全文获取类型
收费全文 | 391013篇 |
免费 | 5636篇 |
国内免费 | 2204篇 |
专业分类
电工技术 | 7466篇 |
技术理论 | 5篇 |
综合类 | 3448篇 |
化学工业 | 58183篇 |
金属工艺 | 20369篇 |
机械仪表 | 15580篇 |
建筑科学 | 9457篇 |
矿业工程 | 2813篇 |
能源动力 | 7192篇 |
轻工业 | 29398篇 |
水利工程 | 4736篇 |
石油天然气 | 7479篇 |
武器工业 | 243篇 |
无线电 | 41343篇 |
一般工业技术 | 78531篇 |
冶金工业 | 53935篇 |
原子能技术 | 6784篇 |
自动化技术 | 51891篇 |
出版年
2021年 | 2483篇 |
2019年 | 2107篇 |
2018年 | 22714篇 |
2017年 | 22240篇 |
2016年 | 15980篇 |
2015年 | 3767篇 |
2014年 | 4843篇 |
2013年 | 11588篇 |
2012年 | 12394篇 |
2011年 | 24844篇 |
2010年 | 21506篇 |
2009年 | 19043篇 |
2008年 | 20432篇 |
2007年 | 22996篇 |
2006年 | 8611篇 |
2005年 | 11533篇 |
2004年 | 9235篇 |
2003年 | 8582篇 |
2002年 | 7217篇 |
2001年 | 6472篇 |
2000年 | 6166篇 |
1999年 | 5948篇 |
1998年 | 12917篇 |
1997年 | 9567篇 |
1996年 | 7327篇 |
1995年 | 5552篇 |
1994年 | 5119篇 |
1993年 | 4984篇 |
1992年 | 3970篇 |
1991年 | 3803篇 |
1990年 | 3823篇 |
1989年 | 3770篇 |
1988年 | 3537篇 |
1987年 | 3019篇 |
1986年 | 3050篇 |
1985年 | 3408篇 |
1984年 | 3321篇 |
1983年 | 3074篇 |
1982年 | 2703篇 |
1981年 | 2905篇 |
1980年 | 2642篇 |
1979年 | 2839篇 |
1978年 | 2736篇 |
1977年 | 2843篇 |
1976年 | 3696篇 |
1975年 | 2457篇 |
1974年 | 2291篇 |
1973年 | 2321篇 |
1972年 | 1981篇 |
1971年 | 1787篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Local Strain Measurement within Tendon 总被引:2,自引:0,他引:2
Abstract: Tendon is a dense connective tissue, responsible for transmitting the forces generated by muscles to the skeleton. It is composed of a hierarchical arrangement of crimped collagen fibres, interspersed with proteoglycan matrix and cells, known as tenocytes. During physiological loading, tendons are subjected to strains in the region of 5–6%, which result in the straightening and realignment of the collagen fibres, generating variable local strain fields within the tendon. This study demonstrates a technique for analysing local strains within viable tendon explants, during both loading and unloading of the tissue. Samples were strained in a custom-designed rig, allowing real-time visualisation of cell nuclei, used as local discrete markers, on a confocal microscope. Results indicated that local strains within the fascicle are smaller than the applied strains, never exceeding 1.2%, even at 8% gross applied strain. By contrast, the sliding of adjacent collagen units was recorded at each strain increment in this study, reaching a mean maximum of 3.9% of the applied displacement. Loading–unloading studies indicated that sliding behaviour is reversible up to strains of 5%, and provides the major extension mechanism within the rat-tail tendon. This technique can be extended to further analyse shearing behaviour within the matrix. 相似文献
942.
The theoretical-and-experimental investigation has been performed on the stability of smooth cylindrical shells of steel with a single local dent. All the shells manufactured using the same process were tested with the fulfillment of identical conditions for observations and measurements. Theoretical calculations were carried out by the mesh method with the use of the nonlinear theory of shells. A comparison of the experimental and theoretical values of the critical loads has been made. The theoretical-and-experimental approach proposed enables one to evaluate the quality of shells by studying local dents and other specific imperfections. 相似文献
943.
We study the stressed state of an inhomogeneous welded joint containing an interlayer of a more high-strength material under the action of tensile loads. It is assumed that the contact boundary has a cracklike defect. We deduce analytic dependences of the fracture load on the mechanical inhomogeneity of the joint, thickness of the interlayer, and depth of the defect. The maximum depth of the defect to which the joint is insensitive is established. The proposed theoretical results are innovative and agree with the experimental data obtained for specimens cut out from a pipe of 14KhGS steel. 相似文献
944.
Auto-correlation function analysis of phase formation in iron ion-implanted amorphous silicon layers
High-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis have been applied to investigate the evolution of structural order in iron ion-implanted amorphous silicon layers. β-FeSi2 nanocrystallites as small as 5 nm in size were detected in 600 °C annealed for 60 min a-Si layers. The embedded nanocrystalline β-FeSi2 was found to grow in the interlayer with annealing temperature. 相似文献
945.
In this paper we show that by the analysis of 2D images collected with a laboratory X-ray microdiffractometer it is possible to non-destructively evaluate the structure, the microstructure, and the preferred orientation of films. In particular, the structural analysis of Co/Au multilayers on Si(1 0 0) deposited at different Ar pressures are reported and discussed. 相似文献
946.
L. N. Dmitruk S. Kh. Batygov L. V. Moiseeva O. B. Petrova M. N. Brekhovskikh V. A. Fedorov 《Inorganic Materials》2007,43(7):793-796
We have studied the effect of In3+, Pb2+, Gd3+, and Cl (heavier ions) substitutions for Al3+, Ba2+, La3+, and F? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF4-BaF2-LaF3-AlF3-NaF system). We obtained stable glasses containing InF3 and BaCl2 instead of AlF3 and BaF2, respectively, and offering increased IR transmission. The presence of CCl4 in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs. 相似文献
947.
Sorin Manolache Petru Eles Zebo Peng 《International journal of parallel programming》2007,35(2):125-156
As feature sizes shrink, transient failures of on-chip network links become a critical problem. At the same time, many applications
require guarantees on both message arrival probability and response time. We address the problem of transient link failures
by means of temporally and spatially redundant transmission of messages, such that designer-imposed message arrival probabilities
are guaranteed. Response time minimisation is achieved by a heuristic that statically assigns multiple copies of each message
to network links, intelligently combining temporal and spatial redundancy. Concerns regarding energy consumption are addressed
in two ways. First, we reduce the total amount of transmitted messages, and, second, we minimise the application response
time such that the resulted time slack can be exploited for energy savings through voltage reduction. The advantages of the
proposed approach are guaranteed message arrival probability and guaranteed worst case application response time. 相似文献
948.
Formaldehyde is used in ruminant feeding for different purposes including the protection of dietary proteins from ruminal degradation. The formaldehyde content of milk of goats fed various levels of formaldehyde-treated soybean oil-meal has been determined by using a sensitive HPLC method. Results showed a significant linear correlation between ingested formaldehyde and formaldehyde concentration in milk. About 0.02% of ingested formaldehyde was excreted in milk, as free formaldehyde. 相似文献
949.
E. L. Zil'berbrand A. A. Kozhushko V. I. Polozenko G. S. Pugachev A. B. Sinani 《Strength of Materials》1991,23(9):1007-1010
The process of interaction of a ductile projectile with a many times harder brittle target is analyzed in the 500–1000 m/sec range of velocities. The effect of hardness of the target and its fragmentation on the penetration depth is shown.Translated from Problemy Prochnosti, No. 9, pp. 60–62, September, 1991. 相似文献
950.