全文获取类型
收费全文 | 116995篇 |
免费 | 4594篇 |
国内免费 | 2556篇 |
专业分类
电工技术 | 3469篇 |
技术理论 | 2篇 |
综合类 | 4894篇 |
化学工业 | 16859篇 |
金属工艺 | 6445篇 |
机械仪表 | 4832篇 |
建筑科学 | 5249篇 |
矿业工程 | 1601篇 |
能源动力 | 1968篇 |
轻工业 | 6999篇 |
水利工程 | 1994篇 |
石油天然气 | 1962篇 |
武器工业 | 335篇 |
无线电 | 13162篇 |
一般工业技术 | 19991篇 |
冶金工业 | 3857篇 |
原子能技术 | 720篇 |
自动化技术 | 29806篇 |
出版年
2024年 | 148篇 |
2023年 | 722篇 |
2022年 | 1294篇 |
2021年 | 1725篇 |
2020年 | 1405篇 |
2019年 | 1067篇 |
2018年 | 15549篇 |
2017年 | 14521篇 |
2016年 | 11008篇 |
2015年 | 2155篇 |
2014年 | 2174篇 |
2013年 | 2502篇 |
2012年 | 5758篇 |
2011年 | 12053篇 |
2010年 | 10457篇 |
2009年 | 7548篇 |
2008年 | 8724篇 |
2007年 | 9568篇 |
2006年 | 1852篇 |
2005年 | 2609篇 |
2004年 | 2045篇 |
2003年 | 1955篇 |
2002年 | 1236篇 |
2001年 | 753篇 |
2000年 | 892篇 |
1999年 | 701篇 |
1998年 | 559篇 |
1997年 | 451篇 |
1996年 | 456篇 |
1995年 | 325篇 |
1994年 | 312篇 |
1993年 | 224篇 |
1992年 | 199篇 |
1991年 | 164篇 |
1990年 | 107篇 |
1989年 | 100篇 |
1988年 | 63篇 |
1987年 | 42篇 |
1986年 | 35篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 43篇 |
1965年 | 44篇 |
1960年 | 30篇 |
1959年 | 45篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 955 毫秒
991.
A commercial Co---Mo/Al2O3 catalyst was labeled with the radioisotope 35S in hydrodesulfurization (HDS) of 35S-labeled dibenzothiophene (35S-DBT) in a high-pressure flow reactor at 50 kg/cm2. Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H2S were carried out on the labeled catalyst at 50 kg/cm2 and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of 35S---H2S released from the 35S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT> 4-MDBT> 4,6-DMDBT. In the sulfur exchange reaction with H2S, the adsorption of H2S on the catalyst reached saturation above a H2S partial pressure of 0.36 kg/cm2. It was suggested that the release of H2S from the labile sulfur may be the rate determining step of the HDS reaction. 相似文献
992.
Supramolecular assemblies from chitosan-graft-β-cyclodextrin (CS-g-CD) and benzimidazole ended poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL-BM) were formed based on the inclusion complexation between β-cyclodextrin and benzimidazole. The supra-amphiphiles self-assembled into complex vesicles with PCL/β-CD as the hydrophobic membrane, hydrophilic PEG and CS as the corona. The hydrophobic membrane and aqueous lumen of vesicles exhibited efficient entrapment both for hydrophobic curcumin (CUR) and hydrophilic doxorubicin (DOX). The drug loading of vesicles was more than 20.2% and 38.4% for CUR and DOX, respectively. Decreasing pH to acidic condition or increasing temperature, more controllable and rapid release of two drugs was observed. Cytotoxicity assays revealed that dual drug-loaded vesicles retained high cell proliferation inhibition efficiency than free drugs.GRAPHICAL ABSTRACT 相似文献
993.
专利申请号:01129726.3公开号:1412382专利名称:可持续释放香味的纺织品或纸制品的生产方法本发明是采用微分子保留剂包裹香料分子,直接与纤维物相结合,从而制成一种可持续释放香味的纺织品或纸制品,这些纺织品或纸制品在静止状态时能释放出清香优雅的气味,而当纤维遇到摩擦或温度升高时,能立即释放出浓郁的香味。其特征是把香料或其衍生物与分散剂、保留剂、乳化剂、去离子水经低、高速搅拌制成组合互溶物,把纤维物置于互溶物中浸泡、脱水、烘干而成为成品。其成品能自然释放出愉悦的芳香气味,令人精神爽利,并具有杀菌、驱虫、除臭等功效。… 相似文献
994.
995.
996.
Julian Chojnowski Slawomir Rubinsztajn Witold Fortuniak Jan Kurjata 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):173-187
Summary Reactions of hexamethylcyclotrisiloxane, D3, with 1,1,3,3-tetramethyldisiloxane, HMMH, 1,1,1,3,3-pentamethyldisiloxane, HMM, phenyldimethylsilane and phenylmethylsilane catalyzed by tris(pentafluorophenyl)borane were studied. These reactions lead
to ring opening of D3 by the SiH reactant producing open chain oligomers with hydrosilane functionality at one or both chain ends. The reactivity
of the hydrosilanes toward D3 decreases in the series: PhMeSiH2 > HMMH > PhMe2SiH > HMM. Competitive self-oligomerization of HMMH and HMM also occurs. Primary products of these processes are able to enter into reactions with the SiH and D3 reactants; some also undergo cyclization. Thus, consecutive and competitive processes lead to a series of various oligohomologues.
Gas chromatography in conjunction with chemical ionization mass spectroscopy permitted identification of structure and determination
of the basic directions of these oligomerization processes. Polysiloxanes of higher molecular weight may be also formed in
some of these systems. The reactions, which occur in the systems studied, are rationalized on the basis of the mechanism involving
the hydride transfer from silicon to trivalent boron. This includes the transient formation of tertiary trisilyloxonium borate
which decomposes by the hydride transfer to one of the silicon atoms of the trisilyloxonium center.
Footnote: This paper is dedicated to Professor Ian Manners in recognition of his significant contributions to the field of
organometallic polymers. 相似文献
997.
Marwa A. Abd El-Fattah Moawad I. Dessouky Alaa M. Abbas Salaheldin M. Diab El-Sayed M. El-Rabaie Waleed Al-Nuaimy Saleh A. Alshebeili Fathi E. Abd El-samie 《International Journal of Speech Technology》2014,17(1):53-64
This paper proposes an adaptive Wiener filtering method for speech enhancement. This method depends on the adaptation of the filter transfer function from sample to sample based on the speech signal statistics; the local mean and the local variance. It is implemented in the time domain rather than in the frequency domain to accommodate for the time-varying nature of the speech signals. The proposed method is compared to the traditional frequency-domain Wiener filtering, spectral subtraction and wavelet denoising methods using different speech quality metrics. The simulation results reveal the superiority of the proposed Wiener filtering method in the case of Additive White Gaussian Noise (AWGN) as well as colored noise. 相似文献
998.
Thomas Uchida Alfonso Callejo Javier García de Jalón John McPhee 《Multibody System Dynamics》2014,31(3):371-392
Efficient dynamic simulation code is essential in many situations (including hardware-in-the-loop and model-predictive control applications), and highly beneficial in others (such as design optimization, sensitivity analysis, parameter identification, and controller tuning tasks). When the number of modeling coordinates n exceeds the degrees-of-freedom of the system f, as is often the case when closed kinematic chains are present, the governing dynamic equations consist of n second-order ordinary differential equations (ODEs) coupled with m=n?f algebraic constraint equations. This set of n+m index-3 differential-algebraic equations can be difficult to solve in an efficient yet accurate manner. Embedding (or generalized coordinate partitioning) can be used to obtain f ODEs (one for each independent acceleration), which are generally more amenable to numerical integration; however, the dependent positions are typically computed from the independent positions at each time step. Newton–Raphson iteration is often used for solving the position-level kinematics, but only provides solutions to within a specified tolerance, and can require several iterations to converge. In this work, Gröbner bases are used to obtain recursively solvable symbolic solutions for the dependent positions, which can then be evaluated to within machine precision using a fixed number of arithmetic operations. Natural coordinates are particularly attractive in this context, since the resulting constraint equations are maximally quadratic polynomials and are, therefore, easily triangularized. The proposed approach is suitable for use in an automated formulation procedure and, as demonstrated by three examples, is capable of generating highly efficient simulation code with minimal additional effort required at the formulation stage. 相似文献
999.
Dynamics modeling and analysis of a flexible-base space robot for capturing large flexible spacecraft 总被引:2,自引:0,他引:2
Wenfu Xu Deshan Meng Yongquan Chen Huihuan Qian Yangsheng Xu 《Multibody System Dynamics》2014,32(3):357-401
Space robots are in huge demand due to the rapid growth of their service targets, i.e., spacecraft. There are generally large flexible components on spacecraft, such as antenna reflectors and solar paddles. Due to the vibratility of their structure, it is challenging for a space robot with flexible appendages (the base is then called flexible-base) to capture and repair the large flexible spacecraft. After capturing, the two spacecraft with flexible appendages are connected by a space manipulator, and a compounded system is formed. In this paper, we developed a dynamic model and a closed-loop simulation system, to provide a means to verify path planning and control algorithms. Initially, the dynamic characteristics of different capturing stages (preimpact and post-impact) were analyzed. The topologies of a flexible-base space robot and the compounded system were described based on incidence and channel matrices. Secondly, the recursive dynamics was formulated and resolved by an effective numerical method. The modeling was verified by Adams’ model. Thirdly, we implemented a dynamics calculation block in Matlab/Simulink environment using the S-function package for the C program, and developed a closed-loop simulation system, which was composed of the Planning and Controller, the Multibody Dynamic, and the 3D Display modules. Finally, based on the simulation system, two typical missions—target berthing and on-orbital manipulation of the target along a circle, were simulated and evaluated. Dynamics analysis results presented some useful rules for the path planning and control to suppress the vibration of the flexible structure. 相似文献
1000.
Large volume of online review data can reveal consumers’ major interests on domain product, which attracts great research interests from the academic community. Most of the existing works focus on the problems of review summarization, aspect identification or opinion mining from an item’s point of view such as the quality or popularity of products. Considering the fact that users who generate those review texts draw different attentions to product aspects with respect to their own interests, in this article, we aim to learn K users’ interest groups indicated by their review writings. Such K interest groups’ identification can facilitate better understanding of major and potential consumers’ concerns which are crucial for applications like product improvement on customer-oriented design or diverse marketing strategies. Instead of using a traditional text clustering approach, we treat the groupId/clusterId as a hidden variable and use a permutation-based structural topic model called KMM. Through this model, we infer K interest groups’ distribution by discovering not only the frequency of product aspects (Topic Frequency), but also the occurrence priority of respective aspects (Topic Order). They jointly present an informative summarization on the raw review corpus. Our experiment on several real-world review datasets demonstrates a competitive solution. 相似文献