全文获取类型
收费全文 | 260896篇 |
免费 | 7669篇 |
国内免费 | 3490篇 |
专业分类
电工技术 | 7619篇 |
技术理论 | 2篇 |
综合类 | 4230篇 |
化学工业 | 37335篇 |
金属工艺 | 11160篇 |
机械仪表 | 9506篇 |
建筑科学 | 8715篇 |
矿业工程 | 2883篇 |
能源动力 | 6333篇 |
轻工业 | 18347篇 |
水利工程 | 2764篇 |
石油天然气 | 6755篇 |
武器工业 | 531篇 |
无线电 | 34866篇 |
一般工业技术 | 44941篇 |
冶金工业 | 48376篇 |
原子能技术 | 4188篇 |
自动化技术 | 23504篇 |
出版年
2023年 | 1418篇 |
2022年 | 2552篇 |
2021年 | 3825篇 |
2020年 | 2894篇 |
2019年 | 3030篇 |
2018年 | 4033篇 |
2017年 | 4203篇 |
2016年 | 4062篇 |
2015年 | 3951篇 |
2014年 | 5618篇 |
2013年 | 11539篇 |
2012年 | 8481篇 |
2011年 | 10520篇 |
2010年 | 8581篇 |
2009年 | 9262篇 |
2008年 | 9498篇 |
2007年 | 9454篇 |
2006年 | 9271篇 |
2005年 | 8313篇 |
2004年 | 7344篇 |
2003年 | 6868篇 |
2002年 | 6465篇 |
2001年 | 6734篇 |
2000年 | 6457篇 |
1999年 | 7133篇 |
1998年 | 17093篇 |
1997年 | 11559篇 |
1996年 | 9057篇 |
1995年 | 6716篇 |
1994年 | 5830篇 |
1993年 | 5581篇 |
1992年 | 3803篇 |
1991年 | 3617篇 |
1990年 | 3471篇 |
1989年 | 3245篇 |
1988年 | 2962篇 |
1987年 | 2354篇 |
1986年 | 2398篇 |
1985年 | 2664篇 |
1984年 | 2342篇 |
1983年 | 2083篇 |
1982年 | 1929篇 |
1981年 | 2059篇 |
1980年 | 1811篇 |
1979年 | 1668篇 |
1978年 | 1663篇 |
1977年 | 2026篇 |
1976年 | 2714篇 |
1975年 | 1431篇 |
1974年 | 1371篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Explicit analytic design rules are derived for both 3 dB and full adiabatic couplers. The design rules are in excellent agreement with numerical calculations using the beam propagation method (BPM). It is shown that the length scaling for 3 dB couplers compared to full couplers makes the former more difficult to design. The design for each case is optimized to obtain the upper limit of performance and a comparison is carried out between two different design geometries for both 3 dB and full adiabatic couplers 相似文献
132.
133.
134.
Penetrating injuries of the eye are an important cause of unilateral visual loss. We studied a series of 82 cases of penetrating injuries treated here from 1987 through 1993. The injuries were caused by sharp objects in 66% and blunt trauma in 6%. The prognosis after a penetrating injury is greatly influenced by the nature of the injury and the extent of the initial drainage. Among factors associated with an unfavorable visual outcome were diminished preoperative visual acuity and scleral wounds with dense vitreous hemorrhage. 相似文献
135.
As shown previously for two-dimensional geometries, anisotropy effects should not be ignored in electrical impedance tomography (EIT) and structural information is important for the reconstruction of anisotropic conductivities. Here, we describe the static reconstruction of an anisotropic conductivity distribution for the more realistic three-dimensional (3-D) case. Boundaries between different conductivity regions are anatomically constrained using magnetic resonance imaging (MRI) data. The values of the conductivities are then determined using gradient-type-algorithms in a nonlinear-indirect approach. At each iteration, the forward problem is solved by the finite element method. The approach is used to reconstruct the 3-D conductivity profile of a canine torso. Both computational performance and simulated reconstruction results are presented together with a detailed study on the sensitivity of the prediction error with respect to different parameters. In particular, the use of an intracavity catheter to better extract interior conductivities is demonstrated 相似文献
136.
137.
Polycarpou A.C. Balanis C.A. Aberle J.T. Birtcher C. 《Antennas and Propagation, IEEE Transactions on》1998,46(9):1297-1306
A three-dimensional finite-element method hybridized with the spectral/spatial domain method of moments is presented for the analysis of ferrite-tuned cavity-backed slot antennas. The cavity, which is partially filled with magnetized ferrite layers, is flush mounted on an infinite ground plane with possible dielectric or magnetic overlay. The antenna operates primarily in the ultrahigh-frequency band. The finite-element method is used to solve for the electric-field distribution inside the cavity, whereas the spectral-domain approach is used to solve for the exterior region. An asymptotic extraction of the exponential behavior of the Green's function followed by a spatial evaluation of the resulting integral is used to improve computational speed. Radar cross section, input impedance, return loss, gain, and efficiency of ferrite-tuned cavity-backed slots (CBS) are calculated for various biasing conditions. Numerical results are compared with experimental data 相似文献
138.
Saitoh T. Mattori S. Kinugawa S. Miyagi K. Taniguchi A. Kourogi M. Ohtsu M. 《Lightwave Technology, Journal of》1998,16(5):824-832
We report the modulation characteristics of a waveguide-type optical frequency comb generator (WG-OFCG) with the advantages of compactness, high modulation index and low driving power. The characteristics of the optical frequency comb (OFC) generated when the modulation index exceeds 2π are discussed. The power of the modulation sidebands was measured by the optical heterodyne method with an external-cavity laser as a local oscillator. The dependence of the modulation index of the WG-OFCG on the modulation frequency up to 40 GHz was measured. The generation span of the OFC at the modulation frequency detuned from an integer multiple of the free spectral range (FSR) is discussed 相似文献
139.
Kobayashi K. Kameyama M. Higuchi T. 《Industrial Electronics, IEEE Transactions on》1997,44(3):418-426
A new token-passing mechanism, priority token passing, which features real-time access and fast detection and recovery of transmission errors, is discussed in detail in comparison with standard token-passing protocols, and its large-scale integration (LSI)-oriented design concept is described. Priority token passing includes only a small performance overhead, due to its switching functions, which can change network topology from ring to broadcast medium. A token-holding node passes the token to another node after determining the successor through priority comparison. Errors occurring during token passing can, thus, be detected and corrected simply and promptly. Priority token passing has a simple hardware implementation, requiring only small additions to the frame control circuitry, and has a small implementation overhead. The priority token-passing protocol and two other important network communication functions, dual ring network reconfiguration and high-level data link control (HDLC) normal response mode-based message transmission, are designed as a single finite-state machine, and implemented into a compact LSI chip. This integrated instrument network (IINET) chip provides complete network communication services and requires only three additional external electronic components for operation 相似文献
140.
Business process redesign (BPR) has been widely touted as a means for leveraging the power of information technology to change business processes radically, resulting in substantial improvements in organizational effectiveness and efficiency. This study represents an early attempt at examining the strategic nature of the phenomenon. Because BPR is radical change and has the ability to alter both the competitive and operational nature of the corporation, it is critical that BPR be coordinated with corporate strategy. Through a survey of information system executives, the relationships between corporate competitive strategy and three types of BPR – intrafunctional, interfunctional and interorganizational – were examined. It was found that organizations following a cost strategy tended to do more BPR projects on interfunctional processes. Furthermore, the positive effect of a cost strategy on interfunctional BPR was found to be strengthened by the degree of integration of IS and business planning. It was also found that while interorganizational BPR was not related to a specific strategy, it was strongly related directly with IS–business planning integration. 相似文献