全文获取类型
收费全文 | 13111篇 |
免费 | 306篇 |
国内免费 | 36篇 |
专业分类
电工技术 | 192篇 |
综合类 | 17篇 |
化学工业 | 1943篇 |
金属工艺 | 277篇 |
机械仪表 | 315篇 |
建筑科学 | 492篇 |
矿业工程 | 23篇 |
能源动力 | 248篇 |
轻工业 | 1622篇 |
水利工程 | 107篇 |
石油天然气 | 30篇 |
无线电 | 1410篇 |
一般工业技术 | 1872篇 |
冶金工业 | 3111篇 |
原子能技术 | 167篇 |
自动化技术 | 1627篇 |
出版年
2022年 | 109篇 |
2021年 | 193篇 |
2020年 | 118篇 |
2019年 | 168篇 |
2018年 | 208篇 |
2017年 | 199篇 |
2016年 | 246篇 |
2015年 | 142篇 |
2014年 | 282篇 |
2013年 | 605篇 |
2012年 | 472篇 |
2011年 | 580篇 |
2010年 | 467篇 |
2009年 | 465篇 |
2008年 | 525篇 |
2007年 | 501篇 |
2006年 | 414篇 |
2005年 | 415篇 |
2004年 | 325篇 |
2003年 | 318篇 |
2002年 | 294篇 |
2001年 | 295篇 |
2000年 | 289篇 |
1999年 | 326篇 |
1998年 | 1006篇 |
1997年 | 629篇 |
1996年 | 467篇 |
1995年 | 348篇 |
1994年 | 283篇 |
1993年 | 293篇 |
1992年 | 161篇 |
1991年 | 143篇 |
1990年 | 148篇 |
1989年 | 146篇 |
1988年 | 138篇 |
1987年 | 107篇 |
1986年 | 116篇 |
1985年 | 156篇 |
1984年 | 109篇 |
1983年 | 98篇 |
1982年 | 74篇 |
1981年 | 97篇 |
1980年 | 92篇 |
1979年 | 93篇 |
1978年 | 49篇 |
1977年 | 112篇 |
1976年 | 160篇 |
1975年 | 54篇 |
1974年 | 42篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
J. Buytaert L. De Boeck F. Verbeure
C. Bricman
F. Cao C. De Clercq L. Etienne B. Goorens J. Lemonne F. Stichelbaut S. Tavernier G. Van Beek C. Vander Velde W. Van Doninck L. Van Lancker J. WickensE. Daubie
F. Defontaines F. Grard J. Kesteman O. Pingot C. Poiret 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1991,310(3):596-606The layout and construction of the muon drift chambers equipping the end caps of the DELPHI detector are described. The performance of this forward muon detection system, determined from cosmic ray tests and data collected during the first year of LEP operation, is presented. 相似文献
72.
Influence of Storage Time and Temperature on Absorption of Flavor Compounds from Solutions by Plastic Packaging Materials 总被引:1,自引:0,他引:1
R. Van Willige D. Schoolmeester A. Van Ooij J. Linssen A. Voragen 《Journal of food science》2002,67(6):2023-2031
ABSTRACT: Linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle), and polyethylene naphthalate (PEN) were stored in a model solution containing 10 flavor compounds at 4, 20, and 40 °C and flavor absorption by the plastic materials was followed in time. The absorption rate and/or total amount absorbed increased considerably with temperature from 4 to 40 °C. Depending on storage temperature, total flavor absorption by the polyolefins (LLDPE and OPP) was 3 to 2400 times higher than by the polyesters (PC, PET, and PEN). Therefore, in the factor of flavor absorption, polyesters are preferred over polyolefins as packaging material. 相似文献
73.
74.
J G De Nobel F M Klis A Ram H Van Unen J Priem T Munnik H Van Den Ende 《Yeast (Chichester, England)》1991,7(6):589-598
To study cell-cycle-related variations in wall permeability of Saccharomyces cerevisiae, two approaches were used. First, an asynchronous culture was fractionated by centrifugal elutriation into subpopulations containing cells of increasing size. The subpopulations represented different stages of the cell cycle as judged by light microscopy. Cell wall porosity increased when these subpopulations became enriched with budded cells. Secondly, synchronous cultures were obtained by releasing MATa cells from alpha-factor induced G1-arrest. These cultures grew synchronously for at least two generations. The cell wall porosity increased sharply in these cultures, shortly before buds became visible and was maximal during the initial stages of bud growth. It decreased in cells which had completed nuclear migration and before abscission of the bud had occurred. The porosity reached its lowest value during abscission and in unbudded cells. We examined the incorporation of mannoproteins into the wall during the cell cycle. SDS-extractable mannoproteins were incorporated continuously. However, the incorporation of glucanase-extractable mannoproteins, which are known to affect cell wall porosity, showed cyclic oscillations and reached its maximum after nuclear migration. This coincided with a rapid decrease in cell wall porosity, indicating that glucanase-extractable mannoproteins might contribute to this decrease. 相似文献
75.
An analysis is made of longitudinal effects in semiconductor lasers with low facet reflectivities. For this purpose, a self-consistent model is used based on the beam propagation method, which takes into account both the lateral and longitudinal dimension. The calculations show that longitudinal effects have a significant influence on the output fields in the laser. 相似文献
76.
77.
Evin Van Griethuysen Erwin Flaschel Albert Renken 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):129-138
The pH-dependence of the reaction kinetics of lactase (β-galactosidase) from Aspergillus oryzae in different reaction media is presented in terms of a two-parameter model. The lactase from A. oryzae seems to have replaced the A. niger lactase on the market owing to a better activity/price ratio and may be utilised for lactose hydrolysis in acid as well as in neutral milk products. Its pH optimum is around pH 4.5. However, in the neutral pH-range its activity depended strongly on the salt content of the substrate solution. For example, its activity in whey (pH 6.5) fell to only 30% of its expected activity in a pure lactose solution at the same pH. The whey effect was the same for both soluble and immobilised lactase. The two parameter kinetic model, which included a term for competitive product inhibition gave excellent agreement with experimental data, and may thus be useful for the prediction of reactor performance with this enzyme. 相似文献
78.
For a PC-mobile download system which is embedded with streaming download protocol, there are problems that the data cannot be transmitted correctly from the PC to the mobile, or the transmission is unacceptably slow. To solve these problems, we carry out a formal analysis for the protocol with some timing parameters and a given probability of message loss and unordered data using a probabilistic model checking tool PRISM. We introduce a technique to reduce the state space of the system modeling the protocol which is a network of probabilistic timed automata. The experimental results in PRISM give us a clear explanation to the problems, and are helpful in identifying the optimal parameter settings to meet industrial requirements. 相似文献
79.
P. R. J. M. Smits P. H. Van Lieshout A. A. F. Van De Ven 《Journal of Engineering Mathematics》1989,23(2):157-186
A variational principle for the magnetoelastic stability problem of superconductors is constructed. Independently, a pair of integral equations is derived, from which the initial and the perturbed field can be computed. The integral equations are solved for in-plane buckling of a slender pair of concentric tori, and out-of-plane buckling of a slender pair of equal coaxial tori. By using the variational principle, it is shown that both cases can become unstable when the currents on the two tori are equally directed, and the pertinent buckling values are calculated. The thus obtained buckling values are compared with the results of an alternative, mathematically less rigorous, method. A good correspondence between the two methods is found (at least as long as the two tori are not too near). 相似文献
80.
The kinetics of the transition metal-catalysed direct addition of amine NH bonds to carbon--carbon multiple bonds (hydroamination) has been explored by in situ spectroscopic techniques. From an open mass balance it was concluded that an intermediate species was formed during the cyclisation of 6-aminohex-1-yne. This species was identified as the enamine 2-methylene-piperidine, which is the primary hydroamination product. 相似文献