全文获取类型
收费全文 | 12560篇 |
免费 | 918篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 168篇 |
综合类 | 7篇 |
化学工业 | 3115篇 |
金属工艺 | 266篇 |
机械仪表 | 467篇 |
建筑科学 | 477篇 |
矿业工程 | 22篇 |
能源动力 | 519篇 |
轻工业 | 2097篇 |
水利工程 | 154篇 |
石油天然气 | 53篇 |
武器工业 | 2篇 |
无线电 | 876篇 |
一般工业技术 | 2129篇 |
冶金工业 | 1078篇 |
原子能技术 | 91篇 |
自动化技术 | 1983篇 |
出版年
2024年 | 32篇 |
2023年 | 137篇 |
2022年 | 332篇 |
2021年 | 566篇 |
2020年 | 359篇 |
2019年 | 416篇 |
2018年 | 512篇 |
2017年 | 524篇 |
2016年 | 554篇 |
2015年 | 398篇 |
2014年 | 554篇 |
2013年 | 941篇 |
2012年 | 832篇 |
2011年 | 1027篇 |
2010年 | 690篇 |
2009年 | 755篇 |
2008年 | 689篇 |
2007年 | 555篇 |
2006年 | 436篇 |
2005年 | 319篇 |
2004年 | 281篇 |
2003年 | 250篇 |
2002年 | 241篇 |
2001年 | 179篇 |
2000年 | 159篇 |
1999年 | 150篇 |
1998年 | 349篇 |
1997年 | 277篇 |
1996年 | 188篇 |
1995年 | 128篇 |
1994年 | 91篇 |
1993年 | 71篇 |
1992年 | 46篇 |
1991年 | 42篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1979年 | 15篇 |
1977年 | 24篇 |
1976年 | 29篇 |
1975年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
João Vicente-Neto Maria Cristina Bressan Peter Bitencourt Faria Josye Oliveira e Vieira Maria das Graças Cardoso Maria Beatriz de Abreu Glória Luis Telo da Gama 《Meat science》2010
Chemical composition and fatty acid profiles were determined in Caiman yacare meat originating from the neck and tail cuts of animals raised in the wild (n = 6) or in captivity (n = 6), slaughtered at a live weight of approximately 6 kg. All experimental methods were approved by the appropriate environmental protection agencies. Most chemical components were affected by the origin-cut interaction, with the tail cut of wild animals having the highest amount of intramuscular fat (19.2% of DM) and the lowest of moisture (71.8%) and protein (77.0% of DM). Yacare meat had low amounts of SFA (35.1%), which were similar (P > 0.05) in the cuts and origins studied. The total amount of PUFA was higher (P < 0.05) in wild (31.0%) than in captive animals (23.6%), and n − 3 fatty acids had means of about 5% and 2% for the same groups, respectively (P < 0.05). In general, the FA profile of intramuscular fat in yacare meat had a desirable PUFA/SFA ratio above 0.4. 相似文献
992.
César Valderrama Xavier Gamisans Jose L Cortina Adriana Farrán F Xavier de las Heras 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(2):236-245
BACKGROUND: Sorption of polycyclic aromatic hydrocarbons (PAHs) on activated carbon and the Macronet polymeric sorbent MN200 was investigated to determine the effectiveness of each sorbent for removal of pollutants from aqueous solution and their possible use as sorbent materials for groundwater. Experiments were carried out to determine the loading capacities of a family of PAHs (acenaphthene, anthracene, fluoranthene, fluorene, naphthalene and pyrene). RESULTS: Activated carbon was the more effective sorbent, with maximum loadings of PAHs between 90 and 230 g kg?1, while MN200 resin showed values of 25–160 g kg?1. Loading isotherms based on the Langmuir, Freundlich and Redlich–Peterson models were determined. The hydrophobic character of the pollutants appeared as an important parameter related to the sorption process. Equilibrium and kinetic parameters were used to determine the retardation factors for each PAH. CONCLUSION: The calculated values for the simulation of barrier thickness using both sorbents, taking into account EU requirements for PAHs in groundwater effluent, were perfectly reasonable as a first estimate. The better kinetic properties of MN200 are evident in lower hydraulic residence times and consequently in a lower barrier thickness. Copyright © 2008 Society of Chemical Industry 相似文献
993.
André Andrian Padial João Carlos Nabout Tadeu Siqueira Luis Mauricio Bini José Alexandre Felizola Diniz-Filho 《Scientometrics》2010,85(1):1-12
Citation frequency has been considered a biased surrogate of publication merit. However, previous studies on this subject
were based on small sample sizes and were entirely based on null-hypothesis significance testing. Here we evaluated the relative
effects of different predictors on citation frequency of ecological articles using an information theory framework designed
to evaluate multiple competing hypotheses. Supposed predictors of citation frequency (e.g., number of authors, length of articles)
accounted for a low fraction of the total variation. We argue that biases concerning citation are minor in ecology and further
studies that attempt to quantify the scientific relevance of an article, aiming to make further relationships with citation,
are needed to advance our understanding of why an article is cited. 相似文献
994.
F. H. S. Sales Ana L. Dantas V. D. Mello A. S. Carri?o 《Journal of Materials Science》2010,45(18):5036-5039
We report a theoretical investigation of new magnetic phases of thin dysprosium films. At the surfaces, the balance between
exchange and anisotropy energies favors the alignment of spins along the basal plane easy axis directions. Near the Curie
temperature, the helimagnetic phase is strongly modified, allowing surface spins to lock into the basal plane anisotropy easy
directions. As the temperature raises, we find transitions to other surface lockin patterns, which are tunable by external
field strengths of a few hundred milli-Oersteds. 相似文献
995.
Previous work by the authors has shown that the effects of calcium aluminate cement (CAC) and hydratable alumina (HA) can modify the magnesia hydration behavior in aqueous suspensions. As a consequence of these studies, the present paper highlights how varying the content of these binders can affect magnesia hydration in refractory castables using pH, apparent volumetric expansion, mechanical strength and porosity measurements and hydration–dehydration tests. Furthermore, as mechanical strength, porosity and refractoriness also play an important role in these materials, binder-free, magnesia-free and magnesia-and-binder-free samples were also tested as references. It was found that the deleterious effects of magnesia hydration can be greatly minimized by the binder and its selection content. 相似文献
996.
Mnica Mendes Fbris Kossoski Ana I. Lozano Joo Pereira-da-Silva Rodrigo Rodrigues Joo Ameixa Nykola C. Jones Sren V. Hoffmann Filipe Ferreira da Silva 《International journal of molecular sciences》2021,22(12)
We report absolute photoabsorption cross sections for gas-phase 2- and 5-bromopyrimidine in the 3.7–10.8 eV energy range, in a joint theoretical and experimental study. The measurements were carried out using high-resolution vacuum ultraviolet synchrotron radiation, with quantum chemical calculations performed through the nuclear ensemble approach in combination with time-dependent density functional theory, along with additional Franck–Condon Herzberg–Teller calculations for the first absorption band (3.7–4.6 eV). The cross sections of both bromopyrimidines are very similar below 7.3 eV, deviating more substantially from each other at higher energies. In the 7.3–9.0 eV range where the maximum cross-section is found, a single and broad band is observed for 5-bromopyrimidine, while more discernible features appear in the case of 2-bromopyrimidine. Several π* ← π transitions account for the most intense bands, while weaker ones are assigned to transitions involving the nitrogen and bromine lone pairs, the antibonding σ*Br orbital, and the lower-lying Rydberg states. A detailed comparison with the available photo-absorption data of bromobenzene is also reported. We have found significant differences regarding the main absorption band, which is more peaked in bromobenzene, becoming broader and shifting to higher energies in both bromopyrimidines. In addition, there is a significant suppression of vibrational structures and of Rydberg states in the pair of isomers, most noticeably for 2-bromopyrimidine. 相似文献
997.
Antonio Luiz P. S. Campos Adaildo Gomes d'Assunção Marcos A. Barbosa de Melo 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(3):461-475
A full wave analysis is developed for frequency selective surfaces composed of rectangular patches mounted on a dielectric anisotropic substrate and covered with a uniaxial anisotropic superstrate. The moment method is used in combination with the spectral domain immittance approach to determine the FSS structure reflection and transmission coefficients. 相似文献
998.
B Fortu?o L Torres E Simal A Seoane JA Uriel C Santacruz 《Canadian Metallurgical Quarterly》1997,15(10):536-539
BACKGROUND: This review summarizes the different species of dermatophytes isolates in our laboratory between 1991 and 1995. We describe the clinical forms and establish the distribution over this period of time. METHODS: Retrospective survey of samples from outpatients of the Dermatology Service in Miguel Servet Hospital where mycologic cultures are required. The extraction of samples is made by scrapes with a carpet or scalpel and they are cultured on Saboureaud agar with chloramphenicol and dermatophytes agar for 3 weeks. All plates were incubated at 28 degrees C. The identification of isolated strains is made by means of morphologic and physiologic criteria; the doubtful strains were identified in national referral center of Majadahonda CNMVISS. RESULTS: 4004 samples were analyzed from 3934 patients and 543 strains of dermatophytes were isolated. The frequencies were as follow: Microsporum canis (44%), Trichophyton mentagrophytes (31.4%), Trichophyton rubrum (18.6%), Epidermophyton floccosum (2.6%), Microsporum gypseum (1.4%), Trichophyton tonsurans (0.7%), Trichophyton verrucosum (0.7%), Trichophyton violaceum (0.2%) y Microsporum audouinii (0.2%). The most frequently observed dermatophytoses were Tinea corporis (54.8%), followed by Tinea unguium (12.6%), Tinea capitis (12.5%), Tinea pedis (8.3%), Tinea manuum (6.3%), Tinea cruris (4.7%) and Tinea barbae (0.7%). CONCLUSIONS: The zoophylic species are the most prevalent in our area and we have observed a raise of Microsporum canis in recent years. It is important to perform mycologic survey in every suspected lesion in older to determinate the true incidence of human dermatophytoses. 相似文献
999.
1000.
JL Ramírez R Torronteras JP Casta?o A Sánchez-Hormigo JC Garrido S García-Navarro F Gracia-Navarro 《Canadian Metallurgical Quarterly》1997,9(11):841-848
Previous results from our laboratory demonstrated the existence of two subpopulations of porcine somatotropes of low- (LD) and high density (HD) that exhibit differences in ultrastructure and respond in an opposite manner to somatostatin (SRIF) in vitro. In LD cells, SRIF did not affect basal growth hormone (GH) release but partially blocked the stimulatory effect induced by GH-releasing factor (GRF). Conversely, SRIF paradoxically stimulated the secretory activity of HD somatotropes. Here, we have analysed in detail the basic parameters that characterize this differential response. To this end, the time- and dose-dependent effects of SRIF-14 were evaluated on separate monolayer cultures of both subpopulations. Likewise, the direct effect of the peptide on individual somatotropes from each subset was assessed by cell immunoblot assay. Finally, we compared the effects of SRIF-14 and SRIF-28 on cultures of LD and HD cells. SRIF-14 (10(-7) M) induced a rapid (30 min) and sustained (4 h) 2-fold increase in GH release from HD cells, whereas it did not affect GH secretion from LD somatotropes. Surprisingly, a low dose of SRIF (10(-15) M) stimulated GH release from both LD (154.1 +/- 8.2% of basal, P < 0.05) and HD (337.2 +/- 55.5% of basal, P < 0.05) subpopulations, even more effectively than higher doses of the peptide. Results from cell blotting showed that SRIF stimulatory effects were exerted directly upon individual somatotropes. Finally, SRIF-28 elicited similar responses to those observed for SRIF-14 in both somatotrope subpopulations, yet 10(-15) M SRIF-28 was less potent than the same dose of SRIF-14 in stimulating GH release from HD cells. Our present findings demonstrate that SRIF can function as a true GH-releasing factor in cultures of porcine pituitary cells by acting specifically and directly upon somatotropes. Furthermore, together with previous observations, these results strongly suggest that SRIF is not merely an inhibitor of GH release in pigs, but might play a dual modulatory role. Heterogeneity of the somatotrope population contributes greatly to this divergent effect of SRIF. 相似文献