全文获取类型
收费全文 | 21022篇 |
免费 | 613篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 217篇 |
综合类 | 17篇 |
化学工业 | 4415篇 |
金属工艺 | 496篇 |
机械仪表 | 370篇 |
建筑科学 | 942篇 |
矿业工程 | 110篇 |
能源动力 | 541篇 |
轻工业 | 1407篇 |
水利工程 | 261篇 |
石油天然气 | 206篇 |
武器工业 | 1篇 |
无线电 | 1450篇 |
一般工业技术 | 3398篇 |
冶金工业 | 4602篇 |
原子能技术 | 168篇 |
自动化技术 | 3058篇 |
出版年
2022年 | 128篇 |
2021年 | 240篇 |
2020年 | 198篇 |
2019年 | 265篇 |
2018年 | 297篇 |
2017年 | 303篇 |
2016年 | 365篇 |
2015年 | 291篇 |
2014年 | 457篇 |
2013年 | 1273篇 |
2012年 | 757篇 |
2011年 | 946篇 |
2010年 | 760篇 |
2009年 | 763篇 |
2008年 | 886篇 |
2007年 | 954篇 |
2006年 | 784篇 |
2005年 | 741篇 |
2004年 | 653篇 |
2003年 | 609篇 |
2002年 | 587篇 |
2001年 | 368篇 |
2000年 | 368篇 |
1999年 | 365篇 |
1998年 | 459篇 |
1997年 | 408篇 |
1996年 | 391篇 |
1995年 | 369篇 |
1994年 | 316篇 |
1993年 | 361篇 |
1992年 | 316篇 |
1991年 | 232篇 |
1990年 | 277篇 |
1989年 | 284篇 |
1988年 | 269篇 |
1987年 | 254篇 |
1986年 | 284篇 |
1985年 | 305篇 |
1984年 | 298篇 |
1983年 | 295篇 |
1982年 | 232篇 |
1981年 | 260篇 |
1980年 | 256篇 |
1979年 | 252篇 |
1978年 | 230篇 |
1977年 | 230篇 |
1976年 | 206篇 |
1975年 | 197篇 |
1974年 | 179篇 |
1973年 | 180篇 |
排序方式: 共有10000条查询结果,搜索用时 473 毫秒
91.
92.
Ahluwalia Jasjit S.; Nollen Nicole; Kaur Harsohena; James Aimee S.; Mayo Matthew S.; Resnicow Ken 《Canadian Metallurgical Quarterly》2007,26(2):214
Objectives: Examine the effectiveness of an intervention to increase fruits and vegetables (FV) consumption among smokers. Design: Cluster-randomized trial of 20 public housing developments; 10 randomly assigned to an FV intervention and 10 to a smoking cessation intervention. Main outcome measures: Usual (past 7 days) and past 30 days change in daily FV intake at 8 weeks and 6 months postbaseline. Results: Greater increases were seen in the FV group. At Week 8 and Month 6, the FV group had consumed 1.58 (p = .001) and 0.78 (p = .04), respectively, more daily FV servings in the past 7 days than the cessation group. At the same time points, the FV group had consumed 3.61 (p = .01) and 3.93 (p = .01), respectively, more FV servings in the past 30 days than the cessation group. Completing more motivational interviewing sessions (p = .02) and trying more recipes (p = .02) led to significantly greater increases at Month 6 among FV participants. Conclusions: Motivational interviewing counseling and lifestyle modification through trying out healthy recipes may be effective in helping a high-risk population increase their FV intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
Robbins Michael S.; Turner Charles W.; Alexander James F.; Perez Gonzalo A. 《Canadian Metallurgical Quarterly》2003,17(4):534
This study examined the relationship between alliance and retention in family therapy. Alliance was examined at the individual (parent and adolescent) and family levels (within-family differences). Participants were 34 families who received functional family therapy for the treatment of adolescent (aged 12-18 years) behavior problems. Families were classified as treatment dropouts (n=14) or completers (n=20). Videotapes of the first sessions were rated to identify parent and adolescent alliances with the therapist. Results demonstrated that individual parent and adolescent alliances did not predict retention. However, as hypothesized, dropout cases had significantly higher unbalanced alliances (parent minus adolescent) than did completer cases. These findings highlight the importance of alliances in functional family therapy and suggest that how the alliance operates in conjoint family therapy may be a function of systemic rather than of individual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
94.
James J. Mason Ares J. Rosakis 《Mechanics of materials : an international journal》1993,16(4):337-350
Although various approximations have been used to analytically predict the temperature rise at a dynamic crack tip and its relation to the crack tip velocity or the material properties, few experimental investigations of these effects exist. Here, the method of using a high speed infrared detector array to measure the temperature distribution at the tip of a dynamically propagating crack tip is outlined, and the results from a number of experiments on different metal alloys are reviewed. First the effect of crack tip velocity in 4340 steel is investigated, and it is seen that the maximum temperature increases with increasing velocity, the maximum plastic work rate density increases with velocity and the active plastic zone size decreases with increasing velocity. Also, it is observed that a significant change in the geometry of the temperature distribution occurs at higher velocities in steel due to the opening of the crack faces behind the crack tip. Next, the effect of thermal properties is examined, and it is seen that, due to adiabatic conditions at the crack tip, changes in thermal conductivity do not significantly affect the temperature field. Changes in density and heat capacity (as well as material dynamic fracture toughness) are more likely to produce significant differences in temperature than changes in thermal conductivity. Finally, the effect of heat upon the crack tip deformation is reviewed, and it is seen that the generation of heat at the crack tip in steel leads to the localization of deformation in the shear lip. The shear lip is actualy an adiabatic shear band formed at 45° to the surface of the specimen. In titanium, no conclusive evidence of shear localization in the shear lip is seen. 相似文献
95.
Mason G.M. Hamilton D.C. Walpole P.H. Heuerman K.F. James T.L. Lennard M.H. Mazur J.E. 《Geoscience and Remote Sensing, IEEE Transactions on》1993,31(3):549-556
The SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) LEICA instrument is designed to measure ~0.5-5-MeV/nucleon solar and magnetospheric ions over the range from He-Ni. The instrument is a time-of-flight (TOF) mass spectrometer, which measures particle TOF over an ~0.5-m path and the residual energy deposited in an array of Si solid state detectors. Large-area microchannel plates are used, resulting in a large geometrical factor for the instrument (0.6 cm2 sr), which is essential for accurate compositional measurements in small solar flares and in studies of precipitating magnetospheric heavy ions 相似文献
96.
This study examined the hypolipidemic effect of 4 weeks of L-carnitine treatment (170 mg/kg b.w./day) in New Zealand White rabbits fed a high fat diet (5% corn oil/0.5% cholesterol). Specifically, [3H] glycerol and [125I] very low density lipoprotein (VLDL) turnover studies were conducted to examine the effect of treatment on VLDL kinetics. The masses of plasma VLDL-triglycerides (VLDL-TG) and VLDL-apoprotein B (VLDL-apoB) were significantly increased by the high-fat diet. Four weeks of treatment with L-carnitine significantly reduced these masses. Kinetic analysis indicated that fat feeding reduced the fractional catabolic rates (FCRs) of VLDL-TG and VLDL-apoB relative to chow-fed controls. The transport of these VLDL components was not altered by the diet. L-carnitine treatment had no effect on the FCRs of VLDL-TG and VLDL-apoB or on the transport of VLDL-apoB. Yet, treatment significantly lowered the transport of VLDL-TG. These data indicate that the lipid-lowering effect of L-carnitine in this animal model was due, in part, to a decrease in the transport and not due to an alteration in the fractional catabolic rate of VLDL-TG. 相似文献
97.
98.
FV Elmslie AJ Vivian H Gardiner C Hall AP Mowat RM Winter 《Canadian Metallurgical Quarterly》1995,32(4):264-268
Alagille syndrome (AGS) is one of the major forms of chronic liver disease in childhood with severe morbidity and a mortality of 10 to 20%. It is characterised by cholestasis of variable severity with paucity of interlobular bile ducts and anomalies of the cardiovascular system, skeleton, eyes, and face. Previous studies suggest a wide variation in the expression of the disease and a high incidence of new mutations. To determine more accurately the rate of new mutations and to develop criteria for detecting the disorder in parents we systematically investigated parents in 14 families with an affected child. Clinical examination was supplemented by liver function tests, echocardiography, radiographic examination of the spine and forearm, ophthalmological assessment, and chromosome analysis. Six parents had typical anomalies in two or more systems pointing to the presence of autosomal dominant inheritance. Systematic screening of parents for the features defined in this study should improve the accuracy of genetic counselling. 相似文献
99.
Nitrogen addition to iron powder by mechanical alloying 总被引:3,自引:0,他引:3
Nitrogen was alloyed into iron (a) by mechanical processing in a nitrogen gas environment, and (b) by mechanically alloying with iron-nitride powders to characterize resulting nano-structure and nitrogen distribution. Although the infused nitrogen concentration was significantly greater than the thermodynamic equilibrium solubility of iron, no nitrides formed, even for nitrogen concentrations as high as 4.1 wt.% However, a bctFe phase did form. Lattice expansion calculations indicate that the sum of the interstitial bcc-Fe and bctFe nitrogen concentrations was significantly less than the total measured nitrogen concentration. A considerable portion of the mechanically infused nitrogen was determined to be associated with nanograin boundaries. 相似文献
100.
Conditions for stability of the extended Kalman filter and their application to the frequency tracking problem 总被引:1,自引:0,他引:1
Barbara F. La Scala Robert R. Bitmead Matthew R. James 《Mathematics of Control, Signals, and Systems (MCSS)》1995,8(1):1-26
The error dynamics of the extended Kalman filter (EKF), employed as an observer for a general nonlinear, stochastic discrete time system, are analyzed. Sufficient conditions for the boundedness of the errors of the EKF are determined. An expression for the bound on the errors is given in terms of the size of the nonlinearities of the system and the error covariance matrices used in the design of the EKF. The results are applied to the design of a stable EKF frequency tracker for a signal with time-varying frequency.This research was supported by the Co-operative Research Centre for Robust and Adaptive Systems ((CR)2 ASys). The authors wish to acknowledge the funding of the activities of (CR)2 ASys by the Australian Commonwealth Government under the Co-operative Research Centre Program. 相似文献