全文获取类型
收费全文 | 291637篇 |
免费 | 32563篇 |
国内免费 | 21443篇 |
专业分类
电工技术 | 26837篇 |
技术理论 | 4篇 |
综合类 | 27732篇 |
化学工业 | 38070篇 |
金属工艺 | 19367篇 |
机械仪表 | 20091篇 |
建筑科学 | 24325篇 |
矿业工程 | 10353篇 |
能源动力 | 8406篇 |
轻工业 | 26300篇 |
水利工程 | 9019篇 |
石油天然气 | 11729篇 |
武器工业 | 3903篇 |
无线电 | 33481篇 |
一般工业技术 | 26979篇 |
冶金工业 | 11111篇 |
原子能技术 | 4113篇 |
自动化技术 | 43823篇 |
出版年
2024年 | 1431篇 |
2023年 | 4496篇 |
2022年 | 10115篇 |
2021年 | 13566篇 |
2020年 | 9891篇 |
2019年 | 7371篇 |
2018年 | 7972篇 |
2017年 | 9231篇 |
2016年 | 8057篇 |
2015年 | 12750篇 |
2014年 | 16162篇 |
2013年 | 19158篇 |
2012年 | 23451篇 |
2011年 | 24710篇 |
2010年 | 23123篇 |
2009年 | 22368篇 |
2008年 | 22469篇 |
2007年 | 21745篇 |
2006年 | 19336篇 |
2005年 | 15404篇 |
2004年 | 11081篇 |
2003年 | 8213篇 |
2002年 | 7730篇 |
2001年 | 7047篇 |
2000年 | 5571篇 |
1999年 | 3340篇 |
1998年 | 1844篇 |
1997年 | 1467篇 |
1996年 | 1349篇 |
1995年 | 1153篇 |
1994年 | 935篇 |
1993年 | 636篇 |
1992年 | 516篇 |
1991年 | 384篇 |
1990年 | 301篇 |
1989年 | 292篇 |
1988年 | 198篇 |
1987年 | 133篇 |
1986年 | 117篇 |
1985年 | 50篇 |
1984年 | 50篇 |
1983年 | 33篇 |
1982年 | 40篇 |
1981年 | 50篇 |
1980年 | 73篇 |
1979年 | 57篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1959年 | 33篇 |
1951年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
921.
1. Introduction Seismic physical modeling technology is an important method for the research on seismic exploration theory and methods. In seismic physical experiments, the earth, mantle or field site are scaled down to physical models according to the similarity principle, and then the seismic field and its variation are observed in the laboratory for the research work on the theories and methods of the earth structure, earthquake forecasting, energy and mineral resource exploration, and engi… 相似文献
922.
The effect of tetramethylammonium cations (TMA+) on TiO2 crystal morphology in hydrothermal conditions has been studied. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. The morphologies including besom-like particle, nanosheet and nanotube have been observed. The different ways TMA+ cations in the hydrothermal bases affect the crystal growth manner are suggested to be responsible for the different morphologies of the as-synthesized samples. 相似文献
923.
Distributed Denial-of-Service (DDoS) attacks pose a serious threat to Internet security. Most current research focuses on
detection and prevention methods on the victim server or source side. To date, there has been no work on defenses using valuable
information from the innocent client whose IP has been used in attacking packets. In this paper, we propose a novel cooperative
system for producing warning of a DDoS attack. The system consists of a client detector and a server detector. The client
detector is placed on the innocent client side and uses a Bloom filter-based detection scheme to generate accurate detection
results yet consumes minimal storage and computational resources. The server detector can actively assist the warning process
by sending requests to innocent hosts. Simulation results show that the cooperative technique presented in this paper can
yield accurate DDoS alarms at an early stage. We theoretically show the false alarm probability of the detection scheme, which
is insensitive to false alarms when using specially designed evaluation functions.
This work is partially supported by HK Polyu ICRG A-PF86 and CERG Polyu 5196/04E, and by the National Natural Science Foundation
of China under Grant No. 90104005. 相似文献
924.
925.
COMPARATIVE STUDY OF CHEMICAL COMPOSITION AND PHYSICOCHEMICAL PROPERTIES OF DEFATTED WHEAT GERM FLOUR AND ITS PROTEIN ISOLATE 总被引:2,自引:0,他引:2
Chemical composition and physicochemical properties of defatted wheat germ (WG) flour (DWGF) and protein isolate (DWGPI) were evaluated to determine their potential as food ingredients. Protein content of DWGF was 31.42% while that of DWGPI was 84.18%. Comparison of the amino acid composition to the Food and Agriculture Organization/World Health Organization reference pattern indicated that DWGF and DWGPI had well‐balanced amino acid profiles. Both of them were relatively rich in lysine, whereas cystine was lacking. The main mineral constituents of DWGF were potassium, magnesium and calcium, while sodium was the dominating element in DWGPI as a result of salt extraction. Concentrations of potassium, magnesium, calcium, manganese and zinc in DWGPI were significantly decreased because of alkaline extraction compared to those in DWGF. The elements copper and iron were higher in DWGPI than in DWGF. Total flavonoid content of DWGF was about 0.35 g rutin equiv/100 g, whereas that of DWGPI was lower (about 0.24 g rutin equiv/100 g). Compared to soybean protein isolate, DWGPI was easily digested by pepsin in vitro, while DWGF was comparatively indigestible. Nonreduced and reduced sodium dodecyl sulfate‐polyacrylamide gel electrophoresis analyses seem to show that interpolypeptide S‐S bonds were absent in the structure of WG proteins. DWGF and DWGPI shared four groups of bands: (1) 85–70 kDa; (2) 55–50 kDa; (3) 47–40 kDa; and (4) below 20 kDa. 相似文献
926.
文中提出了一种应用RBF神经网络对标准IMM算法中的卡尔曼滤波结果进行校正的方法。网络输人为预测误差、卡尔曼增益以及测量值与估计值之差.网络输出反映了由于目标机动所带来的滤波误差.将网络输出结果和直接由卡尔曼滤波求解得到的结果相加.可以得到更为准确的滤波值。同时.在网络的学习算法中.在网络权值矩阵的修正公式中增加了反映滤波残差的调整项.若卡尔曼滤波的残差较大,网络调整权值的幅度也相应增大。仿真结果表明.在目标发生机动转弯处.校正后的IMM算法的跟踪误差要明显小于标准IMM算法的跟踪误差.跟踪精度较高。 相似文献
927.
它们贯穿手表内外.机芯已经不是它们唯一的居处。当机械痴谜者还沉醉于复杂的机芯时.你是否发现它们的踪影?一只陀飞轮万年历能够清楚地让你知道钱的去向.但除了这些.手表装饰也可以使表的价值迅速窜升。这也可以说是进入高级手表的门槛.[编者按] 相似文献
928.
929.
人-车-路虚拟仿真中人机交互模块开发 总被引:1,自引:1,他引:0
使用VisualC++6.0作为开发平台,论述了基于VegaAPI的人-车-路系统虚拟仿真中人机交互的实现原理,使用Di-rectX的DirectInput组件,实现了在主线程中转向、制动、加速等人机交互驾驶操作信号的读取,并给出了主要的伪代码实现。 相似文献
930.
JI Gang ZHANG Wei-kang ZHOU Qi-dou 《水动力学研究与进展(B辑)》2006,18(2):156-160
1. INTRODUCTION Induced by unbalanced mechanical forces and moments, underwater structures vibrate and radiate The main form of underwater structures, such a submarine, is reinforced double cylindrical structure immersed in water, with fluid media filled between th double cylindrical shells. In essence, this is a coupling problem between fluid and structure. Multipl methods have been used to estimate radiation leve from underwater structures[1-9]. Musha[10] and Chertock[11] estimate the … 相似文献