全文获取类型
收费全文 | 1319篇 |
免费 | 49篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 69篇 |
综合类 | 22篇 |
化学工业 | 269篇 |
金属工艺 | 41篇 |
机械仪表 | 30篇 |
建筑科学 | 15篇 |
矿业工程 | 91篇 |
能源动力 | 55篇 |
轻工业 | 99篇 |
水利工程 | 5篇 |
石油天然气 | 5篇 |
无线电 | 68篇 |
一般工业技术 | 202篇 |
冶金工业 | 249篇 |
原子能技术 | 35篇 |
自动化技术 | 118篇 |
出版年
2023年 | 11篇 |
2022年 | 19篇 |
2021年 | 32篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 17篇 |
2017年 | 24篇 |
2016年 | 31篇 |
2015年 | 20篇 |
2014年 | 36篇 |
2013年 | 58篇 |
2012年 | 47篇 |
2011年 | 109篇 |
2010年 | 79篇 |
2009年 | 61篇 |
2008年 | 63篇 |
2007年 | 60篇 |
2006年 | 34篇 |
2005年 | 37篇 |
2004年 | 75篇 |
2003年 | 70篇 |
2002年 | 73篇 |
2001年 | 54篇 |
2000年 | 34篇 |
1999年 | 52篇 |
1998年 | 60篇 |
1997年 | 32篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1373条查询结果,搜索用时 15 毫秒
151.
Delay of gratification, assessed in a series of experiments when the subjects were in preschool, was related to parental personality ratings obtained a decade later for 95 of these children in adolescence. Clear and consistent patterns of correlations between self-imposed delay time in preschool and later ratings were found for both sexes over this time span. Delay behavior predicted a set of cognitive and social competencies and stress tolerance consistent with experimental analyses of the process underlying effective delay in the preschool delay situation. Specifically, children who were able to wait longer at age 4 or 5 became adolescents whose parents rated them as more academically and socially competent, verbally fluent, rational, attentive, planful, and able to deal well with frustration and stress. Comparisons with related longitudinal research using other delay situations help to clarify the important features of the situations and person variables involved in different aspects of delay of gratification. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
152.
H Yasuda T Mine H Shibata Y Eto Y Hasegawa T Takeuchi S Asano I Kojima 《Canadian Metallurgical Quarterly》1993,92(3):1491-1496
The present study was conducted to examine the effect of activin A on growth of rat hepatocytes. EGF induced a 10-fold increase in DNA synthesis as assessed by [3H]thymidine incorporation in cultured hepatocytes. When activin A was added together with EGF, DNA synthesis induced by EGF was markedly inhibited. Inhibition was detected at a concentration of 10(-10) M, and 5 x 10(-9) M activin A almost completely blocked EGF-mediated DNA synthesis. Similarly, activin A completely blocked DNA synthesis induced by hepatocyte growth factor/scatter factor. Activin A was capable of inhibiting EGF-mediated DNA synthesis, even when added 36 h after the addition of EGF. With the same time interval, TGF-beta also blocked EGF-induced DNA synthesis. Although both activin A and TGF-beta inhibited growth of hepatocytes in a similar manner, either activin A or TGF-beta did not compete with each other in their binding when assessed by competitive binding using an iodinated ligand. When hepatocytes were incubated with EGF, release of bioactivity of activin A into culture medium was detected after 48 h or later. Activity of activin A was released from parenchymal cells but not from nonparenchymal cells. mRNA for beta A subunit of activin was detected only slightly in unstimulated hepatocytes, but markedly increased at 48 h after the addition of EGF. To determine whether endogenously produced activin A affects DNA synthesis, we examined the effect of follistatin, an activin-binding protein that blocks the action of activin A. An addition of follistatin significantly enhanced EGF-induced DNA synthesis. Finally, in partial hepatectomized rat, expression of mRNA for beta A subunit in liver was markedly increased 24 h after the partial hepatectomy. These results indicate that activin A inhibits initiation of DNA synthesis in hepatocytes by acting on its own receptor and that activin A acts as an autocrine inhibitor of DNA synthesis in rat hepatocytes. 相似文献
153.
154.
Catalyst aging or formulation changes can cause a perturbation to the rate constant matrix of a monomolecular reaction system. The techniques of determining a perturbation matrix from a knowledge of the original rate constant matrix and the experimental reaction paths are discussed. Kubo's expansion form is shown to be useful for a short reaction time when the magnitude of a perturbation matrix is rather large. For small perturbations, the eigenvalues and eigenvectors of the perturbed system can be expanded into a Taylor series. 相似文献
155.
156.
The static magnetization of 3He film adsorbed on sintered silver powder has been measured for coverages from 0.10 to 0.54 atoms/»2 in steps of 0.02 atoms/»2 and at a coverage of 4.5 atoms/»2. Below 0.20 atoms/»2 the magnetization well obeys the Curie law, while above that coverage a ferromagnetic tendency appears. The coverage dependence of the magnetization greatly differs from that for graphite. At 0.23 atoms/»2 the magnetization has apeak like that for graphite; however, the magnitude of the peak is not so large. Furthermore, a multipeak structure is found in the isotherm of the magnetization at 0.2 mK. It has two prominent peaks at 0.23 and 0.29 atoms/»2, and two other peaks are found at 0.35 and 0.41 atoms/»2. These appear periodically with an interval of 0.06 atoms/»2, which is nearly equal to the coverage of one liquid layer. 相似文献
157.
Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi1/2Na1/2)TiO3(BNT)-based solid solution, that is, (Bi1/2Na1/2)(1-x)(Pba Bab)xTiO3(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(Fa-tetragonal (Fβ) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi1/2Na1/2)TiO3[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε33Tε0, and a high electromechanical coupling factor k33, along with a high mechanical strength. 相似文献
158.
The components of self-regulation were analyzed, extending the self-imposed delay of gratification paradigm to older children with social adjustment problems. Delay behavior was related to a network of conceptually relevant cognitive person variables, consisting of attention deployment strategies during delay, knowledge of delay rules, and intelligence. A positive relationship was demonstrated between concurrent indexes of intelligence, attention deployment, and actual delay time. Moreover, attention deployment, measured as an individual differences variable during the delay process, had a direct, positive effect on delay behavior. Specifically, as the duration of delay and the frustration of the situation increased, children who spent a higher proportion of the time distracting themselves from the tempting elements of the delay situation were able to delay longer. The effect of attention deployment on delay behavior was significant even when age, intelligence, and delay rule knowledge were controlled. Likewise, delay rule knowledge significantly predicted delay time, even when age, attention deployment, and intelligence were controlled. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
159.
To examine the effects of the relationships between behavior and the situation in which it occurs, we manipulated such relations and exposed subjects to them. Impressions were similar when based on the behaviors presented with situations unspecified (e.g., child hits) or when the situations in which they naturally occurred were specified (e.g., child hits when provoked). However, when situations were specified, subjects' impressions more accurately predicted individual differences in the children's actual levels of overall aggressive behavior. When the veridical situation–behavior relations were increasingly altered, the targets were perceived as being less plausible and increasingly maladjusted and odd, and correlations decreased between the perceived level of the children's aggressiveness and their actual aggressive behavior. Thus, both personality impressions and predictive accuracy were influenced by the relations between the target's behaviors and their situational contexts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
160.
Extraction of a plasma time-activity curve from dynamic brain PET images based on independent component analysis 总被引:1,自引:0,他引:1
Naganawa M Kimura Y Ishii K Oda K Ishiwata K Matani A 《IEEE transactions on bio-medical engineering》2005,52(2):201-210
A compartment model has been used for kinetic analysis of dynamic positron emission tomography (PET) data [e.g., 2-deoxy-2-18F-fluoro-D-glucose (FDG)]. The input function of the model [the plasma time-activity curve (pTAC)] was obtained by serial arterial blood sampling. It is of clinical interest to develop a method for PET studies that estimates the pTAC without needing serial arterial blood sampling. For this purpose, we propose a new method to extract the pTAC from the dynamic brain PET images using a modified independent component analysis [extraction of the pTAC using independent component analysis (EPICA). Source codes of EPICA are freely available at http://www5f.biglobe.ne.jp/?kimura/Software/top.html]. EPICA performs the appropriate preprocessing and independent component analysis (ICA) using an objective function that takes the various properties of the pTAC into account. After validation of EPICA by computer simulation, EPICA was applied to human brain FDG-PET studies. The results imply that the EPICA-estimated pTAC was similar to the actual measured pTAC, and that the estimated blood volume image was highly correlated with the blood volume image measured using 15O-CO inhalation. These results demonstrated that EPICA is useful for extracting the pTAC from dynamic PET images without the necessity of serial arterial blood sampling. 相似文献