全文获取类型
收费全文 | 3216篇 |
免费 | 24篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 86篇 |
金属工艺 | 4篇 |
机械仪表 | 12篇 |
建筑科学 | 37篇 |
矿业工程 | 1篇 |
能源动力 | 17篇 |
轻工业 | 22篇 |
石油天然气 | 1篇 |
无线电 | 285篇 |
一般工业技术 | 120篇 |
冶金工业 | 2515篇 |
原子能技术 | 10篇 |
自动化技术 | 133篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 16篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 21篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 22篇 |
2011年 | 40篇 |
2010年 | 21篇 |
2009年 | 37篇 |
2008年 | 37篇 |
2007年 | 35篇 |
2006年 | 28篇 |
2005年 | 27篇 |
2004年 | 23篇 |
2003年 | 41篇 |
2002年 | 19篇 |
2001年 | 26篇 |
2000年 | 36篇 |
1999年 | 85篇 |
1998年 | 711篇 |
1997年 | 424篇 |
1996年 | 321篇 |
1995年 | 147篇 |
1994年 | 140篇 |
1993年 | 186篇 |
1992年 | 29篇 |
1991年 | 47篇 |
1990年 | 45篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 38篇 |
1986年 | 42篇 |
1985年 | 42篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 30篇 |
1980年 | 29篇 |
1978年 | 8篇 |
1977年 | 72篇 |
1976年 | 160篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1955年 | 2篇 |
排序方式: 共有3254条查询结果,搜索用时 15 毫秒
971.
Lidocaine-induced inactivation of the medial septum immediately after training or prior to testing in a delay radial-arm maze task produced deficits in spatial working memory that reflected impaired acquisition of the task. Injection of lidocaine into the nucleus basalis magnocellularis produced a profile of behavioral changes that indicated that temporary inactivation of this structure impaired the behavioral expression of information already stored in working memory. This appears to reflect an impairment in processes that are required for performance (i.e., attention, motivation, sensorimotor function) of the task but not for retrieval of stored information. Site-specific inactivation of the basal forebrain should help to reveal the involvement of its component structures in different aspects of cognitive function. 相似文献
972.
JS Markowitz P Seu JA Goss H Yersiz JF Markmann DG Farmer RM Ghobrial LI Goldstein P Martin R Stribling RW Busuttil 《Canadian Metallurgical Quarterly》1998,65(4):570-572
BACKGROUND: Although jejunoileal bypass results in end-stage liver disease in up to 100% of patients, little is known about outcome after liver transplantation. METHODS: The clinical courses of six patients who underwent liver transplantation at UCLA for decompensated cirrhosis owing to a jejunoileal bypass were reviewed. Liver function, allograft pathology, renal function, and nutritional status were assessed. RESULTS: Of the four patients with an intact jejunoileal bypass, two of the three who were biopsied had recurrent steatotic liver disease. The two patients whose jejunoileal bypass was reversed at the time of liver transplantation had lower alkaline phosphatase, lower creatinine, higher albumin, and higher cholesterol, and were more obese than their counterparts with intact bypasses. CONCLUSIONS: Patients undergoing liver transplantation for jejunoileal bypass-associated liver disease should, if possible, have their bypass reversed at the time of transplantation; otherwise, they must be followed closely and be biopsied routinely. Recurrent liver disease should prompt reversal of the jejunoileal bypass. 相似文献
973.
Coupled B-snake grids and constrained thin-plate splines for analysis of 2-D tissue deformations from tagged MRI 总被引:2,自引:0,他引:2
Magnetic resonance imaging (MRI) is unique in its ability to noninvasively and selectively alter tissue magnetization and create tagged patterns within a deforming body such as the heart muscle. The resulting patterns define a time-varying curvilinear coordinate system on the tissue, which we track with coupled B-snake grids. B-spline bases provide local control of shape, compact representation, and parametric continuity. Efficient spline warps are proposed which warp an area in the plane such that two embedded snake grids obtained from two tagged frames are brought into registration, interpolating a dense displacement vector field. The reconstructed vector field adheres to the known displacement information at the intersections, forces corresponding snakes to be warped into one another, and for all other points in the plane, where no information is available, a C1 continuous vector field is interpolated. The implementation proposed in this paper improves on our previous variational-based implementation and generalizes warp methods to include biologically relevant contiguous open curves, in addition to standard landmark points. The methods are validated with a cardiac motion simulator, in addition to in-vivo tagging data sets. 相似文献
974.
In a prospective noninterventional study of 75 consecutive patients (mean age 71 +/- 12 years) undergoing surgery for colorectal cancer, standard postoperative energy intake was evaluated. Seventeen patients expended 40%-60% of estimated basal energy during hospitalization, 33 patients 60%-80%, 22 patients 80%-100% and three patients 100%-125%. Weight loss was observed in 67 patients (mean loss 4.7 +/- 4.4%) during hospitalization. Men had a significantly higher mean total calorie deficit (p < 0.001), and mean weight loss percentage (p < 0.01), compared to women. Preoperative nutritional status, nutrition-associated complications and length of hospital stay did not change the nutritional support and intake. Correlation analyses resulted in significant associations between gender and total calorie deficit (rs = 0.41, p < 0.01), postoperative weight loss and total calorie deficit (rs = -0.32, p < 0.01), and between postoperative weight loss and length of stay (rs = 0.27, p < 0.05). We concluded that the patients' energy intake was insufficient compared to estimated basal energy expenditure. These results suggest a need for individualized nutritional care, based on each patient's energy needs and on registration of daily calorie intake, all with the aim of increasing energy intake postoperatively in standard hospital care. 相似文献
975.
FC Denison SC Riley NC Wathen T Chard AA Calder RW Kelly 《Canadian Metallurgical Quarterly》1998,13(8):2292-2295
Monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8) are important chemokines which effect the chemotaxis of monocytes and neutrophils, respectively. There is increasing evidence that such chemokines play an integral role in the control and maintenance of a normal pregnancy from implantation to parturition. However, little is known about the sites of secretion and function of MCP-1 and IL-8 in particular with respect to establishment of the placenta and membranes during first trimester. The aim of this study was therefore to investigate the concentrations and localization of MCP-1 and IL-8 in amniotic fluid and extra-embryonic coelomic fluid (EECF) collected by ultrasound-guided needle aspiration and maternal serum during the first trimester of pregnancy. Using specific enzyme-linked immunosorbent assays, MCP-1 was present at high concentrations in the EECF, significantly higher than those in amniotic fluid and maternal serum. IL-8 was also present predominantly in the EECF with concentrations being significantly higher than the low values detected in maternal serum and the very low amounts found in amniotic fluid. This strict compartmentalization of these cytokines in the fluid compartments of early pregnancy may be important for establishment and development of a viable pregnancy. 相似文献
976.
The study was performed on 30, 8-year-old children living in an industrial town of the Upper Silesia region. Morning urine samples were collected on 6 consecutive days. Intraindividual variation of urinary 1-hydroxypyrene concentrations, calculated as a coefficient of variance (CV), ranged from 14 to 109% whereas inter-individual variation ranged from 69 to 109%. Three-way analysis of variance disclosed a significant effect of sex, exposure to environmental tobacco smoke and day of examination on 1-hydroxypyrene concentrations not corrected for creatinine. The appropriate sample size for population studies and the minimum number of observations for the individual assessment of environmental exposure to PAHs calculated on the basis of inter- and intraindividual variability of 1-hydroxypyrene concentrations in urine amounted to 164 and 99, respectively. Urinary 1-hydroxypyrene may be considered a good indicator of environmental exposure to PAHs at the group level. 相似文献
977.
AIMS: To establish a pharmacodynamic model that allows one to predict the haemoglobin (Hb) response to EPO in children as a function of dose and time, and to derive recommendations for initial dosing and subsequent dose adjustment. METHODS: Haemoglobin was monitored in eight children aged 8-15 years with anaemia due to renal failure during treatment with EPO. All patients were free of conditions known to impair the response to EPO. Pretreatment Hb was 4.9-9.0 g dl(-1). The drug was administered once weekly by subcutaneous injection; doses ranged from 1700 to 6800 U week (-1). Hb was monitored for 4-38 months. The Hb-time data were analysed by applying a population pharmacodynamic model proposed for EPO in adult haemodialysis patients. Internal model validation was carried out by using a bootstrap procedure. RESULTS: The increase of Hb during treatment with EPO was linear until steady state was reached after 103+/-33 days (mean +/- interindividual s.d.). The weekly gain in Hb from the onset of therapy to steady state was 0.0805+/-0.026 g dl(-1) (mean +/- interindividual s.d.) for every 1000 U EPO week (-1); it did not exhibit a dependence on body weight. Estimated mean prediction errors are +/-1.53 g dl(-1) for predictions that are based on the mean population parameters and +/-0.83 g dl(-1) for predictions that take into account the complete individual Hb-time data up to and including steady state. CONCLUSIONS: The model describes the time course of the Hb response to EPO in children with renal anaemia. The required weekly EPO dose should initially be calculated from the individual pretreatment Hb and the desired Hb at steady state by using the mean population estimates of the weekly gain in Hb per dose unit before steady state (beta) and the time needed to reach steady state (tau). A reduction of the initial dose according to body weight is not justified by the available evidence. beta should be re-estimated individually after 6 weeks of treatment and dose should be adjusted accordingly. A final dose adjustment should be made when steady state has been reached based on individual estimates of beta and tau. 相似文献
978.
Chi-Ho Tsang Author Vitae Author Vitae Hanli Wang Author Vitae 《Pattern recognition》2007,40(9):2373-2391
Classification of intrusion attacks and normal network traffic is a challenging and critical problem in pattern recognition and network security. In this paper, we present a novel intrusion detection approach to extract both accurate and interpretable fuzzy IF-THEN rules from network traffic data for classification. The proposed fuzzy rule-based system is evolved from an agent-based evolutionary framework and multi-objective optimization. In addition, the proposed system can also act as a genetic feature selection wrapper to search for an optimal feature subset for dimensionality reduction. To evaluate the classification and feature selection performance of our approach, it is compared with some well-known classifiers as well as feature selection filters and wrappers. The extensive experimental results on the KDD-Cup99 intrusion detection benchmark data set demonstrate that the proposed approach produces interpretable fuzzy systems, and outperforms other classifiers and wrappers by providing the highest detection accuracy for intrusion attacks and low false alarm rate for normal network traffic with minimized number of features. 相似文献
979.
980.
CL Perry DB Bishop G Taylor DM Murray RW Mays BS Dudovitz M Smyth M Story 《Canadian Metallurgical Quarterly》1998,88(4):603-609
OBJECTIVES: A randomized school based trial sought to increase fruit and vegetable consumption among children using a multicomponent approach. METHODS: The intervention, conducted in 20 elementary schools in St. Paul, targeted a multiethnic group of children who were in the fourth grade in spring 1995 and the fifth grade in fall 1995. The intervention consisted of behavioral curricula in classrooms, parental involvement, school food service changes, and industry support and involvement. Lunchroom observations and 24-hour food recalls measured food consumption. Parent telephone surveys and a health behavior questionnaire measured psychosocial factors. RESULTS: The intervention increased lunchtime fruit consumption and combined fruit and vegetable consumption, lunchtime vegetable consumption among girls, and daily fruit consumption as well as the proportion of total daily calories attributable to fruits and vegetables. CONCLUSIONS: Multicomponent school-based programs can increase fruit and vegetable consumption among children. Greater involvement of parents and more attention to increasing vegetable consumption, especially among boys, remain challenges in future intervention research. 相似文献