全文获取类型
收费全文 | 18938篇 |
免费 | 1424篇 |
国内免费 | 599篇 |
专业分类
电工技术 | 891篇 |
技术理论 | 1篇 |
综合类 | 808篇 |
化学工业 | 3218篇 |
金属工艺 | 975篇 |
机械仪表 | 934篇 |
建筑科学 | 1054篇 |
矿业工程 | 347篇 |
能源动力 | 627篇 |
轻工业 | 1146篇 |
水利工程 | 244篇 |
石油天然气 | 771篇 |
武器工业 | 91篇 |
无线电 | 2730篇 |
一般工业技术 | 2786篇 |
冶金工业 | 1346篇 |
原子能技术 | 190篇 |
自动化技术 | 2802篇 |
出版年
2024年 | 65篇 |
2023年 | 211篇 |
2022年 | 383篇 |
2021年 | 633篇 |
2020年 | 413篇 |
2019年 | 406篇 |
2018年 | 507篇 |
2017年 | 535篇 |
2016年 | 507篇 |
2015年 | 621篇 |
2014年 | 823篇 |
2013年 | 1210篇 |
2012年 | 1104篇 |
2011年 | 1213篇 |
2010年 | 1051篇 |
2009年 | 1107篇 |
2008年 | 1041篇 |
2007年 | 1021篇 |
2006年 | 939篇 |
2005年 | 789篇 |
2004年 | 567篇 |
2003年 | 619篇 |
2002年 | 583篇 |
2001年 | 518篇 |
2000年 | 453篇 |
1999年 | 469篇 |
1998年 | 567篇 |
1997年 | 479篇 |
1996年 | 448篇 |
1995年 | 309篇 |
1994年 | 275篇 |
1993年 | 218篇 |
1992年 | 158篇 |
1991年 | 122篇 |
1990年 | 107篇 |
1989年 | 88篇 |
1988年 | 71篇 |
1987年 | 47篇 |
1986年 | 43篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1980年 | 16篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
91.
Mao Ze yu Chen Chang zhi Department of Hydraulic Engineering Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThesimulationofstreamwatertemperatureissignificantlyimportantforthestudyofnumericalmodelingofrivericeprocesses[1] .Historically,themathematicalmodelingofthetransportandfateofheatinawaterbodyhasbeenthesubjectofextensivestudyforvariousre… 相似文献
92.
钛对耐硫变换催化剂性能的影响 总被引:1,自引:0,他引:1
利用常压微反色谱、程序升温还原(TPR)等技术研究了钛对耐硫变换催化剂性能的影响,结果表明:(1)钛能明显提高耐硫变换催化剂的活性,尤其是在低于623K时活性提高最为明显;(2)工业侧流试验后,含钛样品的保留活性及活性保留率均高于K8-11;(3)催化剂中添加助剂TiO2后,能显著提高对原料气中H2S含量变化的适应能力,因此可以拓宽对原料气的选择范围,对工业生产有着十分重要的现实意义。 相似文献
93.
在已经得到的描述鱼雷罐喷粉处理基本参数具体表达式的基础上,运用多目标非线性优化方法,对工艺操作参数进行优化。 相似文献
94.
Tucker Joan S.; Friedman Howard S.; Tsai Catherine M.; Martin Leslie R. 《Canadian Metallurgical Quarterly》1995,10(1):3
Models of the relations between contact with pets and better health are examined in an archival prospective study using data derived from the longitudinal study initiated by Terman in 1921 (current N?=?343 men, 300 women) . In survival analyses of documented longevity, playing with pets in 1977 (M age?=?67 years) was not associated with mortality risk through 1991 for the total sample nor for those who were unmarried or those who were less satisfied with their human relationships. Playing with pets was not associated with health-prone attributes or healthy behaviors such as personality, social ties, education, and smoking. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
95.
节流式差压流量计的发展和现状 总被引:2,自引:0,他引:2
文章介绍节流式差压流量计的特点及标准化进程,煤气流量测量中存在的难点以及正在试图解决的途径。 相似文献
96.
97.
Tsai Jeanne L.; Miao Felicity F.; Seppala Emma; Fung Helene H.; Yeung Dannii Y. 《Canadian Metallurgical Quarterly》2007,92(6):1102
Previous studies have found that in American culture high-arousal positive states (HAP) such as excitement are valued more and low-arousal positive states (LAP) such as calm are valued less than they are in Chinese culture. What specific factors account for these differences? The authors predicted that when people and cultures aimed to influence others (i.e., assert personal needs and change others' behaviors to meet those needs), they would value HAP more and LAP less than when they aimed to adjust to others (i.e., suppress personal needs and change their own behaviors to meet others' needs). They test these predictions in 1 survey and 3 experimental studies. The findings suggest that within and across American and Chinese contexts, differences in ideal affect are due to specific interpersonal goals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
电转化法转化钝顶螺旋藻转化条件的研究 总被引:2,自引:0,他引:2
确定了电转化法转化钝项螺旋藻S6-4的转化条件。无论受体是藻丝还是单细胞/藻丝段,钝项螺旋藻S6-4在对数生长期内,半致死电场强度无显著差别。实验表明以对数中期的螺旋藻用于转化为宜。当脉冲时间是5.0ms时,藻丝受体和单细胞/藻丝段受体的半致死电场强度分别是3.75—5.0kV/cm和3.1—4.4kV/cm,而电击缓冲液分别是1.0mmol/L HEPES(pH7.5)缓冲液和含有0.5mol/L蔗糖的1.0mmol/L HEP—ES(pH7.5)缓冲液。本文的研究结果为螺旋藻转化及外源基因表达提供了实验基础。 相似文献
99.
100.
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