全文获取类型
收费全文 | 45738篇 |
免费 | 2001篇 |
国内免费 | 140篇 |
专业分类
电工技术 | 555篇 |
综合类 | 267篇 |
化学工业 | 8874篇 |
金属工艺 | 962篇 |
机械仪表 | 941篇 |
建筑科学 | 1729篇 |
矿业工程 | 149篇 |
能源动力 | 1506篇 |
轻工业 | 5315篇 |
水利工程 | 374篇 |
石油天然气 | 206篇 |
武器工业 | 6篇 |
无线电 | 3471篇 |
一般工业技术 | 7310篇 |
冶金工业 | 8542篇 |
原子能技术 | 376篇 |
自动化技术 | 7296篇 |
出版年
2023年 | 339篇 |
2022年 | 901篇 |
2021年 | 1414篇 |
2020年 | 947篇 |
2019年 | 1034篇 |
2018年 | 1252篇 |
2017年 | 1284篇 |
2016年 | 1343篇 |
2015年 | 1078篇 |
2014年 | 1536篇 |
2013年 | 2617篇 |
2012年 | 2356篇 |
2011年 | 2874篇 |
2010年 | 2057篇 |
2009年 | 2050篇 |
2008年 | 1975篇 |
2007年 | 1822篇 |
2006年 | 1419篇 |
2005年 | 1383篇 |
2004年 | 1326篇 |
2003年 | 1227篇 |
2002年 | 1174篇 |
2001年 | 929篇 |
2000年 | 743篇 |
1999年 | 743篇 |
1998年 | 2254篇 |
1997年 | 1524篇 |
1996年 | 1110篇 |
1995年 | 797篇 |
1994年 | 639篇 |
1993年 | 686篇 |
1992年 | 342篇 |
1991年 | 363篇 |
1990年 | 355篇 |
1989年 | 315篇 |
1988年 | 291篇 |
1987年 | 257篇 |
1986年 | 270篇 |
1985年 | 285篇 |
1984年 | 220篇 |
1983年 | 168篇 |
1982年 | 213篇 |
1981年 | 212篇 |
1980年 | 185篇 |
1979年 | 162篇 |
1978年 | 137篇 |
1977年 | 213篇 |
1976年 | 285篇 |
1975年 | 128篇 |
1973年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A chromosomally integrated Bradyrhizobium japonicum hoxA mutant is unable to oxidize hydrogen in free-living conditions. Derepressing conditions that induce hydrogenase activity in free-living, wild-type B. japonicum cells cannot induce expression of the hydrogenase structural genes in the hoxA mutant. The DNA-binding capacity of HoxA at the hup promoter region was studied by means of gel retardation. Both heterotrophically growing cells and cells induced to express hydrogenase activity contain a protein that specifically binds to the hup promoter region. Crude protein extracts isolated from a B. japonicum hoxA mutant do not contain this binding compound. The HoxA protein was overexpressed in E. coli and isolated in the form of a maltose-binding protein (MBP)-HoxA fusion. The MBP-HoxA hybrid protein specifically bound to a 50 bp region of the hupSL promoter known to be important for regulation of hupSL expression. 相似文献
62.
Tony Maillet Jacques Barbier Jr. Daniel Duprez 《Applied catalysis. B, Environmental》1996,9(1-4):251-266
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
63.
OD de Rada AC Villaro LM Montuenga A Martínez DR Springall JM Polak 《Canadian Metallurgical Quarterly》1993,162(1-2):121-124
The presence of nitric oxide synthase (NO-synthase), the enzyme responsible for the production of nitric oxide (NO) from L-arginine, is shown immunocytochemically in the intrinsic neurons of the human and porcine respiratory tract. NO-synthase immunoreactivity is demonstrated in a subpopulation of neurons of the microganglia present in the wall of the extra- and intrapulmonary bronchi as well as in the hilar region of the lung in relation to blood vessels. The immunostaining was also found in some nerve fibers of the respiratory nervous system. Human and porcine lung gave similar results. The possible involvement of NO in the nonadrenergic noncholinergic (NANC) nervous regulation of the lung is discussed. 相似文献
64.
R de Franchis 《Canadian Metallurgical Quarterly》1998,10(12):1041-1044
Bleeding oesophageal varices (BOV), resulting from portal hypertension, can prove fatal. Not only is it important to stop the initial bleeding, which may lead to hypovolaemic shock, but also to treat this condition in the longer term, and, consequently, the prevention of rebleeding needs to be addressed. This review highlights the current findings on the haemostatic drug, terlipressin, focusing particular attention on the potential for longer-term treatment strategies in the prevention of rebleeding. The efficacy of terlipressin in treating acute BOV, its low incidence of severe side-effects (comparable to those of somatostatin) and its favourable comparison with sclerotherapy in the prevention of early rebleeds, all indicate the potential for terlipressin administration to be extended to 5 days in the longer-term treatment of BOV. In addition, terlipressin administration, in conjunction with sclerotherapy, can significantly reduce the likelihood of rebleeding compared with sclerotherapy alone and further supports its potential use in the longer-term treatment of BOV. 相似文献
65.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
66.
67.
Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth. 相似文献
68.
69.
Gonzalez A. Valero-Garcia M. Diaz de Cerio L. 《Parallel and Distributed Systems, IEEE Transactions on》1995,6(8):803-814
Many parallel algorithms use hypercubes as the communication topology among their processes. When such algorithms are executed on hypercube multicomputers the communication cost is kept minimum since processes can be allocated to processors in such a way that only communication between neighbor processors is required. However, the scalability of hypercube multicomputers is constrained by the fact that the interconnection cost-per-node increases with the total number of nodes. From scalability point of view, meshes and toruses are more interesting classes of interconnection topologies. This paper focuses on the execution of algorithms with hypercube communication topology on multicomputers with mesh or torus interconnection topologies. The proposed approach is based on looking at different embeddings of hypercube graphs onto mesh or torus graphs. The paper concentrates on toruses since an already known embedding, which is called standard embedding, is optimal for meshes. In this paper, an embedding of hypercubes onto toruses of any given dimension is proposed. This novel embedding is called xor embedding. The paper presents a set of performance figures for both the standard and the xor embeddings and shows that the latter outperforms the former for any torus. In addition, it is proven that for a one-dimensional torus (a ring) the xor embedding is optimal in the sense that it minimizes the execution time of a class of parallel algorithms with hypercube topology. This class of algorithms is frequently found in real applications, such as FFT and some class of sorting algorithms 相似文献
70.