全文获取类型
收费全文 | 81010篇 |
免费 | 4487篇 |
国内免费 | 1387篇 |
专业分类
电工技术 | 2164篇 |
技术理论 | 3篇 |
综合类 | 2037篇 |
化学工业 | 15113篇 |
金属工艺 | 2538篇 |
机械仪表 | 2862篇 |
建筑科学 | 3564篇 |
矿业工程 | 812篇 |
能源动力 | 1984篇 |
轻工业 | 11121篇 |
水利工程 | 1162篇 |
石油天然气 | 1627篇 |
武器工业 | 204篇 |
无线电 | 5429篇 |
一般工业技术 | 12297篇 |
冶金工业 | 12355篇 |
原子能技术 | 559篇 |
自动化技术 | 11053篇 |
出版年
2024年 | 1082篇 |
2023年 | 1243篇 |
2022年 | 1501篇 |
2021年 | 2554篇 |
2020年 | 2110篇 |
2019年 | 2130篇 |
2018年 | 3024篇 |
2017年 | 2977篇 |
2016年 | 3187篇 |
2015年 | 2720篇 |
2014年 | 3372篇 |
2013年 | 5668篇 |
2012年 | 4695篇 |
2011年 | 4651篇 |
2010年 | 3897篇 |
2009年 | 3548篇 |
2008年 | 3538篇 |
2007年 | 3349篇 |
2006年 | 2694篇 |
2005年 | 2297篇 |
2004年 | 1913篇 |
2003年 | 1923篇 |
2002年 | 2014篇 |
2001年 | 1677篇 |
2000年 | 1313篇 |
1999年 | 1288篇 |
1998年 | 3919篇 |
1997年 | 2721篇 |
1996年 | 1869篇 |
1995年 | 1172篇 |
1994年 | 874篇 |
1993年 | 909篇 |
1992年 | 412篇 |
1991年 | 359篇 |
1990年 | 272篇 |
1989年 | 276篇 |
1988年 | 271篇 |
1987年 | 230篇 |
1986年 | 211篇 |
1985年 | 230篇 |
1984年 | 183篇 |
1983年 | 139篇 |
1982年 | 182篇 |
1981年 | 197篇 |
1980年 | 214篇 |
1979年 | 112篇 |
1978年 | 104篇 |
1977年 | 356篇 |
1976年 | 740篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The authors suggest that academic institutions build business-oriented policies and practices into the development of any nurse-run clinic to set the stage for financial independence when special or development funding ends. One university-affiliated program that provides 4,000 to 5,000 annual visits drastically changed its strategies when threatened with closure after free rent and other subsidies were withdrawn. The growing emphasis on ambulatory care roles for nurses at all levels makes such clinics critical to the success of the broad-based curricula of nursing education programs, as well as the clinic's value to communities they serve. Funding difficulties frequently threaten the existence of such nurse-run clinics once the initial grant funding is no longer available. This has caused a new emphasis on running such clinics in a business-wise manner. Among the strategies initiated were: direct full-pay at the time of service; a realistic business management plan; aggressive planned marketing; contracts and agreements with other agencies; obtaining provider status with selected HMOs. 相似文献
22.
M Tuena de Gómez-Puyou F Sandoval JJ García A Gómez-Puyou 《Canadian Metallurgical Quarterly》1998,255(1):303-308
Soluble mitochondrial F1 and F1 in complex with the natural ATPase inhibitor protein (F1-IP) catalyze the spontaneous synthesis of [gamma-32P]ATP from medium [32P]phosphate and enzyme-bound ADP when incubated in media with dimethylsulfoxide (Me2SO); under these conditions, the synthesized [gamma-32P]ATP is not released into the media, it remains tightly bound to the enzymes [Gómez-Puyou, A., Tuena de Gómez-Puyou, M. & de Meis, L. (1986) Eur. J. Biochem. 159, 133-140]. Some of the characteristics of the synthesized [gamma-32P]ATP were studied in F1 and F1-IP (ATPase activities of 70 and 1-3 micromol x min(-1) x mg(-1), respectively). In Me2SO media, gamma-phosphate of synthesized ATP in F1 or F1-IP exchanges with medium phosphate. From the rates of the exchange reaction, the half-times for hydrolysis of the synthesized ATP in F1 and F1-IP were calculated: 45 min and 58 min for F1 and F1-IP, respectively. The course that synthesized [gamma-32P]ATP follows after dilution of the Me2SO synthetic mixture with aqueous buffer was determined. After dilution, the half-life of synthesized ATP in F1 was less than 1 min. In F1-IP, ATP was also hydrolyzed, but at significantly lower rates. In F1-IP, dilution also produced release of the synthesized [gamma-32P]ATP. This was assayed by the accessibility of [gamma-32P]ATP to hexokinase. About 25% of [gamma-32P]ATP synthesized in F1-IP, but not in F1, was released into the media after dilution with aqueous buffer that contained 20 mM phosphate. Release of tightly bound ATP required the binding energy of phosphate and solvation of F1-IP, however, the particular kinetics of F1-IP were also central for medium ATP synthesis in the absence of electrochemical H+ gradients. 相似文献
23.
Chun Hu Ji Zhao Li G.P. Liu P. Worley E. White J. Kjar R. 《Electron Device Letters, IEEE》1995,16(2):61-63
The effects of the plasma etching process induced gate oxide damages on device's low frequency noise behavior are investigated on MOSFET's fabricated with different field plate perimeter to gate area ratio antennas. Abnormal 1/f noise spectrum with a shoulder centered in the frequency range of 100 and to 1 kHz was frequently observed in small geometry devices, and it is attributable to a nonuniform distribution of oxide traps induced by plasma etching process 相似文献
24.
25.
26.
27.
M Flores-Díaz A Alape-Girón B Persson P Pollesello M Moos C von Eichel-Streiber M Thelestam I Florin 《Canadian Metallurgical Quarterly》1997,272(38):23784-23791
We previously isolated a mutant cell that is the only mammalian cell reported to have a persistently low level of UDP-glucose. In this work we obtained a spontaneous revertant whose UDP-glucose level lies between those found in the wild type and the mutant cell. The activity of UDP-glucose pyrophosphorylase (UDPG:PP), the enzyme that catalyzes the formation of UDP-glucose, was in the mutant 4% and in the revertant 56% of the activity found in the wild type cell. Sequence analysis of UDPG: PP cDNAs from the mutant cell showed one missense mutation, which changes amino acid residue 115 from glycine to aspartic acid. The substituted glycine is located within the largest stretch of strictly conserved residues among eukaryotic UDPG:PPs. The analysis of the cDNAs from the revertant cell indicated the presence of an equimolar mixture of the wild type and the mutated mRNAs, suggesting that the mutation has reverted in only one of the alleles. In summary, we demonstrate that the G115D substitution in the Chinese hamster UDPG:PP dramatically impairs its enzymatic activity, thereby causing cellular UDP-glucose deficiency. 相似文献
28.
Summary The crystallization and melting behaviour of poly(butylene terephthalate) has been studied in the pure state and in its blends with a polyarylate of bisphenol A and isophthalic/terephthalic acids. Differential scanning calorimetry has been used as experimental technique and the effects of different thermal treatments have been analyzed. Results show the hindrance for the crystallization of poly(butylene terephthalate) imposed by the presence of polyarylate, as well as the existence of multiple melting after isothermal crystallization. Explanations are given for the observed behaviours. 相似文献
29.
30.