全文获取类型
收费全文 | 281823篇 |
免费 | 3371篇 |
国内免费 | 296篇 |
专业分类
电工技术 | 4291篇 |
综合类 | 111篇 |
化学工业 | 47190篇 |
金属工艺 | 15721篇 |
机械仪表 | 10761篇 |
建筑科学 | 5122篇 |
矿业工程 | 3846篇 |
能源动力 | 4550篇 |
轻工业 | 15171篇 |
水利工程 | 4383篇 |
石油天然气 | 13110篇 |
武器工业 | 33篇 |
无线电 | 21434篇 |
一般工业技术 | 68116篇 |
冶金工业 | 39129篇 |
原子能技术 | 11259篇 |
自动化技术 | 21263篇 |
出版年
2021年 | 3606篇 |
2020年 | 2878篇 |
2019年 | 3526篇 |
2018年 | 6733篇 |
2017年 | 7001篇 |
2016年 | 7363篇 |
2015年 | 4098篇 |
2014年 | 6550篇 |
2013年 | 12638篇 |
2012年 | 9262篇 |
2011年 | 10755篇 |
2010年 | 8814篇 |
2009年 | 9456篇 |
2008年 | 9473篇 |
2007年 | 9083篇 |
2006年 | 7198篇 |
2005年 | 6292篇 |
2004年 | 6144篇 |
2003年 | 5907篇 |
2002年 | 5698篇 |
2001年 | 5340篇 |
2000年 | 5309篇 |
1999年 | 4672篇 |
1998年 | 9278篇 |
1997年 | 7229篇 |
1996年 | 5326篇 |
1995年 | 4234篇 |
1994年 | 3855篇 |
1993年 | 4107篇 |
1992年 | 3396篇 |
1991年 | 3550篇 |
1990年 | 3621篇 |
1989年 | 3512篇 |
1988年 | 3422篇 |
1987年 | 3382篇 |
1986年 | 3265篇 |
1985年 | 3440篇 |
1984年 | 3366篇 |
1983年 | 3239篇 |
1982年 | 3107篇 |
1981年 | 3168篇 |
1980年 | 3202篇 |
1979年 | 3321篇 |
1978年 | 3556篇 |
1977年 | 3683篇 |
1976年 | 4415篇 |
1975年 | 3254篇 |
1974年 | 3333篇 |
1973年 | 3396篇 |
1972年 | 3005篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
G Pons-Lladó F Carreras X Borrás J Palmer J Llauger A Bayés de Luna 《Canadian Metallurgical Quarterly》1997,79(12):1651-1656
To compare the value of echocardiography and magnetic resonance imaging (MRI) in the assessment of the amount and extent of hypertrophy in hypertrophic cardiomyopathy (HC) and, second, to correlate the degree of hypertrophy, as assessed by MRI, with clinical and electrocardiographic parameters, 30 consecutive patients (16 men and 14 women, aged 20 to 74 years) with HC were studied. Measurements of left ventricular wall thickness were performed at 11 predetermined segments (5 basal, 5 midventricular, and 1 apical) by 2-dimensional echocardiography and MRI. Two parameters derived from MRI studies were considered as indicators of the degree and extent of hypertrophy: (1) mean of the measured wall thickness at the 11 segments, and (2) the number of segments with thickness > 15 mm. Results showed that, from a total of 330 myocardial segments, thickness could be measured by echocardiography in 221 (67%), whereas MRI allowed measurement of 320 segments (97%). When compared with clinical and electrocardiographic data, no correlation was found regarding mean wall thickness and number of hypertrophied segments by MRI except for the presence of an abnormal electrocardiographic repolarization pattern. It is concluded that MRI allows a better assessment of the degree and extension of left ventricular hypertrophy than echocardiography in HC. Despite the precise information on hypertrophy provided by MRI, the amount and degree of hypertrophy bears no correlation with most of the clinical data in these patients. 相似文献
992.
S Merino A Aguilar JM Tomás R Bonet MJ Martinez D Simón-Pujol F Congregado 《Canadian Metallurgical Quarterly》1997,22(5):315-320
1. We investigated the effect of exercise on plasma adrenomedullin, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) concentrations and studied the relationship between these peptides and haemodynamic parameters in nine patients with old myocardial infarction (MI) and in eight normal subjects. 2. The exercise protocol consisted of two fixed work loads (40 and 80 W) for 4 min each and venous blood samples were taken at rest, during each exercise stage and after exercise while monitoring the mean arterial pressure (MAP) and heart rate (HR). In MI, pulmonary arterial pressure (PAP), pulmonary capillary wedge pressure (PCWP), left ventricular end-diastolic pressure (LVEDP) and cardiac output (CO) were measured throughout exercise. 3. Adrenomedullin levels did not significantly increase with exercise. Adrenomedullin levels correlated with PAP and PCWP at rest (P < 0.05). Atrial natriuretic peptide levels correlated with PAP, PCWP and LVEDP throughout exercise (P < 0.05) but, on multiple regression analysis, PCWP correlated only with ANP (P < 0.01). Brain natriuretic peptide levels correlated with LVEDP throughout exercise (P < 0.01) and its increment correlated closely with basal BNP levels at rest (P < 0.01). 4. These results suggest that adrenomedullin does not respond to the acute haemodynamic changes of exercise, whereas ANP responds to it and PCWP is the major stimulus factor. Brain natriuretic peptide responds to exercise in proportion to the basal synthesis of BNP in patients with left ventricular dysfunction and LVEDP may play a role in increasing BNP during exercise. 相似文献
993.
V. A. Kotenev 《Protection of Metals》2003,39(4):394-404
General methodological and mathematical aspects of using tomographic approach to reconstructing the inner structure of surface layers and films on the most abundant nonuniformity types characteristic of heterogeneous physico-chemical nanosystems are discussed. Spectral ellipsometric measurement of light reflected from a nonuniform surface nanolayer allows substantiating spectral-tomographic principle and reconstructing the inner structure of the layer by solving an integral equation of the 1st kind. Principles and mathematic fundamentals of ellipsometric spectral tomography are presented, which may be used in nondestructively monitoring the distribution of physico-chemical properties over the bulk of nonuniform metal–oxide surface structures. 相似文献
994.
The effects of induction conditions on production of a soluble antitumor sFv in Escherichia coli 总被引:2,自引:0,他引:2
Jaymie R.Sawyer; Schlom Jeffrey; Kashmiri S. V. S. 《Protein engineering, design & selection : PEDS》1994,7(11):1401-1406
CC49 is a second generation monoclonal antibody(mAb) with highaffinity to a pancarcinoma antigen, TAG-72. A single-chain Fv(sFv)ofCC49 may have a role in managing human carcinomas. Most reportedsFvs have been expressed as insoluble products that must besolubilized and renatured. Soluble sFv expression is advantageousas activity can be assayed directly from the periplasmic fraction.Also, gene-level immunoconjugates may not be amenable to refoldingprotocols. Using a vector that carries the tac promoter andomp A signal, we have examined the effects of four variableson the expression and accumulation of soluble CC49 sFv: (i)linker sequence joining VL and VH, (ii) isopropylthio-ß-D-galactosideconcentration for induction, (iii) temprature, and (iv) theaddition of nonmetabolizable sugars to the medium. We have beenable to demonstrate, using rapidly prepared periplasmic extracts,that the yield of soluble sFv improves by the addition of 0.4Msucrose to the medium and by inducing expression with a verylow concentration of IPTG (0.020.03 mM). Under theseinduction conditions periplasmic extracts demonstrate increasedexpression of the sFv, as shown by the larger amount of a 27kDa band on SDS-polyacrylamide gel, and an increased abilityto inhibit binding of the mAb CC49 to immobilized tumor extracts. 相似文献
995.
Peel strengths at room temperature and under superplastic forming conditions at 530 °C were measured for diffusion-bonded joints in Al-Li 8090 alloy sheet. The bonds were made in the solid state, or via a transient liquid phase using interlayers. The effect of strain rate, sheet thickness and heat treatment were investigated. The significance of these results for the testing of DB joints and for their use in DB/SPF structures is discussed. 相似文献
996.
V. Yu. Glina 《Measurement Techniques》1992,35(3):316-317
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 33–34, March, 1992. 相似文献
997.
V. P. Golovnya 《Journal of Engineering Physics and Thermophysics》1992,62(3):264-269
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 3, pp. 366–372, March, 1992. 相似文献
998.
Translated from Atomnaya Énergiya, Vol. 73, No. 5, pp. 350–354, November, 1992. 相似文献
999.
Evolution of the capillary network in a reactive powder concrete during hydration process 总被引:7,自引:0,他引:7
V. Morin F. Cohen-Tenoudji A. Feylessoufi P. Richard 《Cement and Concrete Research》2002,32(12):1907-1914
Ultrasonic waves in echographic mode, combined with autogenous shrinkage measurements, were used to study the evolution of the capillary network of reactive powder concrete (RPC) from the time after the mixing. Two characteristic porous classes have been identified: the first, between 10 and 20 nm, begins when the material reaches its solid hyperstatic state, and the second about 1 or 2 nm. The first class is associated with the porous space between the C-S-H hydrate clusters and the second with the internal porosity of the hydrate. The evolution of the active capillary radius as a function of the degree of hydration allows us to understand the strong interaction between the capillary network size and the chemical activity given by the dissipated calorimetric power curve. Indeed, the maximum point of the chemical activity marks the transition of the first class of pores to the second one. Finally, measurements of electrical conductivity through RPC samples show that after the maximum of the dissipated power, the curve of this electrical conductivity presents the same evolution as the capillary radius. As the electrical conductivity clearly depends on the evolution of the capillary network, the similarity between the results confirms our analysis in pore classes. 相似文献
1000.