全文获取类型
收费全文 | 170720篇 |
免费 | 17522篇 |
国内免费 | 10666篇 |
专业分类
电工技术 | 14256篇 |
技术理论 | 4篇 |
综合类 | 14237篇 |
化学工业 | 23564篇 |
金属工艺 | 10407篇 |
机械仪表 | 11489篇 |
建筑科学 | 14283篇 |
矿业工程 | 5663篇 |
能源动力 | 5114篇 |
轻工业 | 12993篇 |
水利工程 | 4243篇 |
石油天然气 | 8345篇 |
武器工业 | 2009篇 |
无线电 | 20637篇 |
一般工业技术 | 16971篇 |
冶金工业 | 7884篇 |
原子能技术 | 1931篇 |
自动化技术 | 24878篇 |
出版年
2024年 | 855篇 |
2023年 | 2768篇 |
2022年 | 5573篇 |
2021年 | 7647篇 |
2020年 | 5743篇 |
2019年 | 4442篇 |
2018年 | 4946篇 |
2017年 | 5908篇 |
2016年 | 5094篇 |
2015年 | 7645篇 |
2014年 | 9622篇 |
2013年 | 11379篇 |
2012年 | 13280篇 |
2011年 | 13794篇 |
2010年 | 12812篇 |
2009年 | 12051篇 |
2008年 | 11899篇 |
2007年 | 11251篇 |
2006年 | 10188篇 |
2005年 | 7962篇 |
2004年 | 5551篇 |
2003年 | 4702篇 |
2002年 | 4517篇 |
2001年 | 3981篇 |
2000年 | 3175篇 |
1999年 | 2550篇 |
1998年 | 1916篇 |
1997年 | 1480篇 |
1996年 | 1343篇 |
1995年 | 1106篇 |
1994年 | 921篇 |
1993年 | 596篇 |
1992年 | 441篇 |
1991年 | 336篇 |
1990年 | 265篇 |
1989年 | 232篇 |
1988年 | 167篇 |
1987年 | 121篇 |
1986年 | 105篇 |
1985年 | 63篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 38篇 |
1981年 | 47篇 |
1980年 | 49篇 |
1979年 | 25篇 |
1977年 | 34篇 |
1976年 | 98篇 |
1975年 | 14篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
121.
Wenying Wei Zhen Wang Yanhua Yin Jinyu Han Wen Xu 《Korean Journal of Chemical Engineering》2008,25(3):562-567
Composition Group Vector Space (CGVS) method for estimating melting and boiling point T
m
, T
b
of organic compound has been proposed, and the principle of this method has been elucidated. The models for estimating T
m
, T
b
have been established and the numerical values of relative parameters have been presented. The average percentage deviations
of T
m
, T
b
estimation are 7.53 and 1.58, respectively, which show that the present method demonstrates significant improvement in applicability
to predict the above properties, compared to conventional group methods. 相似文献
122.
123.
124.
125.
126.
本文介绍了目前国内外研究者们提出的各种射频激励相干阵列波导CO2激光器技术,讨论了射频激励相干阵列波导CO2激光器技术的一个研究方向。 相似文献
127.
Genetic studies of the nematode Caenorhabditis elegans have defined a variety of single-gene mutations that have specific effects on programmed cell death. Analyses of the genes defined by these mutations have revealed that cell death is an active process that requires gene function in cells that die. Specific genes are required not only to cause cell death but also to protect cells from dying. Gene interaction studies have defined a genetic pathway for the execution phase of programmed cell death in C. elegans. Molecular and biochemical findings are consistent with the pathway proposed from these genetic studies and have also revealed that the protein products of certain cell-death genes interact directly. This pathway appears to be conserved among organisms as diverse as nematodes and humans. Important questions remain to be answered about programmed cell death in C. elegans. For example, how does a cell decide to die? How is cell death initiated? What are the mechanisms of action of the cell-death protector and killer genes? What genes lie downstream of the cell-death execution pathway? The conservation of the central cell-death pathway suggests that additional genetic analyses of programmed cell death in C. elegans will help answer these questions, not only for this nematode but also for other organisms, including ourselves. 相似文献
128.
F Deák á Horváth á Kiss Z Seres A Galonsky CK Gelbke H Hama L Heilbronn D Krofcheck WG Lynch DW Sackett HR Schelin MB Tsang J Kasagi T Murakami 《Canadian Metallurgical Quarterly》1995,52(1):219-227
An extruding wire knife was used to give adult male CFHB rats a minimally traumatic unilateral mechanical lesion of the medial forebrain bundle. In addition, some rats received bilateral intrastriatal injections of one of three fluorescent retrograde tracers either eight days before or eight days after the lesion. Injections made after the lesion revealed that about half of the animals had complete lesions of the nigrostriatal tract, while the other half were incompletely lesioned, the mean proportion of non-axotomized neurons being 23%. Over the 10 weeks following the lesions, the number of tyrosine hydroxylase-immunoreactive cells in the lesioned substantia nigra fell linearly, reaching a mean of 29% of that of the control substantia nigra. In the animals which were completely lesioned, neuronal survival at 10 weeks varied between 6 and 12%. That the disappearance of tyrosine hydroxylase-immunoreactive neurons was due to cell death rather than the loss of tyrosine hydroxylase itself was confirmed by labelling the cells with Fluoro Gold before axotomy; the tracer was seen in survival neurons, microglia and in a few involuted neurons which continued to be tyrosine hydroxylase-immunoreactive. This percentage of neurons surviving axotomy corresponds to the proportion of substantia nigra neurons which project to the contralateral striatum, and these neurons were in the region of the substantia nigra from which the contralateral projection originated. It is concluded that following mechanical transection of the nigrostriatal tract, all truly axotomized substantia nigra neurons die over a period of about 10 weeks. 相似文献
129.
130.
M Wei C Gonzalez SM Haffner DH O'Leary MP Stern 《Canadian Metallurgical Quarterly》1996,16(11):1388-1392
Measurements of carotid artery wall thickness are often used as a surrogate for atherosclerosis. However, few studies have performed these measurements in populations of Mexican origin. Since Mexicans in Mexico City consume high-carbohydrate diets and have carbohydrate-induced dyslipidemia (high triglyceride and low HDL cholesterol levels) compared with Mexican Americans living in San Antonio, Tex, we questioned whether they also had more atherosclerosis than San Antonio Mexican Americans. Mean maximum intimal-medial thickness (IMT) of the common (CCA) and internal (ICA) carotid arteries were measured in 867 subjects aged 35 to 64 years (40% men) in two Mexican-origin populations, one from San Antonio (n = 202) and the other from Mexico City (n = 665). IMT's in the two cities were compared, and their associations with cardiovascular risk factors were analyzed. Older age, male sex, high levels of total cholesterol, low levels of HDL cholesterol, and high systolic blood pressure were positively associated with both CCA IMT and ICA IMT. Cigarette smoking was significantly associated with ICA IMT. CCA and ICA IMTs in diabetic subjects were thicker than in nondiabetic subjects in both men and women (all P < = .05). CCA IMT was thicker in the San Antonio than the Mexico City subjects after adjustment for cardiovascular risk factors (0.81 versus 0.76 mm in men and 0.77 versus 0.71 mm in women; P < .001 for city difference). San Antonio men also had thicker ICA IMT than their counterparts in Mexico City (0.88 versus 0.83 mm), but the reverse was true for women (0.73 versus 0.77 mm; interaction between sex and city, P < .05). Our results indicate that men had higher carotid IMTs than women. CCA IMT was thicker in San Antonio Mexican Americans than in Mexico City residents. The differences in ICA IMTs between San Antonio and Mexico City were inconsistent. Thus, since Mexico City residents consume high-carbohydrate diets, the data do not support an atherogenic effect of such diets. The interaction between sex and city on ICA IMT deserves further study. 相似文献