全文获取类型
收费全文 | 212463篇 |
免费 | 2795篇 |
国内免费 | 582篇 |
专业分类
电工技术 | 3636篇 |
综合类 | 150篇 |
化学工业 | 33274篇 |
金属工艺 | 10501篇 |
机械仪表 | 7418篇 |
建筑科学 | 4117篇 |
矿业工程 | 2163篇 |
能源动力 | 4861篇 |
轻工业 | 13487篇 |
水利工程 | 2942篇 |
石油天然气 | 7731篇 |
武器工业 | 22篇 |
无线电 | 22617篇 |
一般工业技术 | 46539篇 |
冶金工业 | 34774篇 |
原子能技术 | 6690篇 |
自动化技术 | 14918篇 |
出版年
2021年 | 2263篇 |
2019年 | 2173篇 |
2018年 | 3896篇 |
2017年 | 3933篇 |
2016年 | 4239篇 |
2015年 | 2453篇 |
2014年 | 4099篇 |
2013年 | 9166篇 |
2012年 | 6120篇 |
2011年 | 7736篇 |
2010年 | 6198篇 |
2009年 | 6875篇 |
2008年 | 6952篇 |
2007年 | 6744篇 |
2006年 | 5843篇 |
2005年 | 5334篇 |
2004年 | 4833篇 |
2003年 | 4733篇 |
2002年 | 4540篇 |
2001年 | 4614篇 |
2000年 | 4307篇 |
1999年 | 4321篇 |
1998年 | 10375篇 |
1997年 | 7316篇 |
1996年 | 5575篇 |
1995年 | 4210篇 |
1994年 | 3662篇 |
1993年 | 3895篇 |
1992年 | 3024篇 |
1991年 | 3032篇 |
1990年 | 2920篇 |
1989年 | 2874篇 |
1988年 | 2875篇 |
1987年 | 2524篇 |
1986年 | 2582篇 |
1985年 | 2865篇 |
1984年 | 2702篇 |
1983年 | 2564篇 |
1982年 | 2303篇 |
1981年 | 2272篇 |
1980年 | 2350篇 |
1979年 | 2366篇 |
1978年 | 2385篇 |
1977年 | 2491篇 |
1976年 | 2884篇 |
1975年 | 2191篇 |
1974年 | 2069篇 |
1973年 | 2167篇 |
1972年 | 1941篇 |
1971年 | 1755篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
In the present paper a new method is presented for the evaluation of torsional stressing of diesel-generator sets consisting of components with uncertain torsional characteristics. A frequency scanning technique is implemented for eigenvalue analysis of the elastic system. Due to the uncertainty of the values of stiffness and damping coefficients, a sensitivity analysis method is also presented, suitable for the evaluation of the range of the mechanical stresses. Special consideration is given to the correct simulation of the coupling to the electric network, including the influence of generator regulators and possible network interactions. An exact formula is extracted for the synchronizing and damping torque coefficients. The method presented was checked in a diesel power station of the autonomous electric system of a Greek island 相似文献
972.
973.
N. Realdon M. Dal Zotto E. Ragazzi G. Dalla Fini 《Drug development and industrial pharmacy》1996,22(2):125-134
The release rate of a drug dissolved in the liquid phase of lipogels may be greatly affected by the type and concentration of gelling agent and by processing conditions and mechanical treatment of the ointment. These differences in release rate are reduced after application of mechanical stress comparable with the strain exerted on the ointment during application to the skin. Therefore, changes in the concentration of gelling agents used to achieve suitable consistency and manufacturing and packing processes that meet industrial and marketing requirements do not appear to exert a practical influence on drug availability after application to the skin. 相似文献
974.
N Fahl Júnior 《Canadian Metallurgical Quarterly》1996,8(7):627-38; quiz 640
Veneer restorations are well suited for conservative and aesthetic improvement of the anterior dentition. Laboratory fabricated porcelain and composite resin veneers present optimal aesthetics and durability. Although there are disadvantages associated with direct bonding, it provides control of color and contour for the operator, particularly in the case of a single anterior central incisor. Direct/indirect composite resin veneers utilize the advantages of both direct and indirect techniques in reconstruction of restorations with improved physical properties. The learning objective of this article is to review the available composite resins, opaquers, and tints, and present a step-by-step protocol for predictable restoration of discolored anterior dentition with direct/indirect heat-treated composite resin veneers in a single appointment. Patient evaluation, preoperative aesthetic considerations, selection of the restorative composite resins, and the clinical procedure are discussed. 相似文献
975.
976.
977.
Fukuda H. Ebara M. Kobayashi A. Sugiura N. Yoshikawa M. Saisho H. Kondo F. Yoshino S. Yahagi T. 《IEEE transactions on bio-medical engineering》1998,45(3):396-400
To objectively evaluate the parenchymal echo pattern of cirrhotic liver and chronic hepatitis, the authors applied an image analyzing system (IAS) using a neural network. Autopsy specimens in a water tank (n=13) were used to examine the relationship between the diameter of the regenerative nodule and the coarse score (CS) calculated by IAS. CS was significantly correlated with the diameter of the regenerative nodule (p<0.0001, r=0.966). CS is considered to be useful for evaluating the coarseness of the parenchymal echo pattern 相似文献
978.
Standard Gibbs free energy of formation (ΔGf0), an important property needed in design calculations has been estimated using molar refraction, RM. The linear relationships derived between ΔGf0 and RM tested with the data on 8 series of hydrocarbons at 228 compounds yielded average deviations comparable to the methods cited in recent literature. The method can be used as an alternative to the existing ones, because of its simplicity combined with reasonable accuracy. 相似文献
979.
A family of new 4-noded membrane elements with drilling degrees of freedom and unsymmetric assumed stresses is presented; it is derived from a mixed variational principle originally formulated for finite strain analysis and already used in the literature to develop a purely kinematic membrane model. The performance of these elements, investigated through some well established benchmark problems, is found to be fairly good and their accuracy is comparable with that given by models with a larger number of nodal parameters. 相似文献
980.
S Taba Shiwa N Garibay-Nieto P Angulo-Hernández F Vargas-Vorackova D Kershenobich 《Canadian Metallurgical Quarterly》1996,61(3):263-271
Surfactant abnormalities may contribute to the impairment of gas exchange observed in Pneumocystis carinii pneumonia. Analysis of rat bronchoalveolar lavage (BAL) lipid extracts from normal controls, steroid controls, trimethaprim-sulfamethoxazole (TMP-SMX) controls, TMP-SMX/P. carinii pneumonia controls, and P. carinii pneumonia animals reveal similar total phospholipid and total protein levels. However, there was a marked reduction in phosphatidylglycerol (PG) from the BAL of P. carinii pneumonia rats as compared with control animals, with a decrease from 4.91 +/- 1.29 nmol/mg protein to 0.46 +/- 0.57 nmol/mg protein (p<0.05) and a decrease, as a percent of total phospholipids, from 7.7% +/- 0.88% to 0.91% +/- 0.59% (p<0.001). Furthermore, in vitro surface activities of BAL lipid extracts from control and P. carinii pneumonia rats revealed minimum surface tension increases from 9.38 +/- 1.71 mN/m in controls to 16.36 +/- 0.83 mN/m in P. carinii pneumonia rats (p<0.05) and likewise maximum surface tension increases from 22.14 +/- 4.34 mN/m to 38.57 +/- 2.07 mN/m (p<0.01). Of interest, the surface activity of PG-deficient P. carinii pneumonia BAL lipid extracts is completely restored to that of normal controls by the addition of exogenous PG. These findings suggest that a functionally abnormal surfactant occurs in P. carinii pneumonia and that this may account, in part, for the impairment of gas exchange observed in this disorder. 相似文献