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   2548篇
  免费   204篇
  国内免费   1篇
电工技术   17篇
化学工业   893篇
金属工艺   19篇
机械仪表   31篇
建筑科学   90篇
矿业工程   3篇
能源动力   53篇
轻工业   899篇
水利工程   13篇
石油天然气   27篇
无线电   102篇
一般工业技术   303篇
冶金工业   116篇
原子能技术   4篇
自动化技术   183篇
  2024年   6篇
  2023年   19篇
  2022年   95篇
  2021年   138篇
  2020年   60篇
  2019年   65篇
  2018年   82篇
  2017年   78篇
  2016年   100篇
  2015年   90篇
  2014年   106篇
  2013年   187篇
  2012年   168篇
  2011年   214篇
  2010年   135篇
  2009年   157篇
  2008年   146篇
  2007年   132篇
  2006年   103篇
  2005年   82篇
  2004年   75篇
  2003年   51篇
  2002年   57篇
  2001年   33篇
  2000年   34篇
  1999年   36篇
  1998年   47篇
  1997年   42篇
  1996年   32篇
  1995年   26篇
  1994年   17篇
  1993年   21篇
  1992年   22篇
  1991年   10篇
  1990年   13篇
  1989年   17篇
  1988年   9篇
  1987年   5篇
  1986年   7篇
  1985年   3篇
  1984年   5篇
  1983年   1篇
  1982年   5篇
  1981年   7篇
  1980年   4篇
  1979年   3篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1957年   1篇
排序方式: 共有2753条查询结果,搜索用时 15 毫秒
91.
BACKGROUND: Cerebral circulation delivers the blood flow to the brain through a dedicated network of sanguine vessels. A healthy human brain can regulate cerebral blood flow (CBF) according to any physiological or pathological challenges. The brain is protected by its self-regulatory mechanisms, which are dependent on neuronal and support cellular populations, including endothelial ones, as well as metabolic, and even myogenic factors. OBJECTIVES: Accumulating data suggest that “non-pharmacological” approaches might provide new opportunities for stroke therapy, such as electro-/acupuncture, hyperbaric oxygen therapy, hypothermia/cooling, photobiomodulation, therapeutic gases, transcranial direct current stimulations, or transcranial magnetic stimulations. We reviewed the recent data on the mechanisms and clinical implications of these non-pharmaceutical treatments. METHODS: To present the state-of-the-art for currently available non-invasive, non-pharmacological-related interventions in acute ischemic stroke, we accomplished this synthetic and systematic literature review based on the Preferred Reporting Items for Systematic Principles Reviews and Meta-Analyses (PRISMA). RESULTS: The initial number of obtained articles was 313. After fulfilling the five steps in the filtering/selection methodology, 54 fully eligible papers were selected for synthetic review. We enhanced our documentation with other bibliographic resources connected to our subject, identified in the literature within a non-standardized search, to fill the knowledge gaps. Fifteen clinical trials were also identified. DISCUSSION: Non-invasive, non-pharmacological therapeutic/rehabilitative interventions for acute ischemic stroke are mainly holistic therapies. Therefore, most of them are not yet routinely used in clinical practice, despite some possible beneficial effects, which have yet to be supplementarily proven in more related studies. Moreover, few of the identified clinical trials are already completed and most do not have final results. CONCLUSIONS: This review synthesizes the current findings on acute ischemic stroke therapeutic/rehabilitative interventions, described as non-invasive and non-pharmacological.  相似文献   
92.
Teriflunomide (TFN) limits relapses in relapsing–remitting multiple sclerosis (RRMS) by reducing lymphocytic proliferation through the inhibition of the mitochondrial enzyme dihydroorotate dehydrogenase (DHODH) and the subsequent modulation of de novo pyrimidine synthesis. Alterations of mitochondrial function as a consequence of oxidative stress have been reported during neuroinflammation. Previously, we showed that TFN prevents alterations of mitochondrial motility caused by oxidative stress in peripheral axons. Here, we aimed to validate TFN effects on mitochondria and neuronal activity in hippocampal brain slices, in which cellular distribution and synaptic circuits are largely preserved. TFN effects on metabolism and neuronal activity were investigated by assessing oxygen partial pressure and local field potential in acute slices. Additionally, we imaged mitochondria in brain slices from the transgenic Thy1-CFP/COX8A)S2Lich/J (mitoCFP) mice using two-photon microscopy. Although TFN could not prevent oxidative stress-related depletion of ATP, it preserved oxygen consumption and neuronal activity in CNS tissue during oxidative stress. Furthermore, TFN prevented mitochondrial shortening and fragmentation of puncta-shaped and network mitochondria during oxidative stress. Regarding motility, TFN accentuated the decrease in mitochondrial displacement and increase in speed observed during oxidative stress. Importantly, these effects were not associated with neuronal viability and did not lead to axonal damage. In conclusion, during conditions of oxidative stress, TFN preserves the functionality of neurons and prevents morphological and motility alterations of mitochondria.  相似文献   
93.
Fetal stress is known to increase susceptibility to cardiometabolic diseases and hypertension in adult age in a process known as fetal programming. This study investigated the relationship between vascular RAS, oxidative damage and remodeling in fetal programming. Six-month old Sprague-Dawley offspring from mothers that were fed ad libitum (CONTROL) or with 50% intake during the second half of gestation (maternal undernutrition, MUN) were used. qPCR or immunohistochemistry were used to obtain the expression of receptors and enzymes. Plasma levels of carbonyls were measured by spectrophotometry. In mesenteric arteries from MUN rats we detected an upregulation of ACE, ACE2, AT1 receptors and NADPH oxidase, and lower expression of AT2, Mas and MrgD receptors compared to CONTROL. Systolic and diastolic blood pressure and plasma levels of carbonyls were higher in MUN than in CONTROL. Vascular morphology evidenced an increased media/lumen ratio and adventitia/lumen ratio, and more connective tissue in MUN compared to CONTROL. In conclusion, fetal undernutrition indices RAS alterations and oxidative damage which may contribute to the remodeling of mesenteric arteries, and increase the risk of adverse cardiovascular events and hypertension.  相似文献   
94.
The preparation, characterization, and controlled release of hydroxyapatite (HAp) nanoparticles loaded with streptomycin (STR) was studied. These nanoparticles are highly appropriate for the treatment of bacterial infections and are also promising for the treatment of cancer cells. The analyses involved scanning electron microscopy, dynamic light scattering (DLS) and Z-potential measurements, as well as infrared spectroscopy and X-ray diffraction. Both amorphous (ACP) and crystalline (cHAp) hydroxyapatite nanoparticles were considered since they differ in their release behavior (faster and slower for amorphous and crystalline particles, respectively). The encapsulated nanoparticles were finally incorporated into biodegradable and biocompatible polylactide (PLA) scaffolds. The STR load was carried out following different pathways during the synthesis/precipitation of the nanoparticles (i.e., nucleation steps) and also by simple adsorption once the nanoparticles were formed. The loaded nanoparticles were biocompatible according to the study of the cytotoxicity of extracts using different cell lines. FTIR microspectroscopy was also employed to evaluate the cytotoxic effect on cancer cell lines of nanoparticles internalized by endocytosis. The results were promising when amorphous nanoparticles were employed. The nanoparticles loaded with STR increased their size and changed their superficial negative charge to positive. The nanoparticles’ crystallinity decreased, with the consequence that their crystal sizes reduced, when STR was incorporated into their structure. STR maintained its antibacterial activity, although it was reduced during the adsorption into the nanoparticles formed. The STR release was faster from the amorphous ACP nanoparticles and slower from the crystalline cHAp nanoparticles. However, in both cases, the STR release was slower when incorporated in calcium and phosphate during the synthesis. The biocompatibility of these nanoparticles was assayed by two approximations. When extracts from the nanoparticles were evaluated in cultures of cell lines, no cytotoxic damage was observed at concentrations of less than 10 mg/mL. This demonstrated their biocompatibility. Another experiment using FTIR microspectroscopy evaluated the cytotoxic effect of nanoparticles internalized by endocytosis in cancer cells. The results demonstrated slight damage to the biomacromolecules when the cells were treated with ACP nanoparticles. Both ACP and cHAp nanoparticles were efficiently encapsulated in PLA electrospun matrices, providing functionality and bioactive properties.  相似文献   
95.
The aim of this review is to shed light over the most recent advances in Coenzyme Q10 (CoQ10) applications as well as to provide detailed information about the functions of this versatile molecule, which have proven to be of great interest in the medical field. Traditionally, CoQ10 clinical use was based on its antioxidant properties; however, a wide range of highly interesting alternative functions have recently been discovered. In this line, CoQ10 has shown pain-alleviating properties in fibromyalgia patients, a membrane-stabilizing function, immune system enhancing ability, or a fundamental role for insulin sensitivity, apart from potentially beneficial properties for familial hypercholesterolemia patients. In brief, it shows a remarkable amount of functions in addition to those yet to be discovered. Despite its multiple therapeutic applications, CoQ10 is not commonly prescribed as a drug because of its low oral bioavailability, which compromises its efficacy. Hence, several formulations have been developed to face such inconvenience. These were initially designed as lipid nanoparticles for CoQ10 encapsulation and distribution through biological membranes and eventually evolved towards chemical modifications of the molecule to decrease its hydrophobicity. Some of the most promising formulations will also be discussed in this review.  相似文献   
96.
Breast (BrCa) and prostate (PCa) cancers are the most common malignancies in women and men, respectively. The available therapeutic options for these tumors are still not curative and have severe side effects. Therefore, there is an urgent need for more effective antineoplastic agents. Herein, BrCa, PCa, and benign cell lines were treated with two ionic liquids and two quinoxalines and functional experiments were performed—namely cell viability, apoptosis, cytotoxicity, and colony formation assays. At the molecular level, an array of gene expressions encompassing several molecular pathways were used to explore the impact of treatment on gene expression. Although both quinoxalines and the ionic liquid [C2OHMIM][Amp] did not show any effect on the BrCa and PCa cell lines, [C16Pyr][Amp] significantly decreased cell viability and colony formation ability, while it increased the apoptosis levels of all cell lines. Importantly, [C16Pyr][Amp] was found to be more selective for cancer cells and less toxic than cisplatin. At the molecular level, this ionic liquid was also associated with reduced expression levels of CPT2, LDHA, MCM2, and SKP2, in both BrCa and PCa cell lines. Hence, [C16Pyr][Amp] was shown to be a promising anticancer therapeutic agent for BrCa and PCa cell lines.  相似文献   
97.
Aspirin (ASA) has attracted wide interest of numerous scientists worldwide thanks to its chemopreventive and chemotherapeutic effects, particularly in colorectal cancer (CRC). Incorporation of selenium (Se) atom into ASA has greatly increased their anti-tumoral efficacy in CRC compared with the organic counterparts without the Se functionality, such as the promising antitumoral methylseleno-ASA analog (1a). Nevertheless, the efficacy of compound 1a in cancer cells is compromised due to its poor solubility and volatile nature. Thus, 1a has been formulated with native α-, β- and γ-cyclodextrin (CD), a modified β-CD (hydroxypropyl β-CD, HP-β-CD) and Pluronic F127, all of them non-toxic, biodegradable and FDA approved. Water solubility of 1a is enhanced with β- and HP- β-CDs and Pluronic F127. Compound 1a forms inclusion complexes with the CDs and was incorporated in the hydrophobic core of the F127 micelles. Herein, we evaluated the cytotoxic potential of 1a, alone or formulated with β- and HP- β-CDs or Pluronic F127, against CRC cells. Remarkably, 1a formulations demonstrated more sustained antitumoral activity toward CRC cells. Hence, β-CD, HP-β-CD and Pluronic F127 might be excellent vehicles to improve pharmacological properties of organoselenium compounds with solubility issues and volatile nature.  相似文献   
98.
Moderate alcohol consumption is associated with increased plasma high-density lipoprotein (HDL)-cholesterol concentrations and reduced risk for cardiovascular disease. Plasma cholesteryl ester transfer activity (CETA) mediates the exchange of HDL-cholesteryl ester (CE) for the triacylglycerol (TAG) of very-low-density lipoproteins. We compared the effects of oral challenges of Alcohol, saturated fat (SAT), and (Alcohol + SAT) on plasma CETA, cholesterol, nonesterified fatty acids (NEFA), and TAG among normo-triglyceridemic (NTG) and mildly hypertriglyceridemic (HTG) volunteers having a range of plasma TAG concentrations. The major changes were (1) CETA increased more after ingestion of SAT and (Alcohol + SAT) in the HTG group versus the NTG group; (2) after all three challenges, elevation of plasma TAG concentration persisted longer in the HTG versus NTG group. Plasma cholesterol was not affected by the three dietary challenges, while Alcohol increased NEFA more in the HTG group than the NTG group. Plasma TAG best predicted plasma CETA, suggesting that intestinally derived lipoproteins are acceptors of HDL-CE. Unexpectedly, ingestion of (Alcohol + SAT) reduced the strength of the correlation between plasma TAG and CETA, that is the effects of (SAT and Alcohol) on plasma CETA are not synergistic nor additive but rather mutually suppressive. The alcohol-mediated inhibition of CE-transfer to chylomicrons maintains a higher plasma HDL-cholesterol concentration, which is athero-protective, although the suppressive metabolite underlying this correlation could be acetate, the terminal alcohol metabolite, other factors, including CETA inhibitors, are also likely important.  相似文献   
99.
Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.  相似文献   
100.
Vitamins A and E were determined by HPLC in 20 starting, milk-based powdered infant formulae from local markets. We traced the evolution of these compounds, once the packets had been opened, during 0, 30 and 70 days of storage at room temperature (≈25 °C; min. 23 °C, max. 25.5 °C). Immediately after opening the packets, vitamin A ranged from 0.55 to 0.94 mg RE/100 g (93.3–183 μg RE/100 kcal) and vitamin E from 6.58 to 27.8 mg α-TE/100 g (1.36–5.39 mg α-TE/100 kcal). All the samples had higher vitamins A and E contents than those declared on the label, vitamin A mean adequacy values: 134% ± 17, min. 98%, max. 162%, and vitamin E 185% ± 47, min. 101%, max. 286%, including values at 0, 30 and 70 days of storage.  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