全文获取类型
收费全文 | 11017篇 |
免费 | 116篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 98篇 |
综合类 | 2篇 |
化学工业 | 1063篇 |
金属工艺 | 101篇 |
机械仪表 | 300篇 |
建筑科学 | 216篇 |
矿业工程 | 28篇 |
能源动力 | 130篇 |
轻工业 | 879篇 |
水利工程 | 107篇 |
石油天然气 | 15篇 |
无线电 | 863篇 |
一般工业技术 | 1034篇 |
冶金工业 | 5451篇 |
原子能技术 | 108篇 |
自动化技术 | 747篇 |
出版年
2021年 | 69篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 60篇 |
2017年 | 83篇 |
2016年 | 65篇 |
2015年 | 47篇 |
2014年 | 110篇 |
2013年 | 319篇 |
2012年 | 161篇 |
2011年 | 259篇 |
2010年 | 238篇 |
2009年 | 231篇 |
2008年 | 260篇 |
2007年 | 242篇 |
2006年 | 246篇 |
2005年 | 219篇 |
2004年 | 178篇 |
2003年 | 201篇 |
2002年 | 200篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 256篇 |
1998年 | 1420篇 |
1997年 | 844篇 |
1996年 | 663篇 |
1995年 | 434篇 |
1994年 | 363篇 |
1993年 | 403篇 |
1992年 | 143篇 |
1991年 | 149篇 |
1990年 | 162篇 |
1989年 | 167篇 |
1988年 | 172篇 |
1987年 | 173篇 |
1986年 | 138篇 |
1985年 | 166篇 |
1984年 | 94篇 |
1983年 | 102篇 |
1982年 | 84篇 |
1981年 | 105篇 |
1980年 | 97篇 |
1979年 | 79篇 |
1978年 | 79篇 |
1977年 | 178篇 |
1976年 | 390篇 |
1975年 | 78篇 |
1974年 | 71篇 |
1973年 | 63篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The effects of azadirachtin, salannin, nimbin, and 6-desacetylnimbin on ecdysone 20-monooxygenase (E-20-M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabeled ecdysone and increasing concentrations (from 1 x 10(-8) to 1 x 10(-3) M) of the four compounds isolated from seed kernels of the neem tree, Azadirachta indica. All four neem tree compounds were found to inhibit, in a dose-dependent fashion, the E-20-M activity in three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 2 x 10(-5) to 1 x 10(-3). 相似文献
22.
Vibrio cholerae causes epidemic diarrhea throughout the world. Fluid replacement is the primary therapy for cholera; however, high mortality rates often necessitate the use of antibiotics. V. cholerae, like most bacteria, has developed resistance to some antibiotics. In the early 1990s a new serotype strain, Bengal 0139, began a new wave of cholera epidemics. Bengal isolates showed unique trends in antimicrobial resistance. Many clinical laboratories use automated antibiotic susceptibility testing for V. cholerae. It is important to know if automated susceptibility test results for V. cholerae coincide with reported trends in antibiotic susceptibility. In the present study, we used the Vitek automated susceptibility system to determine the susceptibilities of 79 V. cholerae O1 isolates, 100 O139 isolates, and 112 non-O1 isolates. Vitek susceptibilities for V. cholerae showed a good correlation with preestablished epidemiological data. Although the new O139 serogroup showed a trend of increased resistance to trimethoprim-sulfamethoxazole and nitrofurantoin, it was more susceptible to ampicillin than previous serogroup O1 and non-O1 strains. Regardless of serogroup, > or = 98% of the V. cholerae isolates tested were susceptible to most antibiotics tested by us. It is important to continue susceptibility testing of all new isolates of V. cholerae because of emerging resistant strains. However, V. cholerae remains susceptible to most of the available antibiotics. 相似文献
23.
24.
Johnson J 《Environmental science & technology》1996,30(11):481A-482A
Society. 相似文献
25.
Ovarian mucinous cystadenocarcinoma with mural nodules of anaplastic carcinoma: report of a case and review of the literature 总被引:1,自引:0,他引:1
A decline of cytosol protein kinase C activity was observed in rat myocardial cells at 4 and 8 h after endotoxin administration, and membrane-associated protein kinase C activity rose at the same time. The activity of membrane protein kinase C in aortic smooth muscle cells at 0.5 and 4 h after endotoxin injection was higher than that in control, while cytosol protein kinase C activity was lower. The results indicate that protein kinase C was activated in myocardial cells and aortic smooth muscle cells during various phases of endotoxemia. 相似文献
26.
RA Newman JC Vidal LJ Viskatis J Johnson MA Etcheverry 《Canadian Metallurgical Quarterly》1993,11(2-3):151-159
Two purified animal venom toxins, crotoxin and cardiotoxin, have been combined to produce a unique natural product (VRCTC-310) currently under investigation as an antitumor agent by the National Cancer Institute. In vitro, it has demonstrated cytotoxic disease specificity and a unique mechanism of action when submitted to COMPARE analysis. In vivo, tolerance was developed to the neurotoxic properties of crotoxin which allowed comparison of several schedules of fixed and escalating daily i.m. doses to mice bearing s.c. Lewis Lung carcinoma. An 83% inhibition of tumor growth was achieved using an escalating dose schedule starting at 1.8 mg/kg and reaching 6.3 mg/kg/day on day 20. Although some irritation around the sites of i.m. injection was noted, animal weight loss was negligible and there were no other signs of adverse toxicity. This natural product represents a new, membrane interactive anticancer agent which produces a unique spectrum of cytotoxicity in vitro and which has demonstrated interesting in vivo antitumor efficacy. 相似文献
27.
We compared the data from four growth hormone (GH) immunoassays for analyzing 24-h GH profiles in four apparently normal subjects and four obese subjects (508 serum samples). The detection limit was 0.02 microgram/L for one immunochemiluminometric assay (ICMA), 0.1 microgram/L for two IRMAs, and 0.4 microgram/L for one RIA. All GH pulses with a peak ICMA value > 1 microgram/L were detected by each of the other methods. Overall, the correlation coefficient between the values obtained with all four assays exceeded 0.90. However, for GH concentrations < or = 0.25 microgram/L, acceptable concordance (r2 > or = 0.80) was reached only between the ICMA and one IRMA; between the ICMA and the RIA, concordance was acceptable only for GH concentrations > or = 10 micrograms/L. In the normal subjects, the percentage of undetectable values was 0% with the ICMA but 29% with one of the IRMAs; in obese subjects, the corresponding values were 12% and 38%. 相似文献
28.
29.
30.
A concept is proposed for utilizing artificial neural networks to enhance the high-speed tracking accuracy of robotic manipulators. Tracking accuracy is a function of the controller's ability to compensate for disturbances produced by dynamical interactions between the links. A model-based control algorithm uses a nominal model of those dynamical interactions to reduce the disturbances. The problem is how to provide accurate dynamics information to the controller in the presence of payload uncertainty and modeling error. Neural network payload estimation uses a series of artificial neural networks to recognize the payload variation associated with a degradation in tracking performance. The network outputs are combined with a knowledge of nominal dynamics to produce a computationally efficient direct form of adaptive control. The concept is validated through experimentation and analysis on the first three links of a PUMA-560 manipulator. A multilayer perceptron architecture with two hidden layers is used. Integration of the principles of neural network pattern recognition and model-based control produces a tracking algorithm with enhanced robustness to incomplete dynamic information. Tracking efficacy and applicability to robust control algorithms are discussed. 相似文献