全文获取类型
收费全文 | 39952篇 |
免费 | 4381篇 |
国内免费 | 2298篇 |
专业分类
电工技术 | 2767篇 |
技术理论 | 1篇 |
综合类 | 3008篇 |
化学工业 | 6132篇 |
金属工艺 | 1956篇 |
机械仪表 | 2081篇 |
建筑科学 | 3139篇 |
矿业工程 | 979篇 |
能源动力 | 1127篇 |
轻工业 | 4072篇 |
水利工程 | 888篇 |
石油天然气 | 1484篇 |
武器工业 | 356篇 |
无线电 | 5103篇 |
一般工业技术 | 4723篇 |
冶金工业 | 2538篇 |
原子能技术 | 460篇 |
自动化技术 | 5817篇 |
出版年
2024年 | 326篇 |
2023年 | 1037篇 |
2022年 | 1871篇 |
2021年 | 2488篇 |
2020年 | 1737篇 |
2019年 | 1412篇 |
2018年 | 1519篇 |
2017年 | 1607篇 |
2016年 | 1407篇 |
2015年 | 1800篇 |
2014年 | 2258篇 |
2013年 | 2573篇 |
2012年 | 2696篇 |
2011年 | 2795篇 |
2010年 | 2252篇 |
2009年 | 2157篇 |
2008年 | 2122篇 |
2007年 | 1957篇 |
2006年 | 1748篇 |
2005年 | 1443篇 |
2004年 | 1107篇 |
2003年 | 1051篇 |
2002年 | 1132篇 |
2001年 | 981篇 |
2000年 | 696篇 |
1999年 | 634篇 |
1998年 | 810篇 |
1997年 | 550篇 |
1996年 | 443篇 |
1995年 | 285篇 |
1994年 | 281篇 |
1993年 | 213篇 |
1992年 | 148篇 |
1991年 | 139篇 |
1990年 | 108篇 |
1989年 | 113篇 |
1988年 | 66篇 |
1987年 | 58篇 |
1986年 | 64篇 |
1985年 | 54篇 |
1984年 | 44篇 |
1983年 | 46篇 |
1982年 | 47篇 |
1981年 | 36篇 |
1980年 | 39篇 |
1979年 | 29篇 |
1977年 | 43篇 |
1976年 | 65篇 |
1975年 | 19篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
P Le Guellec S Dumas GE Volle E Pidoux MS Moukhtar F Treilhou-Lahille 《Canadian Metallurgical Quarterly》1993,41(3):389-395
We report here an efficient and rapid method for the specific detection of calcitonin in tumor C-cells of medullary thyroid carcinoma (MTC). This occasionally aggressive tumor arises from the endocrine thyroid C-cells. Its principal marker is calcitonin, the predominant C-cell secretion, which is detected in patients and in our animal model by radioimmunoassay of the plasma, as well as by immunohistochemistry of thyroid tissues. Although calcitonin is easily detectable in normal C-cells, its content is greatly reduced in tumor cells owing to the disappearance of the secretory granules that store the mature peptide. This finding suggests cell dedifferentiation correlated with an increasing aggressivity of the tumor. We therefore developed a rapid detection of calcitonin mRNA by in situ hybridization on routine paraffin sections, using a synthetic oligodeoxyribonucleotide probe labeled with digoxigenin-dUTP. The reaction was detected with an anti-digoxigenin antibody conjugated with alkaline phosphatase, and the enzyme catalyzed the appearance of a dark blue color. The signal was exclusively restricted to the normal, hyperplastic, and tumor C-cells. It was specific, as increasing concentrations of the unlabeled oligonucleotide led to progressive disappearance of the reaction. Its sensitivity was slightly diminished as compared with corresponding frozen sections, but the intensity of the signal was quite acceptable. High levels of calcitonin mRNA were found in all normal and hyperplastic C-cells. They were increased in most of the tumor MTC cells, which did not correlate with the amount of intracellular peptide stores but explained the abnormally high basal levels of circulating calcitonin of the tumor-bearing rats. ISH is therefore of greater value than ICC for an early anatomopathological detection of this tumor. Our data show that the tumor cells are not "dedifferentiated." They only lack the granular compartment storing the mature peptide before exocytosis, but CT biosynthesis and the rest of the secretory process seem to be complete. Our results suggest that factors expressed in malignant C-cells affect basic cell mechanisms involved in the storage of the mature calcitonin, rather than the expression of the CALC gene. 相似文献
992.
993.
994.
995.
A new compound with composition Cu0.75 VS2 has been prepared. Its preparation, X-Ray structure, electrical and magnetic properties are reported. The structure is related to the CdI2-type, as in the case of the previously described CuxTiS2 (1); in Cu0.75 VS2, Cu atoms are ordered in tetrahedral sites between the CdI2-type subunits, whereas in CuxTiS2 Cu atoms are disordered in two independent sites. The vanadium atoms are shifted with respect to the titanium sites which leads a monoclinic distortion of the hexagonal cell. The relation between the CdI2 unit cell and the true monoclinic cell of Cu0.75 VS2 is: In Cu0.75 VS2, vanadium atoms occupy two independent sites, three vanadium atoms forming a triangular cluster (V2—V3 distances are 2.91 Å and V3—V3 are 2.92 Å) while one vanadium atom is isolated ( and . The physical properties exhibit a transition at 50°K approximately, the magnetic susceptibility being temperature-independent above and temperature dependent below the transition (Curie-Weiss behavior). Resistivity and Hall measurements confirm the metallic nature of the compound and show the existence of the low temperature transition. The observed properties could be interpreted as a result of the low temperature localisation of the 3d electron of V1. 相似文献
996.
J. L. Le H. C. Bai A. A. Mishunin A. V. Starov 《Combustion, Explosion, and Shock Waves》2003,39(3):292-299
Results of an experimental study of a full scramjet model operating on kerosene, which was performed in an IT-302M hotshot wind tunnel based at the Institute of Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Sciences, and an experimental study of a model operating on hydrogen, which was performed in a hotshot wind tunnel with fire heating based at the China Aerodynamic Research and Development Center, are reported. The tests were performed for Mach numbers 5 and 6 for flow parameters close to in-flight conditions. An optimal system for kerosene injection under these conditions was determined, and the thrust characteristics of the engine model were examined. The possibility of controlling kerosene combustion in tests in the short-duration wind tunnel was analyzed, and special features of fuel ignition in a short combustor were considered. Intense combustion of kerosene was achieved with upstream injection of more than 3% of hydrogen, which allowed obtaining effective thrust. The distributions of static pressure and force characteristics of the model in the case of kerosene and hydrogen combustion were compared. 相似文献
997.
998.
999.
The problem of successive transverse plane reconstruction in single photon emission computerized tomography (SPECT) is modeled in its more general form, which implies the definition of emission tomographic operators (ETO's) for which an analytical solution can be derived. The properties of the attenuated tomographic operator (ATO) are described and discussed, including the attenuation which is distributed on the reconstruction domain. For this particular operator, a regularizing method (RIM) is proposed, for which it is demonstrated and tested with simulation studies that a filtered, accurate solution can be extracted for the tomographic images as obtained using a single photon emission tomograph based on a rotating gamma camera in clinical use. 相似文献
1000.