全文获取类型
收费全文 | 4863篇 |
免费 | 328篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 71篇 |
综合类 | 4篇 |
化学工业 | 1189篇 |
金属工艺 | 74篇 |
机械仪表 | 88篇 |
建筑科学 | 169篇 |
矿业工程 | 18篇 |
能源动力 | 191篇 |
轻工业 | 887篇 |
水利工程 | 24篇 |
石油天然气 | 20篇 |
无线电 | 270篇 |
一般工业技术 | 789篇 |
冶金工业 | 319篇 |
原子能技术 | 21篇 |
自动化技术 | 1059篇 |
出版年
2024年 | 10篇 |
2023年 | 46篇 |
2022年 | 162篇 |
2021年 | 206篇 |
2020年 | 132篇 |
2019年 | 153篇 |
2018年 | 194篇 |
2017年 | 186篇 |
2016年 | 190篇 |
2015年 | 168篇 |
2014年 | 211篇 |
2013年 | 369篇 |
2012年 | 353篇 |
2011年 | 387篇 |
2010年 | 306篇 |
2009年 | 264篇 |
2008年 | 277篇 |
2007年 | 234篇 |
2006年 | 183篇 |
2005年 | 164篇 |
2004年 | 116篇 |
2003年 | 119篇 |
2002年 | 119篇 |
2001年 | 48篇 |
2000年 | 53篇 |
1999年 | 49篇 |
1998年 | 91篇 |
1997年 | 68篇 |
1996年 | 41篇 |
1995年 | 57篇 |
1994年 | 24篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 3篇 |
排序方式: 共有5193条查询结果,搜索用时 78 毫秒
951.
This article demonstrates that the large feed-in tariffs currently guaranteed for solar electricity in Germany constitute a subsidization regime that threatens to reach a level comparable to that of German hard coal production, a notoriously outstanding example of misguided political intervention. Yet, as a consequence of the coexistence of the German Renewable Energy Sources Act (EEG) and the EU Emissions Trading Scheme (ETS), the increased use of renewable energy technologies does not imply any additional emission reductions beyond those already achieved by ETS alone. Similarly disappointing is the net employment balance, which is likely to be negative if one takes into account the opportunity cost of this form of solar photovoltaic (PV) support. Along the lines of the international energy agency [IEA, 2007. Energy policies of IEA countries: Germany, 2007 review. International Energy Agency, OECD, Paris, p. 77], we recommend the immediate and drastic reduction of the magnitude of the feed-in tariffs granted for solar-based electricity. Ultimately, producing electricity on this basis is among the most expensive greenhouse gas abatement options. 相似文献
952.
James Manuel Jae-Kwang Kim Jou-Hyeon Ahn Gouri Cheruvally Ghanshyam S. Chauhan Jae-Won Choi Ki-Won Kim 《Journal of power sources》2008
The inorganic–organic hybrid maghemite (γ-Fe2O3)/polypyrrole (PPy) was synthesized and evaluated as cathode-active material for room temperature lithium batteries. The nanometer-sized core–shell structure of the hybrid consisting of the maghemite core with surface modified by PPy was evidenced from the morphological examination. The cathode fabricated with the as-prepared hybrid material delivered an initial discharge capacity of 233 mAh g−1 and a reversible capacity of ∼62 mAh g−1 after 50 charge–discharge cycles. A much higher performance with an initial discharge capacity of 378 mAh g−1 and a reversible capacity of ∼100 mAh g−1 was achieved with the cathode based on the segregated active material, which was obtained by subjecting the as-prepared hybrid material to an additional ball-milling process. The study demonstrates the promising lithium insertion characteristics of the nanometer-sized core–shell maghemite/PPy particles prepared under optimized conditions for application in secondary batteries. 相似文献
953.
Sandra Almeida Ernesto Rivera Juan Manuel Reyna-González Gloria Huerta Fernando Tapia Martha Aguilar-Martínez 《Synthetic Metals》2009
Two novel thiophene containing monomers (TM): 3-methyltetra(oxyethylene)oxy-4-methylthiophene (TM1) and 3-(((2-aminobenzo-18-crown-6-ethyl)triethoxy)oxy)-4-methylthiophene (TM2) were synthesized and characterized. Both monomers were polymerized in the presence of FeCl3 to give the corresponding copolymer (CPT1). TM2 was also copolymerized in the presence of 3-dodecylthiophene to lead a second copolymer (CPT2). On the other hand, TM1 and TM2 were homopolymerized under the same reaction conditions to give poly[3-methyltetra(oxyethylene)oxy-4-methylthiophene] (PT1) and poly[3-(((2-aminobenzo-18-crown-6-ethyl)triethoxy)oxy)-4-methylthiophene] (PT2), where the former was used as reference compound. Solvatochromic and thermochromic behaviors of these polymers were investigated. All polymers exhibited solvatochromism; in a mixture of chloroform–methanol 20:80, CPT1 gives a violet solution and its polymer backbone adopts a planar conformation. By contrast, in chloroform CPT1 adopts a twisted conformation, giving an orange solution. This copolymer exhibits also an extended conjugation length in the solid state at room temperature (dark red) and a less conjugated conformation after heating (yellow). CPT2 shows a similar thermochromic behavior as CPT1 in chloroform, but in the solid state its color changes from dark red to orange. 相似文献
954.
This paper describes a one-dimensional mathematical model that allows simulating the heat exchange in a steam generator working with water at supercritical pressure. The model has been developed in order to simulate the full and part load behaviour of heat recovery steam generators (HRSGs) of combined cycle gas turbine (CCGT) power plants. It takes into account the strong variation of some of the thermal and transport properties of fluids at supercritical pressure and discusses what parameters may be considered as constant along the heat exchanger.On the one hand, the model is useful because going supercritical is considered a way to further improve the efficiency of CCGT power plants and, on the other hand, because part load operation is the most usual operation mode in power plants. 相似文献
955.
Ana M. Aguilera Manuel Escabias Gilbert Saporta 《Chemometrics and Intelligent Laboratory Systems》2010,104(2):289-305
There are many chemometric applications, such as spectroscopy, where the objective is to explain a scalar response from a functional variable (the spectrum) whose observations are functions of wavelengths rather than vectors. In this paper, PLS regression is considered for estimating the linear model when the predictor is a functional random variable. Due to the infinite dimension of the space to which the predictor observations belong, they are usually approximated by curves/functions within a finite dimensional space spanned by a basis of functions. We show that PLS regression with a functional predictor is equivalent to finite multivariate PLS regression using expansion basis coefficients as the predictor, in the sense that, at each step of the PLS iteration, the same prediction is obtained. In addition, from the linear model estimated using the basis coefficients, we derive the expression of the PLS estimate of the regression coefficient function from the model with a functional predictor. The results provided by this functional PLS approach are compared with those given by functional PCR and discrete PLS and PCR using different sets of simulated and spectrometric data. 相似文献
956.
Manuel Perez-Tello Hong Yong Sohn Philip John Smith 《Metallurgical and Materials Transactions B》2001,32(5):869-886
A fluid-dynamics computer model of the flash-converting furnace shaft, which is based on basic principles, is presented. The
model is fully three-dimensional and incorporates the transport of momentum, heat, and mass and the reaction kinetics between
the gas and particles in a particle-laden turbulent gas jet. The k-ɛ model was used to describe gas-phase turbulence in an Eulerian framework. The particle-cloud model was used to track the
particle phase in a Lagrangian framework. The coupling of gas and particle equations was performed through the source terms
in the Eulerian gas-phase governing equations. Copper matte particles were represented as Cu2S · yFeS
x
. Based on experimental observation, the oxidation products were assumed to be Cu2O, CuO, Fe3O4, and SO2. A reaction mechanism involving the external mass transfer of oxygen from the gas to the particle surface and diffusion of
the oxygen through the successive layers of Cu2O-Fe3O4 and CuO-Fe3O4 was proposed. The predictions of the computer model were compared with the experimental data collected in a large laboratory
furnace. Reasonable agreement between the model predictions and the measurements was obtained in terms of the fractional completion
of the oxidation reactions and the sulfur remaining in the reacted particles. The relevance of the computational model for
further analysis and optimization of an industrial flash-converting operation is discussed. 相似文献
957.
M. Ángeles Gil M. Teresa López-García M. Asunción Lubiano Manuel Montenegro 《TEST》2001,10(1):183-201
In this paper we develop regression and corrclation analyses of a certain general linear relation between two random elements
whose values are non-empty compact intervals. To this purpose, we firstly extend the least-squares method to deal with the
involved random elements on the basis of a generalized metric defined on the space of the considered intervals. As a complementary
study, a coefficient quantifying the strength of the linear relation between the two random elements is also presented, and
a discussion of the extreme values for this measure is presented. A real-life example illustrates these studies.
Research partially supported by DGESIC/MEC Grants No. DGE-99-PB98-1534 and No. DGE-98-PB97-1282. 相似文献
958.
Beatriz Cardees Irene Clares Víctor Toribio Lucía Pascual Soraya Lpez-Martín Alvaro Torres-Gomez Ricardo Sainz de la Cuesta Esther M. Lafuente Manuel Lpez-Cabrera María Yez-M Carlos Cabaas 《International journal of molecular sciences》2021,22(18)
Approximately 25% of colorectal cancer (CRC) patients develop peritoneal metastasis, a condition associated with a bleak prognosis. The CRC peritoneal dissemination cascade involves the shedding of cancer cells from the primary tumor, their transport through the peritoneal cavity, their adhesion to the peritoneal mesothelial cells (PMCs) that line all peritoneal organs, and invasion of cancer cells through this mesothelial cell barrier and underlying stroma to establish new metastatic foci. Exosomes produced by cancer cells have been shown to influence many processes related to cancer progression and metastasis. In epithelial ovarian cancer these extracellular vesicles (EVs) have been shown to favor different steps of the peritoneal dissemination cascade by changing the functional phenotype of cancer cells and PMCs. Little is currently known, however, about the roles played by exosomes in the pathogenesis and peritoneal metastasis cascade of CRC and especially about the molecules that mediate their interaction and uptake by target PMCs and tumor cells. We isolated exosomes by size−exclusion chromatography from CRC cells and performed cell-adhesion assays to immobilized exosomes in the presence of blocking antibodies against surface proteins and measured the uptake of fluorescently-labelled exosomes. We report here that the interaction between integrin α5β1 on CRC cells (and PMCs) and its ligand ADAM17 on exosomes mediated the binding and uptake of CRC-derived exosomes. Furthermore, this process was negatively regulated by the expression of tetraspanin CD9 on exosomes. 相似文献
959.
Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Hisayuki Imamura Kiyoshi Hirao Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(3):495-500
Si3 N4 ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike β-Si3 N4 particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f 0 , was affected by seed size, and small-seed addition led to the highest f 0 value. This material exhibited high bending strength (∼1.4 GPa) and high fracture toughness (∼12 MPa. m1/2 ) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure. 相似文献
960.
Review of book: Manuel Furer, Edward Nersessian, and Carmela Perri (Eds.) Controversies in contemporary psychoanalysis: Lectures from the faculty of the New York Psychoanalytic Association. Madison, CT: International Universities Press, 1998, xiv + 197 pp.. Reviewed by Antonio R. Virsida (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献