全文获取类型
收费全文 | 817342篇 |
免费 | 10512篇 |
国内免费 | 2399篇 |
专业分类
电工技术 | 14523篇 |
综合类 | 3328篇 |
化学工业 | 121549篇 |
金属工艺 | 31375篇 |
机械仪表 | 23993篇 |
建筑科学 | 20410篇 |
矿业工程 | 3467篇 |
能源动力 | 21386篇 |
轻工业 | 70223篇 |
水利工程 | 8060篇 |
石油天然气 | 11890篇 |
武器工业 | 44篇 |
无线电 | 95640篇 |
一般工业技术 | 155444篇 |
冶金工业 | 147598篇 |
原子能技术 | 14242篇 |
自动化技术 | 87081篇 |
出版年
2021年 | 6343篇 |
2020年 | 4633篇 |
2019年 | 5938篇 |
2018年 | 23227篇 |
2017年 | 21943篇 |
2016年 | 19409篇 |
2015年 | 7756篇 |
2014年 | 12202篇 |
2013年 | 34261篇 |
2012年 | 21862篇 |
2011年 | 35126篇 |
2010年 | 28301篇 |
2009年 | 28662篇 |
2008年 | 30402篇 |
2007年 | 30943篇 |
2006年 | 21222篇 |
2005年 | 20485篇 |
2004年 | 19717篇 |
2003年 | 19447篇 |
2002年 | 18070篇 |
2001年 | 17821篇 |
2000年 | 16798篇 |
1999年 | 17723篇 |
1998年 | 45008篇 |
1997年 | 31765篇 |
1996年 | 24558篇 |
1995年 | 18552篇 |
1994年 | 16464篇 |
1993年 | 16020篇 |
1992年 | 11677篇 |
1991年 | 10999篇 |
1990年 | 10791篇 |
1989年 | 10486篇 |
1988年 | 9947篇 |
1987年 | 8658篇 |
1986年 | 8647篇 |
1985年 | 9871篇 |
1984年 | 9088篇 |
1983年 | 8248篇 |
1982年 | 7665篇 |
1981年 | 7853篇 |
1980年 | 7392篇 |
1979年 | 7238篇 |
1978年 | 6843篇 |
1977年 | 8346篇 |
1976年 | 10897篇 |
1975年 | 5986篇 |
1974年 | 5706篇 |
1973年 | 5790篇 |
1972年 | 4766篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
4-Pentafluoroethylumbelliferyl-beta-D-glucoside is proposed as an efficient substrate for human leukocyte acid beta-glucosidase. Its synthesis is described. This substrate was compared directly with 4-trifluoromethylumbelliferyl-beta-D-glucoside synthesized by us earlier and with 4-methylumbelliferyl-beta-D-glucoside which is commonly used for acid beta-glucosidase activity assay. The specific activity of acid beta-glucosidase with 4-pentafluoroethylumbelliferyl-beta-D-glucoside was 3- and 8-fold higher than it was with the substrates mentioned above. The kinetic parameters KM and VMAX for human leukocyte acid beta-glucosidase with the three substrates was determined. One possible application of the newly synthesized substrate is its use in the diagnosis of acid beta-glucosidase hereditary deficiency (Gaucher's disease). 相似文献
992.
G La Nasa A Pizzati A Ledda A Vacca M Arras L Contu 《Canadian Metallurgical Quarterly》1996,81(2):178-181
OBJECTIVE: To determine the distribution and amount of elastic fibers in the dermis of clinically normal dogs and dogs with dermatoses, particularly solar dermatitis. DESIGN: Skin specimens from 7 anatomic sites were obtained from 19 clinically normal dogs after euthanasia to evaluate the normal distribution of elastic fibers. Biopsy specimens also were obtained from 34 dogs with dermatoses, including 16 with solar dermatitis. Tissue sections were stained with H&E, Verhoeff-van Gieson, and periodic acid-Schiff. ANIMALS: 19 clinically normal dogs and 34 dogs with dermatoses. PROCEDURE: Numbers of elastic fibers were graded subjectively. Comparisons between clinically normal dogs and dogs with dermatoses were made. RESULTS: Normal elastic fibers were present in low numbers in the dermis of adult dogs, regardless of anatomic site or presence or severity of dermatitis. Condensed elastotic material was visualized in only 2 dogs with solar dermatitis. In both dogs, the elastotic material was Verhoeff-van Gieson and periodic acid-Schiff stain positive but was not visible with H&E stain. The most frequent histopathologic finding in the dermis of dogs with solar dermatitis was superficial dermal fibrosis. CONCLUSIONS: The dermis of clinically normal dogs does not contain abundant elastic fibers. Alterations of elastic fibers in dogs with solar dermatitis are rare. Superficial dermal fibrosis may be a better indicator of solar damage. 相似文献
993.
R Lehtinen H Siev?nen J Viik V Turjanmaa K Niemel? J Malmivuo 《Canadian Metallurgical Quarterly》1996,78(9):1002-1006
In this comparative cross-sectional study, we evaluated whether a novel computerized diagnostic variable, ST-segment depression/heart rate ST/HR analysis during both the exercise and postexercise recovery phases of the exercise electrocardiography (ECG) test, can detect coronary artery disease more accurately than methods using either exercise or recovery phase alone. The study population comprised 347 clinical patients referred for a routine bicycle exercise ECG test at Tampere University Hospital, Finland. Of these, 127 had angiographically proven coronary artery disease, whereas 13 had no coronary artery disease according to angiography, 18 had no perfusion defect according to technetium-99m sestamibi single-photon emission computed tomography, and 189 were clinically normal with respect to cardiac diseases. For each patient, the maximum values of the ST/HR hysteresis, ST/HR index, end-exercise ST depression, and recovery ST depression were determined from the Mason-Likar modification of the standard 12-lead exercise electrocardiogram [aVL, aVR, and V1 excluded]. The diagnostic performance of these continuous diagnostic variables was compared by means of receiver-operating characteristic analysis. The area under the receiver-operating characteristic curve of the ST/HR hysteresis was 89%, which was significantly larger than that of the end-exercise ST depression (76%, p < or = 0.0001), recovery ST depression (84%, p = 0.0063), or ST/HR index (83%, p = 0.0023), indicating superior diagnostic performance of the ST/HR hysteresis independent of the partition value selection. In conclusion, computerized analysis of the HR-adjusted ST depression pattern during the exercise phase, integrated with the HR-adjusted ST depression pattern during the recovery phase after exercise, can significantly improve the diagnostic performance and clinical utility of the exercise ECG test for the detection of coronary artery disease. 相似文献
994.
We report a case of a giant intrasacral schwannoma expanding into the presacral space. 'En bloc' resection was accomplished by an anterior, transabdominal approach. The advantages of such a procedure are discussed. 相似文献
995.
996.
Of 1,666 patients who underwent fine needle aspiration for breast lumps, 4 developed pneumothorax as a complication. The incidence of this complication in our patients is 1:417. The clinical manifestations were immediate chest pain, shoulder pain and, occasionally, dyspnea that developed later. Observation is sufficient treatment in most patients, and rarely is drainage of the pneumothorax required. 相似文献
997.
998.
Sabha Kesraoui-Ouki Christopher R. Cheeseman Roger Perry 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(2):121-126
This paper assesses the potential of natural zeolite utilization as a low-cost ion-exchange and sorbent material in pollution control and recovery of metals. The improvement of the purity of natural zeolites coupled with their chemical modification capabilities in order to provide specific properties may provide a cost-effective alternative for the treatment of heavy metal contaminated soil and water. The application of natural zeolites in industrial pollution control is becoming important and the level of technical effort is increasingly expanding. The extent of application is unlikely to be related solely to their low cost, but also to improved properties and performance characteristics, which will advance the practical implementation of natural zeolites' technology. 相似文献
999.
R. P. Voitovich Yu. V. Naidich G. A. Kolesnichenko 《Powder Metallurgy and Metal Ceramics》1992,31(6):494-497
Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 40–44, June, 1992. 相似文献
1000.
S. I. Glinchak Yu. A. Egorov R. R. Aliev E. D. Radchenko B. K. Nefedov N. A. Grigor'ev 《Chemistry and Technology of Fuels and Oils》1992,28(3):175-177
Translated from Khimiya i Tekhonologiy Topliv i Masel, No. 3, pp. 33–34, March, 1992. 相似文献