全文获取类型
收费全文 | 407836篇 |
免费 | 4812篇 |
国内免费 | 1374篇 |
专业分类
电工技术 | 7638篇 |
综合类 | 322篇 |
化学工业 | 60674篇 |
金属工艺 | 16509篇 |
机械仪表 | 13559篇 |
建筑科学 | 8464篇 |
矿业工程 | 2177篇 |
能源动力 | 11662篇 |
轻工业 | 28675篇 |
水利工程 | 4285篇 |
石油天然气 | 7929篇 |
武器工业 | 17篇 |
无线电 | 49727篇 |
一般工业技术 | 83733篇 |
冶金工业 | 75637篇 |
原子能技术 | 9215篇 |
自动化技术 | 33799篇 |
出版年
2022年 | 2623篇 |
2021年 | 3992篇 |
2020年 | 3038篇 |
2019年 | 3898篇 |
2018年 | 6594篇 |
2017年 | 6587篇 |
2016年 | 7015篇 |
2015年 | 4392篇 |
2014年 | 7239篇 |
2013年 | 20299篇 |
2012年 | 11544篇 |
2011年 | 15462篇 |
2010年 | 12301篇 |
2009年 | 13864篇 |
2008年 | 14214篇 |
2007年 | 13944篇 |
2006年 | 12555篇 |
2005年 | 11241篇 |
2004年 | 10617篇 |
2003年 | 10501篇 |
2002年 | 9906篇 |
2001年 | 9811篇 |
2000年 | 9191篇 |
1999年 | 9587篇 |
1998年 | 24475篇 |
1997年 | 16815篇 |
1996年 | 12875篇 |
1995年 | 9576篇 |
1994年 | 8431篇 |
1993年 | 8448篇 |
1992年 | 6116篇 |
1991年 | 5742篇 |
1990年 | 5722篇 |
1989年 | 5352篇 |
1988年 | 5088篇 |
1987年 | 4457篇 |
1986年 | 4339篇 |
1985年 | 4870篇 |
1984年 | 4470篇 |
1983年 | 4033篇 |
1982年 | 3687篇 |
1981年 | 3764篇 |
1980年 | 3462篇 |
1979年 | 3357篇 |
1978年 | 3362篇 |
1977年 | 3781篇 |
1976年 | 4881篇 |
1975年 | 2874篇 |
1974年 | 2688篇 |
1973年 | 2758篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
952.
953.
954.
OBJECTIVE AND DESIGN: The anti-inflammatory effect of myricetinglucuronide (MGL) was investigated and structurally-related compounds were compared to examine the structure/activity-relationship in carrageenan-induced rat paw edema. MATERIALS AND SUBJECTS: In vitro studies were performed using rat basophilic leukemia (RBL-1) cells, human polymorphonuclear leukocytes (PMNL), COX-1 from ram seminal vesicle, COX-2 from sheep placenta and human venous blood. For the in vivo tests male Wistar rats were used, for the ex vivo test perfused rabbit ears. TREATMENT: 1-300 microg/kg MGL or myricetinmethylglucuronate and 0.1-5 mg/kg other related compounds administered p.o. (carrageenan edema). 5, 50 and 150 microg/kg MGL p.o. for 14 days (Freund's adjuvant arthritis), 5 and 50 microg/kg p.o. for 6 days (ulceration). METHODS: Anti-inflammatory effects were measured in carrageenan edema and in adjuvant arthritis. Incidence of gastric lesions was tested in an ulcerogenicity model in vivo. Influence on COX was determined in the perfused rabbit ear, in PMNL and in a test assay using COX-1 and COX-2. 5-LOX activity was studied using PMNL and RBL-1. The influence on platelet aggregation was evaluated measuring light transmission. RESULTS: MGL exerted a marked and dose-dependent anti-inflammatory effect in acute (carrageenan edema, ED50 15 microg/kg, indomethacin ED50 10 mg/kg) and chronic (adjuvant arthritis, inhibition at 150 microg/kg 18.1 % left paw, 20.6% right paw, indomethacin 3 mg/kg 18.0% and 19.4%)) models of inflammation. In the perfused rabbit ear 1 microg MGL inhibited the release of PGI2, PGD2 and PGE2 to the same extent as 1 microg indomethacin. The inhibition of COX-1 in the intact cell system was IC50 = 0.5 microM, that of indomethacin 0.0038 microM. In the isolated enzyme preparations of COX-1 and COX-2 the IC50 was 10 microM and 8 microM, that of indomethacin 9.2 mM and 2.4 microM. In the RBL-1 and PMNL test assay the inhibition of 5-LOX was 0.1 microM and 2.2 microM. An orally administered dose of 50 microg/kg/day induced no gastric ulcers in rats treated for 6 days. The investigations on carrageenan edema showed a close relationship between the structure of MGL and the anti-inflammatory effect. CONCLUSIONS: MGL is a COX-1, COX-2 and 5-LOX inhibitor. In view of the moderate in vitro activity and the very potent in vivo activity an additive mechanism must be involved. Small changes in the molecular structure lead to the loss or reduction of the anti-inflammatory activity. 相似文献
955.
956.
Haemangiopericytoma of nose and paranasal sinuses is relatively uncommon tumour. It occurs in adults in sixth and seventh decades of life. In view of paucity of intranasal haemangiopericytoma old in Indian literature and young age of patient, we are reporting one case in 28-year-old female who presented with recurrent, profuse epistaxis. 相似文献
957.
S Cohrs G Herrendorf J Wiltfang A Rodenbeck J Kinkelbur L Adler G Hajak 《Canadian Metallurgical Quarterly》1996,146(13-14):366-368
10 patients with obstructive sleep apnea syndrome (OSAS) have been treated with the new surgical procedure functional palatoraphy and modified genioplasty. 5 months after surgery 7 patients with an apnea hypopnea index under 10 were cured. Three therapy refractory patients were all overweight with a body mass index of more than 29 kg/m2. Excessively overweight patients should therefore not be operated. Following the selection criteria we introduced an effective new treatment method for OSAS. 相似文献
958.
C Matache M Stefanescu A Onu G Szegli M Barel S Tanaseanu I Matei S Bouillie R Frade 《Canadian Metallurgical Quarterly》1996,24(4):217-228
A comparative study of tyrosine phosphorylation was performed on peripheral blood lymphocytes from systemic lupus erythematosus (SLE) patients and from healthy donors. Freshly isolated SLE lymphocytes presented an elevated tyrosine phosphorylation level when compared to healthy donors lymphocytes (p = 0.005). Among all phosphorylated proteins, those called p120, p110, p80 and p55-p60 were more phosphorylated. The level of tyrosine phosphorylation of p120 and p110 proteins discriminated significantly (p = 0.0048, respectively, p = 0.02) between SLE patients and healthy donors. Lymphocytes form SLE patients and healthy donors were then stimulated by cross-linking T cell antigens (CD3, CD4, CD8) to further distinguish the signal transduction between normal and pathologic lymphocytes. No statistical differences in the tyrosine phosphorylation pattern, following CD4 or CD8 cross-linking, were observed between SLE patients and healthy donors lymphocytes. CD3 cross-linking induced an effect on tyrosine phosphorylation different in SLE patients versus healthy donors lymphocytes. Thus, the lymphocytes of SLE patients were refractile in anti-CD3 stimulation in comparison with the healthy donors lymphocytes. Chi-square analysis demonstrated that a significantly larger number of healthy donors responded to anti-CD3 stimulation compared to SLE patients (p = 0.03). The high frequency of tyrosine phosphorylation of p110 and p80 proteins, following CD3 stimulation, in normal versus SLE lymphocytes, suggested that these proteins could be involved in abnormal signal transduction in SLE cells. 相似文献
959.
S. Arimoto T. Nakayama 《Mechatronics, IEEE/ASME Transactions on》1996,1(2):168-180
Dynamics and control of nonlinear mechanical systems and advanced mechatronic systems can be investigated more vividly and efficiently by using corresponding nonlinear position-dependent circuits that describe Lagrange's equations of motions and interactions with objects or/and task environments. Such expressions of Lagrange's equations via nonlinear circuits are indebted to lumped-parameter discretization of mechanical systems as a set of rigid bodies through equations of motion due to Newton's second law. This observation is quite analogous to validity of electric circuits that can be derived as lumped parameter versions of Maxwell's equations of electromagnetic waves. Couplings of nonlinear mechanical circuits with electrical circuits through actuator dynamics are also discussed. In such electromechanical circuits the passivity should be a generalization of impedance concept in order to cope with general nonlinear position-dependent circuits and play a crucial role in their related motion control problems. In particular, it is shown that the passivity as an input-output property gives rise to a necessary and sufficient characterization of H/sub /spl infin//-tuning for disturbance attenuation of robotic systems, which can give another system theoretic interpretation of the energy conservation law. 相似文献
960.
Personick S.D. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1993,81(11):1549-1557
An overview is given of how fiber optics technology has emerged from the drawing board into the marketplace over the last, roughly, 25 years, and how the low-cost bandwidth that fiber provides enables bandwidth-intensive applications such as access to multimedia information, customized television programming, and multimedia real-time communications and messaging. A prognosis for future applications in the environment of broadband, personalized communication services is also given 相似文献