全文获取类型
收费全文 | 406338篇 |
免费 | 33724篇 |
国内免费 | 18981篇 |
学科分类
工业技术 | 459043篇 |
出版年
2024年 | 865篇 |
2023年 | 6000篇 |
2022年 | 10051篇 |
2021年 | 15698篇 |
2020年 | 11998篇 |
2019年 | 9608篇 |
2018年 | 11096篇 |
2017年 | 12502篇 |
2016年 | 11484篇 |
2015年 | 15985篇 |
2014年 | 20199篇 |
2013年 | 24186篇 |
2012年 | 26874篇 |
2011年 | 29505篇 |
2010年 | 26198篇 |
2009年 | 24992篇 |
2008年 | 24631篇 |
2007年 | 23254篇 |
2006年 | 23441篇 |
2005年 | 20304篇 |
2004年 | 13885篇 |
2003年 | 12370篇 |
2002年 | 11842篇 |
2001年 | 10545篇 |
2000年 | 10049篇 |
1999年 | 10228篇 |
1998年 | 7681篇 |
1997年 | 6553篇 |
1996年 | 6069篇 |
1995年 | 5040篇 |
1994年 | 4069篇 |
1993年 | 2757篇 |
1992年 | 2191篇 |
1991年 | 1653篇 |
1990年 | 1286篇 |
1989年 | 1052篇 |
1988年 | 855篇 |
1987年 | 516篇 |
1986年 | 401篇 |
1985年 | 255篇 |
1984年 | 200篇 |
1983年 | 145篇 |
1982年 | 138篇 |
1981年 | 81篇 |
1980年 | 106篇 |
1979年 | 49篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The stress intensity factors for a short crack partially penetrating an inclusion of arbitrary shape
Some approximate solutions for predicting the stress intensity factor of a short crack penetrating an inclusion of arbitrary
shape have been developed under mode I and mode II loading conditions. The derivation of the fundamental formula is based
on the transformation toughening theory. The transformation strains in the inclusion are induced by the crack-tip field and
remotely applied stresses, and approximately evaluated by the Eshelby equivalent inclusion theory. As validated by detailed
finite element (FE) analyses, the developed solutions have good accuracy for different inclusion shape and for a wide range
of modulus ratio between inclusion and matrix material. 相似文献
992.
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
993.
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
994.
995.
交流,共享,流动——现代大空间办公模式的优劣与对策 总被引:1,自引:0,他引:1
讨论了现代办公空间设计出现的新要求,通过办公空间演变趋势的探讨,归纳为若干大空间办公模式,并分析、比较其空间性质及特点,以及采用开放式办公布局的优势、不足及解决对策. 相似文献
996.
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
997.
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
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