全文获取类型
收费全文 | 193427篇 |
免费 | 14514篇 |
国内免费 | 7441篇 |
专业分类
电工技术 | 10345篇 |
技术理论 | 10篇 |
综合类 | 10899篇 |
化学工业 | 31779篇 |
金属工艺 | 11634篇 |
机械仪表 | 11796篇 |
建筑科学 | 12013篇 |
矿业工程 | 4696篇 |
能源动力 | 4387篇 |
轻工业 | 11167篇 |
水利工程 | 3699篇 |
石油天然气 | 10859篇 |
武器工业 | 1317篇 |
无线电 | 20463篇 |
一般工业技术 | 29785篇 |
冶金工业 | 12289篇 |
原子能技术 | 5063篇 |
自动化技术 | 23181篇 |
出版年
2024年 | 821篇 |
2023年 | 2677篇 |
2022年 | 5182篇 |
2021年 | 7113篇 |
2020年 | 5339篇 |
2019年 | 4633篇 |
2018年 | 5788篇 |
2017年 | 6284篇 |
2016年 | 5766篇 |
2015年 | 6615篇 |
2014年 | 8470篇 |
2013年 | 10270篇 |
2012年 | 11120篇 |
2011年 | 11962篇 |
2010年 | 10283篇 |
2009年 | 10180篇 |
2008年 | 9979篇 |
2007年 | 9440篇 |
2006年 | 9013篇 |
2005年 | 7627篇 |
2004年 | 5851篇 |
2003年 | 5840篇 |
2002年 | 6108篇 |
2001年 | 5491篇 |
2000年 | 4505篇 |
1999年 | 4087篇 |
1998年 | 3175篇 |
1997年 | 2651篇 |
1996年 | 2414篇 |
1995年 | 2110篇 |
1994年 | 1735篇 |
1993年 | 1478篇 |
1992年 | 1388篇 |
1991年 | 1185篇 |
1990年 | 1178篇 |
1989年 | 1084篇 |
1988年 | 957篇 |
1987年 | 878篇 |
1986年 | 777篇 |
1985年 | 735篇 |
1984年 | 715篇 |
1982年 | 676篇 |
1979年 | 739篇 |
1978年 | 778篇 |
1977年 | 739篇 |
1976年 | 755篇 |
1975年 | 713篇 |
1974年 | 719篇 |
1973年 | 723篇 |
1972年 | 705篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
992.
993.
A.L. Yarin A.Yu. GelfgatP.Z. Bar-Yoseph 《International Journal of Heat and Mass Transfer》2002,45(3):555-570
The effect of axial flow on the mass transfer through a liquid-liquid interface in a two-layer Taylor-Couette system is studied. The mass transfer of a passive scalar is driven by the diffusion through the boundary, enhanced by the convective mass transport due to the Taylor-Couette vortical flow, which is in turn affected by the axial pressure gradient. Numerical modeling shows that the axial flow obviates the symmetry of the distribution of the local Sherwood number, Sh, in a vortical cell and leads to decrease of its average counterpart. For better physical insight into this effect, simplified kinematic models of the phenomenon were considered. The numerical model shows at Sc=1 to 10 (Sc being the Schmidt number) that the mass transfer is enhanced by vortical flow in the regions where the motion is directed towards the interface. The axial throughflow makes for elongation of the Taylor vortices in the axial direction and reduces the area of the above regions, thereby increasing the local concentration gradient and reducing the mass transfer rate. Simplified analytical results for Sc?1 indicate redistribution of the mass flux over the interface compared with the case of Sc=1 to 10. The origin of this phenomenon is explained. It is also demonstrated that Sh scales as Pe1/2 for the whole range of Sc, Pe being the Peclet number of the vortical motion. 相似文献
994.
I. G. Dovgyallo F. F. Tsaruk N. A. Dolbin Yu. N. Kondeev G. G. Zavirukho 《Strength of Materials》1989,21(10):1316-1319
Results are presented in a statistical arrangement for studying the effect of loading frequency on the fatigue life in bending of plates with a stress concentrator. The nature of change in microhardness, electrical conductivity, dislocation density, and block dimensions during fatigue at frequencies of 2.8, 8.8, and 18 kHz has been demonstrated. It has been established that in spite of some qualitative difference the main indicators of fatigue at these frequencies are retained.S. M. Kirov Belorussian Technology Institute, Minsk. Translated from Problemy Prochnosti, No. 10, pp. 31–34, October, 1989. 相似文献
995.
996.
新岭大桥转体施工技术 总被引:1,自引:0,他引:1
新岭大桥采用有平衡重的平面转体法施工 ,这在我省尚属首例。施工中因地制宜采用拉链葫芦滑轮组进行牵引 ,仅用 3小时就使拱肋平稳、安全地转体就位 ,牵引施工获得成功 ,为我省的桥梁施工积累了经验 ,具有推广价值 相似文献
997.
JN Yu FH Fahey HD Gage CG Eades BA Harkness CA Pelizzari JW Keyes 《Canadian Metallurgical Quarterly》1995,36(12):2333-2338
The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action. 相似文献
998.
Zheng Qi; Yang Wan-Ming; Yu Wen-Hao; Cai Bin; Teng Xin-Chen; Xie Yi; Sun Hong-Zhe; Zhang Ming-Jie; Huang Zhong-Xian 《Protein engineering, design & selection : PEDS》2003,16(12):865-870
MT3 shows apparently different properties and function fromMT1 even though they have 70% sequence homology. Possibly thetwo inserts, Thr5 and a negatively charged hexapeptide at position-55in MT3, play important roles. A series of MT3 variants aroundthe EAAEAE hexapeptide have been prepared by site-directed mutagenesisand their properties and reactivity towards pH, EDTA and DTNBhave been studied. Our detailed studies revealed that the EAAEAEinsert is essential to the property of MT3. It is the hexapeptideinsert, to some extent, making the MT3 相似文献
999.
1000.
I. M. Kosareva M. K. Savushkina Yu. M. Volin S. A. Kabakchi O. M. Kovalevich V. D. Akhunov A. I. Borzunov S. V. D'yakov V. M. Korotkevich E. G. Kudryavtsev V. A. Lebedev 《Atomic Energy》2003,94(5):325-332
The qualitative and quantitative radiochemical composition of liquid wastes is substantiated. This makes possible further safe operation of deep waste disposal sites at the Mining-Chemical Plant and the Siberian Chemical Plant. The toxicity and temperature in a formation with the wastes removed are used as the assessment criteria, satisfaction of which guarantees that the wastes will remain localized within the assigned boundaries of the waste-disposal formation site. It is concluded that the standard limit should be imposed on the specific activity of the long-lived group of radionuclides – 90Sr and 137Cs – rather than on the total specific activity of the wastes placed in deep disposal sites. For maximum specific activity of 90Sr and 137Cs of 37 GBq/dm3 and total specific activity not exceeding 185 GBq/dm3 for buried wastes with radionuclide composition characteristic of modern radiochemical production operations, it is impossible for potentially dangerous radiation and thermochemical processes to occur in the waste-disposal formation site. The recommended limit permits reducing substantially the volume of buried wastes and therefore the region over which the wastes propagate in the deep disposal site. 相似文献