全文获取类型
收费全文 | 5867篇 |
免费 | 320篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 80篇 |
综合类 | 9篇 |
化学工业 | 988篇 |
金属工艺 | 69篇 |
机械仪表 | 97篇 |
建筑科学 | 209篇 |
矿业工程 | 6篇 |
能源动力 | 173篇 |
轻工业 | 359篇 |
水利工程 | 52篇 |
石油天然气 | 41篇 |
无线电 | 587篇 |
一般工业技术 | 1358篇 |
冶金工业 | 1097篇 |
原子能技术 | 22篇 |
自动化技术 | 1047篇 |
出版年
2023年 | 58篇 |
2022年 | 60篇 |
2021年 | 149篇 |
2020年 | 119篇 |
2019年 | 127篇 |
2018年 | 134篇 |
2017年 | 150篇 |
2016年 | 173篇 |
2015年 | 143篇 |
2014年 | 204篇 |
2013年 | 355篇 |
2012年 | 334篇 |
2011年 | 413篇 |
2010年 | 321篇 |
2009年 | 309篇 |
2008年 | 349篇 |
2007年 | 280篇 |
2006年 | 249篇 |
2005年 | 231篇 |
2004年 | 168篇 |
2003年 | 157篇 |
2002年 | 160篇 |
2001年 | 83篇 |
2000年 | 77篇 |
1999年 | 90篇 |
1998年 | 159篇 |
1997年 | 153篇 |
1996年 | 106篇 |
1995年 | 69篇 |
1994年 | 84篇 |
1993年 | 76篇 |
1992年 | 53篇 |
1991年 | 28篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 27篇 |
1987年 | 40篇 |
1986年 | 20篇 |
1985年 | 47篇 |
1984年 | 28篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 42篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 27篇 |
1976年 | 47篇 |
1975年 | 18篇 |
1973年 | 11篇 |
排序方式: 共有6194条查询结果,搜索用时 109 毫秒
71.
A new technique for understanding the organization of complex circuits in the vertebrate brain, scanning laser photostimulation, is described. This approach is based on the photolysis of a caged form of the excitatory neurotransmitter glutamate. Computer-controlled photostimulation and whole cell recording in brain slices allow the construction of detailed maps of the position, strength, sign and number of inputs converging on a single postsynaptic neuron. Scanning laser photostimulation offers many advantages over current techniques: spatial resolution is superb, fibers of passage are not activated, and thousands of presynaptic locations can be stimulated. This review describes the technique of photostimulation, outlines the instrumentation, necessary to implement it, and discusses the interpretation of photostimulation-derived data. Several examples of applications, ranging from mapping circuits in the mammalian visual cortex to determining receptor distributions on single neurons are considered. Although still in its early stages, scanning laser photostimulation offers neuroscientists a powerful tool for determining the organization and function of local brain circuits. 相似文献
72.
Thomas G. OConnor Jonathan A. Dantzig 《Metallurgical and Materials Transactions B》1994,25(3):443-457
A three-dimensional mathematical model has been developed to compute the thermomechanical state in the mold of thin-slab continuous
casters. The thin-slab mold differs from those used in conventional slab casters in that the upper portion of the broad side
walls defines a funnel-shaped chamber which allows the nozzle to be submerged into the liquid metal. The chamber converges
with distance down the mold, reducing to the rectangular cross section of the finished casting near the mold exit. The new
mold, along with casting speeds up to 6 m/min, allows slabs to be cast 50–60 mm thick, compared with 150 to 350 mm in conventional
continuous slab casting. However, the mold shape and high casting speed lead to higher mold temperatures and shorter mold
life than are found in conventional slab casters. In this article, we develop mathematical models of the process to determine
the role of various process parameters in determining the mold life. Finite-element analysis is used to determine the temperatures
in the mold and cast slab, and these data are then used in an elastic-viscoplastic analysis to investigate the deformation
of the mold wall in service. Cyclic inelastic strains up to 1.75 Pct are found in a region below the meniscus along the funnel
edge. These large strains result from the combination of locally high temperatures coupled with geometric restraint of the
mold. The deformation leads to short mold life because of thermal fatigue cracking of the mold. The computed locations and
time to failure of the mold in fatigue agree very well with observations of the appearance of mold surface cracks in an operating
caster. The models are also used to develop an improved mold design.
Formerly Research Assistant, Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 相似文献
73.
Both Soviet and American youth show a great concern about the possible effects of nuclear war, with heavy media users in both countries more optimistic, but the relation was stronger among Soviet students. 相似文献
74.
The surface-crack-in-flexure (SCF) method uses a Knoop indenter to create small, semielliptical surface precracks in beam specimens. Lateral cracks may interfere with the primary median crack and cause errors of up to 10% in determination of fracture toughness, particularly for materials for which the fracture toughness is ∼3 MPa·m1/2 or less. Although the residual-stress-damage zone is ground or polished away by hand by removing 4.5–5 times the indentation depth, this amount may not be sufficient to completely remove the lateral cracks in low-fracture-toughness materials. A series of tests were conducted on sintered alpha silicon carbide with different amounts of material removed after indentation. Once the lateral cracks were fully removed, the SCF results concurred with single-edged-precracked-beam and chevron-notched-beam data collected in accordance with ASTM Designation C1421. A simple remedy for the SCF method is to examine the outer ground surface for remnants of lateral cracks before fracture and to remove more material if necessary. 相似文献
75.
A sensing strategy for the reverse engineering of machined parts 总被引:1,自引:0,他引:1
The reverse engineering of machined parts requires sensing an existing part and producing a design (and perhaps a manufacturing process) for it. We have developed a reverse engineering system that has proven effective with a set of machined parts. This paper describes the system, presents some results, and discusses strategy for a new system.This work was supported by ARPA under ARO grant number DAAH04-93-G-0420, DARPA grant N00014-91-J-4123, NSF grant CDA 9024721, and a University of Utah Research Committee grant. All opinions, findings, conclusions or recommendations expressed in this document are those of the authors and do not necessarily reflect the views of the sponsoring agencies. 相似文献
76.
The Rules of Beeping: Exchanging Messages Via Intentional "Missed Calls" on Mobile Phones 总被引:1,自引:0,他引:1
Jonathan Donner 《Journal of Computer-Mediated Communication》2007,13(1):1-22
This article explores the practice of "beeping" or "missed calling" between mobile phone users, or calling a number and hanging up before the mobile's owner can pick up the call. Most beeps are requests to call back immediately, but they can also send a pre-negotiated instrumental message such as "pick me up now" or a relational sign, such as "I'm thinking of you." The practice itself is old, with roots in landline behaviors, but it has grown tremendously, particularly in the developing world. Based on interviews with small business owners and university students in Rwanda, the article identifies three kinds of beeps (callback, pre-negotiated instrumental, and relational) and the norms governing their use. It then assesses the significance of the practice using adaptive structuration theory. In concluding, the article contrasts beeping with SMS/text messaging, discusses its implications for increasing access to telecommunications services, and suggests paths for future research. 相似文献
77.
THE IMPORTANCE OF NEUTRAL EXAMPLES FOR LEARNING SENTIMENT 总被引:2,自引:0,他引:2
Most research on learning to identify sentiment ignores "neutral" examples, learning only from examples of significant (positive or negative) polarity. We show that it is crucial to use neutral examples in learning polarity for a variety of reasons. Learning from negative and positive examples alone will not permit accurate classification of neutral examples. Moreover, the use of neutral training examples in learning facilitates better distinction between positive and negative examples. 相似文献
78.
Barch Deanna M.; Cohen Jonathan D.; Servan-Schreiber David; Steingard Sandra; Steinhauer Stuart S.; van Kammen Daniel P. 《Canadian Metallurgical Quarterly》1996,105(4):592
Semantic priming in word pronunciation was examined at 5 stimulus onset asynchronies (SOAs) in 75 medicated and 25 unmedicated people with schizophrenia (SCZ) and in 10 depressed and 28 normal controls. At SOAs 相似文献
79.
Two generations of outcome research demonstrate the potential efficacy of marital therapy in the treatment of depression. After reviewing treatment outcome studies on marital therapy for depression, we examine basic research linking aspects of the marital relationship to depressive symptoms. In doing so, we highlight a number of theoretical perspectives and research findings that can inform work with couples in which one spouse is depressed. Finally, we identify potential innovations that may lead to a third generation of marital interventions for depression and several avenues of inquiry for a third generation of outcome research on marital therapy for depression. 相似文献
80.
Hyperglycemia before ischemia worsens cerebral outcome. The aim of this study was to determine the cerebral effects of giving glucose with or without insulin after asphyxial cardiac arrest. Rats underwent 8 min of asphyxial cardiac arrest. After arrest, Group 1 received NaCl; Group 2, insulin; Group 3, glucose; and Group 4, glucose plus insulin, all intravenously. Neurological deficit (ND) scores were 14+/-10%, 22+/-12%, 12+/-10% and 2+/-2% in Groups 1-4, respectively, 72 h after reperfusion. Overall histological damage (HD) scores were 4, 2, 3 and 1, respectively. Group 4 fared significantly better than group 1 on both scores. Glucose after asphyxial cardiac arrest in rats produces no increased brain damage while glucose plus insulin improves cerebral outcome. 相似文献