全文获取类型
收费全文 | 3439篇 |
免费 | 49篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 23篇 |
综合类 | 6篇 |
化学工业 | 240篇 |
金属工艺 | 24篇 |
机械仪表 | 22篇 |
建筑科学 | 52篇 |
矿业工程 | 3篇 |
能源动力 | 24篇 |
轻工业 | 139篇 |
水利工程 | 31篇 |
石油天然气 | 41篇 |
武器工业 | 1篇 |
无线电 | 114篇 |
一般工业技术 | 264篇 |
冶金工业 | 2366篇 |
原子能技术 | 14篇 |
自动化技术 | 136篇 |
出版年
2021年 | 7篇 |
2020年 | 16篇 |
2019年 | 11篇 |
2018年 | 20篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 21篇 |
2013年 | 54篇 |
2012年 | 31篇 |
2011年 | 70篇 |
2010年 | 44篇 |
2009年 | 35篇 |
2008年 | 46篇 |
2007年 | 39篇 |
2006年 | 39篇 |
2005年 | 53篇 |
2004年 | 37篇 |
2003年 | 55篇 |
2002年 | 63篇 |
2001年 | 42篇 |
2000年 | 24篇 |
1999年 | 94篇 |
1998年 | 733篇 |
1997年 | 453篇 |
1996年 | 276篇 |
1995年 | 168篇 |
1994年 | 136篇 |
1993年 | 139篇 |
1992年 | 40篇 |
1991年 | 52篇 |
1990年 | 39篇 |
1989年 | 49篇 |
1988年 | 49篇 |
1987年 | 33篇 |
1986年 | 37篇 |
1985年 | 34篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 32篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 65篇 |
1976年 | 136篇 |
1975年 | 12篇 |
1974年 | 11篇 |
1973年 | 14篇 |
1971年 | 7篇 |
排序方式: 共有3500条查询结果,搜索用时 0 毫秒
91.
C. V. SUNDARAM A. K. TANEJA CH. SRIDHAR RAO 《Mineral Processing and Extractive Metallurgy Review》2013,34(1):239-265
The reactive and refractory metals zirconium, titanium, tantalum and niobium have been in commercial production and industrial application over the last 30 years and more. With growing experience, there has been progressive improvement in process and equipment designs in the industrial practice. There has also been a continuous drive to develop entirely new processes, and to diversify the applications of these metals. The paper reviews the present status and the emerging trends, and places the Indian work in the global perspective. 相似文献
92.
In this paper discrete-time bilinear systems are considered. Necessary and sufficient conditions are developed which ensure that for any constant input in an unbounded control domain, the trajectories of the system tend to the origin as time increases. 相似文献
93.
With an aim to combine the performance-enhancing properties of Ca with the stability-promoting properties of In in the swedenborgite YBaCo4O7+δ-based cathodes for solid oxide fuel cells (SOFC), cation-substituted Y1−x−yInxCayBaCo3ZnO7+δ (0.2 ≤ (x + y) ≤ 0.5) oxides have been explored. All samples presented in this work are stable in air after 120 h exposure to 600, 700, and 800 °C. Increasing In content shows a negligible impact on polarization resistances (Rp), but causes an increase in the activation energies (Ea) of (Y,In,Ca)BaCo3ZnO7+δ + Gd0.2Ce0.8O1.9 (GDC) composite cathodes on 8 mol% yttria-stabilized zirconia (8YSZ) electrolyte supported symmetric cells. Increasing Ca content shows a decrease in Rp and an increase in Ea on similar electrochemical cells. All (Y,In,Ca)BaCo3ZnO7+δ samples investigated here show superior performance compared to the unsubstituted YBaCo3ZnO7+δ + GDC cathode in the range of 400–800 °C. Especially, the Y0.5In0.1Ca0.4BaCo3ZnO7+δ + GDC composite cathode exhibits good performance on GDC electrolytes in the range of 400–600 °C. With superior phase stability and electrochemical performance, the (Y,In,Ca)BaCo3ZnO7+δ series of oxides are attractive cathode candidates for intermediate temperature SOFCs. 相似文献
94.
Evaluating overall model fit for growth curve models involves 3 challenging issues. (a) Three types of longitudinal data with different implications for model fit may be distinguished: balanced on time with complete data, balanced on time with data missing at random, and unbalanced on time. (b) Traditional work on fit from the structural equation modeling (SEM) perspective has focused only on the covariance structure, but growth curve models have four potential sources of misspecification: within-individual covariance matrix, between-individuals covariance matrix, marginal mean structure, and conditional mean structure. (c) Growth curve models can be estimated in both the SEM and multilevel modeling (MLM) frameworks; these have different emphases for the evaluation of model fit. In this article, the authors discuss the challenges presented by these 3 issues in the calculation and interpretation of SEM- and MLM-based fit indices for growth curve models and conclude by identifying some lines for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
96.
Throughout much of the parallel processing community there is the sense that writing software for distributed-memory parallel processors Is subject to a ‘no pain—no gain’ rule: that In order to reap the benefits of parallel computation one must first suffer the pain of converting the application to run on a parallel machine. We believe this Is the result of Inadequate programming tools and not a problem Inherent to parallel processing. We will show that one can parallelize real scientific applications and obtain good performance with little effort If the right tools are used. Our vehicle for this demonstration is a 6000-line DNA and protein sequence comparison application that we have implemented in Mental, an object-oriented parallel processing system for both parallel and distributed architectures. We briefly describe the application and present performance information for both the Mentat version and a hand-coded parallel version of the application. 相似文献
97.
Manfred Schulz Gerd West Sakum Ourk Ingo Strunz 《Advanced Synthesis \u0026amp; Catalysis》1980,322(2):295-304
Azoperoxides. VI. Selective Decomposition of β-Azoacylperoxides The selective decomposition of the O O-Groups in the azoperoxides 1 and 2 is possible by reaction with dimethylaniline at 35°C. Rate constants were measured and the decomposition products were analyzed. Intermediates are azoalkyl radicals. The radical yield of the amine induced decomposition of 2 in ethylbenzene is 8.2% at 35°C. UV irradiation of the azoperoxides 1 and 2 at 20°C in ethylbenzene results in a quantitative and selective decomposition of the azo groups. Intermediates are C-radicals with intact peroxide groups. The reaction of 1 and 2 with triethylstannane yields reduction products of the O O-groups and the NN-groups, respectively. 相似文献
98.
Effects of heat-stress on production in dairy cattle 总被引:34,自引:0,他引:34
West JW 《Journal of dairy science》2003,86(6):2131-2144
The southeastern United States is characterized as humid subtropical and is subject to extended periods of high ambient temperature and relative humidity. Because the primary nonevaporative means of cooling for the cow (radiation, conduction, convection) become less effective with rising ambient temperature, the cow becomes increasingly reliant upon evaporative cooling in the form of sweating and panting. High relative humidity compromises evaporative cooling, so that under hot, humid conditions common to the Southeast in summer the dairy cow cannot dissipate sufficient body heat to prevent a rise in body temperature. Increasing air temperature, temperature-humidity index and rising rectal temperature above critical thresholds are related to decreased dry matter intake (DMI) and milk yield and to reduced efficiency of milk yield. Modifications including shade, barns which enhance passive ventilation, and the addition of fans and sprinklers increase body heat loss, lowering body temperature and improving DMI. New technologies including tunnel ventilation are being investigated to determine if they offer cooling advantages. Genetic selection for heat tolerance may be possible, but continued selection for greater performance in the absence of consideration for heat tolerance will result in greater susceptibility to heat stress. The nutritional needs of the cow change during heat stress, and ration reformulation to account for decreased DMI, the need to increase nutrient density, changing nutrient requirements, avoiding nutrient excesses and maintenance of normal rumen function is necessary. Maintaining cow performance in hot, humid climatic conditions in the future will likely require improved cooling capability, continued advances in nutritional formulation, and the need for genetic advancement which includes selection for heat tolerance or the identification of genetic traits which enhance heat tolerance. 相似文献
99.
Brett J West Hisanori Tani Afa K Palu Charles B Tolson C Jarakae Jensen 《Journal of the science of food and agriculture》2007,87(14):2583-2588
BACKGROUND: Noni (Morinda citrifolia L.) leaves have a documented history of food use. However, previous safety and antinutrient studies are absent. The current investigation was conducted to assess the utility of noni leaves as food. RESULTS: No evidence of toxicity or differences in weight gain were observed in acute, subacute, and subchronic oral toxicity tests of ethanol–water (1:1 v/v) and hot‐water extracts of noni leaves in mice at doses of 2000, 200, and 20 mg kg?1 body weight, respectively. Acute systemic anaphylaxis tests of the ethanol–water (4:1 v/v) and hot‐water extracts were negative. Further, leaf proteins were readily digested in simulated gastric fluid. Tannic acid concentrations in frozen and dried leaf were 1.6 and 25.8 g kg?1, respectively. Phytic acid was not detected in the raw leaf (<1 g kg?1). The average oxalic acid content was 1 g kg?1 and was fairly uniform among 22 leaf samples from 11 islands throughout French Polynesia. Similarly, campesterol, stigmasterol, and β‐sitosterol content did not vary widely, suggesting low inter‐island content variability. CONCLUSIONS: The apparent lack of toxicity of the leaves and the hardiness of the plant make it ideal for further agricultural development, especially where sustained growth of other food crops is difficult. Copyright © 2007 Society of Chemical Industry 相似文献
100.
The phase diagram for the CuO-rich part of the La2 O3 ─CuO join was redetermined. La2 Cu2 O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7 O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2 O3 ─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9 Ca1.1 Cu2 O5.9 and LaCa2 Cu3 O8.6 , were stable at these temperatures, with three binary phases, Ca2 CuO3 , CaCu2 O3 , and La2 CuO4 . La2 Cu2 O5 and La8 Cu7 O19 were stable only at 1020°C, and did not support solid-solution formation. 相似文献