全文获取类型
收费全文 | 2961篇 |
免费 | 58篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 68篇 |
综合类 | 8篇 |
化学工业 | 596篇 |
金属工艺 | 77篇 |
机械仪表 | 42篇 |
建筑科学 | 151篇 |
矿业工程 | 15篇 |
能源动力 | 33篇 |
轻工业 | 341篇 |
水利工程 | 13篇 |
石油天然气 | 7篇 |
无线电 | 207篇 |
一般工业技术 | 364篇 |
冶金工业 | 793篇 |
原子能技术 | 17篇 |
自动化技术 | 291篇 |
出版年
2018年 | 30篇 |
2017年 | 28篇 |
2016年 | 49篇 |
2015年 | 39篇 |
2014年 | 36篇 |
2013年 | 135篇 |
2012年 | 63篇 |
2011年 | 95篇 |
2010年 | 70篇 |
2009年 | 82篇 |
2008年 | 85篇 |
2007年 | 93篇 |
2006年 | 93篇 |
2005年 | 90篇 |
2004年 | 83篇 |
2003年 | 77篇 |
2002年 | 70篇 |
2001年 | 47篇 |
2000年 | 43篇 |
1999年 | 58篇 |
1998年 | 76篇 |
1997年 | 74篇 |
1996年 | 61篇 |
1995年 | 43篇 |
1994年 | 55篇 |
1993年 | 59篇 |
1992年 | 46篇 |
1991年 | 32篇 |
1990年 | 37篇 |
1989年 | 49篇 |
1988年 | 44篇 |
1987年 | 32篇 |
1986年 | 31篇 |
1985年 | 47篇 |
1984年 | 55篇 |
1983年 | 52篇 |
1982年 | 40篇 |
1981年 | 41篇 |
1980年 | 45篇 |
1979年 | 37篇 |
1978年 | 45篇 |
1977年 | 44篇 |
1976年 | 58篇 |
1975年 | 38篇 |
1974年 | 32篇 |
1973年 | 28篇 |
1972年 | 38篇 |
1971年 | 31篇 |
1970年 | 28篇 |
1966年 | 28篇 |
排序方式: 共有3023条查询结果,搜索用时 15 毫秒
1.
2.
3.
Hans-Jürgen Odenthal Herbert Pfeifer Ina Lemanowicz Rainer Gorissen 《Metallurgical and Materials Transactions B》2002,33(2):163-172
The present work describes quantitative digital particle image velocimetry measurements of a full-scale water model of a thin
slab mold. Different casting speeds and two submerged entry nozzles with one and two outlet ports have been investigated.
The flow pattern of the single-port nozzle shows a counterclockwise-rotating double vortex that is nearly steady-state but
leads to high stationary surface waves. The flow jets out of the two-port nozzle oscillate and produce a transient flow pattern
with low wave amplitudes. The amplitudes for the one-port nozzle show a linear variation with the volumetric flow rate. The
experimental results lead to a good interpretation of the flow phenomena and are used to validate steady-state numerical simulations
with the commercial program, CFX, on the basis of the Reynolds equations. To describe anisotropic turbulence effects, the
Reynolds stress model (RSM) is used for the flat single-port nozzle and the standard k-ɛ model for the mold flow. The calculated mean velocities and wave amplitudes, predicted from pressure distribution at the
water surface, are generally in the consensus of the experimental data.
An erratum to this article is available at . 相似文献
4.
5.
The vicissitudes of the Israeli-Palestinian peace process since 1967 are analyzed using attitudes and related concepts where relevant. The 1967 war returned the two peoples' zero-sum conflict around national identity to its origin as a conflict within the land both peoples claim. Gradually, new attitudes evolved regarding the necessity and possibility of negotiations toward a two-state solution based on mutual recognition, which became the building stones of the 1993 Oslo agreement. Lacking a commitment to a final outcome, the Oslo-based peace process was hampered by reserve options, which increased avoidance at the expense of approach tendencies as the parties moved toward a final agreement. The resulting breakdown of the process in 2000 produced clashing narratives, reflecting different anchors for judgment and classical mirror images. Public support for violence increased, even as public opinion continued to favor a negotiated two-state solution. Reviving the peace process requires mutual reassurance about the availability of a partner for negotiating a principled peace based on a historic compromise that meets the basic needs and validates the identities of both peoples. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
Marsh and Parker (1984) described the big-fish–little-pond effect ({bflpe}), whereby equally able students have lower academic self-concepts in high-ability schools than in low-ability schools. The present investigation, a reanalysis of the Youth in Transition data, supported the generality of the earlier findings and demonstrated new theoretical implications of the {bflpe}. First, differences in the academic self-concepts of Black and White students, sometimes assumed to represent response biases, were explicable in terms of the {bflpe}. Second, equally able students earned higher grades in lower ability schools. This frame-of-reference effect for grades was distinct from, but contributed to, the {bflpe} for academic self-concept. Third, a longitudinal analysis demonstrated that academic self-concept had a direct effect on subsequent school performance beyond the effects of academic ability and prior school performance. About one quarter of this effect could be explained in terms of the {bflpe}. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献
8.
Academically selective schools are intended to affect academic self-concept positively, but theoretical and empirical research demonstrates that the effects are negative. The big-fish--little-pond effect (BFLPE), an application of social comparison theory to educational settings, posits that a student will have a lower academic self-concept in an academically selective school than in a nonselective school. This study, the largest cross-cultural study of the BFLPE ever undertaken, tested theoretical predictions for nationally representative samples of approximately 4,000 15-year-olds from each of 26 countries (N=103,558) who completed the same self-concept instrument and achievement tests. Consistent with the BFLPE, the effects of school-average achievement were negative in all 26 countries (M beta=-.20, SD=.08), demonstrating the BFLPE's cross-cultural generalizability. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
European Food Research and Technology - Bei Bestimmungen des Proteingehalts von Haselnüssen in verschiedenen Handelsprodukten wie Nuß-Nougatcremes and Nußmus mit der... 相似文献
10.
Laura Akers Herbert H Severson Judy A Andrews Edward Lichtenstein 《Nicotine & tobacco research》2007,9(9):907-914
This study assessed the cost-effectiveness of two low-intensity programs for quitting smokeless tobacco, based on results of a randomized trial with 1,069 volunteer participants. Cost data were collected for two levels of intervention: manual only (a self-help manual) and assisted self-help (the manual plus a videotape and two supportive phone calls from tobacco cessation counselors). Incremental cost-effectiveness ratios were calculated for assisted self-help vs. quitting on one's own, using the manual-only quit rate and data from another study as alternative proxies for no intervention. A threshold analysis was conducted to determine the spontaneous quit rate at which the manual-only intervention becomes more cost-effective than assisted self-help. The cost to provide and receive the assisted self-help intervention averaged US $56 per participant vs. $20 for the manual-only intervention (societal perspective, Year 2000 dollars). Estimates for incremental cost per quit for the assisted self-help intervention ranged from $922 to $1,758, depending on the proxy used for no intervention. The manual-only intervention was more cost-effective than assisted self-help if quitting among motivated chewers who do not receive treatment does not exceed 3.4%. Support from a wife or partner added little cost to a quit attempt for male chewers ($3-$4). Providing a manual, video, and brief phone counseling to smokeless tobacco users who want to quit is a reasonable use of health care resources. The self-help quitting guide also may be a cost-effective treatment, but it remains to be demonstrated whether it is more effective than quitting on one's own. 相似文献