全文获取类型
收费全文 | 280084篇 |
免费 | 3076篇 |
国内免费 | 1308篇 |
专业分类
电工技术 | 4802篇 |
综合类 | 519篇 |
化学工业 | 40533篇 |
金属工艺 | 11132篇 |
机械仪表 | 8428篇 |
建筑科学 | 6470篇 |
矿业工程 | 1576篇 |
能源动力 | 6984篇 |
轻工业 | 22610篇 |
水利工程 | 3054篇 |
石油天然气 | 5783篇 |
武器工业 | 43篇 |
无线电 | 33567篇 |
一般工业技术 | 56625篇 |
冶金工业 | 51751篇 |
原子能技术 | 7489篇 |
自动化技术 | 23102篇 |
出版年
2021年 | 2180篇 |
2019年 | 2080篇 |
2018年 | 3599篇 |
2017年 | 3695篇 |
2016年 | 3919篇 |
2015年 | 2510篇 |
2014年 | 4384篇 |
2013年 | 12049篇 |
2012年 | 7139篇 |
2011年 | 9800篇 |
2010年 | 7601篇 |
2009年 | 8819篇 |
2008年 | 9180篇 |
2007年 | 9224篇 |
2006年 | 7863篇 |
2005年 | 7324篇 |
2004年 | 7257篇 |
2003年 | 7025篇 |
2002年 | 6769篇 |
2001年 | 6897篇 |
2000年 | 6524篇 |
1999年 | 6804篇 |
1998年 | 16317篇 |
1997年 | 11611篇 |
1996年 | 8948篇 |
1995年 | 6880篇 |
1994年 | 6049篇 |
1993年 | 6092篇 |
1992年 | 4438篇 |
1991年 | 4191篇 |
1990年 | 4113篇 |
1989年 | 4081篇 |
1988年 | 3787篇 |
1987年 | 3428篇 |
1986年 | 3418篇 |
1985年 | 3772篇 |
1984年 | 3477篇 |
1983年 | 3245篇 |
1982年 | 3057篇 |
1981年 | 3070篇 |
1980年 | 3052篇 |
1979年 | 2858篇 |
1978年 | 2885篇 |
1977年 | 3158篇 |
1976年 | 4107篇 |
1975年 | 2431篇 |
1974年 | 2394篇 |
1973年 | 2405篇 |
1972年 | 2021篇 |
1971年 | 1782篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A modification to the `shape-invariant' sinusoidal speech model is proposed, whereby the phases of the component sinewaves used for the excitation are made to add coherently at each glottal closure. Applied to pitch and time-scale modification, higher quality synthetic speech is produced when large changes are required 相似文献
42.
Based on a variational analysis, the authors demonstrate that the noise-induced Gordon-Haus timing jitter in a dispersion-managed soliton transmission system can be substantially reduced by appropriate placement of the amplifiers 相似文献
43.
Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal 相似文献
44.
45.
46.
PURPOSE: To assess the role postoperative mydriatics play after extracapsular cataract extraction (ECCE) and posterior chamber intraocular lens (IOL) implantation in causing iris modifications and in controlling inflammation. SETTING: Outpatients Department, Ninewells Hospital, Dundee, Scotland. METHODS: The prospective study comprised 136 patients who had standardized ECCE. Half the patients used a mydriatic for 2 weeks postoperatively. Anterior chamber activity, pain, and eye redness were evaluated at 2 weeks postoperatively; pupil shape, peripheral anterior synechias, IOL position, and iris adhesions, at 6 weeks. RESULTS: Iris-lens adhesions were significantly more common in the group using a mydriatic. There was no difference between the two groups in postoperative inflammation. CONCLUSION: Mydriatics should not be used routinely after ECCE with posterior chamber IOL implantation. 相似文献
47.
Storage performance-metrics and benchmarks 总被引:2,自引:0,他引:2
Chen P.M. Patterson D.A. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1993,81(8):1151-1165
The metrics and benchmarks used in storage performance evaluation are discussed. The technology trends taking place in storage systems, such as disk and tape evolution, disk arrays, and solid-state disks, are highlighted. The current popular I/O benchmarks are then described, reviewed, and run on three systems: a DECstation 5000/200 running the Sprite Operating System, a SPARCstation 1+ running SunOS, and an HP Series 700 (Model 730) running HP-UX. Two approaches to storage benchmarks-LADDIS and a self-scaling benchmark with predicted performance-are also described 相似文献
48.
The thermal expansion of tellurides of germanium, bismuth, and intermetallic compounds is investigated over the temperature range 293-973 K.Belarusian Agricultural Technical University, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 5, pp. 612–616, May 1994. 相似文献
49.
The kinetics of substrate removal by the liver and the resulting nonlinear changes in unbound fraction along the flow path at varying input drug concentrations were examined by a model simulation study. Specifically, we varied the binding association constant, KA, and the Michaelis-Menten constants (Km and Vmax) to examine the steady state drug removal (expressed as hepatic extraction ratio E) and changes in drug binding for (i) unienzyme systems and (ii) simple, parallel metabolic pathways; zonal metabolic heterogeneity was also added as a variable. At low KA, E declined with increasing input drug concentration, due primarily to saturation of enzymes; only small differences in binding were present across the liver. At high KA, a parabolic profile for E with concentration was observed; changes in unbound fraction between the inlet and the outlet of the liver followed in parallel fashion. Protein binding was the rate-determining step at low input drug concentrations, whereas enzyme saturation was the rate-controlling factor at high input drug concentration. Heterogeneous enzymic distribution modulated changes in unbound fraction within the liver and at the outlet. Despite marked changes in unbound fraction occurring within the liver for different enzymic distributions, the overall transhepatic differences were relatively small. We then investigated the logarithmic average unbound concentration and the length averaged concentration as estimates of substrate concentration in liver in the presence of nonlinear drug binding. Fitting of simulated data, with and without assigned random error (10%), to the Michaelis-Menten equation was performed; fitting was repeated for simulated data obtained with presence of a specific inhibitor of the high-affinity, anteriorly distributed pathway. Results were similar for both concentration terms: accurate estimates were obtained for anterior, high affinity pathways; an overestimation of parameters was observed for the lower affinity posteriorly distributed pathways. Improved estimations were found for posteriorly distributed pathways upon inhibition with specific inhibitors; with added random error, however, the improvement was much decreased. We applied the method for fitting of several sets of metabolic data obtained from rat liver perfusion studies performed with salicylamide (SAM) (i) without and (ii) with the presence of 2,6-dichloro-4-nitrophenol (DCNP), a SAM sulfation inhibitor. The fitted results showed that SAM sulfation was a high-affinity high-capacity pathway; SAM glucuronidation was of lower affinity but comparable capacity as the sulfation pathway, whereas SAM hydroxylation was of lower affinity and lower capacity. 相似文献
50.