全文获取类型
收费全文 | 2777篇 |
免费 | 48篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 45篇 |
综合类 | 8篇 |
化学工业 | 339篇 |
金属工艺 | 58篇 |
机械仪表 | 43篇 |
建筑科学 | 37篇 |
矿业工程 | 8篇 |
能源动力 | 36篇 |
轻工业 | 165篇 |
水利工程 | 10篇 |
石油天然气 | 5篇 |
无线电 | 233篇 |
一般工业技术 | 377篇 |
冶金工业 | 1171篇 |
原子能技术 | 48篇 |
自动化技术 | 244篇 |
出版年
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 42篇 |
2015年 | 26篇 |
2014年 | 40篇 |
2013年 | 100篇 |
2012年 | 73篇 |
2011年 | 98篇 |
2010年 | 85篇 |
2009年 | 73篇 |
2008年 | 72篇 |
2007年 | 71篇 |
2006年 | 52篇 |
2005年 | 63篇 |
2004年 | 59篇 |
2003年 | 45篇 |
2002年 | 48篇 |
2001年 | 42篇 |
2000年 | 28篇 |
1999年 | 69篇 |
1998年 | 363篇 |
1997年 | 200篇 |
1996年 | 155篇 |
1995年 | 106篇 |
1994年 | 80篇 |
1993年 | 82篇 |
1992年 | 35篇 |
1991年 | 36篇 |
1990年 | 44篇 |
1989年 | 42篇 |
1988年 | 31篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1978年 | 18篇 |
1977年 | 35篇 |
1976年 | 73篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 18篇 |
排序方式: 共有2827条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
GB Lipford T Sparwasser M Bauer S Zimmermann ES Koch K Heeg H Wagner 《Canadian Metallurgical Quarterly》1997,27(12):3420-3426
Certain bacterial immunostimulatory (i.s.) DNA sequences containing unmethylated CpG motifs stimulate antigen-presenting cells (APC) to express a full complement of costimulatory molecules and to produce cytokines including interleukin (IL)-12 and tumor necrosis factor (TNF)-alpha. While IL-12 is key to their T helper cell (Th)1-promoting adjuvant activity, secretion of toxic levels of TNF-alpha is harmful in that it promotes toxic shock. Given the beneficial as well as harmful consequences of i.s. DNA, we investigated the possibility of identifying DNA sequences, i.e. CpG oligodeoxynucleotides (ODN) which differentially activate IL-12 versus TNF-alpha cytokine production in APC. Here, we describe an i.s. DNA sequence with these characteristics. While its potential to induce IL-12 is preserved, its ability to trigger TNF-alpha release is strongly curtailed both in vitro and in vivo. I.s. DNA could be segregated into lethal and non-lethal in a mouse toxic shock model. The non-toxic i.s. DNA was useful as an adjuvant, thus allowing cytotoxic T cell responses to the soluble protein ovalbumin and conferring a resistant Th 1 phenotype to BALB/c mice lethally infected with Leishmania major. This i.s. CpG motif may thus be prototypic for a useful immunostimulating DNA sequence that lacks harmful side effects. 相似文献
5.
Self-selected food intake of 15 reduced-obese women living in a metabolic ward was studied for 14 consecutive days to determine the effect of exercise and other metabolic and behavioral variables on energy intake. A choice of prepared food items were offered at breakfast, lunch and dinner, and a variety of additional food items were available continuously 24 h/day. Subjects performed either moderate intensity aerobic exercise (A-EX) (n = 8) expending 354 +/- 76 kcal/session or low intensity resistance weight training (R-EX)(n =7) expending 96 +/- kcal/session, 5 days/week. Mean energy intakes (kcal/day, +/- SEM) of the exercise groups were similar: 1867 +/- 275 for A-EX, 1889 +/- 294 for R-EX. Mean energy intakes of individuals ranged from 49 to 157% of the predetermined level required for weight maintenance. Resting metabolic rate per kg 0.75 and the Eating Inventory hunger score contributed significantly to the between subject variance in energy intake, whereas exercise energy expenditure did not. Regardless of exercise, eight women consistently restricted their energy intake (undereaters), and seven other consumed excess energy (overeaters). Overeaters were distinguished by higher Eating Inventory disinhibition (P = 0.023) and hunger (p = 0.004) scores. The overeaters' diet had a higher fat content 34 +/- 1% (p = 0.007). Also, overeaters took a larger percentage of their daily energy, than that of undereaters, 27 +/- 1 energy intake in the evening, 13 +/- 2%, compared to undereaters, 7 +/- 1% (p = 0.005). We conclude that the Eating Inventory is useful for identifying reduced-obese women at risk of overeating, and these individuals may benefit from dietary counseling aimed at reducing fat intake and evening snacking. 相似文献
6.
BACKGROUND/AIMS: Nitric oxide (NO) is an important mediator in the regulation of vascular tone. However, no data exist on the physiological role of NO in the regulation of the hepatic microcirculation. This study was designed to evaluate the role of NO in the hepatic microcirculation in vivo under physiological conditions. METHODS: The hepatic microcirculation was investigated in anesthetized rats by intravital fluorescence microscopy after injection of fluorescein-isothiocyanate-labeled erythrocytes. Following assessment of baseline sinusoidal perfusion, animals were randomly treated with L-NMMA (n=6), L-arginine (n=6), nitroprusside sodium (NPS, n=5) or a comparable volume of NaCl (n=4). Drugs were given through a portal vein catheter at three doses (Dx), each followed by intravital microscopy. L-NMMA was given: 5 mg/kg (D1), 25 mg/kg (D2), 50 mg/kg (D3); L-arginine 30 mg/kg (D1), 150 mg/kg (D2), 300 mg/kg (D3); and NPS continuously 80 microg x kg(-1) x h(-1). RESULTS: L-NMMA induced a significant increase of mean arterial blood pressure (MAP) (114 vs. 129 mm Hg; p<0.05). In contrast, MAP of NPS-treated animals decreased (107 vs. 91 mm Hg; p<0.01) whereas MAP of animals receiving L-arginine did not significantly differ. Sinusoidal blood flow revealed dose-dependent changes: L-NMMA significantly decreased perfusion of sinusoids (D1: 65%, D2: 57%, D3: 50% of baseline, p<0.05). Injection of L-arginine increased the sinusoidal flow even with the lowest dose (D1: 137%, D2: 133%, D3: 123%, p<0.05). Continuous infusion of NPS had little effect on sinusoidal blood flow at the first and second times of microscopy but sinusoidal blood flow was significantly increased at the third time (D1: 103%, D2: 106%, D3: 122%). CONCLUSIONS: Inhibition of NOS results in a dose-dependent disturbance of the hepatic microcirculation despite significantly increased MAP, whereas L-arginine increases the sinusoidal blood flow. The results indicate an important role for NO in the regulatory mechanisms of hepatic sinusoidal perfusion under physiological conditions. 相似文献
7.
8.
Visual and auditory stimulus discrimination tasks, analogous to those used in the Reitan-Klove Sensory Perceptual Examination, were performed by 12 cocaine-dependent and 5 alcohol-dependent patients after 1 week, 3 weeks, and 3 months of verified abstinence. Sixteen control subjects, who were not substance-dependent, performed the same tasks after comparable intervals. During each task, either visual or auditory stimuli were presented in the left, in the right, or in both sensory fields. A simple key press was made to discriminate these conditions. Cocaine-dependent patients responded more slowly than control subjects during both tasks. The reaction-time slowing persisted across all three sessions, spanning a 3-month period of abstinence. There were no significant differences between the cocaine-dependent and control groups in response accuracy. In the context of other findings, these findings are interpreted as reflecting an enduring effect of prior cocaine dependence on motor as opposed to sensory functioning. 相似文献
9.
Accumulation of ochratoxin A in rat kidney in vivo and in cultivated renal epithelial cells in vitro
Biological applications of triplex forming oligonucleotides will require the development of oligomers with high avidity and specificity. We examined the binding enhancement resulting from intercalator conjugation to both parallel design (polythymidine T15) and antiparallel design (polypurine AG15, for binding a 15 base pair polypurine-polypyrimidine sequence in the IL-2R alpha gene enhancer) oligomers under various ionic strength and temperature conditions. Oligonucleotides were conjugated through a urea link to 6,9 diamino-3-methoxy acridine (to give T15C and AG15C). Intercalator conjugation dramatically enhanced the specific triplex binding avidity (Kd = 5 nM for AG15C and 275 nM for T15C at 25 degrees C, compared to 2 microM for AG15 and > 50 microM for T15 at 25 degrees C), without detectable binding to an inappropriate target sequence. Surprisingly, triplex formation with AG15C occurred at lower Mg2+ concentrations than with T15C. AG15 and AG15C showed rapid Mg2+ dependent self association, but not T15C or T15. T15C triplex formation occurred rapidly (completion in less than 4 min), while AG15C bound to its target sequence more slowly over 20-24 h. Thus, binding constants in the low nanomolar range are now achievable with intercalator conjugated polypurine antiparallel binding oligonucleotides, a prerequisite for biological applications of such agents. 相似文献
10.