全文获取类型
收费全文 | 338052篇 |
免费 | 23025篇 |
国内免费 | 1142篇 |
专业分类
362219篇 |
出版年
2018年 | 14177篇 |
2017年 | 12984篇 |
2016年 | 10741篇 |
2015年 | 4348篇 |
2014年 | 4987篇 |
2013年 | 6994篇 |
2012年 | 11475篇 |
2011年 | 20524篇 |
2010年 | 17160篇 |
2009年 | 12819篇 |
2008年 | 16517篇 |
2007年 | 18230篇 |
2006年 | 7080篇 |
2005年 | 7004篇 |
2004年 | 7373篇 |
2003年 | 7242篇 |
2002年 | 6846篇 |
2001年 | 12348篇 |
2000年 | 12174篇 |
1999年 | 9252篇 |
1998年 | 2704篇 |
1997年 | 2797篇 |
1996年 | 2739篇 |
1995年 | 2502篇 |
1994年 | 2458篇 |
1993年 | 2369篇 |
1992年 | 7235篇 |
1991年 | 7063篇 |
1990年 | 7112篇 |
1989年 | 6906篇 |
1988年 | 6414篇 |
1987年 | 6064篇 |
1986年 | 5389篇 |
1985年 | 5686篇 |
1984年 | 4494篇 |
1983年 | 3895篇 |
1982年 | 2683篇 |
1981年 | 2507篇 |
1980年 | 2320篇 |
1979年 | 4124篇 |
1978年 | 3144篇 |
1977年 | 2893篇 |
1976年 | 2834篇 |
1975年 | 3278篇 |
1974年 | 3502篇 |
1973年 | 3532篇 |
1972年 | 3302篇 |
1971年 | 3110篇 |
1970年 | 2544篇 |
1969年 | 2306篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
Elevated serum gamma-glutamyl transferase (GGT) levels were found in 29% of 155 chronic alcoholics undergoing detoxification treatment. Alkaline phosphatase (AP) was increased in 16%, alanine aminotransferase--SGPT (ALT) in 12% of the patients, while 23% had elevations of either AP or ALT or both. Of the foregoing parameters, GGT was the best single indicator of liver involvement. In course of the follow-ups GGT/ALT correlation improved, but GGT/AP correlation deteriorated. In 9 patients, abstinence during follow-up was associated with progressive decrease in previously elevated serum GGT. Because of its unique sensitivity, GGT may be useful as a screening and/or monitoring aid in alcoholism. 相似文献
132.
133.
Serological comparison of bovine T-mycoplasmas 总被引:1,自引:0,他引:1
134.
135.
136.
R factors of compatibility group A 总被引:4,自引:0,他引:4
137.
Abstract— In contrast to mouse brain, the content of putrescine in fish brain considerably exceeds that of spermine and spermidine. While we observed constant protein, RNA and spermidine concentrations in fish brains of weights between 60 and 800 mg, DNA and spermine concentrations diminished with increasing brain weight, the content of spermine per cell being constant throughout life. It can be concluded from our results that growth of fish brain results both from cell enlargement and cell proliferation. The concomitant changes of spermine and DNA concentrations in the growing fish brain are the first example of a direct quantitative relationship between these cell constituents and provides evidence on their possible functional relationship in the cell nucleus. 相似文献
138.
Ferredoxin from Bacillus polymyxa 总被引:5,自引:0,他引:5
Y I Shethna N A Stombaugh R H Burris 《Biochemical and biophysical research communications》1971,42(6):1108-1116
139.
140.
Winnie W.Y. Lau Marlene M. Martinez 《Journal of experimental marine biology and ecology》2003,295(1):1-21
Hydrodynamic forces can affect survival as well as limit the movement of motile benthic animals. An animal's danger of dislodgement depends on the hydrodynamic forces it experiences in its microhabitat relative to the force required to dislodge it (tenacity) from the substratum. We measured water flow and substratum characteristics in two different habitats of the shore crab Pachygrapsus crassipes: a wave-swept rocky shore and an intertidal mudflat. The maximum water velocities and accelerations in the microhabitats of the crabs at the wave-swept site were three times and two times greater, respectively, than at the mudflat site. In the laboratory, we measured the tenacity of crabs of various sizes on different substrata, and also measured their drag, lift and added-mass coefficients. Using these data, we calculated the flow conditions under which crabs would be overturned or sheared off the substratum in their two habitats. The net horizontal force (drag plus acceleration reaction) required to dislodge a crab on a rugose rock substratum was an order of magnitude greater than on smooth rock and two orders of magnitude greater than on mud. Our calculations indicate that, under non-storm conditions, crabs will not be dislodged from the substratum in either the mudflat or the wave-swept habitat when grasping the substratum with maximum tenacity. Moving crabs have lower tenacity and our calculations predict that hydrodynamic forces will restrict the mobility of large crabs more than that of small ones on smooth, but not on rugose rock. 相似文献