全文获取类型
收费全文 | 10947篇 |
免费 | 375篇 |
国内免费 | 113篇 |
专业分类
电工技术 | 249篇 |
综合类 | 193篇 |
化学工业 | 2171篇 |
金属工艺 | 379篇 |
机械仪表 | 385篇 |
建筑科学 | 383篇 |
矿业工程 | 105篇 |
能源动力 | 419篇 |
轻工业 | 706篇 |
水利工程 | 126篇 |
石油天然气 | 165篇 |
武器工业 | 16篇 |
无线电 | 1251篇 |
一般工业技术 | 2486篇 |
冶金工业 | 1208篇 |
原子能技术 | 127篇 |
自动化技术 | 1066篇 |
出版年
2023年 | 103篇 |
2022年 | 200篇 |
2021年 | 267篇 |
2020年 | 214篇 |
2019年 | 182篇 |
2018年 | 305篇 |
2017年 | 244篇 |
2016年 | 267篇 |
2015年 | 234篇 |
2014年 | 306篇 |
2013年 | 676篇 |
2012年 | 438篇 |
2011年 | 524篇 |
2010年 | 445篇 |
2009年 | 441篇 |
2008年 | 427篇 |
2007年 | 381篇 |
2006年 | 336篇 |
2005年 | 282篇 |
2004年 | 250篇 |
2003年 | 240篇 |
2002年 | 224篇 |
2001年 | 187篇 |
2000年 | 229篇 |
1999年 | 240篇 |
1998年 | 317篇 |
1997年 | 276篇 |
1996年 | 247篇 |
1995年 | 205篇 |
1994年 | 195篇 |
1993年 | 181篇 |
1992年 | 162篇 |
1991年 | 159篇 |
1990年 | 106篇 |
1989年 | 118篇 |
1988年 | 131篇 |
1987年 | 122篇 |
1986年 | 103篇 |
1985年 | 144篇 |
1984年 | 137篇 |
1983年 | 154篇 |
1982年 | 111篇 |
1981年 | 118篇 |
1980年 | 99篇 |
1979年 | 99篇 |
1978年 | 88篇 |
1977年 | 75篇 |
1976年 | 83篇 |
1975年 | 70篇 |
1974年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
Navneet Rao 《电子设计应用》2007,(12):16-16,18,20,22,24,37
SRIO IP解决方案提供真实双向数据流,大大增强连接功能。目前,对高速通信与超快计算的需求正与日俱增。有线和无线通信标准的应用随处可见,数据处理架构每天都在扩展。较为普遍的有线通信方式是以太网(LAN、WAN和MAN网络)。手机通信是最为常见的无线通信方式,由应用了DSP的 相似文献
53.
本文提出了适于三种序号的Chrestenson函数序列的复制方法,对其复制过程进行了数学分析,并指出当Chrestenson函数退化为Walsh函数时,此方法即为复制理论中的平移复制方法。 相似文献
54.
55.
56.
Optimal operation of a multibasin reservoir system 总被引:1,自引:0,他引:1
A simulation-optimization procedure is presented for evaluating the extent of interbasin transfer of water in the Peninsular
Indian river system consisting of 15 reservoirs on four river basins. A system-dependent simulation model is developed incorporating
the concept of reservoir zoning to facilitate releases and transfers. The simulation model generates a larger number of solutions
which are then screened by the optimization model. The Box complex nonlinear programming algorithm is used for the optimization.
The performance of the system is evaluated through simulation with the optimal reservoir zones with respect to four indices,
reliability, resiliency, vulnerability and deficit ratio. The results indicate that by operating the system of 15 reservoirs
as a single unit the existing utilization of water may be increased significantly. 相似文献
57.
Xylose reductase (XR) from Neurospora crassa was purified to homogeneity and was found to be specific to NADPH (nicotinamide adenine dinucleotide phosphate). The purified enzyme showed M(r) of 60 and 29 kDa by gel filtration and SDS-PAGE indicating the presence of two subunits. The kinetic mechanism of xylose reductase is 'iso-ordered bi bi'. Inactivation of XR by N-bromosuccinimide (NBS) was found to be biphasic with second-order rate constants of 2.5 x 10(2) and 80 M-1S-1 for the fast (kf) and slow phase (ks), respectively. NADPH protected 90% of XR activity against inhibition by NBS. The fluorescence and circular dichroism (CD) studies revealed that inactivation was not due to gross conformational change in the enzyme. Analysis of the modified Stern-Volmer plot indicated that 49% of the tryptophanyl fluorescence was available for quenching which was completely abolished in the presence of NADPH confirming the involvement of tryptophan at the coenzyme binding site. Experimental evidence presented here serves to implicate the involvement of a tryptophan residue at the low-affinity NADPH binding site and the nature of this site has been assessed by using the hydrophobic probe ANS. 相似文献
58.
K V S Rama Rao 《Bulletin of Materials Science》1993,16(6):491-499
Pseudobinary alloy, Tb0·27Dy0·73Fe2−δ
, belonging to C-15 cubic Laves phase having MgCu2-type structure, possesses large magnetostriction and high magnetomechanical coupling coefficient. The advantages of this
material over existing piezoelectric materials, particularly for SONAR applications, are highlighted. Recent results on the
influence of cobalt (Co) on magnetic and magnetomechanical properties of Tb0·27Dy0·73Fe2 are discussed. 相似文献
59.
OBJECTIVES: Injury is the leading cause of death in the male working population of Brazil. An important fraction of these deaths are work related. Very few cohort studies of steel workers, and none from developing countries, have reported on mortality from injuries. This paper analyses mortality from work and non-work related injuries among Brazilian steel workers. METHODS: Deaths during employment from 1 January 1977 to 30 November 1992 were analysed in a cohort of 21,816 male steel workers. Mortality rates specific for age and calendar year among the workers were compared with those of the male population of the state where the plant is located. Work related injuries were analysed by comparing the mortality rates for different subgroups of the cohort. RESULTS: The number of deaths (391) was less than half that expected based on death rates of the general population. Over 60% (242) of deaths were due to injuries. Mortality from most causes was substantially below that in the general population, but that from unintentional injury, was 50% above that of the general population. Standardised mortality ratios (SMRs) were highest for the youngest and the oldest employees and for labourers and clerical workers. Mortality from motor vehicle injury was twice that expected from population rates (SMR = 209, 95% confidence interval (95% CI) 176-244). There was a 67% fall in the age adjusted mortality from occupational injuries in the study period. CONCLUSION: The healthy worker effect in this cohort was greater than that commonly found in studies of occupational groups in developed countries, probably because of a greater socioeconomic gap between employed and unemployed populations in Brazil, and unequal distribution of health care resources. Mortality was especially high for motor vehicle injuries. The fall in mortality from occupational injuries during the study period was probably due to improvement in safety standards, increased automation, and better medical care. There is a need to investigate risk factors for unintentional injuries among steel workers, especially those due to motor vehicle injuries. Prevention of occupational and nonoccupational injuries should be a main priority in Brazil. 相似文献
60.
PMR1, a P-type ATPase cloned from the yeast Saccharomyces cerevisiae, was previously localized to the Golgi, and shown to be required for normal secretory processes (Antebi, A., and Fink, G.R. (1992) Mol. Biol. Cell 3, 633-654). We provide biochemical evidence that PMR1 is a Ca2+-transporting ATPase in the Golgi, a hitherto unusual location for a Ca2+ pump. As a starting point for structure-function analysis using a mutagenic approach, we used the strong and inducible heat shock promoter to direct high level expression of PMR1 from a multicopy plasmid. Yeast lysates were separated on sucrose density gradients, and fractions assayed for organellar markers. PMR1 is found in fractions containing the Golgi marker guanosine diphosphatase, and is associated with an ATP-dependent, protonophore-insensitive 45Ca2+ uptake activity. This activity is virtually abolished in the absence of the expression plasmid. Furthermore, replacement of the active site aspartate within the phosphorylation domain had the expected effect of abolishing Ca2+ transport activity entirely. Interestingly, the mutant enzymes (Asp-371 --> Glu and Asp-371 --> Asn) demonstrated proper targeting to the Golgi, unlike analogous mutations in the related yeast H+-ATPase. Detailed characterization of calcium transport by PMR1 showed that sensitivity to inhibitors (vanadate, thapsigargin, and cyclopiazonic acid) and affinity for substrates (MgATP and Ca2+) were different from the previously characterized sarco/endoplasmic reticulum and plasma membrane Ca2+-ATPases. PMR1 therefore represents a new and distinct P-type Ca2+-ATPase. Because close homologs of PMR1 have been cloned from rat and other organisms, we suggest that Ca2+-ATPases in the Golgi will form a discrete subgroup that are important for functioning of the secretory pathway. 相似文献