首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1050篇
  免费   57篇
  国内免费   6篇
电工技术   16篇
综合类   3篇
化学工业   245篇
金属工艺   25篇
机械仪表   19篇
建筑科学   52篇
矿业工程   36篇
能源动力   29篇
轻工业   129篇
水利工程   22篇
无线电   60篇
一般工业技术   208篇
冶金工业   178篇
原子能技术   5篇
自动化技术   86篇
  2023年   13篇
  2022年   10篇
  2021年   31篇
  2020年   18篇
  2019年   19篇
  2018年   27篇
  2017年   25篇
  2016年   25篇
  2015年   33篇
  2014年   32篇
  2013年   49篇
  2012年   46篇
  2011年   71篇
  2010年   56篇
  2009年   42篇
  2008年   47篇
  2007年   50篇
  2006年   49篇
  2005年   34篇
  2004年   27篇
  2003年   31篇
  2002年   19篇
  2001年   13篇
  2000年   17篇
  1999年   15篇
  1998年   51篇
  1997年   23篇
  1996年   24篇
  1995年   12篇
  1994年   11篇
  1993年   13篇
  1992年   8篇
  1991年   6篇
  1990年   4篇
  1987年   6篇
  1986年   7篇
  1983年   5篇
  1981年   12篇
  1980年   4篇
  1976年   9篇
  1971年   4篇
  1970年   7篇
  1964年   10篇
  1961年   3篇
  1960年   6篇
  1958年   4篇
  1957年   4篇
  1956年   24篇
  1954年   7篇
  1920年   4篇
排序方式: 共有1113条查询结果,搜索用时 46 毫秒
1.
Many media processing applications create a load that varies significantly over time. Hence, if such an application is assigned a lower processing-time budget than needed in its worst-case load situation, deadline misses are likely to occur. This problem can be dealt with by designing media processing applications in a scalable fashion. A scalable media processing application can run in multiple qualities, leading to correspondingly different resource demands. The problem we consider is to find an accompanying quality control strategy, which minimizes both the number of deadline misses and the number of quality changes, while maximizing the quality of processing. We present an initial approach to the above problem by modeling it as a Markov decision process (MDP). Our model is based on measuring relative progress at milestones. Solving the MDP results in a quality control strategy that can be applied during runtime with only little overhead. We evaluate our approach by means of a practical example, which concerns a scalable MPEG-2 decoder.  相似文献   
2.
3.
4.
Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'.  相似文献   
5.
OBJECTIVE: To evaluate the efficacy of terazosin, an alpha-blocker, for the treatment of idiopathic oligozoospermia. PATIENTS AND METHODS: Thirty couples with infertility whose only detectable abnormality was male idiopathic subfertility entered the study. The diagnosis of idiopathic subfertility in all males studied, aged 26 to 38 years (mean 28.2 years), was confirmed after exclusion of any iatrogenic, systemic, congenital, infectious, autoimmune or endocrinological cause. In order to start with a baseline value before the study, at least three semen samples were evaluated in accordance with the WHO recommendation. Before initiation of treatment, blood samples were drawn for measurement of FSH, LH, testosterone, prolactin, dihydrotestosterone, and estradiol. Fifteen randomly selected patients (Group A) received 2 mg/d of alpha-blocker (terazosin), while another 15 (Group B) were administered an identically packed placebo tablet. Both groups received therapy for 6 months. RESULTS: The mean seminal volume changed insignificantly between the two groups (4.15 +/- 1.95 vs. 4.10 +/- 1.95). There was a statistically significant increase of the sperm concentration in patients who received the alpha-blocker compared to those receiving placebo (24.76 +/- 9.45 vs. 13.15 +/- 11.55 millions/mL; P < .001). No improvement of the mean percentage of abnormal spermatozoa was observed in the treated patients, nor a statistically significant difference of sperm motility in the treated group compared to the placebo group. Side effects were not observed in the patients receiving terazosin treatment, or were so minimal that therapy was continued. The pregnancy rates did not differ between the two groups to a statistically significant degree. CONCLUSION: The administration of terazosin to patients with idiopathic oligozoospermia has a demonstrably positive effect, especially on sperm concentration.  相似文献   
6.
Peripheral benzodiazepine receptors (PBRs) are expressed in a variety of tissues but are normally found at low levels in the brain. Following various types of nerve injury, a reactive gliosis results that exhibits a high expression of this receptor. To further characterize the expression of PBRs following neuronal injury, we evaluated PBR expression in the facial nucleus following facial nerve axotomy (FNA). Injury to a peripheral nerve results in a complex series of metabolic and morphological changes around the injured neuron. Transections of the facial nerve results in a rapid activation of both astrocytes and microglia around axotomized motor neurons. FNA resulted in an increase in the staining for both astrocytes (glial fibrillary acidic protein) and activated microglia (OX42). There was also a reduction in synaptic contacts with the motor nucleus as evidenced by reduced staining for the synaptic marker, synaptophysin. In sections labeled with [3H]-PK11195, the subsequent autoradiograms displayed marked increases in the labeling for PBRs. This increase was observed at 5, 7 and 10 days after nerve transection. The increase was primarily in the level of expression (Bmax), with no change in the affinity of the ligand (Kd). The increase in PBR expression after FNA supports the hypothesis that PBRs can be used as a sensitive marker for CNS injury.  相似文献   
7.
Microcapsules are used for the formulation of drug controlled release and drug targeting dosage forms. Encapsulated hydrophobic drugs are often applied as their solutions in plant oils. The uptake of the oils in the complex coacervate microcapsules can be improved by the addition of surfactants. In this study, soybean, olive and peanut oils were chosen as the representatives of plant oils. The well characterized complex coacervation of gelatin and acacia has been used to produce the microcapsules. The amount of encapsulated oil has been determined gravimetrically. The encapsulation of the oils was high (75-80%). When the surfactants with HLB values from 1.8 to 6.7 were used, the amount of encapsulated oil was high (65-85%). A significant decrease of the oil content in the microcapsules was found when Tween 61 with HLB = 9.6 had been added into the mixture. No oil was found inside the microcapsules from the coacervate emulsion mixture containing Tween 81 (HLB = 10) and Tween 80 (HLB = 15), respectively. The results of the experiment confirm the dependence of hydrophobic substance encapsulation on the HLB published recently for Squalan.  相似文献   
8.
OBJECTIVE: Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery. METHODS: A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored. RESULTS: The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min). CONCLUSIONS: Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.  相似文献   
9.
10.
Fertilisers may contain pollutants that are applied to the field together with the nutrients. Comparing fertilisers is difficult because of their different concentrations of nutrients and pollutants. In this study an already existing model was taken. It was further developed to compare nutrient fluxes (N, P, K, Ca, Mg, S, humus) and pollutants (heavy metals and pharmaceuticals) of pig and cattle slurry as well as human urine. The data used is taken from literature and, in the case of pharmaceuticals in urine, daily excretion rates were calculated. An amount of 19 m3 ha(-1) a(-1) undiluted urine can be applied, limiting factor is sulphur. Without taking over-fertilisation into account, an addition of mineral fertiliser is required to any organic fertiliser application. In general, heavy metal, antibiotic, and hormone fluxes are higher by using animal manure then urine as fertiliser. However, additional loads of other pharmaceuticals consumed by humans have to be considered. Overall, the model is a suitable tool worthwhile to be extended in aspects of hygiene, environmental impacts as for example, degradation processes as well as ecotoxicology.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号