全文获取类型
收费全文 | 11777篇 |
免费 | 404篇 |
国内免费 | 201篇 |
专业分类
电工技术 | 279篇 |
综合类 | 252篇 |
化学工业 | 1302篇 |
金属工艺 | 307篇 |
机械仪表 | 472篇 |
建筑科学 | 452篇 |
矿业工程 | 141篇 |
能源动力 | 186篇 |
轻工业 | 1158篇 |
水利工程 | 293篇 |
石油天然气 | 113篇 |
武器工业 | 74篇 |
无线电 | 1107篇 |
一般工业技术 | 1241篇 |
冶金工业 | 3751篇 |
原子能技术 | 163篇 |
自动化技术 | 1091篇 |
出版年
2022年 | 128篇 |
2021年 | 184篇 |
2020年 | 135篇 |
2019年 | 129篇 |
2018年 | 131篇 |
2017年 | 156篇 |
2016年 | 145篇 |
2015年 | 190篇 |
2014年 | 289篇 |
2013年 | 522篇 |
2012年 | 405篇 |
2011年 | 483篇 |
2010年 | 407篇 |
2009年 | 445篇 |
2008年 | 452篇 |
2007年 | 453篇 |
2006年 | 394篇 |
2005年 | 350篇 |
2004年 | 271篇 |
2003年 | 277篇 |
2002年 | 278篇 |
2001年 | 226篇 |
2000年 | 198篇 |
1999年 | 242篇 |
1998年 | 884篇 |
1997年 | 568篇 |
1996年 | 484篇 |
1995年 | 323篇 |
1994年 | 271篇 |
1993年 | 284篇 |
1992年 | 117篇 |
1991年 | 133篇 |
1990年 | 140篇 |
1989年 | 140篇 |
1988年 | 139篇 |
1987年 | 140篇 |
1986年 | 117篇 |
1985年 | 130篇 |
1984年 | 96篇 |
1983年 | 104篇 |
1982年 | 72篇 |
1981年 | 93篇 |
1980年 | 74篇 |
1979年 | 81篇 |
1978年 | 72篇 |
1977年 | 126篇 |
1976年 | 232篇 |
1975年 | 73篇 |
1974年 | 71篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
汾河沉积物中重金属污染及生态风险评价 总被引:1,自引:0,他引:1
研究针对汾河太原段的沉积物进行采样,对重金属进行分析。测定结果表明:汾河太原段沉积物中重金属的含量很高,4种重金属之间、12个采样点之间含量差别较大;含量反映了工业排放是造成汾河太原段重金属含量高的主要原因。重金属污染状况评价表明:所研究的4种重金属都处于中等以上污染水平,污染程度排行为:Pb〉Cr〉Cu〉Ni;对采样点进行综合污染状况评价表明,所有采样点均处于一个较高或很高的污染水平,污染最严重的是胜利桥和涧河。潜在生态风险评价表明:Cu处于较高的潜在生态风险,Pb、Cr和Ni处于中、低的潜在风险;采样点的潜在风险评价表明:胜利桥、涧河和南沙河的综合潜在生态风险处于较高水平。 相似文献
192.
Garrett BC Dixon DA Camaioni DM Chipman DM Johnson MA Jonah CD Kimmel GA Miller JH Rescigno TN Rossky PJ Xantheas SS Colson SD Laufer AH Ray D Barbara PF Bartels DM Becker KH Bowen KH Bradforth SE Carmichael I Coe JV Corrales LR Cowin JP Dupuis M Eisenthal KB Franz JA Gutowski MS Jordan KD Kay BD Laverne JA Lymar SV Madey TE McCurdy CW Meisel D Mukamel S Nilsson AR Orlando TM Petrik NG Pimblott SM Rustad JR Schenter GK Singer SJ Tokmakoff A Wang LS Wettig C Zwier TS 《Chemical reviews》2005,105(1):355-390
193.
无线网络节点中的离群失联节点在进行通信时信号质量不稳定,需要对离群失联节点进行准确定位,以提高无线网络通信质量.离群失联节点的信号特征与正常节点的信号特征相比有很大差异,传统的定位方法,在进行定位时需要将离群失联节点的信息都传送到参考节点才能得到定位信息,对于参考节点的依赖程度较大,导致定位的准确度和速度都较低.提出一种概率离群失联节点定位方法.对节点之间的距离进行测量,测量结果符合高斯函数,能够利用概率密度函数来描述,通过求解概率密度最大值,能够实现离群失联节点定位,避免了传统定位方法的弊端.实验证明,利用改进的离群失联节点定位方法,能够快速准确的对离群失联节点进行定位,定位准确率较高. 相似文献
194.
Light intensity gradients and light exposure time gradients were combined to produce contours of constant dose on a sample substrate. These polymerized samples were subsequently analyzed using high-throughput Fourier transform infrared spectroscopy to measure conversion as a function of both gradients. Three (meth)acrylate monomers were analyzed over light doses ranging from 0 mJ/cm2 to 920 mJ/cm2, demonstrating that in thin films, higher light intensities at a constant light dose produce higher conversion due to a decreased oxygen inhibition time and larger thermal excursions. At a light dose of 75 mJ/cm2, the conversion of 2-ethylhexyl acrylate increases from 40 ± 2% at a light intensity of 0.9 mW/cm2 to 59 ± 3% at 7.2 mW/cm2. The two acrylate monomers exhibited rapid photopolymerization up to a specific conversion, after which additional radiation dose produced only marginal increases in overall conversion. For hexanediol diacrylate, a light dose of 300 mJ/cm2 was the minimum amount required to reach the maximum conversion over the entire range analyzed. For the dimethacrylate system, a similar effect was seen, with a reduced oxygen inhibition time and conversion above 70% showing a similar conversion at a constant light dose of 500 mJ/cm2. In all three systems, dose contours were used to determine a range of light intensities at which a statistically similar conversion would occur for a specified light dose. 相似文献
195.
William W. Christie Elizabeth Y. Brechany Susan B. Johnson Ralph T. Holman 《Lipids》1986,21(10):657-661
The pyrrolidide and picolinyl ester derivatives of the fatty acids in two natural lipid samples rich in unsaturated fatty
acids, pig testis lipids and cod liver oil were satisfactorily resolved on capillary columns of fused silica coated with stationary
phases of varying polarity. The picolinyl esters, in particular, when subjected to gas chromatography-mass spectrometry on
a column containing a cross-linked methyl silicone, gave distinctive mass spectra, which could be interpreted in terms of
both the numbers and positions of the double bonds. 相似文献
196.
Four cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions,
respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first
three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally
strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene
fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation
and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible
for 9,10-desaturation. 相似文献
197.
为了快速准确的获取银行卡号信息,文章介绍了一种改进的LeNet-5神经网络结构.首先需要对原始数据预处理,通过数学形态学进行粗定位,最后通过卡行号的位置和特征进行精确定位.在卡号分割阶段,通过转换颜色空间对背景信息进行了去除,再使用了投影分析法对银行卡号分布形态做出了判断,最后使用K均值聚类算法对卡号行图像进行分割.在卡号识别阶段,先对数据进行数据增强,再用其对模型进行训练,将分割后的单独字符图像输入改进后的卷积神经网络LeNet-5对卡号进行识别,识别率达到了99.6%. 相似文献
198.
Justin McKetney Daniel J. Panyard Sterling C. Johnson Cynthia M. Carlsson Corinne D. Engelman Joshua J. Coon 《Proteomics. Clinical applications》2021,15(2-3):2000072
Proteomic analysis of cerebrospinal fluid (CSF) holds great promise in understanding the progression of neurodegenerative diseases, including Alzheimer's disease (AD). As one of the primary reservoirs of neuronal biomolecules, CSF provides a window into the biochemical and cellular aspects of the neurological environment. CSF can be drawn from living participants allowing the potential alignment of clinical changes with these biochemical markers. Using cutting-edge mass spectrometry technologies, we perform a streamlined proteomic analysis of CSF. We quantify greater than 700 proteins across 10 pairs of age- and sex-matched participants in approximately one hour of analysis time each. Using the paired participant study structure, we identify a small group of biologically relevant proteins that show substantial changes in abundance between cognitive normal and AD participants, which were then analyzed at the peptide level using parallel reaction monitoring experiments. Our findings suggest the utility of fractionating a single sample and using matching to increase proteomic depth in cerebrospinal fluid, as well as the potential power of an expanded study. 相似文献
199.
选择全国重要的加工业及旅游热点城市西安市作为研究对象,借助RS、GIS等空间信息分析工具,采用西安市2000年、2007年、2014年3个时相的遥感数据反演地表温度,对地表温度进行归一化处理,根据城市热岛分布特点,分析了城市化进程中城市热岛的变化特征.研究表明:随着建设用地的扩张,热岛区域面积逐渐增加并由城市中心向外围延伸,而绿岛区分布在秦岭附近的自然景区、山林水体区域,说明绿色植被及水域有明显的降温作用. 相似文献
200.
Matthew F. Johnson Colin R. Thorne Janine M. Castro G. Mathias Kondolf Celeste Searles Mazzacano Stewart B. Rood Cherie Westbrook 《河流研究与利用》2020,36(1):3-12
River management based solely on physical science has proven to be unsustainable and unsuccessful, evidenced by the fact that the problems this approach intended to solve (e.g., flood hazards, water scarcity, and channel instability) have not been solved and long‐term deterioration in river environments has reduced the capacity of rivers to continue meeting the needs of society. In response, there has been a paradigm shift in management over the past few decades, towards river restoration. But the ecological, morphological, and societal benefits of river restoration have, on the whole, been disappointing. We believe that this stems from the fact that restoration overrelies on the same physical analyses and approaches, with flowing water still regarded as the universally predominant driver of channel form and structural intervention seen as essential to influencing fluvial processes. We argue that if river restoration is to reverse long‐standing declines in river functions, it is necessary to recognize the influence of biology on river forms and processes and re‐envisage what it means to restore a river. This entails shifting the focus of river restoration from designing and constructing stable channels that mimic natural forms to reconnecting streams within balanced and healthy biomes, and so levering the power of biology to influence river processes. We define this new approach as biomic river restoration. 相似文献