全文获取类型
收费全文 | 243476篇 |
免费 | 2947篇 |
国内免费 | 1243篇 |
专业分类
电工技术 | 4829篇 |
综合类 | 264篇 |
化学工业 | 35411篇 |
金属工艺 | 10861篇 |
机械仪表 | 7066篇 |
建筑科学 | 6238篇 |
矿业工程 | 481篇 |
能源动力 | 6273篇 |
轻工业 | 24147篇 |
水利工程 | 1836篇 |
石油天然气 | 1335篇 |
武器工业 | 3篇 |
无线电 | 31035篇 |
一般工业技术 | 44881篇 |
冶金工业 | 50106篇 |
原子能技术 | 3860篇 |
自动化技术 | 19040篇 |
出版年
2021年 | 1566篇 |
2019年 | 1423篇 |
2018年 | 2321篇 |
2017年 | 2223篇 |
2016年 | 2444篇 |
2015年 | 1907篇 |
2014年 | 3159篇 |
2013年 | 10793篇 |
2012年 | 5449篇 |
2011年 | 7786篇 |
2010年 | 6284篇 |
2009年 | 6962篇 |
2008年 | 7558篇 |
2007年 | 7658篇 |
2006年 | 7031篇 |
2005年 | 6519篇 |
2004年 | 6245篇 |
2003年 | 6261篇 |
2002年 | 6239篇 |
2001年 | 6371篇 |
2000年 | 5802篇 |
1999年 | 6417篇 |
1998年 | 16558篇 |
1997年 | 11597篇 |
1996年 | 8948篇 |
1995年 | 6689篇 |
1994年 | 5907篇 |
1993年 | 5727篇 |
1992年 | 4051篇 |
1991年 | 3994篇 |
1990年 | 3582篇 |
1989年 | 3504篇 |
1988年 | 3440篇 |
1987年 | 2907篇 |
1986年 | 2842篇 |
1985年 | 3413篇 |
1984年 | 3050篇 |
1983年 | 2743篇 |
1982年 | 2547篇 |
1981年 | 2568篇 |
1980年 | 2430篇 |
1979年 | 2271篇 |
1978年 | 2235篇 |
1977年 | 2808篇 |
1976年 | 4171篇 |
1975年 | 1899篇 |
1974年 | 1795篇 |
1973年 | 1783篇 |
1972年 | 1460篇 |
1971年 | 1317篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
891.
Sell B. Avellan A. Krautschneider W.H. 《Device and Materials Reliability, IEEE Transactions on》2002,2(1):9-12
A new simple method of measuring capacitance-voltage characteristics of MOS devices is presented. Proceeding from the charge-based capacitance measurement technique suggested recently, a compact test structure with high resolution has been developed, which only requires measurement of do quantities. The method was tested on a 0.6-μm CMOS process with small and large area capacitors and compared to well-known high-frequency capacitance-voltage results. Beside using a reference structure, a second means of extracting parasitic effects is demonstrated for small structures. The test structure allows measurements in a wide frequency range with high accuracy and low noise contribution at small capacitance levels 相似文献
892.
Flexion-extension moments acting at the L5/S1 level and hip joints were calculated using three different techniques; a pure static analysis, a static analysis including the inertial force of the load, and a dynamic analysis. Ten subjects participated in the study and were asked to lift a box weighing either 50 N or 150 N, using a freestyle technique. The lifts were performed at normal and fast speed. The intra-subject lifting techniques were consistent when lifting the same loads. The moments predicted by the dynamic analysis and the static analysis were the same when holding weights in static postures. When performing the lifts, differences in the peak moments occurred between static and dynamic analyses. These differences were influenced by external load and by lifting speed. Taking the effect of the inertia of load into account in the static analysis resulted in an increase in the moment magnitude, but the predicted moment was still much less than in the dynamic analysis which yielded the largest moment magnitudes. The difference between dynamic and static analysis was greatest when lifting 50 N at fast speed; an 87% increase in L5/S1 moment and a 95% increase in hip moment was observed when replacing the pure static with a dynamic analysis. 相似文献
893.
D Sapoznikov M H Luria Y Mahler M S Gotsman 《Computer methods and programs in biomedicine》1992,39(1-2):75-84
Analysis of heart rate variability (HRV) with Holter monitoring is often difficult due to excessive artifacts and arrhythmias. While short sudden surges are treated successfully by most methods, slow heart rate (HR) variations, nocturnal trapezoidally-shaped HR increases and special types of arrhythmias which are similar to normal HRV fluctuations may distort further time domain and spectral analysis. This paper examines the advantages and disadvantages of different methods for preprocessing of HR data. We have developed the following approach to the analysis of HRV. (1) A combination method based on the absolute difference between HR values and both the last normal HR value and an updated mean is used for removal of artifacts and arrhythmias. This method can detect both sudden surges in HR values as well as longer periods of noise combined with slow normal variations. An additional stage of wild point removal is then optionally applied. (2) Certain special problems such as large T-waves, bigeminal rhythm, slow HR variations and nocturnal trapezoidally-shaped HR increases are also identified. Although none of the algorithms can be applied successfully to all cases, the final computer analysis for preprocessing described in the present study has proved to be superior to the simplified methods which are usually used and provides more suitable data for HRV analysis. 相似文献
894.
A logic language is suitable for specification if it is equipped with features for data abstraction and modularization. In this paper, an effective mechanism to incorporate function and type into logic programming is presented as the means to embed data abstraction mechanism into logic programming. This incorporation is essentially based on Horn clause logic with equality and a polymorphic type system that is an extension of Mycroft and O’Keefe’s system. This paper also presents an implementation based on Warren Abstract Machine (WAM) and shows the performance, along with a comparison with WAM. 相似文献
895.
Durney C.H. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1992,80(1):194-199
Medical and biological applications of antennas can be classified into two broad groups: (1) therapeutic and (2) informational (including diagnostics and measurement of material electromagnetic (EM) properties). Most of these applications involve EM coupling into or out of the body which requires a device such as an antenna or other applicator. A common characteristic of many applications is the difficulty of coupling EM energy into the interior of the body without damaging the surface. Rapidly increasing computing power and new developments in numerical EM techniques are expected to have a great impact on the use of EM devices in medicine and biology 相似文献
896.
Memory reallocation is used to construct a run-time data structure for fast/efficient storage of information during collection and analysis. The data structure presented uses dynamic memory but does not require the use of pointers to link nodes of information together. It allows for simple and efficient access to data via array indexing rather than through the use of lists or tree structures and it provides flexibility for competing storage requirements that are determined dynamically. The data structure is developed in the C programming language and a suite of ANSI standard C subroutines that make up a run-time data structure management system is provided. 相似文献
897.
The authors propose techniques for adaptive nonlinear cancellation of intersymbol interference (ISI) in the electrical signal at the receiver in Gb/s lightwave systems and describe several demonstrations of these techniques. Techniques for adjustable nonlinear cancellations are discussed and demonstrations of these techniques using commercially available integrated circuits (ICs) at data rates as high as 1.7 Gb/s are described. Techniques for automatic adjustment are discussed, and a demonstration of adaptive nonlinear cancellation at 450 Mb/s is described. The authors discuss how these techniques can be integrated onto the detector IC for operations at 2.5 Gb/s and higher data rates. These techniques allow a single IC detector with adaptive nonlinear cancellation to be used in long-haul and undersea lightwave systems to optimize the detector threshold and compensate for the ISI 相似文献
898.
A multiserver queueing model of access control strategies for a wideband integrated services digital network (ISDN) is considered. There are two types of service requests (SRs): Type 1 SR requires b servers (basic bandwidth units, BBUs) of the c available servers, while Type 2 SR requires a single server. Both types of SRs are queuable in two separate infinite-size buffers. A Type 1 SR is allowed to seize d (⩽b ) servers at first and then acquire additional servers as they become available to meet the original requirement of b servers. The arrival processes of both types of SRs are Poisson and the service times are exponentially distributed with mean b /d μ1 and 1/μ2 for Type 1 SR and Type 2 SR, respectively. Preemptive and nonpreemptive priority disciplines with movable boundary are analyzed using the Neuts' matrix-analytic approach. Numerical examples of the queue length distribution and the mean waiting time of the SRs are presented 相似文献
899.
900.
We consider the effects of spin-phonon coupling within the slave-boson mean-field treatment of the extended t-J model. With no additional assumptions the theory is found to give a semi-quantitative account of the frequency and linewidth anomalies observed for certain phonon modes in Y Ba2Cu3O7 at the superconducting transition. We report also investigations of the role of this coupling in affecting thermodynamic properties and spin dynamics. 相似文献