首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   30002篇
  免费   1141篇
  国内免费   113篇
电工技术   398篇
综合类   229篇
化学工业   5451篇
金属工艺   648篇
机械仪表   638篇
建筑科学   1014篇
矿业工程   95篇
能源动力   973篇
轻工业   4184篇
水利工程   270篇
石油天然气   168篇
武器工业   6篇
无线电   2331篇
一般工业技术   4335篇
冶金工业   6366篇
原子能技术   251篇
自动化技术   3899篇
  2024年   53篇
  2023年   161篇
  2022年   536篇
  2021年   837篇
  2020年   576篇
  2019年   660篇
  2018年   740篇
  2017年   814篇
  2016年   783篇
  2015年   591篇
  2014年   929篇
  2013年   1534篇
  2012年   1348篇
  2011年   1684篇
  2010年   1232篇
  2009年   1278篇
  2008年   1170篇
  2007年   1021篇
  2006年   822篇
  2005年   865篇
  2004年   940篇
  2003年   840篇
  2002年   824篇
  2001年   714篇
  2000年   562篇
  1999年   541篇
  1998年   2077篇
  1997年   1358篇
  1996年   948篇
  1995年   623篇
  1994年   485篇
  1993年   542篇
  1992年   226篇
  1991年   284篇
  1990年   229篇
  1989年   196篇
  1988年   209篇
  1987年   166篇
  1986年   170篇
  1985年   182篇
  1984年   129篇
  1983年   90篇
  1982年   117篇
  1981年   122篇
  1980年   118篇
  1979年   96篇
  1978年   76篇
  1977年   142篇
  1976年   226篇
  1975年   83篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
The functional properties of Caryodendron orinocense protein product were investigated and compared with those of soybean (Glycina maxima). The product protein content was 24.47 g/100 g (Nx6.25). Solubility increased at both sides of the isoelectric point (pH 4.0) and with increased NaCl concentration up to 0.5M. Compared with soybean flour (50% protein), the protein product exhibited higher water and oil absorption, but lower emulsifying activity, emulsion stability, foaming capacity, and foam stability, the last one increase at higher pH. Emulsifying activity, foaming capacity, and foam stability were ionic strength dependent. C. orinocense protein product increased its emulsifying activity steadily from 0.05M to 0.75M NaCl, while it remained almost constant for soybean flour. Foaming capacity increased drastically at pH 10. The minimum time and concentration to form a gel was 20% in 4 min and 10% in 8 min for the Caryodendron protein product and soybean flour, respectively. The bulk density was 0.5056+/-0.0041 g/mL.  相似文献   
72.
Pyrethroids, considered as a general class of compounds, have been shown to provide effective protection from the larvae of the keratin-digesting insects Tineola bisselliella H., Tinea pellionella Linn., Hofmannophila pseudo-spretella Station and Attagenus piceus Oliv. The position regarding the susceptibility of the furniture carpet beetle to pyrethroids is less clear, however. It has been reported that both deltamethrin and permethrin are effective against Anthrenus flavipes Le Conte, whilst permethrin is also reported elsewhere to be effective against the same species. Results obtained in our laboratory, however, have indicated that pyrethroids may offer inadequate protection against Anthrenus vorax Waterh. [1, 2]. This latter species is identical to Anthrenus flavipes var. seminiveus Casey, a colour variety of Anthrenus flavipes Le Conte. The 1,3-disubstituted5-phenylcarbamoyl-2,4,6-trioxo- and 4,6-dioxo-2-thione-hexahydropyrimidine derivatives described in this paper exhibit a surprisingly high and selective toxicity to the Anthrenus species. Thus, a combination of an appropriate hexahydropyrimidine with a suitable pyrethroid, e.g. permethrin, provides complete control of a wide range of commonly encountered textile insect pests. The influence of substituents on the mothproofing activity is discussed.  相似文献   
73.
The effect of Pd-loading on Pd-NaZSM-5 and Pd-NaMordenite catalysts prepared by ion exchange was studied for methane combustion with excess oxygen (1% CH4, 18% O2, balance N2) in the temperature range 40–500°C. Fresh and calcined samples (3 h, 450°C) showed methane conversions proportional to Pd-loading on Pd-NaZSM-5 catalysts, while conversions decreased with Pd-loading on calcined Pd-NaMordenite catalysts. TOF (number of methane molecules converted per second per Pd2+ ion) for over exchanged Pd-NaZSM5-116 was low as compared to under exchanged Pd-NaZSM5-80 and Pd-NaZSM5-58 samples. Close TOF's were found for the last two samples at 330°C. TOF differences in Pd-NaMordenite catalysts demonstrate the heterogeneity of Pd+2 sites due to structurally nonidentical locations of cations. TOF's appear to be related to Na/Pd ratios in both catalyst types. Apparent activation energies for Pd-NaZSM-5 materials are higher than those for Pd-NaMordenite catalysts.  相似文献   
74.
Amorphous silica influences tricalcium aluminate (C3A) hydration both in pastes and in suspensions. Two heat peaks are found by isothermal calorimetry during the paste hydration of C3A. The addition of amorphous silica causes the second heat peak to shift towards shorter reaction times and become more pronounced. In suspensions, the change in ion concentration in the water phase is not influenced by the presence of amorphous silica except that the change in concentration occurs more quickly. Quantitative X-ray analysis shows that more 3CaO.Al2O3.6H2O is present in suspensions containing amorphous silica than in silica-free suspensions at equal hydration times.  相似文献   
75.
A non-destructive method is presented to study the combining properties of a number of hardened cement pastes for NaCl and CaCl2. Cements hardened with solutions of NaCl and of CaCl2 are equilibrated in solutions of these electrolytes in a special way. To interpret the results, the equilibrium between the pore solution and the hardened cement is taken as a general solid/solution equilibrium. The equilibrium between the pore solution and the equilibrating solution is considered to be a liquid/liquid equilibrium. That means that the equilibrium concentrations in the equilibrating solution and the pore solution are equaL. Thus it is possible to calculate the dependence of the amount of chloride combined by the cement on the total amount added to the cement.  相似文献   
76.
77.
78.
79.
80.
Fractal dimension applied to plant identification   总被引:2,自引:0,他引:2  
This article discusses methods to identify plants by analysing leaf complexity based on estimating their fractal dimension. Leaves were analyzed according to the complexity of their internal and external shapes. A computational program was developed to process, analyze and extract the features of leaf images, thereby allowing for automatic plant identification. Results are presented from two experiments, the first to identify plant species from the Brazilian Atlantic forest and Brazilian Cerrado scrublands, using fifty leaf samples from ten different species, and the second to identify four different species from genus Passiflora, using twenty leaf samples for each class. A comparison is made of two methods to estimate fractal dimension (box-counting and multiscale Minkowski). The results are discussed to determine the best approach to analyze shape complexity based on the performance of the technique, when estimating fractal dimension and identifying plants.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号