全文获取类型
收费全文 | 18572篇 |
免费 | 3612篇 |
国内免费 | 2935篇 |
专业分类
电工技术 | 1238篇 |
技术理论 | 2篇 |
综合类 | 2069篇 |
化学工业 | 1485篇 |
金属工艺 | 237篇 |
机械仪表 | 764篇 |
建筑科学 | 1313篇 |
矿业工程 | 294篇 |
能源动力 | 545篇 |
轻工业 | 582篇 |
水利工程 | 252篇 |
石油天然气 | 497篇 |
武器工业 | 136篇 |
无线电 | 2890篇 |
一般工业技术 | 1434篇 |
冶金工业 | 366篇 |
原子能技术 | 156篇 |
自动化技术 | 10859篇 |
出版年
2024年 | 137篇 |
2023年 | 409篇 |
2022年 | 699篇 |
2021年 | 819篇 |
2020年 | 924篇 |
2019年 | 822篇 |
2018年 | 831篇 |
2017年 | 955篇 |
2016年 | 1053篇 |
2015年 | 1103篇 |
2014年 | 1385篇 |
2013年 | 1448篇 |
2012年 | 1632篇 |
2011年 | 1826篇 |
2010年 | 1408篇 |
2009年 | 1352篇 |
2008年 | 1405篇 |
2007年 | 1539篇 |
2006年 | 1069篇 |
2005年 | 869篇 |
2004年 | 657篇 |
2003年 | 534篇 |
2002年 | 424篇 |
2001年 | 319篇 |
2000年 | 263篇 |
1999年 | 238篇 |
1998年 | 165篇 |
1997年 | 156篇 |
1996年 | 125篇 |
1995年 | 123篇 |
1994年 | 76篇 |
1993年 | 53篇 |
1992年 | 46篇 |
1991年 | 40篇 |
1990年 | 44篇 |
1989年 | 26篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Xin Song Xiaoyu Qi Bin Hao Yinbo Qu 《European Journal of Lipid Science and Technology》2008,110(12):1095-1101
Although lipases are widely applied in a wide variety of reactions, available information on the factors that are responsible for the substrate specificities of lipases from different sources is scarce. In this paper, nine lipase‐producing microorganism strains were isolated from oil‐containing samples. The properties of these enzymes, including pH optima, temperature optima, thermal stability, and pH stability, vary significantly with the different sources from which these lipases were isolated. The substrate specificities of the nine lipases, including fatty acid and positional specificities, were also studied. The fatty acid specificities of the nine lipases were observably different toward 15 substrates with different carbon chain lengths, different saturation degrees and different side chains. The lipases from S3 Penicillium citrinum (PCL), MJ1 Aspergillus niger (ANL), MJ2 Aspergillus oryzae (AOL), YM Bacillus coughing (BCL), S9 Geotrichum candidum (GCL), and S11 Candida lypolytica (CLL) showed the strongest specificities to short‐chain esters, and the other lipases showed strong selectivity for medium‐ or long‐chain and branched esters. The positional specificities were examined by analyzing the hydrolytic products of triolein catalyzed by the nine lipases, using TLC. The lipases can be mainly classified into two groups by their specificities for the ester bond at position 2 of triglycerides; one group can selectively hydrolyze the ester bond at position 2 of the triglycerides, the other group cannot. All these nine lipases were divided into four groups by hierarchical clustering analysis on the basis of the results of fatty acid and positional specificities. 相似文献
53.
厦门市气源转换的技术分析 总被引:3,自引:2,他引:1
分析了气源转换时原有输配系统的管道、调压设备、计量设备、用气设备与天然气系统相适应的问题,提出了相应的措施。 相似文献
54.
In this paper we present the results of a simulation study to explore the ability of Bayesian parametric and nonparametric models to provide an adequate fit to count data of the type that would routinely be analyzed parametrically either through fixed-effects or random-effects Poisson models. The context of the study is a randomized controlled trial with two groups (treatment and control). Our nonparametric approach uses several modeling formulations based on Dirichlet process priors. We find that the nonparametric models are able to flexibly adapt to the data, to offer rich posterior inference, and to provide, in a variety of settings, more accurate predictive inference than parametric models. 相似文献
55.
给出平凹谐振腔和凹平凹谐振腔失调时光轴确定方法。在二维轴对称折迭-组合腔 激光器小角度失调运行时,对非相干并和和相干并和后的输出光束的近场强度分布做了分析和模拟。结果表明:小角度失调对4cm以内的近场影响不大,光强分布仍具有高斯状分布;对4cm以外的近场影响较大,光强分布发生相应的形变,且随着失调角度变大而变大。 相似文献
56.
Many research projects require accurate delineation of different secondary succession (SS) stages over large regions/subregions of the Amazon basin. However, the complexity of vegetation stand structure, abundant vegetation species, and the smooth transition between different SS stages make vegetation classification difficult when using traditional approaches such as the maximum likelihood classifier (MLC). Most of the time, classification distinguishes only between forest/non-forest. It has been difficult to accurately distinguish stages of SS. In this paper, a linear mixture model (LMM) approach is applied to classify successional and mature forests using Thematic Mapper (TM) imagery in the Rondônia region of the Brazilian Amazon. Three endmembers (i.e., shade, soil, and green vegetation or GV) were identified based on the image itself and a constrained least-squares solution was used to unmix the image. This study indicates that the LMM approach is a promising method for distinguishing successional and mature forests in the Amazon basin using TM data. It improved vegetation classification accuracy over that of the MLC. Initial, intermediate, and advanced successional and mature forests were classified with overall accuracy of 78.2% using a threshold method on the ratio of shade to GV fractions, a 7.4% increase over the MLC. The GV and shade fractions are sensitive to the change of vegetation stand structures and better capture biophysical structure information. 相似文献
57.
Calculation methods for comparing the performance of pure and mixed working fluids in heat pump applications 总被引:2,自引:0,他引:2
Three methods for comparing cycle performance of working fluids, pure as well as non-azeotropic mixtures, are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively, equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition are explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures. 相似文献
58.
Existence results for the LQG-controller are investigated. An infimal Riccati equation based controller may potentially give closed loop eigenvalues on the unit circle. Assuming left and right invertibility it is shown that there exists an optimal controller if and only if the Riccati equation based controller stabilizes the closed loop system after removal of all its unobservable and uncontrollable modes. Furthermore this reduced controller is the optimal controller, and its transfer function is unique. This existence condition is a considerable simplification of the more general geometric condition recently derived by Trentelman and Stoorvogel. 相似文献
59.
Poly(4-methylstyrene)-graft-poly(ethylene oxide)s were prepared via polymerisation of ethylene oxide on to poly(4-methylstyrene)s functionalised with hydroxyl groups. In this way, many ‘comb-like’ polymers having different hydrophobic backbone length, hydrophilic branch length and frequency of branches were synthesised. These polymers were tested as dispersants in coal-water mixtures in order to correlate the dispersing properties of this class of polymers with the investigated parameters. 相似文献
60.