全文获取类型
收费全文 | 193180篇 |
免费 | 2787篇 |
国内免费 | 217篇 |
专业分类
电工技术 | 2712篇 |
综合类 | 129篇 |
化学工业 | 31888篇 |
金属工艺 | 9838篇 |
机械仪表 | 6239篇 |
建筑科学 | 3766篇 |
矿业工程 | 1937篇 |
能源动力 | 3173篇 |
轻工业 | 13875篇 |
水利工程 | 2998篇 |
石油天然气 | 8799篇 |
武器工业 | 13篇 |
无线电 | 15485篇 |
一般工业技术 | 42239篇 |
冶金工业 | 32594篇 |
原子能技术 | 6987篇 |
自动化技术 | 13512篇 |
出版年
2021年 | 2223篇 |
2019年 | 2208篇 |
2018年 | 4158篇 |
2017年 | 4241篇 |
2016年 | 4535篇 |
2015年 | 2586篇 |
2014年 | 4010篇 |
2013年 | 8482篇 |
2012年 | 5953篇 |
2011年 | 6825篇 |
2010年 | 5611篇 |
2009年 | 5907篇 |
2008年 | 6001篇 |
2007年 | 5842篇 |
2006年 | 4760篇 |
2005年 | 4352篇 |
2004年 | 4143篇 |
2003年 | 3986篇 |
2002年 | 3851篇 |
2001年 | 3759篇 |
2000年 | 3586篇 |
1999年 | 3480篇 |
1998年 | 8701篇 |
1997年 | 6186篇 |
1996年 | 4468篇 |
1995年 | 3266篇 |
1994年 | 2868篇 |
1993年 | 2999篇 |
1992年 | 2330篇 |
1991年 | 2373篇 |
1990年 | 2464篇 |
1989年 | 2366篇 |
1988年 | 2387篇 |
1987年 | 2259篇 |
1986年 | 2303篇 |
1985年 | 2354篇 |
1984年 | 2260篇 |
1983年 | 2166篇 |
1982年 | 2013篇 |
1981年 | 2251篇 |
1980年 | 2109篇 |
1979年 | 2295篇 |
1978年 | 2459篇 |
1977年 | 2521篇 |
1976年 | 3287篇 |
1975年 | 2276篇 |
1974年 | 2332篇 |
1973年 | 2379篇 |
1972年 | 2157篇 |
1971年 | 1930篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
Two novel peptides, named PACAP (pituitary adenylate cyclase activating polypeptide) containing 38 (PACAP38) and 27 residues (PACAP27) were recently isolated from ovine hypothalami. In order to investigate the pituitary cell type(s) that bear a receptor for PACAP, PACAP38 was biotinylated and used for cytochemical examination of binding. The cells were also identified by immunocytochemical methods using the antisera against each of the rat anterior pituitary hormones or an antiserum against S-100 protein, a marker for pituitary folliculo-stellate (FS) cells. Biotinylated PACAP38 (biot-PACAP) exhibited adenylate cyclase stimulating activity (ACSA) comparable to PACAP38 in rat pituitary cell cultures, and displaced the bound 125I-PACAP27 to the rat pituitary membrane preparation to the same extent as PACAP38. After 2-4 days of culture, dispersed rat pituitary cells were incubated with varying concentrations of biot-PACAP at room temperature or 4 degrees C. The bound biot-PACAP38 was visualized by avidin-biotin-peroxidase complex (ABC) method with nickel intensification. Biot-PACAP-positive and pituitary hormone or S-100-positive cells were counted. More than 90% of S-100-positive cells bound biot-PACAP38. A considerable number of GH and PRL cells and a lesser number of ACTH cells also bound biot-PACAP38, whereas only a few identified LH, FSH, or TSH cells bound biot-PACAP38. These results suggest that FS cells are a major target cell type for PACAP. A recent study from our laboratory demonstrated that PACAP stimulated the release of interleukin (IL)-6 in rat pituitary cell cultures. FS cells are known to produce IL-6. 相似文献
963.
M Kü?ükaydin H Okur C Turan M I?er M Zorlu A Kazez 《Canadian Metallurgical Quarterly》1993,159(9):487-489
OBJECTIVE: To describe our experience with Swenson's operation for Hirschsprung's disease done during the neonatal period. DESIGN: Retrospective study. SETTING: University department of paediatric surgery. SUBJECTS: 10 Neonates with Hirschsprung's disease. INTERVENTIONS: Rectosigmoidectomy and pull through (Swenson's operation), with covering transverse colostomy. MAIN OUTCOME MEASURES: Mortality, morbidity, and continence. RESULTS: The median age at definitive operation was 25 days (range 15-35). There was one late death three weeks after discharge from hospital of respiratory and cardiac failure. Two patients presented with caecal perforation and two with intestinal obstruction; in all four Hirschsprung's disease was diagnosed on frozen section, a transverse colostomy was done, and the Swenson's operation was done electively. The other six were diagnosed by barium enema examination and biopsy, and underwent total bowel irrigation followed by Swenson's operation and transverse colostomy. The colostomies were closed three to four weeks later. There were no postoperative complications. All nine surviving patients were continent (3-4 stools/day), at a mean (SD) follow up of 21 (5) months. CONCLUSION: With the current high standards of anaesthesia and neonatal intensive care, and an experienced surgeon, Swenson's operation for neonatal Hirschsprung's disease is safe and the procedure of choice for this condition. 相似文献
964.
Rat brain cortex slices and synaptosomes preincubated with [3H]noradrenaline were used to investigate whether the NMDA-evoked noradrenaline release is modulated by agonists or antagonists at presynaptic alpha 2-adrenoceptors. In experiments on slices, noradrenaline and the preferential alpha-adrenoceptor agonists talipexole (former B-HT 920) and clonidine inhibited the NMDA-evoked tritium overflow whereas the selective alpha 1-adrenoceptor agonists cirazoline and methoxamine were ineffective. The alpha 2-adrenoceptor antagonists rauwolscine and idazoxan facilitated the NMDA-evoked tritium overflow whereas the preferential alpha 1-adrenoceptor antagonist prazosin was ineffective. The concentration-response curve of talipexole for its inhibitory effect on NMDA-evoked overflow was shifted to the right by idazoxan (apparent pA2 = 7.5). The EC50 of NMDA (97 mumol/l) for its stimulating effect on tritium overflow was not substantially changed by blockade of alpha 2-autoreceptors with 1 mumol/l rauwolscine (EC50 of NMDA in the presence of the alpha 2-adrenoceptor antagonist, 155 mumol/l), but the maximal overflow of tritium was increased 2.5 fold by this rauwolscine concentration. In experiments on synaptosomes, talipexole and noradrenaline inhibited the NMDA-evoked tritium overflow. The inhibitory effect of talipexole was abolished by idazoxan which, given alone, was ineffective, as was prazosin. Talipexole did also not produce an inhibition when tritium overflow was evoked by NMDA in the presence of omega-conotoxin GVIA 0.1 mumol/l; the latter, by itself, decreased the response to NMDA by about 55%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
965.
We describe a patient with aspergillosis of the maxillary antrum, and systemic affectation (anemia, anorexia, fever). Through a Caldwell-Luck approach, the maxillary antrum was opened and an irregular mass removed, postoperatively the patient has done well, disappearing in two months the ORL and systemic symptoms. 相似文献
966.
This article describes a test piece that minimizes the spread of the results of testing of composite materials on a metal base by extension in the direction of a reinforcing fiber and, from the results, determines the mechanical properties of intermediate and finished products made of these materials.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 39–40, October, 1993. 相似文献
967.
A computer-based measurement system has been designed and built for noncontact nondestructive measurement of charge and potential distribution on dielectric and semiconductor layers and films for various purposes.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 49–51, August, 1993. 相似文献
968.
Molecular cloning of a novel melanocortin receptor 总被引:2,自引:0,他引:2
I Gantz Y Konda T Tashiro Y Shimoto H Miwa G Munzert SJ Watson J DelValle T Yamada 《Canadian Metallurgical Quarterly》1993,268(11):8246-8250
Using the technique of the polymerase chain reaction primed with oligonucleotides based on the homologous transmembrane regions of seven transmembrane G protein-linked receptors, we isolated three full-length human genes that encode a novel subgroup of this receptor family. Recently, two of these receptors were identified as specific for alpha-melanocyte-stimulating hormone (alpha-MSH) and adrenocorticotropic hormone. We report the molecular cloning and pharmacologic characterization of a third member of this subgroup. The gene for this receptor encodes a protein of 361 amino acids in length. Its pharmacology characterizes it as an MSH receptor specific to the heptapeptide core common to adrenocorticotropic hormone and alpha-, beta-, and gamma-MSH. By Northern blot hybridization and polymerase chain reaction, it is expressed in brain, placental, and gut tissues but not in melanoma cells or in the adrenal gland. These findings may yield insight into the physiology of peptides derived from pro-opiomelanocortin post-translational processing. 相似文献
969.
O. I. Velichko A. A. Egorov S. K. Fedoruk 《Journal of Engineering Physics and Thermophysics》1993,65(5):1091-1096
A model is developed and a study is performed for amphoteric diffusion of silicon in gallium arsenide. A comparison of predictions with experimental data indicated adequacy of the devised model and high efficiency of the numerical method for solving the diffusion equation.Belorussian State University, Minsk. Minsk Radio Engineering Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 567–572, November, 1993. 相似文献
970.
Problems of heat/mass transfer and structure formation in easily deformable natural disperse systems
I. I. Lishtvan 《Journal of Engineering Physics and Thermophysics》1993,64(6):606-614
The results of studies of the processes of structure formation and moisture transfer in shaped organogenous materials are presented Principles have been formulated for selecting and using SAS and HMS for desired variation of moisture transfer and migration of ions in natural disperse systems. The results of experimental and theoretical investigations of heat/mass transfer and structure formation in freezing organogenous systems are given.Institute for Problems of Use of Natural Resources and Ecology, Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 6, pp. 752–762, June, 1992. 相似文献