全文获取类型
收费全文 | 68799篇 |
免费 | 3276篇 |
国内免费 | 74篇 |
专业分类
电工技术 | 721篇 |
综合类 | 109篇 |
化学工业 | 14711篇 |
金属工艺 | 1547篇 |
机械仪表 | 1433篇 |
建筑科学 | 2360篇 |
矿业工程 | 222篇 |
能源动力 | 1603篇 |
轻工业 | 11236篇 |
水利工程 | 600篇 |
石油天然气 | 240篇 |
武器工业 | 7篇 |
无线电 | 3082篇 |
一般工业技术 | 12651篇 |
冶金工业 | 11710篇 |
原子能技术 | 432篇 |
自动化技术 | 9485篇 |
出版年
2023年 | 631篇 |
2022年 | 991篇 |
2021年 | 1705篇 |
2020年 | 1270篇 |
2019年 | 1432篇 |
2018年 | 2288篇 |
2017年 | 2281篇 |
2016年 | 2473篇 |
2015年 | 1982篇 |
2014年 | 2491篇 |
2013年 | 4963篇 |
2012年 | 3687篇 |
2011年 | 4042篇 |
2010年 | 3237篇 |
2009年 | 3025篇 |
2008年 | 2985篇 |
2007年 | 2731篇 |
2006年 | 2040篇 |
2005年 | 1723篇 |
2004年 | 1549篇 |
2003年 | 1447篇 |
2002年 | 1380篇 |
2001年 | 1038篇 |
2000年 | 967篇 |
1999年 | 991篇 |
1998年 | 3701篇 |
1997年 | 2515篇 |
1996年 | 1735篇 |
1995年 | 1078篇 |
1994年 | 894篇 |
1993年 | 949篇 |
1992年 | 401篇 |
1991年 | 400篇 |
1990年 | 304篇 |
1989年 | 330篇 |
1988年 | 300篇 |
1987年 | 288篇 |
1986年 | 237篇 |
1985年 | 382篇 |
1984年 | 338篇 |
1983年 | 253篇 |
1982年 | 292篇 |
1981年 | 315篇 |
1980年 | 301篇 |
1979年 | 192篇 |
1978年 | 193篇 |
1977年 | 458篇 |
1976年 | 881篇 |
1975年 | 166篇 |
1973年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Villares R Real C Fernández JA Aboal J Carballeira A 《The Science of the total environment》2007,374(2-3):379-387
In the present study we investigated possible contamination by trace elements due to the oil slick caused by the shipwreck of the Prestige oil tanker, in two species of brown macroalgae (Fucus vesiculosus and Fucus ceranoides) collected from the coastal area most severely affected by the spill (Galicia, NW Spain). The oil slick apparently did not cause significant increases in the concentrations of the trace elements studied, except vanadium. It appears that the magnitude of terrestrial inputs to coastal waters is sufficiently high to mask the inputs of trace elements from the fuel. The observed exception of V suggests that bioaccumulation of this element by the two species of Fucus may be used to indicate exposure to petrochemical products similar to the Prestige fuel. The findings of the study are another example of the importance of the existence of Environmental Specimen Banks for studies of this type. 相似文献
992.
Vega J Murari A Pereira A González S Pastor I 《The Review of scientific instruments》2010,81(10):10E118
The charge-coupled device camera of the TJ-II Thomson scattering (TS) can capture five different classes of images. Typically, different data processing is performed depending on the kind of image that is acquired. The procedure can be automated to recognize the type of image. To this end, machine learning methods (MLM) are applied. However, usually, MLM classify without confidence estimates. An image classifier based on conformal predictors has been developed for the TJ-II TS. It provides a couple of indicators (confidence and credibility) for each classification that measures the accuracy and reliability of the prediction. Results achieve success rates of about 97%. The implemented classifier is valid for any kind of images. 相似文献
993.
Decommissioning of nuclear facilities becomes an important issue in all areas of nuclear technology, mainly in their energetic applications. Decommissioning process has to be planned in the safe, ecological and economic manner. It determines the requirements on appropriate evaluation of needed technologies, media, amount of solid materials released into the environment, radioactivity of effluents, amount of radioactive waste for disposal, number and exposure of personnel and finally the financial demands. A detailed evaluation of these parameters may be done by analytical calculation approach. This approach models a real process of decommissioning with its individual basic activities. The methodology of integrated material flow and radioactivity distribution within this calculation evaluation tool is applied and implemented to describe the real decommissioning activities and their mutual relations to obtain more accurate outputs. 相似文献
994.
O. Moutanabbir Y.J. Chabal M. Chicoine S. Christiansen R. Krause-Rehberg F. Schiettekatte R. Scholz O. Seitz S. Senz F. Süßkraut U. Gösele 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1264-1268
The underlying physics and the role of H-defect interaction in H ion-induced splitting of GaN were investigated by transmission electron microscopy, high resolution X-ray diffraction, positron annihilation spectroscopy, ion channeling, elastic recoil detection, and infrared spectroscopy. A high concentration of void-like nanoscopic structures, nanobubbles, is detected immediately after implantation. Positron annihilation measurements demonstrate that the detected structures are vacancy clusters. FTIR data show that H-defect vibrational spectrum peaks at 3141 cm?1 mode attributed to VGa–H4. A large fraction of H was found to be trapped in higher frequency modes which we associate tentatively to N–H stretch modes in the internal surfaces of nanobubbles. These nanobubbles persist during annealing up to 450 °C. An increase of the strain is observed in this temperature range. This strain relaxes partially above 450 °C following the formation of the platelets which are embryos of the microcracks. 相似文献
995.
It is probable that only an insignificant amount of β-cyclodextrin is absorbed in unchanged form from the intestinal tract. The oral administration of the conversion mixture (38% β-cyclodextrin, 2.8% α-cyclodextrin, the rest partially decomposed starch) to rats and dogs, as well as the crystalline β-cyclodextrin (97%) at doses of 200, 400 and 600 mg/kg of bodyweight daily, according to the clinico-biochemical tests has not caused significant changes. The pathological and histopathological studies performed after a 6 months treatment have not proved any observable changes. β-Cyclodextrin proved not to be embryotoxic and teratogenic. The chromosoma test performed on rats treated for 6 months has not increased the incidence of spontaneous aberration and no change relating to mutation could be observed, either. 相似文献
996.
Manuel Gacitúa Alexander Carreo Rosaly Morales-Guevara Dayn Pez-Hernndez Jorge I. Martínez-Araya Eyleen Araya Marcelo Preite Carolina Otero María Macarena Rivera-Zaldívar Andrs Silva Juan A. Fuentes 《International journal of molecular sciences》2022,23(5)
Searching for adequate and effective compounds displaying antimicrobial activities, especially against Gram-positive bacteria, is an important research area due to the high hospitalization and mortality rates of these bacterial infections in both the human and veterinary fields. In this work, we explored (E)-4-amino-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino) benzoic acid (SB-1, harboring an intramolecular hydrogen bond) and (E)-2-((4-nitrobenzilidene)amino)aniline (SB-2), two Schiff bases derivatives. Results demonstrated that SB-1 showed an antibacterial activity determined by the minimal inhibitory concentration (MIC) against Staphylococcus aureus, Enterococcus faecalis, and Bacillus cereus (Gram-positive bacteria involved in human and animal diseases such as skin infections, pneumonia, diarrheal syndrome, and urinary tract infections, among others), which was similar to that shown by the classical antibiotic chloramphenicol. By contrast, this compound showed no effect against Gram-negative bacteria (Klebsiella pneumoniae, Escherichia coli, and Salmonella enterica). Furthermore, we provide a comprehensive physicochemical and theoretical characterization of SB-1 (as well as several analyses for SB-2), including elemental analysis, ESMS, 1H and 13C NMR (assigned by 1D and 2D techniques), DEPT, UV-Vis, FTIR, and cyclic voltammetry. We also performed a computational study through the DFT theory level, including geometry optimization, TD-DFT, NBO, and global and local reactivity analyses. 相似文献
997.
Markta Kadle
kov Kateina Skopalov Barbora Ptokov Erik Wrzecionko Elika Daov Karolína Kocourkov Ale Mr
ek Lenka Musilov Petr Smolka Petr Humpolí
ek Antonín Minaík 《International journal of molecular sciences》2022,23(5)
The pseudo 3D hierarchical structure mimicking in vivo microenvironment was prepared by phase separation on tissue culture plastic. For surface treatment, time-sequenced dosing of the solvent mixture with various concentrations of polymer component was used. The experiments showed that hierarchically structured surfaces with macro, meso and micro pores can be prepared with multi-step phase separation processes. Changes in polystyrene surface topography were characterized by atomic force microscopy, scanning electron microscopy and contact profilometry. The cell proliferation and changes in cell morphology were tested on the prepared structured surfaces. Four types of cell lines were used for the determination of impact of the 3D architecture on the cell behavior, namely the mouse embryonic fibroblast, human lung carcinoma, primary human keratinocyte and mouse embryonic stem cells. The increase of proliferation of embryonic stem cells and mouse fibroblasts was the most remarkable. Moreover, the embryonic stem cells express different morphology when cultured on the structured surface. The acquired findings expand the current state of knowledge in the field of cell behavior on structured surfaces and bring new technological procedures leading to their preparation without the use of problematic temporary templates or additives. 相似文献
998.
Ho Sn Lam G. Zimmermann G. Anders G. Bach D. Rennecke W. Zychlinski 《Advanced Synthesis \u0026amp; Catalysis》1985,327(5):759-766
Studies on Thermal Conversion of Phenyleyclopentane, -hexane, -heptane, and -octane in the Gas Phase The title compounds were pyrolyzed from 700 to 780°C in a metallic laboratory tubular reactor in the presence of steam. The reaction products were analyzed by gas chromatography and by a combination of gas chromatography and mass spectrometry. From the phenylcyclanes tested, more than 65 hydrocarbons could be detected in the liquids, besides gaseous reaction products. In most cases unambiguous structures could be derived by using different analytical methods. As typical initial-step products phenylcyclenes, ω-phenyl-1-alkenes and 1-phenyl-1-alkenes are formed by dehydrogenation and isomerization of the title compounds. The detection of phenylalkenes corresponds well with the isomerization of unsubstituted cyclanes to the corresponding α-olefines described in former papers. 相似文献
999.
Anna Broto-Ribas Claudia Vignatti Alicia Jimenez-Almarza Javier Luis-Barrera Zahra Dolatkhah Felipe Gandara Inhar Imaz Ruben Mas-Balleste Jose Aleman Daniel Maspoch 《Nano Research》2021,14(2):458-465
A well-established strategy to synthesize heterogeneous,metal-organic framework(MOF)catalysts that exhibit nanoconfinement effects,and specific pores with highly-localized catalytic sites,is to use organic linkers containing organocatalytic centers.Here,we report that by combining this linker approach with reticular chemistry,and exploiting three-dimensioanl(3D)MOF-structural data from the Cambridge Structural Database,we have designed four heterogeneous MOF-based catalysts for standard organic transformations.These programmable MOFs are isoreticular versions of pcu IRMOF-16,feu UiO-68 and pillared-pcu SNU-8X,the three most common topologies of MOFs built from the organic linker p.p'-terphenyldicarboxylic acid(tpdc).To synthesize the four squaramide-based MOFs,we designed and synthesized a linker,4,4’-((3,4-dioxocyclobut-1-ene-1,2-diyl)bis(azanedyil))dibenzoic acid(Sq_tpdc),which is identical in directionality and length to tpdc but which contains organocatalytic squaramide centers.Squaramides were chosen because their immobilization into a framework enhances its reactivity and stability while avoiding any self-quenching phenomena.Therefore,the four MOFs share the same organocatalytic squaramide moiety,but confine it within distinct pore environments.We then evaluated these MOFs as heterogeneous H-bonding catalysts in organic transformations:a Friedel-Crafts alkylation and an epoxide ring-opening.Some of them exhibited good performance in both reactions but all showed distinct catalytic profiles that reflect their structural differences. 相似文献
1000.
Laura Frutos-Rincn Jos Antonio Gmez-Snchez Almudena Íigo-Portugus M. Carmen Acosta Juana Gallar 《International journal of molecular sciences》2022,23(6)
The cornea is an avascular connective tissue that is crucial, not only as the primary barrier of the eye but also as a proper transparent refractive structure. Corneal transparency is necessary for vision and is the result of several factors, including its highly organized structure, the physiology of its few cellular components, the lack of myelinated nerves (although it is extremely innervated), the tightly controlled hydration state, and the absence of blood and lymphatic vessels in healthy conditions, among others. The avascular, immune-privileged tissue of the cornea is an ideal model to study the interactions between its well-characterized and dense sensory nerves (easily accessible for both focal electrophysiological recording and morphological studies) and the low number of resident immune cell types, distinguished from those cells migrating from blood vessels. This paper presents an overview of the corneal structure and innervation, the resident dendritic cell (DC) subpopulations present in the cornea, their distribution in relation to corneal nerves, and their role in ocular inflammatory diseases. A mouse model in which sensory axons are constitutively labeled with tdTomato and DCs with green fluorescent protein (GFP) allows further analysis of the neuro-immune crosstalk under inflammatory and steady-state conditions of the eye. 相似文献