全文获取类型
收费全文 | 2633篇 |
免费 | 11篇 |
专业分类
电工技术 | 20篇 |
综合类 | 1篇 |
化学工业 | 129篇 |
金属工艺 | 27篇 |
机械仪表 | 15篇 |
建筑科学 | 36篇 |
矿业工程 | 1篇 |
能源动力 | 15篇 |
轻工业 | 99篇 |
水利工程 | 14篇 |
无线电 | 75篇 |
一般工业技术 | 169篇 |
冶金工业 | 1911篇 |
原子能技术 | 8篇 |
自动化技术 | 124篇 |
出版年
2021年 | 5篇 |
2019年 | 7篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 108篇 |
2012年 | 19篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 29篇 |
2008年 | 25篇 |
2007年 | 37篇 |
2006年 | 25篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 21篇 |
1999年 | 57篇 |
1998年 | 566篇 |
1997年 | 323篇 |
1996年 | 234篇 |
1995年 | 126篇 |
1994年 | 112篇 |
1993年 | 124篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 36篇 |
1988年 | 40篇 |
1987年 | 27篇 |
1986年 | 43篇 |
1985年 | 40篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 25篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 52篇 |
1976年 | 111篇 |
1975年 | 9篇 |
1973年 | 5篇 |
1971年 | 6篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有2644条查询结果,搜索用时 0 毫秒
981.
982.
983.
JD Churchill SE Voss DP Miller JE Steinmetz PE Garraghty 《Canadian Metallurgical Quarterly》1998,39(6):584-589
The aim of the present study was to assess the role of vascular alpha 1D-adrenoceptors in the sympathetic vasopressor response in vivo. Specifically, we evaluated the effect of a selective alpha 1D-adrenoceptor antagonist, BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4,5)dec ane-7,9- dione 2HCl), on the vasopressor response induced by preganglionic (T7-T9) sympathetic stimulation in the pithed rat. The vasopressor response was dose-dependently sensitive to inhibition by intravenous BMY 7378 (0.1, 0.31, 1 and 3.1 mg/kg), doses of 1 and 3.1 mg/kg being equally effective. Like BMY 7378, 5-methylurapidil (0.1, 0.31, 1 and 3.1 mg/kg) antagonized the vasopressor response to spinal stimulation; doses of 1 and 3.1 mg/kg were also equally effective. In combination experiments, BMY 7378 (1 mg/kg, i.v.) and the alpha 1A-adrenoceptor antagonist, 5-methylurapidil (1 mg/kg, i.v.), showed an additive effect. The present results demonstrate that the alpha 1D-adrenoceptor subtype plays an important role in the pressor response to sympathetic nerve stimulation in the pithed rat, and confirm the participation of the alpha 1A-adrenoceptor subtype in the same response. 相似文献
984.
Studies of the cardiac myosin fragment 1 concentration dependence of the rate constants for adenosine 5'-triphosphate (ATP) binding and steady-state hydrolysis reveal that the observed rate constants are remarkably dependent on the protein concentration. The kinetics for ATP binding are biphasic, and both the fast- and slow-phase rate constants and the respective fractions of fast and slow material vary as a function of protein concentration. Two different types of kinetic experiments were conducted, one in which the ATP concentration was fixed but the subfragment 1 concentration was varied and another for which the ATP/subfragment 1 ratio was fixed but both concentrations were varied. The results of these two experiments on cardiac subfragment 1 are consistent with an ATP-dependent reversible aggregation. Light-scattering experiments confirm the presence of this aggregation and the ATP dependence. Similar studies on rabbit skeletal subfragment 1 give monophasic, protein-independent kinetics consistent with a monomeric species in solution. a simple monomer--dimer mechanism can account for the cardiac subfragment 1 kinetic results when changes in tryptophan fluorescence are used. However, the light-scattering results show that cardiac myosin subfragment 1 undergoes multiple reversible molecular weight changes in solution and may be tetrameric at high concentrations. 相似文献
985.
M.G. Knight L.C. Wrobel J.L. Henshall L.A. De Lacerda 《International Journal of Fracture》2002,114(1):47-61
The purpose of the present work is a parametrical study of the interaction between a propagating edge-crack and an embedded elastic fibre using the Boundary Element (BE) technique. Uniaxial fibre reinforced composites generally have very good properties in the direction of the fibres, but in conventional multi-layer crossply laminates it is cracking in the transverse direction which effectively limits the strength of a stressed body. Therefore, in this study the propagation of a crack in the transverse direction is considered, i.e., in a plane containing the fibre axes, rather than perpendicular to the fibres. Crack deflection/attraction mechanisms and their associated energy release rate variations are investigated for a range of Young's moduli and Poisson's ratio mismatches, and crack offsets with respect to the inclusion centreline. Furthermore, the effects of a third-phase, i.e., coating, applied to the fibre's surface are analysed, and results have been obtained for different coating thicknesses and elastic moduli ratios. From this investigation it was found that the Poisson's ratio of the different phases could have a significant effect on the crack trajectory, and hence the energetics involved in the process of crack deflection are also dramatically altered. This opens up the possibility of enhancing the fracture toughness of fibre reinforced composite materials by considering the Poisson's ratio of the individual phases when selecting the particular material combination. 相似文献
986.
Ortiz R.R. Knight J.P. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2002,10(3):327-340
Dynamic logic is an alternative way of making logic circuit cells and numerous techniques have been developed to take advantage of its unique characteristics. Particularly, techniques such as the true-single-phase-clock (TSPC) have been used very successfully for fast and low-power applications. However one cannot synthesize dynamic logic gates with the same ease as static gates. One reason is there are no simple rules to connect the many circuit types of dynamic gates to static gates. This paper addresses the problem of finding connection rules for a given set of gate types. The fundamental cell circuit types for dynamic logic gates are analyzed first together with static logic gates. A common set of principles of operation and connections is then identified and later applied to discover which are the feasible connections between cell circuit types identified. 相似文献
987.
After years of systematic experimentation, we finally uncovered one thing the dorsal system contributes to hearing which the ventral system may not -- the mechanism for orienting to an elevated sound source [Sutherland, D.P., Masterton, R.B., Glendenning, K.K. (1998) Behav. Brain Res. in press]. This paper follows up this one positive result on a historical background of uniformly negative results. The focus of this report is on the fusiform cells of the dorsal cochlear nucleus whose axons course through the dorsal acoustic stria (DAS). Because electrophysiological studies have shown that the cues for sensing the elevation of a sound source would seem to be best analyzed by the dorsal cochlear nucleus, we tested, behaviorally, normal cats and cats deprived of their DAS or intermediate acoustic stria, bilaterally or ipsilaterally (with or without their contralateral ear deafened), for their ability to orient to elevated sources of broad-band noise. For behavioral testing, we made use of a conventional shock-avoidance procedure. The results lead to the conclusion that DCN and DAS may play no role in learned elevation discriminations. This result builds on that of another of our papers which suggests that a deficit in reflexive discrimination of elevation is strictly auditory in nature [Sutherland, D.P., Masterton, R.B., Glendenning, K.K. (1998) Behav. Brain Res. in press]. 相似文献
988.
The necessity for policy makers to follow the processes in relation to sustainability demands new tools for management, a major aspect of which is integrated attention to economic and sociocultural influences together with environmental issues. North and South have specific positions and responsibilities with regard to sustainable development, and management tools--such as indicators--should reflect them. Because the North-South dialogue is changing, different approaches to deal with the relationships are needed (e.g., introduction of reciprocity, equity, and participation), while at the same time doing justice to the individual social, economic, and cultural characteristics of a country. Ecosystem health can be defined by requirements such as resilience, vigor, organization, and relations, which may be used for totally different systems as well. Because integration is a crucial aspect of the new tools, it is argued that integrating conceptual tools such as the environment-economy-society triangle, the PSIR-causality chain, and the Daly triangle in addition to other described integration tools is fundamental for decision makers. Crucial issues when dealing with indicators for sustainable development are integration and balance, attention to users, use of system characteristics, and understanding southern perspectives in this context. 相似文献
989.
JJ Manly SW Miller RK Heaton D Byrd J Reilly RJ Velasquez DP Saccuzzo I Grant 《Canadian Metallurgical Quarterly》1998,4(3):291-302
The development of a novel class of nonsteroidal human progesterone receptor (hPR) agonists, 5-aryl-1,2-dihydro-5H-chromeno[3,4-f]quinolines 2, is described. The introduction of a 5-aryl group into the 1,2-dihydrocoumarino[3,4-f]quinoline core 1 is the key for progestational activities. The structure-activity relationship (SAR) studies of the 5-aryl substituents generated a series of potent hPR agonists, which exhibited similar biological activity (EC50 = 8-30 nM) to the natural hormone progesterone (EC50 = 2.9 nM) in cell-based assays with efficacies ranging from 28% to 96%. Most of the analogues displayed similar or greater binding affinity (Ki = 0.41-3.6 nM) than progesterone (Ki = 3.5 nM). Three representative analogues (13, 15, and 24) demonstrated in vivo activities in mammary gland morphology/uterine wet weight assay in ovariectomized rats. 相似文献
990.
JJ Seibert R Avva TN Hronas R Mocharla T Vanderzalm K Cox D Kinder B Lidzy KL Knight 《Canadian Metallurgical Quarterly》1998,18(4):879-890
In pediatric neurosonography, conventional color Doppler imaging has been the primary adjunct to routine gray-scale imaging. Power Doppler sonography is a relatively recent development that does not have the limitations of conventional color Doppler ultrasound. The power Doppler technique measures the energy of moving red blood cells instead of the velocity and direction of flow. Advantages of this technique include increased sensitivity for identifying flow in slow-flow states, more complete evaluation of a vessel, and more accurate evaluation of the course of the vessel. Power Doppler sonography is helpful in evaluation of the neonatal brain in a variety of clinical situations: identifying the exact locations of extraaxial fluid collections, differentiating intraventricular clot from normal choroid plexus, detecting intraventricular hemorrhage, and demonstrating asymmetries in cerebral perfusion. However, in certain difficult cases, use of both conventional color Doppler sonography and power Doppler sonography produces increased diagnostic accuracy because these techniques furnish complementary information. 相似文献