全文获取类型
收费全文 | 7310篇 |
免费 | 157篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 35篇 |
综合类 | 3篇 |
化学工业 | 849篇 |
金属工艺 | 59篇 |
机械仪表 | 79篇 |
建筑科学 | 96篇 |
矿业工程 | 36篇 |
能源动力 | 152篇 |
轻工业 | 393篇 |
水利工程 | 29篇 |
石油天然气 | 8篇 |
无线电 | 259篇 |
一般工业技术 | 436篇 |
冶金工业 | 4460篇 |
原子能技术 | 31篇 |
自动化技术 | 546篇 |
出版年
2023年 | 42篇 |
2022年 | 105篇 |
2021年 | 151篇 |
2020年 | 98篇 |
2019年 | 81篇 |
2018年 | 102篇 |
2017年 | 90篇 |
2016年 | 108篇 |
2015年 | 79篇 |
2014年 | 148篇 |
2013年 | 213篇 |
2012年 | 207篇 |
2011年 | 215篇 |
2010年 | 168篇 |
2009年 | 130篇 |
2008年 | 162篇 |
2007年 | 131篇 |
2006年 | 93篇 |
2005年 | 86篇 |
2004年 | 65篇 |
2003年 | 58篇 |
2002年 | 52篇 |
2001年 | 45篇 |
2000年 | 41篇 |
1999年 | 159篇 |
1998年 | 1283篇 |
1997年 | 802篇 |
1996年 | 497篇 |
1995年 | 297篇 |
1994年 | 235篇 |
1993年 | 288篇 |
1992年 | 52篇 |
1991年 | 63篇 |
1990年 | 67篇 |
1989年 | 61篇 |
1988年 | 84篇 |
1987年 | 61篇 |
1986年 | 57篇 |
1985年 | 61篇 |
1984年 | 16篇 |
1983年 | 18篇 |
1982年 | 40篇 |
1981年 | 43篇 |
1980年 | 51篇 |
1979年 | 11篇 |
1977年 | 136篇 |
1976年 | 250篇 |
1975年 | 14篇 |
1972年 | 11篇 |
1943年 | 21篇 |
排序方式: 共有7471条查询结果,搜索用时 15 毫秒
61.
62.
It has been previously reported that Bryostatin 1 (Bryo1) induces differentiation of the human acute lymphoblastic leukemia (ALL) cell line, Reh, to a monocytoid B-cell stage. In this study we demonstrate that a novel protein, ubiquitin COOH-terminal hydrolase (UCH-L1), is associated with this differentiation. Reh cells were treated with 200 nmol/l of Bryo1 for 72 h and analyzed for changes in morphology, surface immunophenotype, acid phosphatase and terminal deoxynucleotidyl transferase. Protein patterns of the parent and differentiated cells, by two-dimensional polyacrylamide gel electrophoresis (2D PAGE), were studied. Bryo1-treated cells expressed morphologic, phenotypic and enzymatic features of the monocytoid B-cell stage. The UCH-L1 enzyme (MW-pl 34-5.3) was detected by 2 D PAGE in the differentiated, but not in parent cells. The presence of UCH-L1 in the Bryo1-treated cells was further confirmed by immunoblotting of 2 D PAGE using UCH-L1 polyclonal antibody. Ubiquitin expression was studied in parent and Bryo1-treated cells and was compared with 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells. Both agents, TPA and Bryo1, increased the level of ubiquitin expression as detected by flow cytometry. Sodium borohydride, an inhibitor of UCH-L1, inhibited the Bryo1-induced differentiating effect on Reh cells. To date, the mechanism by which Bryo1, exerts its B-cell differentiating effect is not fully understood. This study shows that UCH-L1 expression may play a major role in Bryo1-induced differentiation in pre-B-ALL. 相似文献
63.
In the 1960s the promise of the Brantigan lung reduction surgery was shattered when it was shown that the improvement in airway conductance drifted back towards the preoperative value over a period of 12 to 18 months. Since then there has been a marked improvement in our understanding of emphysema, its pathology, and techniques for obtaining images of the lung. In addition, reliable automated cardiopulmonary and physiologic testing, advances in critical care medicine, and new pharmacologic agents have improved patient care. Surgical techniques now allow better control of air leaks and access to anatomic regions not previously accessible. The combination of all of the above makes lung reduction surgery worth re-examining as a palliative procedure for severely symptomatic patients. Clearly, it is not a panacea but can in some cases produce dramatic improvements in symptomatology and quality of life. This article presents the available data describing potential mechanisms of improvement and clinical outcomes following lung reduction surgery. It also outlines areas that need further work, such as patient selection and surgical techniques. 相似文献
64.
With the object of assessing the long-term prognosis and the frequencies of recurrence and remission in women chronic low abdominal pain without laparoscopically visible cause, questionnaire were sent in 1985 and 1991 to 55 women who had been submitted to laparoscopy in 1982-1984 for this reason. These women had been told that there was no demonstrable explanation of the pain experienced and were then discharged. 65% and 55% respectively had experienced and unfavourable course with considerable and continued symptoms. Only 22% stated in both investigations that they had experienced a favourable course and that they were, by and large, free from pain. 36% changed from an unfavourable to a favourable course or the reverse. The assessment made by the women was confirmed by a series of subordinate questions and this demonstrated a marked difference between the favourable and unfavourable courses of the condition. It is concluded that laparoscopy with exclusion of significant pathology is not, in itself, satisfactory as treatment of this patient group and that no improvement occurs in the course of time. The condition varies greatly with many recurrences and remissions and, for this reason, uncontrolled reports of the therapeutic effects are of no significance. When compared with the literature, it is suggested that this patient group should be referred early in the course of the condition to a therapist with specialist psychological/sexological insight and/or to a physiotherapist with interest in this patient group. 相似文献
65.
RM Effros C Murphy A Hacker RM Schapira R Bongard 《Canadian Metallurgical Quarterly》1994,77(3):1460-1465
The use of methylene blue (MB) to estimate dilution of epithelial lining fluid, which occurs during bronchoalveolar lavage (BAL), is complicated by loss of this redox dye from the air spaces. The rate of MB uptake from the air spaces of isolated rat lungs and the effects of oxidation and reduction on this process were investigated in this study. Movement of MB from the air spaces to perfusate was compared with the corresponding transport of 125I-labeled albumin, [14C]-dextran, 99mTc-labeled diethylenetriaminepentaacetate, [3H]-sucrose, and 3H2O. By the end of 2 min, MB concentrations in the BAL had fallen by 58 +/- 4% (SE; n = 11) and 3H2O by 78 +/- 2% (n = 13), whereas concentrations of the other indicators decreased by approximately 6%. All but 10% of the 3H2O lost from the air spaces was found in the perfusate, whereas 19% of the lost MB was not recovered in the perfusate, suggesting retention of MB in the pulmonary tissues. Absorption of MB from the air spaces was slowed by 20% when the lungs were left unperfused, and absorption was accelerated threefold by reduction of MB to leukomethylene blue with Na2S2O4. In contrast, MB losses from the air space were slowed by the oxidizing agent K3Fe(CN)6 and by addition of superoxide dismutase or ascorbic oxidase. It is therefore possible that ascorbic acid and O2- entering the air spaces reduce MB to the uncharged leuko form. Lowering the pH of the BAL fluid to 3.5 also slowed MB reabsorption. This suggests that acid aspiration may stimulate release of oxidants into the air spaces. 相似文献
66.
Sandra Aparecida de Assis Pedro Fernandes Bruno Sommer Ferreira Joaquim MS Cabral Olga Maria Mascarenhas Faria Oliveira 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(3):277-280
A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry 相似文献
67.
The outcome of treatment for bilateral congenital cataracts was studied retrospectively in a group of 51 patients. Two major categories of lens opacities were identified. In the first category, the opacities were extensive and visual impairment was evident early in the first year. These cataracts often occurred in eyes with small corneal diameters and poorly dilating pupils. Postoperative strabismus was nearly universal; nystagmus developed in over 50%; and late onset open-angle glaucoma developed in 8 of the 29 patients studied. Early surgery did not seem to abort the development of nystagmus in this group of patients. In the second category, the lens opacities were partial, often lamellar in configuration, and visual impairment was less severe. Surgery was usually performed after 3 years of age, with good visual results if the opacities were symmetrical and there was no nystagmus. No deprivation amblyopia developed in this group, even when surgery was delayed into the second decade. Strabismus developed postoperatively in about a third, but so far, no delayed open-angle glaucoma has been identified. 相似文献
68.
Bruno Buchmayr 《国际钢铁研究》1992,63(10):446-446
69.
Schilling D.L. Milstein L.B. Pickholtz R.L. Bruno F. Kanterakis E. Kullback M. Erceg V. Biederman W. Fishman D. Salerno D. 《Communications Magazine, IEEE》1991,29(11):86-93
Multipath propagation in a broadband CDMA environment is described. A propagation model for broadband spread-spectrum signals is presented. Experimental results relating to the sharing of the band by fixed service microwave users and mobile personal communications network (PCN) users are discussed. Field tests indicate that PCN systems can provide high-quality communications when sharing the spectrum with fixed-service microwave systems in suburban and urban areas 相似文献
70.
A model for building integrated photovoltaic systems has been developed and implemented in a dynamic simulation tool. This tool takes into account the thermal interactions between the PV collector and the building. The influence of the type of integration upon the PV collector efficiency has been evaluated and hybrid PV/air collectors have been studied. An overall efficiency is defined, including the production of electricity and heat. A case study has been performed on two different typical buildings. In the case of a multi-crystalline silicon PV collector integrated on the roof of a single family house located in Paris, the efficiency of unventilated PV modules fixed on the roof is 14%. If the PV collector is used to preheat the ventilation air, the efficiency reaches 20%. A proper building integration also improves the environmental balance of PV technologies over their life cycle. 相似文献