全文获取类型
收费全文 | 1257篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
综合类 | 5篇 |
化学工业 | 292篇 |
金属工艺 | 15篇 |
机械仪表 | 34篇 |
建筑科学 | 65篇 |
矿业工程 | 8篇 |
能源动力 | 21篇 |
轻工业 | 180篇 |
水利工程 | 16篇 |
石油天然气 | 2篇 |
无线电 | 112篇 |
一般工业技术 | 194篇 |
冶金工业 | 209篇 |
原子能技术 | 12篇 |
自动化技术 | 113篇 |
出版年
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 65篇 |
2012年 | 37篇 |
2011年 | 53篇 |
2010年 | 47篇 |
2009年 | 37篇 |
2008年 | 54篇 |
2007年 | 48篇 |
2006年 | 38篇 |
2005年 | 26篇 |
2004年 | 24篇 |
2003年 | 35篇 |
2002年 | 19篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 61篇 |
1997年 | 42篇 |
1996年 | 41篇 |
1995年 | 32篇 |
1994年 | 38篇 |
1993年 | 29篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 27篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1966年 | 9篇 |
排序方式: 共有1288条查询结果,搜索用时 1 毫秒
91.
M Dietrich K Kedzior T Zagrajek 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》1991,205(1):19-26
An experimental study of spinal biomechanics both in vivo and in vitro is difficult and often not reliable enough. The mathematical modelling and computer simulation approach is one that can be successfully applied. Modelling in this case is difficult due to the very complicated, heterogeneous nature of the object under investigation. The paper presents a biomechanical model of the spine system consisting of the spinal column (vertebrae, discs), ligaments, muscles directly and indirectly acting on the spinal column, as well as the rib-cage, abdomen and part of the pelvis. The finite element method combined with the optimization approach has been used for modelling. Typical results of these investigations are presented. 相似文献
92.
93.
94.
Jason P. Dietrich James N. Bowlby Bruce J. Morrison Nicholas E. Jones 《Journal of Great Lakes research》2008,34(3):495-505
We compared the impacts of stocking age-0 Atlantic salmon (Salmo salar) at high and low densities, and no stocking on abundance and growth of age-0 rainbow trout (Oncorhyncus mykiss) in Barnum House Creek, Ontario during 1993 to 2005. A similar stream, Shelter Valley Creek, was chosen as an appropriate reference stream where age-0 Atlantic salmon were not stocked. The catches of age-0 rainbow trout in Barnum House and the reference stream were highly correlated (r = 0.96) during years when no stocking occurred; however, this relationship did not persist in years when Atlantic salmon were stocked. The catch of age-0 rainbow trout in Barnum House Creek was significantly lower under both high (P = 0.00026) and low (P = 0.011) density Atlantic salmon stocking treatments compared with the no stocking treatment. The catches of age-0 rainbow trout and age-0 Atlantic salmon were negatively correlated in Barnum House Creek (r = −0.63). The length of age-0 rainbow trout in Barnum House Creek was depressed significantly (P = 0.004), under the high intensity Atlantic salmon stocking treatment, but not under the low intensity treatment (P = 0.20). In contrast, the length of age-0 rainbow trout in Shelter Valley Creek was unchanged over the same period. Restoration stocking of Atlantic salmon in Lake Ontario tributaries may impact rainbow trout abundance and growth. 相似文献
95.
B. Buschinger C. Geibel M. Weiden C. Dietrich G. Cordier G. Olesch J. K hler F. Steglich 《Journal of Alloys and Compounds》1997,260(1-2):44-49
Ternary compounds with the stoichiometry R2T3X9 (R=La, Ce, U, T=Rh, Ir, X=Al, Ga) were synthesized for the first time and were found to crystallize in the orthorhombic Y2Co3Ga9-type structure. Preliminary measurements of the resistivity, the susceptibility, the specific heat, and the Seebeck coefficient revealed a rather unconventional behavior for the Ce-compounds, which exhibit characteristics of both intermediate valent and of heavy fermion compounds. The U counterparts were found to order antiferromagnetically at temperatures below 40 K. 相似文献
96.
Calcium phosphates were electrocrystallized on titanium substrate by electrochemical deposition technique, in which the electrolyte was 0.167 M CaCl2 and 0.1 M NH4H2PO4. Different current densities (0.375, 1.5, 3, 6 mA/cm2) were applied. The pH of the solution after mixing of equal volumes was 4.6. The surface morphology, chemical composition and phase identification of the coatings were investigated by scanning electron microscopy associated with an energy dispersive spectrometer (SEM-EDXS) and X-ray diffractometry (XRD). Effects of the current density on the morphology and the structure of the coating were also discussed.The results showed that at all current densities tested, the coating is brushite (dicalcium phosphate dihydrate CaHPO4 · 2H2O). Furthermore, the results showed that coating thickness and weight gain are increased and the morphology changed with increasing deposition current density (from 0.375 to 6 mA/cm2). On contrary, thickness and weight gain are decreased with sodium hydroxide treatment. NaOH treatment converts brushite of Ca/P ratio 1:1 to hydroxyapatite of Ca/P ratio of 1.667. So, chemical analysis of the solution shows soluble P2O5 content. Coating thickness at 6 mA/cm2 was about 20 and 30 µm with and without treatment, respectively. It decreased to about 9.5 and 12 µm at 0.375 mA/cm2 current density, with and without treatment, respectively. However, the formed phase is not changed with increasing current density. In addition, it is found that, even at high current density (6 mA/cm2), no hydroxyapatite was directly electrocrystallized due to low corresponding potential (less than 5 V) and low corresponding voltage (468 mV). 相似文献
97.
Enning B. Vodhanel R.S. Dietrich E. Patzak E. Meissner P. Wenke G. 《Lightwave Technology, Journal of》1989,7(3):459-464
Polarization diversity is an alternative technique for coherent receivers to prevent loss to signal due to variations in the states of polarization (SOP) of the received signal field. It is shown experimentally and theoretically that there is no significant power penalty difference between a receiver with optimally adjusted gains and receivers with linear envelope detection and square-law detection. Experimentally, two amplitude-shift keying (ASK) heterodyne polarization diversity receivers with envelope detectors were demonstrated at 560 Mb/s, one using linear rectifiers, the other using square-law rectifiers. In both cases, the receiver sensitivity of -35 dBm at BER=10 -9 was degraded by less than 1 dB as the received signal SOP was varied, in agreement with theory 相似文献
98.
Dietrich E. Enning B. Grosskopf G. Kuller L. Ludwig R. Molt R. Patzak E. Weber H.G. 《Lightwave Technology, Journal of》1989,7(12):1941-1955
The application of semiconductor laser optical amplifiers in multichannel coherent optical transmission systems is investigated. The amplifiers considered (λ=1.3 μm) exhibit a gain of 24 dB at a grain ripple <2 dB and a 3-dB bandwidth of about 4000 GHz. The characteristics of these amplifiers and transmission experiments with these amplifiers are described. The investigations concern noise accumulation in an amplifier chain, generation of echoes due to backward gain in cascaded amplifiers, crosstalk in multichannel transmission, and the effect of gain saturation due to spontaneous emission. A good fit is shown between the advantages of multichannel coherent optical transmission systems and the properties of semiconductor laser optical amplifiers, which are very promising for future long-haul optical transmission systems 相似文献
99.
The bootstrap method is a computer intensive statistical method that is widely used in performing nonparametric inference. Categorical data analysis, in particular the analysis of contingency tables, is commonly used in applied field. This work considers nonparametric bootstrap tests for the analysis of contingency tables. There are only a few research papers which exploit this field. The p-values of tests in contingency tables are discrete and should be uniformly distributed under the null hypothesis. The results of this article show that corresponding bootstrap versions work better than the standard tests. Properties of the proposed tests are illustrated and discussed using Monte Carlo simulations. This article concludes with an analytical example that examines the performance of the proposed tests and the confidence interval of the association coefficient. 相似文献
100.
Otto T. Iancu Dietrich Munz Bernd Eigenmann Berthold Scholtes Eckard Macherauch 《Journal of the American Ceramic Society》1990,73(5):1144-1149
The residual stress state of brazed ceramic/metal compounds is described by means of X-ray residual stress determinations and analytical calculations using a model of three elastic infinite plates. It is shown that the residual stress state of the soldered compound depends on the materials combination and on the geometrical conditions. The combination of X-ray residual stress measurements and analytical calculations allows decisions on whether the assumption of a linear elastic model, based on elementary bending theory, is valid for the particular compounds. 相似文献