全文获取类型
收费全文 | 343577篇 |
免费 | 4304篇 |
国内免费 | 1223篇 |
专业分类
电工技术 | 5900篇 |
综合类 | 2648篇 |
化学工业 | 48602篇 |
金属工艺 | 14900篇 |
机械仪表 | 11505篇 |
建筑科学 | 8326篇 |
矿业工程 | 1632篇 |
能源动力 | 7544篇 |
轻工业 | 26466篇 |
水利工程 | 3809篇 |
石油天然气 | 4255篇 |
武器工业 | 70篇 |
无线电 | 43882篇 |
一般工业技术 | 66204篇 |
冶金工业 | 49380篇 |
原子能技术 | 5677篇 |
自动化技术 | 48304篇 |
出版年
2021年 | 2101篇 |
2019年 | 2095篇 |
2018年 | 17629篇 |
2017年 | 16632篇 |
2016年 | 13542篇 |
2015年 | 2975篇 |
2014年 | 4360篇 |
2013年 | 11619篇 |
2012年 | 9752篇 |
2011年 | 18201篇 |
2010年 | 15158篇 |
2009年 | 13419篇 |
2008年 | 15376篇 |
2007年 | 16256篇 |
2006年 | 8033篇 |
2005年 | 8390篇 |
2004年 | 8031篇 |
2003年 | 7924篇 |
2002年 | 6950篇 |
2001年 | 6595篇 |
2000年 | 6370篇 |
1999年 | 6340篇 |
1998年 | 14315篇 |
1997年 | 10317篇 |
1996年 | 8167篇 |
1995年 | 6432篇 |
1994年 | 5729篇 |
1993年 | 5599篇 |
1992年 | 4565篇 |
1991年 | 4236篇 |
1990年 | 4056篇 |
1989年 | 3785篇 |
1988年 | 3634篇 |
1987年 | 3173篇 |
1986年 | 3068篇 |
1985年 | 3613篇 |
1984年 | 3384篇 |
1983年 | 3032篇 |
1982年 | 2853篇 |
1981年 | 2953篇 |
1980年 | 2772篇 |
1979年 | 2650篇 |
1978年 | 2500篇 |
1977年 | 2946篇 |
1976年 | 3556篇 |
1975年 | 2317篇 |
1974年 | 2312篇 |
1973年 | 2318篇 |
1972年 | 1850篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Natallia V. Dubashynskaya Anton N. Bokatyi Anatoliy V. Dobrodumov Igor V. Kudryavtsev Andrey S. Trulioff Artem A. Rubinstein Arthur D. Aquino Yaroslav A. Dubrovskii Elena S. Knyazeva Elena V. Demyanova Yuliya A. Nashchekina Yury A. Skorik 《International journal of molecular sciences》2023,24(1)
The growth of microbial multidrug resistance is a problem in modern clinical medicine. Chemical modification of active pharmaceutical ingredients is an attractive strategy to improve their biopharmaceutical properties by increasing bioavailability and reducing drug toxicity. Conjugation of antimicrobial drugs with natural polysaccharides provides high efficiency of these systems due to targeted delivery, controlled drug release and reduced toxicity. This paper reports a two-step synthesis of colistin conjugates (CT) with succinyl chitosan (SucCS); first, we modified chitosan with succinyl anhydride to introduce a carboxyl function into the polymer molecule, which was then used for chemical grafting with amino groups of the peptide antibiotic CT using carbodiimide chemistry. The resulting polymeric delivery systems had a degree of substitution (DS) by CT of 3–8%, with conjugation efficiencies ranging from 54 to 100% and CT contents ranging from 130–318 μg/mg. The size of the obtained particles was 100–200 nm, and the ζ-potential varied from −22 to −28 mV. In vitro release studies at pH 7.4 demonstrated ultra-slow hydrolysis of amide bonds, with a CT release of 0.1–0.5% after 12 h; at pH 5.2, the hydrolysis rate slightly increased; however, it remained extremely low (1.5% of CT was released after 12 h). The antimicrobial activity of the conjugates depended on the DS. At DS 8%, the minimum inhibitory concentration (MIC) of the conjugate was equal to the MIC of native CT (1 µg/mL); at DS of 3 and 5%, the MIC increased 8-fold. In addition, the developed systems reduced CT nephrotoxicity by 20–60%; they also demonstrated the ability to reduce bacterial lipopolysaccharide-induced inflammation in vitro. Thus, these promising CT-SucCS conjugates are prospective for developing safe and effective nanoantibiotics. 相似文献
152.
Kristina A. Sharlo Irina D. Lvova Svetlana P. Belova Ksenia A. Zaripova Boris S. Shenkman Tatiana L. Nemirovskaya 《International journal of molecular sciences》2023,24(1)
Muscle unloading leads to signaling alterations that cause muscle atrophy and weakness. The cellular energy sensor AMPK can regulate myofiber-type shift, calcium-dependent signaling and ubiquitin-proteasome system markers. We hypothesized that the prevention of p-AMPK downregulation during the first week of muscle unloading would impede atrophy development and the slow-to-fast shift of soleus muscle fibers, and the aim of the study was to test this hypothesis. Thirty-two male Wistar rats were randomly assigned to four groups: placebo control (C), control rats treated with metformin (C + M), 7 days of hindlimb suspension (HS) + placebo (7HS), and 7 days of HS + metformin administration (7HS + M). In the soleus of the 7HS rats, we detected a slow-to-fast fiber-type shift as well as a significant downregulation of MEF-2D and p300 in the nuclei. In the 7HS group, we also found decreases in p-ACC (AMPK target) protein level and in the expression of E3 ubiquitin ligases and p-CaMK II protein level vs. the C group. The 7-day metformin treatment for soleus muscle unloading (1) prevented slow-to-fast fiber-type shift; (2) counteracted changes in the p-ACC protein level; (3) hindered changes in the nuclear protein level of the slow myosin expression activators MEF-2D and p300, but did not affect NFATc1 signaling; and (4) attenuated the unloading-induced upregulation of MuRF-1, atrogin-1, ubiquitin and myostatin mRNA expression, but did not prevent soleus muscle atrophy. Thus, metformin treatment during muscle disuse could be useful to prevent the decrease in the percentage of slow-type fatigue-resistant muscle fibers. 相似文献
153.
Eugenia D. Namiot Aleksandr V. Sokolov Vladimir N. Chubarev Vadim V. Tarasov Helgi B. Schith 《International journal of molecular sciences》2023,24(1)
Nanoparticles are heterologous small composites that are usually between 1 and 100 nanometers in size. They are applied in many areas of medicine with one of them being drug delivery. Nanoparticles have a number of advantages as drug carriers which include reduced toxic effects, increased bioavailability, and their ability to be modified for specific tissues or cells. Due to the exciting development of nanotechnology concomitant with advances in biotechnology and medicine, the number of clinical trials devoted to nanoparticles for drug delivery is growing rapidly. Some nanoparticles, lipid-based types, in particular, played a crucial role in the developing and manufacturing of the two COVID-19 vaccines—Pfizer and Moderna—that are now being widely used. In this analysis, we provide a quantitative survey of clinical trials using nanoparticles during the period from 2002 to 2021 as well as the recent FDA-approved drugs (since 2016). A total of 486 clinical trials were identified using the clinicaltrials.gov database. The prevailing types of nanoparticles were liposomes (44%) and protein-based formulations (26%) during this period. The most commonly investigated content of the nanoparticles were paclitaxel (23%), metals (11%), doxorubicin (9%), bupivacaine and various vaccines (both were 8%). Among the FDA-approved nanoparticle drugs, polymeric (29%), liposomal (22%) and lipid-based (21%) drugs were the most common. In this analysis, we also discuss the differential development of the diverse groups of nanoparticles and their content, as well as the underlying factors behind the trends. 相似文献
154.
Hemraj Dahiya Anupam Agrawal Ganesh D. Sharma Abhishek Kumar Singh 《半导体学报》2022,43(9):092302-1-092302-7
This article demonstrates the fabrication of organic-based devices using a low-cost solution-processable technique. A blended heterojunction of chlorine substituted 2D-conjugated polymer PBDB-T-2Cl, and PC71BM supported nanocapsules hydrate vanadium penta oxides (HVO) as hole transport layer (HTL) based photodetector fabricated on an ITO coated glass substrate under ambient condition. The device forms an excellent organic junction diode with a good rectification ratio of ~200. The device has also shown excellent photodetection properties under photoconductive mode (at reverse bias) and zero bias for green light wavelength. A very high responsivity of ~6500 mA/W and high external quantum efficiency (EQE) of 1400% have been reported in the article. The proposed organic photodetector exhibits an excellent response and recovery time of ~30 and ~40 ms, respectively. 相似文献
155.
Amber L.Williams Jessica E.Fitzgerald Fernando Ivich Eduardo D.Sontag Mark Niedre 《光:科学与应用(英文版)》2021,(10):1998-1999
Dear Editor,
Circulating tumor cells (CTCs) are instrumental in hematogenous metastasis and are widely studied using liquid biopsy methods. 相似文献
156.
Water pollution caused by industrial dyes has become a severe problem in the modern world. Biosorbents can be used in an eco-friendly manner to remove industrial dyes. In this study, five biosorbents were selected: palmyrah sprout casing (PSC), manioc peel, lime peel, king coconut husk, and coconut kernel. Batch adsorption experiments were conducted to identify the best biosorbent with the highest ability to adsorb methylene blue (MB) from wastewater. The detailed mechanisms of PSC used in the adsorptive removal of MB in aqueous phase were investigated. Of the five biosorbents, PSC exhibited the best removal performance with an adsorption capacity at equilibrium (qe) of 27.67 mg/g. The qe values of lime peel, king coconut husk, manioc peel, and coconut kernel were 24.25 mg/g, 15.29 mg/g, 10.84 mg/g, and 7.06 mg/g, respectively. To explain the mechanisms of MB adsorption with the selected biosorbents, the Fourier transform infrared (FTIR) spectrometry and X-ray diffraction (XRD) analyses were performed to characterize functional properties, and isotherm, kinetic, rate-limiting, and thermodynamic analyses were conducted. The FTIR analysis revealed that different biosorbents had different functional properties on their adsorptive surfaces. The FTIR and XRD results obtained before and after MB adsorption with PSC indicated that the surface functional groups of carbonyl and hydroxyl actively participated in the removal process. According to the isotherm analysis, monolayer adsorption was observed with the Langmuir model with a determination coefficient of 0.998. The duration to reach the maximum adsorption capacity for MB adsorption with PSC was 120 min, and the adsorption process was exothermic due to the negative enthalpy change (-9.950 kJ/mol). Moreover, the boundary layer thickness and intraparticle diffusion were the rate-limiting factors in the adsorption process. As a new biosorbent for MB adsorption, PSC could be used in activated carbon production to enhance the performance of dye removal. 相似文献
157.
There is difficulty for distinguishing of river and shadow in Synthetic Aperture Radar (SAR) images. A method of river segmentation in SAR images based on wavelet energy and gradient is proposed in this paper. It mainly includes two algorithms: coarse segmentation and refined segmentation. Firstly, The river regions are coarsely segmented by the wavelet energy feature,and then refined segmented accurately by the gradient threshold which is got adaptively. The experimental results show the validity of the method, which provides a good foundation for targets detection above the river. 相似文献
158.
我们考虑了满足Clausius-Puhem不等式的一类二维Rivlin Ericksen流体.对于严格孤立的流体,我们证明了如果处于均衡时Helmhdtz自由能量非最小,则在一定条件下所有原始扰动不仅会放大而且会增加.这些结果推广了Fosclish Rajagopal在1982年得到的二维Rivlin Ericksen流体的一种特例一二等级流体的相关结果. 相似文献
159.
东京是一个捉摸不透的城市。从将要降落在成田机场的航班上看它,纵横阡陌的道路,排列整齐的房屋,黑白灰的色彩搭配,简单中富有层次,让我恍然想起了布莱克的石版画。那是以各种颜料,甚至各种肌理的布、纸拼贴的画面,没有过多的颜色重叠.沉静的中间色和原色恰如其分地协调其中,超凡脱俗。 相似文献
160.
Akchurin R. Z. Bogatov A. A. Salikhyanov D. R. Ovchinnikov A. S. 《Metallurgist》2019,62(9-10):1039-1047
Metallurgist - Thin-walled and extremely thin-walled tubes made of copper alloys, i.e., brass grades L96, L68, L63, LANKMts, and the bronze grades BrOF6.5-0.15, BrOF4-0.25, are in great demand in... 相似文献