全文获取类型
收费全文 | 8530篇 |
免费 | 207篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 448篇 |
综合类 | 20篇 |
化学工业 | 2071篇 |
金属工艺 | 191篇 |
机械仪表 | 190篇 |
建筑科学 | 181篇 |
矿业工程 | 5篇 |
能源动力 | 309篇 |
轻工业 | 624篇 |
水利工程 | 38篇 |
石油天然气 | 16篇 |
无线电 | 789篇 |
一般工业技术 | 1539篇 |
冶金工业 | 1424篇 |
原子能技术 | 245篇 |
自动化技术 | 675篇 |
出版年
2023年 | 47篇 |
2022年 | 107篇 |
2021年 | 188篇 |
2020年 | 84篇 |
2019年 | 109篇 |
2018年 | 116篇 |
2017年 | 92篇 |
2016年 | 171篇 |
2015年 | 108篇 |
2014年 | 197篇 |
2013年 | 388篇 |
2012年 | 347篇 |
2011年 | 422篇 |
2010年 | 336篇 |
2009年 | 384篇 |
2008年 | 406篇 |
2007年 | 324篇 |
2006年 | 314篇 |
2005年 | 235篇 |
2004年 | 241篇 |
2003年 | 257篇 |
2002年 | 226篇 |
2001年 | 189篇 |
2000年 | 163篇 |
1999年 | 190篇 |
1998年 | 615篇 |
1997年 | 389篇 |
1996年 | 297篇 |
1995年 | 182篇 |
1994年 | 183篇 |
1993年 | 167篇 |
1992年 | 114篇 |
1991年 | 101篇 |
1990年 | 85篇 |
1989年 | 97篇 |
1988年 | 67篇 |
1987年 | 83篇 |
1986年 | 64篇 |
1985年 | 77篇 |
1984年 | 55篇 |
1983年 | 65篇 |
1982年 | 68篇 |
1981年 | 69篇 |
1980年 | 39篇 |
1979年 | 49篇 |
1978年 | 42篇 |
1977年 | 41篇 |
1976年 | 61篇 |
1975年 | 21篇 |
1973年 | 22篇 |
排序方式: 共有8765条查询结果,搜索用时 11 毫秒
31.
32.
K Tarao H Hoshino A Shimizu S Ohkawa M Harada Y Nakamura Y Ito S Tamai N Okamoto 《Canadian Metallurgical Quarterly》1995,75(6):1255-1262
BACKGROUND: The relationship between echosonographic patterns of patients with cirrhosis who are antihepatitis C virus (HCV)-positive, the DNA synthesis of hepatocytes, and the risk for HCC were studied. METHODS: Thirty-eight patients with anti-C-100 antibody-positive and Child's grade A posthepatitic cirrhosis were studied. DNA synthesis activity was measured by a bromodeoxyuridine (BrdU, a thymidine analogue)-labeling index (LI), using the BrdU-anti-BrdU in vitro method, and the patients were followed prospectively by frequent liver ultrasonography for 3 years. The ultrasound patterns were classified into fine, coarse, and coarse-nodular (CN) patterns, and the reproducibility of the classification in practical use also was confirmed. RESULTS: Of the 21 patients with high DNA synthesizing cirrhosis (BrdU LI > or = 1.5%), 10 (48%) showed coarse-nodular, 5 (24%) coarse, and 6 (29%) fine pattern in ultrasonography. Conversely, of the 17 patients with low DNA synthesizing LC (BrdU LI < 1.5%), only 1 (6%) showed coarse-nodular, 2 (12%) coarse, and 14 (82%) fine pattern. A significant relationship was found between the two groups of BrdU LI and ultrasound imaging patterns (P < 0.05). The incidence of CN pattern was significantly higher (P < 0.01) in the high DNA synthesizing group than in low DNA synthesizing group. Of the 11 patients with CN pattern by ultrasound imaging, 10 (91%) were in the high DNA synthesizing group, and 9 (82%) developed HCC during the follow-up period, compared with 3 of 7 (43%) with coarse, and only one of 20 (5%) with fine pattern developed HCC. The incidence of HCC was significantly higher (P < 0.01) in patients with a CN cirrhosis pattern than in those with a fine pattern. CONCLUSIONS: In patients with cirrhosis who are anti-HCV-positive, the CN pattern by ultrasound imaging indicates increased DNA synthesis of hepatocytes and a high risk for developing HCC. 相似文献
33.
STATEMENT OF PROBLEM: Improved dental stone has been widely used for producing dies for the fabrication of restorations with the lost-wax technique. Improved dental stone is used for several reasons, but it is selected most often because of its reasonable cost, ease of use, and ability to produce consistent results. PURPOSE: This study evaluated the ability of an epoxy resin die material and a type IV dental stone to dimensionally reproduce a custom-fabricated metal die. MATERIAL AND METHODS: Dies were fabricated and measurements were made from three reference lines. Measurements were repeated three times for the master die and for the specimen dies. A mean measurement and percent relative change for each dimension was calculated. RESULTS: A significant difference in the relative change for die height was found between the groups studied (p < 0.003). CONCLUSIONS: This epoxy die system will provide a degree of dimensional accuracy comparable to gypsum when used with addition silicone impression material. 相似文献
34.
35.
36.
S Tanihara T Zhang T Ojima Y Nakamura H Yanagawa M Kobayashi 《Canadian Metallurgical Quarterly》1997,44(9):688-693
A secondary medical area is defined as a medical administrative area under the Medical Care Law by which every prefectural government is expected to provide general medical care supplies such as beds for inpatients. This study evaluated the distribution in medical supplies among the secondary medical areas in Japan and the correlation between medical supply and demand. The numbers of hospital inpatients (residence of patients), physicians, and general beds excluding those for mental disorders and tuberculosis were analysed in relation to the population in all secondary medical areas in Japan. Those data were obtained from surveys conducted by the Ministry of Health and Welfare. The main results were as follows; 1) The distribution of physicians and general hospital beds among the secondary medical areas was not equal. 2) Even adjusted for the sex and age distribution, the highest hospital inpatients/population ratio among the secondary medical areas was four times as large as that of the lowest. 3) With multiple regression models, two independent variables (normal hospital beds/population ratio and aged 65 and over/total population ratio) accounted about 60% of the variance in hospital inpatients/population ratio. 4) The differences in medical supplies among the secondary medical areas may cause the differences in hospital inpatients/population ratio. 相似文献
37.
38.
Temperature dependences of the soft phonon frequency and the damping constant in Tris-Sarcosine Calcium Chloride (TSCC) single crystal have been investigated between 5K and 100K by using a Fourier-transform far-infrared spectrometer. It has been observed that the soft phonon frequency decreases gradually and the damping constant increases as the transition temperature is approached from below The damping constant varies from 7cm-1 a 90K to less than 0.5cm-1 at 5K. It has been found that the damping constant is approximately proportional to temperature below about 60K. 相似文献
39.
A Antonini JR Moeller T Nakamura P Spetsieris V Dhawan D Eidelberg 《Canadian Metallurgical Quarterly》1998,51(3):803-810
OBJECTIVE: To identify regional metabolic brain networks related specifically to the presence of tremor in PD. BACKGROUND: The pathophysiology of parkinsonian tremor is unknown. Because tremor in PD occurs mainly in repose, we used resting state PET with 18F-fluorodeoxyglucose (FDG) to identify specific metabolic brain networks associated with this clinical manifestation. METHODS: We studied two discrete groups of eight PD patients with and without tremor using FDG/PET. Both patient groups were matched for gender, age, and Unified Parkinson Disease Rating Scale ratings for akinesia and rigidity. Ten normal volunteer subjects served as controls. RESULTS: Network analysis with the Scaled Subprofile Model was performed in two steps. 1) We computed the expression of the PD-related pattern (PDRP) identified by us previously in each of the PD patients and control subjects. Although PDRP subject scores were abnormally elevated in the combined PD cohort (p < 0.005), these values did not differ in the PD patient groups with and without tremor (p = 0.36). 2) We used SSM to analyze the data from the combined PD cohort comprising both patient groups. We found that PD patients with tremor were characterized by increased expression of a metabolic network comprising the thalamus, pons, and premotor cortical regions. Subject scores for this pattern were elevated in the tremor group compared with the atremulous patient group and the normal control group (p < 0.005). CONCLUSIONS: The findings suggest that PD patients with tremor are characterized by distinct increases in the functional activity of thalamo-motor cortical projections. Modulation of this functional anatomic pathway is likely to be the mechanism for successful interventions for the relief of parkinsonian tremor. 相似文献
40.
M Watanabe M Nakamura K Sato M Kano MI Simon Y Inoue 《Canadian Metallurgical Quarterly》1998,10(6):2016-2025
Ligand binding to neurotransmitter and hormone receptors which couple to the Gq subclass of GTP-binding protein leads to the activation of phospholipase Cbeta (PLCbeta) which hydrolyses phosphatidyl-inositol 4,5-bisphosphate, yielding a pair of second messengers, diacylglycerol and inositol 1,4,5-trisphosphate (IP3). The expression of PLCbeta1-4 mRNAs was comparatively examined by in situ hybridization in the mouse brain. In adults, PLCbeta1 mRNA was expressed predominantly in the telencephalon, including the cerebral cortex, hippocampus, amygdala, lateral septum and olfactory bulb, with little expression in most thalamic nuclei. PLCbeta2 mRNA was distributed in the white matter, suggesting its expression in non-neuronal cells, most likely oligodendrocytes. PLCbeta3 mRNA was specifically expressed in cerebellar Purkinje cells. The highest levels of PLCbeta4 mRNA were detected in Purkinje cells. High levels of PLCbeta4 mRNA were also found in the thalamus and medial septum, whereas weak signals were detected in most telencephalic regions, thus showing an expression pattern almost reciprocal to that of PLCbeta1 mRNA. During development, such characteristic regional expression of PLCbeta1 and PLCbeta4 were observed starting in late foetal stages, while specific expression of PLCbeta2 and PLCbeta3 appeared in early postnatal stages. We conclude that despite the existence of four PLCbeta isoforms, only one or two of them is expressed in individual neurons and glial cells. The distinct expression of PLCbetas provides a molecular basis for analysing the nature of the specific signal transduction pathway leading to the production of diacylglycerol and IP3 in distinct cell types and in different regions of the brain. 相似文献