全文获取类型
收费全文 | 17625篇 |
免费 | 129篇 |
国内免费 | 236篇 |
专业分类
电工技术 | 279篇 |
综合类 | 92篇 |
化学工业 | 1785篇 |
金属工艺 | 433篇 |
机械仪表 | 896篇 |
建筑科学 | 1081篇 |
矿业工程 | 491篇 |
能源动力 | 72篇 |
轻工业 | 4017篇 |
水利工程 | 336篇 |
石油天然气 | 462篇 |
武器工业 | 98篇 |
无线电 | 936篇 |
一般工业技术 | 5511篇 |
冶金工业 | 334篇 |
原子能技术 | 184篇 |
自动化技术 | 983篇 |
出版年
2021年 | 36篇 |
2018年 | 39篇 |
2016年 | 31篇 |
2015年 | 45篇 |
2014年 | 68篇 |
2013年 | 73篇 |
2012年 | 1588篇 |
2011年 | 1995篇 |
2010年 | 413篇 |
2009年 | 217篇 |
2008年 | 1534篇 |
2007年 | 1484篇 |
2006年 | 1249篇 |
2005年 | 1068篇 |
2004年 | 906篇 |
2003年 | 758篇 |
2002年 | 745篇 |
2001年 | 564篇 |
2000年 | 596篇 |
1999年 | 334篇 |
1998年 | 213篇 |
1997年 | 200篇 |
1996年 | 161篇 |
1995年 | 214篇 |
1994年 | 187篇 |
1993年 | 143篇 |
1992年 | 179篇 |
1991年 | 195篇 |
1990年 | 160篇 |
1989年 | 188篇 |
1988年 | 176篇 |
1987年 | 206篇 |
1986年 | 211篇 |
1985年 | 211篇 |
1984年 | 195篇 |
1983年 | 193篇 |
1982年 | 197篇 |
1981年 | 150篇 |
1980年 | 145篇 |
1979年 | 95篇 |
1978年 | 76篇 |
1977年 | 31篇 |
1976年 | 30篇 |
1975年 | 48篇 |
1974年 | 32篇 |
1973年 | 34篇 |
1966年 | 30篇 |
1965年 | 48篇 |
1964年 | 33篇 |
1956年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Nowak E 《Applied ergonomics》1989,20(2):136-139
The paper discusses anthropometric research for design for children and youth. Two-dimensional dimensional manikins are one of the forms of presenting anthropometric data. Manikins of children aged 1-6 are the object of the paper. The set consists of eight plexiglass models scaled 1:5. The models were prepared with regard to 5th and 95th percentile values and two views - i e, side view when the figure is in the sagittal plane, and top view when the figure is in the transverse plane. the models are used in design and ergonomics assessment of products including equipment and furnishings earmarked for children. 相似文献
82.
Twenty-four veal calves were stunned with a captive bolt. Twelve calves were shackled by the left, the other twelve by the right hindleg. Approximately 1 min after sticking, six carcasses of each of these subgroups were stimulated electrically with equipment relying on a combined high (3000 V, 0·83 pulses s(-1), 1·5 ms duration) and low 35 V, 14 pulsess(-1)) voltage action. The remaining carcasses were left unharmed. At 24 h post-mortem hindquarters were boned to commercial primal cuts. Surrounding connective tissue and cut-up surfaces of primals as well as certain locations vulnerable for blood splash were further dissected. Neither electrical stimulation nor shackling by either of the hindlegs significantly affected the prevalence and severity of blood splash. Post-mortem factors promoting blood splash and possibly related to electrical stimulation and shackling are discussed. At 7 days post-mortem the sensory meat quality was assessed. In general, electrical stimulation did not significantly affect waterbinding and colour characteristics in longissimus (M. longissimus dorsi) and semimembranosus samples. Sarcomere lengths were similar in stimulated and control groups in longissimus but not in semimembranosus muscle. In both muscles shear force values were lower after electrical stimulation. In general, neither longissimus nor semimembranosus samples excised ipsilaterally from the shackled leg side exhibited differences in tenderness and sarcomere length. It is concluded that shackling by one leg or the other does not interfere with the tenderising effect of electrical stimulation. 相似文献
83.
At present, the diagnosis of cardiac left ventricular regional wall motion abnormalities (RWMA) in nuclear medicine is aided mainly by phase images and amplitude images, which picture the spatial distribution of the phase and of the amplitude of the first harmonics of pixel time activity curves, respectively. However, they do not utilize other information contained in the original radionuclide images, and they do not offer a direct diagnostic interpretation of the data. The proposed Fourier classification images (FCI) overcome these deficiencies. Their pixel intensities express directly the diagnostic class of RWMA. The FCI pixel intensities are functions of pixel coordinates, Fourier features of pixel time activity curves, and their distribution parameters, and they are not limited by the first harmonics model. The derivation of the pixel classifier includes normalization transformation of coordinates and activities. Fourier analysis of raw image data, and teaching the computer by examples of already diagnosed cases with the help of discriminant analysis. FCI offer direct and robust diagnosis of RWMA, superior to that derived from phase and amplitude images, especially in the detection of mild RWMA. 相似文献
84.
The interfacial properties of proteins extracted from muscle using salt solutions of different concentration and for different extraction times were determined by the drop volume method. At a bulk phase concentration of 10(-2) wt%, it appears that the sarcoplasmic-rich fraction of muscle is more surface active than the salt-soluble fraction. The average equilibrium surface pressure at the air-liquid interface was 21·5 mN m(-1) for an aqueous extract and 20·1 mN m(-1) for a 1m KCl-extract. The equilibrium surface pressure decreased from 21·7 mN m(-1) to 19·50mN m(-1) as the extraction time with Weber-Edsall solution increased from 15 min to 48 h. 相似文献
85.
An assessment was made of the microbiological quality of the final product (different retail cuts), produced by two different retail supermarket groups (A & B). The influence of sanitary conditions on the microbiological quality of the final product was evaluated, and the possible influences on shelf life were determined. Supermarket group A (Sup group A) received carcasses with significantly lower surface counts of micro-organisms than supermarket group B (Sup group B), while the latter had a more efficient overall sanitation programme than supermarket group A. Five cuts were monitored for the presence of total aerobic counts, psychrotrophic counts, lactobacilli, Enterobacteriaceae and numbers of Pseudomonadaceae present. A shelf life study was also executed by repeating these enumerations on the same meat samples after refrigerated storage at 5°C for 2 and 4 days, respectively. It is generally accepted that a good refrigeration or chilling regime will preserve the inherent meat quality, but in this study it was found that neither served as a guarantee of quality. The more stringent hygiene at retail level of Sup group B yielded consistently lower mean counts of the different bacterial groups for all the meat cuts monitored and, thus meat with an extended shelf life. The total count (at 30°C) on meat cuts was the highest, followed by the psychrotrophs, the Pseudomonadaceae the Enterobacteriaeae and the lactobacilli. Minced meat generally had the highest mean aerobic total microbial counts. This count on minced meat might be a suitable indicator for monitoring the overall sanitary condition of a retail premises. The results re-emphasized the multi-factorial complexity of fresh meat quality and shelf life. The microbial quality of the raw material (carcasses), the maintenance of the cold chain, sanitary condition of premises, equipment and personnel surfaces and general management practices are factors that collectively determine the microbiological quality of the product. 相似文献
86.
A spatial representation of the Green's function for anisotropic halfspace is considered. This representation can be used for analyzing an electric field connected with planar metal structures applied in surface-acoustic-wave devices 相似文献
87.
The influence of different centralised pre-packaging systems (PVC, modified atmosphere packaging (MAP), 25% CO(2) and 75% O(2), vacuum skin packaging (VSP) and the mother bag concept, 100% CO(2)) on the shelf-life (0, 7, 14 and 21 days at 0°C) of fresh pork was determined using microbiological, colour, odour and acceptability characteristics. All the packaging treatments were equally efficient for the first 4 days of retail display. In the extended shelf-life study (7, 14 and 21 days) the mother bag centralised packaging system gave the most promising shelf-life results (21 days) and was also judged superior in terms of odour. Modified atmosphere packaging (14 days) and VSP (7 days) may be considered as other possible options. 相似文献
88.
Ayme-Bellegarda E Habashy TM 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1992,39(1):11-18
The authors focus on the multidimensional inverse scattering of objects buried in an inhomogeneous elastic background structure. The medium is probed by an ultrasonic force and the scattered field is observed along a receiver array. The goal is to retrieve both the geometry (imaging problem) and the constitutive parameters (inverse problem) of the object through an appropriate multiparameter direct linear inversion. The problem is cast in terms of a vector integral equation elastic scattering framework. The multidimensional inverse scattering problem, being nonlinear and ill-posed, is linearized within the Born approximation for inhomogeneous background, and a minimum-norm least-square solution to the discretized version of the vector integral formulation is sought. The solution is based on a singular value decomposition of the forward operator matrix. The method is illustrated on a 2-D problem where constrained least-square inversion of the object is performed from synthetic data. A Tikhonov regularization scheme is examined and compared to the minimum-norm least-square estimate. 相似文献
89.
Hoffman AJ van Rooyen E 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1992,39(1):138-147
A three-dimensional model for the propagation of finite acoustic waves in nonlinear media is developed. This model implicitly includes the effects of acoustic attenuation and divergence due to diffraction. The generation of intermodulation products in the case of a two-tone input signal is numerically analyzed. It is found that acoustic diffraction can have a significant effect on the dynamic range of a Bragg cell if the acoustic field extends well into the Fraunhofer region. Inclusion of the effect of diffraction in the model predicts a dynamic range that can be considerably larger than the value obtained by using the infinite plane wave assumption. It is shown that acoustic attenuation significantly reduces the level of the acoustic intermodulation products relative to the level of the fundamental modes. This also increases the dynamic range. The influence of these effects on design considerations for Bragg cells is discussed. 相似文献
90.
Kähkönen E Nykyri E Ilmarinen R Ketola R Lusa S Nygård CH Suurnäkki T 《Applied ergonomics》1992,23(3):186-190
A study was made of the appraisers' effect on the estimation of metabolic rate with the Edholm scale and a table of the ISO 7243 heat stress standard. The appraisers, five experienced and five inexperienced persons, estimated the metabolic rate of three different work tasks from videotapes. Analysis of variance indicated significant ( [Formula: see text] ) differences in the appraisers' recordings of the activities. The appraisers were grouped according to the similarity of the estimated values they gave. The groups thus contained both experienced and inexperienced appraisers, and it was not possible to classify the appraisers into experienced and inexperienced groups according to their earlier experience. The metabolic rates according to the Edholm scale were higher than according to the ISO 7243 table. The differences in metabolic rates given by the individual observers varied from 38 to 118 W/m(2). The variations in the estimation of metabolic rates were greater when the Edholm scale was used. This variation caused considerable variation also in the predicted mean vote, PMV index. It is recommended that the appraisers be selected carefully, because it is not possible to know whether a randomly selected appraiser is an 'average' or an 'extreme' appraiser without a test. Before conducting extensive field surveys where several appraisers estimate the metabolic rates, it would be useful to arrange training in order to calibrate the levels of the Edholm scale as well as ISO method among the appraisers because training clearly unified the estimation. 相似文献