全文获取类型
收费全文 | 246817篇 |
免费 | 11180篇 |
国内免费 | 14269篇 |
专业分类
化学 | 47903篇 |
晶体学 | 688篇 |
力学 | 10106篇 |
综合类 | 1725篇 |
数学 | 35513篇 |
物理学 | 38773篇 |
综合类 | 137558篇 |
出版年
2024年 | 467篇 |
2023年 | 1700篇 |
2022年 | 3335篇 |
2021年 | 3560篇 |
2020年 | 3687篇 |
2019年 | 3751篇 |
2018年 | 3351篇 |
2017年 | 3944篇 |
2016年 | 4439篇 |
2015年 | 5277篇 |
2014年 | 9708篇 |
2013年 | 11794篇 |
2012年 | 11796篇 |
2011年 | 13280篇 |
2010年 | 10948篇 |
2009年 | 13538篇 |
2008年 | 14487篇 |
2007年 | 17256篇 |
2006年 | 16004篇 |
2005年 | 14449篇 |
2004年 | 12513篇 |
2003年 | 12009篇 |
2002年 | 11132篇 |
2001年 | 9118篇 |
2000年 | 8062篇 |
1999年 | 6826篇 |
1998年 | 5767篇 |
1997年 | 4882篇 |
1996年 | 4453篇 |
1995年 | 4007篇 |
1994年 | 3767篇 |
1993年 | 3172篇 |
1992年 | 3044篇 |
1991年 | 2579篇 |
1990年 | 2293篇 |
1989年 | 2133篇 |
1988年 | 1806篇 |
1987年 | 1241篇 |
1986年 | 906篇 |
1985年 | 713篇 |
1984年 | 647篇 |
1983年 | 326篇 |
1982年 | 525篇 |
1981年 | 656篇 |
1980年 | 528篇 |
1979年 | 515篇 |
1978年 | 452篇 |
1977年 | 383篇 |
1976年 | 312篇 |
1973年 | 223篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper develops a mathematical model of the ring-spinning process that takes into account its non-stationary nature. A complex system of differential equations is obtained, which from a mathematical point of view constitutes a ‘free-boundary’ problem. Its solution involves definition of suitable boundary conditions related to the mechanical characteristics of the process and of the spinning machine itself. The boundary conditions which determine the solution are pointed out. A numerical solution of the system of differential equations can be obtained by the Finite-Segments method, as shown in an example. 相似文献
992.
993.
Sokolova T. N. Grishin Yu. K. Timofeev I. V. Kartashov V. R. 《Russian Chemical Bulletin》1994,43(6):1044-1047
Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994. 相似文献
994.
S. V. Popkov L. V. Kovalenko V. P. Tashchi L. Ya. Bogel'fer 《Russian Chemical Bulletin》1994,43(8):1363-1367
The reaction of dimethylsulfonium methylide with the carbonyl function of 2-arylidene-cyclohexanones obtained from 2-methylcyclohexanone affords the corresponding spirooxiranes. The application of this reaction to 2,2-dimethyl-6-(5-methylfurfurylidene)cyclohexanone and 2,2-dimethyl-6-(5-chlorofurfurylidene)cyclohexanone leads to substituted 4,4-dimethyl-1-furyl-1,-3,4,5,6,7-hexahydroisobenzofurans.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1439–1443, August, 1994. 相似文献
995.
Polypropylenes of differing morphologies were examined by differential thermal analysis. The problems of reordering during
the programmed heating are discussed. Four potential procedures by which the reordering could be inhibited are considered,
and three of these are experimentally assessed. Their advantages and deficiencies are identified. Two pretreatments, an etching
and a crosslinking, are recognised as able to qualitatively characterise the initial morphology, with a preference for the
former. A test to identify the occurrence of reordering is identified.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献
996.
Dai Lu David Rutledge Milan Kovacevic Jon Hacker 《International Journal of Infrared and Millimeter Waves》2002,23(5):693-704
This paper presents an active patch array designed at 24 GHz. It can be used as a front-end component for a phased array. A series resonant array structure is chosen which is compact and easy excite. With 5 elements, the array proved a 12-dB antenna gain. A power amplifier and a low noise amplifier are designed on a single GaAs chip (PALNA). Bias switch is used in the PALNA, which greatly reduces the switch loss in a transceiver and increases the efficiency. 20-dB small signal gain is achieved in both power amplifier and low noise amplifier. The active patch array is built by the combination of the patch array and PALNA. The measured active gain of this antenna is 35-dB for the PA mode and 31-dB for the LNA mode. This active patch array can obtain an EIRP of 34 dBm with a total radiated power of 22dBm and a maximum PAE of 32%. To check the noise performance, we applied sources at both normal temperature and 77K (liquid nitrogen) and extracted the noise figure (3.5 dB) of the active antenna by the Y factor method. The results proved that the active antenna is working efficiently as both a transmitting and receiving antenna. 相似文献
997.
高抗冲聚丙烯序列结构的综合表征 总被引:3,自引:0,他引:3
用高分辨^13C NMR、FTIR等手段获得了高抗冲聚丙烯的组成和序列分布等链结构方面的信息。用DSC、WAXD等方法研究了它们的结晶行为、熔融转变及晶体结构,多种方法相结合有效地表征了高抗冲聚丙烯的序列结构。 相似文献
998.
The acute influences of arsenic compounds on the metabolism of porphyrins and heme in various organs of rats after oral or intratracheal administration of disodium arsenate (Na2HAsO4) and gallium arsenide (GaAs) were examined and compared. For the oral administration experiments, 21 or 84 mg of Na2HAsO4, or 2 or 4 g of GaAs, per cm3 saline per kg body weight of each animal was administered to Jcl: Wistar male rats and the organs were removed after exsanguination from the vein of the right axilla under anesthesia with ether, 16 h after administration. In the case of intratracheal administration, rats given 8.2 or 16.4 mg of Na2HAsO4, or 0.2 or 0.4 g GaAs per cm3 saline per kg body weight were examined under the same experimental conditions as for the administration route. Increase in the body weight of rats was suppressed after intratracheal administration of the two arsenic compounds. In these rats the hematocrit value increased significantly. These changes were not shown by the orally administered rats. Elevation in δ-aminolevulinate synthase (ALA-S, EC 2.3.1.37) activity in erythroblasts by Na2HAsO4 was much higher after intratracheal administration than after oral administration. Suppression in the activities of δ-aminolevulinate dehydratase (ALA-D, EC 4.2.1.24) and porphobilinogen deaminase (PBG-D, EC 4.3.1.8) in peripheral erythrocytes by Na2HAsO4 and GaAs were stronger by intratracheal administration than by the oral route. Influences of GaAs on the activity of PBG-D in rat liver were shown to be more effective by oral administration than by the intratracheal route. Oral administration of Na2HAsO4 and GaAs had a stronger suppression effect on the activities of ALA-D and PBG-D in rat kidney. It seems from these results that the different extents of the influence of arsenic compounds might depend on the routes of intake. 相似文献
999.
1000.