全文获取类型
收费全文 | 41961篇 |
免费 | 2048篇 |
国内免费 | 38篇 |
专业分类
电工技术 | 283篇 |
综合类 | 33篇 |
化学工业 | 7634篇 |
金属工艺 | 740篇 |
机械仪表 | 831篇 |
建筑科学 | 1319篇 |
矿业工程 | 74篇 |
能源动力 | 821篇 |
轻工业 | 5600篇 |
水利工程 | 382篇 |
石油天然气 | 176篇 |
武器工业 | 4篇 |
无线电 | 2343篇 |
一般工业技术 | 7396篇 |
冶金工业 | 10524篇 |
原子能技术 | 206篇 |
自动化技术 | 5681篇 |
出版年
2023年 | 360篇 |
2022年 | 369篇 |
2021年 | 937篇 |
2020年 | 782篇 |
2019年 | 731篇 |
2018年 | 1554篇 |
2017年 | 1556篇 |
2016年 | 1601篇 |
2015年 | 1150篇 |
2014年 | 1450篇 |
2013年 | 2826篇 |
2012年 | 2443篇 |
2011年 | 2302篇 |
2010年 | 1814篇 |
2009年 | 1606篇 |
2008年 | 1852篇 |
2007年 | 1611篇 |
2006年 | 1218篇 |
2005年 | 1001篇 |
2004年 | 938篇 |
2003年 | 823篇 |
2002年 | 739篇 |
2001年 | 473篇 |
2000年 | 480篇 |
1999年 | 629篇 |
1998年 | 3370篇 |
1997年 | 2022篇 |
1996年 | 1307篇 |
1995年 | 764篇 |
1994年 | 660篇 |
1993年 | 638篇 |
1992年 | 211篇 |
1991年 | 224篇 |
1990年 | 225篇 |
1989年 | 213篇 |
1988年 | 190篇 |
1987年 | 166篇 |
1986年 | 182篇 |
1985年 | 214篇 |
1984年 | 184篇 |
1983年 | 132篇 |
1982年 | 165篇 |
1981年 | 172篇 |
1980年 | 155篇 |
1979年 | 127篇 |
1978年 | 122篇 |
1977年 | 198篇 |
1976年 | 418篇 |
1975年 | 89篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Bourque Paul; Blanchard Louis; Saulnier Jo?l; Vézina Jean 《Canadian Metallurgical Quarterly》1992,24(1):118
Studied the relationship among age, physical health status, and psychic and somatic symptoms of depression among elderly adults. Human Ss: 318 male and female Canadian older adults (aged 65–102 yrs). Information on sociodemographic factors and health status was obtained using the Older American Research Scale, French version, by R. Lefran?ois et al (1988). A French version by P. Bourque and D. Beaudette (1982) of the Beck Depression Inventory was also used. The results were evaluated according to each S's sex, age, institutionalized residence status, and health status. Statistical tests were used. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
142.
The binding of 125I-labelled tissue plasminogen activator (tPA), the tPA A- or B-chain to endothelial cells (EC) were studied in suspensions of cultured human umbilical vein EC (HUVEC) or immortalized microvascular EC (HMEC). By determinations of the concentration-dependent binding it was shown that both the A-chain and the B-chain, which were isolated after partial reduction of two-chain tPA, contain ligands for binding to EC. The affinity for the B-chain was much higher than for the A-chain according to Scatchard analysis (Kd 24 and 515 nM, respectively), whereas the number of binding sites was higher for the A-chain than for the B-chain (Bmax 8 x 10(5) and 1.2 x 10(5), respectively). There were no cross interactions between the A- and B-chains and their binding sites. The binding of tPA to EC induced an almost 100-fold increase of the activation rate when compared to the same amount of enzyme in free solution, which in contrast to the fibrin-induced stimulation was not inhibited by antibodies against fibrin. The enzymatic activity of the B-chain was much less affected by the association to the cells. Both tPA and the tPA B-chain were largely protected against inhibition by an excess plasminogen activator type-1 (PAI-1) when bound to EC, whereas the same amount of free tPA was totally inactivated. The competition studies strongly indicated that an N-terminal segment in the B-chain, AKHRRSPGER, may be the ligand part of the B-chain. It is interesting to note that this polypeptide segment also participates in a binding site for PAI-1, necessary for effective inhibition. This implies a possible competition between PAI-1 and a tPA-receptor for binding of tPA. High molecular weight urokinase had no quenching effect on the binding of the B-chain to EC. 相似文献
143.
144.
radon and radon daughter concentrations have been measured in 33 “energy-efficient” homes in a small subdivision in Kanata, Ontario. Integrated radon measurements were determined over three month periods for a year using solid state nuclear track detectors. Radon and radon daughter grab sample determinations were made during corresponding periods and confirm the distributions of the integrated radon measurements.Annual average individual home radon concentrations show an 8 fold concentration range between homes. This variability in radon concentrations is not reflected in the range of air exchange rates for the homes. A distinct seasonal variation is noted for the median values of the radon and radon daughter concentrations and the equilibrium factor F in the dwellings. 相似文献
145.
The effect of gas-liquid contacting conditions in a static mixer on ozone transfer efficiency and reduction of Bacillus subtilis spores was studied in an experimental ozone contactor. An empirical mathematical model was developed that related the transfer efficiency in the experimental system to the superficial liquid velocity in the mixer, the gas-liquid flow rate ratio and the height of the down-stream bubble column. Spore reduction was determined primarily by the dissolved ozone concentration-time (Cavgtm) product in the reactive flow segment and was independent of the gas-liquid contacting conditions in the static mixer. In an integrated ozone contacting system, the static mixer should be designed to maximize ozone mass transfer while the reactive flow segment should be designed for efficient microorganism reduction. 相似文献
146.
This paper presents a new massively parallel MIMD architecture, halfway between the Connection Machine and hypercubes based on 32-bit processors. It is built from specific 8-bit processors arranged in a 2-D grid and communicating by message transfers. We discuss the communication problems, the instruction set of the basic processing unit, the programmation of the whole array and the use of a high level data-flow language. 相似文献
147.
P. Dubé F. Kerdouss F. Laplante P. Proulx L. Brossard H. Ménard 《Journal of Applied Electrochemistry》2003,33(6):541-547
The electrocatalytic hydrogenation of cyclohexanone has been investigated with catalytic powder particles made of metal nanoaggregates deposited on a nonconductive material such as activated carbon and alumina. The catalytic powder particles were suspended in the solution under vigorous stirring conditions. The brief contact of the powder particles with a porous carbon cathode was sufficient to form adsorbed hydrogen on the metallic nanoaggregates through water electrolysis and initiate the electrohydrogenation process. It is demonstrated that the key parameters of the electrohydrogenation process are both the nature of the metallic nanoaggregates and the nature of the non-conductive material. The hydrodynamics of the solution under vigorous stirring conditions have also been studied for the particular cell used in the present study. 相似文献
148.
149.
This research focused on the syllable as a processing unit in handwriting. Participants wrote, in uppercase letters, words that had been visually presented. The interletter intervals provide information on the timing of motor production. In Experiment 1, French participants wrote words that shared the initial letters but had different syllable boundaries. In Experiment 2, French- and Spanish-speaking participants wrote cognates and pseudowords with a letter sequence that was always intrasyllabic in French and intersyllabic in Spanish. In Experiment 3, French-Spanish bilinguals wrote the cognates and pseudowords with the same type of sequences. In the 3 experiments, the critical interletter intervals were longer between syllables than within syllables, indicating that word syllable structure constrains motor production both in French and Spanish. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
150.
The composition of yellow bronze coatings deposited from acidic sulfate solutions added with polyether laprol and the electrodeposition
conditions are studied by voltammetry and XPS. It is found that halides in rather low (micromolar) concentrations affect significantly
the partial electrodeposition processes. Chlorides increases cathodic polarization, widen the current window of the yellow
bronze electrodeposition, and favor the increase in tin content of the coatings. Bromides narrow the current window, lower
the tin content in the coatings, and hinder the yellow bronze surface oxidation. Iodides inhibit the copper electroreduction
markedly, which makes the yellow bronze deposition practically impossible.
Original Russian Text ? Z. Mockus, S. Kanapeckaité, V. Jasulaitiené, A. Survila, 2006, published in Zashchita Metallov, 2006,
Vol. 42, No. 5, pp. 526–531. 相似文献