全文获取类型
收费全文 | 4294篇 |
免费 | 302篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 65篇 |
综合类 | 15篇 |
化学工业 | 1043篇 |
金属工艺 | 91篇 |
机械仪表 | 85篇 |
建筑科学 | 165篇 |
矿业工程 | 40篇 |
能源动力 | 86篇 |
轻工业 | 431篇 |
水利工程 | 26篇 |
石油天然气 | 1篇 |
无线电 | 318篇 |
一般工业技术 | 879篇 |
冶金工业 | 667篇 |
原子能技术 | 15篇 |
自动化技术 | 672篇 |
出版年
2023年 | 70篇 |
2022年 | 76篇 |
2021年 | 151篇 |
2020年 | 125篇 |
2019年 | 101篇 |
2018年 | 157篇 |
2017年 | 140篇 |
2016年 | 178篇 |
2015年 | 155篇 |
2014年 | 213篇 |
2013年 | 259篇 |
2012年 | 245篇 |
2011年 | 280篇 |
2010年 | 165篇 |
2009年 | 200篇 |
2008年 | 193篇 |
2007年 | 176篇 |
2006年 | 129篇 |
2005年 | 110篇 |
2004年 | 100篇 |
2003年 | 86篇 |
2002年 | 59篇 |
2001年 | 64篇 |
2000年 | 43篇 |
1999年 | 69篇 |
1998年 | 184篇 |
1997年 | 127篇 |
1996年 | 94篇 |
1995年 | 66篇 |
1994年 | 46篇 |
1993年 | 49篇 |
1992年 | 18篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 28篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 39篇 |
1974年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有4599条查询结果,搜索用时 15 毫秒
1.
Pyrolysis experiments were performed in high vacuum and under reduced air pressure (100 Pa). The volatile products of pure cellulose and cellulose containing various amounts of flame retardant 2,2′-oxybis (5,5-dimethyl-1,3,2-dioxaphosphorinane-2,2′-disulfide), i.e., Sandoflam 5060 of Sandoz AG, were studied by means of gas chromatography in combination with mass spectroscopy. The volatile products were characterized with infrared spectroscopy. The studied revealed that the incorporation of the flame retardant enhanced the water release and shifted the onset of this reaction to lower temperature. On the basis of these findings an explanation for the mechanism of flame retardancy in generated cellulose fibers modified with this particular flame retardant is attempted. From experiments with different residual air pressure the influence of oxygen on the primary processes of the pyrolytic degradation of cellulose is being discussed. 相似文献
2.
Heidi Bernas Arie J. Plomp Johannes H. Bitter Dmitry Yu. Murzin 《Catalysis Letters》2008,120(1-2):8-13
The density functional theory (DFT/B3LYP) calculations were applied to investigate the interaction of a Pt6 particle with the ZSM-5 zeolite framework. The electronic structure of the metal particle is strongly affected by the interaction with basic framework oxygens and acid sites of the zeolite support. Adsorption on basic sites (Eads = 6 kcal/mol) favors the formation of the electron enriched metal cluster. Interaction of the platinum cluster with the acid site characterized by stabilization energy of 47 kcal/mol results in oxidation of the metal particle and suppression of Brønsted acidity of the support. The hypothesis is put forward that the oxidized platinum particle can function as an active site for the alkane isomerisation on platinum supported high silica zeolites. 相似文献
3.
Pre-pruning and Post-pruning are two standard techniques for handling noise in decision tree learning. Pre-pruning deals with noise during learning, while post-pruning addresses this problem after an overfitting theory has been learned. We first review several adaptations of pre- and post-pruning techniques for separate-and-conquer rule learning algorithms and discuss some fundamental problems. The primary goal of this paper is to show how to solve these problems with two new algorithms that combine and integrate pre- and post-pruning. 相似文献
4.
S Benk? S Drabant G Grézal I Urm?s M Cs?rg? I Klebovich 《Canadian Metallurgical Quarterly》1997,47(8):913-916
A comparative pharmacokinetic study has been performed in 19 healthy male volunteers in a single-dose, randomized, two way cross-over design with two preparations of gemfibrozil (CAS 25812-30-0) capsules each of them containing 300 mg active ingredient. The test preparation was Innogem 300 mg capsule. The plasma concentration of gemfibrozil was determined by a validated HPLC-UV analytical method. The statistical comparison of individual pharmacokinetic parameters (AUC0-16, AUC0-oc Cmax, tmax) of the two capsule preparations was performed by three-way analysis of variance (ANOVA), Wilcoxon's, Westlake's, Schuirmann's and Hanck-Anderson's method as well as by the calculation of confidence intervals on the ratio of test/reference. The relative bioavailability of the test preparation with respect to the reference preparation in terms of the AUC0-oc was 104.06 +/- 21.61%. No statistically significant difference was found between the pharmacokinetic parameters, calculated from plasma concentration-time curves, indicating that the two preparations were bioequivalent. 相似文献
5.
R. Meyer Hilde Hardtdegen R. Carius D. Grützmacher M. Stollenwerk P. Balk A. Kux B. Meyer 《Journal of Electronic Materials》1992,21(3):293-298
This paper presents a study of the structural and optical properties of strained GaInAs/ InP multiple quantum well (MQW) structures
fabricated by LP-MOVPE. The composition of the Ga
x
In1−x
As films ranged fromx = 0.17 tox = 1.0 and was determined by sputtered neutral mass spectrometry (SNMS) on thick layers. The structures of the MQW samples
with well widths from 1.5 to 5 nm were investigated by high resolution x-ray diffraction (HR-XRD). Simulations of the diffraction
patterns showed that transition layers of approximately 2 monolayer (ML) thickness with high lattice mismatch exist at the
interfaces. Photoluminescence (PL) measurements indicate well widths of a multiple of a monolayer with local variations of
one monolayer. The PL peak energies vary smoothly with the Ga concentration. These results were confirmed by optical absorption
measurements. 相似文献
6.
The improved performance of gain-coupled DFB lasers incorporating a titanium surface Bragg grating and a strained layer multiquantum well active region for operation at 1.55 μm is presented. Besides the essentially simplified fabrication process, the incorporation of the metallic, absorptive grating yields stable singlemode operation with a high sidemode suppression 相似文献
7.
Olivier Klein Steve Donovan Martin Dressel George Grüner 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(12):2423-2457
This report reviews the analysis used to extract the complex conductivity of a compound from a microwave cavity perturbation measurement. We intend to present a generalized treatment valid for any spheroidally shaped sample of arbitrary conductivity which is placed at either the electric or magnetic field antinode of the cavity. To begin with, we establish the relationship between the measured parameters and the conductivity for a spherical sample. Next, we extend these results to the case of spheroids; and for the first time, we cover all different configurations that one can possibly use to study an arbitrary conducting sample inside a cavity: in particular, all possible orientations of the sample with respect to the applied field are solved. 相似文献
8.
Droplet formation on Si surfaces bombarded by 10 keV beams from a liquid metal indium ion source has been observed. It has been verified that excess indium is transported in the ion beam, probably in the form of charged droplets. SIMS, SEM and RBS techniques have been used to study the distribution of droplets at the surface. At the specified ion source operating conditions, equilibrium droplet coverage is of the order of 25%. Individual droplets have an average diameter of 0.35 ωm and an average height of 2.2 nm. At a bombardment current density of 0.1 mA cm?2, equilibrium coverage is reached in about 1 s. 相似文献
9.
Dynamics of the explosive growth of a vapor bubble in microgravity is investigated by direct numerical simulation. A front tracking/finite difference technique is used to solve for the velocity and the temperature field in both phases and to account for inertia, viscosity, and surface deformation. The method is validated by comparison of the numerical results with the available analytical formulations such as the evaporation of a one-dimensional liquid/vapor interface, frequency of oscillations of capillary waves, and other numerical results. Evolution of a three-dimensional vapor nucleus during explosive boiling is followed and a fine scale structure similar to experimental results is observed. Two-dimensional simulations yield a similar qualitative instability growth. 相似文献
10.
We propose a method for non-uniform reconstruction of 3D scalar data. Typically, radial basis functions, trigonometric polynomials or shift-invariant functions are used in the functional approximation of 3D data. We adopt a variational approach for the reconstruction and rendering of 3D data. The principle idea is based on data fitting via thin-plate splines. An approximation by B-splines offers more compact support for fast reconstruction. We adopt this method for large datasets by introducing a block-based reconstruction approach. This makes the method practical for large datasets. Our reconstruction will be smooth across blocks. We give reconstruction measurements as error estimations based on different parameter settings and also an insight on the computational effort. We show that the block size used in reconstruction has a negligible effect on the reconstruction error. Finally we show rendering results to emphasize the quality of this 3D reconstruction technique. 相似文献