全文获取类型
收费全文 | 398115篇 |
免费 | 32146篇 |
国内免费 | 17614篇 |
学科分类
工业技术 | 447875篇 |
出版年
2024年 | 789篇 |
2023年 | 5804篇 |
2022年 | 9505篇 |
2021年 | 15090篇 |
2020年 | 11514篇 |
2019年 | 9377篇 |
2018年 | 10934篇 |
2017年 | 12191篇 |
2016年 | 11130篇 |
2015年 | 15515篇 |
2014年 | 19523篇 |
2013年 | 23654篇 |
2012年 | 25684篇 |
2011年 | 28386篇 |
2010年 | 25088篇 |
2009年 | 23843篇 |
2008年 | 23352篇 |
2007年 | 22286篇 |
2006年 | 22668篇 |
2005年 | 19812篇 |
2004年 | 13583篇 |
2003年 | 12076篇 |
2002年 | 11378篇 |
2001年 | 10198篇 |
2000年 | 9905篇 |
1999年 | 10495篇 |
1998年 | 8174篇 |
1997年 | 6949篇 |
1996年 | 6378篇 |
1995年 | 5329篇 |
1994年 | 4277篇 |
1993年 | 2971篇 |
1992年 | 2339篇 |
1991年 | 1781篇 |
1990年 | 1380篇 |
1989年 | 1143篇 |
1988年 | 943篇 |
1987年 | 562篇 |
1986年 | 463篇 |
1985年 | 305篇 |
1984年 | 217篇 |
1983年 | 162篇 |
1982年 | 156篇 |
1981年 | 103篇 |
1980年 | 113篇 |
1979年 | 64篇 |
1978年 | 26篇 |
1977年 | 39篇 |
1976年 | 47篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
Yunlei Li Dick de Ridder Robert P.W. Duin Marcel J.T. Reinders 《Pattern recognition》2008,41(1):320-330
Samples can be measured with different precisions and reliabilities in different experiments, or even within the same experiment. These varying levels of measurement noise may deteriorate the performance of a pattern recognition system, if not treated with care. Here we seek to investigate the benefit of incorporating prior knowledge about measurement noise into system construction. We propose a kernel density classifier which integrates such prior knowledge. Instead of using an identical kernel for each sample, we transform the prior knowledge into a distinct kernel for each sample. The integration procedure is straightforward and easy to interpret. In addition, we show how to estimate the diverse measurement noise levels in a real world dataset. Compared to the basic methods, the new kernel density classifier can give a significantly better classification performance. As expected, this improvement is more obvious for small sample size datasets and large number of features. 相似文献
992.
I. A. Zvereva O. I. Silyukov A. V. Markelov A. B. Missyul’ M. V. Chislov I. A. Rodionov D. -Sh. Li 《Glass Physics and Chemistry》2008,34(6):749-755
The processes of phase formation in the Na2CO3-TiO2 and Na2CO3-TiO2-Nd2O3 systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO4 compound occurs through the reaction of the intermediate product Na8Ti5O14 with neodymium oxide in the temperature range 720–780°C. The optimum method is proposed for synthesizing NaNdTiO4, which makes it possible to reduce the temperature of the synthesis, to avoid the formation of impurities, and to obtain the product in a finely dispersed state. 相似文献
993.
994.
介绍了安装在液压试验机上的一种集冲裁、切口作用于一体的复合冲裁模的设计,解决了没有压力机的情况下冲裁件的加工问题。 相似文献
995.
The Jian kiln, located in present-day Jianyang county of Fujian province, mainly produced black-glazed tea bowls. Jian tea bowl was used as a utensil for tea tasting and was greatly appreciated by emperor Huizong of the Northern Song dynasty. The black glaze of Jian bowl was sometimes marked with streaks or spots, usually called “hare's fur” or “oil spot”, which are the crystalline markings of iron oxide precipitated during firing in the dragon kiln. In this study, black-glazed Jian bowl sherds excavated from the late Northern Song strata of Luhuaping and Daluhoumen Jian kiln sites were adopted as test samples. Based on the physico-chemical foundation for the formation of glaze microstructure, the correlation among composition, microstructure, and visual appearance has been investigated by means of energy-dispersive X-ray fluorescence, X-ray diffraction, and field emission electron microscopy. For the first time, the study provides realizing proofs for two kinds of microstructural forming mechanics. 相似文献
996.
Xiaojun Xie Yonghong Cheng Hong Wang Qian Wang Xiaolin Chen Caixin Sun 《Ceramics International》2008,34(4):689-693
In the ideal A2B2O6O′ pyrochlore structure, the x-value of O atom position is a variable parameter. In Bi1.5ZnNb1.5−xTaxO7 (BZNT) cubic pyrochlores, the x-values alter with the different compositions of Nb/Ta. In this work, a series of initial models for BZNT were established by analyzing X-ray diffraction data. Then three structure modifying methods, including Rietveld refinement, Rietveld refinement with energy and geometry optimization based on quantum mechanics, were employed to obtain the precise models using Materials Studio. Moreover, the reflectivities of BZNT were computed by quantum mechanical simulation based on the refined models. Comparing the simulation results from different modifying models with the experimental results, it is found that Rietveld refinement with energy optimization is the most accurate method for BZNT pyrochlores. According to the simulation results, the different reflectivities correspond well with various x-values of O atom positions in BZNT pyrochlores. 相似文献
997.
冲击响应谱在惯导减振防冲设计中的应用 总被引:3,自引:0,他引:3
根据冲击原理,研究惯导减振系统在半正弦冲击激励下的响应特性,绘制了惯导系统在半正弦冲击激励下的冲击响应谱图。根据冲击响应谱图,可为惯导系统防冲设计提供正确、有效的理论依据,同时,为使减振器同时具备减振、防冲两种性能,冲击响应谱对于减振器关键参数选择、减振系统优化也具有重要应用价值。最后文章依据该研究结论,对某惯导系统进行了实际设计计算。 相似文献
998.
999.
1000.
The effects of key parameters on the preparation and regeneration of protoplast from the β-carotene-producing fungus Blakeslea trispora were discussed in this paper, including the combination of various enzymes, mycelial age, digesting time and temperature,
pH value, osmotic stabilizers, pretreatment, culture medium and culture method. Under the condition of mixed enzymes in osmotic
stabilizer (0.6 M NaCl) combined with 2% lysozyme, 3% cellulase and 3% snailase, the highest protoplast yield, as high as
7.48×106 protoplasts/mL, was obtained when mycelial age was 60 h at pH 5.0–6.0 with digesting for 14–16 h at 28 °C. After
purification of the obtained protoplasts, they were regenerated in PDA regenerative medium using bilayer plate culture method.
To validate the usability of the protoplasts, a novel plasmid with green fluorescent protein (GFP) was used in transformation
for easy visual observation. The results showed that the protoplasts prepared by the optimized method were active and applicable
in further gene manipulation experiments.
This work was presented at 13
th
YABEC symposium held at Seoul, Korea, October 20–22, 2007. 相似文献