全文获取类型
收费全文 | 9572篇 |
免费 | 688篇 |
国内免费 | 290篇 |
专业分类
电工技术 | 377篇 |
综合类 | 354篇 |
化学工业 | 1678篇 |
金属工艺 | 421篇 |
机械仪表 | 622篇 |
建筑科学 | 808篇 |
矿业工程 | 247篇 |
能源动力 | 259篇 |
轻工业 | 890篇 |
水利工程 | 111篇 |
石油天然气 | 545篇 |
武器工业 | 60篇 |
无线电 | 1085篇 |
一般工业技术 | 1403篇 |
冶金工业 | 536篇 |
原子能技术 | 109篇 |
自动化技术 | 1045篇 |
出版年
2024年 | 35篇 |
2023年 | 175篇 |
2022年 | 275篇 |
2021年 | 367篇 |
2020年 | 291篇 |
2019年 | 265篇 |
2018年 | 281篇 |
2017年 | 341篇 |
2016年 | 314篇 |
2015年 | 327篇 |
2014年 | 483篇 |
2013年 | 573篇 |
2012年 | 560篇 |
2011年 | 696篇 |
2010年 | 545篇 |
2009年 | 532篇 |
2008年 | 533篇 |
2007年 | 442篇 |
2006年 | 436篇 |
2005年 | 380篇 |
2004年 | 278篇 |
2003年 | 242篇 |
2002年 | 206篇 |
2001年 | 183篇 |
2000年 | 175篇 |
1999年 | 263篇 |
1998年 | 204篇 |
1997年 | 200篇 |
1996年 | 135篇 |
1995年 | 109篇 |
1994年 | 91篇 |
1993年 | 72篇 |
1992年 | 46篇 |
1991年 | 51篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 27篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1917年 | 12篇 |
1916年 | 13篇 |
1914年 | 23篇 |
1913年 | 17篇 |
1912年 | 18篇 |
1911年 | 12篇 |
1909年 | 15篇 |
1905年 | 13篇 |
1904年 | 15篇 |
1902年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
管材超声波分层检测作为控制产品质量的关键步骤,必须引起相关从业人员的重视,特别是要重点分析分层缺陷检测中盲区的构成原因和分布特征。只有这样,才能切实保证检测结果的准确性,更好地控制管材质量。通过对超声波分层缺陷检测的重要性进行阐释,分析了其中盲区的构成和分布等问题。 相似文献
52.
基于重金属对脲酶的抑制作用,研制了用于测定铜离子的生物传感器。该生物传感器的制备以壳聚糖为载体,将脲酶固定于pH电极表面。由于壳聚糖对Cu2+的富集,该生物传感器展现出高灵敏度。在样品溶液中加入5 mmol/L NaI,可以消除Hg2+和Ag+的干扰,从而实现Cu2+的选择性检测。在0.005~0.5μg/mL的浓度范围内,脲酶活性的抑制率与Cu2+浓度的对数呈良好的线性响应关系,其检出限为0.002μg/mL。将使用后的生物传感器浸泡于0.5 mmol/L的EDTA溶液再生5 min,被Cu2+抑制的脲酶的活性可以得到恢复。 相似文献
53.
54.
Multilayered protein films which contained ordered layers of photosynthetic reaction center (RC) from Rhodobacter Sphaeroides (RS601) were assembled by means of alternate electrostatic adsorption with positively charged poly(diallyldimethylammonium chloride) (PDDA). The assembly of RC was monitored by spectrometry and photocurrent measurement. Linear film growth was observed up to about 20 cycles of adsorption. For the monolayer film, the photocurrent was about 8.5 nA cm−2. For the multilayered film, the total photocurrent was about 77 nA cm−2 for the 24-layer RC film, while the average photocurrent increment per adsorption cycle was about 3.2 nA cm−2. The overall light-to-electricity conversion efficiency for a 24-layer film was about eight times higher than that for the monolayer one. The effects of electrode potential and pH on the photocurrent were also measured to illustrate the light-to-electric converting mechanism. 相似文献
55.
Coordination between strategic forest management and tactical logistic and production planning in the forestry supply chain 总被引:1,自引:0,他引:1
Jiehong Kong Mikael Rönnqvist 《International Transactions in Operational Research》2014,21(5):703-735
In this paper, we study the coordination mechanism in the forestry supply chain between strategic forest management and tactical production planning. We first formulate an integrated model to establish a theoretical benchmark for performance of the entire supply chain. It is a mixed integer programming model that involves harvesting, bucking, transportation, production, and sales decisions for both tactical and strategic planning levels. We then present two sequential approaches S‐A and S‐B where the coordination is done through internal pricing. S‐A is the approach currently used in practice where harvesting in the forest is the main driver of the supply chain activities and internal pricing is introduced to control bucking decision in a separate stage. In contrast, S‐B takes downstream demand information into consideration and internal pricing directly influences harvesting decision in the first stage. In order to find the appropriate setting of internal pricing that leads to the system optimum, we suggest two heuristics H‐I and H‐II. The internal pricing in H‐I is based on dual values and in H‐II, it is derived from a Lagrangian decomposition. A real‐life case study in the Chilean forestry industry is used to compare the results of different approaches. It is shown that the new sequential approach S‐B generates as good feasible solution as that obtained from the integrated approach but in much less time. Both heuristics H‐I and H‐II bring about near‐optimal feasible solutions. H‐II also provides optimistic bound of the optimal objective function value, which can be used as a measure of the solution quality. 相似文献
56.
Baoqing Deng Shanshan Kong Chang Nyung Kim 《Korean Journal of Chemical Engineering》2007,24(4):577-582
In this paper, a mathematical model is presented to describe the photocatalytic degradation of VOCs in a packed bed reactor.
Here, the adsorption of VOCs on the wall of the reactor is taken into account and the diffusion of VOCs in the axial direction
is neglected. First-order kinetics is used to describe the photocatalytic oxidation of VOCs. The analytical solution of the
present model is obtained by traveling wave method. The solution shows that the reactor performance is totally dependent on
the inlet concentration of VOCs when the time is large enough. The present model is validated through the experimental result
of the photocatalytic oxidation of trichloroethylene in a packed bed and the predicted results accord well with the experimental
data. The influence of flow rate and inlet concentration on the performance of the reactor is discussed in detail. High flow
rate offers high reaction rate and low conversion efficiency. The different inlet conditions and different reaction patterns
are also investigated. The model would be useful to estimate the rate constant and help to the design of the reactor. 相似文献
57.
孔向军 《网络安全技术与应用》2014,(6):97-97,99
随着计算机网络技术的不断发展,计算机互联网在人们的生活中应用越来越广泛,网络安全问题也随之而来。目前的计算机安全存在着诸多因素的威胁,研究人员也在致力于这方面的研究与发展,应用先进的技术来保证计算机安全,为计算机用户的信息安全提供更高的保障。本文将针对计算机安全问题进行分析,探讨数据加密技术在计算机安全中的应用。 相似文献
58.
Summary A new route for the preparation of soluble fullerenated polymer through the reaction of carbanion intermediates of polymers with fullerenes, particularly C60, is demonstrated. Confirmation of the covalent attachment of C60 to the polystyrene backbone is by a variety of techniques such as UV-Vis, FT-IR, TGA, SEM and 13C NMR etc. The product, which has a visibly brownish yellow cast when compared with the unreacted polymer, is soluble in some common organic solvents. The thermal stability of pure polystyrene is enhanced by C60-chemical modification, and no bonds within the carbon sphere are broken. 相似文献
59.
60.