全文获取类型
收费全文 | 3721篇 |
免费 | 182篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 66篇 |
综合类 | 5篇 |
化学工业 | 1216篇 |
金属工艺 | 76篇 |
机械仪表 | 54篇 |
建筑科学 | 170篇 |
矿业工程 | 13篇 |
能源动力 | 76篇 |
轻工业 | 391篇 |
水利工程 | 20篇 |
石油天然气 | 7篇 |
无线电 | 268篇 |
一般工业技术 | 549篇 |
冶金工业 | 514篇 |
原子能技术 | 22篇 |
自动化技术 | 459篇 |
出版年
2023年 | 35篇 |
2022年 | 66篇 |
2021年 | 111篇 |
2020年 | 77篇 |
2019年 | 98篇 |
2018年 | 91篇 |
2017年 | 83篇 |
2016年 | 100篇 |
2015年 | 82篇 |
2014年 | 110篇 |
2013年 | 144篇 |
2012年 | 117篇 |
2011年 | 171篇 |
2010年 | 108篇 |
2009年 | 103篇 |
2008年 | 119篇 |
2007年 | 126篇 |
2006年 | 98篇 |
2005年 | 75篇 |
2004年 | 70篇 |
2003年 | 67篇 |
2002年 | 48篇 |
2001年 | 41篇 |
2000年 | 54篇 |
1999年 | 45篇 |
1998年 | 116篇 |
1997年 | 87篇 |
1996年 | 64篇 |
1995年 | 54篇 |
1994年 | 49篇 |
1993年 | 48篇 |
1992年 | 47篇 |
1991年 | 39篇 |
1990年 | 41篇 |
1989年 | 33篇 |
1987年 | 39篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 40篇 |
1980年 | 31篇 |
1978年 | 39篇 |
1977年 | 34篇 |
1976年 | 42篇 |
1974年 | 69篇 |
1973年 | 61篇 |
1972年 | 67篇 |
1971年 | 59篇 |
1970年 | 63篇 |
1969年 | 53篇 |
1968年 | 48篇 |
排序方式: 共有3906条查询结果,搜索用时 15 毫秒
11.
Rudolf Habison 《International Journal of Project Management》1985,3(3):178-181
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs. 相似文献
12.
13.
14.
CJ Von Zuben 《Canadian Metallurgical Quarterly》1997,31(5):523-530
Some aspects of the widely observed over-dispersed pattern of the distribution of parasites within the host population are examined. It has been established in the parasitological literature that most hosts usually harbour few parasites, while only few hosts harbour a large proportion of the parasite population. Factors that may influence the pattern of distribution of parasites, the relation between the level of parasite aggregation and the prevalence of infection, and changes in this level of aggregation as a function of host age are analysed. Factors which determine the diversity of species in parasite communities are presented, and aspects of exploitative and interference competition among parasites and their relations with biological control procedures are also considered. Attention is also focused on the regulatory and destabilizing processes influencing the dynamic behaviour of host-parasite population interactions. 相似文献
15.
W Eggert-Kruse G Rohr H Kerbel B Schwalbach T Demirakca K Klinga W Tilgen B Runnebaum 《Canadian Metallurgical Quarterly》1996,11(4):784-789
To determine the clinical usefulness of Acridine Orange (AO) staining of spermatozoa as a screening test for the evaluation of semen quality during basic infertility investigation, semen smears from 103 randomly chosen males of subfertile couples were examined. The median duration of infertility was 4.5 years (range 1-15) and the median age was 33 years (range 21-43). The outcome of AO staining ranged from 5 to 81%, with a median of 24%, green fluorescent spermatozoa. Results were not significantly related to the parameters of semen analysis (sperm count, motility, standard morphology, viability, pH and volume, as well as fructose concentration and number of found cells) or to local sperm antibody testing and semen cultures. Fluorescence after AO staining was also not related to sperm functional capacity (evaluated using sperm-mucus interaction tests in vitro and in vivo), or the medical history of the patient. No significant differences in the AO test outcome were seen in patients with explained and unexplained infertility, or with regard to subsequent fertility [with a median value of 21% (range 5-46) green fluorescence in the fertile group, compared with a median value of 28% (range 9-81) green fluorescence in the other men]. The results of this prospective study indicate that under the usual conditions of conception, the AO test is not clinically useful as a screening procedure to determine semen quality during basic infertility investigation. 相似文献
16.
17.
18.
Heinrich Heydt Philipp Eisenbarth Karin Feith Klaus Urgast Gerhard Maas Manfred Regitz 《Israel journal of chemistry》1986,27(1):96-104
Amino-substituted cyclopropenylium salts ( 11a,b ) react with diazomethyl compounds ( 12a-i ) in dichloromethane or acetonitrile in the presence of a base (ethyldiisopropylamine, 1,5-diazabicyclo[4.3.0] non-5-ene) to form 4-aminopyridazines ( 13a-i ) specifically. The reaction is interpreted in terms of an initial electrophilic diazoalkane substitution to give diazomethylcyclopropenes ( 11 + 12 → 14 ) which undergo a [1.5]-cyclisation to form the betaines 16 which, in turn, isomerise with opening of the bridging bond to give the aminopyridazines 13 . In a similar manner, the tris[amino] cyclopropenylium salts 8a,b and 10a-c are converted to the 3,4,5-tris[amino]-pyridazines ( 21a-k ) by treatment with diazomethyl compounds ( 12a, c-f ). 相似文献
19.
20.
R. Bunk U. Leske R. Krompass Z. Pretch K. Rudolf R. Herbig K. Pitch V. A. Tsykanov O. V. Skiba V. A. Makarov L. P. Bol'shakov P. T. Porodnov A. A. Maershin S. S. Keruchen'ko 《Atomic Energy》1989,67(5):802-806
Translated from Atomnaya Énergiya, Vol. 67, No. 5, pp. 320–323, November, 1989. 相似文献