全文获取类型
收费全文 | 18099篇 |
免费 | 467篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 238篇 |
综合类 | 9篇 |
化学工业 | 3578篇 |
金属工艺 | 280篇 |
机械仪表 | 310篇 |
建筑科学 | 1105篇 |
矿业工程 | 109篇 |
能源动力 | 511篇 |
轻工业 | 1382篇 |
水利工程 | 158篇 |
石油天然气 | 194篇 |
武器工业 | 1篇 |
无线电 | 1064篇 |
一般工业技术 | 2877篇 |
冶金工业 | 4167篇 |
原子能技术 | 162篇 |
自动化技术 | 2439篇 |
出版年
2022年 | 138篇 |
2021年 | 216篇 |
2020年 | 170篇 |
2019年 | 223篇 |
2018年 | 267篇 |
2017年 | 260篇 |
2016年 | 319篇 |
2015年 | 238篇 |
2014年 | 381篇 |
2013年 | 1101篇 |
2012年 | 663篇 |
2011年 | 872篇 |
2010年 | 675篇 |
2009年 | 663篇 |
2008年 | 858篇 |
2007年 | 871篇 |
2006年 | 685篇 |
2005年 | 719篇 |
2004年 | 559篇 |
2003年 | 569篇 |
2002年 | 509篇 |
2001年 | 329篇 |
2000年 | 300篇 |
1999年 | 303篇 |
1998年 | 313篇 |
1997年 | 300篇 |
1996年 | 299篇 |
1995年 | 333篇 |
1994年 | 267篇 |
1993年 | 304篇 |
1992年 | 272篇 |
1991年 | 164篇 |
1990年 | 237篇 |
1989年 | 283篇 |
1988年 | 204篇 |
1987年 | 215篇 |
1986年 | 211篇 |
1985年 | 265篇 |
1984年 | 258篇 |
1983年 | 227篇 |
1982年 | 217篇 |
1981年 | 213篇 |
1980年 | 172篇 |
1979年 | 187篇 |
1978年 | 176篇 |
1977年 | 177篇 |
1976年 | 147篇 |
1975年 | 178篇 |
1974年 | 165篇 |
1973年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
A group's staffing level can play an important role in its socialization practices. For example, a group that is understaffed should be more open than an overstaffed group to both prospective and new members. To test this prediction, the leaders of nearly 100 student groups on a college campus were interviewed. These interviews yielded qualitative and quantitative data about the staffing levels in the groups and the methods that they used for recruiting prospective members and assimilating new ones. Analyses of the qualitative data clarified issues such as when understaffing and overstaffing are likely to occur, what kinds of problems they produce in groups, and how groups try to solve those problems. Analyses of the quantitative data revealed that our prediction was correct: As their staffing levels decrease, most groups become more open to prospective and new members. Implications of the results are discussed, and some suggestions for future research are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Jarrett Robin B.; Basco Monica R.; Risser Richard; Ramanan Janaki; Marwill Maria; Kraft Dolores; Rush A. John 《Canadian Metallurgical Quarterly》1998,66(6):1036
Two pilot studies evaluated the rate of relapse or recurrence (i.e., major depressive disorder) after cognitive therapy (CT). Two sequential cohorts included outpatients who responded to acute phase CT (A-CT) and who agreed to monthly, treatment-free follow-up. In Study 1, the Kaplan-Meier technique estimated relapse and recurrence rates of 40% at 6 months, 45% at 8 months, 50% at 12 months, 67% at 18 months, and 74% at 24 months. In Study 2, responders to A-CT received 8 months (10 sessions) of continuation phase CT (C-CT). In Study 2, relapse or recurrence was 20% at 6 and 8 months, 27% at 12 months, and 36% at 18 and 24 months after A-CT. An exploratory log-rank test showed that relapse or recurrence-free survival was greater in Study 2 than in Study 1. If replicated, this result suggests that C-CT can reduce depressive relapse or recurrence. Alternative explanations are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Kofi E. Aidoo Richard F. Tester Janet E. Morrison & David MacFarlane 《International Journal of Food Science & Technology》1996,31(5):433-438
Composition and microbiological contamination was measured in samples of pre-packed dates purchased from a number of stores and retail outlets in Greater Glasgow. The sugar content of dried pitted dates was c . 74%, about 10% more than reported on those packs where nutritional information was given. Potentially pathogenic bacteria like Escherichia coli, Staphylococcus aureus and Bacillus cereus were identified in some of the samples together with lactic acid bacteria, yeasts and moulds, Aspergillus flavus and A. parasiticus . Fresh dates were the most heavily contaminated of all samples, probably owing to the high moisture content. 相似文献
104.
Richard B. Hetnarski Józef Ignaczak 《International Journal of Engineering Science》1996,34(15):1767-1787
An analysis of soliton-like waves propagating in a low-temperature nonlinear thermoelastic solid given in J. Ignaczak, J. Thermal Stresses 13, 73–98 (1990) is extended by introducing a low-temperature parameter ω ? (0, 1 ] into the basic equations. The two ω-parametrized one-dimensional soliton-like thermoelastic waves that propagate with finite speeds in a given direction are obtained in an implicit form for a large range of other parameters involved, by using the method similar to that employed by Ignaczak. If ω = 1 the thermoelastic soliton-like waves from Ignaczak's article are recovered. In addition, on the basis of an approximate system of nonlinear governing equations valid for a small ω, two fast-moving soliton-like thermoelastic waves are examined in detail. Each of these two waves reveals a fountain effect in a neighborhood of a moving front, and is close to a thermodynamical equilibrium far from the front. Schematic graphs illustrate both the exact and the approximate soliton-like waves. 相似文献
105.
A stepwise degradation of a kerogen concentrate of Green River oil shale was effected by oxidation with perchloric acid of varying boiling point and concentration. Dissolution of the kerogen concentrate occurred between 160 and 170°C. Several model compounds were also oxidized with perchloric acid. The model compounds were polyethylene, graphite, nylon, and polyethylene oxide. The results indicated that the kerogen was similar to polyethylene oxide. The results of this study and previous work were used to present a model for the structure of the kerogen of Green River oil shale. 相似文献
106.
Murphy Philip N.; Bentall Richard P.; Ryley Lisa D.; Ralley Richard 《Canadian Metallurgical Quarterly》2003,17(2):167
Admission scores from a model comprising 3 motivation factors concerning the cessation of heroin use and a confidence scale concerning postdischarge abstinence were tested for their ability to predict postdischarge outcomes in patients beginning inpatient opiate detoxification. Statistically significant prediction of abstinence from heroin 30 days after discharge and the number of heroin-free days in the 3 months following admission was based on the confidence scale and a factor concerned with externally imposed constraints on continued heroin use. The single-scale confidence measure made the largest contribution to each prediction, indicating that such scales may be potentially useful outcome predictors for postdischarge abstinence. External constraints on heroin use may not provide a basis for success in this treatment modality. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
Longabaugh Richard; Wirtz Philip W.; Beattie Martha C.; Noel Nora; Stout Robert 《Canadian Metallurgical Quarterly》1995,63(2):296
Patients were randomly assigned to 1 of 3 treatments: brief broad-spectrum (BBS), extended relationship enhancement (ERE), or extended cognitive–behavioral (ECB). A hierarchical latent growth model was used to analyze the data of 188 patients (82%) followed for 18 months. ERE treatment was significantly more effective in increasing abstinence of patients entering treatment with a network unsupportive of abstinence or with a low level of investment in their network, whereas BBS treatment was more effective for patients with either (a) both a social network unsupportive of abstinence and a low level of network investment or (b) high investment in a network supportive of abstinence. ECB outcomes were neither as good as those matched nor as bad as those mismatched to the different exposures of relationship enhancement. This suggests that dose of relationship enhancement should be determined after assessing patient relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Christensen Anne-Lise; Malmros Richard; Townes Brenda D. 《Canadian Metallurgical Quarterly》1987,1(2):45
After suffering a rupture of a left-sided aneurysm on the middle cerebral artery with prolonged arterial spasms, the prognosis for recovery of speech and motor functions of a 27-yr-old male patient was considered to be poor. Based on a Luria neuropsychological investigation that revealed many areas of preserved brain functions, rehabilitation efforts were directed toward training of specific abilities as well as compensatory skills using intact functions. This case demonstrates the interaction between the training program and the levels of motivation and persistence of the S and his family necessary to produce optimal rehabilitation outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
109.
Testing for the equivalence of factor covariance and mean structures: The issue of partial measurement invariance. 总被引:1,自引:0,他引:1
Byrne Barbara M.; Shavelson Richard J.; Muthén Bengt 《Canadian Metallurgical Quarterly》1989,105(3):456
Addresses issues related to partial measurement invariance using a tutorial approach based on the {lisrel} confirmatory factor analytic model. Specifically, we demonstrate procedures for (a) using "sensitivity analyses" to establish stable and substantively well-fitting baseline models, (b) determining partially invariant measurement parameters, and (c) testing for the invariance of factor covariance and mean structures, given partial measurement invariance. We also show, explicitly, the transformation of parameters from an all-X to an all-Y model specification, for purposes of testing mean structures. These procedures are illustrated with multidimensional self-concept data from low (n?=?248) and high (n?=?582) academically tracked high school adolescents. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
110.
Attention deficit and conduct disorders require an important yet often difficult differential diagnosis. Prior efforts to determine which symptoms are optimal for making this differential diagnosis have been limited by a reliance on statistics that do not supply the probability of the disorders given a symptom's presence (positive predictive power) or the probability that the disorder is not present given the absence of the symptom (negative predictive power). This investigation examined the utility of these latter statistics in the differential diagnosis of childhood attention deficit and conduct disorders. The data consisted of symptoms from a standardized maternal psychiatric interview collected for a sample of 76 clinic-referred boys. Results indicated that some symptoms are optimal as inclusion criteria, some as exclusion criteria, some as neither, and some as both. Furthermore, some symptoms that have been traditionally associated with the diagnosis of one disorder were actually found to be more useful in the diagnosis of the other disorder. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献