全文获取类型
收费全文 | 23918篇 |
免费 | 1906篇 |
国内免费 | 1053篇 |
专业分类
电工技术 | 1275篇 |
技术理论 | 3篇 |
综合类 | 1458篇 |
化学工业 | 4182篇 |
金属工艺 | 1362篇 |
机械仪表 | 1546篇 |
建筑科学 | 1735篇 |
矿业工程 | 937篇 |
能源动力 | 776篇 |
轻工业 | 1660篇 |
水利工程 | 468篇 |
石油天然气 | 1484篇 |
武器工业 | 158篇 |
无线电 | 2517篇 |
一般工业技术 | 3025篇 |
冶金工业 | 1351篇 |
原子能技术 | 230篇 |
自动化技术 | 2710篇 |
出版年
2024年 | 108篇 |
2023年 | 446篇 |
2022年 | 679篇 |
2021年 | 995篇 |
2020年 | 745篇 |
2019年 | 662篇 |
2018年 | 775篇 |
2017年 | 816篇 |
2016年 | 757篇 |
2015年 | 916篇 |
2014年 | 1189篇 |
2013年 | 1474篇 |
2012年 | 1512篇 |
2011年 | 1599篇 |
2010年 | 1442篇 |
2009年 | 1306篇 |
2008年 | 1310篇 |
2007年 | 1226篇 |
2006年 | 1193篇 |
2005年 | 1065篇 |
2004年 | 743篇 |
2003年 | 678篇 |
2002年 | 700篇 |
2001年 | 582篇 |
2000年 | 535篇 |
1999年 | 596篇 |
1998年 | 484篇 |
1997年 | 412篇 |
1996年 | 374篇 |
1995年 | 317篇 |
1994年 | 298篇 |
1993年 | 224篇 |
1992年 | 170篇 |
1991年 | 118篇 |
1990年 | 65篇 |
1989年 | 68篇 |
1988年 | 74篇 |
1987年 | 47篇 |
1986年 | 34篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1954年 | 4篇 |
1947年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
《无机及分析化学》在多媒体教学的应用及思考 总被引:1,自引:0,他引:1
对多媒体技术在无机及分析化学教学的应用进行了,阐述和分析,指出使用多媒体教学应注意的问题。 相似文献
92.
93.
The modern society is fuelled by very comprehensive grids of gas and liquid pipelines. In recent years, various in-pipe robots have been developed for inspection and maintenance tasks inside such pipes. In this paper, a novel in-pipe robot is proposed and developed for gas/oil well interventions at thousands of meters downhole. Due to the nature of such intervention, in-pipe robot design must be capable of carrying a very large payload, as large as 2500?N inside a pipe with diameter as small as 54?mm. The proposed design concept is based on a compound planetary gearing system. One of the major novelties of this design is the use of pipe wall as a ring gear for one stage of the compound planetary gear system; the other novelty is the generation of helical angle when the planetary gears are expanded to press on the pipe wall. The proposed concept is compact, efficient, and has never been reported before. In this paper, the helical angle, the velocity, and load capability of the proposed system will be analyzed. The load transportation capability of the proposed robot is also measured based on an experiment. Initial data have shown great potential in carrying large payloads. 相似文献
94.
Carl Yuheng Ren Victor Prisacariu Ian Reid 《International Journal of Computer Vision》2014,106(3):269-281
We propose a novel regression based framework that uses online learned shape information to reconstruct occluded object contours. Our key insight is to regress the global, coarse, properties of shape from its local properties, i.e. its details. We do this by representing shapes using their 2D discrete cosine transforms and by regressing low frequency from high frequency harmonics. We learn this regression model using Locally Weighted Projection Regression which expedites online, incremental learning. After sufficient observation of a set of unoccluded shapes, the learned model can detect occlusion and recover the full shapes from the occluded ones. We demonstrate the ideas using a level-set based tracking system that provides shape and pose, however, the framework could be embedded in any segmentation-based tracking system. Our experiments demonstrate the efficacy of the method on a variety of objects using both real data and artificial data. 相似文献
95.
96.
This study examines the incorporation of highly unsaturated n−3 fatty acids (HUFA) into triacylglycerols (TAG) of brown adipose
tissue (BAT), and their effect on the positional distribution of saturated (SFA) and of unsaturated (UFA) 16- or 18-carbon
fatty acids. To this end, rats were fed a fish oil diet for up to four weeks. The stereospecific analysis of TAG was based
on generation ofsn-1,2- andsn-2,3-acylglycerols by Grignard degradation, followed by synthesis of phosphatidic acid and specific hydrolysis with phospholipase
A2. From the end of the first week of fish oil feeding, a steady-state in the fatty acid composition of TAG in BAT was reached.
HUFA concentration increased 30-fold, mainly at the expense of n−9 UFA and of SFA. The amount of SFA decreased selectively
at position 3, where these fatty acids were progressively replaced by n−3 HUFA. By contrast, the amount of UFA decreased at
all positions, and their positional distribution was not affected. About 60% of HUFA was incorporated at position 3. Nearly
twice as much 22∶6n−3 was incorporated into TAG than had been previously observed in white adipose tissue (WAT) [Leray, C.,
Raclot, T., and Groscolas, R. (1993)Lipids 28, 279–284]. At the steady-state, the distribution of HUFA was characterized by high proportions of 22∶6n−3 and 20∶5n−3 in
position 3. Moreover, in each position of TAG, a steady level was reached rapidly (within 1 wk). It is concluded that, during
fish-oil feeding, fatty acids in TAG of BAT show characteristic time-course changes that lead to a characteristic composition
and a tissue-specific positional distribution. This suggests that adipose tissue has its own specificity in controlling the
build-up of TAG stores, which is likely to be regulated by the specificity of acylating enzymes as well as molecular rearrangements. 相似文献
97.
沉淀铁催化剂上F-T合成反应的研究 总被引:2,自引:1,他引:2
制备了物相组成为 Quartz- Si O2 ,Hermatite- Fe2 O3 和 Fe2 O3 - Iron Oxide的沉淀铁催化剂 ,研究了该催化剂作用上固定床积分反应器中费托合成反应特性 .发现 2 .6MPa,80 0 h-1,H2 /CO=2 /3,2 60℃~ 2 90℃时 ,随着温度的升高 ,CO和 H2 的转化率增大 ,CO2 选择性减小 ;40 0 h-1,65 0 h-1,80 0 h-1低空速和 2 4 0 0 h-1,32 0 0 h-1,40 0 0 h-1,640 0 h-1高空速时 ,随着空速的升高 ,H2转化率、CO转化率选择性下降 ,CO2 的选择性升高 ;2 80℃ ,2 .6MPa,H2 /CO进料比 2 /3,1 /1 ,2 /1时 ,随着 H2 /CO进料比的增加 ,CO转化率 ,H2 /CO利用比和 CH4选择性都增加 ,H2 转化率和 CO2选择性减小 . 相似文献
98.
A novel sol–gel method based on V2O5·nH2O hydro-gel was developed to synthesize nanocrystalline Li3V2(PO4)3/carbon composite material. In this route, V2O5·nH2O hydro-gel, NH4H2PO4, Li2CO3 and high-surface-area carbon were used as starting materials to prepare precursor, and the Li3V2(PO4)3/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li3V2(PO4)3 sample is monoclinic structure with the space group of P21/n. The TEM image indicates that the Li3V2(PO4)3 particles modified by conductive carbon are about 70 nm in diameter. The Li3V2(PO4)3/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li3V2(PO4)3/carbon composite material which may offer some favorable properties for commercial application. 相似文献
99.
Aihong Ren Yuping Wang Xingsi Xue 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2014,18(5):995-1009
In this paper, we address a class of bilevel linear programming problems with fuzzy random variable coefficients in objective functions. To deal with such problems, we apply an interval programming approach based on the $\alpha $ -level set to construct a pair of bilevel mathematical programming models called the best and worst optimal models. Through expectation optimization model, the best and worst optimal problems are transformed into the deterministic problems. By means of the Kth best algorithm, we obtain the best and worst optimal solutions as well as the corresponding range of the objective function values. In this way, more information can be provided to the decision makers under fuzzy random circumstances. Finally, experiments on two examples are carried out, and the comparisons with two existing approaches are made. The results indicate the proposed approaches can get not only the best optimal solution (ideal solution) but also the worst optimal solution, and is more reasonable than the existing approaches which can only get a single solution (ideal solution). 相似文献
100.
In this paper, it is shown that the Heisenberg model of spin-1 chain can be constructed from the Birman–Wenzl algebra generator while we have got that the Heisenberg model of spin- $\frac{1}{2}$ chain can be constructed from the Temperley–Lieb algebra generator in our previous work (Sun et al. in EPL 94:50001, 2011). Here, we investigate the topological space, we find that the number of topological basis states raise from the previous two to three, and they are also the three eigenstates of a closed four-qubit Heisenberg model of spin-1 chain. Specifically, all the topological basis states are also the spin single states and one of them is the energy single state of the system. It is worth noting that all conclusions we get in this paper are consistent with our previous work (Sun et al. in EPL 94:50001, 2011). These just indicate that the topological basis states have particular properties in the system. 相似文献