全文获取类型
收费全文 | 1441篇 |
免费 | 38篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 104篇 |
综合类 | 1篇 |
化学工业 | 457篇 |
金属工艺 | 32篇 |
机械仪表 | 35篇 |
建筑科学 | 25篇 |
能源动力 | 76篇 |
轻工业 | 117篇 |
无线电 | 87篇 |
一般工业技术 | 230篇 |
冶金工业 | 199篇 |
原子能技术 | 40篇 |
自动化技术 | 79篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 27篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 26篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 36篇 |
2013年 | 61篇 |
2012年 | 47篇 |
2011年 | 79篇 |
2010年 | 71篇 |
2009年 | 54篇 |
2008年 | 49篇 |
2007年 | 57篇 |
2006年 | 51篇 |
2005年 | 48篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 47篇 |
2001年 | 24篇 |
2000年 | 32篇 |
1999年 | 36篇 |
1998年 | 82篇 |
1997年 | 52篇 |
1996年 | 57篇 |
1995年 | 28篇 |
1994年 | 30篇 |
1993年 | 32篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 19篇 |
1975年 | 5篇 |
1974年 | 8篇 |
排序方式: 共有1482条查询结果,搜索用时 0 毫秒
971.
Three experiments were conducted to test the hypothesis that a vitamin D deficiency alters the immune responses of female broiler chicks. The control diet contained 800 IU of cholecalciferol (vitamin D3)/kg and the deficient diet was the same except without supplemental vitamin D3. The vitamin D deficiency status was established on the basis of a significantly lower blood ionized calcium or total serum calcium (75 to 85% of the control). Vitamin D-deficient chicks also had lower growth rate and bone ash. In Experiment 1 at 8 d of age, and Experiment 2 at 23 d of age, the cutaneous basophil hypersensitivity response as determined by the increase in interdigital skin thickness 20 h after a single injection of 100 microg phytohemagglutinin-P was significantly depressed in vitamin D-deficient chicks (62 to 64% of the control). Thymus weight, adjusted for body weight, was significantly lower in the vitamin D-deficient chicks at 24 d of age (61% of the control). Primary and secondary antibody responses against SRBC in vitamin D-deficient chicks were not different from the control. In Experiment 3, in 17-d-old chicks, vitamin D deficiency decreased the number of abdominal macrophages phagocytizing SRBC in vitro within 45 min from 14.7 to 10.1%. These results indicate that vitamin D deficiency depresses the cellular immune responses in young broiler chicks. 相似文献
972.
Oxidation and creep behaviors of a Ni‐Mo‐based alloy (Hastelloy‐X) with a diffusion barrier coating consisting of duplex, inner Re‐based alloy, and outer β‐NiAl layers were investigated at 1243 K in air with an external tensile stress of 22.5 MPa. For comparison the alloys, as‐received, heat treated, and with the Ni‐aluminide coating, were oxidized under creep deformation. Creep rapture time for the diffusion barrier‐coated alloy was longer than those for the bare alloy and with the β‐NiAl‐coated alloy. After creep deformation to a strain of 3.5% for 190 h, it was found that the Re‐based alloy layer has few cracks and flaws and the β‐NiAl layer has the similar structure and composition before and after the creep test. The external scale mainly consisted of θ‐Al2O3 at the early stage of creep, and with further oxidation the external scale became a duplex layer, inner, equi‐axed α‐Al2O3, and outer, plate‐like θ‐Al2O3, which exfoliated significantly. It was concluded that the Re‐based alloy layer acts effectively as a barrier against inward Al diffusion and outward diffusion of alloy elements under creep deformation. 相似文献
973.
The efficacy of encephalo-myo-synangiosis (EMS) using muscle free flap was evaluated for the treatment of ischemic cerebrovascular disease in adult patients. Three patients with adult moyamoya disease and three patients with atherosclerotic ischemic cerebrovascular disease were treated. EMS used four latissimus dorsi muscles and two serratus anterior muscles. Postoperative selective angiography showed collateral circulation from the transferred muscle to the brain in four of the six patients. The other two patients showed patent nutrient artery of the transferred muscle flap. Cerebral blood flow study disclosed postoperative improvement of perfusion reserve capacity in all sides. One patient suffered a perioperative stroke by hemoconcentration due to poor control of diabetes mellitus. The mean follow-up period was 23 months. EMS using muscle free flap is a possible procedure in selected patients with impaired cerebral perfusion reserve capacity due to multiple stenosis or occlusion of cerebral arteries including moyamoya disease or who required cerebral blood flow augmentation in the anterior and/or posterior cerebral artery territories due to internal carotid artery occlusion. 相似文献
974.
Sn Kα1-detecting Sn K-edge XANES spectrum was successfully measured for Pt-Sn/SiO2 catalyst (2.5 wt.% Pt, Sn/Pt atomic ratio 1.0) in the energy resolution 5.0 eV using Rowland-type fluorescence spectrometer equipped with Ge(13,13,13) bent crystal. The steeper, more clearly resolved XANES spectrum thus obtained could be compared quantitatively to theoretical XANES spectra generated by ab initio calculations for thirteen plausible Pt-Sn site models (alloy, adsorbed Sn, and mixture models). This spectral simulation suggested that fluorescence-detecting XANES is a simple method to judge the plausible site structure without detailed spectral analyses. The comparison supported an adsorbed Sn site model structure on highly dispersed Pt[-Sn] nanoparticles on SiO2. 相似文献
975.
M Kanai Y Horimoto H Yoshioka S Fujino T Takano 《Canadian Metallurgical Quarterly》1996,45(7):869-872
Twelve month old boy had been suffering from a neck lymphangioma. Partial resection was carried out in his newborn period at another hospital, and he was obliged to be tracheostomied because of severe airway obstruction due to postoperative edema. He was scheduled for partial glossectomy since his tongue had increased in mass, which could easily be injured by teeth, and he had difficulties in swallowing recently. His airway was not obstructive even during sleep and preoperative MRI showed adequate space around the larynx. We induced anesthesia by a mask and he was subseqently intubated with a fiberscope via his nose because his huge and less mobile tongue could not allow the insertion of a laryngoscope and this might cause bleeding. We did not extubate the endotracheal tube for fear of airway obstruction attributable to postoperative edema. Marked edema around the neck persisted longer than we expected. We tried to evaluate the degree of diminution of edema with MRI twice to decide when extubation could be attempted. However, examination with MRI could not give us useful informations. Consequently we evaluated the timing of extubation by examining whether he could close his mouth or not, whether his tongue could move freely and the degree of edema. We realized lymphangioma caused marked and extensive edema after the operation and we should keep in mind that lymphangioma of the tongue might cause various anesthetic problems especially on airways. 相似文献
976.
977.
This is, we believe, the first report on nano-sized domain inversion characteristics in congruent LiNbO3 (CLN), MgO doped LiNbO3 (MgO:LN) and stoichiometric LiNbO3 (SLN) single crystals brought out using scanning dielectric nonlinear microscopy method. Thin crystal plates for forming nano-sized domain inversions were prepared by chemical mechanical polishing and an ion beam etching process. The small domain dot of 13 nm in radius was formed in CLN. However, the domain dots in CLN tended to disappear. The smallest domain dot of 6.1 nm in radius was obtained in MgO:LN. The domain dot array was also successfully formed at a density of 558 Gbit/in.2. In case of higher application voltage, a unique result was obtained in MgO:LN showing that the sizes of domain inversions were almost constant against the voltage pulse width. It is not easy to form domain dot array in SLN since the sidewise growth speed in SLN is very fast. 相似文献
978.
Identification and Characterization of the Streptazone E Biosynthetic Gene Cluster in Streptomyces sp. MSC090213JE08
下载免费PDF全文
![点击此处可从《Chembiochem : a European journal of chemical biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shoto Ohno Dr. Yohei Katsuyama Yuka Tajima Dr. Miho Izumikawa Dr. Motoki Takagi Dr. Manabu Fujie Dr. Noriyuki Satoh Dr. Kazuo Shin‐ya Dr. Yasuo Ohnishi 《Chembiochem : a European journal of chemical biology》2015,16(16):2385-2391
Streptazone derivatives isolated from Streptomyces species are piperidine alkaloids with a cyclopenta[b]pyridine scaffold. Previous studies indicated that these compounds are polyketides, but the biosynthetic enzymes responsible for their synthesis are unknown. Here, we have identified the streptazone E biosynthetic gene cluster in Streptomyces sp. MSC090213JE08, which encodes a modular type I PKS and tailoring enzymes that include an aminotransferase, three oxidoreductases, and two putative cyclases. The functions of the six tailoring enzymes were analyzed by gene disruption, and two putative biosynthetic intermediates that accumulated in particular mutants were structurally elucidated. On the basis of these results, we propose a pathway for the biosynthesis of streptazone E in which the two putative cyclases of the nuclear transport factor 2–like superfamily are responsible for C?C bond formation coupled with epoxide ring opening to give the five‐membered ring of streptazone E. 相似文献
979.
Alexander A. Tokmakov Vasily E. Stefanov Tetsushi Iwasaki Ken-Ichi Sato Yasuo Fukami 《International journal of molecular sciences》2014,15(10):18659-18676
Calcium is a universal messenger that mediates egg activation at fertilization in all sexually reproducing species studied. However, signaling pathways leading to calcium generation and the mechanisms of calcium-induced exit from meiotic arrest vary substantially among species. Here, we review the pathways of calcium signaling and the mechanisms of meiotic exit at fertilization in the eggs of the established developmental model, African clawed frog, Xenopus laevis. We also discuss calcium involvement in the early fertilization-induced events in Xenopus egg, such as membrane depolarization, the increase in intracellular pH, cortical granule exocytosis, cortical contraction, contraction wave, cortical rotation, reformation of the nuclear envelope, sperm chromatin decondensation and sister chromatid segregation. 相似文献
980.
Naoko Yui Hirotaka Yoshioka Hiroto Fujiya Haruki Musha Moroe Beppu Rie Karasawa Kazuo Yudoh 《International journal of molecular sciences》2014,15(9):14921-14934
Apurinic/apyrimidinic endonuclease 2 (Apex 2) plays a critical role in DNA repair caused by oxidative damage in a variety of human somatic cells. We speculated that chondrocyte Apex 2 may protect against the catabolic process of articular cartilage in osteoarthritis (OA). Higher levels of Apex 2 expression were histologically observed in severely compared with mildly degenerated OA cartilage from STR/OrtCrlj mice, an experimental model which spontaneously develops OA. The immunopositivity of Apex 2 was significantly correlated with the degree of cartilage degeneration. Moreover, the OA-related catabolic factor interleukin-1β induced the expression of Apex 2 in chondrocytes, while Apex 2 silencing using small interfering RNA reduced chondrocyte activity in vitro. The expression of Apex 2 in chondrocytes therefore appears to be associated with the degeneration of articular cartilage and could be induced by an OA-related catabolic factor to protect against the catabolic process of articular cartilage. Our findings suggest that Apex 2 may have the potential to prevent the catabolic stress-mediated down-regulation of chondrocyte activity in OA. 相似文献