全文获取类型
收费全文 | 5733篇 |
免费 | 172篇 |
国内免费 | 17篇 |
学科分类
工业技术 | 5922篇 |
出版年
2023年 | 50篇 |
2022年 | 76篇 |
2021年 | 132篇 |
2020年 | 120篇 |
2019年 | 121篇 |
2018年 | 152篇 |
2017年 | 147篇 |
2016年 | 124篇 |
2015年 | 101篇 |
2014年 | 141篇 |
2013年 | 375篇 |
2012年 | 209篇 |
2011年 | 275篇 |
2010年 | 225篇 |
2009年 | 223篇 |
2008年 | 236篇 |
2007年 | 196篇 |
2006年 | 194篇 |
2005年 | 193篇 |
2004年 | 149篇 |
2003年 | 131篇 |
2002年 | 113篇 |
2001年 | 115篇 |
2000年 | 88篇 |
1999年 | 107篇 |
1998年 | 221篇 |
1997年 | 163篇 |
1996年 | 116篇 |
1995年 | 81篇 |
1994年 | 114篇 |
1993年 | 107篇 |
1992年 | 89篇 |
1991年 | 68篇 |
1990年 | 61篇 |
1989年 | 49篇 |
1988年 | 62篇 |
1987年 | 55篇 |
1986年 | 52篇 |
1985年 | 73篇 |
1984年 | 58篇 |
1983年 | 48篇 |
1982年 | 39篇 |
1981年 | 50篇 |
1980年 | 41篇 |
1979年 | 38篇 |
1978年 | 38篇 |
1977年 | 45篇 |
1976年 | 46篇 |
1974年 | 32篇 |
1973年 | 35篇 |
排序方式: 共有5922条查询结果,搜索用时 265 毫秒
21.
Irvin Roy Hentzel 《Computers & Mathematics with Applications》1991,22(12):61-66
We are interested in deciding if a given nonassociative polynomial h is an identity for a variety of nonassociative algebras. We present an algorithm for constructing a certain homomorphic image of a free nonassociative algebra which is sufficient to answer the question. The algorithm resembles dynamic programming in that the algebra is built by constructing a sequence of subspaces; the basis of each subspace is determined by the basis of previous subspaces. The number of arithmetic operations required to construct the algebra is bounded by a polynomial in the degree of h and the dimension of the resulting algebra. 相似文献
22.
23.
24.
Identification of a specific biomolecular target appropriately sensitive to a wide array of anesthetics has been elusive. At concentrations close to their respective ED50's for anesthesia in man or other species, 18 compounds, differing in potencies up to 66,000 fold, inhibited cytochrome P450 mediated metabolism of aminopyrine, a synthetic substrate, and arachidonic acid (AA), an endogenous substrate, in isolated liver microsomes. There was a highly significant correlation for both substrates between the absolute concentrations required for anesthesia (EC50) and for inhibition of P450 activity (Ki or IC50). The mean Ki/EC50 ratio was 0.97 for inhibition of aminopyrine demethylase. The mean IC50/EC50 ratios were 0.42 and 0.64 for inhibition of two AA-derived products and 2.8 for a third; a mean ratio of 1.4 for inhibition of overall AA metabolism suggests interaction of general anesthetics with a composite of P450 isozymes. The universal cytochrome P450 monooxygenases, in conjunction with other lipid oxygenases (cyclooxygenases and lipoxygenases) participate in the second messenger AA cascade. In nerve cells the sensitivity of these enzymes to hydrophobic neurodepressant drugs may underlie the state of general anesthesia: reversible disruption of intracellular and intercellular signalling without impairment of enzymes vital to cell respiration. 相似文献
25.
Also with the Department of Agronomy. 相似文献
26.
On-body communications around the human torso are considered, using ultra-wideband transmissions. The velocity of the diffracted wave propagating around the body is extracted from frequency- domain spatial correlation analyses. 相似文献
27.
L. J. Singh S. Choudhury S. Singha Roy K. P. Ghatak 《Electrical Engineering (Archiv fur Elektrotechnik)》2005,87(1):1-9
An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs2, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions. 相似文献
28.
Roy S. Berns 《Color research and application》2007,32(4):334-335
The term “color gamut” historically has been associated with color output such as optimal color stimuli and additive and subtractive imaging systems. Recently, this term has been used with input devices such as scanners and digital cameras. It is proposed that the term “color‐gamut rendering” should be used instead of input devices. This clarifies the distinction between input (analysis) and output (synthesis) color systems in terms of the effect of an input system on defining the colorimetric properties of an output system. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 334–335, 2007 相似文献
29.
This paper describes the spatial distribution of customer demand, supply of customer services and facility investment, as the outcome of a three-level game-like interaction between customers (e.g., shoppers), suppliers (e.g., retailers) and developers (e.g., landlords). Treating both the suppliers and developers at each centre as competitors, oligopolistic equilibria of the Nash-Stackelberg type are developed, and conditions for their existence and uniqueness established. Uncertain customer demand is specified in probabilistic terms, representing the suppliers' perception of expected customer behaviour. 相似文献
30.
Nanosized lead zirconate titanate (PZT) powder with Zr:Ti ratio in the morphotropic phase boundary region was synthesized by homogeneous precipitation of metal ions. The powder precipitated at 90°C and at pH 6.7 resulted single-phase perovskite lead zirconate titanate powder when calcined at 550°C and above for 4 hours in air. The solution pH and the precipitation temperature strongly affect the composition of the calcined powder. The results obtained by structural characterization of homogeneously precipitated powder were compared with that obtained from the conventional precipitation method using ammonia in terms of crystallization, homogeneity, and microstructure. The homogeneously precipitated powder showed smaller particle size, minimum agglomeration and uniform shape on calcination and annealing. Powdered samples that precipitated by homogeneous precipitation crystallized directly to perovskite PZT, without any intermediate pyrochlore phase formation. In contrast, the NH3 precipitated powder converted to perovskite PZT via metastable pyrochlore and it showed phase segregation upon annealing at higher temperatures. The reaction kinetics has been studied by X-ray diffraction, differential thermal analysis, and differential scanning calorimetry. 相似文献