全文获取类型
收费全文 | 3902篇 |
免费 | 11篇 |
专业分类
电工技术 | 19篇 |
综合类 | 16篇 |
化学工业 | 149篇 |
金属工艺 | 38篇 |
机械仪表 | 34篇 |
建筑科学 | 36篇 |
矿业工程 | 18篇 |
能源动力 | 21篇 |
轻工业 | 54篇 |
水利工程 | 17篇 |
石油天然气 | 5篇 |
武器工业 | 2篇 |
无线电 | 79篇 |
一般工业技术 | 150篇 |
冶金工业 | 3164篇 |
原子能技术 | 19篇 |
自动化技术 | 92篇 |
出版年
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2016年 | 8篇 |
2014年 | 14篇 |
2013年 | 34篇 |
2012年 | 26篇 |
2011年 | 43篇 |
2010年 | 31篇 |
2009年 | 33篇 |
2008年 | 45篇 |
2007年 | 74篇 |
2006年 | 29篇 |
2005年 | 42篇 |
2004年 | 19篇 |
2003年 | 22篇 |
2002年 | 31篇 |
2001年 | 22篇 |
2000年 | 19篇 |
1999年 | 94篇 |
1998年 | 871篇 |
1997年 | 515篇 |
1996年 | 300篇 |
1995年 | 203篇 |
1994年 | 181篇 |
1993年 | 201篇 |
1992年 | 36篇 |
1991年 | 57篇 |
1990年 | 66篇 |
1989年 | 61篇 |
1988年 | 53篇 |
1987年 | 51篇 |
1986年 | 58篇 |
1985年 | 47篇 |
1984年 | 15篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 41篇 |
1980年 | 37篇 |
1979年 | 11篇 |
1978年 | 23篇 |
1977年 | 112篇 |
1976年 | 208篇 |
1975年 | 17篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 11篇 |
1971年 | 5篇 |
1970年 | 5篇 |
排序方式: 共有3913条查询结果,搜索用时 15 毫秒
61.
In this paper,we address the need for better hands-on learning materials in computing education and the need for integrating mobile computing education into computing curricular.We propose an innovative learning approach that uses state-of-the-art mobile computing technologies and devices to design a highly accessible and real-world relevant hands-on labware for computing education.The labware employs a modular design such that the learning materials can both be combined together into a single course of mobile program development and be integrated into the related computing courses as building blocks.The labware will help students understand the concepts,improve their problem solving skills,and prepare them for the mobile computing industrial workforce.The pilot modules of the labware have been presented to undergraduate students and have received positive feedbacks. 相似文献
62.
In this paper, we present lower and upper bounds on the size of limited width, bounded and unbounded fan-out parallel prefix circuits. The lower bounds on the sizes of such circuits are a function of the depth, width, and number of inputs. The size requirement of an N input bounded fan-out parallel prefix circuit having limited width W and extra depth k (the difference between allowed and minimum possible depth) is shown to be (N log2
W/2
k
+ N) for k log2
W. This implies that insisting on minimum depth causes the circuit size to be nonlinear, while as little as log2log2
W of extra depth can possibly reduce the size to linear. Also, we show that there is a clear difference between the two cases of bounded and unbounded fan-out by proving the size of a limited width, unbounded fan-out parallel prefix circuit lies between a lower bound of ((2 + 21–k
/3)N) and an upper bound of O((2 + 21–k
)N).Uniform, systolic constructions of limited width parallel prefix circuits are provided here and shown to be asymptotically optimal. By associating the width of the circuit with the number of processors and the fan-out capabilities of the circuit with the interconnection structure of a multiprocessor, time- and processor-efficient algorithms may be developed. 相似文献
63.
SR DeMeester GA Patterson RS Sundaresan JD Cooper 《Canadian Metallurgical Quarterly》1998,115(3):681-688
Methanol-induced conformational transitions of hen egg white lysozyme were investigated with a combined use of far- and near-UV CD and NMR spectroscopies, ANS binding and small-angle X-ray scattering. Addition of methanol induced no global change in the native conformation itself, but induced a transition from the native state to the denatured state which was highly cooperative, as shown by the coincidence of transition curves monitored by the far- and near-UV CD spectroscopy, by isodichroic points in the far- and near-UV CD spectra and by the concomitant disappearance of individual 1H NMR signals of the native state. The ANS binding experiments could detect no intermediate conformer similar to the molten globule state in the process of the methanol denaturation. However, at high concentration of methanol, e.g., 60% (v/v) methanol/water, a highly helical state (H) was realized. The H state had a helical content much higher than the native state, monitored by far-UV CD spectroscopy, and had no specific tertiary structure, monitored both by near-UV CD and NMR spectroscopy. The radius of gyration in the H state, 24.9 angstroms, was significantly larger than that in the native state (15.7 angstroms). The Kratky plot for the H state did not show a clear peak and was quite similar to that for the urea-denatured state, indicating a complete lack of globularity. Thus we conclude that the H state has a considerably expanded, flexible broken rod-like conformation which is clearly distinguishable from the "molten globule" state. The stability of both N and H states depends on pH and methanol concentration. Thus a phase diagram involving N and H was constructed. 相似文献
64.
Previously, we identified PG-1000 as part of a disulfide-linked complex of two large proteoglycans (PG-1000 and the beta component) and three smaller proteins purified from the extracellular matrix of elasmobranch electric organ (Iwata and Carlson, 1991, J. Biol. Chem. 266: 323-333). PG-1000 is a chondroitin sulfate/keratan sulfate proteoglycan with a molecular mass of about 1.2 x 16(6) daltons. When visualized in the electron microscope, PG-1000 has the typical "bottle-brush" appearance expected for a proteoglycan with an average total length of about 345 nm and about 20 chains of approximately 110 nm (Carlson and Wight, 1987, J. Cell Biol. 105: 3075-3086). Using immunocytochemical methods, we now demonstrate that PG-1000 is a component of the interstitial extracellular matrix of the electric organ. PG-1000 immunoreactivity is found throughout the interstitial matrix, but it is highly concentrated in that region of the matrix immediately adjacent to the basal lamina, the reticular lamina. The reticular and basal laminae together form the basement membrane. PG-1000 immunoreactivity is especially apparent on basal laminae that surround nerve fibers and nerve terminals. When the disulfide-linked PG-1000 complexes are purified and examined in the electron microscope following rotary shadowing, they appear as bottle-brush structures which are often attached at a central region and radiate like spokes of a wheel. These aggregates contain two to six proteoglycan monomers. We hypothesize that the PG-1000 complexes are disulfide-stabilized parts of an extended network of linked proteoglycans in the reticular lamina. 相似文献
65.
A new method of autoallodermoplasty is proposed which is as follows: a patient's skin band is cut out 40 times less than the total area of the wound surface. The wound in the donor area is sutured tightly. The skin flap is dissected to thin transverse rectangular pieces with a special microdermatome or with a razor and then they are laid with their lateral side onto the wound and covered with the allo-skin. Experimental and clinical observations have shown that at remote terms both the anatomical and functional restitution of the integument occurred. The method is indicated for huge dermal defects of the "functionally passive" areas in patients with restricted, not big resources of the donor sites, especially in patients with high operative risk. 相似文献
66.
R Wrigglesworth CS Walpole S Bevan EA Campbell A Dray GA Hughes I James KJ Masdin J Winter 《Canadian Metallurgical Quarterly》1996,39(25):4942-4951
Structural features of three regions of the capsaicin molecule necessary for agonist properties were delineated by a previously reported modular approach. These in vitro agonist effects were shown to correlate with analgesic potency in rodent models. Combination of optimal structural features from each of these regions of the capsaicin molecule have led to highly potent agonists (eg., 1b). Evaluation in vivo established that 1b had analgesic properties but poor oral activity, short duration of action, and excitatory side effects which precluded further development of this compound. Preliminary metabolism studies had shown that the phenol moiety of 1b was rapidly glucuronidated in vivo, providing a possible explanation for the poor pharmacokinetic profile. Subsequent specific modification of the phenol group led to compounds 2a-j, which retained in vitro potency. The in vivo profiles of two representatives of this series, 2a,h, were much improved over the "parent" phenol series, and they are candidates for development as analgesic agents. 相似文献
67.
JW Lynch GA Kaplan RD Cohen J Tuomilehto JT Salonen 《Canadian Metallurgical Quarterly》1996,144(10):934-942
Much remains to be understood about how low socioeconomic status (SES) increases cardiovascular disease and mortality risk. Data from the Kuopio Ischemic Heart Disease Risk Factor Study (1984-1993) were used to estimate the associations between acute myocardial infarction and income, all-cause mortality, and cardiovascular mortality in a population-based sample of 2,272 Finnish men, with adjustment for 23 biologic, behavioral, psychologic, and social risk factors. Compared with the highest income quintile, those in the bottom quintile had age-adjusted relative hazards of 3.14 (95% confidence interval (CI) 1.77-5.56), 2.66 (95% CI 1.25-5.66), and 4.34 (95% CI 1.95-9.66) for all-cause mortality, cardiovascular mortality, and AMI, respectively. After adjustment for risk factors, the relative hazards for the same comparisons were 1.32 (95% CI 0.70-2.49), 0.70 (95% CI 0.29-1.69), and 2.83 (95% CI 1.14-7.00). In the lowest income quintile, adjustment for risk factors reduced the excess relative risk of all-cause mortality by 85%, that of cardiovascular mortality by 118%, and that of acute myocardial infarction by 45%. These data show how the association between SES and cardiovascular mortality and all-cause mortality is mediated by known risk factor pathways, but full "explanations" for these associations will need to encompass why these biologic, behavioral, psychologic, and social risk factors are differentially distributed by SES. 相似文献
68.
Bender H Carlson C Frayer D Johnson D Jones K Meidinger A Ekdahl C 《The Review of scientific instruments》2007,78(1):013301
We have developed a quasianamorphic optical tomography system coupled to a streak camera to provide continuous recording of the electron beam profile of an intense, long-pulse induction accelerator. A tomographic reconstruction method based on a maximum-entropy algorithm is used to reconstruct the images. The system has simplified the calculation of beam moments, eliminated ambiguity due to beam motion, and contributed to accelerator tuning. 相似文献
69.
This paper presents two examples of how impedance cardiography may be used to interpret the hemodynamic influences on blood pressures measured during behavioral stress. In Study 1, blood pressure changes which were similar during two tasks were shown to have important differences in their cardiac output and vascular resistance components. During work on a reaction time task having aversive incentives compared with a neutral task, the blood pressure changes were seen to be associated with lowered vascular resistance and raised cardiac activity, a "fight-flight" pattern. In Study 2, blood pressure response differences between two subject groups working on an identical task were found to have blood pressure changes differing in their underlying cardiac and vascular components as measured by impedance. Such uses impedance cardiography have widespread potential application in psychophysiological research with humans. 相似文献
70.
Content analyses of research published in the 1982 volumes of the Journal of Personality and Social Psychology indicate that social psychologists have largely failed to study subjects drawn from meaningfully defined social groups, to consider social structural variables, to study genuine social interaction, to observe social influences on psychological functioning, or to ask Ss about social issues. It is maintained that with few exceptions, personality researchers have failed to study groups other than college students, to use biographical materials or personal documents, to devise appropriate experimental treatments, to study persons over time, or even to retain the individual as a unit of analysis. Currently, the 2 fields of social and personality psychological research appear to be linked mainly by their deficiencies and appear to have little content worth sharing. Reexamination of each field's traditions and priorities is urgently needed. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献