全文获取类型
收费全文 | 4683篇 |
免费 | 113篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 73篇 |
化学工业 | 443篇 |
金属工艺 | 31篇 |
机械仪表 | 47篇 |
建筑科学 | 109篇 |
矿业工程 | 5篇 |
能源动力 | 83篇 |
轻工业 | 293篇 |
水利工程 | 23篇 |
石油天然气 | 14篇 |
无线电 | 409篇 |
一般工业技术 | 438篇 |
冶金工业 | 2433篇 |
原子能技术 | 55篇 |
自动化技术 | 350篇 |
出版年
2022年 | 24篇 |
2021年 | 47篇 |
2020年 | 22篇 |
2019年 | 53篇 |
2018年 | 50篇 |
2017年 | 53篇 |
2016年 | 71篇 |
2015年 | 35篇 |
2014年 | 61篇 |
2013年 | 163篇 |
2012年 | 85篇 |
2011年 | 113篇 |
2010年 | 100篇 |
2009年 | 92篇 |
2008年 | 131篇 |
2007年 | 111篇 |
2006年 | 85篇 |
2005年 | 77篇 |
2004年 | 64篇 |
2003年 | 72篇 |
2002年 | 63篇 |
2001年 | 83篇 |
2000年 | 60篇 |
1999年 | 119篇 |
1998年 | 628篇 |
1997年 | 395篇 |
1996年 | 254篇 |
1995年 | 138篇 |
1994年 | 161篇 |
1993年 | 174篇 |
1992年 | 50篇 |
1991年 | 56篇 |
1990年 | 76篇 |
1989年 | 69篇 |
1988年 | 91篇 |
1987年 | 70篇 |
1986年 | 51篇 |
1985年 | 72篇 |
1984年 | 33篇 |
1983年 | 35篇 |
1982年 | 34篇 |
1981年 | 40篇 |
1980年 | 44篇 |
1979年 | 25篇 |
1978年 | 37篇 |
1977年 | 95篇 |
1976年 | 151篇 |
1975年 | 39篇 |
1974年 | 14篇 |
1973年 | 16篇 |
排序方式: 共有4806条查询结果,搜索用时 15 毫秒
1.
Activity-directed synthesis (ADS) is a structure-blind, functional-driven molecular discovery approach. In this Concept, four case studies highlight the general applicability of ADS and showcase its flexibility to support different medicinal chemistry strategies. ADS deliberately harnesses reactions with multiple possible outcomes, and allows many chemotypes to be evaluated in parallel. Resources are focused on bioactive molecules, which emerge in tandem with associated synthetic routes. Some of the future challenges for ADS are highlighted, including the realisation of an autonomous molecular discovery platform. The prospects for ADS to become a mainstream lead generation approach are discussed. 相似文献
2.
Predicting Forest Age Classes from High Spatial Resolution Remotely Sensed Imagery Using Voronoi Polygon Aggregation 总被引:1,自引:0,他引:1
Efficient identification of forest age is useful for forest management and ecological applications. Here we propose a user-assisted method for determining forest age using high spatial resolution remotely sensed imagery. This method requires individual trees to be extracted from imagery and represented as points. We use a local maximum filter to generate points that are converted to Voronoi polygons. Properties of the Voronoi polygons are correlated with forest age and used to aggregate points (trees) into areas (stands) based on three forest age classes. Accuracy of the aggregation ranges from approximately 68% to 78% and identification of the mature class is more consistent and accurate than the younger classes. 相似文献
3.
GW Pratt 《Canadian Metallurgical Quarterly》1997,(23):30-32
A discussion is presented of contributing factors to the injury to the foreleg of the Thoroughbred racehorse. The critical part of the step is taken to be the first 10-20 ms after ground contact as the hoof slides forward and stops. Large nonaxial loads associated with the deceleration of the hoof are shown to arise. Results of accelerometer measurements on the hoof of a horse running at racing speed are presented as well as mechanical properties of the racing surface. The mechanical properties of the track surface, the type of shoe, and the degree of fatigue of the horse all work together to determine the level of risk. 相似文献
4.
5.
6.
Several simple 3D experiments are used to provide J correlations between methionine C epsilon methyl carbons and either the C gamma H2 protons or C beta and C gamma. The intensity of the J correlations provides information on the size of the three-bond J couplings and thereby on the chi 3 torsion angle. In addition, a simple 3D version of the HMBC experiment provides a sensitive link between the C epsilon H3 methyl protons and C gamma. The methods are demonstrated for a 20 kDa complex between calmodulin and a 26-residue peptide fragment of skeletal muscle myosin light chain kinase. 相似文献
7.
Comparison of two methods of surfactant administration and the effect on dosing-associated hypoxemia
M Nelson JJ Nicks MA Becker LA Vrlenich V Bhatt-Mehta RE Schumacher 《Canadian Metallurgical Quarterly》1997,17(6):450-454
OBJECTIVE: The purpose of our study was to test the hypothesis that surfactant dosing through a proximal sideport adapter on an endotracheal tube leads to more dosing-associated hypoxemia compared with a method of dosing that uses a double-lumen endotracheal tube. STUDY DESIGN: Using adequate sample size to compare significant changes in O2 saturation (power > 0.8, alpha < 0.05) we enrolled 36 infants with respiratory distress syndrome in this randomized trial. A 10% change in O2 saturation was considered clinically significant. Nineteen infants received 38 doses of surfactant through the sideport adapter. Seventeen infants received 31 doses of surfactant through the nonventilation lumen of a double-lumen endotracheal tube. Two main outcome measures were assessed: time-averaged O2 saturation values 30 minutes after dosing and the largest absolute fall in O2 saturation for each patient. RESULTS AND CONCLUSIONS: Time-averaged O2 saturation measures were higher in the proximal sideport group (p = 0.02), but the magnitude of difference was probably not clinically significant. No significant difference was detected between groups when we compared largest absolute drop in O2 saturation. Secondary analyses found no effect of birth weight or dose number (second vs third dose) on either outcome measure. 相似文献
8.
JD Nelson 《Canadian Metallurgical Quarterly》1996,335(12):885-886
9.
A value-based test is presented for economic screening of electric utility demand-side management (DSM) programs. The widely used least cost test is valid if the programs do not alter the amount or value of energy services provided to customers. But, in general, DSM programs have such effects and, as a result, the value consumers receive is changed. A more general economic efficiency test, the most value test, provides a practical method for considering the effects of DSM on customer value. The version presented allows for multiple load periods and can account for rate impacts on several customer classes. Four typical DSM programs are evaluated as illustrations 相似文献
10.