/g dry wt) and lowest at the periphery (5.71 +/- 1.14 mg/g dry wt). The midumbilical cord glycogen level showed strong direct correlations (P < .001) with birth weight, umbilical cord weight, and total calculated umbilical cord glycogen and somewhat lower but significant (P < .037) direct correlations with the calculated mean umbilical cord glycogen level, total calculated placental glycogen content, and placental weight. The glycogen level in the middisk parenchymal section from the fetal surface correlated directly with gestational age. Periodic acid-Schiff stains showed that magenta glycogen granules were most abundant in the cytoplasm of the vascular smooth muscle cells. These data show significant variations in glycogen levels among sampling sites. Definition of the precise sampling site is important for clinicopathologic studies of placental glycogen and for interstudy correlations. 相似文献
100.