全文获取类型
收费全文 | 15329篇 |
免费 | 1280篇 |
国内免费 | 617篇 |
专业分类
电工技术 | 853篇 |
技术理论 | 2篇 |
综合类 | 856篇 |
化学工业 | 2727篇 |
金属工艺 | 933篇 |
机械仪表 | 964篇 |
建筑科学 | 1159篇 |
矿业工程 | 519篇 |
能源动力 | 443篇 |
轻工业 | 894篇 |
水利工程 | 239篇 |
石油天然气 | 1223篇 |
武器工业 | 102篇 |
无线电 | 1682篇 |
一般工业技术 | 1895篇 |
冶金工业 | 836篇 |
原子能技术 | 160篇 |
自动化技术 | 1739篇 |
出版年
2024年 | 78篇 |
2023年 | 303篇 |
2022年 | 480篇 |
2021年 | 662篇 |
2020年 | 527篇 |
2019年 | 450篇 |
2018年 | 519篇 |
2017年 | 516篇 |
2016年 | 444篇 |
2015年 | 601篇 |
2014年 | 771篇 |
2013年 | 834篇 |
2012年 | 938篇 |
2011年 | 1005篇 |
2010年 | 881篇 |
2009年 | 856篇 |
2008年 | 879篇 |
2007年 | 751篇 |
2006年 | 792篇 |
2005年 | 659篇 |
2004年 | 540篇 |
2003年 | 451篇 |
2002年 | 437篇 |
2001年 | 372篇 |
2000年 | 353篇 |
1999年 | 400篇 |
1998年 | 296篇 |
1997年 | 277篇 |
1996年 | 240篇 |
1995年 | 214篇 |
1994年 | 175篇 |
1993年 | 119篇 |
1992年 | 104篇 |
1991年 | 68篇 |
1990年 | 64篇 |
1989年 | 47篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1970年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
21.
The purpose of this clinical trial is to evaluate the efficacy and safety of fleroxacin and to compare with those of lomefloxacin. A randomized controlled study was carried out to treat sixty patients with urinary tract and respiratory tract bacterial infections, thirty in each group with one of the two drugs, and fifty cases were treated with fleroxacin in an open trial. Altogether there were one hundred and ten cases. Both fleroxacin and lomefloxacin were given orally, the dosage was 200 mg every 12 hours or 400 mg every 24 hours for 7-14 days. The clinical efficacy rate was 93.3%; the culturing rate in the fleroxacin group was 83.3%; the bacterial clearance rate was 92.3%, the incidence of adverse reactions was 9.4%, while in the lomefloxacin group they were 90.0%, 80.0%, 87.5% and 6.7% respectively, with no statistically significant difference between the two groups (P > 0.05). In the open and randomized trials, fleroxacin cured eighty cases of bacterial infections, the overall clinical efficacy rate was 90.0%, the culturing rate in the flero-xacin group was 83.8%, the bacterial clearance rate was 88.2% and the incidence of adverse reactions was 9.6%. It is shown that fleroxacin is an antibiotic of broad-spectrum, high efficacy and safety. 相似文献
22.
Gabriel C.M.W. Heffels J.J.M. Hou X. Ouibrahim H. 《Electronics & Communication Engineering Journal》1993,5(2):103-112
Introduction of the broadband integrated services digital network (B-ISDN) will enable network users to make use of advanced multimedia, multiparty services. With this aim in view, RACE II project R2044, MAGIC, is investigating long-term signalling requirements, architecture and protocols for B-ISDN. New service concepts are being developed in MAGIC which will provide more flexibility when compared to narrowband ISDN (N-ISDN). The service requirements and other signalling requirements, such as the separation between call and associated connections at the network-node interface, are used to determine the distribution of functions over the network. The signalling protocols which are used to exchange the signalling information are subsequently developed. These signalling protocols are simulated to prove the performance and the feasibility of call handling concepts 相似文献
23.
24.
聚苯硫醚酰胺的合成与表征 总被引:7,自引:1,他引:6
用4-氯苯甲酰4′-氯苯胺和硫化钠为原料在常压下合成了聚苯硫醚酰胺,并对其进行了表征。结果表明所合成的产物为结晶性聚合物,并且有较高的热稳定性。 相似文献
25.
26.
27.
28.
This paper is concerned with the inversion of confluent Vandermonde matrices. A novel and simple recursive algorithm for inverting confluent Vandermonde matrices is presented. The algorithm is suitable for classroom use in both numerical as well as symbolic computation. Examples are included to illustrate the proposed algorithm. 相似文献
29.
Hyperdynamic circulation of cirrhotic rats: role of substance P and its relationship to nitric oxide
CJ Chu FY Lee SS Wang FY Chang YT Tsai HC Lin MC Hou SL Wu CC Tai SD Lee 《Canadian Metallurgical Quarterly》1997,32(8):841-846
BACKGROUND: It has been suggested that excessive formation of nitric oxide (NO) is responsible for the hyperdynamic circulation observed in portal hypertension. Substance P is a neuropeptide partly cleared by the liver and causes vasodilatation through the activation of the endothelial NO pathway. However, there are no previously published data concerning the plasma level of substance P in cirrhotic rats and its relationship to NO. METHODS: Plasma concentrations of substance P and nitrate/nitrite (an index of NO production) were determined in control rats and cirrhotic rats with or without ascites using an enzyme-linked immununosorbent assay and a colorimetric assay, respectively. In addition, systemic and portal hemodynamics were evaluated by a thermodilution technique and catheterization. RESULTS: Cirrhotic rats with and without ascites had a lower systemic vascular resistance (2.6 +/- 0.2 and 3.9 +/- 0.4 mmHg ml(-1) x min x 100 g body weight, respectively) and higher portal pressure (14.6 +/- 0.6 and 11.3 +/- 1.8 mmHg) than control rats (6.5 +/- 0.3 mmHg x ml(-1) x min x 100 g BW and 6.8 +/- 0.2 mmHg, respectively, P < 0.05), and cirrhotic rats with ascites had the lowest systemic vascular resistance. Plasma levels of nitrate/nitrite progressively increased in relation to the severity of liver dysfunction (control rats, 2.7 +/- 0.5 nmol/ml; cirrhotic rats without ascites, 5.6 +/- 1.3 nmol/ml; cirrhotic rats with ascites, 8.3 +/- 2.2 nmol/ml; P < 0.05). Cirrhotic rats with ascites displayed higher plasma values of substance P (57.7 +/- 5.9 pg/ml) than cirrhotic rats without ascites (37.9 +/- 3.1 pg/ml, P < 0.05) and control rats (30.1 +/- 1.0 pg/ml, P < 0.05). There was no significant difference in plasma substance P values between control rats and cirrhotic rats without ascites (P > 0.05). No correlation was found between plasma levels of substance P and nitrate/nitrite (r = 0.318, P > 0.05). CONCLUSIONS: Excessive formation of NO may be responsible, at least partly, for the hemodynamic derangements in cirrhosis. Although substance P may not participate in the initiation of a hyperdynamic circulation in cirrhosis, it may contribute to the maintenance of the hyperdynamic circulation observed in cirrhotic rats with ascites. 相似文献
30.
通过对已产生纵向裂缝、倾斜和基部风化剥蚀严重的高危烟囱的定向(向倾斜相反方向)倒塌爆破实践表明:设计中选用爆破参数及施工措施是有效的。 相似文献