全文获取类型
收费全文 | 51766篇 |
免费 | 2302篇 |
国内免费 | 1490篇 |
专业分类
电工技术 | 1587篇 |
综合类 | 813篇 |
化学工业 | 7851篇 |
金属工艺 | 3709篇 |
机械仪表 | 2164篇 |
建筑科学 | 1508篇 |
矿业工程 | 755篇 |
能源动力 | 1755篇 |
轻工业 | 3226篇 |
水利工程 | 609篇 |
石油天然气 | 1741篇 |
武器工业 | 125篇 |
无线电 | 5179篇 |
一般工业技术 | 11724篇 |
冶金工业 | 7618篇 |
原子能技术 | 908篇 |
自动化技术 | 4286篇 |
出版年
2023年 | 478篇 |
2022年 | 1049篇 |
2021年 | 1459篇 |
2020年 | 1110篇 |
2019年 | 984篇 |
2018年 | 1252篇 |
2017年 | 1310篇 |
2016年 | 1274篇 |
2015年 | 1233篇 |
2014年 | 1608篇 |
2013年 | 3151篇 |
2012年 | 2252篇 |
2011年 | 2691篇 |
2010年 | 2100篇 |
2009年 | 2275篇 |
2008年 | 2016篇 |
2007年 | 2058篇 |
2006年 | 1606篇 |
2005年 | 1359篇 |
2004年 | 1248篇 |
2003年 | 1120篇 |
2002年 | 1093篇 |
2001年 | 1146篇 |
2000年 | 986篇 |
1999年 | 1019篇 |
1998年 | 2132篇 |
1997年 | 1676篇 |
1996年 | 1456篇 |
1995年 | 997篇 |
1994年 | 761篇 |
1993年 | 776篇 |
1992年 | 599篇 |
1991年 | 574篇 |
1990年 | 527篇 |
1989年 | 486篇 |
1988年 | 370篇 |
1987年 | 402篇 |
1986年 | 367篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 353篇 |
1979年 | 344篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1973年 | 311篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Owing to the strong affinity of thiols to Au and Ag, they are often employed to modify the surfaces of nanoparticles (NPs). Recently, these strong ligand-interface interactions have been employed to control NP growth, and this technique has emerged as a unique modulation strategy for creating unconventional plasmonic hybrid nanostructures. In these systems, the roles of the non-mercapto components of the thiol molecules and their structures are still unknown. Therefore, we herein present our investigation into this phenomenon. Primary amino (–NH2) groups in thiols are found to play a key role in regulating growth kinetics, i.e., in accelerating Ag deposition on Au NPs. The–NH2 groups are thought to bring Ag ions to the particle surface by coordinating to them, and thereby assist their reduction. The effect of molecular structure is non-trivial and thus provides the possibility of selective thiol detection. Based on the dependence of kinetic modulation on the non-mercapto components and molecular structures of molecules, we demonstrate the highly sensitive and specific detection of cysteine (limit of detection: 6 nM) in a mixture of 19 natural amino acids based on Ag growth on Au nanospheres. In addition, based on this modulation effect, we reveal the entrapping of chiral thiols within the growth layer through their plasmonic circular dichroism (PCD) responses. We believe that thiol-based growth regulation has great potential for creating plasmonic nanostructures with novel functionalities. 相似文献
992.
Yiru Wang Tinghui Yin Zhenwei Su Chen Qiu Yong Wang Rongqin Zheng Meiwan Chen Xintao Shuai 《Nano Research》2018,11(7):3710-3721
Although gas-filled microbubbles with high echogenicity are widely applied inclinical ultrasonography, the micron scale particle size impedes their use in the treatment of solid tumors,which are accessible to objects less than several hundred nanometers. We herein propose an unusual approach involving apH-induced core–shell micelle-to-vesicle transition to prepare ultrasound-sensitive polymeric nanospheres (polymersomes in structure) possessing multiple features, including nanosize, monodispersity, and incorporation of a phase-transitional imaging agent into the aqueous lumen. These features are not achievable via the conventional double-emulsion method for polymersome preparation. The nanospheres were constructed based on a novel triblock copolymer with dual pH sensitivity. The liquid-to-gas phase transition of the imaging agent induced by external low-frequency ultrasound may destroy the nanospheres for a rapid drug release, with simultaneous tissue-penetrating drug delivery inside a tumor. These effects may provide new opportunities for the development of an effective cancer therapy with few adverse effects. 相似文献
993.
Wang Yicun Shi Hongxi Dong Shuai Li Yan Wang Meng Huai Yanyan Zhang Xintong Chen Xi Mao Chuanbin Gao Xiang Wang Li 《Nano Research》2018,11(4):2248-2255
Nano Research - Candida albicans (C. albicans) infection has a high mortality rate in immunocompromised patients. Owing to the inefficiency of the current diagnostic system and the absence of... 相似文献
994.
目的 阐明提高生鲜水产品贮藏保鲜性能的适用方法,指出现有水产品保鲜技术和保鲜材料存在的问题及不足,对未来生鲜水产品保鲜材料的发展作出展望性分析。方法 介绍生鲜水产品保鲜常用的物理、化学和生物保鲜技术的优势和不足。从分类、应用范围及抗菌、抗氧化等性能多角度出发分析保鲜膜、保鲜衬垫的研究现状。结果 传统的保鲜技术虽对生鲜水产品有一定的保鲜作用,但其保鲜性能有限,保鲜膜、保鲜衬垫辅以抗菌、抗氧化等性能的生物保鲜剂,可延长生鲜水产品的货架期。结论 保鲜膜、保鲜衬垫同生物保鲜剂联合使用,以获得具有高效、长效保鲜性能的新型保鲜材料,提高了生鲜水产品的鲜度品质。新型保鲜材料具有广阔的发展前景。 相似文献
995.
996.
H Tlaskalová-Hogenová R St?pánková L Tucková MA Farré DP Funda EF Verdú J Sinkora T Hudcovic Z Reháková B Cukrowska H Kozáková L Prokesová 《Canadian Metallurgical Quarterly》1998,43(5):545-550
Despite the fact that target antigens and the genetic basis of several autoimmune diseases are now better understood, the initial events leading to a loss of tolerance towards self-components remain unknown. One of the most attractive explanations for autoimmune phenomena involves various infections as possible natural events capable of initiating the process in genetically predisposed individuals. The most accepted explanation of how infection causes autoimmunity is based on the concept of "molecular mimicry" (similarity between the epitopes of an autoantigen and the epitopes in the environmental antigen). Infectious stimuli may also participate in the development of autoimmunity by inducing an increased expression of stress proteins (hsp), chaperones and transplantation antigens, which leads to abnormal processing and presentation of self antigens. Superantigens are considered to be one of the most effective bacterial components to induce inflammatory reactions and to take part in the development and course of autoimmune mechanisms. It has long been known that defects in the host defense mechanism render the individual susceptible to infections caused by certain microorganisms. Impaired exclusion of microbial antigens can lead to chronic immunological activation which can affect the tolerance to self components. Defects in certain components of the immune system are associated with a higher risk of a development of autoimmune disease. The use of animal models for the studies of human diseases with immunological pathogenesis has provided new insights into the influence of immunoregulatory factors and the lymphocyte subsets involved in the development of disease. One of the most striking conclusion arising from work with genetically engineered immunodeficient mouse models is the existence of a high level of redundancy of the components of the immune system. However, when genes encoding molecules involved in T cell immunoregulatory functions are deleted, spontaneous chronic inflammation of the gut mucosa (similar to human inflammatory bowel disease) develops. Surprisingly, when such immunocompromised animals were placed into germfree environment, intestinal inflammation did not develop. Impairment of the mucosal immune response to the normal bacterial flora has been proposed to play a crucial role in the pathogenesis of chronic intestinal inflammation. The use of immunodeficient models colonized with defined microflora for the analysis of immune reactivity will shed light on the mode of action of different immunologically important molecules responsible for the delicate balance between luminal commensals, nonspecific and specific components of the mucosal immune system. 相似文献
997.
MD Ercegovac N Vojvodi? Soki?DV SM Jankovi? J Drulovi? N Stojsavljevi? Z Levi? 《Canadian Metallurgical Quarterly》1998,126(9-10):335-344
CONCLUSION: We conclude that despite inevitable variability the clinical picture of JME is characteristic. It is easy to diagnose JME if one thinks of it while the history should be thoroughly analyzed. An EEG recording during sleep confirms the diagnosis. An early diagnosis of JME permits adequate prognosis of the subsequent course of epilepsy, and adequate therapy brings remission in most of the patients. If treatment starts following the large number of severe GTC seizures, the response to therapy is incomplete. The persistency of the illness throughout the life, the need for continuous medication and therapeutic unresponsiveness in cases with late diagnosis, do not justify the increasing misconception that JME is of benign nature. Diagnosis of JME is rare because of insufficient familiarily of physicians with the illness. BACKGROUND: Juvenile myoclonic epilepsy (JME) is an idiopathic generalized epileptic syndrome characterized with the combination of myoclonic, generalized tonic-clonic (GTC) and absence seizures that are readily provoked by sleep deprivation. PATIENTS: Forty-three patients, aged from 14 to 51 years, participated in a 5-year follow-up study. Diagnosis was made according to the criteria (Table 1) for diagnosis of JME set by Panayiotopoulos et al. (1994). Nineteen patients made their first contact with a neurologist at the Institute of Neurology and were diagnosed as JME, while the remaining 24 were referred to from other medical institutions with a diagnosis of therapy resistant to focal epilepsy. All patients underwent a somatic and neurological examination, "mini mental test," EEG in waking and CT scan of the brain. Some patients had EEG performed during sleep and some had MRI of the head. RESULTS: JME began between 9 and 26 (average 17) years. All patients had myoclonic seizures, 98% had GTC and 23% absence seizures. The first myoclonic seizure occurred between 9 and 24 years while the frst GTC seizure occurred between 10 and 32 years. Myoclonic seizures (83% of patients) and GTC seizures (70% of patients) occurred most often immediately after awaking. The most frequent provocative factors were insufficient sleep, alcohol abuse and tiredness. Epilepsy in the family was present in 39%, focal neurological deficiency in 9% and pathological findings on of CT and MRI in 7% of patients. Waking EEG was pathological in 77% of patients; it included generalized spike-wave discharges in 73%, multiple spike-wave complexes in 33% and focal discharges in 12% of patients, respectively. In all 26 patients tested, sleep EEG was pathological most often with multiple spike-wave complexes in 85% and 3-4 Hz spike-wave complexes in 57% of patients. The correct diagnosis of JME following a comprehensive examination was made in 24 (56%) patients after a delay of 1 to 35 years. In 24 patients with delayed diagnosis of JME the replacement of earlier medication with valproic acid (VPA) induced remission in 18 patients (75%) while 1 patient (4%) experienced a reduction in the number of seizures. Five patients (21%) did not respond to VPA medication: 2 due to a weak compliance, another 2 due to inefficient medication and 1 because of the preexistent malabsorption syndrome. In 19 patients (44%) with initial diagnosis of JME, VPA was introduced immediately upon diagnosis. Of them, 15 (79%) had excellent response to VPA, 1 refused therapy and for 3 patients there is no information. In 2 patients VPA was substituted due to side effects (hepatotoxicity and alopetia) with lamotrigine (low doses), which brought about decrease in frequency and mitigation in myoclonic seizures. 相似文献
998.
Z Duracková 《Canadian Metallurgical Quarterly》1998,99(7):351-358
Free radicals are, on the one hand, necessary for the physiological function of some systems but, on the other had, they play an important pathologic role. The formation of free radicals can be the result of various conditions and can initiate various diseases. Their formation may also be a consequence of certain pathological state of the organism. In this way generated free radicals can cause in the secondary to the damage organism. The metabolism of free radicals is significantly influenced by transition metals. These metals are present in the organism at given oxidative state chelated in the proteins. In this form the metalloproteins to have unique catalytical and redox properties. The transition metals are a part of an active centre of many enzymes. Iron and copper are the predominant transition metals in human organism. These metals are vitally important, but if present in high concentration, in unsuitable oxidative state and at improper site, they can catalyse the formation of highly toxic reactive metabolities of oxygen, for example hydroxyl radicals. The toxic damage may be direct if the metals are present in high oxidative state Fe(IV) or Fe(V). These "ferryl" compounds are strong prooxidants. The organism maintains the iron metabolism in equilibrium. If the iron plasma concentration reaches 40 micro-mol/L, it is a sign, that iron is released from physiological protein structures and forms so called "catalytically active iron". In this form iron can be involved in Fenton reaction in which hydroxyl radical is formed. The article discussed the toxic effect of "catalytically" active iron at a given oxidative state with its influence on some diseases. 相似文献
999.
In this paper, stability and boundedness theorems for delay difference systems with the condition are given, where Δ is the backward difference operator. Some known results are generalized. 相似文献
δV(n,x(n))≤-W2(|x(n)|)+σ
1000.
We have directly determined the amide band resonance Raman spectra of the "average" pure alpha-helix, beta-sheet, and unordered secondary structures by exciting within the amide pi-->pi* transitions at 206.5 nm. The Raman spectra are dominated by the amide bands of the peptide backbone. We have empirically determined the average pure alpha-helix, beta-sheet, and unordered resonance Raman spectra from the amide resonance Raman spectra of 13 proteins with well-known X-ray crystal structures. We demonstrate that we can simultaneously utilize the amide I, II, and III bands and the Calpha-H amide bending vibrations of these average secondary structure spectra to directly determine protein secondary structure. The UV Raman method appears to be complementary, and in some cases superior, to the existing methods, such as CD, VCD, and absorption spectroscopy. In addition, the spectra are immune to the light-scattering artifacts that plague CD, VCD, and IR absorption measurements. Thus, it will be possible to examine proteins in micelles and other scattering media. 相似文献