全文获取类型
收费全文 | 37933篇 |
免费 | 1001篇 |
国内免费 | 67篇 |
专业分类
电工技术 | 431篇 |
综合类 | 38篇 |
化学工业 | 7544篇 |
金属工艺 | 946篇 |
机械仪表 | 698篇 |
建筑科学 | 1976篇 |
矿业工程 | 280篇 |
能源动力 | 1084篇 |
轻工业 | 3215篇 |
水利工程 | 360篇 |
石油天然气 | 219篇 |
武器工业 | 2篇 |
无线电 | 2750篇 |
一般工业技术 | 5820篇 |
冶金工业 | 8111篇 |
原子能技术 | 363篇 |
自动化技术 | 5164篇 |
出版年
2022年 | 228篇 |
2021年 | 435篇 |
2020年 | 367篇 |
2019年 | 424篇 |
2018年 | 541篇 |
2017年 | 549篇 |
2016年 | 558篇 |
2015年 | 503篇 |
2014年 | 802篇 |
2013年 | 2383篇 |
2012年 | 1352篇 |
2011年 | 1758篇 |
2010年 | 1281篇 |
2009年 | 1406篇 |
2008年 | 1588篇 |
2007年 | 1647篇 |
2006年 | 1412篇 |
2005年 | 1294篇 |
2004年 | 1170篇 |
2003年 | 1169篇 |
2002年 | 1141篇 |
2001年 | 735篇 |
2000年 | 699篇 |
1999年 | 691篇 |
1998年 | 926篇 |
1997年 | 733篇 |
1996年 | 764篇 |
1995年 | 685篇 |
1994年 | 649篇 |
1993年 | 659篇 |
1992年 | 561篇 |
1991年 | 390篇 |
1990年 | 510篇 |
1989年 | 489篇 |
1988年 | 452篇 |
1987年 | 463篇 |
1986年 | 430篇 |
1985年 | 564篇 |
1984年 | 555篇 |
1983年 | 506篇 |
1982年 | 529篇 |
1981年 | 515篇 |
1980年 | 415篇 |
1979年 | 416篇 |
1978年 | 373篇 |
1977年 | 372篇 |
1976年 | 334篇 |
1975年 | 364篇 |
1974年 | 269篇 |
1973年 | 312篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Jeong-Soo Lee Yang-Kyu Choi Daewon Ha Balasubramanian S. Tsu-Jae King Bokor J. 《Electron Device Letters, IEEE》2003,24(3):186-188
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin. 相似文献
12.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps. 相似文献
13.
Sheldon H. Jacobson Julie L. Virta Jon M. Bowman John E. Kobza John J. Nestor 《IIE Transactions》2003,35(3):259-269
Aviation security protects vital national interests, as well as passengers and aircraft. Key components of an aviation security system include baggage and passenger screening devices and operations. Determining how and where to assign (deploy) such devices can be quite challenging. Moreover, even after such systems are in place, it can be difficult to measure their effectiveness. This paper describes how discrete optimization models can be used to address these questions, based on three performance measures that quantify the effectiveness of airport baggage screening security device systems. These models are used to solve for optimal airport baggage screening security device deployments considering the number of passengers on a set of flights who have not been cleared using a security risk assessment system in use by the Federal Aviation Administration (i.e., passengers whose baggage is subjected to screening), the number of flights in this set, and the size of the aircraft for such flights. Several examples are provided to illustrate these results, including an example that uses data available from the Official Airline Guide. 相似文献
14.
Superconducting qubits are solid state electrical circuits fabricated using techniques borrowed from conventional integrated circuits. They are based on the Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit element available at low temperature. In contrast to microscopic entities such as spins or atoms, they tend to be well coupled to other circuits, which make them appealling from the point of view of readout and gate implementation. Very recently, new designs of superconducting qubits based on multi-junction circuits have solved the problem of isolation from unwanted extrinsic electromagnetic perturbations. We discuss in this review how qubit decoherence is affected by the intrinsic noise of the junction and what can be done to improve it.
PACS: 03.67.-a, 03.65.Yz, 85.25.-j, 85.35.Gv 相似文献
15.
Use of X-ray computed microtomography to understand why gels reduce relative permeability to water more than that to oil 总被引:1,自引:0,他引:1
R. S. Seright J. Liang W. Brent Lindquist John H. Dunsmuir 《Journal of Petroleum Science and Engineering》2003,39(3-4):217
X-ray computed microtomography (XMT) was used to investigate why gels reduce relative permeability to water more than that to oil in strongly water-wet Berea sandstone. XMT allows saturation differences to be monitored for individual pores during various stages of oil, water, and gelant flooding. The method also characterizes distributions of pore size, aspect ratio, and coordination number for the porous media. We studied a Cr(III) acetate–HPAM gel that reduced permeability to water (at Sor) by a factor 80–90 times more than that to oil (at Swr). In Berea, the gel caused disproportionate permeability reduction by trapping substantial volumes of oil that remained immobile during water flooding (i.e., 43.5% Sor before gel placement versus 78.7% Sor after gel placement). With this high trapped oil saturation, water was forced to flow through narrow films, through the smallest pores, and through the gel itself. In contrast, during oil flooding, oil pathways remained relatively free from constriction by the gel. 相似文献
16.
John Chisholm 《数码世界》2004,3(19)
合作伙伴的实时反馈是客户关系管理(PR M)的必备要素之一.实时合作伙伴反馈采用调研的形式通过在线、电话、交互式语音应答(IVR)、无线通讯等手段搜集来自终端用户和合作伙伴的实时反馈.此类调研提供针对终端用户及合作伙伴的看法、意向和感受的可行性智能,使企业精益求精: 相似文献
17.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
18.
McWayne Christine M.; Fantuzzo John W.; McDermott Paul A. 《Canadian Metallurgical Quarterly》2004,40(4):633
The present concurrent study combined developmental and ecological considerations to examine the unique contribution of multiple preschool competencies to an indicator of early academic success. Participants included 195 Head Start children from 32 classrooms representative of a large, urban Head Start program. Dimensional (variable-centered) analyses revealed 3 distinct classroom competency dimensions (i.e., General Classroom Competencies, Specific Approaches to Learning, and Interpersonal Classroom Behavioral Problems). The first 2 of these dimensions were found to be uniquely associated with early academic success. Findings from typological (person-centered) analyses supported the dimensional findings. Typological analyses revealed 7 profiles of classroom competency distinguished by high scores on the dimensions of General Competencies and Approaches to Learning, and these profiles were found to relate differentially to the indicator of early academic success. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Shamachary Sathish John H. Cantrell William T. Yost 《Journal of the American Ceramic Society》1996,79(1):209-212
Scanning acoustic microscopy of SCS-6 silicon carbide fiber reveals large radial variations in acoustic reflectivity associated with the chemical composition and microstructure of a given fiber region. Rayleigh wave fringe patterns observed in each of five subregions are used to calculate the average Young modulus of that subregion. The Young modulus is found to increase monotonically from 40 GPa in the carbon core to a value of 413 GPa in the stoichiometric SiC region. The effective Young modulus of the fiber as a whole is estimated from the moduli of the individual regions and it is compared with mechanical measurements reported in the literature. 相似文献
20.
A King 《Canadian Metallurgical Quarterly》1997,48(4):576-593
By using a 'cultural' definition of 'postmodernism' (derived from Jameson and Martin) in which postmodernism is regarded as the transgression of modern boundaries, this article traces the emergence of postmodern aspects to violent male fandom at football games since the 1960s. It is argued that at games, male fans have created imaginary masculine and national boundaries by which they have affirmed their identities but that in fighting they have sought to breach these boundaries in postmodern fashion. 相似文献