全文获取类型
收费全文 | 382281篇 |
免费 | 4424篇 |
国内免费 | 1422篇 |
专业分类
电工技术 | 7434篇 |
综合类 | 364篇 |
化学工业 | 57148篇 |
金属工艺 | 14297篇 |
机械仪表 | 11695篇 |
建筑科学 | 9861篇 |
矿业工程 | 1231篇 |
能源动力 | 10575篇 |
轻工业 | 35719篇 |
水利工程 | 3164篇 |
石油天然气 | 3786篇 |
武器工业 | 20篇 |
无线电 | 50776篇 |
一般工业技术 | 74326篇 |
冶金工业 | 69513篇 |
原子能技术 | 6980篇 |
自动化技术 | 31238篇 |
出版年
2021年 | 2835篇 |
2019年 | 2642篇 |
2018年 | 4203篇 |
2017年 | 4264篇 |
2016年 | 4492篇 |
2015年 | 3134篇 |
2014年 | 5470篇 |
2013年 | 17222篇 |
2012年 | 8846篇 |
2011年 | 12417篇 |
2010年 | 9908篇 |
2009年 | 11308篇 |
2008年 | 12236篇 |
2007年 | 12315篇 |
2006年 | 10952篇 |
2005年 | 9895篇 |
2004年 | 9617篇 |
2003年 | 9766篇 |
2002年 | 9313篇 |
2001年 | 9762篇 |
2000年 | 9048篇 |
1999年 | 9403篇 |
1998年 | 22026篇 |
1997年 | 15816篇 |
1996年 | 12521篇 |
1995年 | 9731篇 |
1994年 | 8757篇 |
1993年 | 8536篇 |
1992年 | 6477篇 |
1991年 | 6303篇 |
1990年 | 6106篇 |
1989年 | 5870篇 |
1988年 | 5612篇 |
1987年 | 4902篇 |
1986年 | 4790篇 |
1985年 | 5434篇 |
1984年 | 4969篇 |
1983年 | 4746篇 |
1982年 | 4427篇 |
1981年 | 4306篇 |
1980年 | 4100篇 |
1979年 | 3978篇 |
1978年 | 3694篇 |
1977年 | 4465篇 |
1976年 | 5859篇 |
1975年 | 3183篇 |
1974年 | 3023篇 |
1973年 | 2994篇 |
1972年 | 2549篇 |
1971年 | 2228篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
W Eggert-Kruse G Rohr H Kerbel B Schwalbach T Demirakca K Klinga W Tilgen B Runnebaum 《Canadian Metallurgical Quarterly》1996,11(4):784-789
To determine the clinical usefulness of Acridine Orange (AO) staining of spermatozoa as a screening test for the evaluation of semen quality during basic infertility investigation, semen smears from 103 randomly chosen males of subfertile couples were examined. The median duration of infertility was 4.5 years (range 1-15) and the median age was 33 years (range 21-43). The outcome of AO staining ranged from 5 to 81%, with a median of 24%, green fluorescent spermatozoa. Results were not significantly related to the parameters of semen analysis (sperm count, motility, standard morphology, viability, pH and volume, as well as fructose concentration and number of found cells) or to local sperm antibody testing and semen cultures. Fluorescence after AO staining was also not related to sperm functional capacity (evaluated using sperm-mucus interaction tests in vitro and in vivo), or the medical history of the patient. No significant differences in the AO test outcome were seen in patients with explained and unexplained infertility, or with regard to subsequent fertility [with a median value of 21% (range 5-46) green fluorescence in the fertile group, compared with a median value of 28% (range 9-81) green fluorescence in the other men]. The results of this prospective study indicate that under the usual conditions of conception, the AO test is not clinically useful as a screening procedure to determine semen quality during basic infertility investigation. 相似文献
942.
Baghai-Ravary L. Beet S.W. Tokhi M.O. 《Vision, Image and Signal Processing, IEE Proceedings -》1996,143(6):337-343
The authors describe and discuss the new technique, multistep adaptive flux interpolation (MAFI), and its application to image data for coding. When applied to an image, MAFI produces an output which is also in an image form, but which has a more uniform feature density and a greatly reduced size. MAFI warps the input image by removing those rows and columns which contain a majority of redundant pixels. The side information required for reconstruction is minimal, and the image can be further compressed using conventional coders, making the compression ratio even higher. Because of its warped nature, the MAFI output's statistics are also more consistent with the properties assumed by block-based discrete cosine transform (DCT) methods 相似文献
943.
A unified theoretical method for the calculation of the radio capacity of multiple-access schemes such as FDMA (frequency-division multiple access), TDMA (time-division multiple access), CDMA (code-division multiple access) and SSMA (spread-spectrum multiple access) in noncellular and cellular mobile radio systems is presented for AWGN (additive white Gaussian noise) channels. The theoretical equivalence of all the considered multiple-access schemes is found. In a fading multipath environment, which is typical for mobile radio applications, there are significant differences between these multiple-access schemes. These differences are discussed in an illustrative manner revealing several advantages of CDMA and SSMA over FDMA and TDMA. Novel transmission and reception schemes called coherent multiple transmission and coherent multiple reception are briefly presented 相似文献
944.
Community studies in Guinea-Bissau have found that exposure to measles prior to 6 months of age is associated with delayed mortality later in childhood. In an attempt to understand the underlying mechanism, we examined the role of pre-exposure nutritional status and the impact of exposure to measles on growth and subsequent mortality in these outbreaks. Though exposed children were lighter than controls, there was no association between pre-exposure weight-for-age and subsequent mortality adjusting for age. Although exposure was strongly associated with excess mortality, it did not have a negative impact on growth. Adjustment for state of nutrition did not alter the mortality ratio (MR) between 6 and 59 months of age for exposed children and controls; exposed children examined anthropometrically between 6-17 months had a MR of 3.70 compared with controls. This trend was the same for anthropometric measurements obtained at 18-59 months of age. Among the controls, there was a significant association between weight-for-age and subsequent mortality to the age of 5 years. However, for exposed children there was no association; the relation between weight-for-age and subsequent mortality was significantly different for exposed children compared with controls (tests for interaction between exposure and anthropometric measurements at 6-17 months: P = 0.05). Growth faltering as a consequence of early exposure to measles does not explain the marked excess mortality among these children. Further studies of the process underlying delayed mortality after early exposure to measles are warranted. 相似文献
945.
946.
Dynamic Programming (DP) applies to many signal and image processing applications including boundary following, the Viterbi algorithm, dynamic time warping, etc. This paper presents an array processor implementation of generic dynamic programming. Our architecture is a SIMD array attached to a host computer. The processing element of the architecture is based on an ASIC design opting for maximum speed-up. By adopting a torus interconnection network, a dual buffer structure, and a multilevel pipeline, the performance of the DP chip is expected to reach the order of several GOPS. The paper discusses both the dedicated hardware design and the data flow control of the DP chip and the total array.This work was supported in part by the NATO, Scientific and Environmental Affairs Division, Collaborative Research Grant SA.5-2-05(CRG.960201)424/96/JARC-501. 相似文献
947.
Large signal analysis of the LCC-type parallel resonant converterusing discrete time domain modeling
A discrete time domain model for the LCC-type parallel resonant power converter has been derived. This model has been used to predict the large signal behavior of the power converter. The peak component stresses and the dynamic response of the key state variables, as obtained from the large signal analysis, using PRO-MATLAB software are plotted. SPICE results are included to verify the analytical results. Experimental results are also presented to verify the theory 相似文献
948.
Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed. 相似文献
949.
对经固溶处理的二种Al-Li合金(1.94wt.%Li和2.75wt.%Li)的时效过程进行了研究。结果表明:δ’的生长速率遵从Ostward粗化动力学。1.94wt.%Li合金δ’产生于时效过程中,而2.75wt.%Li合金的δ’产生于时效的前期阶段。前者的表现体积分数明显大于根据相图估算的数伍,真实体积分数则与此值接近;后者的体积分数低于根据相图估算的数值,这可能归咎于δ’固相线的位置、统计学误差及Li更易在时效过程中贫化。 相似文献
950.
A neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The use of power flow dynamics provides a PSS for a wide range of operation with reduced size neural networks. The neuro-PSS consists of two neural networks: neuro-identifier and neuro-controller. The low-frequency oscillation is modeled by the neuro-identifier using the power flow dynamics, then a generalized backpropagation-through-time (GBTT) algorithm is developed to train the neuro-controller. The simulation results show that the neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS 相似文献