全文获取类型
收费全文 | 2425篇 |
免费 | 92篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 36篇 |
综合类 | 13篇 |
化学工业 | 574篇 |
金属工艺 | 33篇 |
机械仪表 | 39篇 |
建筑科学 | 132篇 |
矿业工程 | 4篇 |
能源动力 | 48篇 |
轻工业 | 153篇 |
水利工程 | 5篇 |
石油天然气 | 2篇 |
无线电 | 192篇 |
一般工业技术 | 451篇 |
冶金工业 | 421篇 |
原子能技术 | 14篇 |
自动化技术 | 401篇 |
出版年
2023年 | 21篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 43篇 |
2019年 | 39篇 |
2018年 | 55篇 |
2017年 | 28篇 |
2016年 | 55篇 |
2015年 | 34篇 |
2014年 | 85篇 |
2013年 | 112篇 |
2012年 | 98篇 |
2011年 | 173篇 |
2010年 | 107篇 |
2009年 | 94篇 |
2008年 | 101篇 |
2007年 | 98篇 |
2006年 | 99篇 |
2005年 | 67篇 |
2004年 | 70篇 |
2003年 | 58篇 |
2002年 | 76篇 |
2001年 | 58篇 |
2000年 | 37篇 |
1999年 | 54篇 |
1998年 | 149篇 |
1997年 | 80篇 |
1996年 | 57篇 |
1995年 | 54篇 |
1994年 | 37篇 |
1993年 | 25篇 |
1992年 | 29篇 |
1991年 | 14篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 26篇 |
1975年 | 14篇 |
1973年 | 10篇 |
1971年 | 8篇 |
排序方式: 共有2518条查询结果,搜索用时 15 毫秒
21.
S Kwon RA Hess D Bunick H Nitta L Janulis Y Osawa JM Bahr 《Canadian Metallurgical Quarterly》1995,53(6):1259-1264
We recently found that cytochrome P450 aromatase (P450arom) is present in germ cells of the mammalian testis and is capable of converting androgens to estrogens in the male reproductive tract. The objective of the present study was to determine whether testicular germ cells and epididymal sperm of an avian species are also capable of synthesizing estrogen. P450arom was localized in the rooster testis and epididymal region by immunocytochemistry, using an antiserum generated against purified human placental cytochrome P450arom. Immunostaining was present in pachytene spermatocytes, round spermatids, elongated spermatids, flagella of late spermatids, and sperm in the epididymal region. A positive reaction was also found in nonciliated cells of the epididymal region. However, the absence of mRNA for P450arom in the epididymal region indicated that the immunoreactive protein present in the epididymal region is not synthesized in this region. The immunoreactive P450arom found in epididymal sperm was shown to be active through use of a 3H2O assay. On the basis of these data, we conclude that rooster testicular germ cells and epididymal sperm are sites for the synthesis of estrogen, a potential regulator or modulator of germinal epithelium in the testis and the epithelium of the epididymal region of the avian species. 相似文献
22.
23.
E Buskens EW Steyerberg J Hess JW Wladimiroff DE Grobbee 《Canadian Metallurgical Quarterly》1997,87(6):962-967
OBJECTIVES: This study assessed the potential impact of fetal ultrasound screening on the number of newborns affected by cardiac anomalies. METHODS: A decision model was developed that included the prevalence and history of congenital heart disease, characteristics of ultrasound, risk of abortion, and attitude toward pregnancy termination. Probabilities were obtained with a literature survey; sensitivity analysis showed their influence on expected outcomes. RESULTS: Presently, screening programs may prevent the birth of approximately 1300 severely affected newborns per million second-trimester pregnancies. However, over 2000 terminations of pregnancy would be required, 750 of which would have ended in intrauterine death or spontaneous abortion. Further, 9900 false-positive screening results would occur, requiring referral. Only the sensitivity of routine screening and attitude toward termination of pregnancy appeared to influence the yield substantially. CONCLUSIONS: The impact of routine screening for congenital heart disease appeared relatively small. Further data may be required to fully assess the utility of prenatal screening. 相似文献
24.
25.
26.
Micro- and nanodevices require the controlled delivery of energy to power a variety of processes. The current paradigm of connecting a miniaturized device to a set of macroscopic auxiliary devices, such as power supplies or pumps, for the delivery of electrical and mechanical energy needs to be replaced to enable the design of stand-alone integrated bionanodevices with applications in remote biosensing or nanomedicine. Biological nanomachines, such as the motor protein kinesin, can efficiently convert energy stored in chemical compounds, in particular adenosine 5'-triphosphate (ATP), into mechanical work. This ability is an attractive feature of hybrid devices powered by biomolecular motors, since it removes the need for the storage and conversion of electrical energy. The consequences are a simplified fabrication process and packaging, leading to higher yields and lower costs, and the broadening of the applications, which can now include field-deployable nanodevices. Here, the potential of caged ATP as fuel for such engineering applications is discussed. Caged ATP can be stored in the buffer solution of a bionanodevice, "uncaged" by UV light, and utilized as fuel by many enzymes to catalyze chemical changes or power active transport. We demonstrate that DMNPE-caged ATP can be stored in sufficient amounts in a typical device and that the activation can be triggered with a UV lamp or even sunlight. 相似文献
27.
Reliability aspects of microsensors and micromechatronic actuators for automotive applications 总被引:1,自引:0,他引:1
In modern cars microsensors and micromechatronic actuators play an essential and still increasingly important role as the interface between the vehicle with its complex functions of motor management, chassis systems, safety as well as comfort and convenience on the one hand and the respective electronic control units on the other hand. They have to fulfill their task in a harsh environment over the entire lifetime of an automobile. Therefore reliability aspects have moved more and more into the focus of engineering and research activities in microsystem technology. A methodical procedure is described that allows reliability issues to be approached efficiently. The implementation of the methodology is illustrated with real-life examples of reliability aspects of hot film mass air flow sensors, inertial sensors as well as piezoelectric actuators. 相似文献
28.
The appraisal process consists of the subjective evaluation that occurs during an individual's encounter with significant events in the environment, determining the nature of the emotional reaction and experience. Placed in the context of appraisal theories of emotion-elicitation and differentiation, the aim of the present research was to test empirically the hypothesis that the intrinsic pleasantness evaluation occurs before the goal conduciveness evaluation. In two studies, intrinsically pleasant and unpleasant images were used to manipulate pleasantness, and a specific event in a Pacman-type videogame was used to manipulate goal conduciveness. Facial EMG was used to measure facial reactions to each evaluation. As predicted, facial reactions to the intrinsic pleasantness manipulation were faster than facial reactions to the goal conduciveness manipulation. These results provide good empirical support for the sequential nature of the appraisal process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Hahlweg Kurt; Markman Howard J.; Thurmaier Franz; Engl Jochen; Eckert Volker 《Canadian Metallurgical Quarterly》1998,12(4):543
This article reports on the development and long-term evaluation of a marital distress prevention program for German couples, the Ein Partnerschaftliches Lernprogramm (EPL, A Couple's Learning Program). The EPL is a 6-session program designed to teach couples effective communication and problem-solving skills. In the current article, the EPL is evaluated in a prospective, quasi-experimental, controlled trial. The results of the 3-year follow-up are reported, contrasting 55 EPL couples with a control group of 17 couples. Significant differences emerged with regard to the couples' dissolution rates, relationship satisfaction, and positive and negative communication behavior favoring the EPL couples. These results demonstrate the utility of the EPL program in assisting happy couples who are preparing for marriage. The implications of the findings for prevention research and for the dissemination of prevention programs are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
JS Sheikh M Sharma A Kunath DA Fritz CJ Glueck EV Hess 《Canadian Metallurgical Quarterly》1996,23(7):1288-1291
We describe 2 patients with a Sj?gren-like syndrome apparently secondary to hypertriglyceridemia. Both had bilateral parotitis in addition to musculoskeletal and sicca symptoms. Parotid gland histology revealed fatty infiltration with no inflammation. Therapy with dietary modification and triglyceride lowering drugs resulted in resolution of symptoms and parotid swelling in one patient. In the 2nd patient, hypertriglyceridemia was resistant to triglyceride lowering drugs, and parotid symptoms and swelling continued unabated. Our findings suggest aggressive treatment of hyperlipidemia in pseudo-Sj?gren's syndrome may result in amelioration of musculoskeletal and parotid symptoms. 相似文献